What Is Activated Sludge?

Activated sludge is a process in sewage treatment in which air or oxygen is forced into sewage liquor to develop a biological floc which reduces the organic content of the sewage. In all activated sludge plants, once the sewage has received sufficient treatment, excess mixed liquor is discharged into settling tanks and the supernatant is run off to undergo further treatment before discharge. Part of the settled material, the sludge, is returned to the head of the aeration system to re-seed the new sewage entering the tank. The remaining sludge is further treated prior to disposal.

Activated sludge: Biomass produced in raw or settled wastewater (primary effluent) by the growth of organisms in aeration tanks in the presence of dissolved oxygen. The term "activated" comes from the fact that the particles are teeming with bacteria, and protozoa. Activated sludge is different from primary sludge in that the sludge contains many living organisms which can feed on the incoming wastewater.

Activated Sludge Process: A biological treatment process in which a mixture of sewage and activated sludge is agitated and aerated. The activated sludge is subsequently separated from the treated sewage by settlement and may be re-used. A common method of disposing of pollutants in wastewaters.

In the process, large quantities of air are bubbled through wastewaters that contain dissolved organic substances in open aeration tanks. Oxygen is required by bacteria and other types of microorganisms present in the system to live, grow, and multiply in order to consume the dissolved organic "food", or pollutants in the waste. After several hours in a large holding tank, the water is separated from the sludge of bacteria and discharged from the system. Most of the activated sludge is returned to the treatment process, while-the remainder is disposed of by one of several accepted methods.

Sewage is domestic, municipal, or industrial liquid waste products. How it is disposed varies by the area, and the local commitment to the environment. In some countries, notably the United States, national law mandates sanitary treatment of sewage, and outfalls are regulated. Surprisingly, many quite wealthy countries have untreated outfalls directly to surface water, often causing disease, pollution and undrinkable tapwater.

Sewage may be carried directly through pipelines to outfalls, or from upstream sources via river systems. Sewage is often from storm water runoff of streets, parking lots, lawns and commercial and industrial areas. In some urban areas, sewage is carried separately in sanitary sewers while runoff from streets is carried in storm drains. Access to either of these is typically through a manhole.

Sewage may drain directly into major watersheds with minimal or no treatment. When untreated, sewage can have serious impacts on the quality of an environment and on the health of people. Pathogens can cause a variety of illnesses. Some chemicals pose risks even at very low concentrations and can remain a threat for long periods of time because of bioaccumulation in animal or human tissue.

The solution, of course, is sewage treatment.

Sewage contains mineral, animal and vegetable matter in suspension, as well as large numbers of bacteria. It may contain paper, food, grease, cigarettes, leaves, faeces, and urine. Other items that occasionally are flushed down toilets include child care-related waste (such as disposable diapers, training pants, baby wipes, bibs, pacifiers, and outgrown clothing), feminine hygiene materials (tampons and pantiliners), medical waste from hospitals, and industrial chemicals. Some items are disposed of in the sewage system for illicit purposes. Drugs are often disposed of this way in a raid, as are legitimate medications at the end of their useful life. In some prisons, inmates flush blankets down the powerful vacuum suction toilets in vain hopes of amusement caused by a clogged line. Sewage odors are unacceptable to most people. In a confined space such as a manhole or lift station housing, gases such as hydrogen sulfide may be concentrated to dangerous levels, requiring special breathing apparatus and rescue apparatus for workers who must enter such spaces. A special hazard of hydrogen sulfide is that it becomes odorless at high concentrations. Another dangerous gas that can form in sewers is methane, which is both toxic and explosive.

Sludge is a solid waste extracted in the process of sewage treatment. When fresh sewage water is added to a settling tank, approximately 50% of the suspended solid matter will settle out in the period of an hour and a half or so. This collection of solids is known as fresh sludge. Such sludge will become actively putrescent in a short time and must be removed from the sedimentation tank before this happens.

This is commonly accomplished by two different ways. In an Imhoff tank, fresh sludge is passed through a slot to the lower story or digestion chamber where decomposition by anaerobic bacteria takes place resulting in liquefaction and a reduction in the volume of the sludge. After digesting for 6 to 9 months, the result is called "digested" sludge and may be disposed of by drying and then landfilling. It has value as fertilizer, being similar to humus. Alternately, the fresh sludge may be continuously extracted from the tank by mechanical means and passed on to separate sludge digestion tanks which operate at higher temperatures than the lower story of the Imhoff tank and as a result digest much more rapidly and efficiently.

Microbiology, 2004 Nov, 150(Pt 11), 3613 - 30
Antibiotic multiresistance plasmid pRSB101 isolated from a wastewater treatment plant is related to plasmids residing in phytopathogenic bacteria and carries eight different resistance determinants including a multidrug transport system; Szczepanowski R et al.; Ten different antibiotic resistance plasmids conferring high-level erythromycin resistance were isolated from an activated sludge bacterial community of a wastewater treatment plant by applying a transformation-based approach . One of these plasmids, designated pRSB101, mediates resistance to tetracycline, erythromycin, roxythromycin, sulfonamides, cephalosporins, spectinomycin, streptomycin, trimethoprim, nalidixic acid and low concentrations of norfloxacin . Plasmid pRSB101 was completely sequenced and annotated . Its size is 47 829 bp . Conserved synteny exists between the pRSB101 replication/partition (rep/par) module and the pXAC33-replicon from the phytopathogen Xanthomonas axonopodis pv . citri . The second pRSB101 backbone module encodes a three-Mob-protein type mobilization (mob) system with homology to that of IncQ-like plasmids . Plasmid pRSB101 is mobilizable with the help of the IncP-1alpha plasmid RP4 providing transfer functions in trans . A 20 kb resistance region on pRSB101 is located within an integron-containing Tn402-like transposon . The variable region of the class 1 integron carries the genes dhfr1 for a dihydrofolate reductase, aadA2 for a spectinomycin/streptomycin adenylyltransferase and bla(TLA-2) for a so far unknown Ambler class A extended spectrum beta-lactamase . The integron-specific 3'-segment (qacEDelta1-sul1-orf5Delta) is connected to a macrolide resistance operon consisting of the genes mph(A) (macrolide 2'-phosphotransferase I), mrx (hydrophobic protein of unknown function) and mphR(A) (regulatory protein) . Finally, a putative mobile element with the tetracycline resistance genes tetA (tetracycline efflux pump) and tetR was identified upstream of the Tn402-specific transposase gene tniA . The second 'genetic load' region on pRSB101 harbours four distinct mobile genetic elements, another integron belonging to a new class and footprints of two more transposable elements . A tripartite multidrug (MDR) transporter consisting of an ATP-binding-cassette (ABC)-type ATPase and permease, and an efflux membrane fusion protein (MFP) of the RND-family is encoded between the replication/partition and the mobilization module . Homologues of the macrolide resistance genes mph(A), mrx and mphR(A) were detected on eight other erythromycin resistance-plasmids isolated from activated sludge bacteria . Plasmid pRSB101-like repA amplicons were also obtained from plasmid-DNA preparations of the final effluents of the wastewater treatment plant indicating that pRSB101-like plasmids are released with the final effluents into the environment.

Biodegradation, 2004 Oct, 15(5), 289 - 301
Isolation and growth characteristics of an EDTA-degrading member of the alpha-subclass of Proteobacteria; Weilenmann HU et al.; A Gram-negative, ethylenediaminetetraacetic acid (EDTA)-degrading bacterium (deposited at the German Culture Collection as strain DSM 9103) utilising EDTA as the only source of carbon, energy and nitrogen was isolated from a mixed EDTA-degrading population that was originally enriched in a column system from a mixture of activated sludge and soil . Chemotaxonomic analysis of quinones, polar lipids and fatty acids allowed allocation of the isolate to the alpha-subclass of Proteobacteria . 16S rDNA sequencing and phylogenetic analysis revealed highest similarity to the Mesorhizobium genus followed by the Aminobacter genus . However, the EDTA-degrading strain apparently forms a new branch within the Phyllobacteriaceae/Mesorhizobia family . Growth of the strain was rather slow not only on EDTA (micro(max) = 0.05 h(-1)) but also on other substrates . Classical substrate utilisation testing in batch culture suggested a quite restricted carbon source spectrum with only lactate, glutamate, and complexing agents chemically related to EDTA (nitrilotriacetate, iminodiacetate and ethylenediaminedisuccinate) supporting growth . However, when EDTA-limited continuous cultures of strain DSM 9103 were pulsed with fumarate, succinate, glucose or acetate, these substrates were assimilated immediately . Apparently, the strain can use a broader spectrum than indicated by traditional substrate testing techniques . The EDTA species CaEDTA and MgEDTA served as growth substrates of the strain because in the mineral medium employed EDTA was predicted to be mainly present in the form of these two complexes . The bacterium was not able to degrade Fe3+-complexed EDTA.

Water Environ Res, 2004 Sep-Oct, 76(5), 444 - 52
Use of extant kinetic parameters to predict effluent concentrations of specific organic compounds at full-scale facilities; Ellis TG et al.; To use the results of kinetic tests to predict effluent concentrations of specific contaminants in activated sludge systems, the fraction of the biomass that has an ability to degrade the test compound (i.e., competent biomass) must be estimated . A calibration procedure was developed to assess the competent biomass concentration because the chemical oxygen demand (COD) fraction tended to underestimate the degrading fraction for three of the four test compounds . Acetone, for instance, had a measured influent COD fraction of 0.08%, and the actual competent fraction was estimated to be 2.3%, based on the model calibration . Once the competent biomass fraction in the mixed liquor was determined, the extant kinetic parameters were subsequently used to predict activated sludge system performance . Predicted effluent concentrations were within 2, 5, and 16% of the average measured concentrations for acetone, linear alkylbenzene sulfonate, and furfural, respectively . Day-to-day predictions for these compounds were less accurate, possibly because of the non-steady-state nature of the activated sludge systems studied . The difference between the fraction of the influent COD contributed by the target compounds and the competent biomass fraction in the mixed liquor was found to be more significant when the target compound contributed less than 1% of the influent organic matter . The chemical structure of the target compound and chemical composition of the influent likely had an effect on the resulting competent biomass concentration . The total maximum growth rate, microX, was observed to be independent of the influent concentration of acetone and furfural, thus suggesting that the competent biomass concentration for these compounds was not affected by the changes in their influent concentrations . Consequently, a majority of competent biomass growth resulted from the degradation of other substrates, resulting in a competent biomass concentration significantly higher than predicted based on the influent COD fraction contributed by the test compound.

Water Environ Res, 2004 Sep-Oct, 76(5), 425 - 36
A review of biofouling and its control in membrane separation bioreactors; Liao BQ et al.; Membrane separation technology is increasingly becoming an important innovation in biological wastewater treatment . Biofouling of the membrane is a major factor affecting the efficient and economic operation of membrane separation bioreactors (MBRs) . This review summarizes the state-of-the-art progress in understanding the mechanisms and factors affecting membrane biofouling and the strategies for biofouling control . Biofouling mechanisms include the adsorption of soluble and suspended extracellular polymers on membrane surfaces and in membrane pores, the clogging of membrane pore structure by fine colloidal particles and cell debris, and the adhesion and deposition of sludge cake on membrane surfaces . Design and operating conditions of membrane modules and materials, hydrodynamic conditions in MBRs, process and environmental conditions of activated sludge systems, and the physicochemical properties of the wastewater are the dominant factors determining membrane biofouling . Current strategies to control biofouling include periodic relaxation, backwashing, chemical cleaning, and possible manipulation of hydrodynamic conditions and sludge properties . Achieving full integration of MBRs in wastewater treatment technology requires further research and development . Fundamental information on the bacteria, colloid, and membrane interaction, developed through multimethod and multiscale approaches, is particularly needed.

Huan Jing Ke Xue, 2004 Jul, 25(4), 70 - 3
{Effects of Mn2+, Mo6+ and Zn2+ on the components change of extracellular polymeric substances in activated sludge}; Cao XS et al.; By specific oxygen uptake rate, (SOUR) measurements of activated sludge with different metal ion concentration, the optimal stimulation concentrations of Mn2+, Mo6+ and Zn2+ were determined . Then within each metal ion stimulation concentration range, extracellular polymeric substances (EPS) were extracted from activated sludge and its components (protein, polysaccharide and nucleic acid) contents changes were investigated . The results showed that the optimal stimulation concentration of each metal ion is 1mg x L(-1) . EPS components of activated sludge vary obviously with Mn2+ and Zn2+ concentration change but not with Mo6+ . After storage at low temperature, EPS quantities in activated sludge are reduced with polysaccharide reduction is the most.

Huan Jing Ke Xue, 2004 Jul, 25(4), 59 - 64
{Enhancing resistance of a conventional activated sludge system against shock loading of 2,4-DCP through bioaugmentation with special culture}; Quan XC et al.; In this study, conventional activated sludge (CAS) systems, which were generally used to treat municipal wastewater, were modeled to receive intermittent 2,4-dichlorophenol (2,4-DCP) shock loadings . The response and stability of the CAS system augmented with special culture and the non-bioaugmented control CAS system under shock loading conditions were compared . The capability of the bioaugmented CAS systems to degrade 2,4-DCP under long-term continuous operation was investigated . Results showed that for the CAS systems with 5% and 15% special culture addition, their degradation of the target pollutants and resistance against shock loadings was enhanced significantly . When 2,4-DCP shock loading occurred within the first 30 days after single inoculation, the bioaugmented CAS systems maintained high degradation ability to the target pollutants . After 70 days continuous operation without 2,4-DCP in feed, when the CAS systems challenged 2,4-DCP again, the effect of bioaugmentation was greatly reduced and the CAS system failed to remove the pollutants and maintain the system stability effectively . Therefore, re-supplementation was needed for further treatment of 2,4-DCP.

Water Environ Res, 2004 Jul-Aug, 76(4), 353 - 9
Case study II: application of the divalent cation bridging theory to improve biofloc properties and industrial activated sludge system performance-using alternatives to sodium-based chemicals; Higgins MJ et al.; The objective of this study was to investigate the application of the divalent cation bridging theory (DCBT) as a tool in the chemical selection process at an activated sludge plant to improve settling, dewatering, and effluent quality . According to the DCBT, to achieve improvements, the goal of chemical selection should be to reduce the ratio of monovalent-to-divalent (M/D) cations . A study was conducted to determine the effect of using magnesium hydroxide {Mg(OH)2} as an alternative to sodium hydroxide (NaOH) at a full-scale industrial wastewater treatment plant . Floc properties and treatment plant performance were measured for approximately one year during two periods of NaOH addition and Mg(OH)2 addition . A cost analysis of plant operation during NaOH and Mg(OH)2 use was also performed . During NaOH addition, the M/D ratio was 48, while, during Mg(OH)2 addition, this ratio was reduced to an average of approximately 0.1 . During the Mg(OH)2 addition period, the sludge volume index, effluent total suspended solids, and effluent chemical oxygen demand were reduced by approximately 63, 31, and 50%, respectively, compared to the NaOH addition period . The alum and polymer dose used for clarification was reduced by approximately 50 and 60%, respectively, during Mg(OH)2 addition . The dewatering properties of the activated sludge improved dewatering as measured by decreased capillary suction time and specific resistance to filtration (SRF), along with an increase in cake solids from the SRF test . This corresponded to a reduction in the volume of solids thickened by centrifuges at the treatment plant, which reduced the disposal costs of solids . Considering the costs for chemicals and solids disposal, the annual cost of using Mg(OH)2 was approximately 30,000 dollars to 115,000 dollars less than using NaOH, depending on the pricing of NaOH . The results of this study confirm that the DCBT is a useful tool for assessing chemical-addition strategies and their potential effect on activated sludge performance.

Water Environ Res, 2004 Jul-Aug, 76(4), 344 - 52
Case study I: application of the divalent cation bridging theory to improve biofloc properties and industrial activated sludge system performance-direct addition of divalent cations; Higgins MJ et al.; The objectives of this study were to examine the application of the divalent cation bridging theory (DCBT) to improve settling, dewatering, and effluent quality in pilot-scale reactors and a full-scale system treating an industrial wastewater . This was accomplished by lowering the monovalent-to-divalent (M/D) cation ratio by direct divalent cation addition . Research has shown that the M/D ratio is a potential indicator for settling and dewatering problems at wastewater treatment plants, and M/D ratios above 2 have been associated with poor settling, dewatering, and effluent quality . The M/D ratio of the wastewater in this study ranged from 6 to 20 . The cations studied were calcium and magnesium . Results showed that the addition of calcium improved floc properties compared to control reactors with no calcium addition . The reductions in sludge volume index, effluent chemical oxygen demand (COD), and effluent total suspended solids (TSS) were approximately 35, 34, and 55%, respectively, when the M/D ratio was decreased to approximately 2:1 . In addition, the cake solids from a belt filter press simulator increased by 72% and the optimum polymer dose required for conditioning was reduced by 70% in the reactor fed the highest calcium concentration when compared to control reactors with no calcium addition . The addition of calcium also decreased the negative effect of high filamentous organism numbers . In general, the addition of magnesium (Mg2+) had similar effects on effluent quality and dewatering properties, although some differences were measured . A full-scale test using calcium addition was performed . Measurements of effluent quality and floc properties were performed before, during, and after the calcium (Ca2+) addition period . The average M/D ratio during these periods was 6.2, 4.6, and 14.0, respectively . The addition of Ca2+ decreased the effluent five-day biochemical oxygen demand, effluent TSS, and effluent COD . The increased Ca2+ concentration also improved dewatering measured by a decrease in specific resistance to filtration and capillary suction time . Overall, the addition of divalent cations to the pilot- and full-scale activated sludge systems improved floc properties and the data fit well with the DCBT.

Water Environ Res, 2004 Jul-Aug, 76(4), 327 - 33
Effects of chlorination on the adhesion strength and deflocculation of activated sludge flocs; Mascarenhas T et al.; A side effect of the application of chlorine for controlling filamentous bulking is deflocculation of floc-forming bacteria, which may cause unacceptable effluent deterioration depending on dosing . It was assumed that chlorine may adversely affect the adhesion ability of floc bacteria, promoting their erosion in shear flow . The effect of chlorination on the strength of activated sludge flocs was investigated . The adhesion-erosion (AE) model developed by Mikkelsen and Keiding was used to interpret results from deflocculation tests with varying shear and solids concentration . The AE model yields the adhesion enthalpy (deltaHG/R) of cells in sludge flocs and parameters from the model were used to quantify the sludge in terms of floc strength . Two activated sludges with different initial characteristics were studied . The resulting model parameters showed that the AE model was suitable for quantifying the bond energy of particles to the activated sludge exposed to chlorine . For one activated sludge, adhesion of cells was largely unaffected by the applied chlorine doses . A second sludge showed reduced adhesion strength with chlorine, leading to increasing deflocculation . The simple batch test and AE model proved valuable for assessing the effect of chlorination on the flocs in activated sludge . By use of these procedures, it is possible to determine acceptable chlorine dosing to avoid excessive deflocculation and effluent deterioration.

Environ Sci Pollut Res Int, 2004, 11(5), 313 - 20
Changes in toxicity and genotoxicity of industrial sewage sludge samples containing nitro- and amino-aromatic compounds following treatment in bioreactors with different oxygen regimes; Klee N et al.; GOALS, SCOPE AND BACKGROUND: From 2005, deposition of organic waste will be banned in Sweden . Likewise, in Germany and Austria, similar bans are being planned, and further countries will probably follow . Thus, there is a need to develop new methods and to refine established techniques for sludge management in the whole of the European Union . For this end, there is also an urgent need for appropriate ecotoxicological approaches to elucidate and assess the hazard potential of sewage sludge . Therefore, the present study was designed to assess the capacity of various established sludge treatment methods using different oxygen regimes to degrade recalcitrant nitro-substituted organic compounds and reduce their toxicity . Sewage sludge samples from a wastewater treatment plant in Sweden (Cambrex Karlskoga AB, industrial area Bjorkborn) receiving wastewater from industries manufacturing pharmaceutical substances, chemical intermediates and explosives were processed with different sludge treatment methods . Among other treatment methods, bioreactors (for anaerobic and aerobic sludge treatment) were used . In the present investigation, a battery of in vitro bioassays was employed to compare the cytotoxic and genotoxic potentials of different fractions of sludge samples in order to elucidate whether the treatments were suitable to reduce the toxicity of the sludge . METHODS: In order to investigate the cytotoxicity of the extracts of treated and untreated sludge samples, the acute cytotoxicity test with the permanent cell line RTL-W1 was used . Genotoxicity was tested by means of the comet assay (single cell gel electrophoresis) with RTL-W1 cells, and mutagenicity was assessed with the Ames test using the Salmonella typhimurium strains TA98, TA98NR and TA100 . Sludge toxicity was tested in different fractions of organic extracts produced by acetone and hexane extractions . The subsequent clean-up procedure (silica gel chromatography and elution with hexane and dichloromethane) resulted in two fractions, a lipophilic hexane-fraction and a semi-lipophilic dichloromethane-fraction . For the genotoxicity and mutagenicity tests, these fractions were reunited at equal ratios . RESULTS AND DISCUSSION: The acute cytotoxicity test with RTL-W1 cells revealed a high cytotoxic potential for the semi-lipophilic DM-fractions of all sludge samples with NR50 values (= effective concentration for 50% cell death in the neutral red test) from 8.9 up to 20 mg sludge d.w./ml medium . A low cytotoxic potential for the hexane fractions of the untreated sludge samples (NR50 400 to > 400 mg sludge d.w./ml medium) was observed, whereas the hexane fractions of the treated sludge samples showed elevated cytotoxicity increasing further with treatment in the bioreactors . The comet assay indicated that three out of eight of the reunited fractions had a significant genotoxic potential . Whereas the genotoxic potential of one sample treated anaerobically was very high with an induction factor of 11.6, a similar sample (taken from the same anaerobic reactor four months later) and one untreated sample showed lower potentials . The samples treated in another anaerobic bioreactor as well as the samples treated aerobically showed no genotoxic potential . Results indicate that aerobic treatment was basically adequate for reducing the genotoxicity of the sludge, whereas anaerobic treatment was only partly useful for reduction of genotoxicity . The Ames test revealed a very high mutagenic potential for the reunited fractions of the untreated sludge samples with strain TA98 (maximum induction factors (IFmax) up to 45) and a relatively high potential for one of the samples treated aerobically (S2, IFmax = 18 (TA98, S9-)), thus documenting the suitability of both anaerobic and aerobic treatments to reduce the mutagenicity of the samples, however, with the aerobic treatment being less effective . CONCLUSIONS: Overall, none of the microbiological treatments for wastewater sludge in bioreactors was found to be ideal for general toxicity reduction of the sludge samples . Whereas cytotoxicity of the sludge increased or levelled off in most cases following either treatment, genotoxicity both increased or decreased after anaerobic treatment, depending on the specific sample . However, mutagenicity could generally be reduced by anaerobic treatment and, to a lesser degree, by aerobic treatment . RECOMMENDATIONS AND PERSPECTIVES: The complex modification of the diverse damage potentials of sludge sample extracts by use of an in vitro biotest battery following treatment for toxicity reduction in bioreactors showed that considerations of different toxicological endpoints is essential for an adequate hazard assessment . Whereas in the case of cytotoxicity reduction, the reactors proved ineffective, mutagenicity could be reduced significantly at least in some cases in this case study.

Environ Sci Technol, 2004 Oct 1, 38(19), 5232 - 7
Electrochemical inactivation of triclosan with boron doped diamond film electrodes; Wang J et al.; This research investigated an electrochemical method for inactivating contaminated stockpiles of the biocidal agent, triclosan . The goal of the electrolysis was to produce products that were amenable to treatment in conventional activated sludge treatment systems . Triclosan oxidation in electrochemical cells with boron doped diamond (BDD) film anodes was investigated in aqueous solutions at a pH value of 12 . Chronoamperometry experiments showed that direct oxidation of triclosan occurred at potentials below those for H2O, Cl-, or OH- oxidation . Measurable rates of triclosan oxidation began at potentials above 0.4 V with respect to the standard hydrogen electrode (SHE), while potentials of 0.5, 1.3, and 1.8 V were required to obtain measurable oxidation rates of H2O, Cl-, and OH-, respectively . At anode potentials below 2 V, the dominant electrode reaction involved direct triclosan oxidation, while indirect oxidation was the dominant pathway at higher potentials . However, cyclic voltammetry experiments showed that direct oxidation of triclosan resulted in the formation of a passivating film on the electrode that could only be removed by oxidation at potentials above 3 V . Direct triclosan oxidation showed a very weak potential dependence, suggesting that its oxidation was limited by chemical dependent factors rather than by an outer-sphere electron transfer reaction . Organic triclosan oxidation products consisted primarily of chlorinated acetic acids and chlorinated phenolic compounds . Although the byproducts of triclosan oxidation became increasingly less reactive with increasing electrolysis time, triclosan could be completely oxidized to CO2 at current densities above 2 mA/cm2 . Microtox testing indicated that residual triclosan accounted for nearly all the toxicity in the treated water, despite the fact that chlorinated byproduct concentrations were significantly higher than those of triclosan itself.

Environ Sci Technol, 2004 Oct 1, 38(19), 4987 - 94
Investigation of sorption behavior between pyrene and colloidal organic carbon from activated sludge processes; Holbrook RD et al.; The sorption behavior of pyrene for different size fractions of colloidal organic carbon (COC) originating from two biological wastewater treatment facilities (a full-scale activated sludge system (FSAS) and a membrane bioreactor (MBR)) was investigated by fluorescence quenching . Fluorescence lifetime measurements demonstrated a dynamic quenching component in all samples, including the colloidal-free filtrates . COC sorption coefficients (Kcoc) for pyrene ranged from <1 x 10(3) L/kgcoc to 80 x 10(3) L/kgcoc and were comparable to values obtained in the literature for natural organic matter . Both linear and nonlinear behaviors were observed in the Freundlich-described converted isotherms (n = 0.89-2.1) . The aromatic content of COC was quantified by the molar extinction coefficient at 280 nm (e280) . Good correlations were observed between COC-pyrene sorption coefficients and e280 coefficients, suggesting that e280 may be a useful tool for predicting colloidal transport of hydrophobic organic compounds (HOCs) from activated sludge systems . The removal of COC from treated effluents may appreciably reduce the concentrations of HOCs discharged to receiving streams.

Chemosphere, 2004 Dec, 57(9), 1219 - 24
Adsorption capacity of powdered activated carbon for 3,5-dichlorophenol in activated sludge; Widjaja T et al.; The objectives of this study were to evaluate the performance of powdered activated carbon treatment (PACT) process based on the adsorption capacity of powdered activated carbon (PAC) in activated sludge and the effect of dissolved organic substances in activated sludge on the adsorption capacity of PAC . The DCP adsorption capacity of three PACs originated from different raw materials (coal, soft coal and sawdust) in activated sludge were 29%, 34% and 17% of that of new PAC, respectively . The performance of PACT process for shock loading of 3,5-dichlorophenol (3,5-DCP) was different among PACs in spite of the same adsorption capacity in new PAC . The performance of PACT process for removal of DCP is dependent not on the adsorption capacity of new PAC but on the adsorption capacity of PAC in the aeration tank . Dissolved organic matter (DOM) with molecular weight smaller than 50kDa did not affect the adsorption capacity of PAC for 3,5-DCP in the activated sludge reactor . DOM with molecular weight larger than 50kDa and biofilm developed on the surface of PAC seemed to be responsible for the decreased adsorption capacity of PAC for the DCP.

Chemosphere, 2004 Dec, 57(9), 1069 - 77
Investigation of Cr(VI) reduction in continuous-flow activated sludge systems; Stasinakis AS et al.; The aim of this research was to investigate hexavalent chromium, Cr(VI), reduction by activated sludge and to evaluate the use of continuous-flow activated sludge systems for the treatment of Cr(VI)-containing wastewater . Three series of experiments were conducted using two parallel lab-scale activated sludge systems . During the first experiment, one system was used as a control, while the other received Cr(VI) concentrations equal to 0.5, 1, 3 and 5mg l(-1) . For all concentrations added, approximately 40% of the added Cr(VI) was removed during the activated sludge process . Determination of chromium species in the dissolved and particulate phase revealed that the removed Cr(VI) was sorbed by the activated sludge flocs mainly as trivalent chromium, Cr(III), while the residual chromium in the dissolved phase was mainly detected as Cr(VI) . Activated sludge ability to reduce Cr(VI) was independent of the acclimatization of biomass to Cr(VI) and it was not affected by the toxic effect of Cr(VI) on autotrophic and heterotrophic microorganisms . During the second experiment, both systems were operated under two different hydraulic residence time (theta equal to 20 and 28h) and three different initial organic substrate concentration (COD equal to 300, 150 and 0mg l(-1)) . Cr(VI) reduction was favored by an increase of theta, while it was limited by influent COD concentration . Finally, at the last experiment the effect of anoxic and anaerobic reactors on Cr(VI) reduction was investigated . It was observed that the use of an anoxic zone or an anaerobic-anoxic zone ahead of the aerobic reactor favored Cr(VI) reduction, increasing mean percentage Cr(VI) reduction to almost 80%.

Res Microbiol, 2004 Nov, 155(9), 761 - 9
Aggregation-based cooperation during bacterial aerobic degradation of polyethoxylated nonylphenols; Di Gioia D et al.; Three bacterial strains were isolated from activated sludge samples of two treatment plants receiving domestic and industrial wastewaters containing polyethoxylated nonylphenols . One strain (VA160) was isolated on rich medium, and the other two (BCaL1 and BCaL2) on mineral medium containing two industrial mixtures of nonylphenol ethoxylates as the sole carbon source . Strain VA160 was a Gram-positive, spore forming, filamentous bacterium, producing aggregates during growth in liquid medium . On the basis of phylogenetic analysis the strains were assigned to the Bacillus (VA160), Acinetobacter (BCaL1) and Stenothrophomonas (BCaL2) genera . High performance liquid chromatography analysis showed that only the Acinetobacter and Stenothrophomonas strains were involved in the degradation of polyethoxylated nonylphenols . Bacillus VA160, however, when co-cultured with the two degrading strains, induced the formation of cell aggregates and facilitated NPEO degradation . Fluorescent in situ hybridisation on the activated sludge sample from which Bacillus VA160 was isolated, using probes for Gram-positive bacteria with low G + C content, showed that bacteria belonging to this group specifically occurred inside the examined flocs . These observations suggest that the enhanced biodegradation of polyethoxylated nonylphenols in the three-membered co-culture is favoured by VA160-induced aggregation of BcaL1 and BcaL2 cells involved in the process.

Water Sci Technol, 2004, 50(5), 253 - 60
Removal of selected non-steroidal anti-inflammatory drugs (NSAIDs), gemfibrozil, carbamazepine, beta-blockers, trimethoprim and triclosan in conventional wastewater treatment plants in five EU countries and their discharge to the aquatic environment; Paxeus N; The removal of commonly used pharmaceuticals (ibuprofen, naproxen, diclofenac, gemfibrozil, carbamazepine, atenolol, metoprolol and trimethoprim) and a biocide (triclosan) in operating wastewater treatment plants in five EU countries has been studied . Under normal operating conditions the acidic drugs and triclosan were partially removed with removal rates varying from ca . 20 to >95% . The highest removal rate was found for ibuprofen and triclosan (>90%) followed by naproxen (80%), gemfibrozil (55%) and diclofenac (39%) . Ibuprofen undergoes an oxidative transformation to corresponding hydroxy- and carboxy-metabolites, which contributes to its high removal rate . Disturbances in the activated sludge process resulted in lower removal rates for all acidic drugs, mostly for diclofenac (<10% removed) but also for ibuprofen (<60% removed) . The treatment of wastewaters by activated sludge usually did not result in any practical removal (<10%) of neutral carbamazepine or basic atenolol, metoprolol and trimethoprim . The removal rates of the investigated drugs and triclosan are discussed in terms of mechanisms responsible for their removal . Discharges of carbamazepine, diclofenac, gemfibrozil, naproxen, triclosan and trimethoprim from WWTPs to the aquatic environment, expressed as the average concentration in the effluent and the daily discharged quantity per person served by WWTPs were assessed.

Water Sci Technol, 2004, 50(5), 219 - 25
Comparison of linear alkylbenzene sulfonates removal in conventional activated sludge systems and membrane bioreactors; De Wever H et al.; The potential of a membrane bioreactor (MBR) and a conventional activated sludge (CAS) system to remove polar micropollutants was evaluated using linear alkylbenzene sulfonates (LAS) as model components . Removal efficiencies over 97% were achieved in both reactor systems . The appearance of biological breakdown metabolites and the respirometric response of the sludges to LAS addition indicated that LAS removal was due to biodegradation, rather than sorption phenomena . The effect of operational variables, such as hydraulic retention time, LAS composition and hydrophobicity of the membrane used in the MBR, was negligible in the range tested . A stepwise increase in LAS influent concentration resulted in higher residual effluent concentrations but did not change the procentual removal efficiency . Because an increase in LAS and SPC effluent concentration occurred to a larger extent in the CAS than in the MBR under similar operating conditions, MBRs may turn out to be be more robust with respect to biological degradation of micropollutants than CAS.

Water Sci Technol, 2004, 50(5), 133 - 40
Behaviour of endocrine disrupting chemicals during the treatment of municipal sewage sludge; Ivashechkin P et al.; Agricultural application of municipal sewage sludge has been emotionally discussed in the last decades, because the latter contains endocrine disrupting chemicals (EDCs) and other organic micropollutants with unknown fate and risk potential . Bisphenol A (BPA) was chosen as a model substance to investigate the influence of sludge conditioning on the end-concentration of EDCs in sludge . Adsorption studies with radioactive-labelled BPA showed that more than 75% BPA in anaerobically digested sludge is bound to solids (log Kd = 2.09-2.30; log Koc = 2.72-3.11) . Sludge conditioning with polymer or iron (III) chloride alone had no influence on the adsorption of BPA . After conditioning with iron (III) chloride and calcium hydroxide desorption of BPA took place . Apparently, it occurred due to the deprotonation of BPA (pKa= 10.3) as the pH-value reached 12.4 during the process . The same behaviour is expected for other phenolic EDCs with similar pKa (nonylphenol, 17beta-estradiol, estron, estriol, 17alpha-ethinylestradiol) . This study shows high affinity of BPA to the anaerobically digested sludge and importance of conditioning in the elimination of EDCs during the sludge treatment . Addition of polymer is favourable in the case of sludge incineration . Conditioning with iron (III) chloride and calcium hydroxide shows advantages for the use of sludge as fertiliser.

Water Sci Technol, 2004, 50(5), 45 - 50
Acclimation of activated sludge to degrade toxic levels of 2,4-dinitrophenol; Jo KH et al.; Biodegradation of 75 and 100 mg/l of 2,4-dinitrophenol (DNP) by activated sludge acclimated in a Sequencing Batch Reactor (SBR) consistently required less than 6 hours although a lag at the beginning of every 48-hour SBR cycle was observed . Other investigators have reported that DNP levels of 100 mg/l and higher are significantly toxic even to acclimated bacteria . The activated sludge acclimated to 75 mg/l initial DNP had over 100 times the DNP-degrading bacteria than an SBR acclimated to 10 mg/l DNP, although the MLSS concentration in both reactors was similar . Results suggest that two mechanisms are responsible for activated sludge acclimation to toxic levels of DNP: maintenance of DNP-degrading biomass sufficiently large to reduce initial DNP to non-toxic levels, allowing for subsequent rapid degradation; and extension of the aeration period well beyond the time required for degradation to prevent gradual accumulation of any by-product which might also be toxic.

J Environ Sci (China), 2004, 16(4), 640 - 5
Immobilization study of biosorption of heavy metal ions onto activated sludge; Wu HS et al.; Activated sludge was immobilized into Ca-alginate beads via entrapment, and biosorption of three heavy metal ions, copper(II), zinc(II), and chromimum(II), from aqueous solution in the concentration range of 10-100 mg/L was studied by using both entrapped activated sludge and inactivated free biomass at pH < or = 5 . A biphasic metal adsorption pattern was observed in all immobilized biomass experiments . The biosorption of metal ions by the biosorbents increased with the initial concentration increased in the medium . The adsorption rate of immobilized pretreated activated sludge(PAS) was much lower than that of free PAS due to the increase in mass transfer resistance resulting from the polymeric matrix . Biosorption equilibrium of beads was established in about 20 h and the adsorbed heavy metal ions did not change further with time . No significant effect of temperature was observed in the test for free biomass while immobilized PAS appeared to be strong temperature dependent in the test range of 10 and 40 degrees C . Besides, the content of activated sludge in the calcium alginate bead has an influence on the uptake of heavy metals . The sorption equilibrium was well modeled by Langmuir isotherm, implying monomolecular adsorption mechanism. , . Carboxyl group in cell wall played an important role in surface adsorption of heavy metal ions on PAS.

J Environ Sci (China), 2004, 16(4), 624 - 6
Characteristics of aerobic granules grown on glucose a sequential batch shaking reactor; Cai CG et al.; Aerobic heterotrophic granular sludge was cultivated in a sequencing batch shaking reactor (SBSR) in which a synthetic wastewater containing glucose as carbon source was fed . The characteristics of the aerobic granules were investigated . Compared with the conventional activated sludge flocs, the aerobic granules exhibit excellent physical characteristics in terms of settleability, size, shape, biomass density, and physical strength . Scanning electron micrographs revealed that in mature granules little filamentous bacteria could be found, rod-shaped and coccoid bacteria were the dominant microorganisms.

J Environ Sci (China), 2004, 16(4), 564 - 9
Sorption of biodegradation end products of nonylphenol polyethoxylates onto activated sludge; Hung NV et al.; Nonylphenol(NP), nonylphenoxy acetic acid (NP1EC), nonylphenol monoethoxy acetic acid (NP2EC), nonylphenol monoethoxylate (NP1EO) and nonylphenol diethoxylate (NP2EO) are biodegradation end products (BEPs) of nonionic surfactant nonylphenolpolyethoxylates (NPnEO) . In this research, sorption of these compounds onto model activated sludge was characterized . Sorption equilibrium experiments showed that NP, NP1EO and NP2EO reached equilibrium in about 12 h, while equilibrium of NP1EC and NP2EC were reached earlier, in about 4 h . In sorption isotherm experiments, obtained equilibrium data at 28 degrees C fitted well to Freundlich sorption model for all investigated compounds . For NP1EC, in addition to Freundlich, equilibrium data also fitted well to Langmuir model . Linear sorption model was also tried, and equilibrium data of all NP, NP1EO, NP2EO and NP2EC except NP1EC fitted well to this model . Calculated Freundlich coefficient (K(F)) and linear sorption coefficient (K(D)) showed that sorption capacity of the investigated compounds were in order NP > NP2EO > NP1EO > NP1EC approximately NP2EC . For NP, NP1EO and NP2EO, high values of calculated K(F) and K(D) indicated an easy uptake of these compounds from aqueous phase onto activated sludge . Whereas, NP1EC and NP2EC with low values of K(F) and K(D) absorbed weakly to activated sludge and tended to preferably remain in aqueous phase.

Water Res, 2004 Nov, 38(19), 4029 - 38
An extension of ASM2d including pH calculation; Serralta J et al.; This paper presents an extension of the Activated Sludge Model No . 2d (ASM2d) including a chemical model able to calculate the pH value in biological processes . The developed chemical model incorporates the complete set of chemical species affecting the pH value to ASM2d describing non-equilibrium biochemical processes . It considers the system formed by one aqueous phase, in which biochemical processes take place, and one gaseous phase, and is based on the assumptions of instantaneous chemical equilibrium under liquid phase and kinetically governed mass transport between the liquid and gas phase . The ASM2d enlargement comprises the addition of every component affecting the pH value and an ion-balance for the calculation of the pH value and the dissociation species . The significant pH variations observed in a sequencing batch reactor operated for enhanced biological phosphorus removal were used to verify the capability of the extended model for predicting the dynamics of pH jointly with concentrations of acetic acid and phosphate . A pH inhibition function for polyphosphate accumulating bacteria has also been included in the model to simulate the behaviour observed . Experimental data obtained in four different experiments (with different sludge retention time and influent phosphorus concentrations) were accurately reproduced.

Chemosphere, 2004 Nov, 57(8), 987 - 96
Considerations about the enantioselective transformation of polycyclic musks in wastewater, treated wastewater and sewage sludge and analysis of their fate in a sequencing batch reactor plant; Berset JD et al.; The present work consists of two distinct parts: in the first part enantioselective GC was used to separate the different enantiomeric/diastereomeric polycyclic musks, PCMs (HHCB, AHTN, AHDI, ATII and DPMI) including the main transformation product of HHCB, HHCB-lactone, in wastewater and sewage sludge . After optimization all PCMs were resolved on a cyclodextrin containing Rt-BDEXcst capillary GC column . Enantiomeric ratios of PCMs in a technical mixture were determined and compared to those obtained from enantioselective separation of wastewater and sewage sludge samples . In general, enantiomeric ratios were similar for most materials in influent, effluent and stabilized sewage sludge . However, the ratios for HHCB, AHDI and particularly ATII suggest some stereospecific removal of these compounds . In the second part, a field study was conducted on a wastewater treatment plant comprising a sequencing batch reactor . Concentrations of HHCB, AHTN, ADBI, AHDI, ATII, DPMI and HHCB-lactone were determined by non-enantioselective GC in daily samples of influent, effluent and activated sludge during one week . Mean concentrations in influent were 6900 and 1520 ng/l for HHCB and AHTN, respectively . The other PCMs exhibited contents 200 ng/l . Mean percent removal was between 61% (AHDI) and 87% (HHCB) resulting in mean effluent concentrations below 860 ng/l . HHCB-lactone concentration increased during wastewater treatment with a mean in the influent of 430 ng/l and in the effluent of 900 ng/l, respectively, indicating a degradation of HHCB.

J Microbiol Methods, 2004 Dec, 59(3), 381 - 93
Use of heterotrophic CO2 assimilation as a measure of metabolic activity in planktonic and sessile bacteria; Roslev P et al.; We have examined whether assimilation of CO2 can be used as a measure of metabolic activity in planktonic and sessile heterotrophic bacteria . CO2 assimilation by environmental samples and pure cultures of heterotrophic bacteria was studied using 14CO2 and 13CO2 as tracers . Heterotrophic growth on complex organic substrates resulted in assimilation of CO2 into cell biomass by activated sludge, drinking water biofilm, and pure cultures of Escherichia coli ATCC 25922, Es . coli ATCC 13706, Rhodococcus ruber, Burkholderia sp., Bacillus circulans, Pseudomonas putida, Pseudomonas stutzeri, and Pseudomonas aeruginosa . Analysis of 13C-labelled phospholipid fatty acids (PLFAs) confirmed that heterotrophic bacteria may assimilate 13CO2 into cell macromolecules such as membrane lipids . All major PLFAs extracted from activated sludge and drinking water biofilm samples were enriched in 13C after incubation with CO2 . Between 1.4% and 6.5% of the biomass produced by cultures of P . putida and a drinking water biofilm during growth in complex media was apparently derived from assimilation of CO2 . Resting cells assimilated less CO2 compared to actively growing cells, and CO2 assimilation activity correlated with the amount of biomass produced during heterotrophic growth . The 14CO2 assimilation assay was evaluated as a tool to examine inhibitory effects of biocides on planktonic and sessile heterotrophs (biofilms) . On the basis of 14CO2 assimilation activity, the minimum inhibitory concentration (MIC) of benzalkonium chloride was estimated to 21.1 and 127.2 mg l(-1) for planktonic and biofilm samples, respectively . The results indicate that assimilation of isotopically labelled CO2 can be used as a relatively simple measure of metabolic activity in heterotrophic bacteria . CO2 assimilation assays may be used to study the effects of antimicrobial agents on growth and survival of planktonic and sessile heterotrophic organisms.

J Microbiol Methods, 2004 Dec, 59(3), 317 - 26
Progress curve analysis for enzyme and microbial kinetic reactions using explicit solutions based on the Lambert W function; Goudar CT et al.; We present a simple method for estimating kinetic parameters from progress curve analysis of biologically catalyzed reactions that reduce to forms analogous to the Michaelis-Menten equation . Specifically, the Lambert W function is used to obtain explicit, closed-form solutions to differential rate expressions that describe the dynamics of substrate depletion . The explicit nature of the new solutions greatly simplifies nonlinear estimation of the kinetic parameters since numerical techniques such as the Runge-Kutta and Newton-Raphson methods used to solve the differential and integral forms of the kinetic equations, respectively, are replaced with a simple algebraic expression . The applicability of this approach for estimating Vmax and Km in the Michaelis-Menten equation was verified using a combination of simulated and experimental progress curve data . For simulated data, final estimates of Vmax and Km were close to the actual values of 1 microM/h and 1 microM, respectively, while the standard errors for these parameter estimates were proportional to the error level in the simulated data sets . The method was also applied to hydrogen depletion experiments by mixed cultures of bacteria in activated sludge resulting in Vmax and Km estimates of 6.531 microM/h and 2.136 microM, respectively . The algebraic nature of this solution, coupled with its relatively high accuracy, makes it an attractive candidate for kinetic parameter estimation from progress curve data.

Water Sci Technol, 2004, 50(4), 291 - 7
Removal of odorous sulphur-containing gases by a new isolate from activated sludge; Geng AL et al.; Biological treatment of odorous sulphur-containing compounds is attracting attention due to its benign eco-friendliness, energy-savings and low operating costs . As the biological treatment efficiency of dimethylsulphide (DMS) reported was often low and variable, selection of useful DMS-degrading microorganisms is of importance for the enhancement of the biological deodorizing process . This paper reports the successful isolation of a DMS-degrading bacterium from activated sludge, using the enrichment isolation technique . The isolate was identified by 16S rRNA gene sequencing, and found to belong to the alpha group of Proteobacteria, with an identity of 99.4% and 99.1% to the 16S rRNA gene sequences of Afipia felis and Pseudomonas carboxydohydrogena, respectively . The isolate was able to metabolize DMS as well as hydrogen sulphide (H2S) . A batch experiment was performed to assess the removal characteristics of DMS by the isolate . The results showed that over half of DMS could be removed by the isolate in 3 hours when the initial DMS amount was approximately 10 micromol and 25 micromol . Removal of H2S by the isolate was evaluated by a continuous test in a 2-L gas-bubbling bottle. , , . Although part of the H2S removal by the mineral medium itself was observed in the control test, the majority of H2S removal was believed to be attributed to the metabolic activity of the isolate . In conclusion, the isolate might be potentially useful for the enhancement of the biological deodorizing processes.

Biodegradation, 2004 Aug, 15(4), 229 - 39
A stereoselective carbon-nitrogen lyase from Ralstonia sp . SLRS7 cleaves two of three isomers of iminodisuccinate; Cokesa Z et al.; Following biodegradation tests according to the OECD guidelines for testing of chemicals 301F different degradation rates were observed for the three stereoisomers of iminodisuccinate (IDS) . A strain was isolated from activated sludge, which used two of three isomers, R,S-IDS and S,S-IDS, as sole source of carbon, nitrogen, and energy . The isolated strain was identified by 16S-rDNA and referred to as Ralstonia sp . SLRS7 . An IDS-degrading lyase was isolated from the cell-free extract . The enzyme was purified by three chromatographic steps, which included anion-exchange chromatography, hydrophobic interaction chromatography and gel filtration . The lyase catalysed the non-hydrolytic cleavage of IDS without requirement of any cofactors . Cleavage of S,S-IDS led to the formation of fumaric acid and L-aspartic acid . Interestingly R,S-IDS yielded only D-aspartic acid besides fumaric acid . R,R-IDS was not transformed . Thus, the IDS-degrading enzyme is a carbon-nitrogen lyase attacking only the asymmetric carbon atom exhibiting the S-configuration . Besides S,S-IDS and R,S-IDS cleavage, the lyase catalysed also the transformation of certain S,S-IDS metal complexes, namely Ca(2+)-, Mg(2+)- and Mn(2+)-IDS . The maximum enzyme activity was found at pH 8.0-8.5 and 35 degrees C . SDS-PAGE analysis revealed a single 57-kDa protein band . The native enzyme was estimated to be around 240 kDa indicating a homotetramer enzyme.

Biotechnol Bioeng, 2004 Dec 5, 88(5), 585 - 92
Volumetric measurements of bacterial cells and extracellular polymeric substance glycoconjugates in biofilms; Staudt C et al.; In this study an enrichment culture developed from activated sludge was used to investigate the architecture of fully hydrated multispecies biofilms . The assessment of biofilm structure and volume was carried out using confocal laser scanning microscopy (CLSM) . Bacterial cell distribution was determined with the nucleic acid-specific stain SYTO 60, whereas glycoconjugates of extracellular polymeric substances (EPS) were stained with the Alexa-488-labeled lectin of Aleuria aurantia . Digital image analysis was employed for visualization and quantification of three-dimensional CLSM data sets . The specific volumes of the polymeric and cellular biofilm constituents were quantified . In addition, gravimetric measurements were done to determine dry mass and thickness of the biofilms . The data recorded by the CLSM technique and the gravimetric data were then compared . It was shown that the biofilm thicknesses determined with both methods agree well for slow-growing heterotrophic and chemoautotrophic biofilms . In addition, for slow-growing biofilms, the volumes and masses calculated from CLSM and the biomass calculated from gravimetric measurements were also comparable . For fast-growing heterotrophic biofilms cultivated with high glucose concentrations the data sets fit to a lesser degree, but still showed the same common trend . Compared with traditional gravimetric measurements, CLSM allowed differential recording of multiple biofilm parameters with subsequent three-dimensional visualization and quantification . The quantitative three-dimensional results recorded by CLSM are an important basis for understanding, controlling, exploiting, and modeling of biofilms.

Curr Opin Biotechnol, 2004 Oct, 15(5), 495 - 502
Quorum sensing and bacterial cross-talk in biotechnology; March JC et al.; Only a decade ago, the secretion and perception of small signalling molecules that in turn are transduced to coordinate behaviour of a 'minimal unit' of microorganisms was termed quorum sensing by EP Greenberg and colleagues . Since then, an explosion (or exponential growth) in understanding and prevalence of quorum-sensing systems has ensued, with sightings ranging from virulence in human and plant pathogens to degradative capacity of activated sludge . Not surprisingly, regulatory mechanisms span traditional inducer/repressor motifs homologous to the lac operon to the recently discovered interfering RNAs . Further characterisation of signalling circuits, coupled with creative niche applications, suggest a wealth of opportunity for advancing commercial biotechnology.

Water Sci Technol, 2004, 50(3), 245 - 52
Advanced treatment by anaerobic process followed by aerobic membrane bioreactor for effluent reuse in paper mill industry; Stahl N et al.; The operation of an activated sludge process at a paper mill (AIPM) in Hedera, Israel, was often characterized by disturbances . As part of a research and development project, a study on new biological treatment was initiated . The study included the operation of three pilot units: a . anaerobic treatment by upflow anaerobic sludge blanket (UASB); b . aerobic treatment by two pilot units including activated sludge and membrane bioreactor (MBR), which have been operated in parallel for comparison reasons . The pilot plant working on anaerobic treatment performed COD reduction from 2,365 to 755 mg/L, expressed as average values . Based on the pilot study, a full scale anaerobic treatment system has been erected . During a period of 100 days, after achieving steady state, the MBR system provided steady operation performance, while the activated sludge produced effluent characterized by oscillatory qualities . The following results, based on average values, indicate much lower suspended solids concentrations in the MBR effluent, 2.5 mg/L, as compared to 25 mg/L in the activated sludge . The ability to develop and maintain a concentration of over 11,000 mg/L of mixed liquor volatile suspended solids in the MBR enabled an intensive bioprocess at relatively high cell residence time . This study demonstrates that the anaerobic process, followed by aerobic MBR can provide effluent of high quality which can be considered for economic reuse in the paper mill industry.

Water Sci Technol, 2004, 50(3), 229 - 38
Ultrafiltration and nanofiltration in the pulp and paper industry using cross-rotational (CR) filters; Manttari M et al.; Ultra- and nanofiltration with high shear CR-filters have been utilized for cleaning of clear filtrates and effluents from the pulp and paper industry . The aim was to find out how different nanofiltration membranes operate at high shear conditions . The filtration efficiency of the membranes was evaluated by measuring flux, retention and fouling at various recovery and pH conditions . High fluxes (approximately 100 L/(m2h)) for nanofiltration membranes were measured when circulation waters from the paper machine were filtered at neutral conditions . In the filtration of discharge of external activated sludge treatment plants we measured fluxes around 150 L/(m2h) even at a concentration factor of 12 . The best NF membranes removed over 80% of the organic carbon and of the conductivity and almost completely eliminated the color . With acidic waters fluxes and retentions were significantly lower . The NF270 membrane from Dow and the Desal-5 membranes from Osmonics had the highest flux and retention properties . However, the Desal-5 membrane lost its retention properties slowly, which restricts its use in the high shear CR-filter . CR-nanofiltration can be used in the pulp and paper industry without feed pre-treatment by ultrafiltration . This increases the attractiveness of high shear CR-nanofiltration.

Water Sci Technol, 2004, 50(3), 167 - 72
Ozonolysis mechanism of lignin model compounds and microbial treatment of organic acids produced; Nakamura Y et al.; Treatment methods comprising ozonolysis and microbial treatment of lignin discharged from the pulp manufacture industries were investigated by using a sulfite pulp wastewater and a lignin model compound, i.e . sodium lignosulfonate . Dynamic behaviors for the formations of intermediate derivatives such as muconic acid, maleic acid, and oxalic acid produced from the ozonolysis of sulfite pulp wastewater were observed from data of UV absorption at 280 nm by a spectrophotometer and at 210 nm by high performance liquid chromatography . The microorganisms that were isolated by the enrichment culture method were used to degrade the organic acids such as oxalic acid and acetic acid . Time courses of biological degradation of these organic acids indicated diauxic growth, which was found in a culture with mixed substrates . In the treatment of sodium lignosulfonate, the ozonolysis and microbial treatment using activated sludge converted sodium lignosulfonate into carbon dioxide and water almost completely.

Water Sci Technol, 2004, 50(3), 131 - 9
N-ViroTech--a novel process for the treatment of nutrient limited wastewaters; Slade AH et al.; As pulp and paper wastewaters are mostly deficient in nitrogen and phosphorus, historical practice has dictated that they cannot be effectively treated using microbiological processes without the addition of supplementary nutrients, such as urea and phosphoric acid . Supplementation is a difficult step to manage efficiently, requiring extensive post-treatment monitoring and some degree of overdosing to ensure sufficient nutrient availability under all conditions . As a result, treated wastewaters usually contain excess amounts of both nutrients, leading to potential impacts on the receiving waters such as eutrophication . N-ViroTech is a highly effective alternative treatment technology which overcomes this nutrient deficiency/excess paradox . The process relies on communities of nitrogen-fixing bacteria, which are able to directly fix nitrogen from the atmosphere, thus satisfying their cellular nitrogen requirements . The process relies on manipulation of growth conditions within the biological system to maintain a nitrogen-fixing population whilst achieving target wastewater treatment performance . The technology has significant advantages over conventional activated sludge operation, including: Improved environmental performance . Nutrient loadings in the final treated effluent for selected nitrogen and phosphorus species (particularly ammonium and orthophosphate) may be reduced by over 90% compared to conventional systems; Elimination of nitrogen supplementation, and minimisation of phosphorus supplementation, thus achieving significant chemical savings and resulting in between 25% and 35% savings in operational costs for a typical system; Self-regulation of nutrient requirements, as the bacteria only use as much nitrogen as they require, allowing for substantially less operator intervention and monitoring. , . This paper will summarise critical performance outcomes of the N-ViroTech process utilising results from laboratory-, pilot-scale and recent alpha-adopter, full-scale trials.

Water Sci Technol, 2004, 50(3), 123 - 30
Full scale implementation of the nutrient limited BAS process at Södra Cell Värö; Malmqvist A et al.; A combination of the suspended carrier biofilm process and the activated sludge process (biofilm-activated sludge--BAS) has been shown to be very successful for the treatment of different types of pulp and paper mill effluents . The robust biofilm pre-treatment in combination with activated sludge results in a stable, compact and highly efficient process . Recent findings have shown that nutrient limited operation of the biofilm process greatly improves the sludge characteristics in the following activated sludge stage, while minimising sludge production and effluent discharge of nutrients . The nutrient limited BAS process was implemented at full scale at the Sodra Cell Varo kraft mill and taken into operation in July 2002 . After start-up and optimisation over about 5 months, the process meets all effluent discharge limits . The removal of COD is close to 70% and the removal of EDTA greater than 90% . Typical effluent concentrations of suspended solids and nutrients during stable operations have been 20-30 mg/L TSS, 0.3-0.5 mg/L phosphorus and 3-5 mg/L nitrogen . The sludge production was 0.09 kgSS/kg COD removed and the sludge volume index was 50-100 mL/g.

Water Sci Technol, 2004, 50(3), 111 - 22
Nutrient minimisation in the pulp and paper industry: an overview; Slade AH et al.; This paper reviews nutrient issues within the pulp and paper industry summarising: nitrogen and phosphorus cycles within treatment systems; sources of nutrients within pulping and papermaking processes; minimising nutrient discharge; new approaches to nutrient minimisation; and the impact of nutrients in the environment . Pulp and paper industry wastewaters generally contain insufficient nitrogen and phosphorus to satisfy bacterial growth requirements . Nutrient limitation has been linked to operational problems such as sludge bulking and poor solids separation . Nutrients have been added in conventional wastewater treatment processes to ensure optimum treatment performance . Minimising the discharge of total nitrogen and phosphorus from a nutrient limited wastewater requires both optimised nutrient supplementation and effective removal of suspended solids from the treated wastewater . In an efficiently operated wastewater treatment system, the majority of the discharged nutrients are contained within the biomass . Effective solids separation then becomes the controlling step, and optimisation of secondary clarification is crucial . Conventional practice is being challenged by the regulatory requirement to reduce nitrogen and phosphorus discharge . Two recent developments in pulp and paper wastewater treatment technologies can produce discharges low in nitrogen and phosphorus whilst operating under conventionally nutrient limited conditions: i) the nutrient limited BAS process (Biofilm-Activated Sludge) which combines biofilm and activated sludge technologies under nutrient limited conditions and ii) an activated sludge process based on the use of nitrogen-fixing bacteria . Aerated stabilisation basins often operate without nutrient addition, relying on settled biomass in the benthal zone feeding back soluble nutrients, or the fixation of atmospheric nitrogen . Thus effective nutrient minimisation strategies require a more detailed understanding of nutrient cycling and utilisation . Where it is not possible to meet discharge constraints with biological treatment alone, a tertiary treatment step may be required . In setting nutrient control guidelines, consideration should be given to the nutrient limitations of the receiving environment, including other cumulative nutrient impacts on that environment . Whether an ecosystem is N or P limited should be integrated with wastewater treatment considerations in the further design and development of treatment technology and regulatory guidelines . End-of-pipe legislation alone cannot predict environmental effects related to nutrients and must be supplemented by an effects-based approach.

Water Sci Technol, 2004, 50(3), 103 - 10
A comparison of conventional activated sludge and low sludge production strategies for advanced treatment of kraft pulp mill effluent; Werker A et al.; Parallel laboratory investigations were conducted to examine aspects of two distinct but related bioprocess strategies for low sludge production in the treatment of the same TCF kraft pulp mill effluent . The purpose of this article has been to compare the performance results from these two bench-scale trials with respect to nutrient demands, nutrient discharge, COD removal, and waste sludge characteristics . The LSP (Low Sludge Production) process can be used to significantly reduce sludge yield with excellent sludge characteristics . These sludge characteristics seemed to be related to elevated protozoan grazing pressures . The BAS (Biofilm-Activated Sludge) process achieves similar reduced sludge yields and sludge characteristics while at the same time significantly reducing the nutrient demands and discharge levels . For both LSP and BAS process optimization, the selector nutrient loading is critical to the overall process performance . Selector nutrient requirements are distinct from the overall process nutrient requirements.

Water Sci Technol, 2004, 50(3), 87 - 94
The formation of colour during biological treatment of pulp and paper wastewater; Milestone CB et al.; Colour discharges are gaining renewed focus in the pulp and paper industry as increasingly strict regulatory limits are placed on wastewater quality and aesthetics . In-mill process improvements, such as ECF bleaching and oxygen delignification, have decreased wastewater colour loadings . However, a survey of 12 pulp and paper mill systems found that effluent treatment using aerated stabilisation basins (ASB) leads to average increases in colour of 20-40% . In some instances, this phenomenon may even double the influent colour levels . Activated sludge systems did not produce a colour increase . The measured increases that follow ASB secondary treatment may be sufficient for a mill to fail prescribed discharge standards . A detailed field survey focusing on sections of an integrated bleached kraft mill ASB treatment system was undertaken . The average increase in colour at the final point of discharge was 45% . The major changes in colour concentration occurred in the inlet to the main treatment pond, and in polishing ponds that followed the main treatment pond . Both of these areas receive little or no aeration . No significant change was observed in the highly aerated main pond . These results, along with literature reports, suggested that redox conditions play a major role in influencing colour behaviour . To test this, two series of paired continuously stirred reactors were used to treat whole mill effluent from two ECF bleached kraft mills in parallel . The first series initially treated under anaerobic conditions, followed by an aerobic reactor, while the second series reversed this order . With the initial anaerobic stage, effluent colour increased by 18% and 19% for the first and second series respectively . Subsequent treatment by aerobic bacteria further increased colour by 14% and 6%, for a total increase of 32% and 25% . Initial aerobic treatment, however, did not lead to any significant change in colour for either effluent . Further anaerobic treatment following aerobic conditions produced only small increases in colour . These results are consistent with the ASB and activated sludge system survey, suggesting that anaerobic conditions at the head of treatment systems initiate the observed increases in effluent colour in ASB treatment systems.

Water Sci Technol, 2004, 50(3), 67 - 77
The assessment of different operating strategies for minimising activated sludge deflocculation under temperature transient conditions; Morgan-Sagastume F et al.; Three operating strategies were tested for decreasing activated sludge deflocculation due to temperature shifts from 30 degrees to 45 degrees C: magnesium sludge enrichment, increased sludge retention time (33 d), and spikes of an easily degradable substrate (methanol) . The temperature shifts were conducted sequentially in 4 parallel lab-scale sequencing batch reactors (SBRs) treating kraft pulp mill effluent . Three SBRs operated at an SRT = 20 days, and in one of them the sludge was not manipulated, thus, serving as a reference SBR . The temperature shift was associated with decreased soluble chemical oxygen demand (SCOD) removals, decreased sludge settleability and substrate removal capacity, and increased effluent suspended solids (ESS) and turbidity levels . The shift also increased the sludge specific respiration rates and reduced the sludge substrate removal capacity . Sludge deflocculation was assessed as floc solubilisation (increased effluent SCOD levels) and floc fragmentation (increase in effluent solids smaller than 50 microm) . Mg enrichment of the sludge and methanol spikes reduced the ESS levels (in 9 and 25%), and the three operating strategies decreased effluent turbidity (in 22-35%) compared to the maximum levels from the non-manipulated reactor (44 mg ESS/L) . The stronger sludge floc structure achieved by magnesium enrichment and a high sludge age of 33 days was unsuccessful in significantly decreasing deflocculation. , , . The mechanisms involved in sludge deflocculation require further fundamental research.

Water Sci Technol, 2004, 50(3), 49 - 55
Common stresses affecting activated sludge health and performance--what the four-assay set can tell us; Archibald F et al.; Previously, we developed a novel biological early warning (BEW) system for directly monitoring the health and performance of activated sludge, the "four-assay set" . In the present work, the four-assay set has been used to measure the effects of four common stresses on activated sludge biomass: high temperature; pH; anoxia; and starvation . The results demonstrate both the utility of the Paprican four-assay set as a biomass-evaluating and BEW tool, and the tolerances of a typical kraft mill activated sludge for these four stresses.

Water Sci Technol, 2004, 50(3), 39 - 48
Occurrence and significance of filamentous bacteria in pulp and paper activated sludge systems; Bergeron J et al.; A microbial survey of 27 activated sludge (AS) systems included 16 conventional activated sludge (CAS) systems, five sequential batch reactors (SBR) and six oxygen-activated sludge (OAS) systems, all treating pulp and paper effluents . The most prevalent filaments observed were Thiothrix (26%) and Type 021N (22%) . The designs of the activated sludge systems seemed to have an effect on the filament types . We found Thiothrix to be the most common filament associated with bulking . For CAS systems, a completely mixed mode of operation promoted Thiothrix and Type 021N growth . Type 021N was favoured in CAS systems with food to microorganism (F/M) ratios higher than 0.2, and with dissolved oxygen (DO) residuals higher than 2 ppm, while Thiothrix generally proliferated at lower F/M ratio and DO residuals . Nutrient deficiencies as well as nutrient dosage variations were suspected in most of the systems having Thiothrix and Type 021N as the most prevalent filaments . Thiothrix appeared to prefer polyphosphate and/or ammonia rather than urea/phosphoric acid as N and P sources . Systems with aerobic selectors showed the lowest filament counts, while systems with no selectors showed the highest filament counts.

Water Sci Technol, 2004, 50(3), 29 - 37
Occurrence and control of filamentous bulking in aerated wastewater treatment plants of the French paper industry; Fourest E et al.; The occurrence of filamentous bacteria was investigated in 15 French pulp and paper activated sludge wastewater treatment plant (WWTP) . Large filamentous populations were present in most of the plants . Identification carried out with conventional methods based on morphological features and staining techniques showed that the four main filamentous bacteria encountered in these industrial WWTP and responsible for bulking belong to the genera Thiothrix sp., Type 021 N, Haliscomenobacter hydrossis and Type 0092 . During two years a specific survey was performed for three of these WWTP showing recurrent bulking phenomena . Data from WWTP performance, chemical data and filaments characterization were compared to correlate the presence of specific filaments with process operating conditions.

Water Sci Technol, 2004, 50(3), 11 - 20
Multi-component kinetics of activated sludge treatment of bleached kraft mill effluent; Helle SS et al.; This study investigated the discrepancies between the BOD removal rates measured during short term assays and those measured during continuous activated sludge treatment of bleached kraft mill effluent (BKME) . A combination of batch tests and fed batch tests with oxygen uptake rate (OUR), chemical oxygen demand (COD), biochemical oxygen demand (BOD), and mixed liquor volatile suspended solids (MLVSS) measurements were used to characterize the degradation rates for the activated sludge treatment of BKME and to divide the soluble readily biodegradable substrate into two to five separate fractions based on biodegradation rates . The removal rates varied by over an order of magnitude between the most readily degradable substrates (1 x 10(-3) mg COD/mg MLVSS minute), and the more slowly degradable substrates (2 x 10(-5) mg COD/mg MLVSS minute) . If the readily biodegradable fraction of BKME was modeled as one substrate, initial rate kinetic measurements from batch tests were heavily influenced by the fractions with the greatest degradation rates, while any remaining BOD in the treated effluent was predominantly from the slowly degradable fraction, giving inconsistent results . Taking the multi-component nature of the wastewater into account, batch test results can be used to predict fed-batch and continuous activated sludge reactor performance.

Water Sci Technol, 2004, 50(3), 1 - 10
Modelling carbon oxidation in pulp mill activated sludge systems: calibration of Activated Sludge Model No 3; Baranao PA et al.; Activated Sludge Model No 3 (ASM3) was chosen to model an activated sludge system treating effluents from a mechanical pulp and paper mill . The high COD concentration and the high content of readily biodegradable substrates of the wastewater make this model appropriate for this system . ASM3 was calibrated based on batch respirometric tests using fresh wastewater and sludge from the treatment plant, and on analytical measurements of COD, TSS and VSS . The model, developed for municipal wastewater, was found suitable for fitting a variety of respirometric batch tests, performed at different temperatures and food to microorganism ratios (F/M) . Therefore, a set of calibrated parameters, as well as the wastewater COD fractions, was estimated for this industrial wastewater . The majority of the calibrated parameters were in the range of those found in the literature.

FEMS Microbiol Lett, 2004 Oct 1, 239(1), 147 - 55
Genetic characterization of the dibenzofuran-degrading Actinobacteria carrying the dbfA1A2 gene homologues isolated from activated sludge; Noumura T et al.; Thirteen dibenzofuran (DF)-utilizing bacteria carrying the DF terminal dioxygenase genes homologous to those of Terrabacter sp . strain DBF63 (dbfA1A2) were newly isolated from activated sludge samples . The amplified ribosomal DNA restriction analysis and the hybridization analyses showed that these strains were grouped into five genetically different types of bacteria . The sequence analyses of the 16S rRNA genes and the dbfA1A2 homologues from these five selected isolates revealed that the isolates belonged to the genus Rhodococcus, Terrabacter or Janibacter and that they shared 99-100% conserved dbfA1A2 homologues . We investigated the genetic organizations flanking the dbfA1A2 homologues and showed that the minimal conserved DNA region present in all five selected isolates consisted of an approximately 9.0-kb region and that their outer regions became abruptly non-homologous . Among them, Rhodococcus sp . strain DFA3 possessed not only the 9.0-kb region but also the 6.2-kb region containing dbfA1A2 homologues . Sequencing of their border regions suggested that some genetic rearrangement might have occurred with insertion sequence-like elements . Also, within their conserved regions, some insertions or deletions were observed.

Water Res, 2004 Nov, 38(18), 3909 - 19
Flocculation of activated sludge flocs by stimulation of the aerobic biological activity; Wilen BM et al.; Activated sludge flocs are known to deflocculate under short-term anaerobic conditions, but little is known about possible reflocculation under subsequent aerobic conditions . When activated sludge flocs from two wastewater treatment plants deflocculated under anaerobic conditions with well-defined shear conditions, they could be almost, but not completely, reflocculated by aeration for 1-2 h under the same shear conditions . If the biological activity was reduced by adding azide, chloramphenicol or by decreasing the temperature, no or only very little reflocculation took place . This indicated that the reflocculation was under direct or indirect microbial control . Only a small part of the reflocculation was due to improved flocculation properties obtained by oxidation of Fe(II) to Fe(III), which is a better flocculant . Fe(II) was produced under the anaerobic conditions by microbial iron reduction, and it was oxidized to Fe(III) within less than one hour after the aeration was started . However, by comparing two different sludges with different capabilities for iron reduction, iron oxidation and responses to substrate addition, it was found that the aerobic biological activity most likely was of greatest significance for the observed reflocculation and floc formation under aerobic conditions . This was further supported by adding organic substrates (glucose or ethanol) during the aerobic reflocculation phase, which promoted reflocculation . However, some substrates had the opposite effect (acetate and lactate), where a deterioration of the reflocculation was observed, probably due to different responses from different groups of microorganisms in the sludges.

J Environ Manage, 2004 Nov, 73(2), 155 - 63
Combined chemical and biological oxidation of penicillin formulation effluent; Alaton IA et al.; Antibiotic formulation effluent is well known for its important contribution to environmental pollution due to its fluctuating and recalcitrant nature . In the present study, the chemical treatability of penicillin formulation effluent (average filtered COD(o)=830 mg/l; average soluble COD(o)=615 mg/l; pH(o)=6.9) bearing the active substances penicillin Amoxicillin Trihydrate (C(16)H(19)N(3)O(5)S.3H(2)O) and the beta-lactamase inhibitor Potassium Clavulanate (C(8)H(8)KNO(5)) has been investigated . For this purpose, the penicillin formulation effluent was subjected to ozonation (applied ozone dose=2500 mg/(lxh)) at varying pH (2.5-12.0) and O(3)+H(2)O(2) (perozonation) at different initial H(2)O(2) concentrations (=2-40 mM) and pH 10.5 . According to the experimental results, the overall Chemical Oxygen Demand (COD) removal efficiency varied between 10 and 56% for ozonation and 30% (no H(2)O(2)) and 83% (20 mM H(2)O(2)) for the O(3)+H(2)O(2) process . The addition of H(2)O(2) improved the COD removal rates considerably even at the lowest studied H(2)O(2) concentration . An optimum H(2)O(2) concentration of 20 mM existed at which the highest COD removal efficiency and abatement kinetics were obtained . The ozone absorption rate ranged between 53% (ozonation) and 68% (perozonation) . An ozone input of 800 mg/l in 20 min was sufficient to achieve the highest BOD(5)/COD (biodegradability) ratio (=0.45) and BOD(5) value (109 mg/l) for the pre-treated penicillin formulation effluent . After the establishment of optimum ozonation and perozonation conditions, mixtures of synthetic domestic wastewater+raw, ozonated and perozonated penicillin formulation effluent were subjected to biological activated sludge treatment at a food-to-microorganisms (F/M) ratio of 0.23 mg COD/(mg MLSSxd), using a consortium of acclimated microorganisms . COD removal efficiencies of the activated sludge process were 71, 81 and 72% for pharmaceutical wastewater containing synthetic domestic wastewater mixed with either raw, ozonated or perozonated formulation effluent, respectively. , , , . The ultimate COD value obtained after 24-h biotreatment of the synthetic domestic wastewater+pre-ozonated formulation effluent mixture was around 100 mg/l instead of 180 mg/l which was the final COD obtained for the wastewater mixture containing raw formulation effluent, indicating that pre-ozonation at least partially removed the non-biodegradable COD fraction of the formulation effluent.

Arch Microbiol, 2004 Dec, 182(6), 429 - 35 Epub 2004 Dec.
Different molecular rearrangements in the integron of the IncP-1beta resistance plasmid pB10 isolated from a wastewater treatment plant result in elevated beta-lactam resistance levels; Szczepanowski R et al.; The multiresistance IncP-1beta plasmid pB10 conferring resistance to ampicillin, streptomycin, sulfonamides, tetracycline and mercury ions was previously obtained from activated sludge bacteria by applying the exogenous isolation method with Pseudomonas sp . strain GFP2 as recipient . A pB10 derivative, designated pB10-1, occurred spontaneously and displays an extended NotI restriction fragment . From the pB10 nucleotide sequence, it is known that the corresponding NotI fragment of this plasmid contains a complete class 1 integron with an oxa2 and an orfE-like gene cassette . Sequencing of the integron-specific variable region present on pB10-1 revealed that a second copy of the oxa2 gene cassette has inserted downstream of the orfE-like cassette . Sequences flanking the second oxa2 cassette indicate that this cassette was excised from pB10 and reinserted at a new site in an integrase-catalyzed manner . Duplication of the oxa2 cassette is associated with a higher level of ampicillin resistance . Another pB10 derivative, designated pB10-2, conferring higher resistance to ampicillin, was shown to carry an IS10 insertion upstream of the oxa2 cassette . Since IS10 possesses a promoter-out activity, it can be assumed that the elevated ampicillin resistance level is due to enhanced transcription of the beta-lactamase gene.

Environ Technol, 2004 Jun, 25(6), 723 - 31
{Rheological measurement used as a tool to assess sludges settleability}; Guibaud G et al.; The activated sludge process is the most widely used biological wastewater treatment method . The measurement of some physico-chemical parameters in aeration tanks do not still allow to avoid clarification operation failure . This study focus on the ability to apply rheological measurements on activated sludge at standard concentrations in order to assess sludge settleability . Measurements in shear flow show a pseudonewtonian region which corresponds to the maximum dispersion of the suspensions that can be detected with the rotational system used . The Bingham's viscosity and shear stress are used to characterise activated sludge . Different shear sensitivities of flocs seem to result from various operational conditions of activated sludge process . Significant relationships with different parameters of settleability point out the ability of Bingham's shear stress to express the compressibility of the activated sludge . According to the protocol of measurement of the study, Bingham's shear stress may influence the nature of the sludge on its settleability.

Environ Technol, 2004 Jun, 25(6), 667 - 72
Production and characterization of immobilized-biomass carriers, using polyacrylamide; Horan NJ et al.; Whole microbial cells from an activated sludge seed were immobilised in spherical polyacrylamide beads using a shrink/swell procedure which increased cell viability more than 100-fold over the seed material . The process was optimised with respect to the seed concentration and incubation time . It was shown that the swell procedure was essential to achieve good immobilisation and that biofilm attachment to the beads made a negligible contribution to the immobilised biomass . The physical and biological properties of the immobilised beads were determined and found to settle well and resist mechanical abrasion . In addition, their preparation did not prove toxic to the immobilised biomass . The beads produced have many applications for instance in enhancing the biomass in wastewater treatment processes . In addition the immobilisation process could be applied to a wide range of microbial consortia including pure cultures of microorganisms.

Syst Appl Microbiol, 2004 Aug, 27(4), 478 - 91
Variation of 16S-23S rRNA intergenic spacer regions (ISRs) in Acinetobacter baylyi (strain B2) isolated from activated sludge; Carr EL et al.; To determine the variability of the 16S-23S rRNA intergenic spacer region (ISR) of the newly described Acinetobacter baylyi, 88 clones containing ISR amplicons were screened and 14 chosen for further analysis . Two different sized 16S-23S rRNA ISRs were distinguished comprising five variable and four conserved nucleotide blocks . The major regions of heterogeneity between the different sized ISRs were due to blocks of substitutions with unique secondary structures interspersed with nucleotide substitutions, rather than differences caused by presence or absence of tRNA genes, which is often the case . Recombination events causing shuffling of nucleotide blocks are considered the most likely explanation for the mosaic structure observed between the different copies of the ISR . Single base differences present in the long ISR (LISR) were then exploited in attempts to detect possible heterogeneity between rrn copies in Acinetobacter baylyi but variability was not detected by RFLP analysis of LISR-specific PCR products . These primers were shown to be highly specific for 3 Acinetobacter baylyi strains based on LISR sequence homogeneity.

Environ Technol, 2004 Aug, 25(8), 919 - 27
Co-digestion with waste activated sludge for improved methanogenesis from high solids industrial waste; Duran M et al.; The objective of this work was to study the anaerobic digestion of an industrial waste with 84% total and 57% volatile solids content . The waste was also characterized by high total COD content, 42% by weight . The anaerobic digestion of the waste alone and its co-digestion with the waste activated sludge (WAS) that is generated at the industrial facility were investigated . Particularly, kinetics of digesting the waste alone and co-digesting it with the WAS were determined . The substrate utilization rates under varying initial substrate concentrations were determined in batch reactors by measuring the methane generation rates . Then the substrate utilization rates were modeled according to the Monod kinetics . The solution to nonlinear regression resulted in the maximum specific substrate utilization rates (k) of 0.138 and 0.165 g COD g VSS(-1).day(-1) for the waste alone and the waste co-digested with the WAS, respectively . The half velocity constants (K s) were 4.390 and 4.860 g COD 1(-1) for the same conditions . It is important to note that since the methane generation data were used to determine the substrate utilization rates, these kinetic constants are likely to represent the methanogenic Archaea rather than the entire anaerobic consortium . It is concluded that the anaerobic co-digestion of this industrial waste with the WAS is beneficial from the digestion kinetics point of view since the k increased approximately 20% with the addition of the WAS . Moreover, there will be cost savings associated with digesting the WAS anaerobically rather than aerobically, the currently used method of WAS management, if anaerobic digestion is adopted in the future.

Bioresour Technol, 2005 Jan, 96(1), 31 - 40
Effects of synthetic polymer on the filamentous bacteria in activated sludge; Juang DF; Filamentous bulking is one of the solid-liquid separation problems always seen in activated sludge process . The addition of synthetic polymer is always one of the popular ways for the treatment plant operator to immediately solve the poor sludge settling problem . Therefore, it may be interesting to understand the effects of synthetic polymer on the filamentous bacteria in activated sludge . In this study, synthetic polymer was applied to a lab-scale wastewater treatment system with the filamentous bulking problem . The population structure of filamentous bacteria and sludge characteristics were investigated under different conditions . When synthetic polymer was added into the system, it was found that poor sludge settleability caused by filamentous bulking was temporarily solved and filamentous branches growing outside the flocs were damaged or inhibited . However, filamentous growth was still observed inside the flocs . After the addition of polymer was halted, filamentous branches extended out of the flocs immediately . Very serious filamentous bulking occurred and sludge settleability became much worse than that occurring before the addition of polymer . And, it took several weeks for the system to return to normal operation.

J Hazard Mater, 2004 Sep 10, 113(1-3), 111 - 21
Effects of nickel(II) addition on the activity of activated sludge microorganisms and activated sludge process; Ong SA et al.; The effects of Ni(II) in a synthetic wastewater on the activity of activated sludge microorganisms and sequencing batch reactor (SBR) treatment process were investigated . Two parallel lab-scale SBR systems were operated . One was used as a control unit, while the other received Ni(II) concentrations equal to 5 and 10 mg/l . The SBR systems were operated with FILL, REACT, SETTLE, DRAW and IDLE modes in the time ratio of 0.5:3.5:1.0:0.75:0.25 for a cycle time of 6 h . The addition of Ni(II) into SBR system caused drastically dropped in TOC removal rate (k) and specific oxygen uptake rate (SOUR) by activated sludge microorganisms due to the inhibitory effects of Ni(II) on the bioactivity of microorganisms . The addition of 5 mg/l Ni(II) caused a slight reduction in TOC removal efficiency, whereas 10 mg/l Ni(II) addition significantly affected the SBR performance in terms of suspended solids and TOC removal efficiency . Termination of Ni(II) addition led to almost full recovery of the bioactivity in microorganisms as shown in the increase of specific oxygen uptake rate (SOUR) and SBR treatment performance.

Environ Toxicol, 2004 Oct, 19(5), 510 - 7
In vitro androgenicity in pulp and paper mill effluents; Svenson A et al.; Pulp and paper mill effluents were examined for in vitro androgenicity using a recombinant yeast-based androgen receptor assay . Low levels of androgenic effects were detected in extracts of some effluents after activated sludge treatment . Yeast cell growth cell was inhibited in some samples, and this interfered with the androgenic response . Solid-phase fractionation revealed androgenicity after partial separation of components in the effluents . Comparison of levels in untreated effluent and in effluent treated in an aerated lagoon showed that this treatment had only a marginal effect on androgenicity . An assay of the fractions eluted with increasing concentrations of methanol showed that androgenic compounds were low to moderately lipophilic . In an attempt to identify these compounds, a number of wood-related compounds (guaiacol, vanillin, beta-sitosterol, betulin, pinosylvin-O-methyl ether, and a wood extract enriched in lignans) were examined but were found not to be androgenic . Raw process water was not androgenic, but water from a highly humified lake and process water from the production of pulp from partly decayed wood had low androgenicity . It therefore can be plausibly suggested that the androgens originated in decaying wood. , , . An assay of androgenicity in the bile of juvenile rainbow trout exposed to effluents for 3 weeks showed increased dose-dependent levels of androgens after enzymatic hydrolysis of hormone conjugates .

Water Res, 2004 Oct, 38(17), 3751 - 9
Degradation of sodium dodecylbenzene sulfonate in water by ultrasonic irradiation; Manousaki E et al.; The potential of using ultrasonic irradiation for the removal of sodium dodecylbenzene sulfonate (SDBS) from aqueous solutions has been investigated . Experiments were performed at initial concentrations of 15, 30 and 100 mgl(-1), ultrasonic frequencies of 20 and 80 kHz, applied power values of 45, 75 and 150 W and liquid bulk temperatures of 20, 40 and 60 degrees C . At the conditions in question, SDBS conversion was found to decrease with increasing temperature and initial solute concentration and decreasing power and frequency . Investigations using the radical scavengers 1-butanol and KBr revealed that SDBS degradation proceeds through radical reactions occurring predominately at the bubble-liquid interface and, to a lesser extent, in the liquid bulk . Addition of NaCl or H(2)O(2) had little or even an adverse effect on SDBS conversion . Conversely, addition of Fe(2+) either alone or in conjunction with H(2)O(2) (Fenton reagent) had a positive effect on degradation . Finally, shake flask tests with activated sludge were performed to assess the aerobic biodegradability before and after sonochemical treatment . At the conditions under consideration, the use of ultrasound enhanced the aerobic degradability of the substrate in question.

Environ Technol, 2004 Jul, 25(7), 825 - 31
Fate of E . coli across mechanical dewatering processes; Monteleone MC et al.; Five UK sludge treatment plants have been monitored for Escherichia coli (E.coli) variation after mechanical belt press and centrifuge dewatering processes . A complementary laboratory trial was also completed to examine the effects of varying centrifugal force on raw sludge E.coli content . An E.coli balance between the numbers contained in the flows entering and exiting four full scale centrifuge dewatering systems indicated a minimum 63 % increase in E.coli numbers between the input feed and sludge cake for a digested sludge input to the centrifuge . For two of the centrifuge sites this increase was statistically significant and corresponded to an increase in E.coli concentration ranging up to 1.4 Log after centrifugation . However, E.coli variation was found to be dependent on the type of sludge, as centrifuge dewatering of raw sludge at full scale resulted in a 40 % decrease in E.coli numbers . The complementary laboratory centrifuge work confirmed that E.coli numbers decreased in raw sludge after centrifugation . E.coli numbers were not observed to increase in digested sludge which had been dewatered using a belt press . A decrease of 44 % was observed.

Environ Technol, 2004 Jul, 25(7), 757 - 61
Adsorption of phthalates by activated sludge and its biopolymers; Fang HH et al.; This study shows diethyl phthalate (DEP) and dibutyl phthalate (DBP) were substantially adsorbed by activated sludge and its extracellular polymeric substance (EPS) . The adsorption characteristics followed Freundlich and Langmuir isotherms . According to the Langmuir isotherm, each gram of activated sludge at maximum adsorbed 0.73 mg of DEP and 17.6 mg of DBP, and each gram of centrifugation-extracted EPS adsorbed 14.3 mg of DEP and 10.6 mg of DBP . The adsorption increased with the hydrophobicity of phthalates . This suggests most phthalates, which are of higher hydrophobicity than DEP and DBP, are likely to be removed from wastewater through adsorption by the activated sludge in the biological treatment process.

Environ Technol, 2004 Jul, 25(7), 751 - 5
Bench-scale assessment of the effectiveness of an anaerobic selector in controlling filamentous bulking; Lee Y et al.; A laboratory scale sequencing batch reactor (SBR) was used to assess the ability of an anaerobic selector to control filamentous growth in an activated sludge plant experiencing bulking problems . The SBR was operated under a sequence of 60 min anaerobic followed by 120 min of aerobic period at 20 degrees C, with a total solids retention time (SRT) of 4 d and a hydraulic retention time (HRT) of 8 h . The apparent soluble organic carbon (SOC) removal from the liquid phase averaged 18% during the anaerobic period, which is significantly less than the 80-90% removal generally considered to be required to suppress the growth of filamentous bacteria . The anaerobic selector was, however, able to control sludge bulking, resulting in an average sludge volume index (SVI) below 140 ml g(-1) . The true amount of the SOC uptake was masked by simultaneous hydrolysis of particulate organic matter during the anaerobic period, a process which should be considered in future studies and comparisons.

Appl Environ Microbiol, 2004 Sep, 70(9), 5569 - 78
Implicating the glutathione-gated potassium efflux system as a cause of electrophile-induced activated sludge deflocculation; Bott CB et al.; The glutathione-gated K(+) efflux (GGKE) system represents a protective microbial stress response that is activated by electrophilic or thiol-reactive stressors . It was hypothesized that efflux of cytoplasmic K(+) occurs in activated sludge communities in response to shock loads of industrially relevant electrophilic chemicals and results in significant deflocculation . Novosphingobium capsulatum, a bacterium consistent with others found in activated sludge treatment systems, responded to electrophilic thiol reactants with rapid efflux of up to 80% of its cytoplasmic K(+) pool . Furthermore, N . capsulatum and activated sludge cultures exhibited dynamic efflux-uptake-efflux responses very similar to those observed by others in Escherichia coli K-12 exposed to the electrophilic stressors N-ethylmaleimide and 1-chloro-2,4-dinitrobenzene and the reducing agent dithiothreitol . Fluorescent LIVE/DEAD stains were used to show that cell lysis was not the cause of electrophile-induced K(+) efflux . Nigericin was used to artificially stimulate K(+) efflux from N . capsulatum and activated sludge cultures as a comparison to electrophile-induced K(+) efflux and showed that cytoplasmic K(+) efflux by both means corresponded with activated sludge deflocculation . These results parallel those of previous studies with pure cultures in which GGKE was shown to cause cytoplasmic K(+) efflux and implicate the GGKE system as a probable causal mechanism for electrophile-induced, activated sludge deflocculation . Calculations support the notion that shock loads of electrophilic chemicals result in very high K(+) concentrations within the activated sludge floc structure, and these K(+) levels are comparable to that which caused deflocculation by external (nonphysiological) KCl addition.

Appl Environ Microbiol, 2004 Sep, 70(9), 5283 - 9
Degradation of estrogens by Rhodococcus zopfii and Rhodococcus equi isolates from activated sludge in wastewater treatment plants; Yoshimoto T et al.; We have isolated four strains of Rhodococcus which specifically degrade estrogens by using enrichment culture of activated sludge from wastewater treatment plants . Strain Y 50158, identified as Rhodococcus zopfii, completely and rapidly degraded 100 mg of 17beta-estradiol, estrone, estriol, and ethinyl estradiol/liter, as demonstrated by thin-layer chromatography and gas chromatography-mass spectrometry analyses . Strains Y 50155, Y 50156, and Y 50157, identified as Rhodococcus equi, showed degradation activities comparable with that of Y 50158 . Using the random amplified polymorphism DNA fingerprinting test, these three strains were confirmed to have been derived from different sources . R . zopfii Y 50158, which showed the highest activity among these four strains, revealed that the strain selectively degraded 17beta-estradiol during jar fermentation, even when glucose was used as a readily utilizable carbon source in the culture medium . Measurement of estrogenic activities with human breast cancer-derived MVLN cells showed that these four strains each degraded 100 mg of 17beta-estradiol/liter to 1/100 of the specific activity level after 24 h . It is thus suggested that these strains degrade 17beta-estradiol into substances without estrogenic activity.

Water Sci Technol, 2004, 50(2), 113 - 9
Membrane bio-reactor for advanced textile wastewater treatment and reuse; Lubello C et al.; Textile wastewater contains slowly- or non-biodegradable organic substances whose removal or transformation calls for advanced tertiary treatments downstream Activated Sludge Treatment Plants (ASTP) . This work is focused on the treatment of textile industry wastewater using Membrane Bio-reactor (MBR) technology . An experimental activity was carried out at the Baciacavallo Wastewater Treatment Plant (WWTP) (Prato, Italy) to verify the efficiency of a pilot-scale MBR for the treatment of municipal wastewater, in which textile industry wastewater predominates . In the Baciacavallo WWTP the biological section is followed by a coagulation-flocculation treatment and ozonation . During the 5 months experimental period, the pilot-scale MBR proved to be very effective for wastewater reclamation . On average, removal efficiency of the pilot plant (93% for COD, 96% for ammonium and 99% for total suspended solids) was higher than the WWTP ones . Color was removed as in the WWTP . Anionic surf actants removal of pilot plant and WWTP were very similar (92.5 and 93.3% respectively), while the non-ionic surfactants removal was higher in the pilot plant (99.2 vs . 97.1) . In conclusion the MBR technology demonstrated to be effective for textile wastewater reclamation, leading both to an improvement of pollutants removal and to a draw-plate simplification.

Water Sci Technol, 2004, 50(2), 55 - 60
Semi-intensive treatment plants for wastewater reuse in irrigation; Juanico M et al.; Semi-intensive technologies are a middle term between intensive ones (e.g., activated sludge with a retention time of hours) and extensive ones (e.g., stabilization ponds with a retention time of several weeks) . The most common semi-intensive configuration used in Israel is made of anaerobic ponds followed by aerated lagoons . These small low-energy units remove about 75-80% of the BOD and are followed by wastewater reservoirs for storage and complementary treatment . The reduction in loading allows a flexible operation of the reservoirs for the removal of other pollutants, while providing storage capacity to cope with the changes in water demand for irrigation during the year . In schemes for wastewater reuse in irrigation, this lay-out has proved to be low-cost, low-energy, flexible, reliable and efficient . Variations of this basic configuration are the use of UASB reactors instead of anaerobic ponds, aerated lagoons in series or low-rate trickling filters instead of aerated lagoons, constructed wetlands or rock-filters for algae removal, etc. , , . Semi-intensive technologies use less energy than intensive ones, and less land than extensive ones . They can remove as much BOD as intensive ones, and as much pathogens and refractory pollutants as extensive ones . They release no or very small amounts of sludge.

Water Sci Technol, 2004, 50(2), 23 - 30
QMRA (quantitative microbial risk assessment) and HACCP (hazard analysis and critical control points) for management of pathogens in wastewater and sewage sludge treatment and reuse; Westrell T et al.; Hazard Analysis and Critical Control Points (HACCP) was applied for identifying and controlling exposure to pathogenic microorganisms encountered during normal sludge and wastewater handling at a 12,500 m3/d treatment plant utilising tertiary wastewater treatment and mesophilic sludge digestion . The hazardous scenarios considered were human exposure during treatment, handling, soil application and crop consumption, and exposure via water at the wetland-area and recreational swimming . A quantitative microbial risk assessment (QMRA), including rotavirus, adenovirus, haemorrhagic E . coli, Salmonella, Giardia and Cryptosporidium, was performed in order to prioritise pathogen hazards for control purposes . Human exposures were treated as individual risks but also related to the endemic situation in the general population . The highest individual health risk from a single exposure was via aerosols for workers at the belt press for sludge dewatering (virus infection risk = 1) . The largest impact on the community would arise if children ingested sludge at the unprotected storage site, although in the worst-case situation the largest number of infections would arise through vegetables fertilised with sludge and eaten raw (not allowed in Sweden) . Acceptable risk for various hazardous scenarios, treatment and/or reuse strategies could be tested in the model.

J Colloid Interface Sci, 2004 Sep 15, 277(2), 387 - 95
Advective flow in a sludge floc; Chu CP et al.; The interior of sludge floc is highly heterogeneous, while the large pores in the floc control the advective flow . This work for the first time numerically details fluid flow and mass transfer processes in pores of activated sludge floc . The dimensionless permeabilities and mass dispersion coefficients were contoured against pore size ratio and the floc Reynolds number . With a pore size less than 20% of the floc size, the commonly adopted homogeneous model overestimates the floc permeability, and pore velocity is less than 2% of the bulk velocity . This is particularly true for flocs with low porosity . Although the convective flux is low, the dispersive mass transfer rate can be much higher than the diffusional rate, attributable to the strong Taylor dispersion effect . The three-dimensional pore structures in waste activated-sludge floc were identified using confocal laser scanning microscope (CLSM) images . Large pores were used to numerically estimate the permeability and dispersion coefficient for these pores . The permeability and the dispersion coefficient of the tortuous pores can be one order of magnitude lower than those for the equivalent straight pores . Besides the dispersion effect, the pore tortuosity appeared as the most important geometrical factor retarding the advective flow in the sludge pores . In addition, the small side pores connected to the large pore had only a mild effect on the flow process, and can be neglected in analysis.

Water Environ Res, 2004 May-Jun, 76(3), 256 - 67
Relative efficacy of intrinsic and extant parameters for modeling biodegradation of synthetic organic compounds in activated sludge: dynamic systems; Magbanua BS Jr et al.; The utility of intrinsic and extant kinetic parameters for simulating the dynamic behavior of a biotreatment system coupled with a distributed, unstructured, balanced microbial growth model were evaluated against the observed response of test reactors to transient loads of synthetic organic compounds (SOCs) . Biomass from a completely mixed activated-sludge (CMAS) system was tested in fed-batch reactors, while a sequencing batch reactor (SBR) was tested by measuring SOC concentrations during the fill and react period . Both the CMAS system and the SBR were acclimated to a feed containing biogenic substrates and several SOCs, and the transient loading tests were conducted with biogenic substrates along with one or more SOCs . Extant parameters more closely reflect the steady-state degradative capacity of activated-sludge biomass than intrinsic parameters and, hence, were expected to be better predictors of system performance . However, neither extant nor intrinsic parameters accurately predicted system response and neither parameter set was consistently superior to the other . Factors that may have contributed to the inability of the model to predict system response were identified and discussed . These factors included the role of abiotic processes in SOC removal, disparity in the bases used to evaluate parameter estimates (substrate mineralization) and reactor performance (substrate disappearance), inhibitory substrate interactions under the severe loading conditions of the SBR, changes in the physiological state of the biomass during the transient loading tests, and the presumed correlation between the competent biomass concentration and the influent SOC concentration.

Water Environ Res, 2004 May-Jun, 76(3), 213 - 9
Activated sludge deflocculation in response to chlorine addition: the potassium connection; Wimmer RF et al.; Chlorination is often used to control filamentous bulking in activated sludge systems . Pure culture and mixed-liquor experiments showed that soluble potassium (K+) concentrations increased by 2.4 mg/L (80%) and 1.5 to 3.6 mg/L (11 to 30%) in the bulk liquid phase of pure and activated sludge cultures that were exposed to chlorine, relative to unchlorinated controls . Effluent turbidity and total suspended solids from settled mixed liquor increased significantly in both short-term batch and sequencing batch reactor experiments when chlorine mass load increased above 6 milligrams of chlorine per gram mixed liquor volatile suspended solids (mg Cl2/g MLVSS) in a single dose, which correlated with a localized chlorine concentration at the dose point of 10 mg/L as Cl2 or greater . The results support the hypothesis that the glutathione-gated potassium efflux (GGKE) bacterial stress response may contribute to increased effluent turbidity associated with high doses of mixed-liquor chlorination . It is suggested that potassium is a useful parameter to monitor at full-scale facilities when determining chlorine mass doses that should be used to control filaments and minimize increases in effluent turbidity.

Huan Jing Ke Xue, 2004 Jan, 25(1), 67 - 71
{Study on the biological activity of activated sludge using a rapid biological activity tester}; Shi HC et al.; Based on a Rapid Biological Activity Tester (RBAT), a study was taken on the sludge activity which is one of the most important parameters in the operation of aerated biological treating unit in WWTP to measure the effect of the external environmental conditions on the sludge activity, such as acidity and alkalinity, temperature, toxicity, etc . It is observed that the variety of the activity parameters is limited in 20% for a long time . While pH is deviated from the normal value, the biological activity drops to some degree, and furthermore, the ability of the microorganism to endure the acerbic environment is much higher than that to endure the alkaline environment . Temperature increase can result in the enhancement of the biological activity, and if the temperature is higher than 42.5 degrees C, the biological activity is greatly inhibite, but the endogenous respiring rate is less influenced by high temperature . Toxicity can greatly inhibit the biological activity of the activated sludge, and the inhibition is probably selective . Finally, the biological activity of the activated sludge from a real wastewater treatment plant was tested, and the standard deviation of the result is less than 20% . The results indicate that the RBAT is a promising method to measure biological activity, and the characteristics of activated sludge can be well expressed.

J Environ Sci Health A Tox Hazard Subst Environ Eng, 2002 Aug, 37(7), 1277 - 93
Polyelectrolyte conditioning for iron-hydroxide-containing sludge produced from electroflocculation of fermentation wastewater; Chen WJ et al.; The purpose of this study is to investigate the application of chemical conditioning method for the post-electroflocculation wastewater sludge treatment with polyelectrolytes of varying ionic characters, namely anionic, cationic and nonionic flocculating agents . Electroflocculation, a combination of the processes of electroflotation and electroprecipitation, was found effective to remove the organic and color components in monosodium glutamate fermentation wastewater . The settleability and dewaterability of the separated sludge, containing 15-20% of iron hydroxides, increased 35% and 60% due to polymer conditioning through a jar-test apparatus . The influence of shear conditions and polymer dose on the floc size, zeta potential, filterability and dewatering performance, and shear resistance of sludges was investigated . Experimental results showed that the anionic polymer acts as a better flocculating agent than both cationic and nonionic polymers, and the optimal polymer doses fall between 4.0 and 10.0 mg/g Fe sludge under corresponding shear rates of 200 300 rpm . This study also indicated that both charge neutralization and polymer bridging mechanisms operate in the sludge conditioning process.

Huan Jing Ke Xue, 2004 May, 25(3), 61 - 4
{Adsorbing capability of chromium-galvanized waste water by yeast-activated sludge}; Yin H et al.; The capability of bioadsorption and bioreduction of chromium-galvanized wastewater by Candida lipolytica 1977, Candida utilis 1225, and activated sludge was discussed in this paper . The experimental results showed that the feasible pH range for C . lipolytica 1977 adsorption was wide . The removal and reduction ratios of C . lipolytica 1977 towards chromium-galvanized wastewater were 85.0%, and 100%, when pH was 3.2-6.0, and the concentrations of Cr(total) and Cr6+ were 30.2 mg/L, 27.7 mg/L respectively . The removal ratio increased to 91.1%, when the chromium-galvanized wastewater was treated by two strains together . The aerobic bioadsorption treatment of chromium-galvanized wastewater was investigated . The results demonstrated that this method was the optimal one for the treatment of this kind of wastewater in the study, the removal ratio was 93.8%, when the concentrations of yeast, activated sludge, Cr(total) and Cr6+ were 10 g/L, 5 g/L, 50.3 mg/L and 46.2 mg/L, respectively . The removal ratio increased to 99.5% accordingly, when the activated sludge content was 10 g/L.

Appl Microbiol Biotechnol, 2005 Feb, 66(5), 575 - 588 Epub 2004 Aug 18.
Monitoring the impact of bioaugmentation on the start up of biological phosphorus removal in a laboratory scale activated sludge ecosystem; Dabert P et al.; The acclimatisation of activated sludge to enhanced biological phosphorus removal (EBPR) conditions requires a period of about 40-100 days but its output remains hazardous . The impact of bioaugmentation on the start-up of a laboratory scale EBPR sequencing batch reactor was evaluated by process parameters measurement and microbial community dynamics monitoring using 16S rDNA targeted polymerase chain reaction-single strand conformation polymorphism electrophoresis (PCR-SSCP) . Bioaugmentation: (1) speeded up the installation of good and stable EBPR in the bioaugmented reactor by about 15 days; (2) correlated with the transient enrichment of the sludge in the added microbial populations; and (3) favoured the long-term enrichment of the sludge in the phosphorus-accumulating organism (PAO) Candidatus Accumulibacter phosphatis . However, despite a lag time period, the control non-bioaugmented reactor ended up with comparable reactor parameters and microbial community evolution, suggesting that the same PAO populations were already present from the beginning in the original non-P-accumulating seed sludge. , , , . The potential of a true installation of the added microbial populations within the bioaugmented reactor compared to their substitution by indigenous similar populations is discussed . Competition between PAOs and the antagonistic glycogen accumulating organism Candidatus Competibacter phosphatis is also highlighted during EBPR start-up.

Anal Chem, 2004 Aug 15, 76(16), 4756 - 64
Trace determination of macrolide and sulfonamide antimicrobials, a human sulfonamide metabolite, and trimethoprim in wastewater using liquid chromatography coupled to electrospray tandem mass spectrometry; Gobel A et al.; An analytical method has been developed and validated for the simultaneous trace determination of four macrolide antibiotics, six sulfonamides, the human metabolite N(4)-acetylsulfamethoxazole, and trimethoprim in wastewater . The method was validated for tertiary, secondary, and-unlike in previously published methods-also for primary effluents of municipal wastewater treatment plants . This wide range of application is necessary to thoroughly investigate the occurrence and fate of chemicals in wastewater treatment . Wastewater samples were enriched by solid-phase extraction, followed by reversed-phase liquid chromatography coupled to tandem mass spectrometry using positive electrospray ionization . Recoveries from all sample matrixes were generally above 80%, and the combined measurement uncertainty varied between 2 and 18% . Concentrations measured in tertiary effluents ranged between 10 ng/L for roxithromycin and 423 ng/L for sulfamethoxazole . Corresponding levels in primary effluents varied from 22 to 1450 ng/L, respectively . Trace amounts of these emerging contaminants reach ambient waters, since all analytes were not fully eliminated during conventional activated sludge treatment followed by sand filtration . In the case of sulfamethoxazole, the amount present as human metabolite N(4)-acetylsulfamethoxazole had to be taken into account in order to correctly assess the fate of sulfamethoxazole in wastewater treatment.

Environ Microbiol, 2004 Sep, 6(9), 911 - 20
The application of two-dimensional polyacrylamide gel electrophoresis and downstream analyses to a mixed community of prokaryotic microorganisms; Wilmes P et al.; Summary In the post-genomic era, the focus of numerous researchers has moved to studying the functional products of gene expression . In microbiology, these "omic" approaches have largely been limited to pure cultures of microorganisms . Consequently, they do not provide information on gene expression in a complex mixture of microorganisms as found in the environment . Our method enabled the successful extraction and purification of the entire proteome from a laboratory-scale activated sludge system optimized for enhanced biological phosphorus removal, its separation by two-dimensional polyacrylamide gel electrophoresis and the mapping of this metaproteome . Highly expressed protein spots were excised and identified using quadrupole time-of-flight mass spectrometry with de novo peptide sequencing . The proteins isolated were putatively identified as an outer membrane protein (porin), an acetyl coenzyme A acetyltransferase and a protein component of an ABC-type branched-chain amino acid transport system . These proteins possibly stem from the dominant and uncultured Rhodocyclus-type polyphosphate-accumulating organism in the activated sludge . We propose the term "metaproteomics" for the large-scale characterization of the entire protein complement of environmental microbiota at a given point in time.

Appl Biochem Biotechnol, 1999 Spring, 77-79, 389 - 400
Accumulation of biopolymers in activated sludge biomass; Chua H et al.; In this study, activated sludge bacteria from a conventional wastewater treatment process were induced to accumulate polyhydroxyalkanoates (PHAs) under different carbon-nitrogen (C:N) ratios . As the C:N ratio increased from 20 to 140, specific polymer yield increased to a maximum of 0.38 g of polymer/g of dry cell mass while specific growth yield decreased . The highest overall polymer production yield of 0.11 g of polymer/g of carbonaceous substrate consumed was achieved using a C:N ratio of 100 . Moreover, the composition of polymer accumulated was dependent on the valeric acid content in the feed . Copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) {P(3HB-co-3HV)} was produced in the presence of valeric acid . The 3-hydroxyvalerate (3HV) mole fraction in the copolymer was linearly related to valeric content in the feed, which reached a maximum of 54% when valeric acid was used as sole carbon source . When the 3HV U in the polymer increased from 0-54 mol%, the melting temperature decreased from 178 degrees to 99 degrees C . Thus, the composition, and hence the mechanical properties, of the copolymer produced from activated sludge can be controlled by adjusting the mole fraction of valeric acid in the feed medium.

Water Sci Technol, 2004, 49(11-12), 247 - 54
IAL-CHS (internal airlift loop--ceramic honeycomb supports) reactor used for biodegradation of 2,4-dichlorophenol and phenol; Zhang Y et al.; The internal airlift loop reactor with ceramic honeycomb supports (IAL-CHS) was applied for biodegradation of 2,4-dichlorophenol (2,4-DCP) and phenol . A strain of DCP-degrading bacteria isolated from activated sludge, Achromobacter sp., was rapidly immobilized onto the ceramic honeycomb supports . The immobilized cells effectively biodegraded 2,4-DCP alone and together with phenol in batch and continuous-flow experiments . For example, 2,4-DCP was biodegraded from an influent concentration of 50 mg/L to less than 1 mg/L with a 6-h hydraulic retention time (HRT) in continuous flow tests . The immobilized biomass grew and accumulated through 2,4-DCP biodegradation, and the rate of degradation increased accordingly.

Commun Agric Appl Biol Sci, 2003, 68(2 Pt A), 51 - 8
Bioluminescence-based assay used for toxicity monitoring; Valat C et al.; A new ATP bioluminescence-based method is proposed in order to examine the effect of toxic shock on microbial communities in urban wastewater treatment plant (WWTP) . As the efficiency of WWTP must be improved, the occurrence and toxic effect of hazardous substances have to be evaluated (Directive 2455/2001/EC) . Among bioluminescence assay with firefly luciferase is commonly used for intracellular ATP monitoring . A multienzyme systems catalysed by three enzymes (adenylate kinase, pyruvate kinase and firefly luciferase) for adenine nucleotides (AN = ATP+ ADP+ AMP) estimation is used for monitoring metabolic changes in activated sludge . The AN method provides better sensitivity than ATP quantification alone . The pool of intracellular and extracellular AN is constant during growth and the rate of intracellular AN is correlated with the microbial growth . In the present investigation, the extraction of total adenylate assay is optimized (chemical and mechanical extraction) and applied for monitoring the effect of the toxic shock (eg . Naphthalene) on indigenous biomass activity (intracellular and extracellular AN rates) . In the same time, the removal of naphthalene is addressed Laboratory-scale reactors (4 L) are inoculated with urban activated sludge is under continuous-flow aeration . The reactor, containing non acclimated sludge enriched with naphthalene . The other reactor containing sterilised activated sludge is used as abiotic and volatilisation control system . In all this batch cultures, ATP and AN (intracellular and extracellular) rates and naphthalene concentrations are controlled . One of the objectives of this research is to determine a relation between the ATP/AN ratio and the biodegradation of naphthalene . Evidence is given which demonstrates that the ATP/AN parameter is a possible alternative for monitoring very rapid metabolic changes in complex microbial community such as activated sludge.

Bioresour Technol, 2004 Dec, 95(3), 327 - 30
Production of biodegradable plastics from activated sludge generated from a food processing industrial wastewater treatment plant; Suresh Kumar M et al.; Most of the excess sludge from a wastewater treatment plant (60%) is disposed by landfill . As a resource utilization of excess sludge, the production of biodegradable plastics using the sludge has been proposed . Storage polymers in bacterial cells can be extracted and used as biodegradable plastics . However, widespread applications have been limited by high production cost . In the present study, activated sludge bacteria in a conventional wastewater treatment system were induced, by controlling the carbon: nitrogen ratio to accumulate storage polymers . Polymer yield increased to a maximum 33% of biomass (w/w) when the C/N ratio was increased from 24 to 144, where as specific growth yield decreased with increasing C/N ratio . The conditions which are required for the maximum polymer accumulation were optimized and are discussed.

Environ Microbiol, 2002 Oct, 4(10), 577 - 83
Stable augmentation of activated sludge with foreign catabolic genes harboured by an indigenous dominant bacterium; Watanabe K et al.; Comamonas sp . rN7 is a phenol-degrading bacterium that represents the dominant catabolic population in activated sludge . The present study examined the utility of this bacterium for establishing foreign catabolic genes in phenol-digesting activated sludge . The phc genes coding for phenol hydroxylase and its transcriptional regulators of C . testosteroni R5 were integrated into the chromosome of strain rN7 . The specific phenol-oxygenating activity of a resultant transformant designated rN7(R503) was three times higher than the activity of strain rN7, and the phc genes were stably inherited by rN7(R503) grown in a non-selective laboratory medium . Inoculation of phenol-acclimatized activated sludge with rN7(R503) resulted in a high phenol-oxygenating activity and improved resistance to phenol-shock loading compared to sludge inoculated with either no cells, rN7 or R5 . Quantitative competitive polymerase chain reaction (PCR) showed that the phc genes were retained in the rN7(R503)-inoculated sludge at a density of more than 108 copies per ml of mixed liquor for more than 35 days, whereas those in the R5-inoculated sludge disappeared rapidly . No transfer of the phc genes to other indigenous populations was apparent in the rN7(R503)-harbouring sludge. , , . From these results, we concluded that the phenol treatment of the activated sludge was enhanced by the phc genes harboured by the rN7(R503) population . This study suggests a possible bioaugmentation strategy for stably utilizing foreign catabolic genes in natural ecosystems.

Waste Manag, 2002, 22(7), 703 - 10
Microbiological degradation of phenol using mixed liquors of Pseudomonas putida and activated sludge; Annadurai G et al.; This work investigated the biodegradation potential of phenol using mixed liquors of Pseudomonas putida (ATCC 31800) and activated sludge . Experiments were made as a function of solution pH (6-10), temperature (30-36 degrees C), nitrogen source (NH4)2SO4 (0.5-0.8 g/l), and carbon source glucose (0.5-0.8 g/l) . Response surface methodology by the Box-Behnken model was used to examine the role of four process factors on phenol degradation . It was shown that a second-order polynomial regression model could properly interpret the experimental data with an R2-value of 0.9997 and an F-value of 3605.45, based on which the maximum degradation of phenol was estimated up to 80.1% within the range examined . Interactions between process parameters and each significance effect on phenol degradation were also discussed.

Chemosphere, 2002 Oct, 49(3), 279 - 86
Structure-activity relationships for association of linear alkylbenzene sulfonates with activated sludge; Garcia MT et al.; Sorption of linear alkylbenzene sulfonates (LAS) on sludge particles from wastewater treatment plants was studied . The effect of alkyl chain length and the water hardness were investigated . Sorption on sludge increases with increasing alkyl chain length in the LAS molecules . The results are interpreted in terms of a hydrophobic bonding mechanism being the critical micelle concentration a good index of the surfactant hydrophobicity . The increase in free energy of adsorption for the addition of successive methylene groups to the alkyl chain was estimated as 2.4 kJ/mol . Water hardness clearly enhances the sorption of LAS homologues on sludge and seems to promote cooperative sorption at high surfactant and calcium ion concentrations . An empirical equation was provided that allow to estimate the partition coefficient between aqueous and solid phases for LAS homologues as a function of the alkyl chain length and the water hardness.

Acta Microbiol Pol, 2002, 51(2), 183 - 91
Phenol utilisation by fungi isolated from activated sludge; Boszczyk-Maleszak H et al.; The paper presents the efficiency of phenol removal (concentrations from 500 to 2000 mg/l) by fungi isolated from activated sludge purifying wastewater with high phenol concentration . Five fungal strains were isolated and identified . All isolated strains appeared to be Moniliales from the class of Fungi Imperfecti (Candida sp., Monosporium sp., Trichosporon sp.) Stationary cultures of the individual strains and their mixtures were maintained in Czapek medium containing phenol in concentration from 500 to 2000 mg/l . All isolated strains (except one) were capable of utilising phenol up to a concentration of 1500 mg/l . Depending on investigated strain, phenol in concentration of 500 mg/l was decomposed during 4-25 days, 750 mg/l during 4-14 days . After 20 days, a phenol decline of 1000 mg/l was observed . After 16 days, the phenol decline was 1500 mg/l . Higher phenol concentrations (1500 mg/l) were utilised only by a mixture of two strains . The investigated fungal strains showed good efficiency of phenol removal from high phenol concentration in wastewater and they may be proposed for use in the process of purifying wastewater of this type.

Int J Syst Evol Microbiol, 2002 Sep, 52(Pt 5), 1845 - 9
Kineosphaera limosa gen . nov., sp . nov., a novel Gram-positive polyhydroxyalkanoate-accumulating coccus isolated from activated sludge; Liu WT et al.; A high-G+C gram-positive, motile, non-spore-forming coccus capable of accumulating significant amounts of polyhydroxyalkanoate (PHA) was isolated from an inefficient biological phosphorus removal activated sludge reactor . The cell wall of strain Lpha5T was characterized by the presence of meso-diaminopimelic acid, menaquinone MK-8(H4) and a complex fatty-acid pattern consisting of C16:0 and at least five other major straight-chain saturated and unsaturated fatty acids . Strain Lpha5T also had a high G+C content (71.3 mol%) . The nearest phylogenetic relative of strain Lpha5T, based on 16S rDNA sequence analysis, was the high-G+C gram-positive bacterium Dermatophilus congolensis (similarity value of 94%), of the family Dermatophilaceae, class Actinobacteria . As strain Lpha5T was distinct from D . congolensis in its morphological, phenotypical (i.e . its PHA-accumulating ability and fatty-acid profile) and genetic traits (phylogeny and G+C content), it is proposed that strain Lpha5T be designated as the type species of a novel genus within the Dermatophilaceae . The name Kineosphaera limosa is proposed for strain Lpha5T (= JCM 11399T = DSM 14548T).

Water Sci Technol, 2002, 46(4-5), 99 - 106
A model to control intermittent aeration phases; Carucci A et al.; Dealing with intermittent aeration as a useful practice to improve nitrogen removal efficiency of activated sludge plants, the possibility to plan optimal temporisation during daytime was investigated . A mathematical model (NIDEN) that allows us to manage different situations, with respect to influent load, environmental conditions and operating strategy, was then developed . The model represents a useful tool especially to plan the aeration cycles in small and medium sized plants, where high costs of automatic control through on-line instrumentation might not be justified . Once the input variables have been defined and the set-point values for tank nutrient concentration have been fixed, NIDEN gives an optimal phase temporisation, to obtain either the maximum energy saving or the best total nitrogen removal.

Water Sci Technol, 2002, 46(4-5), 397 - 403
Utilisation of energy from digester gas and sludge incineration at Hamburg's Köhlbrandhöft WWTP; Thierbach RD et al.; At Hamburg's Kohlbrandhoft WWTP the demand for external energy supply is minimised by state of the art sludge treatment . The sludge is subjected to thickening, anaerobic digestion, dewatering, drying and incineration . The digester gas is used in a combined gas and steam turbine process . The sludge incineration also produces steam, which is also used in the steam turbine that follows the gas turbine . The turbines produce electricity, partially expanded steam is used for the sludge drying process . Heat from the condensation of vapours from sludge drying is used to heat the anaerobic digesters . The overall process requires no external heat or fuel and produces 60% of the WWTP's electricity demand.

Water Sci Technol, 2002, 46(4-5), 389 - 96
Regional planning and product recovery as tools for sustainable sludge management; Stypka T et al.; The article presents two aspects of sludge management: regional planning and product recovery . The introduction of these two elements can reduce the cost, close the ecocycle and make the management more sustainable . A spreadsheet program to optimize the regional location of different facilities is presented . The simple example shows the potential of the model . The brief comparison of formal problems concerning sludge disposal in Poland and Sweden is also discussed . Requirements of phosphorus recovery and recycling of phosphorus to the phosphate industry make sludge fractionation in combination with product recovery a new development in wastewater handling . Phosphorus recovery from sludges with chemical bound phosphorus requires complex and expensive process technology and may therefore lead to increased regional sludge management with a central sludge treatment plant.

Water Sci Technol, 2002, 46(4-5), 325 - 32
Simulation study supporting wastewater treatment plant upgrading; Hvala N et al.; The paper presents a study where upgrading of an existing wastewater treatment plant was supported by simulation . The aim of the work was to decide between two technologies to improve nitrogen removal: a conventional activated sludge process (ASP) and a moving bed biofilm reactor (MBBR) . To perform simulations, the mathematical models of both processes were designed . The models were calibrated based on data from ASP and MBBR pilot plants operating in parallel on the existing plant . Only two kinetic parameters needed to be adjusted to represent the real plant behaviour . Steady-state analyses have shown a similar efficiency of both processes in relation to carbon removal, but improved performance of MBBR in relation to nitrogen removal . Better performance of MBBR can be expected especially at low temperatures . Simulations have not confirmed the expected less volume required for the MBBR process . Finally, the MBBR was chosen for plant upgrading . The developed process model will be further used to evaluate the final plant configuration and to optimise the plant operating parameters.

Water Sci Technol, 2002, 46(4-5), 317 - 24
Comparison of the efficiency of large-scale ceramic and membrane aeration systems with the dynamic off-gas method; Libra JA et al.; The aeration systems of two full-scale activated sludge basins were compared over 2.5 years under the same operating conditions using dynamic off-gas testing . Only the material of the diffuser was different, membrane vs . ceramic tube diffusers . The experimental design took the complexity and dynamics of the system into consideration . The investigation has shown that, although the membrane diffusers have higher initial standard oxygen transfer efficiency (SOTE) and standard aeration efficiency (SAE), these decreased over time, while the SAE of the ceramic diffusers started lower, but increased slightly over the whole period . Measurement of air distribution in the basins along with dissolved oxygen concentration profiles have provided important information on improving process control and reducing energy costs . The results show that dynamic off-gas testing can effectively be used for monitoring the aeration system and to check design assumptions under operating conditions . The information can be used to improve the design of new aeration systems or in retro-fitting existing basins.

Water Sci Technol, 2002, 46(4-5), 301 - 7
A quantitative risk analysis tool for design/simulation of wastewater treatment plants; Bixio D et al.; Uncertainty is a central concept in the decision-making process, especially when dealing with biological systems subject to large natural variations . In the design of activated sludge systems, a conventional approach in dealing with uncertainty is implicitly translating it into above-normal safety factors, which in some cases may even increase the capital investments by an order of magnitude . To obviate this problem, an alternative design approach explicitly incorporating uncertainty is herein proposed . A probabilistic Monte Carlo engine is coupled to deterministic wastewater treatment plant (WWTP) models . The paper provides a description of the approach and a demonstration of the general adequacy of the method . The procedure is examined in an upgrade of a conventional WWTP towards stricter effluent standards on nutrients . The results suggest that the procedure can support the decision-making process under uncertainty conditions and that it can enhance the likelihood of meeting effluent standards without entailing above-normal capital investments. , , , . The analysis led to reducing the capital investment by 43%, producing savings of more than 1.2 million euro.

Appl Environ Microbiol, 2002 Oct, 68(10), 4971 - 8
Polyphosphate kinase from activated sludge performing enhanced biological phosphorus removal; McMahon KD et al.; A novel polyphosphate kinase (PPK) was retrieved from an uncultivated organism in activated sludge carrying out enhanced biological phosphorus removal (EBPR) . Acetate-fed laboratory-scale sequencing batch reactors were used to maintain sludge with a high phosphorus content (approximately 11% of the biomass) . PCR-based clone libraries of small subunit rRNA genes and fluorescent in situ hybridization (FISH) were used to verify that the sludge was enriched in Rhodocyclus-like beta-Proteobacteria known to be associated with sludges carrying out EBPR . These organisms comprised approximately 80% of total bacteria in the sludge, as assessed by FISH . Degenerate PCR primers were designed to retrieve fragments of putative ppk genes from a pure culture of Rhodocyclus tenuis and from organisms in the sludge . Four novel ppk homologs were found in the sludge, and two of these (types I and II) shared a high degree of amino acid similarity with R . tenuis PPK (86 and 87% similarity, respectively) . Dot blot analysis of total RNA extracted from sludge demonstrated that the Type I ppk mRNA was present, indicating that this gene is expressed during EBPR . Inverse PCR was used to obtain the full Type I sequence from sludge DNA, and a full-length PPK was cloned, overexpressed, and purified to near homogeneity . The purified PPK has a specific activity comparable to that of other PPKs, has a requirement for Mg(2+), and does not appear to operate in reverse . PPK activity was found mainly in the particulate fraction of lysed sludge microorganisms.

Appl Environ Microbiol, 2002 Oct, 68(10), 4772 - 9
Simultaneous fluorescent gram staining and activity assessment of activated sludge bacteria; Forster S et al.; Wastewater treatment is one of the most important commercial biotechnological processes, and yet the component bacterial populations and their associated metabolic activities are poorly understood . The novel fluorescent dye hexidium iodide allows assessment of Gram status by differential absorption through bacterial cell walls . Differentiation between gram-positive and gram-negative wastewater bacteria was achieved after flow cytometric analysis . This study shows that the relative proportions of gram-positive and gram-negative bacterial cells identified by traditional microscopy and hexidium iodide staining were not significantly different . Dual staining of cells for Gram status and activity proved effective in analyzing mixtures of cultured bacteria and wastewater populations . Levels of highly active organisms at two wastewater treatment plants, both gram positive and gram negative, ranged from 1.5% in activated sludge flocs to 16% in the activated sludge fluid . Gram-positive organisms comprised <5% of the total bacterial numbers but accounted for 19 and 55% of the highly active organisms within flocs at the two plants . Assessment of Gram status and activity within activated sludge samples over a 4-day period showed significant differences over time . This method provides a rapid, quantitative measure of Gram status linked with in situ activity within wastewater systems.

Water Res, 2001 Nov, 35(16), 3993 - 7
Particle size distribution in effluent of trickling filters and in humus tanks; Schubert W et al.; Particles and aggregates from trickling filters must be eliminated from wastewater . Usually this happens through sedimentation in humus tanks . Investigations to characterize these solids by way of particle size measurements, image analysis and particle charge measurements (zeta potential) are made within the scope of Research Center for Science and Technology "Fundamentals of Aerobic biological wastewater treatment" (SFB 411) . The particle size measuring results given within this report were obtained at the Ingolstadt wastewater treatment plant, Germany, which served as an example . They have been confirmed by similar results from other facilities . Particles flushed out from trickling filters will be partially destroyed on their way to the humus tank . A large amount of small particles is to be found there . On average 90% of the particles are smaller than 30 microm . Particle size plays a decisive role in the sedimentation behaviour of solids . Small particles need sedimentation times that cannot be provided in settling tanks . As a result they cause turbidity in the final effluent . Therefore quality of sewage discharge suffers, and there are hardly advantages of the fixed film reactor treatment compared to the activated sludge process regarding sedimentation behaviour.

Water Res, 2001 Nov, 35(16), 3887 - 903
The EAWAG Bio-P module for activated sludge model No . 3; Rieger L et al.; An additional module for the prediction of enhanced biological phosphorus removal is presented on the basis of a calibrated version of ASM3 . The module uses modified processes from ASM2d but neglects the fermentation of readily degradable substrate . Biomass decay is modeled in the form of endogenous respiration as in ASM3 . Moreover, an additional glycogen pool and biologically induced P-precipitation were not taken into account . The module was systematically calibrated with experimental data from various batch experiments, a full-scale WWTP and a pilot plant treating Swiss municipal waste water . A standard parameter set allowed all data to be simulated.

Water Res, 2001 Nov, 35(16), 3867 - 75
Effect of addition of Rhodobacter sp . to activated-sludge reactors treating piggery wastewater; Huang JS et al.; Under aerobic conditions, the decay rates of purple nonsulfur bacteria (Rhodobacter sp.) in the light and dark follow first-order kinetics with rate constants of 0.22 and 0.32 day(-1), respectively . The performance of the conventional activated-sludge reactor (CASR) treating anaerobically pretreated piggery wastewater (656-1.110 mg chemical oxygen demand, COD/L) can be enhanced by the addition of Rhodobacter sp . By performing regressive and statistical analyses using the proposed model and experimental data, the kinetic constants k and Y(T), and the fraction of refractory organic materials (f) of the Rhodobacter sp.-supplemented activated-sludge reactor (RASR) are 40% larger, 21% less, and 34% less than those of the CASR, respectively . From parametric sensitivity analyses, the substrate removal efficiencies of the CASR and RASR are most sensitive to the parameters k and the food to microorganisms ratio (F/M) but least sensitive to the parameter f; the specific oxygen utilization rates of the CASR and RASR are most sensitive to the parameters a and k but least sensitive to the parameter b.

Water Res, 2001 Nov, 35(16), 3833 - 44
Aerobic storage by activated sludge on real wastewater; Carucci A et al.; Activated sludge processes are often operated under dynamic conditions, where the microbial response can include, besides of growth, several COD removal mechanisms, and particularly the storage in form of polymers . While abundant evidence of aerobic storage under dynamic conditions with synthetic substrates can be found (Majone et al., Water Sci . Technol . 39(1) (1999) 61), there is still little knowledge about COD removal mechanisms with real activated sludge and wastewater . The aim of the present paper is therefore to give a direct evidence of storage phenomena occurring when a real sludge is mixed with influent wastewater and of their influence onto OUR profiles in typical respirometric batch tests . For this purpose, respirometric batch tests were performed on the same sludge by using acetate, filtered wastewater and raw wastewater as carbon source along with determination of acetate uptake and storage polymer formation . Comparison of results obtained has shown that poly-3-hydroxybutyrate (PHB) storage gives always the main contribution to acetate removal and that in the case of wastewater PHB is also formed from other substrates . PHB formation clearly occurs during the high-rate RBCOD-phase, however for wastewater it accounts for only a fraction (18-22%) of overall RBCOD removal, so calling for other unidentified storage compounds or other non-storage phenomena . In the low-rate SBCOD phase of respirogram PHB is clearly utilised in tests with acetate as internal reserve material once the acetate is depleted . In tests with filtered and raw wastewater the PHB concentration decreases much slower, probably because more PHB is formed due to the availability of external SBCOD (soluble and not) . Moreover, reported OUR in the SBCOD-phase from filtered or raw wastewater are quite higher than those reported in batch tests with acetate, so confirming a main contribution of external SBCOD . However, the respective contributions for utilisation of previously stored compounds and of external SBCOD cannot be easily separated by the comparison of tests on filtered and raw wastewater, because both substrates are simultaneously present also in tests with the filtered wastewater . As a side consequence, the chemical-physical method for evaluation of true soluble and biodegradable COD tends to overestimate the respirometry-based RBCOD, at least for the wastewater under observation . Even though modelling by ASM3 (Gujer et al., Water Sci . Technol . 39(1) (1999) 183) makes it possible to well describe the whole experimental behaviour, it requires that much more storage compounds are formed than the experimentally observed PHB . These compounds have still to be identified and quantified in order to confirm the conceptual structure of ASM3.

Artif Cells Blood Substit Immobil Biotechnol, 2002 Jul, 30(4), 307 - 18
Bioconversion of domestic wastewater sludge by immobilized mixed culture of penicillum Corylophilum WWZA1003 and Aspergillus niger SCahmA103; Alam MZ et al.; The bioconversion of domestic wastewater sludge by immobilized mixed culture of filamentous fungi was investigated in a laboratory . The potential mixed culture of Penicillium corylophilum WWZA1003 and Aspergillus niger SCahmA103 was isolated from its local habitats (wastewater and sludge cake) and optimized on the basis of biodegradability and dewaterability of treated sludge . The observed results in this study showed that the sludge treatment was highly influenced by the effect of immobilized mixed fungi using liquid state bioconversion (LSB) process . The maximum production of dry filter cake (DFC) was enriched with fungal biomass to about 20.05 g/kg containing 23.47 g/kg of soluble protein after 4 days of fungal treatment . The reduction of COD, TSS, turbidity (optical density against distilled water, 660 nm), reducing sugar and protein in supernatant and filtration rate of treated sludge were influenced by the fungal mixed culture as compared to control (uninnoculated) . After these processes, 99.4% of TSS, 98.05% of turbidity, 76.2% of soluble protein, 98% of reducing sugar and 92.4% of COD in supernatant of treated sludge were removed . Filtration time was decreased tremendously by the microbial treatment after 2 days of incubation . The effect of fungal strain on pH was also studied and presented . Effective bioconversion was observed after 4 days of fungal treatment.

Water Sci Technol, 2002, 46(3), 57 - 64
Mass spectrometric monitoring of the degradation and elimination efficiency for hardly eliminable and hardly biodegradable polar compounds by membrane bioreactors; Schroder HF; Wastewaters containing or spiked with polar compounds--alkylphenolethoxylates (APEOs) and drugs--were treated in membrane-assisted and conventional biological pilot plants to eliminate these pollutants . Elimination resulting in metabolization or ultimate degradation was pursued by substance-specific analysis applying atmospheric pressure chemical ionization (APCI) in combination with mass and tandem mass spectrometric detection (MS and MS-MS) either in the flow injection (FIA) or liquid chromatographic separation (LC) mode . APEOs were diminished by successive cleavage of polyether chain links resulting in short chain APEOs or alkylphenols (AP), if the biocoenosis was adapted to the compounds . Lipid regulating agents (LRA) were either eliminated completely (etofibrate), metabolized to fenofibratic acid (fenofibrate) or diminished to a minimal extent (bezafibrate) . Compared to the membrane microfiltration process the conventional activated sludge process was less successful in both APEO and LRA elimination.

J Hazard Mater, 2002 Oct 14, 94(3), 253 - 72
Feasibility of metal recovery from soil using DTPA and its biostability; Hong PK et al.; Removal of heavy metals from contaminated soil by chelation can be a valid remediation method . Important properties of the chelating agent used are: strength of the chelation bonding, reusability, and biostability during the remediation operation . This work tested the extraction, recovery, and biostability of diethylenetriaminepentaacetate (DTPA) as a remediation agent for soils contaminated with metals . Reported here are effects of parameters such as DTPA concentration, precipitant type and concentration, and pH relative to extraction and recovery efficiencies of the chelator, as well as workable recovery conditions . The assessment of biostability was determined at different DTPA concentrations, in aqueous and soil slurry systems, and in presence of lead using acclimated and unacclimated activated sludge cultures . The results showed that DTPA was capable of extracting lead from the tested contaminated soils and could be recovered by the use of cationic and anionic precipitants in alkaline pH conditions . It was biostable to some extent especially with unacclimated cultures . Thus, DTPA proved to be a strong and reusable chelating agent for some metals in soils, and it was relatively biostable, which makes it a valid remediation agent for soil metal extraction.

Microb Ecol, 2002 Oct, 44(3), 278 - 85 Epub 2002 Sep 12.
Presence of anaerobic bacteroides in aerobically grown microbial granules; Tay ST et al.; Microbial granules were grown in a column-type sequential aerobic sludge blanket reactor inoculated with activated sludge flocs taken from a wastewater treatment plant and containing a medium with glucose as the main carbon source . The reactor selected for granules that could settle rapidly by employing a short settling time of 2 min . Matured granules with diameters between 2 and 3 micro m were examined for anaerobic bacteria as their presence can signal the onset of diffusion limitation problems that can potentially diminish granule stability due to the bacterial production of fermentation gases and organic acids under anaerobic conditions . To detect the anaerobes in the granules, clones were constructed from 16S rRNA PCR amplicons . Two sequence types associated with a strict anaerobe Bacteroides spp . were identified from these clones . Fluorescence in situ hybridization (FISH) followed by confocal laser scanning microscopy (CLSM) demonstrated that cells of Bacteroides spp . were concentrated at a depth of approximately 800 micro m below the surface of the granule . Cell enumeration using flow cytometry showed that the percentage of labeled cells of Bacteroides spp . compared to total bacterial cells in the granules was 0.56% . This is the first study to use a suite of culture-independent techniques to report the presence of a defined species of anaerobic bacteria in aerobically grown microbial granules.

Water Sci Technol, 2002, 46(1-2), 99 - 104
Phylogenetic analysis and in situ identification of "Nostocoida limicola"-like filamentous bacteria in activated sludge from industrial wastewater treatment plants; Snaidr I et al.; The diversity of filamentous bacteria present in industrial wastewater treatment plants was analysed by a combination of classical and molecular-biological approaches . Many unknown filamentous bacteria were observed in about 80 screened activated sludge samples from different industries with sometimes severe bulking sludge problems . A special focus was paid to filaments which resembled "Nostocoida limicola", a filamentous bacterium which was found to be present in many WWTPs . These filamentous bacteria are hardly cultivable and only one strain was obtained and maintained in co-culture with a yeast . The 16S rRNA sequences of several other "Nostocoida limicola"-like filamentous bacteria from different sludge samples were obtained by micromanipulation and different molecular-biological methods . The sequences were phylogenetically analyzed and specific molecular probes were developed and applied . The results clearly demonstrate that "Nostocoida limicola"-like filaments from industrial WWTPs are different from all other "Nostocoida limicola" types investigated so far . Our strains are affiliated to the alpha-subclass of Proteobacteria.

Water Sci Technol, 2002, 46(1-2), 91 - 7
Phylogenetic and physiological characterization of a "Nostocoida limicola"-like organism isolated from activated sludge; Schade M et al.; Ten strains of "Nostocoida limicola"-like organisms were isolated from a municipal wastewater treatment plant with minor industrial effluent . The near complete 16S rDNA sequences were determined for four strains to analyze the position of the organisms within the phylogenetic tree . All four isolates showed the same 16S rRNA sequence and cluster within the green non sulfur bacteria . Hybridization with oligonucleotide probe AHW183 designed complementarily to diagnostic regions of the 16S rRNA sequences showed a positive reaction with all isolated strains . Hybridization of activated sludge samples with probe AHW183 indicates the filamentous "Nostocoida limicola"-like bacteria commonly to occur inside the sludge flocs and to hardly be detected within the flocs without a specific staining . On HA-medium all strains grow as long coiled, unbranched and unsheathed filaments which usually stain gram positive and show a variable Neisser reaction . The isolates grow well in liquid HA-medium at COD values between 1 to 4 g O2 h(-1) and a pH range from 6.0-7.8 . No growth is detected in liquid R2A-medium and several synthetic mineral salts media containing various carbon and nitrogen sources.

Water Sci Technol, 2002, 46(1-2), 81 - 90
Dispelling the "Nocardia amarae" myth: a phylogenetic and phenotypic study of mycolic acid-containing actinomycetes isolated from activated sludge foam; Stainsby FM et al.; Right-angle branched filaments and rods micromanipulated from activated sludge foam and mixed liquor were identified as putatively novel members of the genera Gordonia, Mycobacterium and Rhodococcus using a combination of chemical, molecular and morphological data . Pyrolysis mass spectrometric analyses of gordoniae isolated in both the present and a previous study revealed pyro-groups, distinct from validly described Gordonia species, which could be equated with those based on morphological properties and 16S rDNA data . Putative gordoniae assigned to one of these groups were found to be closely related to strains currently identified as "Rhodococcus australis" . These strains were also found to have properties consistent with their classification in the genus Gordonia . The results of this study highlight the limitations of the microscopic approach to filament identification and cast further doubt on the view that foaming can be attributed to members of one or a few Nocardia species.

Water Sci Technol, 2002, 46(1-2), 73 - 80
Microthrix parvicella, a specialized lipid consumer in anaerobic-aerobic activated sludge plants; Nielsen PH et al.; The in situ physiology of the filamentous bacterium Microthrix parvicella was investigated in anaerobic-aerobic dynamic phases in activated sludge with focus on the uptake of long chain fatty acids (LCFA) and growth . When 14C-labeled oleic acid was added to activated sludge with an excessive growth of M . parvicella, only little 14C-CO2 was produced under anaerobic conditions while a lot was produced under aerobic conditions . Microautoradiographic studies revealed that M . parvicella took up oleic acid under both anaerobic and aerobic conditions, while only a few floc formers were able to take it up under anaerobic conditions . Extraction and separation of the radioactive biomass into different lipid fractions showed that the oleic acid was stored mainly as neutral lipids under anaerobic conditions, whereas conversion to membrane phospholipids occurred almost exclusively under aerobic conditions, indicating growth . The surface properties of M . parvicella and other bacteria were characterized by hydrophobic fluorescent microspheres, which showed that M . parvicella was relatively hydrophobic . Furthermore, a surface-associated extracellular lipase activity was observed, indicating the ability of M . parvicella to degrade lipids near the filament surface . The results support the hypothesis that uptake and storage of LCFA as lipids under anaerobic conditions provide an effective competition strategy against bacteria that can only take up LCFA under aerobic conditions. , , , . Thus, M . parvicella seems to be a specialized lipid consumer with a physiological potential analogous to PAOs and GAOs being able to take up LCFA (but not short chain fatty acids or glucose) under anaerobic conditions and subsequently use the storage material for growth when nitrate or oxygen are available as electron acceptors.

Water Sci Technol, 2002, 46(1-2), 65 - 72
"Microthrix parvicella": a new approach for kinetic and physiological characterization; Rossetti S et al.; Two strains of "Microthrix parvicella" (RN1 and 4B strains) have been physiologically and kinetically characterized by utilizing a new technique particularly suitable for slow growing bacteria . The proposed method is based on the Total Extended Filament Length (TEFL) measure on filaments grown on agar surfaces . This allows us to study more easily and rapidly slow growing bacteria under many different conditions without altering the growth environment during the test . "Microthrix parvicella" appears to have versatile physiological capabilities allowing effective competition against other bacteria in the complex biocenosis of activated sludge . Main peculiarities of this organism are its storage capabilities under an aerobic/anoxic/anaerobic reaction environment, the resistance to long periods of anoxic/anaerobic conditions, the possibility of growing with appreciable kinetics at very low temperatures . In the kinetic characterization low Ks values have been observed; this finding supports the assumption that "Microthrix parvicella" is a "Ks- strategist" with high substrate affinity . Kinetics tests performed in a mixed population of activated sludge bacteria and on pure culture of filaments isolated from the same sludge sample showed that no beneficial effect on the growth rates of "Microthrix parvicella" seems attributable to the presence of activated sludge . This last result confirms the validity of pure culture studies for this microorganism and the reliability of physiological and kinetic data so evaluated in describing real systems.

Water Sci Technol, 2002, 46(1-2), 61 - 4
The effect of reactor configuration and operational mode on Microthrix parvicella bulking and foaming in nutrient removal activated sludge systems; Noutsopoulos C et al.; Three bench-scale nutrient removal activated sludge units were used to examine the effect of the reactor configuration and the intermittent aeration mode on the growth of Microthrix parvicella . According to the results, the plug flow configuration seems to achieve satisfactory Microthrix parvicella control . The imposed concentration gradient for both RBCOD and SBCOD creates a selective advantage for the floc forming bacteria throughout the system (both the anoxic and oxic zones) and limits Microthrix parvicella growth . In terms of the operational mode, the intermittent aeration CSTR nutrient removal system promotes the growth of M . parvicella and deteriorates the settling characteristics of the activated sludge.

Water Sci Technol, 2002, 46(1-2), 559 - 64
Application of oligonucleotide probes for the detection of Thiothrix spp . in activated sludge plants treating paper and board mill wastes; Kim SB et al.; Filamentous bacteria belonging to the genus Thiothrix were detected in activated sludge samples using the fluorescent in situ hybridisation (FISH) technique . A 16S rRNA-targeted oligonucleotide probe was developed for the detection of members of the T . fructosivorans group, and the performance of probe TNI for the detection of Thiothrix nivea group was enhanced by using an unlabeled competitor . A set of 5 probes covering all phylogenetic groups of Thiothrix were used to examine samples taken from selected activated sludge plants treating paper and board mill wastes . Members of the T . eikelboomii group formed the predominant filamentous bacterial population in plants experiencing poor sludge settleability, whereas members of the T . nivea group were commonly found but not dominantly in the remaining plants . Members of the T . fructosivorans group were not detected at any significant level in any of the samples . The distribution of the main Thiothrix types remained unchanged throughout the investigation period . It was evident that mixed populations of Thiothrix spp . were present in all activated sludge samples investigated, the observed differences were in the relative abundance of the various groups . These findings were supported by the results obtained using conventional microscopy.

Water Sci Technol, 2002, 46(1-2), 535 - 42
Filamentous micro-organisms observed in industrial activated sludge plants; Elkelboom DH et al.; As part of the EU-sponsored MACOBS (Monitoring and Control of Bulking Sludge through Molecular Probe Assays) project, the size and the composition of the filamentous population in 73 industrial activated sludge plants, were investigated . The inventory included plants in Denmark, Germany, Italy and The Netherlands . Large filamentous populations were present in about 60% of the plants, which means that bulking of activated sludge, which is no longer a serious problem in modern domestic nutrient removal plants, still occurs frequently in industrial treatment plants . The filamentous micro-organisms present were identified/described by "traditional" methods, based on their morphological features and several staining techniques, and by the application of molecular probes (FISH: Fluorescent In Situ Hybridisation) . Nine species specific probes were available when the project started, nine new probes have been developed during the project . Fifty nine different filamentous species were observed in the samples, including ca . 40 species that have not been described so far . The unknown species are denoted as Type Ind-1, 2, 3, etc . Probes are now available for the identification of about 17 species . Further research aimed at developing additional probes will be necessary in order to establish which species distinguished provisionally are identical, viz . morphotypes of the same filamentous organism.

Water Sci Technol, 2002, 46(1-2), 529 - 33
Are filamentous mycolata important in foaming?
Davenport RJ, Curtis TP.
In a previous study, we showed that there was a significant increase in mycolata numbers associated with foaming events at a wastewater treatment site possessing three activated sludge plants . In this paper, we demonstrate that branched filamentous mycolata were a minor proportion of the mycolata morphotypes present in those activated sludge plants, accounting for less than 21% of the mycolata population in the mixed liquor and foam samples examined . In most samples examined, the number of filamentous mycolata was negligible compared to the number of other mycolata morphotypes present . Furthermore, filamentous mycolata did not contribute to any of the significant differences in mycolata concentration observed between foaming and non-foaming situations (P<0.01) . These findings suggest that conventional microscopic examination for monitoring mycolata populations in foaming plants may be misleading and should be used with caution.

Water Sci Technol, 2002, 46(1-2), 525 - 8
An investigation into studying of the activated sludge foaming potential by using physicochemical parameters; Hladikova K et al.; This paper examines how the physicochemical characteristics of the solids are related to foam formation and describes how the foaming potential of full-scale plants can be assessed . The relations among activated sludge and biological foam hydrophobicity, scum index, aeration tank cover and filamentous population are evaluated . Individual parameter comparison reveals the scumming intensity can be estimated only on the assumption that foams is already established . None of the above mentioned characteristics can be reliably used to predict the foaming episodes at wastewater treatment plants.

Water Sci Technol, 2002, 46(1-2), 519 - 24
Gordonia (nocardia) amarae foaming due to biosurfactant production; Pagilla KR et al.; Gordonia amarae, a filamentous actinomycete, commonly found in foaming activated sludge wastewater treatment plants was investigated for its biosurfactant production capability . Soluble acetate and paringly soluble hexadecane were used as carbon sources for G . amarae growth and biosurfactant production in laboratory scale batch reactors . The lowest surface tension (critical micelle concentration, CMC) of the cell-free culture broth was 55 dynes/cm when 1,900 mg/L acetate was used as the sole carbon source . The lowest surface tension was less than 40 dynes/cm when either 1% (v/v) hexadecane or a mixture of 1% (v/v) hexadecane and 0.5% (w/v) acetate was used as the carbon source . The maximum biomass concentration (the stationary phase) was achieved after 4 days when acetate was used along with hexadecane, whereas it took about 8 days to achieve the stationary phase with hexadecane alone . The maximum biosurfactant production was 3 x CMC with hexadecane as the sole carbon source, and it was 5 x CMC with the mixture of hexadecane and acetate . Longer term growth studies (approximately 35 days of culture growth) indicated that G . amarae produces biosurfactant in order to solubilize hexadecane, and that adding acetate improves its biosurfactant production by providing readily degradable substrate for initial biomass growth . This research confirms that the foaming problems in activated sludge containing G . amarae in the activated sludge are due to the biosurfactant production by G . amarae when hydrophobic substrates such as hexadecane are present.

Water Sci Technol, 2002, 46(1-2), 511 - 8
Fighting foam with phages?
Thomas JA, Soddell JA, Kurtboke DI.
Seventeen (17) phages infective for the mycolata were isolated from six samples of activated sludge using 21 prospective hosts from the genera Dietzia, Gordonia, Nocardia, Rhodococcus, Tsukamurella and Mycobacterium . Their morphology indicated that they were all members of the viral family Siphoviridae, but they varied in the size of the icosahedral head and length of non-contractile tail, suggesting they were different . This was confirmed by host-range studies with 47 strains of mycolata, which showed that each phage had a unique host-range, and this was polyvalent in the majority (15/17) of cases, with 12 phages infective for hosts representing two or three of the genera Gordonia, Nocardia and Rhodococcus . The potential for use of these phages in the control of foaming and other applications is discussed.

Water Sci Technol, 2002, 46(1-2), 507 - 10
A full scale application in the control of the filamentous bulking generated by Type 021 N F . thiothrix sp; Guida M et al.; The presence of industrial effluent in the wastewater incoming to municipal activated sludge treatment plants sometimes causes bulking events . In order to control one of these events a strategy of bacterial selection was applied with an anoxic selector before the main oxidation basin utilising the screw pumps basin . The result of this work confirms what is reported in the literature about the possibility to utilize a metabolic control of some filamentous forms (particularly Type 021 N) with high organic load . The remedial action could be realized using already existing facilities, without any additional costs.

Water Sci Technol, 2002, 46(1-2), 499 - 502
Microthrix parvicella foaming at the Fusina WWTP; Miana P et al.; The Fusina WWTP receives civil and industrial wastewater from Venice and its hinterland . Its treatment capacity is in the range of 4,000-5,000 m3/h . In winter the Fusina WWTP is subjected to brown and viscous foams developed on the surface of the aeration basins and of the clarifiers . The microscopic observation of biological foams and activated sludge samples showed high concentration of the filamentous organism Microthrix parvicella . This paper investigates the growth of M . parvicella from January 1998 to January 1999 and relates it to foams developed on the aeration basins and clarifiers, to temperature, surfactants, BOD5, NH4, NO3, NO2, DO, PO4 and pH of the wastewater influent, to SVI and the other species of filamentous organisms of mixed liquor . The results demonstrate the strong connection of the foams developed with M . parvicella abundance, the synergic action with surfactants, the dependence of M . parvicella on temperature and no relation to the other chemical and physical parameters investigated.

Water Sci Technol, 2002, 46(1-2), 495 - 8
Testing the effect of selectors in the control of bulking and foaming in full scale activated-sludge plants; Davoli D et al.; Selectors were operated at four full-scale activated sludge plants to control bulking and foaming problems due to filamentous microorganisms . Selector effectiveness was not related to reduction of biodegradable organic matter in the contact zone, but was related to soluble COD levels in selector effluent . Significant reductions in the numbers of filamentous m icroorganisms were reported.

Water Sci Technol, 2002, 46(1-2), 487 - 90
The influence of PAX-14 on activated sludge systems and in particular on Microthrix parvicella; Roels T et al.; The amount of wastewater treatment plants (WWTP) dealing with solid separation problems has significantly increased since the new requirements of the EU Directive 271/91 on nutrient removal . In Flanders a number of the nutrient removal WWTP are affected by solid separation problems mostly attributed to Microthrix parvicella being the most common dominant species . The effect of dosing polyaluminium chloride (PAX-14) on activated sludge is illustrated for WWTP solids separation problems, in particular because of Microthrix parvicella . The effects of the addition of PAX-14 on the microbiology and the morphology of Microthrix parvicella were studied in 9 full-scale WWTP . PAX-14 succeeded in reducing high SVI-values and controlled foaming problems whenever caused by Microthrix parvicella . Laboratory trials have shown that the dosage of PAX-14 should be less than 150 microL/L or 7 g Al3+/kg MLSS . At a dosage higher than 250 microL/L, an increase of free bacteria and a decrease of the protozoa activity are observed . In full-scale, PAX-14 is dosed at a concentration of 1.5 to 4.5 g Al3+/kg MLSS . Before addition, the mixed liquor scum layer--if present--should be removed . In our experience, the dosing should last for at least 3 weeks . During the first week, no drastic changes occur . At the end of the first week, an increase of SS and SVI is possible . The SVI and scum start to decrease after 10 to 15 days . The amount of filaments is reduced after 3 to 3 1/2 weeks . The morphological properties of Microthrix parvicella change, while other filaments such as Nostocoida limicola and Nocardia spp . are not affected . This study proves that PAX-14 is effective in controlling bulking and foaming problems at WWTPs when they are due to Microthrix parvicella . Prediction of when the SVI will decrease and when addition should be stopped is possible.

Water Sci Technol, 2002, 46(1-2), 471 - 8
Microbial evaluation of activated sludge and filamentous population at eight Czech nutrient removal activated sludge plants during year 2000; Krhutkova O et al.; The long-term project on the survey of filamentous microorganisms, which started in 1996, was finished in 2000 by the survey of eight Czech activated sludge plants with biological nutrient removal (BNR) systems . At all plants with enhanced biological nutrient removal, specific microbial population (mostly from the point of view of filaments occurrence), operational problems (presence of biological foaming, bulking) and plant operation were observed periodically and longer than 1 year . In our paper the relationship between the composition of activated sludge (especially filaments) consortia and modification of the process with nutrient removal is discussed . At the surveyed plants Type 0092 and Microthrix parvicella were identified as dominant Eikelboom filamentous types.

Water Sci Technol, 2002, 46(1-2), 457 - 64
Bulking sludge solved?!
Kruit J, Hulsbeek J, Visser A.
At present there is still no final theory explaining the bulking of activated sludge . Previous investigations showed that the sludge settling properties become better and more stable when more plug flow conditions are implemented in wastewater treatment plants for biological nutrient removal . In this research the effect of the process configuration (4 wwtp with fully biological nutrient removal) on the sludge settling properties has been investigated . The results show that a separate anoxic reactor can not avoid the presence of LCFA for the growth of M . parvicella in the anaerobic reactor . A SVI < 120 ml/g could be achieved by: of a separate anoxic reactor with plug flow conditions, introducing of a strictly anaerobic reactor (UCT-modification), implementation of an extra anoxic/aerobic reactor, maintaining a high oxygen concentration (> 1.5 mg/l) and creating a low ammonium concentration (< 1 mg/l) in the aerobic reactor.

Water Sci Technol, 2002, 46(1-2), 453 - 6
Characteristics of bacterial populations responsible for uptake of amino acids in activated sludge acclimated to peptone; Ubukata Y et al.; Amino acids (AAs) are produced from the hydrolysis of proteins, which are the major biodegradable organic compounds in municipal sewage . The characteristics of bacterial populations responsible for the assimilation of thirteen AAs into activated sludge (AS) acclimated to peptone are investigated . The results are as follows . (1) The bacterial populations responsible for the uptake of AAs were partly aggregated in AS flocs . (2) The amounts of the bacterial populations responsible for the uptake of leucine, valine, isoleucine, histidine, threonine, lysine and glycine are limited in AS acclimated to peptone . (3) The bacterial populations responsible for the uptake of phenylalanine, leucine and lysine were different . (4) The amounts of bacterial populations responsible for the uptake of aspartate, arginine, alanine, glutamate and phenylalanine are not limited . (5) The functions of the assimilation of these AAs were induced in many bacterial cells as a result of the BOD determination methods applied to these pure AAs.

Water Sci Technol, 2002, 46(1-2), 449 - 52
Genomic fingerprinting of the 16S-23S gene spacer region suggests that novel Acinetobacter isolates are present in activated sludge; Carr E et al.; The taxonomic status of the genus Acinetobacteris currently confused and the role of these organisms in activated sludge is poorly understood . Currently unidentified isolates of Acinetobacterfrom activated sludge were fingerprinted by making use of polymorphisms in their 16S-23S rDNA spacer region . The PCR amplified 16S-23S rDNA spacer region was digested with five different restriction enzymes to further differentiate between the isolates . The resulting band patterns were very diverse and the data suggests that the activated sludge isolates are different to the known genomic species of Acinetobacter which are predominantly clinical isolates . The results of this study imply the existence of yet unrecognised species of Acinetobacter in activated sludge.

Water Sci Technol, 2002, 46(1-2), 431 - 8
Effect of solids retention time on floc structure; Liss SN et al.; Correlative microscopy was applied to study the influence of solids retention time on activated sludge floc structure . Conventional optical microscopy revealed flocs at lower SRTs (4 and 9 days) to be irregular in shape while flocs at higher SRTs (16 and 20 days) had a more spherical and compact structure . Flocs were examined by environmental scanning electron microscopy (ESEM) and by transmission electron microscopy (TEM) coupled with energy-dispersive spectroscopy (EDS) . Distinctive differences in floc structure and the arrangement of EPS were revealed . Flocs from higher SRTs were less hydrated and were found to possess a dense EPS layer that covers much of the surface . Extracellular osmiophilic granules present in these flocs indicate that the cells at the higher SRT may produce more lipid-like material . This EPS layer appears to decrease the floc surface roughness and protects the interior cells from disruption by changes in the external environment . Sludge flocs at higher SRTs were found to be physically more stable than those at lower SRTs.

Water Sci Technol, 2002, 46(1-2), 413 - 7
A comparison among different methods for evaluating the biomass activity in activated sludge systems: preliminary results; Andreottola G et al.; In order to improve activated sludge plant operation (achieving higher efficiency and cost savings) beside influent and effluent characteristics and working parameters (e.g . dissolved oxygen, total and volatile suspended solids, pH, recirculation flow rate, etc.), the biomass activity should be monitored, the bacteria being responsible for the pollutant degradation . Since conventional cultivation based methods are inadequate to quantify environmental microorganisms (due to scarce number of cultivable microorganisms and time-consuming procedures) several "non-conventional" techniques were applied in this study, in order to compare the obtainable information and their routine feasibility . Different measurements (VSS concentration, Oxygen Uptake Rate, microbial counts by cultural and biomolecular methods--MPN-PCR, ATP content, dehydrogenase activity, microbial cell viability and enzymatic activity) were carried out on mixed liquor samples, taken from a municipal activated sludge plant (440,000 p . e.) . The preliminary results of the research are presented in this paper.

Water Sci Technol, 2002, 46(1-2), 397 - 404
Active heterotrophic and autotrophic biomass distribution between fixed and suspended systems in a hybrid biological reactor; Ochoa JC et al.; This paper presents the results obtained when modifying sludge retention time (SRT 8, 5, and 3.7 days during phases A, B and C respectively) for a hybrid biological reactor (HR) compared with a classical activated sludge process . The study was conducted by following active biomass evolution and distribution for two lab-scale pilots plants operating with the same conditions, one acting as HR and the other as the control reactor (CR) without support material . At the end of phase C, support material was split into two fractions between both reactors to study the effect of support to reactor volume ratio (Fr) . Active biomasses in suspended and fixed systems were calculated using respirometric techniques . Evolutions of active autotrophic and heterotrophic biomasses for both reactors are presented during all the operational periods and it is observed that in the HR biomass concentrations are up to double that in the CR, mainly due to the presence of support material . When studying biomass distribution in HR, autotrophic biomass is mainly located over the support material (from 95% to 99% during periods A and C respectively) while only about 60% of heterotrophic biomass is located over the support.

Water Sci Technol, 2002, 46(1-2), 39 - 43
Bacteriophage-host interaction in the enhanced biological phosphate removing activated sludge system; Khan MA et al.; Bacteriophages were isolated from a laboratory scale enhanced biological phosphate removing (EBPR) activated sludge process, and their host range was examined . Bacterial isolates to host the bacteriophages were isolated from the EBPR activated sludge process . Bacteriophages were eluted from the EBPR activated sludge, enriched by incubation with the bacterial isolates, and then tested for plaque formation on each of the bacterial isolates . Out of 12 bacterial isolates isolated, 4 supported plaque formation . Four bacteriophages were obtained from the plaques . The host range test was conducted with the combination of the bacteriophage isolates and the bacterial isolates . Three of the bacteriophages were found to form plaques on more than one host, and one of them formed plaques on both gram +ve and gram -ve bacterial isolates . Two of the four bacteriophages failed to form plaques on their original bacterial host, indicating the existence of mutation on either both or one of the host and the bacteriophage . This study strongly suggests that bacteriophages are an active part of the activated sludge microbial ecosystem, having very complex interaction with their host bacteria.

Water Sci Technol, 2002, 46(1-2), 381 - 7
On the development of a novel image analysis technique to distinguish between flocs and filaments in activated sludge images; Cenens C et al.; The ratio of flocs to filaments in activated sludge wastewater treatment plants is of extreme importance for the overall performance of the plant . In order to control this ratio the individual concentrations of flocs and filaments need to be measurable . However, no sensors which can measure these concentrations are currently available . In this paper it is outlined how a distinction can be made between flocs and filaments by means of image analysis techniques . Combination of this information with the total biomass concentration results in the individual floc and filament concentrations . The distinction of objects of interest from the background is a crucial step in the image analysis procedure . An automatic thresholding algorithm is proposed which selects two thresholds in images with one fraction darker than the background and the other fraction brighter than the background . Once the objects are separated from the background, they are classified as either flocs or filaments by means of the reduced radius of gyration.

Water Sci Technol, 2002, 46(1-2), 371 - 9
Biomass active fraction evaluated by a direct method and respirometric techniques; Andreottola G et al.; The knowledge of the active biomass amount and its characterisation is of primary importance for the management and for the design of wastewater treatment plants on the basis of the recently developed models . OUR curves obtained in aerobic exponential growth tests are proposed by several authors as an indirect method to estimate the active fraction . The aim of this work is the application of a direct method to measure the viable biomass based on flow cytometry techniques and the comparison with the active fraction obtained from respirometric tests . To assess the viable fraction of a biomass expressed in terms of COD concentration it is necessary to estimate the biovolume of viable bacteria and to know the specific carbon content per cell . For the investigated activated sludge samples, the bacterial biomass measured by FCM was 588 mgCOD L(-1) on average in a two-months period . This value of active fraction corresponds to 14% of particulate COD . Active biomass values measured with the respirometric approach were consistent but generally higher than those obtained by FCM.

Water Sci Technol, 2002, 46(1-2), 363 - 9
Study of filamentous bacteria by image analysis and relation with settleability; da Motta M et al.; An automated procedure for the characterisation by image analysis of the morphology of activated sludge has been used to monitor the biomass in a pilot wastewater treatment plant during two runs inoculated with a different sludge and operated at two different temperatures . The bulking events were easily detected by image analysis . Correlations were found between settleability properties (Sludge Volume Index and settling velocity) and the morphological parameters (filament total length, filament number and floc size).

Water Sci Technol, 2002, 46(1-2), 357 - 61
Gas chromatographic analysis of polyhydroxybutyrate in activated sludge: a round-robin test; Baetens D et al.; Polyhydroxyalkanoates (PHA) and poly-beta-hydroxybutyrate (PHB) in particular have become compounds which is routinely investigated in wastewater research . The PHB analysis method has only recently been applied to activated sludge samples where PHA contents might be relatively low . This urges the need to investigate the reproducibility of the gas chromatographic method for PHB analysis . This was evaluated in a round-robin test in 5 European laboratories with samples from lab-scale and full-scale enhanced biological phosphorus removal systems . It was shown that the standard deviation of measurements in each lab and the reproducibility between the labs was very good . Experimental results obtained by different laboratories using this analysis method can be compared . Sludge samples with PHB contents varying between 0.3 and 22.5 mg PHB/mg sludge were analysed . The gas chromatographic method allows for PHV, PH2MB and PH2MV analysis as well.

The activated-sludge process is a biological method of wastewater treatment that is performed by a variable and mixed community of microorganisms in an aerobic aquatic environment. These microorganisms derive energy from carbonaceous organic matter in aerated wastewater for the production of new cells in a process known as synthesis, while simultaneously releasing energy through the conversion of this organic matter into compounds that contain lower energy, such as carbon dioxide and water, in a process called respiration. As well, a variable number of microorganisms in the system obtain energy by converting ammonia nitrogen to nitrate nitrogen in a process termed nitrification. This consortium of microorganisms, the biological component of the process, is known collectively as activated sludge.

Autotrophic bacteria in activated sludge reduce oxidized carbon compounds such as carbon dioxide for cell growth. These bacteria obtain their energy by oxidizing ammonia nitrogen to nitrate nitrogen in a two-stage conversion process known as nitrification. Due to the fact that very little energy is derived from these oxidization reactions, and because energy is required to convert carbon dioxide to cellular carbon, nitrifying bacteria represent a small percentage of the total population of microorganisms in activated sludge. In addition, autotrophic nitrifying bacteria have a slower rate of reproduction than heterotrophic, carbon-removing bacteria. Two genera of bacteria are responsible for the conversion of ammonia to nitrate in activated sludge, Nitrobacter and Nitrosomonas.

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