What Is Biofilter?

A biofilter is simply a bed of organic material (medium), typically amixture of compost and wood chips or shreds, about 10 to 18 inchesdeep. As air passes through the biofilter the microbes on the organicmaterial convert odorous gases to carbon dioxide and water. Theeffectiveness of the biofilter is primarily a function of the amount oftime the odorous air spends in the biofilter (contact time) and the moisture content of the filter material. Contact time is part of thebiofilter design while moisture content is a function of goodmanagement. The size (footprint) of the biofilter dependsprimarily on the amount of air needing treatment. A typicalbiofilter will require 50 to 85 square feet per 1000 cubic feet perminute (cfm) of airflow.

Trickling Filters (TF): a trickling filter or biofilter or percolating filter consists of a basin or tower filled with support media such as stones, plastic shapes, or wooden slats. Wastewater is applied intermittently, or sometimes continuously, over the media. Microorganisms become attached to the media and form a biological layer or fixed film. Organic matter in the wastewater diffuses into the film, where it is metabolized. Oxygen is normally supplied to the film by the natural flow of air either up or down through the media, depending on the relative temperatures of the wastewater and ambient air. Forced air can also be supplied by blowers but this is rarely necessary. The thickness of the biofilm increases as new organisms grow.

Rotating Biological Contactors (RBCs): RBCs are fixed-film reactors similar to biofilters in that organisms are attached to support media. In the case of the RBC, the support media are slowly rotating discs that are partially submerged in flowing wastewater in the reactor. Oxygen is supplied to the attached biofilm from the air when the film is out of the water and from the liquid when submerged, since oxygen is transferred to the wastewater by surface turbulence created by the discs' rotation.

Biofiltration is a technology in which vapor-phase organic contaminants in an air stream are passed through a bed of porous support media where they partition into a thin water film on the media and are degraded by microorganisms. Specific strains of bacteria may be introduced into the filter and optimal conditions provided to preferentially degrade specific compounds. The biofilter provides several advantages over conventional activated carbon adsorbers. First, bioregeneration keeps the maximum adsorption capacity available constantly; thus, the mass transfer zone remains stationary and relatively short. The filter does not require regeneration, and the required bed length is greatly reduced. These features reduce capital and operating expenses. Additionally, the contaminants are destroyed not just removed, as with granular activated carbon (GAC) technologies.

Applicability: As with other biological treatment processes, biofiltration is highly dependent upon the biodegradability of the contaminants. Biofiltration is used primarily to treat nonhalogenated volatile organic compounds (VOCs) and fuel hydrocarbons. Under proper conditions, biofilters can remove and degrade a significant fraction of these contaminants to harmless products. Halogenated VOCs also can be treated, but the process may be less effective. Additionally, biofilters have been successfully used to control odors from compost piles.

Bioreactors are biochemical processing systems designed to degrade contaminants in water with microorganisms through attached or suspended biological systems. In suspended growth systems, such as activated sludge, fluidized beds, or sequencing batch reactors, contaminated groundwater is circulated in an aeration basin where a microbial population aerobically degrades organic matter and produces CO2, H2O, and new cells. The cells form a sludge, which is settled out in a clarifier, and is either recycled to the aeration basin or disposed of. In attached biofilm systems, such as upflow fixed film bioreactors, rotating biological contactors (RBCs), and trickling filters, microorganisms are established on a support matrix to aerobically degrade water contaminants. One promising methodology includes the use of adsorption media, such as activated carbon, which adsorbs contaminants and slowly releases them to the microorganisms for degradation. The microbial population may be derived either from the contaminant source or from an inoculum of organisms specific to a contaminant.

Applicability: Bioreactors are used primarily to treat nonhalogenated VOCs and SVOCs, including gasoline, diesel fuel, JP-4, JP-5, and heavy fuels in extracted groundwater. Cometabolites may be needed to treat PCBs, halogenated VOCs, and halogenated SVOCs in extracted groundwater. Bioreactors with specially adapted microorganisms are used to treat halogenated SVOCs, pesticides, PCBs, and ordnance compounds in extracted groundwater. Sequential anaerobic/aerobic bioreactors are used primarily to treat halogenated VOCs, SVOCs, pesticides, PCBs, and ordnance compounds.

Fixed film processes (Attached growth processes)

In a 1984 survey, there were over 2400 trickling filter systems in the United States, approximately half as many as activated sludge plants. Design trends to maximize performance include power ventilation and daily hydraulic flushing to control sloughing and clean the media. Recirculation of effluent also improves quality. Fine screens are used upstream to reduce media fouling, as at South Bend, Indiana, and Sausalito, California. Synthetic media is now often used, although structural failure of the plastic has been an issue in some locations requiring careful selection of manufacturers. These systems are often upgraded with an add-on suspended growth unit process, in a configuration known as TFSC (Trickling Filter - Solids Contact). The trickling filter provides coarse BOD removal and the solids contact tank provides the digestion capacity of the adsorbed and absorbed organic material. TFSC systems are also being constructed as new facilities where ammonia nitrification is not a key parameter of concern.

Rotating Biological Contactors (RBCs) are fairly common in both Canada and the US for small to medium sized communities. Problems with this technology have included performance below design expectations, structural problems with shafts and media, excessive biomass buildup, and uneven shaft rotation for air driven units. Self aligning bearings, increasing the size of the first stage based on total organic loading, allowing for deteriorating performance below 13oC., and using more air for air driven units than indicated by the manufacturer, as well as improvements in shaft design, have addressed many of these problems. A new technology development has been 85% submergence of the rotor.

Both trickling filters and rotating biological contactors are usually covered for odour and vector (fly) control.

Appl Microbiol Biotechnol . 2005 Jan 13; {Epub ahead of print}
Biofiltration of waste gases with the fungi Exophiala oligosperma and Paecilomyces variotii; Estevez E et al.; Two biofilters fed toluene-polluted air were inoculated with new fungal isolates of either Exophiala oligosperma or Paecilomyces variotii, while a third bioreactor was inoculated with a defined consortium composed of both fungi and a co-culture of a Pseudomonas strain and a Bacillus strain . Elimination capacities of 77 g m(-3) h(-1) and 55 g m(-3) h(-1) were reached in the fungal biofilters (with removal efficiencies exceeding 99%) in the case of, respectively, E . oligosperma and Paecilomyces variotii when feeding air with a relative humidity (RH) of 85% . The inoculated fungal strains remained the single dominant populations throughout the experiment . Conversely, in the biofilter inoculated with the bacterial-fungal consortium, the bacteria were gradually overgrown by the fungi, reaching a maximum elimination capacity around 77 g m(-3) h(-1) . Determination of carbon dioxide concentrations both in batch assays and in biofiltration studies suggested the near complete mineralization of toluene . The non-linear toluene removal along the height of the biofilters resulted in local elimination capacities of up to 170 g m(-3) h(-1) and 94 g m(-3) h(-1) in the reactors inoculated, respectively, with E . oligosperma and P . variotii . Further studies with the most efficient strain, E . oligosperma, showed that the performance was highly dependent on the RH of the air and the pH of the nutrient solution . At a constant 85% RH, the maximum elimination capacity either dropped to 48.7 g m(-3) h(-1) or increased to 95.6 g m(-3) h(-1), respectively, when modifying the pH of the nutrient solution from 5.9 to either 4.5 or 7.5 . The optimal conditions were 100% RH and pH 7.5, which allowed a maximum elimination capacity of 164.4 g m(-3) h(-1) under steady-state conditions, with near-complete toluene degradation.

Biotechnol Bioeng . 2004 Dec 23; {Epub ahead of print}
Modeling of a vapor-phase fungi bioreactor for the abatement of hexane: Fluid dynamics and kinetic aspects; Spigno G et al.; During some previous works, a packed-bed lab-scale biofilter (177 . 10(-6) m(3)), inoculated with a selected strain of Aspergillus niger had been tested for the abatement of hexane vapors, showing a maximum elimination capacity of 200 g hexane/m(3) reactor/h . A steady-state mathematical model taking into account axial dispersion effect was applied to describe the process and predict experimental results, but many model parameters could not be calculated from experimental data . The aim of the present work was to carry out further investigations to accurately determine the dispersion coefficient and the kinetics parameters to verify the effective validity of the model . Analysis of residential time distribution revealed the presence of a certain degree of axial dispersion (dispersion coefficient D of 1.22 . 10(-4) m(2)/s) . Experimental data from kinetic trials carried out in reduced height reactors, together with data from full-scale runs, were elaborated to estimate the kinetic saturation constant (K(s)), the coefficient yield (Y), the maximum growth rate (mu(max)) and maximum substrate degradation rate (r(max)) . All these parameters were introduced into the model, which was then solved by simulation software finding a good correlation between experimental and theoretical results . (c) 2004 Wiley Periodicals, Inc.

Bioresour Technol, 2005 Apr, 96(6), 741 - 5
Compost biofiltration of ammonia gas from bin composting; Hong JH et al.; The effects of the manure compost/coconut peels on the ammonia removal efficiency were examined from dairy manure composting mixed with crop residues . The high rapid composting and manure compost biofiltration experiments consisted of three biofilter vessels with one composter . Dairy manure amended with rice hulls and sawdust was composted in 605L pilot-scale composter using continuous aeration for 19days . Three pilot-scale manure compost biofilter amended with media bed 500mm in depth and 300mm in diameter were built to clean ammonia emission from composter, respectively . The manure compost biofilter media in the three experimental vessels was using a 50:50 by weight mixture of manure compost and coconut peels (MC/CP) . The ammonia concentrations at the inlet and outlet biofilter media were measured by boric acid traps as described by Hong et al . {Hong, J.H., Keener, H.M., Elwell, D.L., 1998 . Preliminary study of the effect of continuous and intermittent aeration on composting hog manure amended with sawdust . Compost Science and Utilization 6 (3), 74-88} . Results indicated that the mixture of MC/CP performed well as a biofilter media and the ammonia removal efficiency was 100% for the filter depth of 500mm.

Waste Manag Res, 2004 Oct, 22(5), 334 - 45
Use of life cycle assessment as decision-support tool for water reuse and handling of residues at a Danish industrial laundry; Jorgensen KR et al.; This analysis presents the results of a life cycle assessment (LCA) carried out on six alternative options for the recycling of water at a Danish industrial laundry for workwear . The study focuses on the handling and disposal of the wet residues generated when wastewater is treated for recycling, and in accounting for long-term potential toxicity impacts . The analysed options are a combination of two water-upgrading technologies: biofilter and ultrafiltration, and three residue disposal alternatives: biogas followed by incineration of sludge at local wastewater treatment plant, thermal vitrification treatment for production of vitrified sand, and mineralization in a sludge bed . It is concluded from the results that with the current Danish environmental policy priorities, the environmental impacts of highest priority are the toxicity effects derived from the presence of heavy metals in the residues . Heavy metals originate from the dirt in the workwear that is washed in the laundry . It is further concluded that the studied water treatment technologies satisfy both the need of clean water for recycling and simultaneously help controlling a safe disposal of pollutants by concentration of the residues . The results of the study also confirm the potential of LCA as a decision-support tool for assisting water recycling initiatives and for residue handling management . The handling of residues has been identified as a stage of the water recycling strategy that bears important environmental impacts . This holistic perspective provided by LCA can be used as input for the definition of environmental management strategies at an industrial laundry, and the prioritization of investments to the environmental profile of laundry processes . In this case-study, the results of the LCA are made operational by, for example, selecting the water treatment technology which is associated wih a safe disposal of the wet residue . It is important to bear in mind that such prioritization depends on national boundary conditions . In the case study analysed, the boundary conditions steer the weighing of the environmental impacts, following the current Danish environmental policy priorities.

Artif Organs, 2004 Dec, 28(12), 1067 - 75
In vivo assessment of intact parathyroid hormone adsorption by different dialysis membranes during hemodialysis; Balducci A et al.; BACKGROUND: Different parathyroid hormone (PTH) behavior during hemodialysis with different types of dialysis membranes has been reported . The behavior of intact parathyroid hormone (iPTH) adsorption using different dialysis membranes was assessed in 12 dialysis patients with secondary hyperparathyroidism . METHODS: The study was performed according to a longitudinal scheme comprising three treatment modalities, each lasting 2 weeks, for 6 weeks altogether . The first treatment consisted of standard bicarbonate dialysis with low-flux polysulfone, followed by acetate-free biofiltration with high-flux-polysulfone or with polyacrylonitrile-AN69 . In the first week of each period, dialysis was delivered by using a 1.3 m(2) surface area and subsequently, a 1.8 m(2) surface area . Intact parathyroid hormone was assayed on the blood and dialysate samples to calculate iPTH adsorption . RESULTS: The results showed that polyacrylonitrile-AN69 and high-flux polysulfone induce a significantly larger drop in PTH serum levels as compared with low-flux-polysulfone, particularly in the first half of the dialysis session, while the ionized calcium increase is comparable in all different hemodialysis treatments . The measurement of iPTH in the dialysate showed lower values than those disappearing on the blood side, thus suggesting the presence of an adsorptive mechanism in the different dialysis membranes . CONCLUSION: High-flux polysulfone is endowed with a comparable adsorptive capacity per surface unit compared to polyacrylonitrile-AN69, although it seems to show a different behavior, as polyacrylonitrile-AN69 saturates early in the first hour of dialysis corresponding to its maximum adsorption power, while high-flux-polysulfone displays a more lasting adsorptive capacity . Thus, iPTH changes during hemodialysis also depend on dialyzer characteristics and the dialysis membrane adsorption.

Appl Microbiol Biotechnol . 2004 Nov 6; {Epub ahead of print}
Treatment of H(2)S using a horizontal biotrickling filter based on biological activated carbon: reactor setup and performance evaluation; Duan H et al.; Biological treatment is an emerging and prevalent technology for treating off-gases from wastewater treatment plants . The most commonly reported odorous compound in off-gases is hydrogen sulfide (H(2)S), which has a very low odor threshold . A self-designed, bench-scale, cross-flow horizontal biotrickling filter (HBF) operated with bacteria immobilized activated carbon (termed biological activated carbon-BAC), was applied for the treatment of H(2)S . A mixed culture of sulfide-oxidizing bacteria dominated by Acidithiobacillus thiooxidans acclimated from activated sludge was used as bacterial seed and the biofilm was developed by culturing the bacteria in the presence of carbon pellets in mineral medium . HBF performance was evaluated systematically over approximately 120 days, depending on a series of changing factors including inlet H(2)S concentration, gas retention time (GRT), pH of recirculation solution, upset and recovery, sulfate accumulation, pressure drop, gas-liquid ratio, and shock loading . The biotrickling filter system can operate at high efficiency from the first day of operation . At a volumetric loading of 900 m(3) m(-3) h(-1) (at 92 ppmv H(2)S inlet concentration), the BAC exhibited maximum elimination capacity (113 g H(2)S/m(-3) h(-1)) and a removal efficiency of 96% was observed . If the inlet concentration was kept at around 20 ppmv, high H(2)S removal (over 98%) was achieved at a GRT of 4 s, a value comparable with those currently reported for biotrickling filters . The bacterial population in the acidic biofilter demonstrated capacity for removal of H(2)S over a broad pH range (pH 1-7) . A preliminary investigation into the different effects of bacterial biodegradation and carbon adsorption on system performance was also conducted . This study shows the HBF to be a feasible and economic alternative to physical and chemical treatments for the removal of H(2)S.

Biotechnol Bioeng, 2004 Dec 20, 88(6), 690 - 8
Thermophilic biohydrogen production from glucose with trickling biofilter; Oh YK et al.; Thermophilic H2 production from glucose was studied at 55-64 degrees C for 234 days using a continuous trickling biofilter reactor (TBR) packed with a fibrous support matrix . Important parameters investigated included pH, temperature, hydraulic retention time (HRT), and glucose concentration in the feed . The optimal pH and temperature were 5.5 and 60 degrees C, respectively . With decreasing HRT or increasing inlet glucose concentration, volumetric H2 production rate increased but the H2 production yield to glucose decreased gradually . The biogas composition was almost constant at 53 +/- 4% (v/v) of H2 and 47 +/- 4% (v/v) of CO2 . No appreciable CH4 was detected when the reactor was under a normal operation . The carbon mass balance showed that, in addition to cell mass, lactate, n-butyrate, CO2, and acetate were major products that comprised more than 85% of the carbon consumed . The maximal volumetric H2 production rate and H2 yield to glucose were 1,050 +/- 63 mmol H2/l.d and 1.11 +/- 0.12 mol H2/mol glucose, respectively . These results indicate that the thermophilic TBR is superior to most suspended or immobilized reactor systems reported thus far . This is the first report on continuous H2 production by a thermophilic TBR system.

Nephron Clin Pract, 2004, 98(3), c79 - 82
Could plasma cystatin C be useful as a marker of hemodialysis low molecular weight proteins removal?
Campo A, Lanfranco G, Gramaglia L, Goia F, Cottino R, Giusto V.
BACKGROUND: Plasma cystatin (pCyst) is a well-assessed tool for measuring renal function, and it could also play a part in hemodialysis adequacy . METHODS: pCyst and other uremic toxins (urea, creatinine, parathyroid hormone, prolactin) were assessed before and after a dialysis session in 18 hemodialysis patients: 7 on bicarbonate hemodialysis (BHD) and 11 on mixed convective dialysis (MCD; 6 standard hemodiafiltration and 5 acetate-free biofiltration) . Plasma levels and reduction ratios (RR) were then compared between the BHD and MCD groups . RESULTS: The mean pre-dialysis pCyst level is nearly the same in both groups (5.3 +/- 0.8 vs . 5.7 +/- 1 mg/l, p = ns), although a substantial decrease occurs after MCD only (mean 2.4 +/- 1 vs . 6.2 +/- 2.2 mg/l after BHD, p = 0.002) . The mean pCyst RR (PCRR) of 55.5% after MCD is poorly related to prolactin and urea RR, fairly comparable to parathyroid hormone RR and very close to creatinine RR (58.4%) . CONCLUSIONS: Only MCD removes pCyst, but the amount of removal is different for other low molecular weight proteins (prolactin and parathyroid hormone) and similar for creatinine, a classic 'little molecule' . In view of the discrepancy of these findings, the use of pCyst in hemodialysis still seems premature and needs further studies . Copyright (c) 2004 S . Karger AG, Basel.

J Anim Sci, 1999, 77 Suppl 2, 169 - 76
Odor control for livestock systems; Powers WJ; Odors are generated primarily as the result of manure storage but also result from animal housing and manure application . Effective odor control is dependent upon implementation of strategies that are complementary to management practices . Some systems use a deep pit or a holding tank for manure storage . In such systems, little or no biological processing occurs, and they are therefore considered high-load systems . In systems where biological processing occurs to a great extent, such as in anaerobic digesters or lagoons, the system would be termed a low-load system . Odor control strategies for manure storage areas, such as solids separation and additives, are best suited for low-load systems, whereas covers and biofilters provide the best results for high-load systems . Strategies that reduce nutrient production, such as dietary restriction of nutrients, are well-suited for all types of manure storage systems . To comply with current or pending odor control regulations, it is imperative that producers be provided with sound recommendations of odor control strategies.

J Hazard Mater, 2004 Oct 18, 114(1-3), 153 - 8
Evaluation of trickle-bed air biofilter performance for MEK removal; Cai Z et al.; A lab-scale trickle-bed air biofilter (TBAB) was operated to evaluate the removal of methyl ethyl ketone (MEK) from waste gas . Three biomass control strategies were investigated, namely, backwashing and two non-use periods (starvation and stagnant) . Five volumetric loading rates from 0.70 to 7.04 kg COD/m(3)day were employed . Backwashing once a week removed the excess biomass and obtained long-term, stable performance over 99% removal efficiency for loading rates less than 5.63 kg COD/m(3)day . The two non-use periods could also sustain 99% removal efficiency and could be employed as another means of biomass control for loading rates up to 3.52 kg COD/m(3)day . The non-use periods did not delay the recovery when the loading rate did not exceed 3.52 kg COD/m(3)day . The pseudo-first-order removal rate constant decreased with increase in volumetric loading rate . The effect of non-use periods on removal rate showed apparent transition from positive to negative with the increase in loading rate.

Water Environ Res, 2004 Jul-Aug, 76(4), 310 - 5
Measurement of biosolids compost odor emissions from a windrow, static pile, and biofilter; Rosenfeld P et al.; A pilot study was conducted to compare odor emissions from a windrow process and an aerated static pile and to determine the odor reduction efficiency of a pilot two-phase biofilter for odor control of biosolids composting . Chemical compounds identified as responsible for odors from biosolids composting include ammonia, dimethyl disulfide, carbon disulfide, formic acid, acetic acid, and sulfur dioxide (or carbonyl sulfide) . Aeration was found to reduce the concentration of ammonia, formic acid, and acetic acid by 72, 57, and 11%, respectively, compared with a nearby windrow, while dimethyl sulfide, carbon disulfide, and sulfur dioxide (or carbonyl sulfide) concentrations were below detection limits . Using dilution-to-threshold olfactometry, aeration followed by biofiltration was found to reduce the odor from biosolids composting by 98% . Biofiltration also altered the character of odor emissions from biosolids composting, producing a less offensive odor with an earthy character . Biofiltration was found to reduce the concentration of ammonia, dimethyl disulfide, carbon disulfide, formic acid, acetic acid, and sulfur dioxide (or carbonyl sulfide) by 99, 90, 32, 100, 34, and 100%, respectively . The concentrations of those odorants were estimated to be 3700, 110000, 26,37,5, and 1.2 times reported human detection limits before the two-phase biofilter, respectively, and 42,9600,18,0,3, and 0 times human detection limits after the biofilter, respectively.

Sci Total Environ, 2004 Dec 1, 334-335, 473 - 9
Sediment accumulation in newly constructed vegetative treatment facilities along a new major road; Hares RJ et al.; The A34 Newbury bypass was opened in England in November 1998 . This 15 km of roadway has nine constructed vegetative treatment systems incorporating oil separators, silt traps, grass filters for primary filtration and chemical absorption, reed wetlands for secondary biofiltration, a deep water pool and outflow device to control the rate of water discharge into existing watercourses . Two of these facilities discharge stormwater into the Lambourn sites of special scientific interest (SSSI) river . An evaluation of the heavy metal levels in these two ponds (Ponds J and K) has been undertaken in the 39-month period after the opening of the bypass . Motorway-derived contaminants including Pb, Cd, Cu and Zn were evaluated within pond sediment throughout these treatment facilities . Results reveal that heavy metal levels within the treatment system that possesses a well-established reed bed system decrease rapidly though the facility . It is postulated that the high reed biomass within this facility may be primarily responsible for reducing hydraulic flow thus allowing a greater residence time for sedimentation, filtration and bioaccumulation processes.

Bioresour Technol, 2005 Mar, 96(5), 557 - 64
Compost liquor bioremediation using waste materials as biofiltration media; Savage AJ et al.; Compost liquor results from the percolation of precipitation through composting waste; the release of liquids from high moisture content feedstocks; and as a result of runoff from hard surfaces and machinery . This research aimed to establish the potential for waste materials to act as media for low-cost compost liquor biofilters . Six types of potential biofilter media were packed into experimental biofilters (1 m longx0.11 m diameter) and irrigated with compost liquor (organic loading rate of 0.6 kg/m(3)/d) for three months . The pH, BOD(5), NH(3)/NH(4)(+), and phytotoxicity of the effluent was monitored regularly . Natural, organic materials (oversize, compost and wood mulch) performed best, when compared to synthetic materials such as polystyrene packaging or inert materials such as broken brick . On average, the best media achieved 78% removal of both BOD(5) and ammoniacal nitrogen during the study period . Although significant improvements in liquor quality were achieved, the effluent remained heavily polluted.

FEMS Microbiol Lett, 2004 Nov 1, 240(1), 61 - 8
Community structure in a methanotroph biofilter as revealed by phospholipid fatty acid analysis; Gebert J et al.; The microbial community structure of two biofilters used for the oxidation of methane and organic trace gases generated in landfills was analysed by phospholipid fatty acid composition . Community structure varied with biofilter depth, reflecting varying conditions of substrate supply as well as of organic carbon content, nutrient status and osmotic stress determined by the different materials used for the individual biofilter layers . Both biofilters were dominated by type II methanotrophs . In the biofilter charged with landfill gas containing significant amounts of trace organics, fatty acid 18:1omega7c constituted 87% of the methanotrophic PLFA, while the recognised signature fatty acids 16:1omega8 and 18:1omega8, which were well represented in the other biofilter, were entirely absent . This indicates the development of a highly specific methanotrophic population, presumably as a result of the adaption to continuous organic trace gas exposure.

J Environ Sci (China), 2004, 16(4), 656 - 61
Biological removal of air loaded with a hydrogen sulfide and ammonia mixture; Chen YX et al.; The nuisance impact of air pollutant emissions from wastewater pumping stations is a major issue of concern to China . Hydrogen sulfide and ammonia are commonly the primary odor and are important targets for removal . An alternative control technology, biofiltration, was studied . The aim of this study is to investigate the potential of unit systems packed with compost in terms of ammonia and hydrogen sulfide emissions treatment, and to establish optimal operating conditions for a full-scale conceptual design . The laboratory scale biofilter packed with compost was continuously supplied with hydrogen sulfide and ammonia gas mixtures . A volumetric load of less than 150 gH2S/(m3 x d) and 230 gNH3/(m3 x d) was applied for about fifteen weeks . Hydrogen sulfide and ammonia elimination occurred in the biofilter simultaneously . The removal efficiency, removal capacity and removal kinetics in the biofilter were studied . The hydrogen sulfide removal efficiency reached was very high above 99%, and ammonia removal efficiency was about 80% . Hydrogen sulfide was oxidized into sulphate . The ammonia oxidation products were nitrite and nitrate . Ammonia in the biofilter was mainly removed by adsorption onto the carrier material and by absorption into the water fraction of the carrier material . High percentages of hydrogen sulfide or ammonia were oxidized in the first section of the column . Through kinetics analysis, the presence of ammonia did not hinder the hydrogen sulfide removal . According to the relationship between pressure drop and gas velocity for the biofilter and Reynolds number, non-Darcy flow can be assumed to represent the flow in the medium.

Chemosphere, 2004 Nov, 57(7), 721 - 30
Effect of gas velocity and influent concentration on biofiltration of gasoline off-gas from soil vapor extraction; Namkoong W et al.; This study was conducted to evaluate the effects of gas inlet concentration and velocity on the biofiltration of gasoline vapor . Gasoline vapor was treated using a compost biofilter operated in an upflow mode for about 3 months . The inlet concentration of gasoline total petroleum hydrocarbon (TPH) ranged from about 300 to 7000 mgm(-3) and gas was injected at velocities of 6 and 15 mh(-1) (empty bed residence time (EBRT)=10 and 4 min, respectively) . The maximum elimination capacities of TPH at 6 and 15 mh(-1) found in this research were over 24 and 19 gm(-3) of filling material h(-1), respectively . TPH removal data was fit using a first-order kinetic relationship . In the low concentration range of 300-3000 mg m(-3), the first-order kinetic constants varied between about 0.10 and 0.29 min(-1) regardless of gas velocities . At TPH concentrations greater than 3000 mgm(-3), the first-order kinetic constants were about 0.09 and 0.07 min(-1) at gas velocities of 6 mh(-1) and 15 mh(-1), respectively . To evaluate microbial dynamics, dehydrogenase activity, CO2 generation and microbial species diversity were analyzed . Dehydrogenase activity could be used as an indicator of microbial activity . TPH removal corresponded well with CO2 evolution . The average CO2 recovery efficiency for the entire biofilter ranged between 60% and 70% . When the gas velocity was 6 mh(-1), most of the microbial activity and TPH removal occurred in the first quarter of the biofilter . However, when the gas velocity was 15 mh(-1), the entire column contributed to removal . Spatial and temporal variations in the biofilter microbial population were also observed . Nearly 60% of the colonies isolated from the compost media prior to biofiltration were Bacillus . After 90 days of biofiltration, the predominant species in the lower portion (0-50 cm) of the filter were Rhodococcus, while Pseudomonas and Acinetobacter dominated the upper portion (75-100 cm) . copyright 2004 Elsevier Ltd.

Water Sci Technol, 2004, 50(4), 319 - 26
Biotechnology-based odour control: design criteria and performance data; Quigley C et al.; As neighbouring areas continue to encroach upon wastewater treatment plants, there is an increasing need for odour control to mitigate potential negative offsite odorous impacts . One technology that is gaining widespread acceptance is biotechnology, which utilises the inherent ability of certain microorganisms to biodegrade offensive odorous compounds . Two main advantages of this form of treatment over other odour control technologies include the absence of hazardous chemicals and relatively low operation and maintenance requirements . The purpose of this paper is to provide information related to odour control design criteria used in sizing/selecting biotechnology-based odour control technologies, and to provide odour removal performance data obtained from several different biotechnology-based odour control systems . CH2M HILL has collected biotechnology-based odour control performance data over the last several years in order to track the continued performance of various biofilters and biotowers over time . Specifically, odour removal performance data have been collected from soil-, organic- and inorganic-media biofilters and inert inorganic media biotowers . Results indicate that biotechnology-based odour control is a viable and consistent technology capable of achieving high removal performance for odour and hydrogen sulphide . It is anticipated that the information presented in this paper will be of interest to anyone involved with odour control technology evaluation/selection or design review.

Water Sci Technol, 2004, 50(4), 299 - 308
Batch experiment on H2S degradation by bacteria immobilised on activated carbons; Yan R et al.; Biological treatments of odorous compounds, as compared to chemical or physical technologies, are in general ecologically and environmentally favourable . However, there are some inefficiencies relative to the media used in biofiltration processes, such as the need for an adequate residence time; the limited lifetime, and pore blockage of media, which at present render the technology economically non-viable . The aim of the study is to develop novel active media to be used in performance-enhanced biofiltration processes, by achieving an optimum balance and combination of the media adsorption capacity with the biodegradation of H2S through the bacteria immobilised on the media . An enrichment culture was obtained from activated sludges in order to metabolise thiosulphate . Batch-wise experiments were conducted to optimise the bacteria immobilisation on activated carbon, so as to develop a novel "biocarbon" . Biofilm was mostly developed through culturing the bacteria with the presence of carbons in mineral media . SEM and BET tests of the carbon along with the culturing process were used to identify, respectively, the biofilm development and biocarbon porosity . Breakthrough tests evaluated the biocarbon performance with varying gas resistance time, inlet H2S concentration, and type of support materials . Fundamental issues were discussed, including type of support material, mode of bacteria immobilisation, pore blockages, and biodegradation kinetics, etc . This batch-wise study provides a basis for our future research on optimisation of the biofiltration process using a bio-trickling reactor.

Water Sci Technol, 2004, 50(4), 215 - 24
A membrane bioreactor for the removal of dimethyl sulphide and toluene from waste air; Van Langenhove H et al.; In biotrickling filters, mass transfer of hydrophobic compounds is the limiting factor . Biofilters are static systems, and so control and regulation of operational parameters such as pH and nutrient supply can be a problem . In membrane bioreactors, these drawbacks can be avoided . The hydrophobic membrane separates the waste air from the aqueous phase, thus avoiding mass-transfer limitation, while pH and nutrient supply can be directly controlled . In this contribution, an overview will be given of results obtained during a four-year project . First, the physical chemical characteristics (solubility, permeability, diffusivity) and microbial adhesion of different membranes were tested . This led to the selection of a composite membrane consisting of a porous polyvinylidenefluoride (PVDF) support layer coated with a thin (1 or 2.5 microm) dense polydimethylsiloxane (PDMS) top layer . This membrane was mounted into a module provided with four parallel rectangular channels for gas flow (in contact with the porous layer) and nutrient solution (in contact with the dense layer) respectively . After inoculation, a biofilm developed on the dense layer . Experiments were performed with dimethyl sulphide and toluene as target VOCs . Operational characteristics such as elimination capacity as a function of the volumetric load and residence time, effect of nutrient supply, long-term performance) were determined . Mass transfer was studied by measuring concentration profiles along the channels of the module in different conditions.

Water Sci Technol, 2004, 50(4), 199 - 205
Hydrogen sulphide removal by activated sludge diffusion; Barbosa VL et al.; Odours from wastewater treatment plants comprise a mixture of various gases, of which hydrogen sulphide (H2S) is the main constituent . Microorganisms commonly found in wastewater can degrade sulphurous compounds . Therefore, the use of activated sludge (AS) for odour control offers an alternative to traditional waste gas treatment processes, such as biofilters, bioscrubbers and biotrickling filters, both in practical terms (use of existing facilities) and economically (minimal capital cost) . The performance of AS diffusion as a bioscrubber for removing H2S at concentrations at 25, 75 and 150 ppmv was evaluated . Pilot-scale trials were undertaken using parallel 60-L aeration tanks and 20-L clarifier reactors at the Bedford Sewage Treatment Works, Carington, UK . Olfactometry measurements were also carried out to determine whether there was any increase in odour concentration owing to H2S diffusion . Hydrogen sulphide removal rates of 100% were obtained, with no noticeable increase in odour concentration throughout the trials as measured by olfactometry . Odour concentration was highest at the beginning of the trials and lowest during the high H2S dosing period, with similar values being obtained for test and control . It was concluded that AS diffusion is an effective bioscrubber for the removal of H2S odour.

Water Sci Technol, 2004, 50(4), 93 - 100
Monitoring of biological odour filtration in closed environments with olfactometry and an electronic nose; Willers H et al.; Air treatment with a compact biological membrane filter, and air quality monitoring with an electronic nose were tested in the laboratory on air from a cage containing six mice . Additional analyses of air to and from the filter were performed using olfactometry and ammonia and hydrogen sulphide gas detection tubes . The biological air filter is a module containing biofilm-coated membrane fibres that separate a closed liquid loop from a gas phase . Odour compounds and oxygen diffuse through the membranes from the gas phase to the biofilm, where they are degraded to carbon dioxide and water . The prototype "ENQBE" electronic nose is based on an array of eight thickness shear mode resonators (TSMR), also known in the literature as quartz microbalance sensors . The chemical sensitivity is given by molecular films of metalloporphyrins and similar compounds . Chemical interaction of compounds in the air with the vibrating sensors induces a frequency change of the vibration that can be measured as a signal . The air from the mouse cage had a strong odour (3490 OUE/m3) . The biological membrane filter performed well, achieving over 80% odour and ammonia reduction . The electronic nose signal could be correlated with the inlet and outlet air-quality of the biological filter, making it a promising method for monitoring air quality in closed environments.

Water Sci Technol, 2004, 50(4), 33 - 8
Ecological assessment of waste air treatment systems in the case of biological waste treatment; Steinberg I et al.; In this paper, the authors present a technique aimed at increasing the efficiency of biological waste air treatment . The objective is to modify the existing biological waste air treatment systems (i.e . biofilters) to reduce the emitted substances and their potential environmental impacts . The principle of the ionization system is described, along with the first experiences of applying those methods during the rotting process . The investigated system is evaluated by means of life cycle impact assessment, with a focus on odour . It is demonstrated which of the measured substances (i.e . VOC) can potentially contribute to the odorant concentration . Further, it is shown which odour-intensive substances can be reduced by deploying ionization . Finally, the authors respond to the fact that the cleaning efficiency of ionization strongly depends on the humidity of the treated waste gas stream.

J Environ Sci Health A Tox Hazard Subst Environ Eng, 2004 Aug, 39(9), 2447 - 63
Effects of periods of nonuse and fluctuating ammonia concentration on biofilter performance; Chen YX et al.; A systematic study on the transient behavior of odor treatment using biofilters is described . The biofilters were exposed to variations in contaminant loading and periods of nonuse . Two bench-scale biofilters with different filter media were used . Mixtures of compost/perlite (5:1) and dry sludge/granular active carbon (5:1) were used as filter media . Ammonia (NH3), one of the main malodorous gases, was used as the target compound . The response of each biofilter to variations in contaminant mass loading, periodic nonuse, water content, and inlet concentration pulse was studied . The nonuse period comprised of two stages: the "idle phase" when no air was passing through the biofilters, and the "no-contaminant-loading phase" when only humidified air was passing through the biofilters . Concentration spike was applied to study the effects of shock loading on the biofilter performance . Biofilters responded effectively to NH3 concentration variations and shock loading by rapidly recovering to the original removal rates within 6-12h . The results indicated re-acclimation times ranged from several hours to longer than a day . Longer idle phase produced longer re-acclimation periods than periods of no contaminant loading . When the media was dried during the biofiltration process, elimination capacity dropped accordingly for both biofilters . After 24 h of drying, the biofilter experiment could be restarted and run for a few days for recovering.

J Biotechnol, 2004 Sep 30, 113(1-3), 305 - 19
Fungal biocatalysts in the biofiltration of VOC-polluted air; Kennes C et al.; Gas-phase biofilters used for the treatment of waste gases were originally packed with compost or other natural filter beds containing indigenous microorganisms . Over the past decade much effort has been made to develop new carrier materials, more performant biocatalysts and new types of bioreactors . Elimination capacities reached nowadays are 5 to 10 times higher than those originally reported with conventional compost biofilters . With the recently developed inert filter beds, inoculation is a prerequisite for successful start-up and operation . Either non-defined mixed cultures or pure bacterial cultures have originally been used . The search for efficient fungal biocatalysts started only a few years ago, mainly for the biofiltration of waste gases containing hydrophobic compounds, such as styrene, alpha-pinene, benzene, or alkylbenzenes . In this review, recently isolated new fungal strains able to degrade alkylbenzenes and other related volatile organic pollutants are described, as well as their major characteristics and their use as biocatalysts in gas-phase biofilters for air pollution control . In biofiltration, the most extensively studied organism belongs to the genus Exophiala, although strains of Scedosporium, Paecilomyces, Cladosporium, Cladophialophora, and white-rot fungi are all potential candidates for use in biofilters . Encouraging results were obtained in most of the cases in which some of those organisms were present in gas-phase biofilters . They allow reaching high elimination capacities and are resistant to low pH values and to reduce moisture content.

Blood Purif, 2004, 22(5), 446 - 52 Epub 2004.
Acetate-free hemodialysis: a feasibility study on a technical alternative to bicarbonate dialysis; Duranti E; This study aimed at evaluating the feasibility of an acetate-free hemodialysis (AFHD) technique, comparing it with acetate-free biofiltration (AFB) and bicarbonate dialysis (BD) . The assessment of the parameters concerned: electrolyte kinetics (Na+, K+), acid-base balance (HCO3-, pH), dialysis efficiency (Kt/V), serum beta2-microglobulin reduction ratio, nutritional status (normalized protein catabolic rate, serum albumin and total proteins, body mass index), hemopoietic status (hemoglobin, hematocrit), and some clinical parameters (systolic and diastolic blood pressures, heart rate, percent blood volume reduction measured by Hemoscan) . Nine patients participated in this study which was conducted using a Latin square randomized experimental design . The results of the last week of each month of the study (1 month for each technique) were analyzed by means of Anova for repeated measures . The different treatments were comparable with regard to the main dialysis parameters such as blood flow (320 ml/min) and weight loss rate (0.6 +/- 0.1 kg/h), while dialysis length and dialysate conductivities were different, depending on the dialysis technique . Electrolyte kinetics and acid-base balance were similar during the three periods . The dialysis efficiency for small molecules (Kt/V of urea) was similar (between 1.4 and 1.6); however, AFB seemed to show a higher beta2-microglobulin reduction rate (47.6 +/- 4 vs . 4.3 +/- 10% for AFHD and vs . 9.9 +/- 5% for BD; p < 0.001) . The nutritional and hemopoietic status maintained stable, and the hemodynamic parameters were comparable during all periods . The percent blood volume reduction at the end of the treatments was not statistically different (-14.9 +/- 9.4% in AFB, -12.1 +/- 5.1% in AFHD, and -12.2 +/- 4.4% in BD), and these results could explain the similar hemodynamic behavior during the three periods . In conclusion, AFHD appears to be a safe technique which has all positive effects of AFB and the low costs of BD . In our opinion, it could be used in patients with few clinical impairments, usually treated with hemodialysis, in whom a biocompatible treatment is indicated.

Langmuir, 2004 Sep 14, 20(19), 8035 - 41
Surface modification of nanoporous alumina surfaces with poly(ethylene glycol); Popat KC et al.; Nanoporous alumina surfaces have a variety of applications in biosensors, biofiltration, and targeted drug delivery . However, the fabrication route to create these nanopores in alumina results in surface defects in the crystal lattice . This results in inherent charge on the porous surface causing biofouling, that is, nonspecific adsorption of biomolecules . Poly(ethylene glycol) (PEG) is known to form biocompatible nonfouling films on silicon surfaces . However, its application to alumina surfaces is very limited and has not been well investigated . In this study, we have covalently attached PEG to nanoporous alumina surfaces to improve their nonfouling properties . A PEG-silane coupling technique was used to modify the surface . Different concentrations of PEG for different immobilization times were used to form PEG films of various grafting densities . X-ray photoelectron spectroscopy (XPS) was used to verify the presence of PEG moieties on the alumina surface . High-resolution C1s spectra show that with an increase in concentration and immobilization time, the grafting density of PEG also increases . Further, a standard overlayer model was used to calculate the thickness of PEG films formed using the XPS intensities of the Al2p peaks . The films formed by this technique are less than 2.5 nm thick, suggesting that such films will not clog the pores which are in the range of 70-80 nm.

Huan Jing Ke Xue, 2004 May, 25(3), 40 - 3
{Comparison on the performance of biostyr and bio-ceramic filter used for biological pretreatment of raw water}; Sang JQ et al.; A new biological filter called biostyr using biostyrene as media to purify raw water was compared with the widely studied bio-ceramic filter . The raw water was taken from a reservoir located in Northern China . It was shown this new biological filter could obviously improve the raw water quality . As far as the raw water investigated in this study was concerned, the removal percentage of COD(Mn), NH4+-N in the filter was 5%-20%, 80%-95%, respectively, and turbidity of the raw water decreased correspondingly, which indicated the feasibility that this filter could be applied in the field of biological pretreatment of raw water . It was also shown that under the uniform operating conditions, the performance of this new filter on the removal of contaminants, especially organics and turbidity, was slightly inferior to the bio-ceramic filter and would be more remarkably affected adversely by backwashing than bioceramic filter.

Water Sci Technol, 2004, 50(1), 1 - 6
Pathogen removal efficiency from UASB + BF effluent using conventional and UV post-treatment systems; Keller R et al.; The aim of this study was to verify the efficiency of removal of microorganisms in effluents of a Wastewater Treatment Plant (WWTP) comprising an association of a UASB reactor followed by three submerged aerated biofilters (BAF) and one tertiary filter . The WWTP designed to treat domestic wastewater from a population of 1,000 inhabitants showed high removal efficiency for organic matter and suspended solids . Helminth eggs were also efficiently removed from the tertiary effluent and were found in the sludge from the UASB reactor; however, removal of bacteria in this system was very low . To enhance the efficiency of the system, the effluent from tertiary filters was submitted to UV disinfection in a real scale reactor . Our results showed that UV irradiation was very effective at lowering the concentrations of E . coli, thermotolerant coliforms and coliphages to acceptable levels for agricultural reuse . Salmonella spp . and helminth eggs were seeded into the tertiary effluent before passing through the UV reactor. , , . Salmonella was not found in the final effluent, but helminth eggs were not completely inactivated by UV irradiation and viable eggs were detected after 28 d of incubation.

Appl Biochem Biotechnol, 1999 Spring, 77-79, 561 - 70
Performance of fibrous bed bioreactor for treating odorous gas: scientific note; Chua H et al.; A fibrous bed bioreactor was used for treatment of odorous volatile fatty acid (VFA) . The effect of gaseous VFA (acetic, propionic, and butyric acids) mass loading on the bioreactor performance was investigated . The VFA degrading microbial culture was selected from activated sludge by the three VFAs using a shake-flask culture . The selected microorganisms were then immobilized in a biofilter using cotton fabric as packing material . In the biofiltration experiment, the inlet gas flow rates ranged from 1 to 4 L/min, the total VFA concentrations ranged from 0.10 to 0.43 g/m3, and the resulting total mass loadings of VFA studied ranged from 9.7 to 104.3 g/m3/h . At total mass loading of 104.3 g/m3/h, the VFA removal efficiency was 87.7% . Higher removal efficiencies (>90%) were achieved at mass loadings below 50.3 g/m3/h.

J Air Waste Manag Assoc, 2004 Jul, 54(7), 871 - 89
Effect of advanced oxidants generated via ultraviolet light on a sequentially loaded and regenerated granular activated carbon biofilter; Dusenbury JS et al.; The objective of this research was to investigate a sequentially loaded and regenerated granular activated carbon (GAC) biofilter system and to determine whether regenerative ozonation/advanced oxidation could improve the removal and biodegradation of a volatile organic compound from a contaminated airstream . Bench-scale reactors were constructed to operate in a manner analogous to a commercially available system manufactured by Terr-Aqua Environmental Systems (only with longer contact time) . The GAC system consisted of two GAC biofilter beds that operated in a cyclical manner . On a given day, the first GAC bed adsorbed methyl isobutyl ketone from a simulated waste airstream, while the second bed underwent regeneration; then on the next day, the second bed was in the adsorption mode while the first was regenerated . Three bench-scale systems were used to compare the performance under three operating conditions: (1) ozone/ associated oxidant regeneration of a GAC biofilter system that was seeded with microorganisms from a field site, (2) a humid air regeneration of a seeded GAC biofilter, and (3) a humid air regeneration of an unseeded GAC biofilter . For the advanced oxidant regenerated GAC biofilter, a maximum removal efficiency of >95% was achieved with an empty bed contact time of 148 sec and an influent concentration of 125 ppm methyl isobutyl ketone, and 90-95% was achieved at 148-sec empty bed contact time and a 1150-ppm influent.

J Air Waste Manag Assoc, 2004 Jul, 54(7), 834 - 44
Design and performance characterization strategy using modeling for biofiltration control of odorous hydrogen sulfide; Martin RW Jr et al.; Biofilter, dynamic modeling software characterizing contaminant removal via biofiltration, was used in the preliminary design of a biofilter to treat odorous hydrogen sulfide (H2S) . Steady-state model simulations were run to generate performance plots for various influent concentrations, loadings, residence times, media sizes, and temperatures . Although elimination capacity and removal efficiency frequently are used to characterize biofilter performance, effluent concentration can be used to characterize performance when treating to a target effluent concentration . Model simulations illustrate that, at a given temperature, a biofilter cannot reduce H2S emissions below a minimum value, no matter how large the biofilter or how long the residence time . However, a higher biofilter temperature results in lower effluent H2S concentrations . Because dynamic model simulations show that shock loading can significantly increase the effluent concentration above values predicted by the steady-state model simulations, it is recommended that, to consistently meet treatment objectives, dynamic feed conditions should be considered . This study illustrates that modeling can serve as a valuable tool in the design and performance optimization of biofilters.

Commun Agric Appl Biol Sci, 2003, 68(2 Pt A), 211 - 3
Examination of the long-term process for purifying gaseous discharges in industrial biofilter; Vinarov A et al.; Results of industrial exploitation of the biofilter unit for purifying gaseous discharges of hazardous organic substances are examined . A population of microbial associated composed by selected strains of yeast and bacterial cells in the biofilm on the surface of the filtering sheets and in the liquid phase were monitoring for a long-term (about 2 years) utilization process in industrial biofilter . Overall, the biofilter with productivity 12,000-15,000 m3 purified flow per hour and very low energy consumption (0.3-0.4 wt.h/m3) as an open and autonomic system maintained its microbial association, thereby providing high degree (93-96%) purification of industrial gaseous discharges from organic pollutants.

Commun Agric Appl Biol Sci, 2003, 68(2 Pt A), 195 - 8
Degradation of isobutyraldehyde and its intermediates in a compost biofilter; Sercu B et al.; This study demonstrates that at low to medium isobutyraldehyde loading rates (191 gm(-3) d(-1)-933 gm(-3) d(-1)), 100% removal efficiencies can be obtained in a compost biofilter . However, increasing the loading rate to 1500-1900 gm(-3) d(-1) caused a drop in degradation efficiency, a pH decrease and production of isobutyl alcohol and isobutyric acid . Additional batch and continuous experiments were performed to study the effect of pH and compost moisture content on the biofiltration of isobutyraldehyde, isobutyl alcohol and isobutyric acid . It was shown that the degradation rate of the three compounds decreased in the order isobutyraldehyde > isobutyl alcohol >> isobutyric acid, with no significant degradation for isobutyric acid . The isobutyl alcohol degradation rate was negatively influenced by the presence of isobutyraldehyde, while isobutyraldehyde degradation was not affected by the presence of either of the two compounds . A pH of 5.2 apparently inhibited the isobutyl alcohol degradation and lowered the isobutyraldehyde degradation rate, although adaptation of the microorganisms to low pH seemed to occur in the biofilters . Moisture content had a smaller effect on the degradation rates, although continuous experiments showed that a very high water content (55% compared to 40%) negatively affected isobutyraldehyde elimination increasingly during the course of the experiment . As a conclusion, it appears that at high loads of isobutyraldehyde, isobutyric acid is accumulated in the biofilter, resulting in a drop of pH . Consequently, isobutyraldehyde removal efficiency decreases and both isobutyl alcohol and isobutyric acid are measured in the effluent . It is suggested that next to moisture control, a pH buffer is necessary to remove high loads of isobutyraldehyde and to avoid persistence of intermediates in the effluent.

Waste Manag, 2004, 24(7), 643 - 53
Long-term behavior of passively aerated compost methanotrophic biofilter columns; Wilshusen JH et al.; The methane oxidation potential of several types of compost methanotrophic biofilter columns were compared in the laboratory over a period of 220 days . The results indicate an increase in methanotrophic activity over a period of about 100 days, up to a maximum of 400 g m(-2) day(-1), and a gradual decline to about 100 g m(-2) day(-1) within the next 120 days . High methane oxidation rates appear to be restricted to a small area of the column, 10-15 cm thick . Based on the laboratory investigations carried out to determine the cause for the decline in methane oxidation rate, it was concluded that the formation of exopolymeric substances (EPS), at the zones of maximum methane oxidation, was responsible for this decline . In monitoring methane oxidation in a column for up to 600 days, it was observed that mixing of the medium after formation of EPS enabled the column to temporarily recover high performance . The results suggest that stable, homogenous compost, with a low C/N and low ammonium content, mixed on a regular basis, could achieve and maintain high methane oxidation efficiencies .

Environ Sci Pollut Res Int, 2004, 11(3), 152 - 7
(M)VOC and composting facilities . Part 2: (M)VOC dispersal in the environment; Muller T et al.; BACKGROUND, AIMS AND SCOPE: Composting facilities are known to release odorous volatiles due to biodegradation of municipal waste and plant residues . Although odour perception and its grading is influenced by experience, attitude and adaptation, these emissions have created a lack of acceptance for residents in the vicinity of composting facilities . Enclosure of compost pile halls, ventilation systems and biofilters are often insufficient to minimise the burden of compost-derived compounds in the air . Moreover, economic considerations forced smaller communities to establish less sophisticated facilities with open storage areas and other relevant sources for wind-borne dispersal of bioaerosols . Aim of the present study was to characterise the immission and dispersal of microbial volatiles (MVOC) and, besides, to find coincidences between MVOC and compost odour . METHODS: In the course of this study, the surroundings of two composting facilities, differing in their type of process engineering, were investigated for emission of volatiles in the environment . Both microbially and plant-derived substances were assessed, several of which have low odour thresholds . Air samples were taken in distances ranging from 50 to 800 m in a downwind direction from each facility . RESULTS AND DISCUSSION: Compost-derived and microbial volatile organic compounds (MVOC) were found at distances of up to 800 m from the composting facilities . Terpenes like alpha-pinene, camphene and camphor were the dominant compounds and coincided with typical compost odour, whereas several typical MVOC were not found at greater distances . The terpenes in combination with certain MVOC may play an important role in the perception of compost odour . Exposure concentrations were not of toxicological relevance, but sensory irritation and psychohygienic effects due to an annoyance potential of such compounds should not be dismissed . RECOMMENDATIONS AND OUTLOOK: Although terpenes are generally associated with pleasant odour characteristics, they seemed to contribute to malodours in a mixture with other VOC, in this context of volatile waste from compost facilities . Malodorous emissions from biowaste have to be considered as sources of health complaints and the investigation of mixtures of compost-derived volatiles is still inevitable . Exposure levels have to be discussed taking VOC mixtures into account . Within composting facilities, technical devices have to be improved to minimise dispersal of volatiles to prevent residents from immissions eventually causing health complaints.

Appl Microbiol Biotechnol . 2004 Jul 14; {Epub ahead of print}
Use of activated carbon as a support medium for H(2)S biofiltration and effect of bacterial immobilization on available pore surface; Ng YL et al.; The use of support media for the immobilization of microorganisms is widely known to provide a surface for microbial growth and a shelter that protects the microorganisms from inhibitory compounds . In this study, activated carbon is used as a support medium for the immobilization of microorganisms enriched from municipal sewage activated sludge to remove gas-phase hydrogen sulfide (H(2)S), a major odorous component of waste gas from sewage treatment plants . A series of designed experiments is used to examine the effect on bacteria-immobilized activated carbon (termed "biocarbon") due to physical adsorption, chemical reaction, and microbial degradation in the overall removal of H(2)S . H(2)S breakthrough tests are conducted with various samples, including microbe-immobilized carbon and Teflon discs, salts-medium-washed carbon, and ultra-pure water-washed carbon . The results show a higher removal capacity for the microbe-immobilized activated carbon compared with the activated carbon control in a batch biofilter column . The increase in removal capacity is attributed to the role played by the immobilized microorganisms in metabolizing adsorbed sulfur and sulfur compounds on the biocarbon, hence releasing the adsorption sites for further H(2)S uptake . The advantage for activated carbon serving as the support medium is to adsorb a high initial concentration of substrate and progressively release this for microbial degradation, hence acting as a buffer for the microorganisms . Results obtained from surface area and pore size distribution analyses of the biocarbon show a correlation between the available surface area and pore volume with the extent of microbial immobilization and H(2)S uptake . The depletion of surface area and pore volume is seen as one of the factors which cause the onset of column breakthrough . Microbial growth retardation is due to the accumulation of metabolic products (i.show $132#e., sulfuric acid); and a lack of water and nutrient salts in the batch biofilter are other possible causes of column breakthrough.

Mar Pollut Bull, 2004 Aug, 49(3), 196 - 205
Dreissena polymorpha (Bivalvia: Dreissenidae) in the Neva Estuary (eastern Gulf of Finland, Baltic Sea): is it a biofilter or source for pollution?
Orlova M, Golubkov S, Kalinina L, Ignatieva N.
The zebra mussel Dreissena polymorpha, a ponto-caspian byssate bivalve, forms permanent dense populations along the shoreline in the northern part of the inner Neva Estuary . Its total biomass along a 17 km transect reached 4980 tons (mean 1060 g m(-2)) in 2000 and 6510 tons (mean 1385 g m(-2)) in 2001 . Being persistent and abundant, the zebra mussel populations played an important role in benthic-pelagic coupling in inner Neva River Estuary . The D . polymorpha population released up to 514 kg day(-1) of dissolved inorganic phosphorus and was, therefore, a major source of bioavailable nutrients in the area . Mussel beds were also efficient biofilters and precipitate 15,020 kg day(-1) of particulate organic matter during the warm season . About 50% of precipitated matter had a relatively long retention time, being utilized within zebra mussel populations, while the rest was deposited as faeces and pseudofaeces and served as a source for organic pollution to the eastern Gulf of Finland.

J Environ Sci Health A Tox Hazard Subst Environ Eng, 2004 Jun, 39(6), 1447 - 54
Design of biological filter for iron and manganese removal from water; Yang H et al.; The technology core of biological removal of iron and manganese by contact oxidation is iron and manganese oxidizing bacteria . This article made a study on down flow and up flow filtration, the results show that down flow filtration of the homogenous filter medium is more adapted to the reproduction of biotic formation . Homogeneous filter increase the depth of effective biological filter and the biomass that develop the bio-chemical capability of the biological filter . Homogeneous filter increase removal capability of Fe/Mn and alleviate the formation of sludge cake, which can get a quite backwash . Down flow homogeneous biological filter can solve some engineering problems of heterogeneous up flow filtration . The down flow homogeneous biological filter is more adapted to the removal of Fe/Mn in groundwater.

Water Sci Technol, 2004, 49(9), 273 - 80
Removal of geosmin and 2-methylisoborneol by biological filtration; Elhadi SL et al.; The quality of drinking water is sometimes diminished by the presence of certain compounds that can impart particular tastes or odours . One of the most common and problematic types of taste and odour is the earthy/musty odour produced by geosmin (trans-1, 10-dimethyl-trans-9-decalol) and MIB (2-methylisoborneol) . Taste and odour treatment processes including powdered activated carbon, and oxidation using chlorine, chloramines, potassium permanganate, and sometimes even ozone are largely ineffective for reducing these compounds to below their odour threshold concentration levels . Ozonation followed by biological filtration, however, has the potential to provide effective treatment . Ozone provides partial removal of geosmin and MIB but also creates other compounds more amenable to biodegradation and potentially undesirable biological instability . Subsequent biofiltration can remove residual geosmin and MIB in addition to removing these other biodegradable compounds . Bench scale experiments were conducted using two parallel filter columns containing fresh and exhausted granular activated carbon (GAC) media and sand . Source water consisted of dechlorinated tap water to which geosmin and MIB were added, as well as, a cocktail of easily biodegradable organic matter (i.e . typical ozonation by-products) in order to simulate water that had been subjected to ozonation prior to filtration . Using fresh GAC, total removals of geosmin ranged from 76 to 100% and total MIB removals ranged from 47% to 100% . The exhausted GAC initially removed less geosmin and MIB but removals increased over time . Overall the results of these experiments are encouraging for the use of biofiltration following ozonation as a means of geosmin and MIB removal . These results provide important information with respect to the role biofilters play during their startup phase in the reduction of these particular compounds. , . In addition, the results demonstrate the potential biofilters have in responding to transient geosmin and MIB episodes.

Water Res, 2004 Jul, 38(12), 2839 - 46
Evaluation of biodegradability of NOM after ozonation; Yavich AA et al.; The major purpose of this study was to develop a simple procedure to describe the kinetics of biodegradation of natural organic matter (NOM) in drinking water and to use this procedure to evaluate changes in the concentration of biodegradable organic matter during ozonation and biotreatment . The proposed approach quantitatively describes the formation and removal of rapidly and slowly biodegradable fractions of NOM . This study showed that, depending on source water, ozonation of NOM may result in either minimal formation of biodegradable organic carbon (BDOC), or the formation of predominantly rapidly biodegradable NOM, or in the formation of both rapidly and slowly biodegradable NOM . The kinetic data obtained in this study suggest that while conventional biofiltration processes are capable of removing the rapidly biodegradable fraction, slowly biodegradable organic matter would remain in the filter effluent and may cause bacterial regrowth in the distribution system . An addition of a small amount of easily biodegradable carbon ("stimulated" biodegradation) to ozonated water appears to be effective for the removal of slowly biodegradable organic matter.

Environ Technol, 2004 Apr, 25(4), 491 - 9
Application of a solvent-tolerant microbial consortium for biofiltration of extremely high concentration gaseous solvent streams; Leethochawalit M et al.; The aerobic biological oxidation of 2-propanol (isopropyl alcohol, IPA) at extremely high concentrations in air by an enriched solvent-tolerant microbial consortium operating at ambient temperature was evaluated for six months . Solvent-tolerant microbial cells were immobilised onto porous glass pall rings and fed with either IPA or its metabolic product acetone as sole carbon source . Successful biofiltration of solvent vapour at a concentration of 24 g m(-3) was achieved with oxidation of up to 100% total inlet carbon . The maximum IPA mass loading and IPA elimination capacity (EC) was 1700 g m(-3) h(-1) . This performance exceeds all previous values published in the literature for similar processes . A slip feed experiment, using acetone, was also performed in order to assess the substrate specificity performance . The biofilter responded successfully to a switch from acetone to IPA as sole carbon source, displaying little reduction in overall organic carbon removal.

J Air Waste Manag Assoc, 2002 Feb, 52(2), 208 - 19
Development and demonstration of an explicit lumped-parameter biofilter model and design equation incorporating monod kinetics; Smith FL et al.; Biofiltration is an economical air pollution control (APC) technology, particularly suitable for the treatment of air-streams having high flow rates and low concentrations of volatile organic compounds (VOCs) . This technology utilizes enzymatic catalysis at ambient conditions to mineralize such pollutants to CO2, H2O, and salts . A pilot-scale study conducted for more than 4 years investigated the development of a new biofiltration technology employing trickle bed air biofilters (TBABs) . Following the completion of this experimental study, additional data analysis was performed to develop a simple lumped-parameter biofilter model, assuming first-order kinetics . This model related the observed biofilter performance to the principle independent physical, thermodynamic, and biochemical parameters . The initial model has subsequently been expanded to incorporate Monod kinetics . In this paper, the development and use of the final explicit lumped-parameter biofilter model and design equation, incorporating Monod kinetics, are presented . To facilitate the application of this model, practical procedures are also presented for the determination of VOC solubility, VOC biokinetic Monod parameters, and the maximum practical biofilter inlet VOC concentration.

Water Res, 2004 May, 38(9), 2258 - 67
Performance of a fungal biofilter treating gas-phase solvent mixtures during intermittent loading; Moe WM et al.; Biological treatment processes used to remove and degrade volatile organic compounds (VOCs) from contaminated gases emitted by industrial operations or waste treatment processes are almost always subjected to transient loading conditions because of the inherently unsteady-state nature of contaminant generating processes . In the study presented here, a laboratory-scale biofilter populated by a mixed culture of fungi was used to study the transient response to various periods of no contaminant loading in a system treating a model waste gas stream containing a mixture of commonly used solvents . The biofilter, packed with cubed polyurethane foam media and operated with an empty bed residence time of 15s, was supplied with a four-component mixture of n-butyl acetate, methyl ethyl ketone, methyl propyl ketone, and toluene at target influent concentrations of 124, 50.5, 174, and 44.6 mg/m(3), respectively . This corresponds to a total VOC loading rate of 94.3g/(m(3)h) . Biofilter performance was evaluated over a 94-day period for three loading conditions intended to simulate processes generating contaminated gases only during daytime operation, daytime operation with weekend shutdown periods, and with long term (9-day) shutdown . Results indicate that fungal biofilters can be an effective alternative to conventional abatement technologies for treating solvent contaminated off-gases even under discontinuous loading conditions.

Appl Microbiol Biotechnol, 2004 Aug, 65(3), 349 - 55 Epub 2004 May 08.
Styrene degradation by Pseudomonas sp . SR-5 in biofilters with organic and inorganic packing materials; Jang JH et al.; Pseudomonas sp . SR-5 was isolated as a styrene-degrading bacterium . In liquid culture containing 1% (v/v) styrene, more than 90% styrene was degraded in 53 h and the doubling time of SR-5 was 2 h . The removal of styrene gas was investigated in biofilters for 31 days using an organic packing material of peat and an inorganic packing material of ceramic inoculated with SR-5 . The maximum-styrene-elimination capacities for peat and ceramic packing materials were 236 and 81 g m(-3) h(-1), respectively . The percentage of styrene converted to low molecular weight compounds including CO(2) in the peat and ceramic biofilters during a 10-day operation were estimated to be 90.4 and 36.7%, respectively . As the pressure drop in the peat bioflter at the end of experiment was significantly higher than that in ceramic biofilter, a biofilter using a mixture of peat and ceramic was tested . We determined that the maximum elimination capacity was 170 g m(-3) h(-1) and the production of low molecular weight compounds was 95% at a low pressure drop for this mixed packing material filter.

J Environ Sci Health A Tox Hazard Subst Environ Eng, 2004 Apr, 39(4), 927 - 37
Odor control in composting plants: results from full-scale experiences; Canovai A et al.; The development and spread of mechanical biological treatment (MBT) and composting plants is often hindered by the problems and concerns arising from emission bad odors . Several technologies are now available to process exhausted air originated from these or similar plants . Exhausted air emissions contain a large amount of organic compounds, most of them in very low concentrations . This determines the advantage in using biological abatement systems (biofilters) instead of physical-chemical treatments . This article describes the operative results obtained in two Italian waste treatment plants, one in Albano, near Rome, and the other in the "ex-Maserati area" of Milan, including (i) the analysis of operational parameters as temperature, pH . humidity, loss of pressure of the biofilter affecting the biofiltration efficiency, for both chemical parameters and odorous compound concentration, measured by means of odor panel evaluation technique and (ii) the efficiency of the biofiltration system for several compounds present in air emissions, analyzing organic substances by means of gas chromatography/mass spectrometry . The two plants used similar biofiltration systems except for the material used as biofilter bed . A bioscrubber pretreatment of the air flow coming from the aerobic reactor was tested in the Albano plant for the purpose of reducing the odor concentration of the most impacting flow going to the biofilter.

Lett Appl Microbiol, 2004, 38(6), 522 - 6
Microbial characterization of organic carrier colonization during a model biofiltration experiment; Pineda R et al.; AIMS: Dynamic microbial characterization of the colonization of organic carrier during a model biofiltration experiment using methanol as air pollutant . METHODS AND RESULTS: A model biofilter was used in order to characterize the micro-organisms involved in the colonization of a model organic carrier . The model system consisted of closed vial as biofilter, peanut shells as lignocellulosic carrier and methanol as air pollutant . The micro-organisms involved in biofiltration were identified and characterized for their lignocellulolytic and methylotrophic activities . Fungi presented a higher lignocellulolytic activity than bacteria . A steady-state was reached after 15 to 20 days . CONCLUSIONS: The consortium naturally associated to peanut shells is limited to few aerobic bacteria and lignocellulolytic fungi . This consortium was able to degrade methanol without external nutrient supply . SIGNIFICANCE AND IMPACT OF THE STUDY: To our knowledge, this is the first paper that focuses on carrier degradation processes and the micro-organisms involved during the start-up period of a biofiltration process.

J Air Waste Manag Assoc, 2004 Apr, 54(4), 450 - 8
Operational characteristics of effective removal of H2S and NH3 waste gases by activated carbon biofilter; Chung YC et al.; Simultaneous removal of hydrogen sulfide (H2S) and ammonia (NH3) gases from gaseous streams was studied in a biofilter packed with granule activated carbon . Extensive studies, including the effects of carbon (C) source on the growth of inoculated microorganisms and gas removal efficiency, product analysis, bioaerosol emission, pressure drop, and cost evaluation, were conducted . The results indicated that molasses was a potential C source for inoculated cell growth that resulted in removal efficiencies of 99.5% for H2S and 99.2% for NH3 . Microbial community observation by scanning electron microscopy indicated that granule activated carbon was an excellent support for microorganism attachment for long-term waste gas treatment . No disintegration or breakdown of biofilm was found when the system was operated for 140 days . The low bioaerosol concentration emitted from the biofilter showed that the system effectively avoided the environmental risk of bioaerosol emission . Also, the system is suitable to apply in the field because of its low pressure drop and treatment cost . Because NH3 gas was mainly converted to organic nitrogen, and H2S gas was converted to elemental sulfur, no acidification or alkalinity phenomena were found because of the metabolite products. , . Thus, the results of this study demonstrate that the biofilter is a feasible bioreactor in the removal of waste gases.

Waste Manag Res, 2004 Feb, 22(1), 42 - 8
Assessment of the methane oxidation capacity of soil; Maurice C et al.; Methane oxidation capacity of three soil matrices was assessed using a new method based on the pressure fall resulting from methane oxidation . The effects of incubation temperature, moisture and methane content on the oxidation capacity were studied . Parameters observed were non-methanotrophic oxygen consumption, methane assimilation, length of the lag period before steady pressure fall was reached, initial pressure fall and maximum pressure fall . Filling material taken from a biofilter was tested . The length of the lag period was an index of prior exposure of the soil to methane emissions . Incubation temperature of 30 degrees C and soil moisture at the water-holding capacity were chosen to standardize the test . Oxygen depletion by non-methanotrophs varied between 40 and 60% of the total oxygen consumption while methane assimilation was at 40 to 50% of the total methane consumption.

Int J Artif Organs, 2004 Mar, 27(3), 186 - 94
Artificial in vivo biofiltration: slow continuous intravenous plasmafiltration (SCIP) and artificial organ support; Handley HH et al.; An intravenous plasmafiltration (SCIP) catheter has been developed and is proposed for clinical investigation into the alleviation of acute fluid overload by SCUF of the extracted plasma . The system utilizes a unique backflushing technique, high intravenous shear flow rates and biocompatible polymers to minimize protein and platelet aggregation along the filter surfaces . The absence of platelets from the extracted plasma promotes the longevity of ultrafiltration cartridges, thus theoretically minimizing attendant labor associated with continuous renal replacement therapies . Clinical studies are currently being planned for the near future . Plasma SCUF is envisioned as a predecessor technology to future applications in therapeutic apheresis, tissue engineering, therapeutic sorbent technologies . Further, with improved longevity profiles, intravenous SCUF or dialysis and implantable or wearable artificial organs based upon artificial in vivo biofiltration are possible.

Biotechnol Bioeng, 2004 May 20, 86(4), 468 - 81
Treatment of MEK and toluene mixtures in biofilters: effect of operating strategy an performance during transient loading; Atoche JC et al.; In recent years, biofiltration has been increasingly applied as an air pollution control technology to minimize or eliminate emissions of volatile organic compounds from industrial sources and environmental remediation activities . Although the ability of this technology to maintain high removal efficiency during relatively steady loading conditions has been well established for many waste streams, relatively little research has focused on development of operating strategies that could improve treatment performance during transient loading conditions typical of industrial operations . In the research described herein, two operating strategies were evaluated over a period of 295 days in biofilters treating a model waste gas stream containing a two-component mixture of methyl ethyl ketone (MEK) and toluene . One biofilter was operated as a sequencing batch biofilter (SBB), and the other was operated as a conventional continuous-flow biofilter (CFB) . During "normal" steady loading conditions, the model waste stream contained MEK concentrations ranging from 80 to 89 ppmv and toluene concentrations ranging from 28 to 30 ppmv . Both biofilter operating strategies resulted in stable long-term performance with greater than 99% contaminant removal during these normal loading conditions . On a regular basis, the influent MEK and toluene concentrations were temporarily increased to five times the normal influent concentration for the duration of 1 h to test performance during transient "shock loading" conditions . Biofilter performance during the model shock loading conditions demonstrate that SBB operating strategies can result in superior treatment in two important areas: (1) overall mass of contaminants removed and (2) minimum instantaneous removal efficiency .

Appl Microbiol Biotechnol, 2004 Aug, 65(2), 235 - 42 Epub 2004 Apr 23.
Biofiltration of waste gases containing a mixture of formaldehyde and methanol; Prado OJ et al.; Several biofilters and biotrickling filters were used for the treatment of a mixture of formaldehyde and methanol; and their efficiencies were compared . Results obtained with three different inert filter bed materials (lava rock, perlite, activated carbon) suggested that the packing material had only little influence on the performance . The best results were obtained in a biotrickling filter packed with lava rock and fed a nutrient solution that was renewed weekly . A maximum formaldehyde elimination capacity of 180 g m(-3) h(-1) was reached, while the methanol elimination capacity rose occasionally to more than 600 g m(-3) h(-1) . Formaldehyde degradation was affected by the inlet methanol concentration . Several combinations of load vs empty bed residence time (EBRTs of 71.9, 46.5, 30.0, 20.7 s) were studied, reaching a formaldehyde elimination capacity of 112 g m(-3) h(-1) with about 80% removal efficiency at the lowest EBRT (20.7 s).

Lab Chip, 2002 Feb, 2(1), 27 - 30 Epub 2001 Dec 06.
An integrated microfluidic biochemical detection system for protein analysis with magnetic bead-based sampling capabilities; Choi JW et al.; This paper presents the development and characterization of an integrated microfluidic biochemical detection system for fast and low-volume immunoassays using magnetic beads, which are used as both immobilization surfaces and bio-molecule carriers . Microfluidic components have been developed and integrated to construct a microfluidic biochemical detection system . Magnetic bead-based immunoassay, as a typical example of biochemical detection and analysis, has been successfully performed on the integrated microfluidic biochemical analysis system that includes a surface-mounted biofilter and electrochemical sensor on a glass microfluidic motherboard . Total time required for an immunoassay was less than 20 min including sample incubation time, and sample volume wasted was less than 50 microl during five repeated assays . Fast and low-volume biochemical analysis has been successfully achieved with the developed biofilter and immunosensor, which is integrated to the microfluidic system . Such a magnetic bead-based biochemical detection system, described in this paper, can be applied to protein analysis systems.

Environ Pollut, 2000 Nov, 110(2), 277 - 83
Removal of toxic metals from solution by leaf, stem and root phytomass of Quercus ilex L . (holly oak); Prasad MN et al.; Increased consciousness for safeguarding the aqueous environment has prompted a search for alternative technologies for the removal of toxic metal ions from aqueous solutions . In this regard, a wide variety of biomass is being considered as adsorbents of heavy metals for treatment of industrial and domestic wastewaters as well as natural waters, including drinking water . In the present investigation, the potential of Quercus ilex phytomass from stem, leaf and root as an adsorbent of chromium (Cr), nickel (Ni), copper (Cu), cadmium (Cd) and lead (Pb) at ambient temperature was investigated . The metal uptake capacity of the root for different metals was found to be in the order: Ni>Cd>Pb>Cu>Cr; stem Ni>Pb>Cu>Cd>Cr; and leaf Ni>Cd>Cu>Pb>Cr . The highest amount adsorbed was Ni (root>leaf>stem) . Data from this laboratory demonstrated that Ni is sequestered mostly in the roots, where concentrations can be as high as 428.4 ng/g dry wt., when 1-year-old seedlings were treated with Ni (2000 mg/l) in pot culture experiments, compared to 7.63 ng/g dry wt., control (garden and greenhouse soil) topsoil where Ni was present in trace amounts . This proves that the root biomass of Q . ilex has the capacity for complexing Ni . Cr exhibited the least adsorption values for all the three types of phytomass compared to other metals . The trend of adsorption of the phytomass was similar for Ni and Cd, i.e . root>leaf>stem . Desorption with 10 mM Na(4) EDTA was effective (55-90%) and, hence, there exists the possibility of recycling the phytomass . The biosorption results of recycled phytomass suggest that the selected adsorbents are re-usable . The advantages and potential of the Q . ilex phytomass as a biofilter of toxic trace metals, the scope and need for enhancing the efficiency of the Q . ilex phytomass as an adsorbent of metals are presented.

Ecotoxicol Environ Saf, 2004 May, 58(1), 117 - 25
Effects of copper on Enteromorpha flexuosa (Chlorophyta) in vitro; Andrade LR et al.; Enteromorpha species are widely used as biomonitors of copper (Cu) contamination in coastal waters, but the effects of Cu at the subcellular level and possible mechanisms of metal resistance are scarcely known . To contribute to the understanding of the Cu accumulation process in macroalgae species, we exposed adult individuals of Enteromorpha flexuosa to 50, 250, and 500 microg Cu/L in seawater for 5 days under controlled conditions . Thereafter, gross photosynthesis rate (GPR) and metal accumulation were measured . Conventional transmission electron microscopy (CTEM) and energy-dispersive X-ray analysis (EDXA) were used to study the metal accumulation process at the cellular level . Treatments with 250 and 500 microg Cu/L were observed to cause an inhibition of the GPR in the algae . Cu accumulation in samples exposed to 500 microgCu/L was 5284+/-561 microg Cu/g (dry wt), whereas in control samples (no Cu addition), accumulation was 9+/-1 microg/g . In cells of plants undergoing the 50 microg Cu/L treatment, the cytoplasm was clearly vacuolated . Thickening of cell walls and increase of relative number of starch granules and of lipid bodies were the main cellular changes observed in plants exposed to 250 and 500 microg Cu/L . EDXA of algae cells after 250 and 500 microg Cu/L exposure detected Cu mainly in vacuole precipitates . Cu was also detected in chloroplasts and in some epiphytic bacteria . It was concluded that E . flexuosa did not avoid penetration of Cu into the cytoplasm and consequently its toxic effects in concentrations of 250 and 500 microg Cu/L . Precipitates containing Cu in vacuoles should be related to a metal immobilization mechanism, minimizing the Cu toxicity for cells . The epiphytic bacteria can act as a biofilter diminishing the availability of free Cu(+2) for algae accumulation.

Kidney Int, 2004 Apr, 65(4), 1499 - 510
Model-based study of the effects of the hemodialysis technique on the compensatory response to hypovolemia; Cavalcanti S et al.; BACKGROUND: Hemodialysis technique (dialysate composition, filter, convection/diffusion ratio, etc.) can have an impact on the patient's tendency to acute hypotension . We have examined the hypothesis that the dialysis technique affects the hypotension risk by altering the cardiovascular compensatory response to hemodialysis-induced hypovolemia . METHODS: Twelve hypotension-prone subjects were studied during six sessions of conventional bicarbonate dialysis (BD) and six sessions of acetate-free biofiltration (AFB) . Blood volume (BV) control system was used in AFB to provide a BV change equivalent to the BV change observed in BD . The efficacy of reflex compensatory mechanisms was assessed by a model-based computer analysis of the BD and AFB sessions . RESULTS: BD sessions were complicated by hypotension more frequently than the AFB ones (34/66 BD vs . 18/66 AFB) . Hypotension arose about 60 minutes earlier in BD (123 +/- 41 minutes in BD vs . 183 +/- 25 minutes in AFB, P < 0.01), and after a smaller BV reduction (hypotension BV 7.9%+/- 2.0% in BD vs . 10.9%+/- 2.6% in AFB, P < 0.05) . Model-based computer analysis of the sessions without hypotension revealed differences in peripheral resistance adaptation (9%+/- 9% BD vs . 19%+/- 7% AFB, P < 0.05) as well as in the stroke volume reduction (19%+/- 8% BD vs . 10%+/- 8% AFB, P < 0.001) . Model analysis of sessions with hypotension indicated that compensatory mechanisms were almost inoperative in BD, whereas a residual capacity to control peripheral resistance and cardiac contractility was present in AFB . Model simulations demonstrated that hypotension occurred later in AFB since the residual compensatory capacity in AFB was able to sustain the arterial pressure for larger BV reductions (8.3% BD vs . 11.2% AFB). , , . CONCLUSION: The increased risk of acute hypotension in BD compared to AFB is caused by a therapy-induced inhibition of reflex compensatory response to hypovolemia.

Biodegradation, 2004 Apr, 15(2), 87 - 96
Treatment of benzene-contaminated airstreams in laboratory-scale biofilters packed with raw and sieved sugarcane bagasse and with peat; Zilli M et al.; Three identical upflow laboratory-scale biofilters, inoculated with the benzene-degrading strain Pseudomonas sp . NCIMB 9688 but filled up with different packing media (PM), specifically raw sugarcane bagasse, sieved sugarcane bagasse and peat, were employed to eliminate benzene from waste air . Biofilters performances were evaluated by continuous runs in parallel at different influent benzene concentrations, sequentially stepped up through three different superficial gas velocities (31, 61, and 122 m h(-1)) . The peat-packed biofilter exhibited the best performances over the whole experimentation, ensuring removal efficiency of 100% for influent benzene concentrations < or = 0.05 g m(-3), regardless of the superficial gas velocity, and up to 0.4 g m(-3) at 31 m h(-1) . Maximum elimination capacities of biofilters packed with raw and sieved sugarcane bagasse and with peat were 3.2, 6.4 and 26 g mPM(-3) h(-1) at 6.1, 12 and 31 g mPM(-3) h(-1) loading rates, resulting in 52, 53 and 84% removals, respectively . The bacterial concentration distribution along the medium was shown to depend on the benzene loading rate and a correlation between specific benzene elimination rate and biomass concentration was established for biofilters packed with sieved sugarcane bagasse and peat . The macrokinetics of the process were also studied using the profiles of benzene and biomass concentrations, collected under different conditions over the height of both biofilters, and a zeroth-order kinetic model was shown to describe successfully the degradation process.

Bioresour Technol, 2004 Jun, 93(2), 131 - 8
Removal of multiple nitrogenous wastes by Aspergillus niger in a continuous fixed-slab reactor; Hwang SC et al.; A biofilter reactor, to which is attached a large variety of microorganisms, can be employed to treat circulating water in an intensive aquaculture system . Some nitrogen-containing wastes, such as ammonium and nitrite, are toxic to the aquatic organisms . The removal rates of the nitrogenous wastes are regarded as indices for the efficiency of treatment by biofilters . In this study, a fungus that was characterized as being able to remediate multiple nitrogenous wastes was identified as Aspergillus niger NBG5 . In a continuous fixed-slab reactor, the heterotrophic fungus utilized ammonium, nitrite, protein, and glucose simultaneously . The fungus assimilated ammonium, nitrite and protein at rates of 0.247, 0.07 and 0.096 g-N/g-cell/day, respectively, at 22 degrees C . The remediation rates of ammonium nitrogenous wastes decreased by a factor of eight at 35 degrees C, while the specific growth rates slightly increased . For nitrogenous wastes, ammonium was a preferred substrate but its rate of consumption declined significantly as temperature increased . The nitrogen consumption rates were inconsistent with the cell yields at high temperature . Further analysis of consumption ratios of C/N revealed that cells grew predominantly from the carbon at high temperature . The A . niger NBG5 consumed glucose rapidly at specific rates of 2-2.5 g-C/g-cell/day at 35 degrees C in the presence of ammonium and nitrite; while sluggish consumption of glucose was observed in the protein substrate . The protein could serve as an alternative carbon source . Further ANOVA statistical analysis with P < 0.05 revealed no significant effects of temperature on the specific growth rates of A . niger on the SG-NH4 and milk-protein substrates, whereas significant effects on the C/N ratio at culture temperatures higher than 25 degrees C were observed . These findings indicated that the carbon utilization rate increased with high temperature, whereas nitrogen utilization increased as temperature declined . A suitable operational temperature was suggested, depending upon the amount of waste contents of C/N . A high temperature stimulates the use of carbon waste, while a low temperature favors remediation of all nitrogenous wastes .

Bioprocess Biosyst Eng, 2004 Jul, 26(4), 223 - 30 Epub 2004 Mar 26.
The mechanism of nutrients dissolved out of a synthetic composite bead filter material in a biofilter; Chan WC et al.; In this study, an optimal process to prepare a synthetic material having nutrient (PVA/peat/KNO(3) composite bead) is developed . The equilibrium water-soluble nitrogen content in the composite bead prepared by this process is 8.25-10.06 mg N/g dry solid . The mass-transport process for the water-soluble nitrogen dissolved out of the composite bead was also investigated . The dissolved out process occurs in two stages: external mass transport occurs in the early stage and the intraparticle diffusion process occurs in the long-term stage . The rate of water-soluble nitrogen dissolved out in both stages is concentration dependent . The path of nitrogen dissolved out is that the nitrogen dispersed in the peat and PVA phases simultaneously diffused into the outer PVA phase and out of the bead surface . The moisture holding capacity of the composite bead bed is better than the compost bed . The percentage of removed volatile organic compounds (VOCs) can remain at levels higher than 99% for a longer time (about 230 d) as the composite bead immersed in a KNO(3) aqueous solution before packing with an optimal concentration of KNO(3) aqueous solution of 0.384 M . The rate of nitrogen dissolved out in the intraparticle diffusion process could be used as an index to predict the microbial growth rate in the biofilter.

Chemosphere, 2004 May, 55(6), 823 - 8
Biomassbed: a biological system to reduce pesticide point contamination at farm level; Vischetti C et al.; A potential method for cleaning water from point-source pollution by organic compounds is using biological reactors . In this study, four reactors were tested for their ability to retain and degrade pesticides . The pesticides tested were the insecticide chlorpyrifos, the fungicide metalaxyl and the herbicide imazamox . The reactors were filled with differing mixtures of vine-branch, citrus peel, urban waste and public green compost . The reactor volume was 188 l . Forced circulation of the contaminated solution was programmed to decontaminate the solution . Both retention and degradation of the compounds by the reactors was studied . Chlorpyrifos was the best retained, due to its physico-chemical characteristics, while only one substrate effectively retained metalaxyl and imazamox (citrus peel+urban waste compost) . Degradation of the pesticides in the reactors was faster than published values for degradation in soil . The half-life of all pesticides in the reactors was less than 14 days, compared to literature values of 60-70 days in soil . The combined retention and fast degradation make the biofilter a feasible technique to reduce spill-related and point environmental contamination by pesticides . The technique is most effective against persistent pesticides, while for mobile pesticides, the efficiency can be improved with several passages of the contaminated solution through biofilters.

J Environ Sci Health A Tox Hazard Subst Environ Eng, 2004, 39(1), 299 - 307
Dynamic behavior of compost biofilters during periods of starvation and fluctuating hydrogen sulfide loadings; Kim KS et al.; To understand transient-state performance of biofilters and the phenomena occurring during changes and interruptions in their operating conditions, dynamic behavior of biofilters exposed to shock loadings of contaminant (H2S) and periods of starvation has been investigated . The initial startup and the response of the biofilters to step changes in the H2S concentration and air-loading rate were also presented and discussed . Biofilters responded very effectively to H2S concentration spikes at H2S mass loading rates of 19.8-48.0 g/m3h by rapidly recovering their original removal rates within 1.2-20.2 min . The recovery time after each spike showed a positive correlation to the total amount of H2S loadings during the spike . Biofilters showed capabilities of withstanding 11-28 days of starvations and recovered their full performances after the starvations without any evident lag period.

J Environ Sci Health A Tox Hazard Subst Environ Eng, 2004, 39(1), 77 - 87
Basic study on anaerobic biological filtration using a floating filter media; Xie W et al.; An experiment of anaerobic filtration using a floating media was carried out in this study . In the present system, a bench-scale column of 50 mm in diameter and of 1500 mm in height and a floating media consisting of S-shaped polystyrene pieces were employed . The purpose of this study was to collect the basic data of anaerobic biological filtration using a floating media . Under the laboratory conditions, it was found that the start-up of an anaerobic biological filter took about half month at 20 degrees C and a lower BOD loading was favorable for this start-up . The BOD removal efficiency over 60% could be achieved at a BOD volumetric loading of the filter bed under 6 kg/m3/d . An effluent BOD concentration became high when the flow rate was high, especially with circulation of treated water, which afforded a large effect on an effluent BOD concentration . As for the mechanism of BOD removal by anaerobic filtration, it was evident that long retention time worked in favor for organic acid generation, and the circulation of treated water promoted decomposition of organic acids.

Environ Technol, 2004 Jan, 25(1), 123 - 32
A mechanistic model for m-xylene treatment with a peat-bed biofilter; Morgado J et al.; The painting of vehicles in the automobile industry generates large quantities of gaseous emissions which contain volatile organic compounds (VOC) like xylenes . This polluted air has a high moisture content and a temperature around 15-20 degrees C . It is thus possible to consider its treatment by a biological way . In this paper, laboratory tests are described which led to the choice of packing material to make a biofilter having good removal efficiency . Moreover this technique is known for its simplicity and low energy cost . The maximum treatment capacity was obtained with peat . A mathematical model which makes it possible to specify the different limiting steps of the process was carried out . This considered both physical parameters of the biofilter and properties of the biofilm . By choosing a lower Henry's constant than typical air:water system, we obtain a better simulation of the xylenes concentration according to the biofilter length and applied load.

Water Res, 2004 Apr, 38(7), 1853 - 61
Laboratory modelling of manganese biofiltration using biofilms of Leptothrix discophora; Hope CK et al.; Laboratory biofilters (pilot-scale, 20 l and laboratory-scale, 5l) were constructed in order to model the bioaccumulation of manganese (Mn) under flow conditions similar to those occurring in biofilters at groundwater treatment sites . The biofilters were operated as monocultures of Leptothrix discophora, the predominant organism in mature Mn oxidising biofilms . Biologically mediated Mn bioaccumulation was successfully modelled in both filter systems . The data obtained showed that in the small-scale biofilter, the Mn concentrations that gave the highest rate of Mn bioaccumulation, shortest maturation time, highest optical density (biomass) and growth rate were between 2000 and 3000 microg x l(-1) . The non-problematic scale-up of the process from the laboratory-scale to the pilot-scale biofilter model suggests that Mn biofilters may be 'seeded' with laboratory grown cultures of L . discophora. , , . By initially operating the biofilter as a re-circulating batch culture, with an initial Mn concentration of approximately 2500 microg x l(-1), it is hoped to reduce the filter maturation time from months to days.

Chemosphere, 2004 May, 55(5), 751 - 6
Biofiltration of trimethylamine-containing waste gas by entrapped mixed microbial cells; Chang CT et al.; The study provides novel attempt to use an aerobic biofiltration system containing entrapped mixed microbial cells (EMMC) for removal of (CH3)3N-dominant waste gases . In the study, heterotrophic microflora-immobilized cellulose was packed into an EMMC reactor to degrade (CH3)3N . Effects of (CH3)3N inlet concentrations in continuous mode of operation at various flow rates are indicated . The result indicated that the (CH3)3N removal efficiency is higher than 90% at inlet loading below 27.2 mgNh(-1) and retention time 5.3 min . In addition, the maximal mass loading to reach approximately 99% efficiency was 95.5 mgNh(-1) for trimethylamine treatment . This EMMC biofiltration system also showed higher tolerance to endure fluctuations in concentrations and flow rates and still maintained in stable performance for removal . Adaptability test in response to gradual shift up and down of inlet TMA loading indicated that lack of steady-state multiplicity and hysteresis guarantees the microbial communities more precisely adapted to continuous treatment for maintaining stability.

Biotechnol Bioeng, 2004 Apr 5, 86(1), 47 - 54
Haloalkane hydrolysis by Rhodococcus erythropolis cells: comparison of conventional aqueous phase dehalogenation and nonconventional gas phase dehalogenation; Erable B et al.; Biofiltration of air polluted by volatile organic compounds is now recognized by the industrial and research communities as an effective and viable alternative to standard environmental technologies . Whereas many studies have focused on solid/liquid/gas biofilters, there have been fewer reports on waste air treatment using other biological processes, especially in a solid/gas biofilter . In this study, a comparison was made of the hydrolysis of halogenated compounds (such as 1-chlorobutane) by lyophilized Rhodococcus erythropolis cells in a novel solid/gas biofilter and in the aqueous phase . We first determined the culture conditions for the production of R . erythropolis cells with a strong dehalogenase activity . Four different media were studied and the amount of 1-chlorobutane was optimized . Next, we report the possibility to use R . erythropolis cells in a solid/gas biofilter in order to transform halogenated compounds in corresponding alcohols . The effect of experimental parameters (total flow into the biofilter, thermodynamic activity of the substrates, temperature, carbon chain length of halogenated substrates) on the activity and stability of lyophilized cells in the gas phase was determined . A critical water thermodynamic activity (a(w)) of 0.4 is necessary for the enzyme to become active and optimal dehalogenase activity for the lyophilized cells is obtained for an a(w) of 0.9 . A temperature of reaction of 40 degrees C represents the best compromise between stability and activity . Activation energy of the reaction was determined and found equal to 59.5 KJ/mol . The pH effect on the dehalogenase activity of R . erythropolis cells was also studied in the gas phase and in the aqueous phase . It was observed that pH 9.0 provided the best activity in both systems . We observed that in the aqueous phase R . erythropolis cells were less sensitive to the variation in pH than R . erythropolis cells in the gas phase . Finally, the addition of volatile Lewis base (triethylamine) in the gaseous phase and the action of the lysozyme in order to permeabilize the cells was found to be highly beneficial to the effectiveness of the biofilter .

Environ Pollut, 2004 May, 129(2), 305 - 14
Methane oxidation and formation of EPS in compost: effect of oxygen concentration; Wilshusen JH et al.; Oxygen concentration plays an important role in the regulation of methane oxidation and the microbial ecology of methanotrophs . However, this effect is still poorly quantified in soil and compost ecosystems . The effect of oxygen on the formation of exopolymeric substances (EPS) is as yet unknown . We studied the effect of oxygen on the evolution of methanotrophic activity . At both high and low oxygen concentrations, peak activity was observed twice within a period of 6 months . Phospholipid fatty acid analysis showed that there was a shift from type I to type II methanotrophs during this period . At high oxygen concentration, EPS production was about 250% of the amount at low oxygen concentration . It is hypothesized that EPS serves as a carbon cycling mechanism for type I methanotrophs when inorganic nitrogen is limiting . Simultaneously, EPS stimulates nitrogenase activity in type II methanotrophs by creating oxygen-depleted zones . The kinetic results were incorporated in a simulation model for gas transport and methane oxidation in a passively aerated biofilter . Comparison between the model and experimental data showed that, besides acting as a micro-scale diffusion barrier, EPS can act as a barrier to macro-scale diffusion, reducing the performance of such biofilters.

Waste Manag Res, 2003 Dec, 21(6), 527 - 34
Removal of ammonia in a modified two-phase food waste anaerobic digestion system coupled with an aerated submerged biofilter; Wang JY et al.; Anaerobic digestion of food waste can reduce its volume, generate fuel biogas containing methane, and produce solid organic residue that can be used as a soil conditioner or fertiliser . Anaerobic digestion is more promising food waste disposal method than incineration and landfilling . The hybrid anaerobic solid-liquid (HASL) system, enhanced with a submerged biofilter for ammonia removal, was proposed for food waste digestion . Application of the submerged biofilter in the HASL system operated in batch mode increased concentrations of dissolved COD and volatile fatty acids in an acidogenic reactor, and total COD removal and methane production in a methanogenic reactor . The gas production in the enhanced HASL system was 86 l while in the conventional HASL system it was 54 l after 14 days of batch process . Methane production in the enhanced HASL system was increased by 26% in comparison with the conventional HASL system.

Water Sci Technol, 2004, 49(1), 87 - 94
Bioremediation of methyl tertiary-butyl ether (MTBE) by an innovative biofilter; Hu C et al.; Methyl tertiary-butyl ether (MTBE) is a synthetic chemical used in unleaded gasoline as an additive to reduce levels of ozone and carbon monoxide from auto exhaust . Due to its chemical and recalcitrant properties, MTBE has caused groundwater contamination worldwide . A laboratory-scale biofilter made of a natural fiber (kenaf) mat and inoculated with MTBE-degrading microorganisms, was evaluated for MTBE removal efficiency . Operational parameters of oxygen flow rate, hydraulic retention time (HRT), yeast extract and initial MTBE concentration were varied and MTBE removal efficiencies determined . Four kinetic models were evaluated to describe the MTBE removal in the reactor . Formaldehyde and tertiary butyl alcohol (the most two reported MTBE biodegradation byproducts) were not found in the effluent; instead, carbon dioxide was monitored as the end product based on the results of a metabolic mass balance evaluation . Toxicity of treated effluent was evaluated by employing the Microtox acute toxicity test and comparing that to the influent.

J Environ Sci (China), 2004, 16(1), 90 - 3
Using a zeolite medium biofilter to remove organic pollutant and ammonia simultaneously; Tian WH et al.; A pilot scale zeolite medium biological aerated filter(ZBAF) was designed and used to treat municipal wastewater . It showed that ZBAF could simultaneously remove chemical oxygen demand(COD), ammonia-N and turbidity to satisfied degree at a hydraulic retention time(HRT) of 0.95 h . Their average removal efficiencies were 73.9%, 88.4% and 96.2% with the corresponding average effluent concentrations of 43.4 mg/L, 3.5 mg/L and 3.7 NTU, respectively . These effluent items met with the water quality standard of the treated water reused for cooling water . The COD removal volumetric loading rate increased proportionally with its applied volumetric loading rate with its maximum of 7.1 kg/(m3 x d) . Ammonia-N removal loading rate also increased proportionally with its applied loading rate at HRT of longer than 0.95 h and the feasible maximum removal loading rate was 0.9 kg/(m3 x d) . The COD loading rate did not affect the ammonia-N removal efficiency significantly when it was lower than 5.5 kg/(m3 x d) . ZBAF has good application prospect for its low cost and high removal efficiency in the future.

J Environ Sci (China), 2004, 16(1), 30 - 3
Biodegradation of mixture of VOC's in a biofilter; Arulneyam D et al.; Volatile organic compounds(VOC' s) in air have become major concern in recent years . Biodegradation of a mixture of ethanol and methanol vapor was evaluated in a laboratory biofilter with a bed of compost and polystyrene particles using an acclimated mixed culture . The continuous performance of the biofilter was studied with different proportion of ethanol and methanol at different initial concentration and flow rates . The result showed significant removal for both ethanol and methanol, which were composition dependent . The presence of either compound in the mixture inhibited the biodegradation of the other.

J Air Waste Manag Assoc, 2004 Jan, 54(1), 24 - 35
Kinetic evaluation of H2S and NH3 biofiltration for two media used for wastewater lift station emissions; Jones KD et al.; In this study, biofiltration using a natural wood chip medium and a commercial biofiltration medium was evaluated for the removal of moderate concentrations of hydrogen sulfide (H2S) (up to 100 parts per million by volume {ppmv}) in the presence of significant concentrations of ammonia (NH3) . These levels were chosen as representative of wastewater lift station emissions in the Brownsville, TX, area . NH3-removing portions of the biofilms may compete with H2S-removing portions and inhibit H2S removal . H2S process removal efficiencies for the commercial and natural media ranged from 90 to 96% depending on inlet loading and media type and bed height . Kinetic analysis of the H2S removal process followed apparent first-order reaction behavior . The average first-order reaction rates were 0.03 sec(-1) for the commercial medium and 0.09 sec(-1) for the natural medium . Pressure drops across the columns ranged from 0.41 in . H2O/ft for the commercial medium to 1.41 in . H2O/ft for the natural medium . NH3 gas levels of up to 80 ppmv did not affect the H2S removal process efficiency, and calculated kinetic rate constants for H2S removal remained almost the same . The NH3 gas also was removed simultaneously with the H2S up to 98% removal efficiency by the commercial medium.

Water Res, 2004 Feb, 38(4), 1044 - 54
Biodegradability of organic by-products after natural organic matter oxidation with ClO2--case study; Raczyk-Stanislawiak U et al.; Apart from well-known chlorites and chlorates, chlorine dioxide also generates easily biodegradable carbonyl compounds and short chain carboxylic acids during water disinfection . The main goal of the presented study was to examine the influence of natural organic matter (NOM) oxidation with chlorine dioxide, on the quantity as well as the quality of formed biodegradable by-products . In the experiments conducted at the pilot plant the sand filtered water (MWI) and ozonated/biofiltrated water (BAF) were oxidised with ClO2 . The amount of BDOC formed as a result of the oxidation of both waters with ClO2 was compared . The results showed considerable differences in formation of ClO2 oxidation by-products between non-ozonated and ozonated/biofiltered waters. , , , . The disinfection of ozonated/biofiltrated water with ClO2 generated comparable amounts of aldehydes and much higher amounts of carboxylic acids than ClO2 oxidation of sand filtered water . These findings are essential for waterworks with ozonation/biofiltration units and ClO2 disinfection implemented.

Appl Microbiol Biotechnol, 2004 May, 64(4), 568 - 75 Epub 2004 Jan 21.
Assessment of microbial populations in methyl ethyl ketone degrading biofilters by denaturing gradient gel electrophoresis; Li C et al.; Denaturing gradient gel electrophoresis (DGGE) analysis of polymerase chain reaction-amplified genes coding for 16S rRNA was used to assess differences in bacterial community structure as a function of spatial location along the height of two biofilters used to treat a model waste gas stream containing methyl ethyl ketone (MEK) . One of the laboratory-scale biofilters was operated as a conventional continuous-flow biofilter (CFB) and the other was operated as a sequencing batch biofilter (SBB) . Both biofilters, inoculated with an identical starting culture and operated over a period lasting more than 300 days, received the same influent MEK concentration and same mass of MEK on a daily basis . The systems differed, however, in terms of the fraction of time during which contaminated air was supplied and the overall operating strategy employed . DGGE analysis indicated that microbial community structures differed as a function of height in each of the biofilters . The DGGE banding patterns also differed between the two biofilters, suggesting that operating strategies imposed on the biofilters imparted a sufficiently large selective pressure to influence microbial community structures . This may explain, in part, the superior performance of the SBB over the CFB during model transient loading conditions, and it may open new possibilities for purposely manipulating the microbial populations in biofilters treating gas-phase contaminants in a manner that leads to more favorable treatment performance .

Trends Plant Sci, 2004 Jan, 9(1), 49 - 56
Poplar genome sequence: functional genomics in an ecologically dominant plant species; Brunner AM et al.; In addition to their value for wood products, members of the genus Populus (poplars) provide a range of ecological services, including carbon sequestration, bioremediation, nutrient cycling, biofiltration and diverse habitats . They are also widely used model organisms for tree molecular biology and biotechnology . The sequencing of the poplar genome to an approximately 6x depth adds to a long list of important attributes for research . These include facile transformation, vegetative propagation, rapid growth, modest genome size and extensive expressed sequence tags . Here, we discuss how the genome sequence and transformability of poplar, together with its high levels of genetic and ecological diversity, are enabling new insights into the genetic programs controlling ontogeny, ecological adaptation and environmental physiology of trees.

Water Res, 2004 Feb, 38(3), 655 - 62
Integrated biofilter-immersed membrane system for the treatment of humic waters; Basu OD et al.; An integrated biofilter-immersed membrane study was conducted to determine the effect of placing a biofilter before or after a membrane for the treatment of a humic type water . The parameters measured included total organic carbon (TOC), organic acids, and specific ultraviolet absorbance (SUVA) . The difference in membrane fouling and microbial growth for the two configurations was also examined . Greater TOC and organic acid removal occurred when the biofilter was located ahead of the membrane . The greatest decrease in SUVA values was associated with the membrane . The membrane located after the biofilter fouled at a slower rate than the membrane ahead of the biofilter . Fouling was slower when turbidity was present in the synthetic feedwater . A new method is proposed for determining the operational cleaning frequency of membranes, using an empirical model.

Huan Jing Ke Xue, 2003 Sep, 24(5), 86 - 91
{Characteristics of aerobic biofilter backwash}; Zhang J et al.; Periodic backwash is the vital stage to keep up the aerobic biofilter's performance . Under the same backwash conditions, a thorough study was done to review the influences on the performances of backwash in such aspects as backwash regimes, biofilter shapes . The experimental results show that the impulse backwash regime was superior to continuous backwash in the backwash performance and that the expansive flow aerobic biofilter was superior to the uniform flow aerobic biofilter in the performances of both backwash process and filter bed recovery . Then the optimal combination of the two factors i.e . the combination of impulse backwash mode and expansive flow filter was determined . Under the fixed filtration conditions, the appropriate impulse backwash parameters of expansive aerobic biofilter were determined as follows: the backwash air-flow intensity was 8-10 L/(s.m2), the backwash water-flow intensity was 2-4 L/(s.m2), and the backwash duration was 5 min.

Xenotransplantation, 2003 Sep, 10(5), 460 - 9
Clinical extracorporeal hybrid liver support--phase I study with primary porcine liver cells; Sauer IM et al.; The objective of this study was to evaluate the feasibility and safety of a hybrid liver support system with extracorporeal plasma separation and bioreactor perfusion in patients with acute liver failure (ALF) who had already fulfilled the criteria for high urgency liver transplantation (LTx) . Eight patients (one male, seven female) were treated in terms of bridging to transplantation . The mean age was 36.5 yr (range 20 to 58) . Etiology of liver failure was drug-related in two patients, hepatitis B infection in three patients, and unknown for three patients . The bioreactors were charged with primary liver cells from specific pathogen-free pigs . Cell viability varied between 91 and 98% . Continuous liver support treatment over a period of 8 to 46 h (mean 27.3 h) was safely performed and well-tolerated by all patients . No complications associated with the therapy were observed during the follow-up period . Thrombocytopenia was considered to be an effect of the plasma separation . Subsequently, all patients were transplanted successfully and were observed over at least 3 yr with an organ and patient survival rate of 100% . Screening of patient's sera for antibodies specific for porcine endogenous retroviruses (PERVs) showed no reactivity--either prior to application of the system, or after extracorporeal treatment . The results encourage us to continue the development of the technology, and further studies appear to be justified . The bioreactor technology has been integrated into a modular extracorporeal liver support (MELS) system, combining biologic liver support with artificial detoxification technology.

Biochem J, 2003 Dec 15, 376(Pt 3), 677 - 86
Recombinant MUC1 mucin with a breast cancer-like O-glycosylation produced in large amounts in Chinese-hamster ovary cells; Backstrom M et al.; We have developed an expression system for the production of large quantities of recombinant MUC1 mucin in CHO-K1 (Chinese-hamster ovary K1) cells . The extracellular part of human MUC1, including 16 MUC1 tandem repeats, was produced as a fusion protein with murine IgG Fc, with an intervening enterokinase cleavage site for the removal of the Fc tail . Stable MUC1-IgG-producing CHO-K1 clones were generated and were found to secrete MUC1-IgG into the culture medium . After adaptation to suspension culture in protein-free medium in a bioreactor, the fusion protein was secreted in large quantities (100 mg/l per day) into the culture supernatant . From there, MUC1 could be purified to homogeneity using a two-step procedure including enterokinase cleavage and ion-exchange chromatography . Capillary liquid chromatography MS of released oligosaccharides from CHO-K1-produced MUC1 identified the main O-glycans as Galbeta1-3GalNAc (core 1) and mono- and di-sialylated core 1 . The glycans occupied on average 4.3 of the five potential O-glycosylation sites in the tandem repeats, as determined by nano-liquid chromatography MS of partially deglycosylated Clostripain-digested protein . A very similar O-glycan profile and site occupancy was found in MUC1-IgG produced in the breast carcinoma cell line T47D, which has O-glycosylation typical for breast cancer . In contrast, MUC1-IgG produced in another breast cancer cell line, MCF-7, showed a more complex pattern with both core 1- and core 2-based O-glycans . This is the first reported production of large quantities of recombinant MUC1 with a breast cancer-like O-glycosylation that could be used for the immunotherapy of breast cancer.

Trends Biotechnol, 2003 Sep, 21(9), 394 - 9
Making recombinant proteins in animals--different systems, different applications; Dyck MK et al.; Transgenic animal bioreactors represent a powerful tool to address the growing need for therapeutic recombinant proteins . The ability of transgenic animals to produce complex, biologically active recombinant proteins in an efficient and economic manner has stimulated a great deal of interest in this area . As a result, genetically modified animals of several species, expressing foreign proteins in various tissues, are currently being developed . However, the generation of transgenic animals is a cumbersome process and remains problematic in the application of this technology . The advantages and disadvantages of different transgenic systems in relation to other bioreactor systems are discussed.

Biosens Bioelectron, 2003 Oct 15, 18(12), 1491 - 9
Encapsulation of glucose oxidase microparticles within a nanoscale layer-by-layer film: immobilization and biosensor applications; Trau D et al.; We report on an immobilization strategy utilizing layer-by-layer encapsulated microparticles of enzymes within a nanoscale polyelectrolyte film . Encapsulation of glucose oxidase (GOD) microparticles was achieved by the sequential adsorption of oppositely charged polyelectrolytes onto the GOD biocrystal surface . The polyelectrolyte system polyallylamine/polystyrene sulfonate was used under high salt conditions to preserve the solid state of the highly water soluble GOD biocrystals during the encapsulation process . The resulting polymer multilayer capsule of about 15 nm wall thickness is permeable for small molecules (glucose), but non-permeable for macromolecules thus preventing the enzyme from leakage and at the same time shielding it from the outer environment e.g., from protease or microbial activity . Decrease of the buffer salt concentration leads to the dissolution of the enzyme under formation of mu-bioreactors . The spherical mu-bioreactors are bearing an extremely high loading of biocompound per volume . Encapsulated GOD was subsequently used to construct a biosensor by nanoengineered immobilisation of mu-bioreactor capsules onto an electrode surface. , , , , . The presented approach demonstrates a general method to encapsulate highly soluble solid biomaterials and an immobilization strategy with the potential to create highly active thin and stable films of biomaterial.

Zhonghua Gan Zang Bing Za Zhi, 2003 Aug, 11(8), 461 - 3
{Preliminary evaluation on the effects of a hybrid bioartificial liver support system in the treatment of hepatic failure}; Wang YJ et al.; OBJECTIVES: To construct a novel hybrid artificial liver support system and evaluate its clinical efficacy in the treatment of hepatic failure . METHODS: A hybrid bioartificial liver support system consisting of plasma exchange device, charcoal perfusion column, and bioreactor cultured human or porcine hepatocytes was developed . 30 patients with hepatic failure were treated using this hybrid system . RESULTS: Both the excellent rate and effectual rate of the artificial liver support system were 43.3% (13/30) . The total effectual rate was 86.7% . Finally, eleven out of 30 patients recovered completely . Six patients were bridged to liver transplantation . Six patients (20%) died of hepatic failure and seven patients (23.3%) discharged due to worsening of disease . CONCLUSIONS: The hybrid artificial liver support system has prominent liver support effects for hepatic failure, which can be regarded as an efficient measure for the treatment of severe hepatitis.

Zhonghua Gan Zang Bing Za Zhi, 2003 Aug, 11(8), 458 - 60
{Study of severe hepatitis treated with a hybrid artificial liver support system}; Li LJ et al.; OBJECTIVES: To evaluate the efficacy of a hybrid artificial liver support system in the treatment of chronic severe hepatitis . METHODS: The hybrid artificial liver support system (HALSS) consisted of a bioreactor containing more than 5 x 10(9) porcine hepatocytes and plasma exchange device . 15 patients with chronic severe viral hepatitis were treated with the hybrid system . RESULTS: All the patients experienced a reduction in symptoms, such as fatigue, abdominal distention or ascites . After each treatment serum total bilirubin decreased markedly (from 493.5 micromol/L+-139.8 micromol/L to 250.9 micromol/L+-91.3 micromol/L, t=8.695, P<0.001), while prothrombin activity increased (from 24.5%+-8.4% to 30.6%+-6.3%, t=3.325, P<0.01) . There were 11 patients whose progress of hepatocytes necrosis stopped after HALSS treatment, and finally they recovered completely . Four patients died of their worsen conditions . No serious adverse events were noted in the 15 patients . CONCLUSION: HALSS is a reliable hepatic support device for chronic severe hepatitis.

J Environ Qual, 2003 Jul-Aug, 32(4), 1212 - 21
pH, dissolved oxygen, and adsorption effects on metal removal in anaerobic bioreactors; Willow MA et al.; Anaerobic bioreactors were used to test the effect of the pH of influent on the removal efficiency of heavy metals from acid-rock drainage . Two studies used a near-neutral-pH, metal-laden influent to examine the heavy metal removal efficiency and hydraulic residence time requirements of the reactors . Another study used the more typical low-pH mine drainage influent . Experiments also were done to (i) test the effects of oxygen content of feed water on metal removal and (ii) the adsorptive capacity of the reactor organic substrate . Analysis of the results indicates that bacterial sulfate reduction may be a zero-order kinetic reaction relative to sulfate concentrations used in the experiments, and may be the factor that controls the metal mass removal efficiency in the anaerobic treatment systems . The sorptive capacities of the organic substrate used in the experiments had not been exhausted during the experiments as indicated by the loading rates of removal of metals exceeding the mass production rates of sulfide . Microbial sulfate reduction was less in the reactors receiving low-pH influent during experiments with short residence times . Sulfate-reducing bacteria may have been inhibited by high flows of low-pH water . Dissolved oxygen content of the feed waters had little effect on sulfate reduction and metal removal capacity.

Adv Biochem Eng Biotechnol, 2003, 85, 29 - 42
Commercialization of a novel fermentation concept; Mazumdar-Shaw K et al.; Fermentation is the core of biotechnology where current methodologies span across technologies based on the use of either solid or liquid substrates . Traditionally, solid substrate fermentation technologies have been the widely practiced in the Far East to manufacture fermented foods such as soya sauce, sake etc . The Western World briefly used solid substrate fermentation for the manufacture of antibiotics and enzymes but rapidly replaced this technology with submerged fermentation which proved to be a superior technology in terms of automation, containment and large volume fermentation . Biocon India developed its enzyme technology based on solid substrate fermentation as a low-cost, low-energy option for the production of specialty enzymes . However, the limitations of applying solid substrate fermentation to more sophisticated biotechnology products as well as large volume fermentations were recognized by Biocon India as early as 1990 and the company embarked on a 8 year research and development program to develop a novel bioreactor capable of conducting solid substrate fermentation with comparable levels of automation and containment as those practiced by submerged fermentation . In addition, the novel technology enabled fed-batch fermentation, in situ extraction and other enabling features that will be discussed in this article . The novel bioreactor was christened the "PlaFractor" (pronounced play-fractor) . The next level of research on this novel technology is now focused on addressing large volume fermentation . This article traces the evolution of Biocon India's original solid substrate fermentation to the PlaFractor technology and provides details of the scale-up and commercialization processes that were involved therein . What is also apparent in the article is Biocon India's commercially focused research programs and the perceived need to be globally competitive through low costs of innovation that address, at all times, processes and technologies that exhibit high degrees of conformance to the international standards of regulatory and good manufacturing practice.

Water Sci Technol, 2003, 47(12), 169 - 76
Comparison of different oxygen transfer testing procedures in full-scale membrane bioreactors; Krause S et al.; Membrane bioreactors (MBRs) for wastewater treatment offer the advantage of a complete removal of solids from the effluent . The secondary clarifier is replaced by a membrane filtration and therefore high biomass concentrations (MLSS) in the reactor are possible . The design of the aeration system is vital for an energy efficient operation of any wastewater treatment plant . Hence the exact measurement of oxygen transfer rates (OTR) and alpha-values is important . For MBRs these values reported in literature differ considerably . The OTR can be measured using non-steady state methods or using the off-gas method . The non-steady state methods additionally require the determination of the respiration rate (oxygen uptake rate OUR), which usually is measured in lab scale units . As there are differences of OUR between lab scale and full scale measurements, off-gas tests (which do not require an additional respiration test) were performed in order to compare both methods at high MLSS concentrations . Both methods result in the same average value of OTR . Due to variations in loading and wastewater composition variations of OTR in time can be pointed out using the off-gas method . For the first time a comparison of different oxygen transfer tests in full scale membrane bioreactors is presented.

Water Sci Technol, 2003, 47(12), 149 - 54
Domestic wastewater treatment by a submerged MBR (membrane bio-reactor) with enhanced air sparging; Chang IS et al.; The air sparging technique has been recognised as an effective way to control membrane fouling . However, its application to a submerged MBR (Membrane Bio-Reactor) has not yet been reported . This paper deals with the performances of air sparging on a submerged MBR for wastewater treatment . Two kinds of air sparging techniques were used respectively . First, air is injected into the membrane tube channels so that mixed liquor can circulate in the bioreactor (air-lift mode) . Second, a periodic air-jet into the membrane tube is introduced (air-jet mode) . Their applicability was evaluated with a series of lab-scale experiments using domestic wastewater . The flux increased from 23 to 33 l m(-2) h(-1) (43% enhancement) when air was injected for the air-lift module . But further increase of flux was not observed as the gas flow increased . The Rc/(Rc+Rf), ratio of cake resistance (Rc) to sum of Rc and Rf (internal fouling resistance), was 23%, indicating that the Rc is not the predominant resistance unlike other MBR studies . It showed that the cake layer was removed sufficiently due to the air injection . Thus, an increase of airflow could not affect the flux performance . The air-jet module suffered from a clogging problem with accumulated sludge inside the lumen . Because the air-jet module has characteristics of dead end filtration, a periodic air-jet was not enough to blast all the accumulated sludge out . But flux was greater than in the air-lift module if the clogging was prevented by an appropriate cleaning regime such as periodical backwashing.

Water Sci Technol, 2003, 48(1), 207 - 14
Carbon and nitrogen removal from tannery wastewater with a membrane bioreactor; Goltara A et al.; A 3.5 L Membrane Sequencing Batch Reactor (MSBR) was used for the treatment of a wastewater coming from the beamhouse section of a tannery . The wastewater, produced after the oxidation of sulphide compounds, contained average COD and ammonium concentrations of 550 and 90 mg/L respectively . The system was operated for a period of 150 days, with no sludge removal during the whole period of operation . The biomass concentration inside the reactor varied considerably, with maximum values close to 10 g/L at the end of operation . Low biomass yield values were achieved probably due to the low feed/microorganisms (F/M) ratio . An important accumulation of organic matter in the reactor was noticed, although the COD effluent was not affected due to the permeation through the membrane . The nature of this organic matter is finally discussed . Removal efficiencies close to 100% in ammonium and 90% in COD were achieved and the TN removal efficiency ranged from 60 to 90%.

Arch Otolaryngol Head Neck Surg, 2003 Aug, 129(8), 889 - 93
Cartilage tissue engineering using cryogenic chondrocytes; Gorti GK et al.; OBJECTIVE: To generate in vitro hyaline cartilage from cryogenically preserved human septal chondrocytes in a simulated microgravity environment on a 3-dimensional biodegradable scaffolding material . METHODS: In this experiment, cryogenically frozen chondrocytes were thawed and cultured in a monolayer in serum-based chondrocyte media . They were seeded onto 3-dimensional biopolymer scaffolds in a spinner flask . The seeded constructs were then transferred to a bioreactor (an environment of solid-body rotation) for 6 weeks . Chondrocyte growth and extracellular matrix production in the constructs were confirmed by cell count, cell viability, and histologic analysis and by electron microscopy . RESULTS: Histologic sections stained with hematoxylin-eosin and Alcian blue (for acidic proteoglycans) confirmed the presence of hyaline cartilage in the cartilage constructs . Ultrastructural examination using transmission electron microscopy demonstrated matrix formation and chondrocyte viability . CONCLUSIONS: This study proves that chondrocytes that are cryogenically stored for extended periods can be used to grow cartilage in vitro . Cryogenically preserved chondrocytes retain their ability to grow in tissue culture, redifferentiate, and produce extracellular matrix.

Appl Microbiol Biotechnol, 2004 Feb, 63(6), 748 - 53 Epub 2003 Aug 15.
The effect of CreA in glucose and xylose catabolism in Aspergillus nidulans; Prathumpai W et al.; The catabolism of glucose and xylose was studied in a wild type and creA deleted (carbon catabolite de-repressed) strain of Aspergillus nidulans . Both strains were cultivated in bioreactors with either glucose or xylose as the sole carbon source, or in the presence of both sugars . In the cultivations on single carbon sources, it was demonstrated that xylose acted as a carbon catabolite repressor (xylose cultivations), while the enzymes in the xylose utilisation pathway were also subject to repression in the presence of glucose (glucose cultivations) . In the wild type strain growing on the sugar mixture, glucose repression of xylose utilisation was observed; with xylose utilisation occurring only after glucose was depleted . This phenomenon was not seen in the creA deleted strain, where glucose and xylose were catabolised simultaneously . Measurement of key metabolites and the activities of key enzymes in the xylose utilisation pathway revealed that xylose metabolism was occurring in the creA deleted strain, even at high glucose concentrations . Conversely, in the wild type strain, activities of the key enzymes for xylose metabolism increased only when the effects of glucose repression had been relieved . Xylose was both a repressor and an inducer of xylanases at the same time . The creA mutation seemed to have pleiotropic effects on carbohydratases and carbon catabolism.

Biomol Eng, 2003 Jul, 20(4-6), 171 - 5
Effect of light intensity on beta-carotene production and extraction by Dunaliella salina in two-phase bioreactors; Hejazi MA et al.; Application of two-phase bioreactors is a useful technique for improvement of the productivity of fermentations . Fermentative extraction of the products in situ is performed in this technique . The effect of light intensity on the extraction of beta-carotene from Dunaliella salina, in the fermentative extraction, has been investigated . Three different average light exposures were applied: 1.5 x 10(-8) (low), 2.7 x 10(-8) (intermediate) and 4.5 x 10(-8) (high) micromol s(-1) per cell . Results show that beta-carotene content of the cells increases by increasing the light exposure . Increase in the beta-carotene content of the cells is not necessarily coupled with an increase in the volumetric production of beta-carotene . Final volumetric production is about the same for the three bioreactors . beta-Carotene extraction rate is enhanced by the increase in the light exposure . The results suggest that extraction rate is related to beta-carotene content of the cells and is not essentially related to the volumetric production of beta-carotene . Although the effectiveness of extraction with respect to the light input is comparable for all light intensities applied, increasing the light input per cell leads to a higher volumetric extraction rate . Moreover, extracted beta-carotene stays very pure even so the extraction increased by the increase of light intensity.

Cell Transplant, 2003, 12(4), 351 - 64
Evaluation of different types of alginate microcapsules as bioreactors for producing endostatin; Rokstad AM et al.; The use of nonautologous cell lines producing a therapeutic substance encapsulated within alginate microcapsules could be an alternative way of treating different diseases in a cost-effective way . Malignant brain tumors have been proposed to be treated locally using engineered cells secreting proteins with therapeutic potential encapsulated within alginate microcapsules . Optimization of the alginate capsule bioreactors is needed before this treatment can be a reality . Recently, we have demonstrated that alginate-poly-L-lysine microcapsules made with high-G alginate and a gelled core disintegrated as cells proliferated . In this study we examined the growth and endostatin secretion of 293-EBNA (293 endo) cells encapsulated in six different alginate microcapsules made with native high-G alginate or enzymatically tailored alginate . Stability studies using an osmotic pressure test showed that alginate-poly-L-lysine-alginate microcapsules made with enzymatically tailored alginate was mechanically stronger than alginate capsules made with native high-G alginate . Growth studies showed that the proliferation of 293 endo cells was diminished in microcapsules made with enzymatically tailored alginate and gelled in a barium solution . Secretion of endostatin was detected in lower amounts from the enzymatically tailored alginate microcapsules compared with the native alginate microcapsules . The stability of the alginate microcapsules diminished as the 293 endo cells grew inside the capsules, while empty alginate microcapsules remained stable . By using microcapsules made of fluorescenamine-labeled alginate it was clearly visualized that cells perforated the alginate microcapsules as they grew, destroying the alginate network . Soluble fluorescence-labeled alginate was taken up by the 293 endo cells, while alginate was not detected in live spheroids within fluorescence-labeled alginate microcapsules . Despite that increased stability was achieved by using enzymatically tailored alginate, the cell proliferation destroyed the alginate microcapsules with time . It is therefore necessary to use cell lines that have properties more suited for alginate encapsulation before this technology can be used for therapy.

Biotechnol Bioeng, 2003 Oct 5, 84(1), 29 - 39
Numerical simulation and PEPT measurements of a 3D conical helical-blade mixer: a high potential solids mixer for solid-state fermentation; Schutyser MA et al.; Helical-blade solids mixers have a large potential as bioreactors for solid-state fermentation (SSF) . Fundamental knowledge of the flow and mixing behavior is required for robust operation of these mixers . In this study predictions of a discrete particle model were compared to experiments with colored wheat grain particles and positron emission particle tracking (PEPT) measurements . In the discrete particle model individual movements of particles were calculated from interaction forces . It was concluded that the predicted overall flow behavior matched well with the PEPT measurements . Differences between the model predictions and the experiments with wheat grains were found to be due to the assumption that substrate particles were spherical, which was in the model . Model simulations and experiments with spherical green peas confirmed this . The mixing in the helical-blade mixer could be attributed to (1) the transport of particles up and down in the interior of the mixer, and (2) dispersion or micro-mixing of particles in the top region of the mixer . It appeared that the mixing rate scaled linearly with the rotation rate of the blade, although the average particle velocity did not scale proportionally . It may be that the flow behavior changes as a function of the rotation rate (e.g., changing thickness of the top region); further study is required to confirm this . To increase the mixing performance of the mixer, a larger blade or a change in the shape of the mixer (larger top surface/volume ratio) is recommended .

Water Res, 2003 Sep, 37(16), 3897 - 904
Phenolic removal in a model olive oil mill wastewater using Pleurotus ostreatus in bioreactor cultures and biological evaluation of the process; Aggelis G et al.; Pleurotus ostreatus grown in bioreactor batch cultures in a model phenolic wastewater (diluted and sterilized olive oil mill wastewater-OMW), caused significant phenolic removal . Laccase, the sole ligninolytic enzyme detected in the growth environment, was produced during primary metabolic growth . The bioprocess was simulated with the aid of a mathematical model and the parameters of growth were determined . When the fungal biomass was increased in the reactor (during repeated batch experiments) the rate of reducing sugars consumption progressively increased, but a phenolic fraction seemed of being strongly resistant to oxidation . The toxicity of OMW against the seeds of Lepidium sativum and the marine Branchiopoda Artemia sp . was significantly decreased after biotreatment . On the contrary, the toxicity against the freshwater Branchiopoda Daphnia magna was not affected by the treatment, whereas on the soil and freshwater sediments Ostracoda Heterocypris incongruens was slightly decreased . Both treated and untreated OMWs, used as water for irrigation of lettuce and tomato plants, did not significantly affect the uptake of several nutrients by the cultivated plants, but resulted in a decrease in the plant yields, which was minimized when high OMW dilutions were used . As a conclusion, P . ostreatus is able to reduce phenolic content and toxicity of sterilized OMW, in bioreactor cultures. , , , . However, high OMW dilutions should be used, and/or additional treatment should be applied before use of the OMW in the environment, e.g . as water for irrigation . Further research should be done in order to transfer this technology under industrial conditions (e.g . by using unsterilized OMW).

Artif Cells Blood Substit Immobil Biotechnol, 2003 Aug, 31(3), 313 - 27
Continuous production of cephalosporin-C by immobilized microbial cells using symbiotic mode in a packed bed bioreactor; Kundu S et al.; Cephalosporins are usually produced semisynthetically from Cephalosporin-C, which is exclusively produced by Cephalosporium acremonium . Free cell studies for the production of Cephalosporin-C had some limitation such as pulpy growth of fungus causing an appreciable rise in the broth viscosity affecting the transfer of oxygen and other nutrients into the cells . High cell concentrations cannot be maintained because of wash out phenomenon at high dilution rates . The whole cell immobilization technique is a potentially important process for Cephalosporin-C biosynthesis, where increase cell densities were maintained and broth-handling problems were reduced . Cephalosporin-C fermentation is a highly aerobic process . The symbiotic relationship of Cephalosporium acremonium and Chlorella pyrenoidosa has been used to increase oxygen transfer rate to the fungi by co-immobilizing it with algae . Co-immobilization of whole cells of fungus and algae were carried out in different immobilizing agents and the systems were coated with polyacrylamide resin of pharmaceutical grade to overcome the problems of leakage . The operational stability of immobilized systems in a packed bed reactor was also studied.

Water Sci Technol, 2003, 47(11), 313 - 9
Investigation of oxygen transfer rates in full scale membrane bioreactors; Cornel P et al.; In membrane bioreactors (MBRs) for wastewater treatment the secondary clarifier is replaced by a membrane filtration . The advantage of this process is a complete removal of solids from the effluent and a small footprint due to possible high biomass concentrations (MLSS) . As oxygen supply counts for more than 70% of total energy cost in municipal WWTPs the design of the aeration system is vital for efficient operation . In this respect the alpha-value is an important influencing factor . The alpha-value depends on the MLSS-concentration as shown in various publications and confirmed by own measurements in two full scale municipal MBRs with MLSS ranging from 7 and 17 kg/m3 . Furthermore it must be taken into account that alpha-values are not static values; they vary with loading rates, surfactant concentrations, air flow rates, MLSS concentrations, etc . The average alpha-value at typical 12 kg/m3 MLSS for municipal MBRs is about 0.6 +/- 0.1 . As submerged configured MBRs are equipped with an additional coarse bubble "crossflow" aeration system for fouling control, supplementary energy is consumed . Therefore MBRs need more energy compared to conventional treatment plants . Measurements of both aeration systems show that the fine bubble aeration system is more efficient by a factor of three concerning oxygen supply compared to the coarse bubble system.

Zhongguo Yi Xue Ke Xue Yuan Xue Bao, 2003 Feb, 25(1), 7 - 12
{Experimental study of cardiac muscle tissue engineering in bioreactor}; Liu X et al.; OBJECTIVE: This study investigates construction of cardiac muscle cell-porous collagen scaffold complex in a bioreactor so as to unveil the possibility of generating 3-dimensional cardiac muscle tissue under the environment that mimics microgravity in vitro . METHODS: 1-2-day old neonatal rat cardiac muscle cells were isolated by sequential digestion and pre-plating methods, then seeded onto porous collagen scaffold . The cell-collagen complex was transferred into rotary cell culture system (RCCS) and incubated for 7 days . Cells cultured in 75 ml flasks and constructs cultures on plates served as control . Morphological changes of the cells were observed by light microscope and metabolic rate was recorded . Ultrastructure of the cells growing in porous collagen was observed by transmission electron microscopy . Content of total DNA and protein in the newly-formed tissue were analyzed . H-E and anti-sarcomeric alpha-actin stains were performed in comparison with native cardiac muscle . RESULTS: The isolated cardiac muscle cells adhered to the bottom of the flasks 24 hours after plating and began to beat spontaneously . When incubated for 7 days in RCCS, cell-collagen constructs of form a continuous outer tissue layer containing cells aligned with each other . The cell population in the interior of the construct was less in density than the outer part . Transmission electron microscopy demonstrated that subcellular elements characteristic of cardiac myocytes were in the outermost layer of constructs . A strongly positive stains of anti-sarcomeric alpha-actin suggested presence of cell population of differentiated cardiac myocytes in these constructs . Construct biomass was not significantly different from that in neonatal rat ventricle and approximately 40% of that in adult rat ventricles . Construsts in plates contained a few of cells which were less than those in RCCS . Metabolic activity of cells cultured in RCCS was higher than that in flasks and plates . CONCLUSIONS: Dissociated cardiac muscle cells cultured on 3-dimensional scaffolds in RCCS under favorable conditions can form engineered constructs with structural and functional features resembling those of native cardiac tissue.

J Agric Food Chem, 2003 Aug 13, 51(17), 4930 - 4
Angiotensin I converting enzyme (ACE) inhibitory activity of hetero-chitooligosaccharides prepared from partially different deacetylated chitosans; Park PJ et al.; Angiotensin I converting enzyme (ACE) inhibitory activity of hetero-chitooligosaccharides (hetero-COSs) prepared from partially different deacetylated chitosans was investigated . Partially deacetylated chitosans, 90, 75, and 50% deacetylated chitosan, were prepared from crab chitin by N-deacetylation with 40% sodium hydroxide solution for durations . In addition, nine kinds of hetero-COSs with relatively high molecular masses (5000-10 000 Da; 90-HMWCOSs, 75-HMWCOSs, and 50-HMWCOSs), medium molecular masses (1000-5000 Da; 90-MMWCOSs, 75-MMWCOSs, and 50-MMWCOSs), and low molecular masses (below 1000 Da; 90-LMWCOSs, 75-LMWCOSs, and 50-LMWCOSs) were prepared using an ultrafiltration membrane bioreactor system . ACE inhibitory activity of hetero-COSs was dependent on the degree of deacetylation of chitosans . 50-MMWCOSs that are COSs hydrolyzed from 50% deacetylated chitosan, the relatively lowest degree of deacetylation, exhibited the highest ACE inhibitory activity, and the IC(50) value was 1.22 +/- 0.13 mg/mL . In addition, the ACE inhibition pattern of the 50-MMWCOSs was investigated by Lineweaver-Burk plots, and the inhibition pattern was found to be competitive.

J Pharm Biomed Anal, 2003 Aug 8, 32(4-5), 715 - 24
Lipases for biocatalysis: development of a chromatographic bioreactor; Calleri E et al.; The development of a new chromatographic reactor based on immobilized Candida rugosa lipase (CRL) is described . The chromatographic system has been used to evaluate the rate differences by which the product enantiomers of esterolytic reactions catalyzed by immobilized CRL are obtained . The method has been applied to a series of racemic 2-aryloxyalkanoic acids and isosteric analogous methyl esters and to some non-steroidal antiinflammatory drugs 2-arylpropanoic acids methyl esters in order to study the structure effects on reaction rate and enantioselectivity . Lipase from C . rugosa has been non-covalently and covalently immobilized on HPLC chromatographic silica supports to develop an immobilized enzyme reactor (IMER) . The reactor was connected through a switching valve to an analytical reversed-phase column, which was used for the on-line determination of the hydrolysis rate by peak area integration . The enantiomeric excess of the hydrolytic reaction products was determined off-line on a CSP utilizing immobilized penicillin G acylase (PGA-CSP).

Appl Microbiol Biotechnol, 2004 Feb, 63(5), 584 - 91 Epub 2003 Jul 31.
Growth characteristics and oxidative capacity of Acetobacter aceti IFO 3281: implications for L-ribulose production; Kylma AK et al.; We studied the growth characteristics and oxidative capacities of Acetobacter aceti IFO 3281 in batch and chemostat cultures . In batch culture, glycerol was the best growth substrate and growth on ethanol occurred only after 6 days delay, although ethanol was rapidly oxidized to acetic acid . In continuous culture, both glycerol and ethanol were good growth substrates with similar characteristics . Resting cells in a bioreactor oxidized ribitol to L-ribulose with a maximal specific rate of 1.2 g g(-1) h(-1)) . The oxidation of ribitol was inhibited by ethanol but not by glycerol . Biomass yield (Y(SX); C-mmol/C-mmol) on ethanol and glycerol was low (0.21 and 0.17, respectively) . In the presence of ribitol the yield was somewhat higher (0.25) with ethanol but lower (0.13) with glycerol, with respectively lower and higher CO(2) production . In chemostat cultures the oxidation rate of ribitol was unaffected by ethanol or glycerol . Cell-free extract oxidized ethanol very slowly but not ribitol; the oxidative activity was located in the cell membrane fraction . Enzymatic activities of some key metabolic enzymes were determined from steady-state chemostat with ethanol, glycerol, or ethanol/glycerol mixture as a growth limiting substrate . Based on the measured enzyme activities, metabolic pathways are proposed for ethanol and glycerol metabolism.

Biotechnol Prog, 2003 Jul-Aug, 19(4), 1342 - 7
Comparison of morphological characteristics of Streptomyces natalensis by image analysis and focused beam reflectance measurement; Pearson AP et al.; A morphological interpretation is presented for data collected during growth of a filamentous organism, using a focused beam reflectance measurement (FBRM) system . The morphology of the organism was also obtained using conventional semiautomatic image analysis to support the interpretation of the FBRM data . The model organism employed is the filamentous soil-borne actinomycete Streptomyces natalensis, which produces the antifungal agent pimaricin . The organism was cultivated both in shake flasks and in a bench-scale stirred tank bioreactor . It was found that FBRM could be used to track changes in the morphology of the organism throughout the course of its growth on both scales . These changes were highlighted using both the median chord length and length-weighted mean chord length obtained from the chord length distribution measured with the FBRM probe . The ability of the FBRM probe to respond to changes in both the size and morphology of mycelial aggregates was supported by standard image analysis parameters, including equivalent diameter, convex area, and compactness.

Biotechnol Prog, 2003 Jul-Aug, 19(4), 1210 - 5
Xylitol production from sugarcane bagasse hydrolyzate in fluidized bed reactor . Effect of air flowrate; Santos JC et al.; Cells of Candida guilliermondii immobilized onto porous glass spheres were cultured batchwise in a fluidized bed bioreactor for xylitol production from sugarcane bagasse hemicellulose hydrolyzate . An aeration rate of only 25 mL/min ensured minimum yields of xylose consumption (0.60) and biomass production (0.14 g(DM)/g(Xyl)), as well as maximum xylitol yield (0.54 g(Xyt)/g(Xyl)) and ratio of immobilized to total cells (0.83) . These results suggest that cell metabolism, although slow because of oxygen limitation, was mainly addressed to xylitol production . A progressive increase in the aeration rate up to 140 mL/min accelerated both xylose consumption (from 0.36 to 0.78 g(Xyl)/L.h) and xylitol formation (from 0.19 to 0.28 g(Xyt)/L.h) but caused the fraction of immobilized to total cells and the xylitol yield to decrease up to 0.22 and 0.36 g(Xyt)/g(Xyl), respectively . The highest xylitol concentration (17.0 g(Xyt)/L) was obtained at 70 mL/min, but the specific xylitol productivity and the xylitol yield were 43% and 22% lower than the corresponding values obtained at the lowest air flowrate, respectively . The concentrations of consumed substrates and formed products were used in material balances to evaluate the xylose fractions consumed by C . guilliermondii for xylitol production, complete oxidation through the hexose monophosphate shunt, and cell growth . The experimental data collected at variable oxygen level allowed estimating a P/O ratio of 1.35 mol(ATP)/mol(O) and overall ATP requirements for biomass growth and maintenance of 3.4 mol(ATP)/C-mol(DM).

Biotechnol Prog, 2003 Jul-Aug, 19(4), 1199 - 209
Effect of shear stress on intrinsic CHO culture state and glycosylation of recombinant tissue-type plasminogen activator protein; Senger RS et al.; Shear stress in suspension culture was investigated as a possible manipulative parameter for the control of glycosylation of the recombinant tissue-type plasminogen activator protein (r-tPA) produced by recombinant Chinese hamster ovary (CHO) cell culture, grown in protein-free media . Resulting fractions of partially glycosylated, Type II, and fully glycosylated, Type I, r-tPA protein were monitored as a direct function of the shear characteristics of the culture environment . The shear-induced response of CHO culture to levels of low shear stress, where exponential growth was not obtained, and to higher levels of shear stress, which resulted in extensive cell death, were examined through manipulation of the bioreactor stirring velocity . Both apparent and intrinsic cell growth, metabolite consumption, byproduct and r-tPA production, and r-tPA glycosylation, from a variable site-occupancy standpoint, were monitored throughout . Kinetic analyses revealed a shear-stress-induced alteration of cellular homeostasis resulting in a nonlinear dependency of metabolic yield coefficients and an intrinsic cell lysis kinetic constant on shear stress . Damaging levels of shear stress were used to investigate the shear dependence of cell death and lysis, as well as the effects on the intrinsic growth rate of the culture . Kinetic models were also developed on the basis of the intrinsic state of the culture and compared to traditional models . Total r-tPA production was maximized under moderate shear conditions, as was the viable CHO cell density of the culture . However, Type II r-tPA production and the fraction of Type II glycoform production ratio was maximized under damaging levels of shear stress . Analyses of biomass production yield coefficients coupled with a plug-flow reactor model of glycan addition in the endoplasmic reticulum (ER) were used to propose an overall mechanism of decreased r-tPA protein site-occupancy glycosylation with increasing shear stress. , , , , . Decreased residence time of r-tPA in the ER as a result of increased protein synthesis related to shear protection mechanisms is proposed to limit contact of site Asn184 with the membrane-bound oligosaccharyltransferase enzyme in the ER.

Environ Sci Technol, 2001 Nov 1, 35(21), 4235 - 41
Biodegradation of methyl tert-butyl ether under various substrate conditions; Pruden A et al.; Five aerobic enrichments efficient at degrading methyl tert-butyl ether (MTBE) under different substrate conditions were developed in well-mixed reactors containing a polyethlene porous pot for biomass retention . The five substrate conditions were as follows: MTBE alone; MTBE and diethyl ether (DEE); MTBE and diisopropyl ether (DIPE); MTBE and ethanol (EtOH); and MTBE with benzene, toluene, ethylbenzene, and xylene (BTEX) . All five cultures demonstrated greater than 99.9% removal of MTBE . Addition of alternative substrate was found to have no effect on the performance of the reactors . The bacterial communities of the reactors were monitored periodically by denaturing gradient gel electrophoresis (DGGE) to determine when homeostasis was achieved . Phylogenetic analysis of the excised DGGE bands was done in order to compare the bacterial community compositions of the reactors . All cultures were found to be mixed cultures, and each enrichment was shown to have a unique composition . A majority of the bands in all reactors represented a group of organisms belonging to the Cytophaga-Flexibacter-Bacterioides (C-F-B) Phylum of bacteria . This was also the only group found in all of the reactors . This study demonstrates that MTBE can be degraded effectively in bioreactors under several substrate conditions and gives insight into the microorganisms potentially involved in the process.

Microbiol Res, 2001, 156(3), 285 - 8
Polysaccharide production by immobilized Aureobasidium pullulans cells in batch bioreactors; West TP et al.; Cells of the fungus Aureobasidium pullulans ATCC 201253 were entrapped within 4% agar cubes or 5% calcium alginate beads and were examined for their production of the polysaccharide pullulan in batch bioreactors . The batch bioreactors were utilized twice for 168 hours of polysaccharide production in medium containing corn syrup as a carbon source . The agar-entrapped cells produced nearly equivalent pullulan concentrations during both production cycles . The alginate-entrapped cells produced higher polysaccharide levels during the second cycle compared to the levels observed during the initial cycle . The agar-entrapped cells elaborated a polysaccharide with a higher pullulan content than did the alginate-entrapped cells during both production cycles.

Cell Transplant, 2001, 10(7), 609 - 14
Effect of flow on the detoxification function of rat hepatocytes in a bioartificial liver reactor; Roy P et al.; Ethoxyresorufin-o-deethylation (EROD) can be used as a sensitive measure of hepatic detoxification function . In this study, we employed a fluorescence assay based on EROD to study the effect of varying Peclet number (or flow) on hepatic function in a microchannel flat-plate bioartificial liver (BAL) reactor containing a coculture of hepatocytes and fibroblasts . Static culture and reactor flow experiments established that: 1) a pseudo-steady-state detoxification rate could be attained at each Peclet number, 2) the steady-state detoxification rate increased nonlinearly with Peclet number (ranging from 167 to 2500), 3) the uptake rate of substrate was a linear function of cell surface substrate concentration (<1 microM), and 4) a shear stress of 10 dyne/cm2 did not adversely affect hepatic function for at least 12 h . A convection-diffusion-reaction model supports the conclusion that increased convective mass transfer of substrate to the cell surface is the primary cause of the observed increase in EROD rate with Peclet number . Our results suggest that detoxification rates can be enhanced by an order of magnitude by choosing an appropriate Peclet number . For our bioreactor configuration, this optimum corresponds to a Peclet number range of 1000-2000 at a Damkohler number of 0.55 . The usefulness of the mathematical model is discussed in the context of scale-up to a clinical BAL reactor for human application.

In Vitro Cell Dev Biol Anim, 2001 Oct, 37(9), 549 - 59
Design of an efficient medium for insect cell growth and recombinant protein production; Ikonomou L et al.; We report the development of a new serum-free medium based on the use of factorial experiments . At first, a variety of hydrolysates were screened using a fractional factorial approach with High-Five cells . From this experiment yeastolate ultrafiltrate was found to have, by far, the most important effect on cell growth . Furthermore, Primatone RL was found to remarkably prolong the stationary phase of Sf-9 and High-Five cell cultures . The optimal concentrations for yeastolate and Primatone were determined to be 0.6 and 0.5%, respectively, on the basis of a complete factorial experiment . This new medium, called YPR, supported good growth of both Sf-9 and High-Five cells in batch cultures, with maximal densities of 5.4 and 6.1 x 10(6) cells/ml, respectively . In addition, both cell lines achieved good growth in bioreactor batch culture and had a prolonged stationary phase of 3-4 d in YPR medium compared to Insect-XPRESS medium . The ability of the new medium to support recombinant protein expression was also tested by infecting Sf-9 or High-Five cells at high density (2 x 10(6) cells/ml) with a baculovirus expressing secreted placental alkaline phosphatase (SEAP) . The maximum total SEAP concentration after 7 d was about 43 lU/ml (58 mg/L) and 28 lU/ml (39 mg/L) for High-Five and Sf-9 cells, respectively.

Biomacromolecules, 2001 Fall, 2(3), 700 - 5
Orientation specific immobilization of organophosphorus hydrolase on magnetic particles through gene fusion; Wang J et al.; Recombinant DNA technology has been utilized to fuse an octapeptide, Asp-Tyr-Lys-Asp-Asp-Asp-Asp-Lys (FLAG), to the C-terminus of organophosphorus hydrolase (OPH, EC 3.1.8.1), an enzyme capable of hydrolyzing organophosphate compounds, such as insecticides and nerve gas agents . The recombinant OPH-FLAG was immobilized onto magnetic beads coated with protein A in the following ways: (a) site-directly through a monoclonal antibody (MAb) specific for the FLAG peptide; (b) through the MAb that was randomly tethered to the beads using glutaraldehyde; (c) randomly by cross-linking OPH-FLAG to protein-coated beads using glutaraldehyde . Kinetic studies demonstrated that the site-directly immobilized enzyme maintained the highest catalytic efficiency . The orientation specific immobilization strategy described in this article can be applied to other proteins, and therefore, it may find potential applications in the design of biosensors, biocatalysts, and bioreactors having immobilized proteins as their biorecognition elements.

Sheng Wu Gong Cheng Xue Bao, 2001 Jul, 17(4), 361 - 4
{Molecular farming has come of age}; Chiao JS; Important development in plant biotechnology has been ushered in the 1990s, the most astounding field is the establishment of various transgenic crops, including cotton, corn, rice, tomato etc . In addition, utilization of transgenic plants for the generation of antibodies, gene epitopes and complex proteins has drawn much attention recently . Among these results, the use of plant parts with inducted antigens such as cholera toxin B subunit, toxigenic E . coli LT-B subunit as oral vaccines is attractive as a new route of medication . Considering their effectiveness as vaccines in animal and clinical tests, and simple agricultural practice for large scale production it is anticipated that these antibodies are bound to offer impact to health care for people of the Third World . In this short review, the laboratory and successful clinical test, merits and demerits in comparison with the currently used bioreactors, methods of extraction, and cost estimation of transgenic plant products for medical purposes are briefly reviewed.

Annu Rev Biomed Eng, 2000, 2, 607 - 32
Extracorporeal tissue engineered liver-assist devices; Tzanakakis ES et al.; The treatment of acute liver failure has evolved to the current concept of hybrid bioartificial liver (BAL) support, because wholly artificial systems have not proved efficacious . BAL devices are still in their infancy . The properties that these devices must possess are unclear because of our lack of understanding of the pathophysiology of liver failure . The considerations that attend the development of BAL devices are herein reviewed . These considerations include choice of cellular component, choice of membrane component, and choice of BAL system configuration . Mass transfer efficiency plays a role in the design of BAL devices, but the complexity of the systems renders detailed mass transfer analysis difficult . BAL devices based on hollow-fiber bioreactors currently show the most promise, and available results are reviewed herein . BAL treatment is designed to support patients with acute liver failure until an organ becomes available for transplantation . The results obtained to date, in this relatively young field, point to a bright future . The risks of using xenogeneic treatments have yet to be defined . Finally, the experience gained from the past and current BAL systems can be used as a basis for improvement of future BAL technology.

Annu Rev Biomed Eng, 1999, 1, 129 - 52
Bioreactors for hematopoietic cell culture; Nielsen LK; Hematopoietic cell culture, or ex vivo expansion of hematopoietic cells, is an enabling technology with many potential applications in bone-marrow transplantation, immunotherapy, gene therapy, and the production of blood products . Hematopoietic cultures are complex, with many different cell types of different stages of development present at any given point in time and never in steady state . Moreover, these cells interact strongly with each other and the environment through cytokines (growth factors) and adhesion molecules, as well as through their metabolism . Despite these significant challenges, cell products produced in bioreactors have shown promise in recent phase 1 clinical trials.

Adv Space Res, 2001, 27(9), 1513 - 22
Aquatic food production modules in bioregenerative life support systems based on higher plants; Bluem V et al.; Most bioregenerative life support systems (BLSS) are based on gravitropic higher plants which exhibit growth and seed generation disturbances in microgravity . Even when used for a lunar or martian base the reduced gravity may induce a decreased productivity in comparison to Earth . Therefore, the implementation of aquatic biomass production modules in higher plant and/or hybrid BLSS may compensate for this and offer, in addition, the possibility to produce animal protein for human nutrition . It was shown on the SLS-89 and SLS-90 space shuttle missions with the C.E.B.A.S.-MINI MODULE that the edible non gravitropic rootless higher aquatic plant Ceratophyllum demeresum exhibits an undisturbed high biomass production rate in space and that the teleost fish species, Xiphophorus helleri, adapts rapidly to space conditions without loss of its normal reproductive functions . Based on these findings a series of ground-based aquatic food production systems were developed which are disposed for utilization in space . These are plant production bioreactors for the species mentioned above and another suitable candidate, the lemnacean (duckweed) species, Wolffia arrhiza . Moreover, combined intensive aquaculture systems with a closed food loop between herbivorous fishes and aquatic and land plants are being developed which may be suitable for integration into a BLSS of higher complexity . Grant numbers: WS50WB9319-3, IVA1216-00588 . c 2001 . COSPAR . Published by Elsevier Science Ltd . All rights reserved.

Tissue Eng, 2001 Oct, 7(5), 495 - 506
Oxygen tension influences proliferation and differentiation in a tissue-engineered model of placental trophoblast-like cells; Ma T et al.; A considerable oxygen gradient exists in vivo, which exerts regulatory effects on tissue development and function . The objective of this study was to evaluate the feasibility of controlling cell proliferation and differentiation by regulating oxygen tension in a tissue-engineered bioreactor model . The effects of oxygen tension on proliferation and differentiation of first-trimester human trophoblast cells (known as ED(27) cells) were studied in a fiber-bed perfusion bioreactor system in which cells were grown in polyethylene terephthalate (PET) nonwoven fibrous matrix . By varying the oxygen tension between 2% and 20%, differential responses of trophoblasts in their proliferation and differentiation activities were observed . There was no significant difference in the rates of glucose consumption and lactate production, and lactate dehydrogenase (LDH) level in the culture media for both 2% and 20% oxygen tension cultures, indicating that cell metabolic activities were not limited by low oxygen tension . However, 2% oxygen stimulated cell proliferation but impeded the secretion of a functional hormone, 17beta-estradiol . In contrast, 20% oxygen tension reduced cell proliferation, but yielded higher hormone secretion . A step change in oxygen tension from 2% to 20% caused cells in the bioreactor to increase 17beta-estradiol secretion and shifted cell cycle from proliferation to differentiation, which were verified with the expression levels of cyclin B1 and p27(kip1) . However, no significant response to a change from 6% to 20% oxygen tension was observed . It is concluded that changes in oxygen tension can be an effective strategy to control cell cycle and long-term tissue development . This work also demonstrated the important role of oxygen tension in regulating placental trophoblast tissue development and the feasibility of using the bioreactor under well-controlled physiological environment for tissue engineering applications.

Appl Microbiol Biotechnol, 2001 Oct, 57(1-2), 56 - 64
Kinetics of hydrogen production with continuous anaerobic cultures utilizing sucrose as the limiting substrate; Chen CC et al.; In this study, local sewage sludge was acclimated to establish H2-producing enrichment cultures, which were used to convert sucrose to H2 with continuously stirred anaerobic bioreactors . The steady-state behaviors of cell growth, substrate utilization, and product formation were closely monitored . Kinetic models were developed to describe and predict the experimental results from the H2-producing cultures . Operation at dilution rates (D) of 0.075-0.167 h(-1) was preferable for H2 production, resulting in a H2 concentration of nearly 0.02 mol/l . The optimal hydrogen production rate was 0.105 mol/h occurring at D=0.125 h(-1) . The major volatile fatty acid produced was butyric acid (HBu), while acetic acid and propionic acid were also produced in lesser quantities . The major solvent product was ethanol, whose concentration was only 15% of that of HBu, indicating that the metabolic flow favors H2 production . The proposed model was able to interpret the trends of the experimental data . The maximum specific growth rate (mu(max)), Monod constant (Ks), and yield coefficient for cell growth (Y(x/s)) were estimated as 0.172 h(-1), 68 mg COD/l, and 0.1 g/g, respectively . The model study also suggests that product formation in the continuous hydrogen-producing cultures was essentially a linear function of biomass concentration.

J Biotechnol, 2002 Jan 31, 93(1), 45 - 57
Anthocyanin production from Vaccinium pahalae: limitations of the physical microenvironment; Meyer JE et al.; Physical microenvironmental parameters conducive to production of flavonoids in vitro from continuous Vaccinium pahalae suspension cultures were examined first in shake flask culture experiments, and results were used to guide adaptations of a bioreactor production environment . Anthocyanin pigments were primarily concentrated in smaller aggregates up to 519 microm diameter . Agitation at 150 rpm and routine use of a mechanical scraper to periodically retrieve cells thrown out of solution was sufficient to keep productive plant cell aggregates in bioreactor suspension . A set up for enhanced irradiance with mercury lamps providing an average of 240 micromol m(-2) s(-1) PPF at the inner surface of the bioreactor vessel was required to sustain anthocyanin productivity through a 10-day production cycle.

J Ind Microbiol Biotechnol, 2001 Oct, 27(4), 208 - 14
Hydrodynamic characteristics and mixing behaviour of Sclerotium glucanicum culture fluids in an airlift reactor with an internal loop used for scleroglucan production; Kang X et al.; The filamentous fungus, Sclerotium glucanicum NRRL 3006, was cultivated in a 0.008 m(3) airlift bioreactor with internal recirculation loop (ARL-IL) for production of the biopolymer, scleroglucan . The rheological behaviour of the culture fluid was characterised by measurement of the fluid consistency coefficient (K) and the flow behaviour index (n) . Based on these measurements, the culture fluid changed from a low viscosity Newtonian system early in the process, to a viscous non-Newtonian (pseudoplastic) system . In addition, reactor hydrodynamics and mixing behaviour were characterised by measurement of whole mean gas hold-up (epsilon(g)), liquid re-circulation velocity (U(ld)) and mixing time (t(m)) . Under identical process conditions, the effects of the viscosity of the culture fluid and air flow rate on epsilon(g), U(ld) and t(m) were examined and empirical correlations for epsilon(g), U(ld) and t(m) with both superficial velocity U(g) and consistency coefficient K were obtained and expressed separately . The correlations obtained are likely to describe the behaviour of real fungal culture fluids more accurately than previous correlations based on Newtonian or simulated non-Newtonian systems.

Biotechnol Annu Rev, 2001, 7, 179 - 94
Enzymatic studies on the key enzymes of vitamin D metabolism; 1 alpha-hydroxylase (CYP27B1) and 24-hydroxylase (CYP24); Inouye K et al.; The key enzymes of vitamin D3 metabolism, renal 25-hydroxyvitamin D3 1 alpha-hydroxylase (CYP27B1) and 24-hydroxylase (CYP24) were expressed in Escherichia coli, and their enzymatic properties were revealed . As expected, mouse CYP27B1 and human CYP27B1 showed the 1 alpha-hydroxylation of 25-hydroxyvitamin D3 with the Michaelis constant, Km, value of 2.7 microM . Unexpectedly, both mouse CYP27B1 and human CYP27B1 showed greater Vmax/Km values toward 24,25-dihydroxyvitamin D3 than 25-hydroxyvitamin D3, suggesting that 24, 25-dihydroxyvitamin D3 is a better substrate than 25-hydroxyvitamin D3 for both CYP27B1 . Enzymatic studies on substrate specificity of CYP27B1 revealed that 25-hydroxyl group of vitamin D3 was essential for the 1 alpha-hydroxylase activity, and 24-hydroxyl group enhanced the activity, but, 23-hydroxyl group greatly reduced the activity . On rat CYP24, it was demonstrated that CYP24 catalyzed four-step monooxygenation towards 25-hydroxyvitamin D3 . Furthermore, in vivo and in vitro metabolic studies on 1 alpha,25-dihydroxyvitamin D3 clearly indicated that CYP24 catalyzed six-step monooxygenation to convert 1 alpha,25-dihydroxyvitamin D3 into calcitroic acid which is known as a final metabolite of 1 alpha,25-dihydroxyvitamin D3 for excretion in bile . These results strongly suggest that CYP24 is highly responsible for the metabolism of both 25-hydroxyvitamin D3 and 1 alpha,25-dihydroxyvitamin D3 . In addition, we have succeeded in the construction of mitochondrial P450 electron transport chain consisting of ADR, ADX and each of CYP27B1 and CYP24 in E . coli cells. , , , . The coexpression system with CYP27B1 might be useful as a bioreactor to produce 1 alpha,25-dihydroxyvitamin D3 . In contrast, the coexpression system with CYP24 would be applied to metabolic studies of vitamin D analogs used as drugs.

Osteoarthritis Cartilage, 2001, 9 Suppl A, S6 - 15
Articular cartilage repair using a tissue-engineered cartilage-like implant: an animal study; Mainil-Varlet P et al.; OBJECTIVE: Because articular cartilage has limited ability to repair itself, treatment of (osteo)chondral lesions remains a clinical challenge . We aimed to evaluate how well a tissue-engineered cartilage-like implant, derived from chondrocytes cultured in a novel patented, scaffold-free bioreactor system, would perform in minipig knees with chondral, superficial osteochondral, and full-thickness articular defects . DESIGN: For in vitro implant preparation, we used full-thickness porcine articular cartilage and digested chondrocytes . Bioreactors were seeded with 20x10(6) cells and incubated for 3 weeks . Subsequent to culture, tissue cartilage-like implants were divided for assessment of viability, formaldehyde-fixed and processed by standard histological methods . Some samples were also prepared for electron microscopy (TEM) . Proteoglycans and collagens were identified and quantified by SDS-PAGE gels . For in vivo studies in adult minipigs, medial parapatellar arthrotomy was performed unilaterally . Three types of defects were created mechanically in the patellar groove of the femoral condyle . Tissue-engineered cartilage-like implants were placed using press-fit fixation, without supplementary fixation devices . Control defects were not grafted . Animals could bear full weight with an unlimited range of motion . At 4 and 24 weeks postsurgery, explanted knees were assessed using the modified ICRS classification for cartilage repair . RESULTS: After 3-4 weeks of bioreactor incubation, cultured chondrocytes developed a 700-microm- to 1-mm-thick cartilage-like tissue . Cell density was similar to that of fetal cartilage, and cells stained strongly for Alcian blue and safranin O . The percentage of viable cells remained nearly constant (approximately 90%) . Collagen content was similar to that of articular cartilage, as shown by SDS-PAGE . At explantation, the gross morphological appearance of grafted defects appeared like normal cartilage, whereas controls showed irregular fibrous tissue covering the defect . Improved histologic appearance was maintained for 6 months postoperatively . Although defects were not always perfectly level upon implantation at explanation the implant level matched native cartilage levels with no tissue hypertrophy . Once in place, implants remodelled to tissues with decreased cell density and a columnar organization . CONCLUSIONS: Repair of cartilage defects with a tissue-engineered implant yielded a consistent gross cartilage repair with a matrix predominantly composed of type II collagen up to 6 months after implantation . This initial result holds promise for the use of this unique bioreactor/tissue-engineered implant in humans.

Microb Ecol, 2001 Aug, 42(2), 150 - 8
Culturability as an indicator of succession in microbial communities; Garland JL et al.; Successional theory predicts that opportunistic species with high investment of energy in reproduction and wide niche width will be replaced by equilibrium species with relatively higher investment of energy in maintenance and narrower niche width as communities develop . Since the ability to rapidly grow into a detectable colony on nonselective agar medium could be considered as characteristic of opportunistic types of bacteria, the percentage of culturable cells may be an indicator of successional state in microbial communities . The ratios of culturable cells (colony forming units on R2A agar) to total cells (acridine orange direct microscopic counts) and culturable cells to active cells (reduction of 5-cyano-2,3-ditolyl tetrazolium chloride) were measured over time in two types of laboratory microcosms (the rhizosphere of hydroponically grown wheat and aerobic, continuously stirred tank reactors containing plant biomass) to determine the effectiveness of culturabilty as an index of successional state . The culturable cell:total cell ratio in the rhizosphere decreased from approximately 0.25 to less than 0.05 during the first 30-50 days of plant growth, and from 0.65 to 0.14 during the first 7 days of operation of the bioreactor . The culturable cell:active cell ratio followed similar trends, but the values were consistently greater than the culturable cell:total cell ratio, and even exceeded I in early samples . Follow-up studies used a cultivation-independent method, terminal restriction fragment length polymorphisms (TRFLP) from whole community DNA, to assess community structure . The number of TRFLP peaks increased with time, while the number of culturable types did not, indicating that the general decrease in culturability is associated with a shift in community structure . The ratio of respired to assimilated C-14-labeled amino acids increased with the age of rhizosphere communities, supporting the hypothesis that a shift in resource allocation from growth to maintenance occurs with time . Results from this work indicate that the percentage of culturable cells may be a useful method for assessing the successional state of microbial communities.

Fresenius J Anal Chem, 2001 Sep, 371(2), 168 - 73
On-line coupling of a miniaturized bioreactor with capillary electrophoresis, via a membrane interface, for monitoring the production of organic acids by microorganisms; Ehala S et al.; Capillary electrophoresis (CE) can be a valuable tool for on-line monitoring of bioprocesses . Production of organic acids by phosphorus-solubilizing bacteria and fermentation of UHT milk were monitored and controlled by use of a membrane-interfaced dialysis device and a home-made microsampler for a capillary electrophoresis unit . Use of this specially designed sampling device enabled rapid consecutive injections without interruption of the high voltage . No additional sample preparation was required . The time resolution of monitoring in this particular work was approximately 2 h, but could be reduced to 2 min . Analytes were detected at low microg mL(-1) levels with a reproducibility of approximately 10% . To demonstrate the potential of CE in processes of biotechnological interest, results from monitoring phosphate solubilization by bacteria were submitted to qualitative and quantitative analysis . Fermentation experiments on UHT milk showed that monitoring of the processes by CE can provide good resolution of complex mixtures, although for more specific, detailed characterization the identification of individual substances is needed.

Life Support Biosph Sci, 2001, 7(4), 301 - 10
Electrolytic removal of nitrate from crop residues; Colon G et al.; The Controlled Ecological Life Support System (CELSS) resource recovery system, which is a waste-processing system,uses aerobic and anaerobic bioreactors to recover plants nutrients and secondary foods from the inedible biomass . Crop residues contain a significant amount of nitrate . There are actually two major problems concerning nitrate: 1) both CELSS biomass production and resource recovery consume large quantities of nitric acid, and 2) nitrate causes a variety of problems in both aerobic and anaerobic bioreactors . The nitrate anion causes several problems in the resource recovery system in such a way that removal prior to the process is highly desirable . The technique proposed to remove nitrate from potato inedible biomass leachate and to satisfy the nitric acid demand was a four-compartment electrolytic cell . In order to establish the electrolytic cell performance variables, experiments were carried out using potato crop residue aqueous leachate as the diluate solution . The variables studied were the potato biomass leachate composition and electrical properties, preparation of compartment solutions to be compatible with the electrolytic system, limiting current density, nutrients removal rates as a function of current density, fluid hydrodynamic conditions, applied voltage, and process operating time during batch recirculation operation . Results indicated that the limiting current density (maximum operating current density) was directly proportional to the solution electrical conductivity an a power function of the linear fluid velocity in the range between 0.083 and 0.403 m/s . During the electrolytic cell once-through operation, the nitrate, potassium, and other nutrient removal rates were proportional to the current density and were inversely proportional to fluid velocity . The removal of monovalent ions was found to be higher than divalent ones . Under batch recirculation operation at constant applied voltage of 4.5 and 8.5 V, it was found that the nutrient removal rates were independent of applied voltage, but were proportional to the ions concentration and operating time.

Life Support Biosph Sci, 2001, 7(4), 291 - 9
On-line removal of volatile fatty acids from CELSS anaerobic bioreactor via nanofiltration; Colon G et al.; The CELSS resource recovery system, which is a waste-processing system, uses aerobic and anaerobic bioreactors to recover plants nutrients and secondary foods from the inedible biomass . The anaerobic degradation of the inedible biomass, by means of culture of rumen bacteria, generates organic compounds such as volatile fatty acids (VFA) (acetic, propionic, butyric) and ammonia . The presence of VFA in the bioreactor medium at fairly low concentrations decreases the microbial population's metabolic reactions due to end-product inhibition . Technologies to remove VFA continuously from the bioreactor are of high interest . Several candidate technologies were analyzed, such as organic solvent liquid-liquid extraction, adsorption and/or ion exchange, dialysis, electrodialysis, and pressure-driven membrane separation processes . The proposed technique for the on-line removal of VFA from the anaerobic bioreactor was a nanofiltration membrane recycle bioreactor . In order to establish the nanofiltration process performance variables before coupling it to the bioreactor, a series of experiments was carried out using a 10,000 molecular weight cutoff (MWCO) tubular ceramic membrane module . The variables studied were the bioreactor slurry permeation characteristics, such as: the permeate flux, VFA and nutrient removal rates as a function of applied transmembrane pressure, fluid recirculation velocity, suspended matter concentration, and process operating time . Results indicated that the permeate flux, VFA, and nutrients removal rates are directly proportional to the fluid recirculation velocity in the range between 0.6 and 1.0 m/s, applied pressure when these are lower than 1.5 bar, and inversely proportional to the total suspended solids concentration in the range between 23,466 and 34,880 mg/L . At applied pressure higher than 1.5 bar the flux is not more linearly dependent due to concentration polarization and fouling effects over the membrane surface . It was also found that the permeate flux declines rapidly during the first 5-8 h, and then levels off with a diminishing rate of flux decay.

Biotechnol Bioeng, 2001 Nov 20, 75(4), 475 - 84
Enzyme microgels in packed-bed bioreactors with downstream amperometric detection using microfabricated interdigitated microsensor electrode arrays; Guiseppi-Elie A et al.; In this article, we describe the use of pH- responsive hydrogels as matrices for the immobilization of two enzymes, glucose oxidase (GOx) and glutamate oxidase (GlutOx) . Spherical hydrogel beads were prepared by inverse suspension polymerization and the enzymes were immobilized by either physical entrapment or covalent immobilization within or on the hydrogel surface . Packed-bed bioreactors were prepared containing the bioactive hydrogels and these incorporated into flow injection (FI) systems for the quantitation of glucose and monosodium glutamate (MSG) respectively . The FI amperometric detector comprised a microfabricated interdigitated array within a thin-layer flow cell . For the FI manifold incorporating immobilized GOx, glucose response curves were found to be linear over the concentration range 1.8-280 mg dL(-1) (0.1-15.5 mM) with a detection limit of 1.4 mg dL(-1) (0.08 mM) . Up to 20 samples can be manually analyzed per hour, with the hydrogel-GOx bioreactor exhibiting good within-day (0.19%) precision . The optimized FI manifold for MSG quantitation yielded a linear response range of up to 135 mg dL(-1) (8 mM) with a detection limit of 3.38 mg dL(-1) (0.2 mM) and a throughput of 30 samples h(-1) . Analysis of commercially produced soup samples gave a within-day precision of 3.6% . Bioreactors containing these two physically entrapped enzymes retained > 60% of their initial activities after a storage period of up to 1 year .

Adv Space Res, 2001, 27(2), 421 - 30
Three-dimensional transgenic cell model to quantify genotoxic effects of space environment; Gonda SR et al.; In this paper we describe a three-dimensional, multicellular tissue-equivalent model, produced in NASA-designed, rotating wall bioreactors using mammalian cells engineered for genomic containment of multiple copies of defined target genes for genotoxic assessment . Rat 2 lambda fibroblasts, genetically engineered to contain high-density target genes for mutagenesis (Stratagene, Inc., Austin, TX), were cocultured with human epithelial cells on Cytodex beads in the High Aspect Ratio Bioreactor (Synthecon, Inc, Houston, TX) . Multi-bead aggregates were formed by day 5 following the complete covering of the beads by fibroblasts . Cellular retraction occurred 8-14 days after coculture initiation culminating in spheroids retaining few or no beads . Analysis of the resulting tissue assemblies revealed: multicellular spheroids, fibroblasts synthesized collagen, and cell viability was retained for the 30-day test period after removal from the bioreactor . Quantification of mutation at the LacI gene in Rat 2 lambda fibroblasts in spheroids exposed to 0-2 Gy neon using the Big Blue color assay (Stratagene, Inc.), revealed a linear dose-response for mutation induction . Limited sequencing analysis of mutant clones from 0.25 or 1 Gy exposures revealed a higher frequency of deletions and multiple base sequencing changes with increasing dose . These results suggest that the three-dimensional, multicellular tissue assembly model produced in NASA bioreactors are applicable to a wide variety of studies involving the quantification and identification of genotoxicity including measurement of the inherent damage incurred in Space . Published by Elsevier Science Ltd on behalf of COSPAR.

J Ind Microbiol Biotechnol, 2001 Aug, 27(2), 67 - 71
Oxygen-limited decomposition of food wastes in a slurry bioreactor; Park JI et al.; The slurry bioreactor system is an effective means for treating highly saline food wastes, which may not be recycled as composts . The effect of aeration rate was investigated in a slurry bioreactor as a major factor affecting the slurry-phase decomposition of food wastes . The aeration rate affected significantly the decomposition performance and the composition profiles of the liquid and solid phases . The decomposed carbon was almost linear with oxygen consumption, indicating that the slurry-phase decomposition of food wastes was limited by oxygen transfer . The oxygen requirement for decomposing 1 g organic carbon in food wastes was estimated to be 61.5 g O(2).

J Biotechnol, 2001 Dec 28, 92(2), 103 - 12
Degradation of household biowaste in reactors; Krzystek L et al.; Household derived biowaste was degraded by biological methods . The system involves the combined method of low-solids (up to 10% w/v of total solids (TS)) anaerobic digestion and aerobic degradation for the recovery of energy (biogas) and the production of fine humus-like material which can be used as a soil amender or a substrate for further thermal treatment (pyrolysis, gasification) . The performance of batch and continuous processes carried out in bioreactors (stirred tank reactor, air-lift) of working volume 6 and 18 dm(3), at different temperatures (25-42 degrees C) was monitored by reduction of TS, volatile solids, chemical oxygen demand, total organic carbon, C/N in time . The application of continuous process with recirculation (33%) caused that for residence time of 8-16 h the obtained degree of organic load reduction was similar to that obtained after 72-96 h of the batch process . The experimental data of batch aerobic degradation was also subjected to kinetic analysis . The sequence of the two processes: aerobic and anaerobic or anaerobic and aerobic showed that the degree of organic load reduction was similar in both cases, while the amount of produced biogas was four times higher when the first stage was anaerobic . The final product after dewatering was subjected to pyrolysis and gasification . The gases obtained were characterised by a high heat of combustion of about 11-15 MJ Nm(-3).

J Biotechnol, 2001 Dec 28, 92(2), 89 - 94
A novel airlift photobioreactor with baffles for improved light utilization through the flashing light effect; Degen J et al.; A newly developed flat panel airlift photobioreactor with a defined circulation path was tested for microalgal culture . The bioreactor exposed the cells to intermittent light to improve the efficiency of light utilization through the flashing-light effect . During batch cultures in the new photobioreactor, the biomass productivity of Chlorella vulgaris was 1.7 times greater than in a randomly mixed bubble column of identical dimension . A reduction in light path from 30 to 15 mm increased the biomass productivity by 2.5-fold . A maximum dry biomass productivity of 0.11 g l(-1) h(-1) was obtained at an artificial illumination of 980 mu E m(-2) s(-1).

Prikl Biokhim Mikrobiol, 2001 Sep-Oct, 37(5), 582 - 5
{Analysis of kinetic parameters of gas phase bioreactors}; Viktorov AA et al.; The dependence of toluene elimination capacity on its load was obtained in five small-scale reactors filled with glass beads carrying biocatalyst cells . With increase in operation time the calculated maximal elimination capacity was shown to increase along with biomass density in the biocatalyst bed . Fivefold increase in trickling intensity did not affect the reactor performance . A simplified mathematical model for evaluation of minimal required biocatalyst bed volume at certain loading was developed based on experimental dependence of elimination capacity vs . loading.

J Biotechnol, 2001 Dec 14, 92(1), 67 - 72
Higher production of rabies virus in serum-free medium cell cultures on microcarriers; Frazzati-Gallina NM et al.; Rabies virus suspensions were obtained from VERO cells cultivated on solid microcarriers in a bioreactor after infection with the Pasteur rabies virus strain (PV) . Virus production-serum free medium (VP-SFM) or Leibovitz 15 (L15) medium supplemented or not with fetal calf serum (FCS) were used to cultivate the VERO cells, before and after virus infection . The cell growth was shown to reach higher densities (1.6 x 10(6) cellsmol(-l)), when VP-SFM supplemented with 1% of FCS was used during the cell growth phase of culture, and then replaced by VP-SFM alone for the virus multiplication phase . In the cultures performed from the beginning with VP-SFM, lower densities accompanied by an altered cell morphology and detachment from the microcarriers were always observed . In rabies virus infected cultures, kinetic studies showed that higher virus yields (10(4.7) FFD(50) per 0.05 ml) were always obtained in cultures performed initially on VP-SFM supplemented with 1% FCS and after infection on VP-SFM alone . In agreement with that, rabies virus production, as measured by the average of virus titers in harvests obtained at different times after infection were shown to be 5.5 times higher in the cell cultures using initially VP-SFM+1%FCS and, following infection, VP-SFM alone . Besides the advantages of using media with a well-controlled composition, these data indicate the usefulness of serum free media also in terms of virus productivity.

Hybrid processes: Hybrid plants are often put into place where an existing system must be upgraded.

Trickling filter plants might be upgraded to an Activated Biofilter, which recycles Return Activated Sludge (RAS) over the filter using plastic or redwood media. This type of system performs well at low organic loads and in warm climates. A example of this technology is the 80 MLD Biocarbone Process located at Sherbrook, Quebec, which is a Swedish technology consisting of a fixed bed reactor in a downflow mode of operation..

Alternatively, a small suspended growth tank can be added downstream of a trickling filter to form a Trickling Filter Solids Contact (TFSC) process. The contact tank is sized for about 10-15 percent of size normally required for activated sludge alone, since the trickling filter removes most of the soluble BOD. Another modification is the roughing filter/activated sludge process, where the trickling filter is a much smaller proportion of the entire process. Separating the two processes with a secondary clarifier is not usually done due to high capital costs when compared to the other processes.

Another form of hybrid system submerges inert support media within suspended growth bioreactors. Moving Bed Biofilm Reactors (MBBRs) utilize neutral buoyancy media. Fluidized bed reactors are used for industrial wastewater treatment.

On-site biological treatment has been used for groundwater cleanup from industrial and agricultural chemicals. The pump-and-treat efficiency is controlled by retardation of contaminants by sorption onto the saturated subsurface solids and by the presence of non-aqueous-phase liquids in the aquifer. On-site bioreactors have been widely used for treatment of contaminants such as petroleum hydrocarbons, monoaromatic hydrocarbons, chlorinated aliphatics and aromatics. The most commonly used reactor types for groundwater include the following: trickling filter, upflow fixed-film reactor and fluidized bed reactor. Bioreactor processes have limitations mainly because of their design to operate at elevated temperatures and thereby by high operational costs.

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