What Is Bioassay?

Bioassay (Biological Assay) is a procedure for the determination of the concentration of a particular constituent of a mixture.

A Bioassay is a measurement of the effects of a substance on living organisms.

Biological Assay is method of measuring the effects of a biologically active substance using an intermediate in vivo or in vitro tissue or cell model under controlled conditions. It includes virulence studies in animal fetuses in utero, mouse convulsion bioassay of insulin, quantitation of tumor-initiator systems in mouse skin, calculation of potentiating effects of a hormonal factor in an isolated strip of contracting stomach muscle, etc.

Examples of Biological Assay:

- Limulus Test

- Endpoint Determination

Limulus Test is a sensitive method for detection of bacterial endotoxins and endotoxin-like substances that depends on the in vitro gelation of Limulus amebocyte lysate (LAL), prepared from the circulating blood (amebocytes) of the horseshoe crab, by the endotoxin or related compound. Used for detection of endotoxin in body fluids and parenteral pharmaceuticals.

Endpoint Determination is an establishment of the level of a quantifiable effect indicative of a biologic process. The evaluation is frequently to detect the degree of toxic or therapeutic effect.

What Is Activated Sludge?

Activated sludge is a 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.

The activated sludge process is a wastewater treatment method in which the carbonaceous organic matter of wastewater provides an energy source for the production of new cells for a mixed population of microorganisms in an aquatic aerobic environment. The microbes convert carbon into cell tissue and oxidized end products that include carbon dioxide and water. In addition, a limited number of microorganisms may exist in activated sludge that obtain energy by oxidizing ammonia nitrogen to nitrate nitrogen in the process known as nitrification.

Bacteria constitute the majority of microorganisms present in activated sludge. Bacteria that require organic compounds for their supply of carbon and energy (heterotrophic bacteria) predominate, whereas bacteria that use inorganic compounds for cell growth (autotrophic bacteria) occur in proportion to concentrations of carbon and nitrogen. Both aerobic and anaerobic bacteria may exist in the activated sludge, but the preponderance of species are facultative, able to live in either the presence of or lack of dissolved oxygen.

Fungi, rotifers, and protozoans are also residents of activated sludge. The latter microorganisms are represented largely by ciliated species, but flagellated protozoans and amoebae may also be present. Protozoans serve as indicators of the activated sluge condition, and ciliated species are instrumental in removing Escherichia coli from sewage. Additionally, viruses of human origin may be found in raw sewage influent, but a large percentage appear to be removed by the activated-sludge process.

The success of the activated-sludge process is dependent upon establishing a mixed community of microorganisms that will remove and consume organic waste material, that will aggregate and adhere in a process known as bioflocculation, and that will settle in such a manner as to produce a concentrated sludge (return activated sludge, or RAS) for recycling. Any of several types of activated sludge solids separations problems indicate an imbalance in the biological component of this process. In the ideal "healthy" system, filamentous organisms grow within a floc (a large aggregate of adherent, or floc-forming, microorganisms, such as bacteria) and give it strength, with few filaments protruding out into the surrounding bulk solution. In such a system, there is no interference with the compaction and settling rates of the activated sludge prior to its recycling.

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.

The overall goal of the activated-sludge process is to remove substances that have a demand for oxygen from the system. This is accomplished by the metabolic reactions (synthesis-respiration and nitrificaction) of the microorganisms, the separation and settling of activated-sludge solids to create an acceptable quality of secondary wastewater effluent, and the collection and recycling of microorganisms back into the system or removal of excess microorganisms from the system.

Aactivated-sludge process contains five essential interrelated equipment components.

The first is an aeration tank or tanks in which air or oxygen is introduced into the system to create an aerobic environment that meets the needs of the biological community and that keeps the activated sludge properly mixed. At least seven modifications in the shape and number of tanks exist to produce variations in the pattern of flow.

Second, an aeration source is required to ensure that adequate oxygen is fed into the tank(s) and that the appropriate mixing takes place. This source may be provided by pure oxygen, compressed air or mechanical aeration. Just as there are modifications in the shape and number of aeration tanks that can be used in the activated-sludge process, different equipment systems exist to deliver air or oxygen into aeration tanks.

Third, in the activated-sludge process, aeration tanks are followed by secondary clarifiers. In secondary clarifiers, activated-sludge solids separate from the surrounding waterwater by the process of flocculation (the formation of large particle aggregates, or flocs, by the adherence of floc-forming organisms to filamentous organisms) and gravity sedimentation, in which flocs settle toward the bottom of the clarifier in a quiescent environment. This separation leads ideally to the formation of a secondary effluent (wastewater having a low level of activated-sludge solids in suspension) in the upper portion of the clarifier and a thickened sludge comprised of flocs, termed return activated sludge, or RAS, in the bottom portion of the clarifier.

Fourth, return activated sludge must be collected from the secondary clarifiers and pumped back to the aeration tank(s) before dissolved oxygen is depleted. In this way, the biological community needed to metabolize influent organic or inorganic matter in the wastewater stream is replenished.

Fifth, activated sludge containing an overabundance of microorganisms must be removed, or wasted (waste activated sludge, or WAS), from the system. This is accomplished with the use of pumps and is done in part to control the food-to-microorganism ratio in the aeration tank(s).

The biological component of the activated sludge system is comprised of microorganisms. The composition of these microorganisms is 70 to 90 percent organic matter and 10 to 30 percent organic matter. Cell makeup depends on both the chemical composition of the wastewater and the specific characteristics of the organisms in the biological community. (Water Environment Association, 1987)

Bacteria, fungi, protozoa, and rotifers constitute the biological component, or biological mass, of activated sludge. In addition, some metazoa, such as nematode worms, may be present. However, the constant agitation in the aeration tanks and sludge recirculation are deterrents to the growth of higher organisms.

The species of microorganism that dominates a system depends on environmental conditions, process design, the mode of plant operation, and the characteristics of the secondary influent wastewater. (Water Environment Association, 1987) The microorganisms that are of greatest numerical importance in activated sludge are bacteria, which occur as microscopic individuals from one micron in size to visible aggregations or colonies of individuals. Some bacteria are strict aerobes (they can only live in the presence of oxygen), whereas others are anaerobes (they are active only in the absence of oxygen). The preponderance of bacteria living in activated sludge are facultative—able to live in either the presence or absence of oxygen, an important factor in the survival of activated sludge when dissolved oxygen concentrations are low or perhaps approaching depletion.

While both heterotrophic and autotrophic bacteria reside in activated sludge, the former predominate. Heterotrophic bacteria obtain energy from carbonaceous organic matter in influent wastewater for the synthesis of new cells. At the same time, they release energy via the conversion of organic matter into compounds such as carbon dioxide and water. Important genera of heterotrophic bacteria include Achromobacter, Alcaligenes, Arthrobacter, Citromonas, Flavobacterium, Pseudomonas, and Zoogloea.

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.

Nitrification generally occurs when the time that the sludge stays in the system (called the mean cell residence time, or MCRT) is increased. A longer mean cell residence time, therefore, allows an adequate population of nitrifying bacteria to be built up. However, because the oxygen demand for complete nitrification is high, both the necessary oxygen supply and power requirements for the system will be increased. Moreover, optimum pH for the growth of nitrifying bacteria is in the 8 to 9 range, with pH levels below 7 causing a substantial reduction in nitrification activity. In the process of converting ammonia to nitrate, mineral acidity is produced. In instances when insufficient alkalinity exists, the pH in the system will drop, potentially inhibiting nitrification. Finally, though nitrification occurs over a wide range of temperatures, a reduction in temperature produces a slower rate of reaction. (Water Environment Society, 1987)

Some activated sludge systems have been designed specifically to promote the higher growth rate of bacteria that remove carbon from influent wastewater, and adding chemicals may suppress nitrification. Other systems are operated to achieve nitrification in the second stage of a two-stage activated-sludge system due to the longer mean cell residence time (MCRT) necessary for nitrification. Still other systems are designed to promote nitrification. (Water Environment Society, 1987)

Fungi are also a constituent of activated sludge. These multicellular organisms metabolize organic compounds and can successfully compete with bacteria under certain environmental conditions in a mixed culture. (Water Environment Society, 1987) In addition, a small number of fungi are capable of oxidizing ammonia to nitrite, and fewer still to nitrate. (Painter, 1970) The most common sewage fungus organisms are Sphaerotilus natans and Zoogloea sp. (Curtis, 1969)

A number of species of protozoa have been identified in activated sludge. Protozoa are single-celled organisms that can consume food such as bacteria and particulate matter. Ciliated protozoa are numerically the most common species in activated sludge, but flagellated protozoa and amoebae may also be present. The species of ciliated protozoa most commonly observed in wastewater treatment processes include Aspidisca costata, Carchesium polypinum, Chilodonella uncinata, Opercularia coarcta and O. microdiscum, Trachelophyllum pusillum, Vorticella convallaria and V. microstoma

Protozoa are a useful biological indicator of the condition of the activated sludge. Being strict aerobes, these microorganisms prove to be excellent indicators of an aerobic environment (though some protozoa are capable of surviving up to 12 hours in the absence of oxygen). Protozoa also act as indicators of a toxic environment, as they exhibit a greater sensitivity to toxicity than bacteria. A clue that toxicity may be a problem in a system is the absence of or a lack of mobility of these organisms in activated sludge. The hallmark of a well-operated, stable activated-sludge system is the existence of large numbers of highly evolved protozoa in the biological mass.

Rotifers are multicellular aquatic microorganisms that look like rapidly revolving wheels when they are in motion. This is due to the fact that the anterior end of the animal is modified into a retractible disc, or corona, bearing circles of strong cilia. Rotifers are able to consume both microbes and particulate matter. Like protozoa, these microorganisms are strict aerobes and are more sensitive to toxic conditions than bacteria. Rotifers are found only in a very stable activated-sludge environment.

Finally, viruses are also found in wastewater, particularly human viruses that are excreted in large quantities in feces. These human enteric viruses can be divided into six major subgroups: adenovirus, coxsackievirus, echovirus, infectious hepatitus, poliovirus, and reovirus. Viruses native to animals and plants exist in lesser quantities in wastewater, and bacterial viruses may also be present. (Grabow, 1968) While Grabow (1968) notes that there is a quantitative reduction of these viruses by the activated-sludge treatment process, the author states that the mechanism by which they are removed or deactivated remains to be clearly explained. Different mechanisms indicated by the work of various researchers included inactivation of viruses by biological antagonists in the sludge, adsorption, and reduction in which suspended solids, colloidal material, aeration, and perhaps toxic substances play a role.

Before ending my discussion of the biological component of the activated-sludge process and discussing solids separation, factors affecting the efficiency of the process in removing carbonaceous organic material and achieving nitrification should be mentioned. These factors have been summarized in Activated Sludge, Manual of Practice #9 (Water Environment Society, 1987) and include: how readily organic material and ammonia can be metabolized by the microorganisms; the mean cell retention time (MCRT) and food-to-microorganism ratio; how readily organic material can be oxidized and used for cell synthesis; the number and types of active microorganisms present in the aeration tank(s); environmental factors such as dissolved oxygen concentration, nutrients, pH, temperature, and presence of toxic materials; adequacy of the original design for mixing, RAS (return activated sludge) and WAS (waste activated sludge) pumping, and aeration capacity; proper maintenance of plant equipment; and adequate training of plant staff.

Achromobacter, Alcaligenes, Arthrobacter, Citromonas, Flavobacterium, Pseudomonas, and Zoogloea, appear to be the primary floc-forming microorganisms.

Immobilization materials mixed with activated sludge as column biofilters for the treatment of gaseous stream containing benzene and toluene. Syu, MJ; Wang, YW. Bioprocess Engineering, 21(3): 239-244. 1999

ABSTRACT Activated sludge has been utilized for the treatment of volatile organic compounds (VOCs) which are emitted from industrial processes. Nevertheless, activated sludge systems often suffer from the problem caused by concentration gradients as well as pressure drops. Channeling is also a major problem in the treatment process. As the bed height of the packed activated sludge system increases, the pressure drop increases accordingly. To solve these problems, we proposed immobilized activated sludge column reactors for treating VOCs in air. The immobilization material used to mix with activated sludge was properly selected in this work. Elemental compositions of these materials were analyzed. In this study, we also proposed a VOC feed system so that more stable inlet concentrations could be achieved. Hence, the equipment and operating costs were reduced and the problem of VOCs leaking from peristaltic pumps was avoided. The moisture content of the system was well maintained and better VOC removal efficiency was achieved. With an operation condition of progressive VOC inlet concentrations, better removal efficiency of benzene and toluene was then obtained. In conclusion, by the utilization of immobilization materials selected from wastes as well as immobilized activated sludge column reactors, significant removal efficiency for both benzene and toluene was demonstrated.

Treating VOC-contaminated gases in activated sludge: Mechanistic model to evaluate design and performance. Bielefeldt, AR; Stensel, HD. Environmental Science & Technology, 33(18): 3234-3240. 1999

ABSTRACT A mechanistic model based on independently measurable mass transfer and biokinetic parameters was developed to describe the removal of volatile organic compounds (VOCs) contained in air sparged into activated sludge (suspended growth) gas treatment reactor. The critical mass transfer parameters are the VOC mass transfer coefficient (Kla(voc)), VOC Henry's coefficient (H) and diffusion coefficient in water, gas flow rate per unit reactor area, and liquid depth. The Kla(voc) is equal to the oxygen Kla (Kla(O2)) multiplied by the ratio of the VDC to oxygen diffusivity coefficients in water raised to the power n. Depending on the system power intensity, n ranges from 0.5 to 1.0; 1.0 provides a conservative design. Biokinetic parameters of importance include the Monod coefficients, biomass yield and endogenous decay coefficients, and solids retention time (SRT). The model accurately predicted BTEX removal from air diffused into a 2-L, 40-cm deep lab-scale reactor. Based on the model, a 2-m deep gas treatment reactor should provide >80% gas treatment efficiency for VOCs with H < 0.35, when the reactor is operated at an SRT which maintains the VOC liquid concentration below 0.1 mg/L, with a Kla(O2) of 40 h(-1) at an air application rate of 55 m(3)/m(2)-h.

Biological deodorization using activated carbon fabric as a carrier of microorganism. Lee-S-K; Shoda-M. J.Ferment.Bioeng.; 68(6): 437-444. 1989

ABSTRACT: The biological deodorization of methyl mercaptan (MM) was studied using an activated C fabric as a support of microorganisms. Seeding the C fabric was done by submerging or spraying with digested sludge obtained from a night soil treatment plant. 2 l/kg dry C fabric of digested sludge was seeded. The weight of packed C fabric was 40 g and the packing volume was 240 ml in each column. The MM concentration decreased with time and was undetectable 1 wk later, and the concentration of DMDS (dimethyl disulfide)increased to a maximum of 1.3 ppm in 1 wk. After 12 days neither DMDS or MM was detected due to the acclimation of microorganisms indigenous to the sludge to both gases. The C fabric was compared with sponge, polyester cloth and carbonized coal as carriers. At an inlet concentration of 20 ppm MM, MM and DMDS were not detected with the C fabric. MM was not detected in the other columns, although DMDS was detected in the effluent for 10 days. The critical load of MM was determined as 0.48 g S/kg C fabric/day. Vmax was 0.69 g S/kg C fabric/day and Ks was 7.7 ppm. About 80% of MM removed in the biofilter was converted into the sulfate ion. (13 ref)

Activated Sludge

Activated Sludge is a widely used aerobic method of sewage treatment. After primary settling, the waste stream is brought to an aeration tank. Air is put in and/or there is mechanical stirring which provides aeration of the waste. Sludge from a previous run is usually reintroduced to the tanks to provide microorganisms. This is why it is called activated sludge. During the period in the aeration tank, large developments of heterotrophic organisms occur. In the activated sludge tank the bacteria occur in free suspension and as aggregates or flocs. Extensive microbial metabolism of organic compunds in the sewage results in the production of new microbial biomass. Most of this biomass becomes associated with flocs that can be removed from suspension by settling. A portion of the settled sewage sludge is recycled and the remainder must be treated by composting or anaerobic digestion. Combined with primary settling, activated sludge reduces the BOD by 85% to 90%. It also drastically reduces the number of intestinal pathogens. An illustration of an aeration basin is shown below.

The water used by each household is transported through a collective underground sewer system that ends at the municipal wastewater treatment plant. When the wastewater first arrives at the treatment plant it undergoes screening to remove the large solids and grit that may be present. The screened water then undergoes primary treatment that involves the settling of suspended solids. The solids are collected as primary sludge, while the primary wastewater then goes onto secondary treatment. In secondary treatment, "activated sludge" microbes consume the dissolved and suspended organics in the wastewater and grow, and then solids are again removed by flocculation and collected. The final 'sludge' is a combination of the primary sludge and the secondary sludge.

Biological Nutrient Removal (Activated Sludge Process)

The heart of the treatment process takes place in this step. This is the biological step in the treatment process occurs, using naturally occurring microbes to decompose the organic material in the wastewater. Primary effluent first enters two baffled zones mixed by submerged propellers. The removal of nitrogen (denitrification) occurs here because the microbes utilize nitrates as a source of oxygen and the nitrogen gas is released into the atmosphere. Methanol is added as necessary to provide a supplemental carbon source to promote denitrification.

Although the organisms that conduct this portion of the treatment are the same organisms that can be found in nature in ponds, lakes and streams, they exist in much higher concentration in the controlled atmosphere of a reclamation plant. To allow these organisms to live in such high concentration, air must be pumped into the oxic zone of these tanks, hence the name "aeration" basin. Ambient oxygen-the same air we breathe-is pumped into the bottom of the 30-foot deep tanks using a fine bubbler aeration system to evenly diffuse the oxygen across the bottom surface of the tanks. Nitrification takes place in this portion of the tank, when nitrogen in the form of ammonia is converted to nitrate. Water remains in the aeration basins approximately five hours.

AS Stasinakis, Aerobic biodegradation of organotin compounds in activated sludge batch reactors. Environ Pollut, April 1, 2005; 134(3): 431-8,
The biodegradation behavior of four organotin (OT) compounds, namely tributyltin (TBT), dibutyltin (DBT), monobutyltin (MBT) and triphenyltin (TPhT), was studied in lab-scale activated sludge batch reactors. The activated sludge was spiked with the OT compounds at a level of 100mugl(-1) as Sn. Determination of the OT compounds by GC-FPD after ethylation in the dissolved and particulate phase revealed that 24h after the start of the experiments, almost the total of OT compounds has been removed from the dissolved phase and is associated with the suspended solids. Calculation of mass balance in batch reactors showed that OT compounds biodegradation was performed via a sequential dealkylation process. Removals due to biodegradation were differentiated according to the parent compound. In experiments with non-acclimatized biomass, a percentage of 27.1, 8.3, 73.8 and 51.3 was still present as TBT, DBT, MBT and TPhT, respectively, at the end of the experiment (18th day). Half-lives (t(1/2)) of 10.2 and 5.1 days were calculated for TBT and DBT, respectively, whereas apparent t(1/2) values could not be determined for MBT and TPhT (t(1/2)>18 days). The capacity of activated sludge to biodegrade OT compounds in the absence of supplemental substrate indicated that these compounds can be metabolized as single sources of carbon and energy in activated sludge systems. Excluding TBT, the presence of low concentrations of supplemental substrate did not affect the biodegradation potential of activated sludge. The acclimatization of biomass on OT compounds enhanced significantly biodegradation, resulting in significant decreases of half-lives of OT compounds. As a result in the presence of acclimatized biomass, half-lives of 1.4, 3.6, 9.8 and 5.0 days were calculated for TBT, DBT, MBT and TPhT, respectively.

A Katsoyiannis, Persistent organic pollutants (POPs) in the conventional activated sludge treatment process: fate and mass balance. Environ Res, March 1, 2005; 97(3): 245-57,
The fate and the mass balance of persistent organic pollutants (POPs) during the conventional activated sludge treatment process were investigated in the wastewater treatment plant of the city of Thessaloniki, northern Greece. The POPs of interest were 7 polychlorinated biphenyls and 19 organochlorine pesticides. Target compounds were determined at six different points across the treatment system: the influent, the effluent of the primary sedimentation tank, the effluent of the secondary sedimentation tank, the primary sludge, the activated sludge from the recirculation stream, and the digested/dewatered sludge. The distribution of POPs between the dissolved and the adsorbed phases of wastewater and sludge was investigated. A good linear relationship between the distribution coefficients, K(d), and the octanol-water partition coefficients, K(ow), of the solutes was observed only in raw wastewater, suggesting that other factors affect the phase distribution of organic compounds in treated wastewater. For all POPs, a significant increase in partitioning with a decreasing solids concentration was observed, revealing an effect from non-settling microparticles remaining in the "dissolved" phase during the separation procedure. A good linear relationship was also revealed between logK(d) and the dissolved organic carbon (DOC) content of wastewater, suggesting that DOC favors the advective transport of POPs in the dissolved phase. Almost all POPs showed good mass balance agreements at both the primary and the secondary treatment. The losses observed for some species could be attributed to biodegradation/biotransformation rather than volatilization. The relative distribution between the treated effluent and the waste sludge streams varied largely among different compounds, with p-p'-DDE being highly accumulated in the waste sludge (98%) but almost 60% of alpha-HCH remaining in the treated effluent.

A Nicolau, Effect of copper in the protistan community of activated sludge. Chemosphere, February 1, 2005; 58(5): 605-14,
Protists have proved to be an interesting tool for assessing the occurrence of pollution in wastewater treatment systems along with its role in the control of pollution itself through grazing of dispersed bacteria and maintenance of a healthy trophic web in those artificial ecosystems. Two sets of assays were carried on in a bench scale pilot plant in order to study the response of the activated sludge community of protists to the exposure of copper: the first set was carried on with synthetic sewage and the second one with real sewage. The results emphasize the ability of activated sludge biological communities to survive and to react to toxicants and highlight the role of protistan communities as indicators of toxicants entrance in treatment systems.

DF Juang, Effects of synthetic polymer on the filamentous bacteria in activated sludge. Bioresour Technol, January 1, 2005; 96(1): 31-40,
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.

JC Vogelaar, Bioflocculation of mesophilic and thermophilic activated sludge. Water Res, January 1, 2005; 39(1): 37-46,
Thermophilic activated sludge treatment is often hampered by a turbid effluent. Reasons for this phenomenon are so far unknown. Here, the hypothesis of the temperature dependency of the hydrophobic interaction as a possible cause for diminished thermophilic activated sludge bioflocculation was tested. Adsorption of wastewater colloidal particles was monitored on different flat surfaces as a function of temperature. Adsorption on a hydrophobic surface varied with temperature between 20 and 60 degrees C and no upward or downward trend could be observed. This makes the hydrophobic interaction hypothesis unlikely in explaining the differences in mesophilic and thermophilic activated sludge bioflocculation. Both mesophilic and thermophilic biomass did not flocculate with wastewater colloidal particles under anaerobic conditions. Only in the presence of oxygen, with biologically active bacteria, the differences in bioflocculation behavior became evident. Bioflocculation was shown only to occur with the combination of wastewater and viable mesophilic biomass at 30 degrees C, in the presence of oxygen. Bioflocculation did not occur in case the biomass was inactivated or when oxygen was absent. Thermophilic activated sludge hardly showed any bioflocculation, also under mesophilic conditions. Despite the differences in bioflocculation behavior, sludge hydrophobicity and sludge zetapotentials were almost similar. Theoretical calculations using the DLVO (Derjaguin, Landau, Verweij and Overbeek) theory showed that flocculation is unlikely in all cases due to long-range electrostatic forces. These calculations, combined with the fact that bioflocculation actually did occur at 30 degrees C and the unlikelyness of the hydrophobic interaction, point in the direction of bacterial exo-polymers governing bridging flocculation. Polymer interactions are not included in the DLVO theory and may vary as a function of temperature.

RW Martin Jr, Low-temperature inhibition of the activated sludge process by an industrial discharge containing the azo dye acid black 1. Water Res, January 1, 2005; 39(1): 17-28,
A municipal wastewater treatment plant (WWTP) receiving industrial dyeing discharge containing acid black 1 (AB1) failed to meet NH(3) and BOD(5) discharge limits, especially for NH(3) during the winter. Dyeing discharge was combined with domestic sewage in volumetric ratios reflecting the range received by the WWTP and fed to sequencing batch reactors at 22 and 7 degrees C. Analysis of the various nitrogen species revealed complete nitrification failure at 7 degrees C with more rapid nitrification failure as the dye concentration increased. Slight nitrification inhibition occurred at 22 degrees C: NH(3) removal decreased from 99.9% for the control compared to only 97.0% removal with dye addition. Dye-bearing wastewater also reduced COD removal by half at 7 degrees C and by one-fifth at 22 degrees C, and increased effluent TSS nearly three-fold at 7 degrees C. Activated sludge quality at 7 degrees C deteriorated after exposure to AB1, as indicated by excessive foaming and the presence of filamentous bacteria and by a decrease in endogenous and exogenous oxygen uptake. Decreasing AB1 loading resulted in partial activated sludge recovery. Eliminating the dye-bearing discharge to the full-scale WWTP led to improved performance bringing the WWTP into compliance with discharge limits.

X Zhang, Optimized sequence retrieval from single bands of temperature gradient gel electrophoresis profiles of the amplified 16S rDNA fragments from an activated sludge system. J Microbiol Methods, Jan 2005; 60(1): 1-11,
Sequence retrieval from single bands of polymerase chain reaction (PCR)-denaturing gel electrophoresis (DGE) profiles is an important but often difficult step for molecular diversity analysis of complex microbial communities such as activated sludge systems. We analyzed the temperature gradient gel electrophoresis (TGGE) profiles of PCR-amplified 16S rDNA fragments from an activated sludge sample of a coking wastewater treatment plant. Single bands were excised, and a clone library was constructed for each. Sequence heterogeneity in each single band was found to be significantly overestimated due to single-stranded DNA (ssDNA) contamination formed during the PCR amplification, since only 10-60% of library clones of each single TGGE band had identical migration behavior compared with the parent band. Three methods, digestion with mung bean nuclease, optimization of PCR amplification, and purification via denatured polyacrylamide gel electrophoresis (d-PAGE), were compared for their ability to minimize ssDNA contamination, with the last one being the most efficient. After using d-PAGE to minimize ssDNA to a nearly nondetectable level, 70-100% of library clones for each single TGGE band had identical migration compared with the parent band. Several sequences were found in each of six single bands, and this co-migration could be predicted with the Poland software. The predominant bacteria of the activated sludge were assessed via a combination of sequence retrieval from each single TGGE band and band intensity analysis. Only beta and alpha subclasses of the Proteobacteria were detected, 93.8% and 6.2%, respectively. Our work suggests that prior to constructing a clone library to retrieve the actual sequence diversity of a single DGE band, it is advisable to minimize ssDNA contamination to a nondetectable level.

F Morgan-Sagastume, Physicochemical properties and stability of activated sludge flocs under temperature upshifts from 30 to 45 degrees C. J Colloid Interface Sci, Jan 2005; 281(1): 136-45,
The impacts of temperature shifts from 30 to 45 degrees C on the structural stability and surface charge of activated sludge flocs were assessed in four sequencing batch reactors (SBRs) treating pulp and paper mill effluent. The improvement in floc stability was tested by sludge magnesium enrichment in one SBR and by operating another reactor at a high sludge retention time (SRT) of 33 days. Floc stability was characterized by dissociation constants with solutions of CaCl(2), KCl, urea, and ethylenediamine tetraacetate (EDTA). Surface charge was assessed by cationic-anionic titration and metals concentrations were also determined. The temperature shift consistently caused an increase in the negative sludge surface charge from approximately -0.180 to -0.300 meq/g MLSS. Magnesium enrichment and a high SRT of 33 days promoted less negatively charged sludge, dampened the increase in negative sludge surface charge, and yielded structurally stronger flocs; however, sludge deflocculation still occurred. Manganese and iron appeared to be released by sludge under the temperature shift. It was concluded that the temperature shift deteriorates the flocculating physicochemical properties of the sludge and that better floc stability achieved by magnesium enrichment and a high SRT is not enough to stop deflocculation. Further research is required to clarify the origin of the increase in negative sludge surface charge, the role of metals, and the governing factors in sludge deflocculation under such temperature shifts.

M Suresh Kumar, Production of biodegradable plastics from activated sludge generated from a food processing industrial wastewater treatment plant. Bioresour Technol, Dec 2004; 95(3): 327-30,
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.

AS Stasinakis, NS Thomaidis, D Mamais, and TD Lekkas Investigation of Cr(VI) reduction in continuous-flow activated sludge systems. Chemosphere, Dec 2004; 57(9): 1069-77.
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%.

T Widjaja, T Miyata, Y Nakano, W Nishijima, and M Okada Adsorption capacity of powdered activated carbon for 3,5-dichlorophenol in activated sludge. Chemosphere, Dec 2004; 57(9): 1219-24.
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.

BM Wilen, K Keiding, and PH Nielsen Flocculation of activated sludge flocs by stimulation of the aerobic biological activity. Water Res, Nov 2004; 38(18): 3909-19.
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.

GA Ekama and MC Wentzel A predictive model for the reactor inorganic suspended solids concentration in activated sludge systems. Water Res, Nov 2004; 38(19): 4093-106.
A simple predictive model for the activated sludge reactor inorganic suspended solids (ISS) concentration (excluding that from chemical precipitant dosing) is presented. It is based on the accumulation of influent ISS in the reactor and an ordinary heterotrophic organism (OHO) ISS content (fiOHO) of 0.15 mg ISS/mg OHO organic (volatile) suspended solids (VSS) and a variable phosphate accumulating organism (PAO) ISS content (fiPAO) proportional to their P content (fXBGP). Organism ISS content is conceptualized as the uptake of dissolved inorganic solids by active organisms, which when dried in the total suspended solids (TSS) test procedure, precipitate and manifest as ISS. The model is validated with data from 22 investigations conducted over the past 15 years on 30 aerobic and anoxic-aerobic nitrification-denitrification (ND) systems and 18 anaerobic-anoxic-aerobic ND biological excess P removal (BEPR) systems variously fed artificial and real wastewater, and operated from 3 to 20 days sludge age. The predicted reactor VSS/TSS ratio reflects the observed relative sensitivity to sludge age, which is low, and to BEPR, which is high. To use the model for design, two parameters need to be known: (1) the influent ISS concentration, which is not commonly measured in wastewater characterization analyses and (2) the P content of PAOs (fXBGP), which can vary considerably depending on the extent of anoxic P uptake BEPR that takes place in the system. Some guidance on the measurement of influent ISS concentration and selection of the PAO P content to calculate the mixed liquor VSS/TSS ratio for design is given.

AM Martins, C Picioreanu, JJ Heijnen, and MC Van Loosdrecht Three-dimensional dual-morphotype species modeling of activated sludge flocs. Environ Sci Technol, Nov 2004; 38(21): 5632-41.
An individual-based model, originally developed for a biofilm system, was adapted to simulate three-dimensional formation of activated sludge flocs. The model was extended to two different bacterial morphotypes (floc-forming and filamentous bacteria), allowing spatial development of the floc according to the bacterial morphology, diffusion, reaction, and growth processes. The model needed also extension with a process for attachment of individual cells. Despite being in an early stage of development, the model is already a tool that enables us to obtain useful information about the microfloc environment. The model indicates that filamentous bacterial morphology and substrate microgradients are important aspects in the formation of bacterial structures. In mass transport-limited regimes filamentous bacterial structures prevail, whereas in growth-limited regimes irregular shaped flocs with fingerlike structures are dominant. These modeling results suggest that activated sludge flocs and biofilms might be different manifestations of the same phenomena. The model results support the hypothesis that floc-macrogradients can be the most important parameter for development of bulking sludge. The model suggests that attachment has a very strong effect on floc structure, leading to enhancement of the effect of substrate microgradients.

YS Ho, Comment on "Sorption of basic dyes from aqueous solution by activated sludge" [J. Hazard. Mater. 108 (2004) 183-188]. J Hazard Mater, Oct 2004; 114(1-3): 241-5.
The adsorption of dyes in the solutions using activated sludge might be a promising approach in wastewater treatment units. The adsorption of Basic Red 18 and Basic Blue 9 from aqueous solution by dried activated sludge was investigated with in a batch system. The activated sludge had the highest dye uptake capacity, having the monolayer adsorption capacity 285.71 and 256.41 mg g−1 for Basic Red 18 and Basic Blue 9, respectively, at pH value of 7.0 and 20 °C. Langmuir and Freundlich adsorption models were used for the mathematical description of the adsorption equilibrium and the equilibrium data fixed very well with both the Langmuir and Freundlich models. The RL values showed that, activated sludge was favorable for the adsorption of basic dyes. The suitability of the kinetic models for the adsorption of dyes on the activated sludge was also discussed. It was clear that the adsorption kinetics of dyes to dried activated sludge obeyed pseudo second-order adsorption kinetics.

Environ Technol. 2004 Jun;25(6):723-31. [Rheological measurement used as a tool to assess sludges settleability] Guibaud G, Dollet P, Tixier N, Dagot C, Baudu M. Laboratoire des Sciences de l'Eau et de l'Environnement, Faculte des Sciences et Techniques, 123, avenue Albert Thomas, 87060 Limoges, France. 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.

Activated sludge consists of a mixed community of microorganisms that metabolize and transform organic and inorganic substances into environmentally acceptable forms. The typical microbiology of activated sludge consists of approximately 95% bacteria and 5% higher organisms (protozoa, rotifers, and higher forms of invertebrates). The term "activated sludge" refers to a biological process. This process cannot be monitored without using a biological tool: the microscope. Nitrification and Denitrification in the Activated Sludge Process, the first in a series on the microbiology of wastewater treatment, comprises the critical topics of cost-effective operation, permit compliance, process control, and troubleshooting in wastewater treatment plants. Avoiding the technical jargon, chemical equations, and kinetics that typically accompany such texts, Nitrification and Denitrification in the Activated Sludge Process directly addresses plant operators and technicians, providing necessary information for understanding the microbiology and biological conditions that occur in the treatment process. k, l. In the activated sludge process wastewater enters an aerated tank. Here bacterial particles are brought in contact with the organic material in the wastewater. The bacteria utilize the organics in wastewater as food. In the second stage of the aeration tank, bacteria known as nitrifying bacteria predominate.

Wei Sheng Yan Jiu. 2004 Mar;33(2):137-9. [Screening and characterization of dominant bacteria for the degradation of endocrine disruptor di-n-butyl phthalate] Wang L, Luo Q. Institute of Environmental Medicine, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China. OBJECTIVE: In order to screen the dominant bacteria for degrading endocrine disruptor di-n-butyl phthalate (DBP). METHODS: The activated sludge was acclimated by DBP as sole carbon source. DBP concentration was increased progressively. 5 strains were isolated from the sludge by the plane-table after 10 weeks, 1 strain of which grew and degraded DBP well. RESULTS: By orthogonal test, it was indicated that the appropriate degradation conditions of DBP for this best strain were degradation time 32 h, DBP concentration 200 mg/L, rate of shaking incubator 100 r/min, pH 7.0, temperature 30 degrees C. The degraded rate of DBP is more than 95% under above conditions. CONCLUSION: The bacterium was identified as Pseudomonas.

Huan Jing Ke Xue. 2003 Nov;24(6):116-20. [Degradation kinetics for Fhhh strain in PTA wastewater] Cheng S, Zhang X, Shi L, Qu M, Zhou T, Hao C, Yan J. National Key Laboratory of PCRR, School of Environment, Nanjing University, Nanjing 210093, China. Degradation kinetics of the purified terephthalic acid (PTA) petrochemical wastewater with the functional strain Fhhh was conducted in this research. Inputting the values of the 6 kinetics parameters obtained from the test, the values of the natural parameter and the values of the standard parameters for discharging wastewater into the environmental biotechnological informatics software (Ebis), the minimum reactor volume (Vmin) required and the specific degradation rate (qA) were calculated based on the activated sludge process. The minimum value of Vmin was 1309 m3 as well as the highest value of qA was 0.0136 h-1 among the Fhhh preparations kept in three different methods. The highest value of Fhhh qA was 4 fold of that of the native bacterium YZ1, and higher than that of the data published by 4 researchers and lower than that of by 2 researchers. The results show that Fhhh has the obvious potential for the degradation of PTA wastewater.

Huan Jing Ke Xue. 2003 Nov;24(6):112-5. [The use of chemical uncoupler to reduce sludge yield in activated sludge process] Ye F, Chen Y, Feng X. Department of Environmental Engineering, Zhejiang University, Hangzhou 310029, China. yefenxia@hotmail.com To determine whether chemical additions can be used to reduce sludge production in biological wastewater treatment, 3,3',4',5-tetrachlorosalicylanilide (TCS), served as a metabolic uncoupler was added to activated sludge cultures. The batch tests have confirmed that TCS is an effective chemical uncoupler in reducing the sludge yield when its concentration is higher than 1.0 mg/L. It was showed that TCS was able to reduce sludge yield by approximately 50% when the TCS concentration was 6.0 mg/L. It was also revealed that substrate removal capability and effluent nitrogen concentration were not affected adversely by the presence of TCS when TCS was dosed every other day in a range of 2.0-3.6 mg/L during the 40 d operation of activated sludge batch cultures. Such a sludge growth reduction is associated with the enhancement of microbial activities in terms of the SOUR and dehydrogenase activity. Sludge settleability from the treated and control samplers was comparable and not significantly different. Meanwhile, there was a finding that the filamentous bacteria still grow in sludge floc in the control reactor after 40 d operation. These results suggested that it might be possible to apply TCS in activated sludge systems to reduce the excess sludge yield.

Huan Jing Ke Xue. 2003 Nov;24(6):83-9. [Aerobic biodegradation performance of six volatile organic compounds by activated sludge acclimated with toluene] Zhang H, Hu H, Xi J. State Key Joint Laboratory of Environment Simulation and Pollution Control, Department of Environmental Science and Engineering, Tsinghua University, Beijing 100084, China. The degradation performance of six volatile organic compounds (VOCs), toluene, o-xylene, m-xylene, p-xylene, benzene and chlorobenzene by activated sludge acclimated with toluene were studied. The experimental results showed that the biodegradation rates of o-xylene, m-xylene, p-xylene, benzene and chlorobenzene increased with increasing of their initial liquid concentration; when concentrations of o-xylene, m-xylene, p-xylene, benzene and chlorobenzene were less than 149 mg/L, 129 mg/L, 133 mg/L, 234 mg/L and 146 mg/L respectively, neither of them brought any notable inhibition or poisonous effects on microbes, and their aerobic biodegradation accorded with first-order reaction. When concentrations of toluene were more than 85 mg/L, its biodegradation rate didn't increase with increasing of its initial liquid concentration and the biodegradation of toluene accorded with the Monod equation.

Ying Yong Sheng Tai Xue Bao. 2003 Nov;14(11):1929-33. [Biodegradation of herbicide pendimethalin by fungi and its characteristics] Lin A, Zhu L, Wang J, Liu A, Sun R. Shandong Agricultural University, Taian 271018, China. Fungi, which can grow on and degrade pendimethalin, were isolated from activated sludge and soil. The biodegradation characterization in vitro was studied. The results showed that pendimethalin could be degraded by fungi, 16 fungi were isolated by enrichment culture, among which, 10 fungi could degrade more than 60% pendimethalin in 5 days in culture fluid. According to the physiological resistance and the capacity to degrade pendimethalin, three fungi were considered as efficiently degrading strains identified as Aspergillus terreus, Monilochaetes and Aspergillus furnigatus. The efficiency of degradation was affected by culture conditions such as pH, temperature, and concentration of cane sugar and pendimethanlin. The results showed that when the additional carbon source was 0.5%-1.0%, pH value was 6-8, and cultivated temperature was 20-30 degrees C, the growth amount of fungi and the degradation rate were enhanced. The fungi grew quickly, and the biodegradation rate was high under pendimethalin concentration being 100 mg.L-1. The removed amount of pendimethalin increased with increasing pendimethalin concentration. The optimal conditions were proposed, which could provide theoretic basis for prevention and control of pesticides pollution.

Huan Jing Ke Xue. 2003 Jul;24(4):99-104. [Studies on aerobic granular sludge cultivated under selective pressure] Wang Q, Chen J, Du G. Key Laboratory of Industrial Biotechnology Under Ministry of Education, Southern Yangtze University, Wuxi 214036, China. As inoculum sludge from a conventional COD removal activated sludge wastewater treatment plant was used, aerobic granular sludge was cultured in sequencing batch reactor (SBR) fed with glucose as carbon substrate. The SBR was operated with decreasing sedimentation time and increasing COD loading rate resulting in the selective pressure to enhance the formation of granular sludge. According to morphology change of sludge, the generation of granule could be divided into three stage. Granules started to appear after 67 days operation. After increasing COD loading rate to 4.8 kg/(m3.d), and superficial gas velocity to 0.0175 m/s, granules were the dominant sludge forms with diameter about 6-9 mm, the minimal settling velocity of 32.7 m/h, and the MLSS of 7800 mg/L. Aerobic granular sludge demonstrates high activity and ability to withstand high COD loading rate. The properties of aerobic granular sludges and the effect of different operational conditions on the formation of these aerobic granules were also analyzed preliminarily.

These bacteria utilize ammonia as food, and through a two stage process convert ammonia into nitrate. The bacteria naturally clump together forming particles called floc. After the wastewater is discharged from the aeration tank, a clarifier separates the floc, or suspended solids from the treated wastewater. Low aeration basin dissolved oxygen (DO) concentration for the applied organic loading (F/M) leads to filamentous bulking by several filaments.The required aeration basin DO concentration to prevent "low DO bulking" is not a constant, rather, is a function of the F/M rate (see Palm et al. JWPCF 52: 2484, 1980). Simply, higher bulk DO is required to prevent the growth of these filaments as the F/M increases, due to faster oxygen use within the floc at higher F/M, oxygen depletion inside the floc, and the need to maintain aerobic conditions in the interior of the floc. A higher bulk DO concentration increases the diffusion of oxygen into the floc interiors. f, g, k. In general, a bulk DO concentration of 2.0 mg/L is recommended for F/M values up to 0.5, typical of most domestic waste plants. This DO concentration should be maintained at the point of greatest oxygen demand in the system, for example, at the headend of a plug-flow system (not the backend).

Huan Jing Ke Xue. 2003 Jul;24(4):94-8. [Cultivation of aerobic granular sludge for simultaneous nitrification and denitrification in SBR system] Yang Q, Li X, Zeng G, Xie S, Liu J. Department of Environmental Science and Technology, Hunan University, Changsha 410082, China. The cultivation of aerobic granular sludge used for nitrogen removal in Sequencing Batch Reactor (SBR) fed with a synthetic municipal wastewater was investigated. The results showed that the aerobic granular sludge with the high activity of simultaneous nitrification and denitrification, could form in the reactor by controlling the addition of carbon source, and the removal rates of COD and NH3-N reached 74.0%-92.8% and 82.3%-98.5%, respectively, in the reactor. The granular formed was averagely 0.5-1.0 mm in diameter, and the Mixed Liquid Suspended Solids (MLSS) and the Sludge Volumetric Index (SVI) in the reactor were above 4.5 g/L and above 32.5, respectively. Compared with the normal aerobic activated sludge process, the system with aerobic granular sludge had a higher concentration of effective biomass and a much stronger ability of nitrogen removal.

Gig Sanit. 2003 May-Jun;(3):11-4. [The evaluation of effluent water toxicity for the activated sludge in water purification facilities] [Article in Russian] Dobrynina LF, Mezhebovskaia GP, Nenasheva MN, Sharipova GF. The condition of activated sludge, which predetermines the efficiency of functioning of purification facilities, depends to a great extent on a toxicity degree of waste-waters coming for purification. The results of a study of toxicity of effluents of an industrial enterprise by using the methods of the chemical-and-analytic and toxicological monitoring are described in the article. The conducted investigations made it possible to specify an effluents' flow, which is most toxic for the activated-sludge microorganisms, for the purpose of its further localization. Publication Types: Evaluation Studies

Huan Jing Ke Xue. 2003 May;24(3):132-5. [Study on biohydrogen production by anaerobic biological fermentation of organic wasters] Fan Y, Liao X, Lu H, Hou H, Lai JJ. Department of Chemistry, Zhengzhou University, Henan Fundamental and Applied Science Research Institute, Zhengzhou 450052, China. Biological hydrogen production is a process of applying anaerobic biological fermentation method to produce hydrogen from organic wastes. Hydrogen production potential of different microbiological source and organic wastes, as well as the composition of fermentation product in liquid phase, were studied in the batch culture experiments. Magnifying experiment of biohydrogen production was carried out in 30 L improvement UASB reactor using anaerobic fermentation of artificial wastewater containing starch by activated sludge process. The experiment confirm that hydrogen and carbon dioxide percentage of biogas were 40%-51% and 49%-60% under the condition of hydrogen production process (pH was 4.5-5.5 sludge VSS was 10 g/L; starch-COD was 5000 mg/L), and no methane was observed. Hydrogen purity was more than 97% by an absorption of sodium hydrate solution, continuous hydrogen production was more than 120 days.

Huan Jing Ke Xue. 2003 May;24(3):70-3. [Observation and comparison on microstructure of immobilized Aerobacillus fusiformis under wastewater treatment] Zhang Y, Zhang Y, Shi H, Wang J, Qian Y. Department of Environmental Engineering, College of Urban Science and Tourism, Shanghai Teachers University, Shanghai 200234, China. Aiming at printing ink wastewater, a strain of bacterium was isolated from activated sludge, and identified as Aerobacillus fusiformis. The Aerobacillus fusiformis was respectively immobilized in calcium alginate gel, polyvinyl alcohol (PVA) and microporous ceramics and their microstructure were observed by scanning electron microscope (SEM). It was found that calcium alginate gel might dissolve in the wastewater, and the activity was restricted as cells wrapped in PVA, so the COD removal ratio was low. The method of immobilized cells using microporous ceramics is simple and COD removal efficiency can be achieved. In addition, the immobilized bacterium could not be separated easily from the ceramics in the wastewater.

Huan Jing Ke Xue. 2003 May;24(3):65-9. [Treatment of carbonization effluent by the ultrasonic radiation and activated sludge process] Ning P, Xu J, Huang D, Ma X, Xu X, Li Z. School of Environmental Science and Engineering, Kunming University of Science and Technology, Kunmimg 650093, China. The paper deals with the degradation of organic pollutants by the ultrasonic irradiation-activated sludge process. The treatment of the real coking wastewater of Kunming coke making-gas plant was studied with the water quality model. Using the ultrasonic irradiation-activated sludge process the organic pollutants in the real coking wastewater can be degraded effectively. The influence factors of the ultrasonic degradation effect such as initial concentration, aerated gas and ultrasonic density were investigated and mechanism was explored. The result shows that the ultrasonic degradation effect was high with the decrease of initial concentration of the CODCr, the presence of aerated gas and the increase of ultrasonic density. At the initial CODCr concentration of 807 mg/L, when air acted as aerated gas and only air itself (no ultrasound) was exerted on the wastewater, the degradation rate of the CODCr will be 4.5%. However, when the ultrasound of the intensity of 119.4 kW/m2 was exerted on the wastewater, the degradation rate of the CODCr will be 65%. Compared with the activated sludge process alone, the combination of the ultrasonic irradiation and activated sludge process can increase the degradation rate of the CODCr from 45% to 81%. The oxygen consumption rate of the carbonization effluent obviously decreased in the presence of the activated sludge. This shows the carbonization effluent is not biotoxic behind the ultrasonic irradiation.

Wei Sheng Yan Jiu. 2003 May;32(3):187-9. [Study on biodegraded characteristics of endocrine disruptor di-n-butyl phthalate] Wang L, Luo Q. Institute of Environmental Medicine, Tongji Medical College, Huazhong University of Science & Technology, Wuhan 430030, China. The biodegraded Characteristics of di-n-butyl Phthalate (DBP), endocrine disruptor were studied. The activated sludge was acclimated using DBP as the only carbon in the culture medium. DBP concentration was increased progressively from 0.05 g/L to 0.5 g/L. The degradation tests were carried out on the constant temperature table using the acclimated sludge at different PH, temperature, DBP concentration and hydraulic residence time. The results showed that DBP could be rapidly degraded-nearly 90% in 48 hours. The appropriate condition for DBP degradation was pH 6.0-8.0, temperature 25 degrees C-35 degrees C, DBP concentration no more than 300 mg/L, and hydraulic residence time 12 h-24 h. The form of biodegradation of DBP can be described as the first-order reaction model.

Some industrial waste systems and high rate domestic plants operated at higher F/M may need higher DO values than 2.0 mg/L due to oxygen diffusion limitations. Type 1701 bulking has occurred in an oxygen activated sludge plant operated at high F/M at a DO concentration of 12-14 mg/L, which was cured by raising the DO to 20 mg/L. As a rule, always trust the microscopic observation of low DO filaments to indicate oxygen limitation rather than the aeration basin DO values. Control of low DO bulking is by raising the aeration basin DO concentration and by raising the aeration basin MLSS concentration (decreasing the F/M). Note that this action is opposite to what intuition directs: to reduce the MLSS concentration, since less biomass needs less oxygen (wrong! -the F/M is increased at lower MLSS concentration and oxygen needs increase). Filamentous bulking is common in completely-mixed, lower F/M systems. a, d, d, e, c. Here, a number of filaments can cause bulking (see Table 1) because they grow better than most activated sludge floc-forming bacteria at low aeration basin BOD concentration. Intermittently-fed and plug-flow systems are more resistant to this type of bulking. Control of low F/M bulking is by reducing the aeration basin MLSS concentration and increasing the F/M (manipulating the "M" component). Lowering the MLSS concentration may not be suitable for many plants as this may cause the loss of nitrification and increase waste sludge production.

Huan Jing Ke Xue. 2003 Mar;24(2):97-101. [Biodegradable plastic production by activated sludge with different carbon sources] Lin D, Zhang Y, Wei C, Shen J. Department of Applied Chemistry, South China University of Science and Technology, Guangzhou 510640, China. Polyhydroxyalkanoates(PHAs) are polyesters synthesized by numerous bacteria in sludge as intracellular carbon and energy storage compounds under the condition of unbalance growth. Another important aspect of PHAs is thermoplastic polyester with the remarkable characteristics of biodegradability. In this paper, using sodium acetate, sodium propionate and sodium butyrate as the unique carbon source, 5.58%, 3.90% and 4.98% PHAs of dry sludge weight were obtained by assimilated sludge as PHAs synthesis strains in the anaerobic condition, and 12.32%, 9.55% and 11.35% PHAs of dry sludge weight were obtained in the anaerobic condition. It was shown that there were large quantities strains which could accumulate PHAs as granules in the cytoplasm of cells, and the yield of PHAs in the anaerobic process were higher than that in the aerobic process. The best result was that 12.32% PHAs of dry sludge weight was obtained in the best experiment condition, and the yield of the PHAs to substrate was 30.65%. The structures of PHAs were analyzed by 1HNMR spectrum, and the relationship of the structure of PHAs and the carbon source was explained.

Huan Jing Ke Xue. 2003 Jan;24(1):75-9. [Effects of phenol presence on the biodegradation of 2,4-dichlorophenol in a bioaugmented system] Quan X, Shi H, Wang J, Qian Y. State Key Joint Laboratory of Environment Simulation and Pollution Control, Department of Environmental Science and Engineering, Tsinghua University, Beijing 100084, China. Special culture for 2,4-Dichlorophenol(2,4-DCP) degradation were supplemented to an activated sludge system and the effects of the presence of phenol at various concentration on the removal of 2,4-DCP were studied. In addition, the changes of the removal rate of 2,4-DCP and phenol under the long existence of phenol was investigated in semicontinuous test. Results show than the presence of phenol at the concentration of 10 mg/L, 50 mg/L, 100 mg/L and 300 mg/L inhibit the biodegradation of 2,4-DCP and the inhibition increased with increasing of phenol concentration. 2, 4-DCP biodegradation rate declined with the run of semi-continuous test, while the biodegradation rate of phenol was much faster than the first run.

Huan Jing Ke Xue. 2002 Sep;23(5):84-7. [The kinetics of biological treatment of bleaching liquor from straw pulp process] Zhang J, Huang X, Ding W, Wang X. ESPC State Key Joint Laboratory, Dept. of Environmental Science and Engineering, Tsinghua University, Beijing 100084, China. zhangjian00@mails.tsinghua.edu.cn The batch test of oxygen uptake rate (OUR) measurement was used to simulate biochemical reaction process in aerobic reactor treating bleaching liquor from straw pulp process. Lawrence-McCarty kinetic model was used to analyze the biochemical reaction process. The kinetic equation of bleaching liquor biological treatment, v = 0.72 S/(60.43 + S), was deduced from results of the OUR experiment and the bench experiment. The specific substrate degradation rate estimated by the kinetic equation was higher than that of practical wastewater treatment plant. The phenomenon was attributed to the decrease of activated sludge activity caused by cellulose suspended solid accumulation in aerobic reactor of practical plant.

Huan Jing Ke Xue. 2002 Sep;23(5):76-9. [Biodegraded characteristics of MGP-wastewater by domestic and screened organisms] Ren Y, Shen Y, Wei C, Sheng G, Fu J. Environmental Science Institute, South China University of Technology, Guangzhou 510640, China, ceyren@scut.edu.cn Among 16 bacteria that were screened out from 5 activated sludge, S-2, Y-3, XH-3 and their mixed strains M-3 were selected to biodegrade MGP (Manufacture gas from petroleum)-wastewater. They can remove 38.4%-44.0% CODCr, 95.4%-97.0% hydroxybenzene and 47.1%-53.7% aromatic compound after 60 h treatment, but the removal rate of NH4(+)-N was only 14.0%-17.6%. About 77 toxic organic compounds were detected by GC/MS analysis, the aromatic compounds which had 3 rings and 4-6 rings can be biodegraded by the bacteria. The removal rate of CODCr, NH4(+)-N and extractable organic compound were improved 13.1%-22.9%, 18.4%-22.7% and 13.1%-18.1% respectively when glucose was added in the wastewater, and when ethanol was existing in the wastewater, the corresponding increase were 12.5%-21.2%, 29.7%-42.2% and 6.7%-7.7%. The total removal rates of aromatic compound were increased 17.7%-21.7%, 15.4%-21.2%. The screened strains can improve the biodegradation rate of MGP-wastewater.

Huan Jing Ke Xue. 2002 Sep;23(5):72-5. [Treatment of drilling wastewater from oil field by using yeast] Wang Y, Yang M, Zheng S, Zhou X, Shen Z. State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China. Two strains of yeast, namely Wickerhamiella domercqii and Candida boidinii, were acquired through screening from soil samples contaminated by drilling wastewater. A TOC removal of 40.5% was acquired when the mixture of the two yeast strains was used for drilling wastewater treatment, a little higher than that with activated sludge acclimated with wastewater (35.2%). Some organic compounds in the fraction of molecular weight above 60,000 were found to be biodegradable.

Sheng Wu Gong Cheng Xue Bao. 2002 Jul;18(4):492-6. [Performance of internal-loop air-lift nitrifying bioreactor] Lin FM, Zheng P, Zhao YY, Hu BL, Chen JS. Department of Environmental Engineering, Zhejiang University, Hangzhou 310029, China. The performance of internal-loop air-lift nitrifying bioreactor was good with strong tolerance to influent ammonia concentration (78.49 mmol/L), high volume converting rate (163.18 mmol/L.d) and obvious working stability (ammonia removal > 94.42%). During operation of internal-loop air-lift bioreactor, the nitrifying activated sludge was granulated. The nitrifying granular activated sludge began to appear on day 45. Its average diameter was 0.83 mm, settling velocity was 55.53 m/h and specific ammonia removal rate was 0.95 mmol (NH4(+)-N)/g (VS).d. The nitrifying granular activated sludge had the activity for anaerobic ammonia oxidation with ammonia oxidation rate of 0.23 mmol (NH4(+)-N)/g(VS).d and nitrite reduction rate of 0.24 mmol (NO2(-)-N)/g(VS).d.

Huan Jing Ke Xue. 2001 Nov;22(6):72-5. [Biosorption of heavy metals by bacteria isolated from activated sludge] Wang Y, Guo J, Liu R. State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China. In this paper, biosorption efficiency of heavy metals by bacteria isolated from activated sludge was tested. It was shown that Pseudomonas pseudoalcaligenes and Micrococcus luteus GC subgroup B had high biosorption capacities for Cu(II) and Pb(II) ions. The adsorption of the two ions on Pseudomonas pseudoalcaligenes and Micrococcus luteus GC subgroup B exhibited Langmuir adsorption behavior with regression coefficient of 0.99. The pH value was the most important effect factor on biosorption of metal ions. The biosorption kinetic curves of Cu(II) and Pb(II) ions by cells showed two processes: rapid sorption on cell surface and slowly longer-term transformation into cells. Cu(II) ion can be desorbed effectively from cells of Micrococcus luteus GC subgroup B.

Huan Jing Ke Xue. 2001 Nov;22(6):61-5. [Non-filamentous activated sludge bulking caused by the deficiency of nitrogen] Gao C, Peng Y, Wang S, Chen Y. College of Environment and Energy Engineering, Beijing Institute of Technology, Beijing 100022, China. The effect of nitrogen deficiency on activated sludge bulking was studied specially in some experiments carried on a sequencing batch reactor fed with beer wastewater in this paper. The experimental results showed that the sludge settled properly at a influent BOD/N value of 100/4. When the value of BOD/N was 100/3 and 100/2 respectively, non-filamentous activated sludge bulking caused by an excessive growth of viscous Zoogloea with high moisture content occurred. When the value of influent BOD/N was 100/0.94, more serious non-filamentous bulking occurred. Furthermore, the effect of nitrogen deficiency on the nitrogen sources and phosphorus sources utilization rate and the COD removal rate was studied in the experiments.

Huan Jing Ke Xue. 2001 Nov;22(6):44-8. [Treatment of ion-exchange monosodium glutamate wastewater by yeast] Yang Q, Yang M, Zheng S, Liu F. State Key Laboratory of Environmental Aquatic Chemistry, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085. Two strains of yeasts, Candida halophila and Rhodotorula glutinis, were acquired through screening from ion-exchange monosodium glutamate wastewater (IEMGW) which was characterized by its high contents of COD (40,690 mg/L), NH(4+)-N (16,914 mg/L) and SO(4)2- (18,000 mg/L). The mixture of the two species had a good COD removal performance for treating IEMGW in a pH rang of 4-9. The yeast technology was superior to the conventional activated sludge in terms of COD removal and COD decomposition rate, In a dilution rate range of wastewater from 1:1 to 1:9, a COD removal of 84.5% and an average COD decomposition rate of over 1.0 kg/(kg.d) were obtained under an initial pH of 4.

Environ Technol. 2001 Oct;22(10):1155-68.

[Performance and simulation of intermittent decanted extended aeration treatment plants in a tropical climate] Dagor C, Sommanawan N, Baudu M, Anderson R. Laboratoire des Sciences de l'Eau et de l'Environnement, Faculte des Sciences, ENSIL-Parc ESTER-16, Limoges France. The paper discusses the design and performance of package sewage treatment plants using the Intermittently Decanted Extended Aeration Process (IDEA-Process) in a tropical climate. This hybrid SBR process has been developed overcome traditional drawbacks associated with the SBR process, such as high Sludge Volume Index, high weir loading rate for decanting, and the need to achieve a better effluent quality, especially in terms of nutrient removal. Three domestic sewage plants in Thailand has been selected for field-testing and results of analyses are presented. The average measured biological removal efficiencies in terms of BOD removal and COD removal are about 95.5% and 90% respectively, and the average total nitrogen removal efficiency is about 90%. A computer model is used to study the performance of IDEA-processes compared to results from laboratory tests. The model experience gained through this research are discussed regarding the limitations of computer models such as ASM 1 (Activated Sludge Model n degrees 1) applied to the IDEA-Process in order to develop a new computer model suitable for design and operation of package treatment plant using IDEA-Process Technology in the future.

Nippon Hoigaku Zasshi. 2001 Jul;55(2):247-54. [Legal and technical issues of formalin disposition in association with autopsy] [Article in Japanese] Nakajima M, Yoshida K. Department of Forensic Medicine, Graduate School of Medicine, University of Tokyo 113-0033 Japan. The Ministry of Public Welfare notified on the disposition of formalin, which was used in the histological examination in association with forensic or pathological autopsy. However, those who concerned on the issue had not known exactly how they dispose formalin. The news on the illegal disposition of formalin from our department drew attention to the legal disposition of formalin. These situations led us to investigate the legal and technical aspects of formalin disposition. We examined the legally-described methods such as oxidation, incineration and activated sludge processes and other methods such as formose, supercritical water oxidation, and wet oxidation processes. From legal point of view, we must process poisonous formaldehyde into non-poisonous products under the control of The Poisonous and Peleterious? Substances Control Law. Additionally, the products are under the control of The Sewage Water Law and Water Pollution Control Law, particularly in terms of Biological Oxygen Demand (BOD). After careful investigation, we tentatively conclude that incineration method is the best at present, though the supercritical oxidation and wet oxidation processes may be better in order to cope with the worldwide movement toward the control of environmental hormones and warm climate. Publication Types: Review Review, Tutorial

Wei Sheng Wu Xue Bao. 2001 Jun;41(3):348-52. [Composition and structure of bioflocculant BP25] Liu Z, Xu G, Liu Z, Yang H. Institute of Microbiology, Chinese Academy of Sciences, Beijing 100080, China. A strain of Bacillus megaterium screened from activated sludge could produce exocellular flocculant. The flocculant was purified through ethanol precipitation and Sephadex S-500 column chromatography. The purified flocculant BP25 was assayed by Bradford reaction, agarose gel electrophoresis and Sulfate-phenol method. The results showed that BP25 was a kind of polysaccharide which contains 36.97% O, 6.28% H, 47.00% C, 0% No NMR assay showed BP-25 contains no uronic acid. Gas-chromatography assay combined with thin-layer chromatography of acid hydralate revealed that BP25 contains Glucose and Mannose with the mole ratio of 4:1. Methylation analysis revealed the polysaccharide contains alpha-1, 6 glycosidicbond and alpha-1, 3 glycosidicbond. The main chains are comprised of Glucose and all the Mannose are in the side chains. Possible repeating unit structure was deduced.

Huan Jing Ke Xue. 2001 May;22(3):20-4. [A comparison between a submerged membrane bioreactor and a conventional activated sludge process] Rui L, Xia H, Ruopeng L, Yi Q. ESPC State Key Joint Laboratory, Department of Environmental Science and Engineering, Tsinghua University, Beijing 100084, China. A comparison between a submerged membrane bioreactor (MBR) and a conventional activated sludge process (CAS) was carried out under similar operational conditions. MBR demonstrated a more stable and excellent effluent quality than CAS. Its effluent COD concentration was 55.5 mg/L on average, much lower than that of CAS (79.7 mg/L). Soluble microbial products accumulated in the MBR during the first 120 days in operation due to membrane interception of macromolecules, but these accumulated substances were degraded at last with microbial acclimation. No similar phenomenon was observed in the CAS system. Compositions of the CAS effluent, MBR supernatant and membrane permeate were found quite different. In the CAS effluent and MBR supernatant, both macromolecules with MW > 60,000 and small molecules with MW < 3,000 were dominant and macromolecules had a much larger occupation in the MBR supernatant. In the membrane permeate, however, small molecules with MW < 3,000 were the major component. The relatively small floc size in the MBR was proved favorable to improve oxygen transfer rate.

Any change in operation that effectively increases the substrate concentration available to the activated sludge and introduces batch or plug-flow characteristics to the aeration basin, even on a short term basis, will help control low F/M bulking. These include: compartmentalization of aeration basins; fed-batch operation; intermittent feeding of wastes; and use of a selector. These latter methods do not reduce the MLSS concentration in the system. A selector is a mixing basin or channel where RAS and influent wastes mix prior to the aeration basin. Selector design is empirical at this time. Successful examples involve a 15-30 minute contact time of the RAS and influent waste; are aerated; and achieve at 70-80% removal of soluble BOD5 through the selector. Several newer designs are either operated anoxic (no free oxygen but nitrate present) or anaerobic, however, these are too new to state their general usefulness. A selector can be too large or too small in size to properly function. The