Indian J Exp Biol, 2001 May, 39(5), 490 - 2 Isolation, screening and identification of bacterial strains for degradation of predigested distillery wastewater; Jain N et al.; Three bacterial isolates from the activated sludge of a distillery wastewater treatment plant identified as Xanthomonas fragariae, Bacillus megaterium and Bacillus cereus were found to remove COD and colour from anaerobically digested distillery wastewater in the range of 55 to 68% and 38 to 58% respectively. 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 et al.; 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. J Environ Sci Health A Tox Hazard Subst Environ Eng, 2001, 36(6), 987 - 98 Biosorption of heavy metals from landfill leachate onto activated sludge; Cecen F et al.; The removal of various heavy metals was studied when activated sludge was exposed to heavy metals in landfill leachate . Batch uptake tests were conducted for this purpose . Adsorption was the main mechanism of removal when biomass was contacted with heavy metals . Activated sludge had a high biosorption capacity and equilibrium was reached in a short time with respect to copper, iron, manganese, zinc and chromium . Adsorption isotherms were generated for those heavy metals and the Freundlich constants were calculated . Among the metals studied, manganese became very concentrated on activated sludge with time. J Environ Sci Health A Tox Hazard Subst Environ Eng, 2001, 36(6), 883 - 95 Biodegradation potential of photocatalyzed surfactant washwater; Maillacheruvu K et al.; Enhanced release of hydrophobic compounds from a soil matrix can be achieved by use of soil-washing or soil-flushing using various surfactants . However, the surfactants used in achieving the desorption of organic contaminants may also cause a problem in subsequent removal/disposal of these contaminants . UV radiation in the presence of TiO2 as a pre-treatment step to achieve initial (or partial) breakdown of naphthalene and Sodium Dodecyl Sulfate (SDS) using batch experiments indicated that 56% to 88% naphthalene degradation occurred within 30 minutes to one hour . Preliminary results on the estimate of the batch aerobic biodegradation potential of photocatalyzed washwater containing naphthalene and SDS suggested that SDS was the major carbon and energy source for an activated sludge enrichment culture and an enrichment culture obtained from microorganisms at a contaminated site . Continuous-flow stirred tank reactors (CSTRs) with with a solids retention time (SRT) of 4 days were not effective, but an SRT of 8 days was successful in biodegrading the naphthalene and surfactant . These results indicated that photocatalytic treatment as a pre-treatment step followed by a biodegradation step may offer potential in cleaning up surfactant washwaters containing organic contaminants. J Biotechnol, 2001 Aug 23, 89(2-3), 175 - 84 Biodegradation, decolourisation and detoxification of textile wastewater enhanced by advanced oxidation processes; Ledakowicz S et al.; Recently, an increasing application of so called advanced oxidation processes (AOPs) to industrial wastewater has been observed . In particular, an integrated approach of biological and chemical treatment of wastewater is advantageous conceptually . The subject of our study was synthetic wastewater, simulating effluents from knitting industry . The wastewater contained components that are very often used in Polish textile industry: an anionic detergent Awiwaz KG conc., a softening agent Tetrapol CLB and an anthraquinone dyestuff-Acid Blue 40, CI 2125 . The toxicity of the detergents and the dye was determined in terms of effective concentration EC50 using mixed cultures of activated sludge as well as pure culture of luminescent bacteria Vibrio fischerii NRRLB-11177 . The dye did not undergo biodegradation without AOPs pretreatment, therefore a degree of its removal (decolourisation) by the AOPs has been determined and its bio-sorption properties on the flocks of activated sludge have been studied . The dye adsorption onto flocks of activated sludge was described by Henry's isotherm . Our investigations focussed on the influence of various oxidants like O3, H2O2 and UV light on biodegradation of single components aqueous solution as well as of the whole textile wastewater . The results of kinetic measurements of the biodegradation (by means of acclimated activated sludge) was described by Monod type of kinetic equation . The experimental evidence of the positive effect of chemical oxidation pretreatment on the biodegradation of recalcitrant compounds was quantified by estimation of the kinetic parameters of the Monod equation . Due to the AOPs pretreatment a decrease of the Monod constant and an increase of maximal specific growth rate was observed . The activity of degradative enzymes of activated sludge was assayed by the methods of 2-{4-iodophenyl}-3-{4-nitrophenyl}-5-phenyltetrazolium chloride test. Water Sci Technol, 2001, 44(1), 87 - 94 Data-based modelling and proportional-integral-plus (pip) control of nitrate in an activated sludge benchmark; Ghavipanjeh F et al.; This paper presents the result of an investigation into the Proportional Integral Plus (PIP) control of nitrate in the second zone of an activated sludge benchmark . A data-based reduced order model is used as the control model and identified using the Simplified Refined Instrumental Variable (SRIV) identification and estimation algorithm . The PIP control design is based on the Non Minimum State Space (NMSS) form and State Variable Feedback (SVF) methodology . The PIP controller is tested against dynamic load disturbances and compared with the response of a well tuned PI controller. Water Sci Technol, 2001, 44(1), 137 - 44 Comparison of different operational modes of a two-stage activated sludge pilot plant for the extension of the Vienna STP; Muller-Rechberger H et al.; A pilot plant has been operated over a period of two years in order to investigate the performance and the operating characteristics of the plant concept developed for the extension of the main Vienna STP and to develop a simulation model which will be applied for operation support of the full stage plant . The pilot plant is a two stage activated sludge plant, each stage comprising of four aeration tanks and a clarifier tank . The pilot plant layout allows three different operational modes, each of which has been operated for several periods . The performance of the pilot plant during these periods is described and the different operational modes are compared to each other. Chemosphere, 2001 Aug, 44(4), 865 - 72 Primary biodegradation of veterinary antibiotics in aerobic and anaerobic surface water simulation systems; Ingerslev F et al.; The primary aerobic and anaerobic biodegradability at intermediate concentrations (50-5000 microg/l) of the antibiotics olaquindox (OLA), metronidazole (MET), tylosin (TYL) and oxytetracycline (OTC) was studied in a simple shake flask system simulating the conditions in surface waters . The purpose of the study was to provide rate data for primary biodegradation in the scenario where antibiotics pollute surface waters as a result of run-off from arable land . The source of antibiotics may be application of manure as fertilizer or excreta of grazing animals . Assuming first-order degradation kinetics, ranges of half-lives for aerobic degradation of the four antibiotics studied were 4-8 days (OLA), 9.5-40 days (TYL), 14-104 days (MET) and 42-46 days (OTC) . OLA and OTC were degraded with no initial lag phase whereas lag phases from 2 to 34 days (MET) and 31 to 40 days (TYL) were observed for other substances . The biodegradation behaviour was influenced by neither the concentrations of antibiotics nor the time of the year and location for sampling of surface water . Addition of 1 g/l of sediment or 3 mg/l of activated sludge from wastewater treatment increased the biodegradation potential which is believed to be the result of increased bacterial concentration in the test solution . Biodegradation was significantly slower in tests conducted in absence of oxygen . Assessments of the toxic properties of antibiotics by studying the influence on the biodegradation rates of 14C-aniline at different concentrations of antibiotics showed that no tests were conducted at toxic concentrations. Chemosphere, 2001 Aug, 44(4), 823 - 6 Biodegradability of ethylenediamine-based complexing agents and related compounds; Pitter P et al.; The biological degradability (Zahn-Wellens test) of ethylenediamine derivatives with carboxymethyl and 2-hydroxyethyl groups was investigated . Mixed bacterial culture (activated sludge) was used as inoculum (non-adapted sludge and sludge adapted at different mean biomass retention time, the so-called sludge age) . Biodegradability of ethylene(propylene)di(tri)amine-based complexing agents depends on the character and number of substituents and nitrogen atoms in the molecule . Tetra(penta)substituted derivatives with two or more tertiary nitrogen atoms and carboxymethyl or 2-hydroxyethyl groups in the molecule (EDTA, DTPA, PDTA, HEDTA) are very stable from an environmental point of view . On the contrary, disubstituted derivatives with two secondary nitrogen atoms in the molecule (e.g., EDDA) are potentially degradable. Chemosphere, 2001 Aug, 44(4), 721 - 8 Degradability of selected azo dye metabolites in activated sludge systems; Ekici P et al.; The stability of eight environmentally relevant azo dye metabolites {o-aminotoluene (2), 4,4'-thiodianiline (4), 4,4'-diaminodiphenylmethane (6), p-chloroaniline (7), 2,4-toluylenediamine (9), p-kresidine (14), 2,4-diaminoanisole (15), and 2-naphthylamine (18)} was investigated in activated sludge systems and compared to their hydrolysis stability . For both studies, test systems of the EC and EPA were used . The results show that degradation under aerobic conditions proceeds via oxidation of the substituents located on the aromatic ring or on the side chain . Under anaerobic conditions, the azo bond is reductively cleaved, which leads to the substituted amines . These are toxic and potentially hazardous to the environment. J Environ Biol, 2001 Jan, 22(1), 23 - 7 Microbial decolourisation of pulp and paper mill effluent in presence of nitrogen and phosphorus by activated sludge process; Chandra R; The effect of pH, nutrient and aeration was studied on the removal of colour and reduction of BOD, COD and heavy metals with addition of readily available source of nitrogen and phosphorus in concentration of 1.0 g/L . Recalcitrant compound was effectively degraded by active microbial consortia . The isolated bacteria were identified as Pseudomonas putida (S1), Citrobacter sp . (S4) and Enterobacter sp . (S5) . These organisms not only decolourised effluent upto 97% but reduced BOD, COD, phenolics and sulfide upto 96.63, 96.80, 96.92 and 96.67% respectively within 24 hrs of aeration and the heavy metals were removed upto 82-99.80% . The TSS and TDS were sharply reduced due to degradation . The absorption maxima was also decreased to 90% . However, in control without the microbial consortium no noticeable change was produced. J Appl Microbiol, 2001 Aug, 91(2), 299 - 305 Synthesis of intracellular storage polymers by Amaricoccus kaplicensis, a tetrad forming bacterium present in activated sludge; Falvo A et al.; AIMS: The study investigated the physiology of Amaricoccus kaplicensis to determine whether it could outcompete polyphosphate accumulating bacteria in activated sludge systems removing phosphorus, by preferentially assimilating substrates in the anaerobic stages of these processes . METHODS AND RESULTS: The storage processes were investigated under anaerobic, anoxic and aerobic conditions in both batch and periodically fed cultures in an aerobic sequencing batch reactor (SBR) . Amaricoccus kaplicensis showed a high capacity for storing aerobically large amounts of acetate as poly beta-hydroxybutyrate (PHB) at high rates . However, no acetate assimilation under anaerobic conditions and very slow assimilation under anoxic conditions could be detected . CONCLUSION: Amaricoccus kaplicensis in pure culture does not behave as polyphosphate accumulating bacteria competitor; therefore it is difficult to understand why anaerobic/aerobic systems often contain such large numbers of Amaricoccus cells . SIGNIFICANCE AND IMPACT OF THE STUDY: Amaricoccus kaplicensis is probably not responsible for the failure of activated sludge systems removing phosphorus, and other organisms capable of anaerobic substrate assimilation should be sought. Water Sci Technol, 2001, 43(12), 183 - 6 Occurrence of Cryptosporidium in Japan and counter-measures in wastewater treatment plants; Suwa M et al.; The outbreak of cryptosporidiosis in Ogose in 1996 forced the wastewater treatment authorities to rethink the level of contamination by Cryptosporidium of wastewater and waters in the watersheds and counter-measures in wastewater treatment plants . A survey of Cryptosporidium concentrations in wastewater and treated wastewater conducted nationwide showed relatively low levels . Also, evaluation of wastewater treatment showed a 2 log oocyst removal with an activated sludge process and an additional 1 log removal with coagulant dosing. J Environ Sci Health A Tox Hazard Subst Environ Eng, 2001 May, 36(5), 819 - 31 Domestic wastewater treatment using immobilized sludge fluidized-bed reactors; An M et al.; Bench-scale fluidized-bed reactors using the immobilized activated sludge process were studied for the treatment of domestic wastewater . Different intermittent aeration patterns were investigated in order to improve the total nitrogen (TN) removal . The best TN removal at 74.4% was achieved at an HRT of 6 hours (with corresponding BOD loading rate of 0.766 kg/m3/d) and an aeration-pattern of 1,3 (the hours of aeration and non-aeration time cycle) . The removal efficiencies for organic carbon, NH4(+)-N, TKN and TSS were not affected and remained at more than 90% . Simultaneous organic carbon and nitrogen removal was accomplished in a single immobilized sludge reactor . The impact of various influent feed patterns on the treatment was examined . The continuous feed pattern was recommended as it ensured good TN removal without any adverse impacts on the removal of organic carbon, NH4(+)-N, TKN and TSS . The immobilized sludge beads exhibited satisfactory mechanical stability without apparent breakage over the 180-day experiment period. Water Res, 2001 Aug, 35(11), 2702 - 10 Nutrient addition to enhance biological treatment of greywater; Jefferson B et al.; This study compares the chemical oxygen demand (COD) removal and respiration rates of a microbial population treating real and synthetic greywaters dosed with nutrient supplements . The nutrient composition of the real and synthetic greywaters was analysed and the dosing regime for nitrogen, phosphorus and a range of trace metals planned accordingly . The doses consisted of eight single additives (macronutrients and trace metals) to the control greywater and six trace metal additions to C: N : P balanced greywater . The COD removal for the control real and synthetic greywater in lab-scale activated sludge systems (0.038 and 0.286 kg COD kg MLSS(-1) d(-1), respectively) confirmed nutrient limitation and the poor degree of greywater treatment . Nutrient dosing increased the COD removal rate and oxygen uptake rate in many cases . The greatest stimulation of microbial activity was observed with zinc additions to C: N: P balanced real greywater (1.291 kg COD kg MLSS(-1) d(-1) over 30 times the control) . Inhibitory effects to various extents were rare and limited mainly to the additions of metals to synthetic greywater . The dominance of chemicals effects was observed on addition of some micronutrients; notably iron and aluminium, metals on which many coagulants for use in biotreatment of other wastewaters are based . The data indicate that the impact of understanding microbial processes and the nutrients required for wastewater treatment can only serve to optimise process efficiency for the proposed treatment of greywater. Water Res, 2001 Aug, 35(11), 2693 - 701 Simultaneous storage and degradation of PHB and glycogen in activated sludge cultures; Carta F et al.; Bacteria in activated sludge are subjected to periods of substrate availability and absence of external substrates . The response of bacteria to such dynamic conditions was studied in a 2 L sequencing batch reactor (SBR) by subjecting a mixed microbial population to successive periods of external substrate availability (feast period) and no external substrate availability (famine period) . In previous studies, acetate or glucose was used as single substrate leading to the storage of polyhydroxybutyrate or glycogen, respectively . In this study, a mixture of acetate and glucose was used . It appeared that both substrates were consumed simultaneously . The relative contribution of growth and storage processes was in these experiments similar as in the systems fed with a single substrate only . The ratio of substrate uptake over substrate storage was 0.6 Cmol/Cmol for both substrates . The uptake rate of acetate was not influenced by the simultaneous uptake of glucose . The degradation kinetics and rates of the storage compounds were the same as for the systems in which only one compound was stored in the activated sludge . The global performance of the culture grown on mixed substrates could therefore be described as the sum of the conversions observed in cultures fed with the individual substrates. Water Res, 2001 Aug, 35(11), 2661 - 8 The storage of acetate under anoxic conditions; Dionisi D et al.; Till now the role of storage in activated sludge processes under transient conditions has been deeply investigated under anaerobic (EBPR processes) or aerobic (bulking control) environments . Little attention has been given to the role of storage in processes including anoxic environments . Hence, the aim of the present work was to investigate the anoxic storage along with other substrate removal mechanisms under transient conditions . Several mixed culture were ad hoc selected under anoxic environment and periodic feeding (acetate as carbon source) at different organic load rate (OLR) and feed length; then their transient response to substrate spike was investigated by batch tests under both anoxic and aerobic conditions . The relative role of different mechanisms in the substrate removal was established on the basis of COD balance assuming that the acetate COD removed from the liquid phase could be oxidised for energy needs or recovered into solids as poly-3-hydroxybutyric acid (PHB) (storage), other internal precursors or intermediates (accumulation) and active biomass (growth, as estimated by ammonium uptake) . In all tested conditions, growth response was very little while PHB storage was prevailing . In some operating conditions, indirect evidence of accumulation (in forms still to be identified) was also found . The transient response was not affected by the presence of free amino acids, at least for the unacclimated mixed culture under observation . Transient response under aerobic condition was quite similar to the anoxic one. Water Res, 2001 Aug, 35(11), 2615 - 20 Effect of acid and surfactant treatment on activated sludge dewatering and settling; Chen Y et al.; The effect of pretreating activated sludge with sulfuric acid and surfactant on its exocellular polymer(ECP), dewaterability and settleability was investigated . It was observed that the centrifugal dewatering efficiency was increased with the decrease of sludge pH value, and which was further improved if the surfactant was simultaneously applied . However, to the filtration dewatering, the water content reached the minimum in the case of pH 2.5, and the additional use of surfactant was also favorable . The water content of sludge dewatered with filtration reached 73.99% when a pH 2.5 and a 0.1 g surfactant were employed, which was reduced by around 2% as compared with surfactant unused . Experimental results indicated that the sludge sedimentation rate was significantly accelerated under pH 2.5 condition, and which was increased once more by the utilization of surfactant . Further studies revealed that treating activated sludge with sulfuric acid at pH 2.5 or combined with surfactant was an effective method to remove the polymers from sludge surface and induced the decrease of ECP, which resulted in the improvement of dewaterability and settleability . This study suggested the potentiality of improving activated sludge mechanical dewaterability by the use of sulfuric acid to control its pH at 2.5 or together with a surfactant. Water Sci Technol, 2001, 43(11), 75 - 82 Activated sludge flocculation: direct determination of the effect of calcium ions; Biggs CA et al.; The effect of calcium on activated sludge flocculation dynamics is investigated using a unique experimental technique . The technique allows on-line analysis of the size of activated sludge flocs during flocculation and provides valuable insight into the mechanisms of flocculation . Activated sludge samples were firstly sonicated for 3 minutes at 50 W and then stirred at 100 rpm . The floc size was subsequently measured on-line using a Malvern Mastersizer/E . For concentrations of calcium less than 4 meq/L no significant increase in final floc size was observed even though an increase in the initial rate of change of floc size could be seen . Addition of calcium greater than 4 meq/L resulted in a dramatic increase in floc size . Results from this investigation support the theory that cations are involved in flocculation through cationic bridging, and will be used in ongoing investigations to model the flocculation process. Water Sci Technol, 2001, 43(11), 51 - 8 Aerobic treatment of inhibitory wastewater using a high-pressure bioreactor with membrane separation; Male PC et al.; Wastewater high in phenolic content (948 mg/l) and dissolved solids (5.4 g/l) had to be treated to remove most of the organic material and toxic compounds . A laboratory scale High Pressure (3 bar) Bioreactor (HPB) was developed and operated to treat the wastewater using a ceramic ultra filtration membrane as biomass separator . The performance of the system was compared to a normal activated sludge plant (ASP) using sludge settling for separation . The HPB was more stable than the ASP, which twice became unstable with a resulting biomass loss . Both reactors removed 90% of the chemical oxygen demand (COD) loading, reducing the phenol concentration below 20 mg/l . The maximum COD removal rate of the HPB was 28 kg/m3.d compared to 15 kg/m3.d of the ASP, while the HPB achieved 16-32 times better oxygen transfer than the ASP . It was concluded that the HPB was the preferred treatment system compared to the ASP, when treating high strength inhibitory wastewaters, due to its stable operating performance and high COD removal rate. Water Sci Technol, 2001, 43(11), 323 - 8 Performance evaluation of a UASB--activated sludge system treating municipal wastewater; von Sperling M et al.; Recent research has indicated the advantages of combining anaerobic and aerobic processes for the treatment of municipal wastewater, especially for warm-climate countries . Although this configuration is seen as an economical alternative, is has not been investigated in sufficient detail on a worldwide basis . This work presents the results of the monitoring of a pilot-scale plant comprising of an UASB reactor followed by an activated sludge system, treating actual municipal wastewater from a large city in Brazil . The plant was intensively monitored and operated for 261 days, divided into five different phases, working with constant and variable inflows . The plant showed good COD removal, with efficiencies ranging from 69% to 84% for the UASB reactor, from 43% to 58% for the activated sludge system only and from 85% to 93% for the overall system . The final effluent suspended solids concentration was very low, with averages ranging from 13 to 18 mg/l in the typical phases of the research . Based on the very good overall performance of the system, it is believed that it is a better alternative for warm-climate countries than the conventional activated sludge system, especially considering the total low hydraulic detention time (4.0 h UASB; 2.8 h aerobic reactor; 1.1 h final clarifier), the savings in energy consumption, the absence of primary sludge and the possibility of thickening and digesting the aerobic excess sludge in the UASB reactor itself. Water Sci Technol, 2001, 43(11), 145 - 52 Transfer number in fine bubble diffused aeration systems; Capela S et al.; On the basis of full-scale data from 58 clean water tests performed in 26 activated sludge tanks equipped with fine bubble diffusers and of a theoretical approach, it can be stated that fine bubble aeration systems with total floor coverage arrangement provide higher kLa values and the lowest spiral liquid circulation . An efficiency criterion for oxygen transfer (NT) was defined on the basis of the dimensional analysis . The transfer number NT allows us to take account of the impact of vertical liquid circulation movements on oxygen transfer . The values of NT calculated from the results of full scale nonsteady-state clean water tests vary from 5.3 x 10(-5) to 9.1 x 10(-5) and are directly dependent upon the arrangement of air diffusers . It has been shown that the highest transfer numbers corresponded to the total floor coverage arrangement and the average calculated NT values is 7.7 x 10(-5), independently of the diffuser density and of the gas velocity, over the ranges studied . The lowest transfer numbers are obtained when the diffusers are located in separate grids, and the transfer number is reduced with increasing air flow rate. Lett Appl Microbiol, 2001 Jul, 33(1), 17 - 20 A microwave-based method for nucleic acid isolation from environmental samples; Orsini M et al.; AIMS: A simple and rapid method was described for DNA isolation directly from activated sludge or other environmental sources, including soil and sediments . METHODS AND RESULTS: The present method is based on microwave thermal shock and provides DNA suitable for further analysis . It is also effective for RNA extraction . CONCLUSION: The protocol is effective, easy, fast and does not require the use of expensive equipment or reagents . SIGNIFICANCE AND IMPACT OF THE STUDY: The described method can be applied to difficult substrates in environmental microbiology studies. J Appl Microbiol, 2001 Jul, 91(1), 168 - 75 Microscopic observation of aerobic granulation in sequential aerobic sludge blanket reactor; Tay JH et al.; AIMS: This paper attempts to provide visual evidence of how aerobic granulation evolves in sequential aerobic sludge blanket reactors . METHODS AND RESULTS: A series of experiments were conducted in two column-type sequential aerobic sludge reactors fed with glucose and acetate as sole carbon source, respectively . The evolution of aerobic granulation was monitored using image analysis and optical and scanning electron microscopy . The results indicated that the formation of aerobic granules was a gradual process from seed sludge to compact aggregates, further to granular sludge and finally to mature granules with the sequential operation proceeding . Glucose- and acetate-fed granules have comparable characteristics in terms of settling velocity, size, shape, biomass density and microbial activity . However, the microbial diversity of the granules was associated with the carbon source supplied . In this work, an important aerobic starvation phase was identified during sequential operation cycles . It was found that periodical aerobic starvation was an effective trigger for microbial aggregation in the reactor and further strengthened cell-cell interaction to form dense aggregates, which was an essential step of granulation . The periodical starvation-induced aggregates would finally be shaped to granules by hydrodynamic shear and flow . CONCLUSION: Aerobic granules can be formed within 3 weeks in the systems . The periodical starvation and hydrodynamic conditions would play a crucial role in the granulation process . SIGNIFICANCE AND IMPACT OF THE STUDY: Aerobic granules have excellent physical characteristics as compared with conventional activated sludge flocs . This research could be helpful for the development of an aerobic granule-based novel type of reactor for handling high strength organic wastewater. Ecotoxicol Environ Saf, 2001 Jul, 49(3), 275 - 80 Toxicity of organotin compounds to activated sludge; Stasinakis AS et al.; Inhibition of respiration rate of activated sludge heterotrophic microorganisms was determined for tributyltin (TBT), dibutyltin (DBT), monobutyltin (MBT), and triphenyltin (TPhT) . TBT, DBT, and TPhT exhibit similar acute toxicity to activated sludge, while MBT is less toxic . The effect of various experimental parameters, such as sludge age, concentrations of suspended solids, and exposure time, on toxicity was investigated . An increase in sludge age or in the concentration of suspended solids reduces the observed inibition . Longer exposure seems to increase the inhibition of TBT, DBT, and TPhT during the first hours of exposure, while later the inhibition remains constant . In the case of MBT, 24 h after exposure, the respiration rate was similar to that of the control biomass . Water Sci Technol, 2001, 43(10), 203 - 9 Feasibility of the membrane bioreactor process for water reclamation; Adham S et al.; The feasibility of the membrane bioreactor (MBR) process for water reclamation was studied . Process evaluation was based on the following: literature review of MBRs, worldwide survey of MBRs, and preliminary costs estimates . The literature review and the survey have shown that the MBR process offers several benefits over the conventional activated sludge process, including: smaller space and reactor requirements, better effluent water quality, disinfection, increased volumetric loading, and less sludge production . The MBR process can exist in two different configurations, one with the low-pressure membrane modules replacing the clarifier downstream the bioreactor (in series), and the second with the membranes submerged within the bioreactor . Four major companies are currently marketing MBRs while many other companies are also in the process of developing new MBRs . The MBR process operates in a considerably different range of parameters than the conventional activated sludge process . The preliminary cost evaluation has shown that the MBR process is cost competitive with other conventional wastewater treatment processes. Environ Toxicol Chem, 2001 Jul, 20(7), 1517 - 27 Reproductive, biochemical, physiological, and population responses in perch (Perca fluviatilis L.) and roach (Rutilus rutilus L.) downstream of two elemental chlorine-free pulp and paper mills; Karels A et al.; Perch (Perca fluviatilis L.) and roach (Rutilus rutilus L.) populations in a state of late vitellogenesis were studied downstream of two pulp and paper mills and at upstream references in southern Lake Saimaa, Finland . The mills used elemental chlorine-free bleaching and activated sludge effluent treatment technologies . The exposure of fish to pulp mill effluents, as measured by concentrations of chlorophenolics in the bile and liver ethoxyresorufin-O-deethylase (EROD) activity, was low and almost similar to the references . Nevertheless, bile resin acid concentrations in exposed perch and roach (260-320 micrograms/ml) and bile beta-sitosterol concentrations in exposed roach (1.5-3.5 micrograms/ml) were, respectively, 10 to 30 times and 2 to 5 times higher compared with the references . Reproductive parameters like plasma 17 beta-estradiol and testosterone levels were lower in exposed male and female perch but the same in roach . Vitellogenin concentrations in plasma and liver cytosol of roach were similar . Gonad weight and fecundity were lower in exposed female perch but similar in roach . The relative liver weight was higher in exposed roach but not in perch . The body condition and immunologic parameters in fish were the same . The growth and age at maturity of exposed perch and roach were similar to the references . The size and age distribution of perch in the recipient of one of the mills was shifted toward smaller and younger fish . Our results show that several reproductive variables were altered in late vitellogenic perch in the vicinity of the mills, but they were not altered in roach. Huan Jing Ke Xue, 2001 Mar, 22(2), 41 - 5 {Biodegradation behavior of ethylenediaminetetraethylene acid}; Yang X et al.; Aerobic and anaerobic degradability of ethylenediaminetetraethylene acid(EDTA) were measured on Warburg respirometer and anaerobic batch reactors . Biodegradation of EDTA as a single substance was poor, but biodegradation of EDTA with co-substrate could be improved . The wastewater containing EDTA can be treated by activated sludge process . The EDTA removal efficiency was 80% under the circumstance HRT 16 h and EDTA removal efficiency reached to 92.5%-95.1% when HRT was 20 h . The main factor affecting the biodegradability of EDTA is sludge remained time. Environ Technol, 2001 May, 22(5), 497 - 507 Evaluation of Activated Sludge Model No . 2 at high phosphorus concentrations; Seco A et al.; This paper presents laboratory scale experimentation carried out to study enhanced biological phosphorus removal at high phosphorus concentrations in a sequencing batch reactor . Four series of data obtained in a sequencing batch reactor are examined in light of the Activated Sludge Model No . 2 . This model was calibrated using data from the first and second series working at low phosphorus concentrations . The Activated Sludge Model No . 2 successfully characterised the enhanced biological phosphorus removal performance of the sequencing batch reactor at low phosphorus concentrations . The calibrated model was then used to adjust experimental results of the other series working at high phosphorus concentration . Differences between model predictions and experimental data could be explained by redissolution in the anaerobic phase and precipitation in the aerobic phase of calcium phosphates not taken into account by the model . This hypothesis can be justified by the conditions of pH and phosphorus concentration prevailing in the experiments and it was confirmed by the results of another experiment in which precipitated phosphorus profile was measured during the cycle. J Ind Microbiol Biotechnol, 1999 Oct, 23(4-5), 374 - 379 Lessons learned from Sphingomonas species that degrade abietane triterpenoids; Mohn WW et al.; Abietane terpenoid-degrading organisms include Sphingomonas spp which inhabit natural environments and biological treatment systems . An isolate from the high Arctic indicates that these organisms occur far from trees which synthesize abietanes and suggests that some of these organisms can occupy a niche in hydrocarbon-degrading soil communities . Abietane-degrading Sphingomonas spp provide additional evidence that the phylogeny of this genus is independent of the catabolic capabilities of its members . Studies of Sphingomonas sp DhA-33 demonstrate that biological treatment systems for pulp mill effluents have the potential to mineralize abietane resin acids . On the other hand, these studies indicate that some chlorinated dehydroabietic acids are quite recalcitrant . Strain DhA-33 grows relatively well on some chlorinated dehydroabietic acids but transforms others to stable metabolites . Using strain DhA-33, a novel method was developed to measure the metabolic activity of an individual population within a complex microbial community . Oligonucleotide hybridization probes were used to assay the 16S rRNA:rDNA ratio of DhA-33 as it grew in an activated sludge community . However, this method proved not to be sufficiently sensitive to measure naturally occurring resin acid-degrading populations . We propose that the same approach can be modified to use more sensitive assays. J Ind Microbiol Biotechnol, 1999 Oct, 23(4-5), 261 - 267 Detection of sphingomonads and in situ identification in activated sludge using 16S rRNA-targeted oligonucleotide probes; Neef A et al.; The increasing significance of members of the genus Sphingomonas in biotechnological applications has led to an increased interest in the diversity, abundance and ecophysiological potential of this group of Gram-negative bacteria . This general focus provides a challenge to improve means for identification of sphingomonads; eg molecular genetic methods for rapid and specific detection could facilitate screening of new isolates . Here, fluorescently labeled oligonucleotide probes targeted against 16S rRNA were used to typify strains previously assigned to the genus . All 46 sphingomonads tested including type strains of 21 Sphingomonasspecies could be detected with a probe originally designed for the genus and all but one with a probe designed for the alpha-4 subgroup of the Proteobacteria . The two probes are suitable for direct detection of sphingomonads in pure and mixed cultures as well as in environmental samples of unknown composition . The probes were used to identify sphingomonads in situ in activated sludge samples . Sphingomonads were rather abundant accounting for about 5-10% of the total cells in municipal sludges . Distinct patterns in aggregation of the cells suggest that these organisms could be involved in the formation process of sludge flocs. Chemosphere, 2001 Jul, 44(1), 37 - 43 Efficiency of biological treatment affected by high strength of ammonium-nitrogen in leachate and chemical precipitation of ammonium-nitrogen as pretreatment; Li XZ et al.; Leachate samples with a high strength of ammonium-nitrogen (NH4+-N) were collected from a local landfill site in Hong Kong . Two experiments were carried out to study (1) the inhibition of microbial activity of activated sludge by NH4+-N and (2) the chemical precipitation of NH4+-N from leachate as a preliminary treatment prior to the activated sludge process . The experimental results demonstrated that the efficiency of COD removal decreased from 97.7% to 78.1%, and the dehydrogenase activity of activated sludge decreased from 9.29 to 4.93 microg TF/mg MLSS, respectively, when the NH4+-N concentration increased from 53 to 800 mg/l . The experiment also demonstrated that the NH4+-N in the leachate can be quickly precipitated as MgNH4PO4 x 6H2O after addition of MgCl2 x 6H2O + Na2HPO4 x 12H2O . The NH4+-N concentration was reduced from 5618 to 112 mg/l within 15 min when a molar ratio of Mg2+:NH+:PO4(3-) = 1:1:1 was used . The optimum pH to reach the minimum solubility of MgNH4PO4 x 6H2O was found to be in the range of 8.5-9.0 . Attention should be given to the high salinity formed in the treated leachate by using MgCl2 x 6H2O + Na2HPO4 x 12H2O, which may affect microbial activity in the following biological treatment processes . Using two other combinations of chemicals {MgO + 85%H3PO4 and Ca(H2PO4)2 x H2O + MgSO4 x 7H2O} could minimise salinity generation after precipitation, while they were less efficient for NH4+-N removal. Appl Microbiol Biotechnol, 2001 May, 55(5), 609 - 18 Insights into the genetic diversity of initial dioxygenases from PAH-degrading bacteria; Moser R et al.; Alpha subunit genes of initial polyaromatic hydrocarbon (PAH) dioxygenases were used as targets for the PCR detection of PAH-degrading strains of the genera Pseudomonas, Comamonas and Rhodococcus which were obtained from activated sludge or soil samples . Sequence analysis of PCR products from several Pseudomonas strains showed that alpha subunits (nahAc allele) of this genus are highly conserved . PCR primers for the specific detection of alpha subunit genes of initial PAH dioxygenases from Pseudomonas strains were not suitable for detecting the corresponding genes from the genera Comamonas and Rhodococcus . Southern analysis using a heterologous gene probe derived from the P . putida OUS82 PAH dioxygenase alpha subunit identified segments of the PAH-degradation gene cluster from C . testosteroni strain H . Parts of this gene cluster containing three subunits of the initial PAH dioxygenase were isolated . These three subunits {ferredoxin (pahAb), alpha (pahAc) and beta (pahAd) subunit} were amplified by PCR as one fragment and expressed in Escherichia coli DH5alpha, resulting in an active initial dioxygenase with the ability to transform indole and phenanthrene . The DNA sequence alignment of alpha subunits from C . testosteroni H and various PAH-degrading bacteria permitted the design of new primers and oligonucleotide probes which are useful for the detection of the initial PAH dioxygenases from strains of Pseudomonas, Comamonas and Rhodococcus. J Environ Sci Health A Tox Hazard Subst Environ Eng, 2001, 36(4), 447 - 63 Toxicity and biodegradation of products from polyester hydrolysis; Kim MN et al.; Toxicity of products from polyester hydrolysis such as succinic acid (SA), adipic acid (AA), mandelic acid (MA), terephthalic acid (TA), 1,4-butanediol (1,4-B), ethylene glycol (EG), styrene glycol (SG) and 1,4-cyclohexane dimethanol (1,4-C) was evaluated by phytotoxicity test on germination of young radish seeds and by cytotoxicity test on HeLa cells . The phytotoxicity test revealed SG > MA > 1,4-C > AA approximately SA > TA approximately EG > 1,4-B in order of decreasing toxicity taking into consideration the growth behavior after germination as well as the percentage of germination . Toxicity on HeLa cells decreased in slightly different order compared to that on young radish seeds, i.e . SG > 1,4-C > MA > TA > SA > AA > EG > 1,4-B . Tests for the phytotoxicity and for cytotoxicity indicated that the aromatic compounds were more harmful than the aliphatic ones . Each group of 4 strains which grew most rapidly on each agar plate containing SA, AA, MA, TA, 1,4-B, EG, SG and 1,4-C respectively as a sole carbon source was identified by the fatty acid methyl esters analysis . The modified Sturm test was carried out using the single isolated strain, an activated sludge or a mixed soil to measure the rate of mineralization of the compounds into carbon dioxide . The aliphatic compounds were mineralized more easily than the aromatic compounds . 1,4-C showed the most exceptionally slow degradation . A scrutiny of residual 1,4-C after degradation is required before polyesters containing 1,4-C could be classified into compostable because 1,4-C has detrimental effects on young radish seeds and HeLa cells and has a tendency to accumulate in the environment due to its slow degradability. Water Res, 2001 Jul, 35(10), 2543 - 53 A simple system to rapidly monitor activated sludge health and performance; Archibald F et al.; A set of four assays designed to rapidly measure the health and biodegradative performance of pulp and paper mill activated sludges was developed . Three of the assays are specific oxygen uptake rates (SOURs) that measure the normal "working" aeration tank BOD (biochemical oxygen demand) removal rate (SOURAT), a near-maximum BOD removal rate (SOURNMAX), and a rate (SOURTOX) used in combination with the SOURNMAX to indicate the presence of toxic or inhibitory substances . The fourth assay is the specific adenosine triphosphate (SATP) content of the sludge, used as a measure of its viable cell content . Fresh biomass (sludge) samples from one laboratory reactor and four mill biotreatment systems were fed raw mill effluents and used to evaluate the four-assay set . The SOURAT values of all systems were 10-40% of their SOURNMAX values: thus the SOURAT:SOURNMAX ratios indicate that each system's free biodegradative capacity was far greater than its operating rate . It was demonstrated using phenol that the SOURNMAX:SOURTOX ratio can indicate the presence of substances toxic or inhibitory to the biomass . The results also indicated that the SOURNMAX is a much better indicator of improving or worsening sludge performance and capacity than the SOURAT . SATP was shown to be a useful monitor of the proportion of viable cells in an activated sludge and a toxicity indicator complementary to the SOURNMAX:SOURTOX ratio and similar in principle to the commercial Microtox toxicity test . This four-assay set was also applied to three practical situations: (a) at-mill monitoring of a biotreatment system; (b) effects of cold storage on biomass; and (c) effects of decreased BOD loading on biomass. Water Res, 2001 Jul, 35(10), 2523 - 33 The fate of xenobiotic organic compounds in wastewater treatment plants; Byrns G; The effective operation of wastewater treatment plants plays an important role in minimising the release of xenobiotic compounds into the aquatic environment . Considerable effort has been expended in developing models to quantify the overall removal and fate of these compounds in biological treatment plants . A synthesis and modification of these approaches has been made and a generalised fate model for organic compounds in an activated sludge plant is presented . The influence of the different removal mechanisms, such as sorption, volatilisation and advection for chemicals with different physico-chemical properties is investigated and the important role of biotransformation is discussed . The effect of some operating parameters has been found to have an important influence upon the concentration of xenobiotic released in the sludges and final effluent . This may have significance for a wide range of ecotoxic compounds and in particular the class of compounds increasingly recognised as having the potential to disrupt endocrine activity in some aquatic vertebrates. Water Res, 2001 Jul, 35(10), 2377 - 84 Experimental analysis of centrifugal dewatering process of polyelectrolyte flocculated waste activated sludge; Chu CP et al.; The study experimentally investigated the centrifugal separation of moisture from activated sludge subject to cationic polyelectrolyte flocculation . An arm-suspended centrifuge was employed which allowed in-situ detection on all positions of interfaces of centrifuged sludge as functions of time . Experimental results revealed that, sludge flocculation would yield a significant sedimentation effect at the first phase of centrifugation . Therefore, not as suggested in conventional centrifugal-filtration models, the most significant moisture-removal stages included filtrate to flow through a wet cake . Moreover, an optimal rotational speed exists at which the moisture-removal rate reaches a maximum value . New theories/correlations are required to describe centrifugation dewatering of polyelectrolyte flocculated sludge. Water Sci Technol, 2001, 43(8), 83 - 90 Evaluation of flocculation and dissolved air flotation as an advanced wastewater treatment; Pinto Filho AC et al.; A bench scale study was carried out in order to evaluate the applicability of dissolved air flotation (DAF) as an advanced treatment for effluents from three different domestic wastewater treatment processes, namely: (i) a tertiary activated sludge plant; (ii) an upflow sludge blanket anaerobic reactor (UASB); and (iii) a high-rate stabilization pond. Environ Sci Technol, 2001 May 15, 35(10), 1989 - 95 Organochlorine pesticide residues in archived UK soil; Meijer SN et al.; Archived background soils ("Broadbalk', 1944-1986) and sludge-amended soils ("Luddington", 1968-1990), collected from long-term agricultural experiments in the UK, were analyzed for a range of organochlorine (OC) pesticides to establish trends over time . Concentrations typically ranged from 0.1 to 10 ng/g of soil (dry weight), with gamma-hexachlorocyclohexane (gamma-HCH), dieldrin, and p,p'-DDE consistently having the highest concentrations . The trends in the Broadbalk background soils are largely consistent with usage patterns, with peak concentrations occurring in the 1960s for DDTs and between the 1960s and the 1980s for the other OCs . In the Luddington control and sludge-amended soils, several of the OCs show a significant decline in concentrations from the late 1960s to 1990, with half-lives ranging from approximately 7 years (alpha-HCH) to approximately 25 years (dieldrin) . The sludge-amended plot received 125 tonnes of sludge per ha in 1968, which was mixed in to a depth of 15 cm . It appears that the sludge treatment had little effect on concentrations in the soil, with no significant difference between control soil and sludge-amended soil for most compounds, except for HCB, p,p'-DDE, and dieldrin . Enantiomeric fractions (EFs) of some chiral pesticides (alpha-HCH, cis- and trans-chlordane, and o,p'-DDT) were determined in the Luddington soils . Results reveal that enantioselective degradation of OC pesticides is occurring in these soils for trans-chlordane (TC) and cis-chlordane (CC) . However, the depletion over time is not statistically significant, and there is no statistically significant difference between EFs in the control soil and sludge-amended soil . This indicates that enantioselective microbial degradation was not consistent over time and that the addition of sludge to soil did not significantly alter the enantiomeric preference of the microbial community. Biotechnol Prog, 2001 May-Jun, 17(3), 462 - 7 Treatment of high strength distillery wastewater (cherry stillage) by integrated aerobic biological oxidation and ozonation; Beltran FJ et al.; The performance of integrated aerobic digestion and ozonation for the treatment of high strength distillery wastewater (i.e., cherry stillage) is reported . Experiments were conducted in laboratory batch systems operating in draw and fill mode . For the biological step, activated sludge from a municipal wastewater treatment facility was used as inoculum, showing a high degree of activity to distillery wastewater . Thus, BOD and COD overall conversions of 95% and 82% were achieved, respectively . However, polyphenol content and absorbance at 254 nm (A(254)) could not be reduced more than 35% and 15%, respectively, by means of single biological oxidation . By considering COD as substrate, the aerobic digestion process followed a Contois' model kinetics, from which the maximum specific growth rate of microorganisms (mu(max)) and the inhibition factor, beta, were then evaluated at different conditions of temperature and pH . In the combined process, the effect of a post-ozonation stage was studied . The main goals achieved by the ozonation step were the removal of polyphenols and A(254) . Therefore, ozonation was shown to be an appropriate technology to aid aerobic biological oxidation in the treatment of cherry stillage. Ecotoxicol Environ Saf, 2001 Jun, 49(2), 144 - 54 Effects of pulp mill effluents and restricted diet on growth and physiology of rainbow trout (Oncorhynchus mykiss); Mattsson K et al.; Juvenile female rainbow trout was exposed for 4.5 months (June to October) to two dilutions of untreated and activated sludge treated whole mill effluent from a pulp mill producing bleached ECF pulp . Two controls were used, on fed ad libitum and a second receiving 0.5% feed of the body weight . All effluent exposed groups were fed ad libitum . Mean weight of the fish was measured monthly . At the end of the experiment a number of physiological and biochemical parameters were analyzed in order to establish the physiological status of the exposed fish in comparison with unexposed fish that obtained ad libitum or restricted amount of feed . The fish exposed to treated effluent grew significantly more than ad libitum control fish until August, whereupon growth retarded in fish exposed to the lower effluent dilution (400 v/v) . The growth of fish exposed to untreated effluent did not deviate significantly from the control fed ad libitum . The results from the hematological analysis clearly showed that fish fed restricted amount of feed deviated significantly in most parameters compared with the control fed ad libitum . Fish exposed to treated effluent showed a response pattern similar to that of the control fed restricted amount of feed, whereas the fish exposed to untreated effluent showed a response pattern that did not deviate from that of the ad libitum control . The metabolic parameters suggested that fish exposed to treated effluent had a higher metabolic demand than ad libitum control and that the energy allocation at the end of the experiment was directed to processes other than growth . The responses on hematology were mainly a consequence of the increased energy demand and were not primary effects . The implications of using feed related parameters at field studies are discussed . Ecotoxicol Environ Saf, 2001 May, 49(1), 40 - 53 Structure of microbial communities in activated sludge: potential implications for assessing the biodegradability of chemicals; Forney LJ et al.; Various methods used to assess the biodegradability of chemicals often employ activated sludge as an inoculum since chemicals that ultimately enter the environment are often discharged through wastewater . Differences in the structure and function of activated sludge microbial communities that may complicate interpretation of biodegradation tests could arise from differences in wastewater composition, wastewater treatment plant (WWTP) operation, or manipulations done after collection of the activated sludge . In this study, various methods were used to characterize the structure of microbial communities found in freshly collected activated sludge from WWTPs in Japan, Europe, and the United States, as well as sludge that had been continuously fed either sewage or a glucose-peptone mixture for several weeks after collection . Comparisons of biomass levels, whole-community substrate utilization (determined using Biolog GN and GP plates), and phospholipid fatty acid (PLFA) profiles indicated there were both geographical and temporal differences among freshly collected activated sludge samples . Moreover, marked shifts in the structure of activated sludge microbial communities occurred upon continuous cultivation in the laboratory for 5 weeks using a glucose-peptone feed . These shifts were evident from whole-community substrate utilization and PLFA profiles as well as differences in the profiles of 16S rDNA genes from numerically dominant populations obtained by denaturing gradient gel electrophoresis and terminal restriction fragment analyses . Further studies are needed to better define the variability within and between activated sludge from wastewater treatment plants and laboratory reactors and to assess the impact of such differences on the outcome of biodegradability tests . Water Sci Technol, 2001, 43(7), 97 - 104 On-line viable biomass measurement and estimation of the specific growth rate of activated sludge from municipal wastewater treatment; November EJ et al.; In order to control wastewater processes, on-line measurements of important process variables are crucial . This contribution focuses on the applicability of the Biomass Monitor for on-line viable biomass measurement of activated sludge from a municipal wastewater plant . In addition, the specific growth rate of the sludge is estimated on-line, based on the information derived from the device under study . Compared to dry weight measurements, the Biomass Monitor hardware offers the advantage of a biologically more appropriate observation of the biomass by only taking into account the viable cells in the population . The optimal measurement frequency of the biomass monitoring device for the given experimental conditions has been determined . Furthermore, the capacitance readings have been correlated with off-line analyses of dry weight of the sludge during the experimental phase in which no death of cells occurred . Finally, an evaluation of the estimator of the specific growth rate including its tuning is presented. Water Sci Technol, 2001, 43(7), 91 - 6 Automated monitoring of activated sludge in a pilot plant using image analysis; 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, in complement to the usual settleability (sludge volume index, settling velocity) and size distribution (by laser granulometry) measurements. Water Sci Technol, 2001, 43(7), 9 - 17 Modelling of activated sludge acclimisation to a non-ionic surfactant; Carvalho G et al.; A model is proposed to describe activated sludge acclimatisation to a non-ionic surfactant . The model was calibrated automatically, using WEST, a specific software environment for wastewater treatment model building, simulation and parameter estimation . The assays have been performed in a sequencing-batch reactor (SBR), using a non-ionic surfactant as sole carbon source and non-acclimatised sludge . The best fitting model was based on the assumption of three sequentially degraded COD fractions, where the second fraction is a metabolite of the original molecule and the third fraction is a more slowly biodegradable metabolite resulting from the secondary degradation . For primary degradation, hydrolysis with no associated growth was assumed . The growth of microorganisms responsible for degradation of the second and third COD fractions was presumed to follow Haldane and first order kinetics, respectively . The model was able to fit four consecutive assays of the same acclimatisation process, using Brij 30 as carbon source, with different food/microorganism ratios . The parameters obtained showed that the (self-)inhibition of the growth on the second COD fraction decreased along acclimatisation. Water Sci Technol, 2001, 43(7), 39 - 46 Modelling and simulation of the steady-state of secondary settlers in wastewater treatment plants; Queinnec I et al.; This paper discusses the steady-state modelling of thickening in circular secondary settlers of activated sludge processes . The limitations of the solid flux theory basic models to represent steady-state operating conditions serve as a basis to introduce more sophisticated models derived from computational fluid dynamics . Parameter identification and sensitivity studies have been performed from lab-scale continuous experiments. Water Sci Technol, 2001, 43(7), 367 - 76 A systematic approach to error isolation in computerized wastewater simulation models; Lennox JA et al.; Activated sludge models are used extensively in the study of wastewater treatment processes . While various commercial implementations of these models are available, there are many people who need to code models themselves using the simulation packages available to them . Quality assurance of such models is difficult . While benchmarking problems have been developed and are available, the comparison of simulation data with that of commercial models leads only to the detection, not the isolation of errors . To identify the errors in the code is time-consuming . In this paper, we address the problem by developing a systematic and largely automated approach to the isolation of coding errors . There are three steps: firstly, possible errors are classified according to their place in the model structure and a feature matrix is established for each class of errors . Secondly, an observer is designed to generate residuals, such that each class of errors imposes a subspace, spanned by its feature matrix, on the residuals . Finally, localising the residuals in a subspace isolates coding errors . The algorithm proved capable of rapidly and reliably isolating a variety of single and simultaneous errors in a case study using the ASM1 activated sludge model . In this paper a newly coded model was verified against a known implementation . The method is also applicable to simultaneous verification of any two independent implementations, hence is useful in commercial model development. Water Sci Technol, 2001, 43(7), 357 - 65 Parameter estimation procedure for complex non-linear systems: calibration of ASM No . 1 for N-removal in a full-scale oxidation ditch; Abusam A et al.; When applied to large simulation models, the process of parameter estimation is also called calibration . Calibration of complex non-linear systems, such as activated sludge plants, is often not an easy task . On the one hand, manual calibration of such complex systems is usually time-consuming, and its results are often not reproducible . On the other hand, conventional automatic calibration methods are not always straightforward and often hampered by local minima problems . In this paper a new straightforward and automatic procedure, which is based on the response surface method (RSM) for selecting the best identifiable parameters, is proposed . In RSM, the process response (output) is related to the levels of the input variables in terms of a first- or second-order regression model . Usually, RSM is used to relate measured process output quantities to process conditions . However, in this paper RSM is used for selecting the dominant parameters, by evaluating parameters sensitivity in a predefined region . Good results obtained in calibration of ASM No . 1 for N-removal in a full-scale oxidation ditch proved that the proposed procedure is successful and reliable. Water Sci Technol, 2001, 43(7), 329 - 38 Identifiability and uncertainty analysis of the river water quality model no . 1 (RWQM1); Reichert P et al.; State of the art models as used in activated sludge modelling and recently proposed for river water quality modelling integrate the knowledge in a certain field . If applied to data from a specific site, such models are nearly always overparameterised . This raises the question of how many parameters can be fitted in a given context and how to find identifiable parameter subsets given the experimental layout . This problem is addressed for the kinetic parameters of a simplified version of the recently published river water quality model no . 1 (RWQM1) . The selection of practically identifiable parameter subsets is discussed for typical boundary conditions as a function of the measurement layout . Two methods for identifiable subset selection were applied and lead to nearly the same results . Assuming upstream and downstream measurements of dissolved substances to be available, only a few (5-8) model parameters appear to be identifiable . Extensive measurement campaigns with dedicated experiments seem to be required for successful calibration of RWQM1 . The estimated prior uncertainties of the model parameters are used to estimate the uncertainty of model predictions . Finally an estimate is provided for the maximum possible decrease in prediction uncertainty achievable by a perfect determination of the values of the identifiable model parameters. Water Sci Technol, 2001, 43(7), 29 - 38 Adequate model complexity for scenario analysis of VOC stripping in a trickling filter; Vanhooren H et al.; Two models describing the stripping of volatile organic contaminants (VOCs) in an industrial trickling filter system are developed . The aim of the models is to investigate the effect of different operating conditions (VOC loads and air flow rates) on the efficiency of VOC stripping and the resulting concentrations in the gas and liquid phases . The first model uses the same principles as the steady-state non-equilibrium activated sludge model Simple Treat, in combination with an existing biofilm model . The second model is a simple mass balance based model only incorporating air and liquid and thus neglecting biofilm effects . In a first approach, the first model was incorporated in a five-layer hydrodynamic model of the trickling filter, using the carrier material design specifications for porosity, water hold-up and specific surface area . A tracer test with lithium was used to validate this approach, and the gas mixing in the filters was studied using continuous CO2 and O2 measurements . With the tracer test results, the biodegradation model was adapted, and it became clear that biodegradation and adsorption to solids can be neglected . On this basis, a simple dynamic mass balance model was built . Simulations with this model reveal that changing the air flow rate in the trickling filter system has little effect on the VOC stripping efficiency at steady state . However, immediately after an air flow rate change, quite high flux and concentration peaks of VOCs can be expected . These phenomena are of major importance for the design of an off-gas treatment facility. Water Sci Technol, 2001, 43(7), 19 - 27 A new approach towards modelling of the carbon degradation cycle at two-stage activated sludge plants; Winkler S et al.; A pilot plant has been operated in order to investigate the performance and operating characteristics of the plant concept developed for the extension of the main Vienna STP . Due to the different operational modes included in the plant concept, modelling of the carbon degradation becomes of crucial importance . A new activated sludge model is introduced which combines parts of the carbon degradation model concepts as they have been released in the ASM1-model and the ASM3-model, respectively . A method is presented which utilises results from mass balance calculations and sludge stabilisation experiments to reduce the uncertainty in the determination of the values of the simulation model parameters. Water Sci Technol, 2001, 43(7), 167 - 74 Application of mathematical tools to improve the design and operation of activated sludge plants . Case study: the new WWTP of Galindo-Bilbao . Part II: Operational strategies and automatic controllers; Galarza A et al.; This paper presents a new sensitivity analysis methodology for Activated Sludge WWTPs . It is based on both (a) the calculation of the range of "manipulated input variables" that satisfy the restrictions imposed on the "output variables" and (b) on the computation of isolines of the output variables inside the feasible operating space . This analysis allows a more precise description of the operating constraints, facilitates the understanding of the steady-state behaviour of the process and detects possible areas where the process is very sensitive to small disturbances . The feasible operating space for two Activated Sludge WWTP processes for CN removal (RDN, DRDN), using SRT and DO level as "input variables" as well as effluent quality and exploitation costs as the main "output variables" is studied . The proposed methodology facilitates the selection of the appropriate operational strategy and the design of automatic controllers . Some examples of the application of this methodology for the design of automatic controllers in a real WWTP are briefly presented. Water Sci Technol, 2001, 43(7), 157 - 65 Application of mathematical tools to improve the design and operation of activated sludge plants . Case study: the new WWTP of Galindo-Bilbao . Part I: Optimum design; Rivas A et al.; This paper presents a mathematical formulation for the optimum design of a new activated sludge WWTP . The WWTP optimum design problem has been formulated as a Mathematical Programming problem, which is solved through a nonlinear optimisation method . The plant model has been based on the ASM1 . The minimum volume of the biological reactors and the minimum total cost (including construction and exploitation costs) have been considered as optimisation criteria . Some practical results are also included, using as a case study the design of the second stage of the Galindo-Bilbao WWTP. Water Sci Technol, 2001, 43(7), 131 - 8 Operational control of storm sewage at an activated sludge process; Chen J et al.; Operational control of storm sewage at a wastewater treatment plant has attracted intensive concern over the last decade in the context of river basin management . The focus is on the exploitation of the full capacity of the wastewater treatment plant in attenuating storm sewage, and minimizing a direct storm sewage bypass to the river . Attention is particularly paid to the surge of storm water on the activated sludge process . Based on two typical rain events, this paper discusses the performance of several practical controllers in achieving an optimal effluent performance under storm loadings, without risking internal biomass stability and sludge overflow . The control algorithms tested include various controls of recycle rate, step-feed and step-sludge . Prediction errors of influent characteristics and process responses are also under consideration in the assessment . The results illustrate well the desirability, effectiveness and robustness of the tested controllers. J Environ Sci Health A Tox Hazard Subst Environ Eng, 2001, 36(2), 243 - 57 Kinetic analysis of inhibitory substrate degradation in bioaugmented activated sludge process; Liu WD et al.; A steady-state model coupling Haldane kinetics and mass conservative principles was developed herein to depict the degradation of a single inhibitory substrate in a bioaugmented activated sludge reactor . The substrate toxicity impact on the bioaugmentation was evaluated for three levels of inhibition coefficient Ki: 0.1, 10, and 1000 mg/L . Under high toxicity conditions of Ki = 0.1 mg/L, the input biomass markedly enhanced the substrate removal . However, at less toxicity of Ki > 10 mg/L, the input biomass was ineffective . The sensitivity study confirmed the parameters of k, Ks, and bd has no connection with Ki, but depends on the amounts of degradative bacteria inside the reactor . Alternatively, parameter Y is important only when Ki is greater than 10 mg/L and the bacteria significantly utilize the substrate . In addition, a novel indicator of marginal solids retention time examines the economic advantages of adding biomass as compared to extending the solids retention time. Water Sci Technol, 2000, 41(3), 195 - 202 Full scale co-digestion of organic waste; Kubler H et al.; Operational results of a co-digestion facility were assessed over a period of 18 months . The organic fraction of municipal solid waste (OFMSW) contains a considerable amount of contaminants and grit (up to 6% w/w) . A BTA-Pulper efficiently treated the different waste streams and converted a high amount of volatile solids (VS) into the digester feedstock . The seasonal fluctuations of the waste composition significantly influenced the biogas production . The impact of this seasonally variant degradability of VS had to be considered by evaluating the operation results . The waste streams investigated did not show any negative impact on digester performance . The hydraulic retention time (HRT) in the digester considerably affected the VS-reduction . Despite a considerable decrease of VS-degradation a reduction of HRT from 14 to 8 days slightly improves the gas production rate (GPR) . An activated sludge system efficiently reduced the pollution of the effluent . The nutrient content of the anaerobic compost was favourable and the content of pollutants was low . The facility produced surplus electrical power up to 290 MJ/t . An overall energy balance shows that the facility substitutes primary energy. Water Sci Technol, 2001, 43(6), 97 - 103 In situ detection of cell surface hydrophobicity of probe-defined bacteria in activated sludge; Nielsen JL et al.; The surface hydrophobicity of different types of bacteria in activated sludge were investigated under in situ conditions by following the adhesion of fluorescent microspheres with defined surface properties to bacterial surfaces (the MAC-method) . This technique was combined with identification of the bacteria with fluorescence in situ hybridization with rRNA-targeted oligonucleotides (FISH) and could thus be used for characterization of surface properties of probe-defined bacteria directly in a complex system without prior enrichment or isolation . This MAC-FISH technique could be used for single bacteria as well as filamentous bacteria . In the investigated activated sludge from an industrial wastewater treatment plant, two types of filamentous bacteria dominated . One morphotype consistently attracted only very few hydrophobic microspheres, indicating that the thin sheath of exopolymers around the cells had a hydrophilic surface . Use of a hierarchical set of gene probes revealed that these filaments were sulphide oxidising Thiothrix spp . The other predominating filamentous morphotype had a thick, very hydrophobic exopolymeric sheath . This filamentous bacterium was found to belong to the alpha-Proteobacteria . The relevance of the significant differences in surface hydrophobicity for the two morphotypes in respect to substrate uptake and floc formation is discussed. Water Sci Technol, 2001, 43(6), 87 - 95 Fluorescence spectroscopy and molecular weight distribution of extracellular polymers from full-scale activated sludge biomass; Esparza-Soto M et al.; Two fractions of extracellular polymer substances (EPSs), soluble and readily extractable (RE), were characterised in terms of their molecular weight distributions (MWD) and 3-D excitation-emission-matrix (EEM) fluorescence spectroscopy signatures . The EPS fractions were different: the soluble EPSs were composed mainly of high molecular weight compounds, while the RE EPSs were composed of small molecular weight compounds . Contrary to previous thought, EPS may not be considered only as macromolecular because most organic matter present in both fractions had low molecular weight . Three different fluorophore peaks were identified in the EEM fluorescence spectra . Two peaks were attributed to protein-like fluorophores, and the third to a humic-like fluorophore . Fluorescence signatures were different from other previously published signatures for marine and riverine environments . EEM spectroscopy proved to be a suitable method that may be used to characterise and trace organic matter of bacterial origin in wastewater treatment operations. Water Sci Technol, 2001, 43(6), 67 - 75 Quantification of the bond energy of bacteria attached to activated sludge floc surfaces; Mikkelsen LH et al.; The great majority of activated sludge bacteria exist incorporated in flocs . The increase in dispersed bacteria when exposed to increasing turbulent shear rates has been successfully modelled by a model assuming that the adhesion and erosion of cells may be considered in analogy to ordinary chemical phase transitions . By this adhesion-erosion model (AE-model), an "enthalpy" of cell adhesion can be estimated, and this value in turn determines the range of shear rates in which erosion of cells predominates . Application of the model has indicated that only a mass fraction less than ca . 6-17% may be released from activated sludge, even when exposed to a severe turbulent environment, i.e . only a small fraction of the flocs is dispersible by means of erosion by turbulence . The shear sensitivity and the dispersible floc fraction were found to depend on the floc composition . A net decrease in the floc EPS content during anaerobic sludge stabilisation causes a dramatic increase in the dispersed fraction, indicating the important role of EPS for the floc strength . It was found also that activated sludge cells do not reflocculate completely after exposure to high shear rates . This may be an indication that the cohesion energy of bacteria growing in colonies is greater than the energy of the more stochastic adhesion of dispersed cells to floc surfaces . It could also be another indicator of the importance of entanglement forces, which do not reform instantly, once broken . When the bond strength of cell attachment to sludge surfaces is altered by changes in the chemical environment, this may cause a change in the dispersible floc fraction as well as a change in the shear range of erosion . When the shear sensitivity constant kss is adopted for sludge characterisation, an increased degree of dispersion under standard test conditions will result in increased shear sensitivity estimates . The shear sensitivity may be used for the estimation of en equivalent change in the Gibb's energy of cell adhesion (delta (delta Gad/RT)). Water Sci Technol, 2001, 43(6), 59 - 66 Adsorption of heavy metals by EPS of activated sludge; Liu Y et al.; Extracellular polymeric substances (EPSs) were extracted by high-speed centrifugation at 20,000 G for 30 min from an activated sludge treating municipal wastewater . Each gram of sludge, as measured in volatile suspended solids (VSS), contained 7.3 mg of EPS, including 6.5 mg of protein (EPSp) and 0.8 mg of carbohydrate (EPSc) . The EPSp had a mean MW of 2.0 x 105; about 18% of EPSp had MW over 5 x 104 and 16% below 5 x 103 . For heavy metal concentrations ranging 10-100 mg/l, EPS on average removed 99% of Zn2+, 98% of Cu2+, 97% of Cr3+, 85% of Cd2+, 69% of Co2+, 37% of Ni2+, and 26% of CrO4(2-) . The relative degrees of metal removals were inconsistent with those reported for the activated sludge process . Each mg of ESP had the capacity to remove up to 1.48 mg of Zn2+, 1.12 mg of Cu2+, 0.83 mg of Cr3+, 0.90 mg of Cd2+, 1.10 mg of Co2+, 0.25 mg each of Ni2+ and CrO4(2-) . Results suggest the feasibility of recovering ESP from waste sludge for use as adsorbent . Freundlich isotherm correlated satisfactorily with the adsorption data of Ni2+, Cu2+, Cd2+, and CrO4(2-) (R2 ranging 0.89-0.97), whereas Langmuir isotherm correlated satisfactorily with those of Zn2+, Cr3+ and Ni2+ (R2 ranging 0.93-0.96) . Both correlated poorly for those of Co2+. Water Sci Technol, 2001, 43(6), 33 - 40 Hydrolysis of wastewater colloidal organic matter by extracellular enzymes extracted from activated sludge flocs; Guellil A et al.; Enzymatic activities associated with the exopolymeric substances (EPSs) extracted from activated sludges were tested for their ability to hydrolyse the organic colloidal fraction of wastewater . Bacteria extracted with EPS and concentrated by wastewater microfiltration were inhibited with NaN3 or KCN . The protein hydrolysis mainly resulted from the enzymatic activity of EPS, whereas the glycolytic activity was mainly present in the organic colloidal fraction of the wastewater. Water Sci Technol, 2001, 43(6), 25 - 31 A new method for extraction of extracellular polymeric substances from biofilms and activated sludge suitable for direct quantification of sorbed metals; Wuertz S et al.; A method for extraction of extracellular polymeric substances (EPSs) with a dicyclohexyl-18-crown-6 ether was developed to determine levels of organic and inorganic contaminants sorbed to EPS . The crown ether selectively binds alkaline and alkaline earth metals but not heavy metals . The effectiveness of the extraction procedure was higher than that of 2 other methods tested and comparable with that of a method based on a cation exchange resin . On average it was possible to extract 20% of the TOC, 12% of the total protein content, and 4% of the total carbohydrate content of sludge or biofilm biomass . Metal sorption studies in activated sludge showed no influence of exposure time on the fractionation of metals within the biomass . Metals sorbed mostly to cellular material . In biofilms 12.2% of the cadmium and 9.1% of the zinc added was found in the EPS . In activated sludge EPS contained only 2.9% zinc . The distribution of metals within the biomass was dose dependent . The percentage of metals found in EPS decreased with increasing metal concentration . This indicates a higher affinity of metals for cellular binding sites . Time course experiments in a rotating biofilm annular reactor, which consisted of an external cylinder with removable slides and an internal solid drum, revealed a gradual change in zinc concentration associated with EPS, although the total zinc concentration in the biomass remained constant . Concurrently, the amount of extractable EPS decreased . This was a consequence of a microbial population shift, with bacterial counts decreasing and algal and fungal biomass increasing . Using confocal laser scanning microscopy and the fluorescent metal complexing agent Newport Green for in situ detection of zinc it was shown that metals were bound to algae and fungi in the latter part of the experiment . The biofilm became more and more heterogeneous coinciding with a decrease in EPS . To summarize, the observed sorption behavior of metals cannot be explained with the conventional paradigm of EPS as hydrophilic gel . Obviously, different binding mechanisms must be invoked to explain the role of EPS in the sorption and removal of toxic substances in activated sludge and biofilm systems . It is important to consider the microbial population to understand differences in sorption in different matrices. Water Sci Technol, 2001, 43(6), 174 - 84 Cell surface and exopolymer characterization of laboratory stabilized activated sludge from a beverage bottling plant; Boyette SM et al.; Fermentor-stabilized activated sludge from an industrial beverage bottling plant was grown on three different food sources: normal plant wastewater, plant wastewater containing high sucrose concentrations, and a synthetic glucose-based feed stock . Surface charge, hydrophobicity, and exopolysaccharide composition were measured on the stabilized bacterial flocs . Cell surface charge was measured by electrophoretic mobility, dye exchange titration, and a standard colloid titration, while cell hydrophobicity was determined using the bacterial adhesion to hydrocarbons (BATH) test . Exopolysaccharide profiles were determined by measuring concentrations of glucose, galactose, mannose, glucuronic, and galacturonic acids in digested exopolymer extractions using HPLC . Changes in the physical surface properties of the bacteria and the chemical composition of the extracted exopolymers were correlated with differences in the three food sources . Cell surface hydrophobicity was similar for cultures grown on different plant wastewaters, while the culture grown on synthetic food produced less floc hydrophobicity . Electrophoretic mobility measurements, charge titrations, and dye exchange titrations showed different total surface charge as well as varying charge availability . Additionally, total surface charge and total exopolysaccharide concentrations appeared less dependent on food source than the food-to-mass ratio . High concentrations of biodegradable food produced dispersed growth and high concentrations of exopolysaccharides that contributed to poor settling. Water Sci Technol, 2001, 43(6), 17 - 23 Remember the water--a comment on EPS colligative properties; Keiding K et al.; The relationship between water and activated sludge components was examined . Reevaluation of published data on freezing point depression, drying rates and dewatering has been performed . The basis of this has been the assumption that the water/sludge relationship is considered to be a colligative effect . Since the results indicate this to be the case, we suggest that the published concepts of "pools of water" are false . Data on swelling properties of EPS as a function of pH suggests that the colligative properties are largely determined by the counterions of charged polymers and surfaces. Water Sci Technol, 2001, 43(6), 105 - 12 SEM-EDS for determining the phosphorus content in activated sludge EPS; Oosthuizen DJ et al.; Not all phosphorus removed in activated sludge systems can be accounted for by polyphosphate accumulating organisms (PAO) . A method for the qualitative and quantitative in situ characterization of PAO cell clusters and closely associated extracellular polysaccharides (EPS) is described . X-ray microanalysis was performed on samples from four activated sludge plants situated in Pretoria, South Africa . Analyses were done by means of Scanning Electron Microscopy (SEM) combined with Energy Dispersive Spectrometry (EDS) . Cell clusters with associated EPS on average contained between 57 and 59% phosphorus, while EPS alone contained on average between 23 and 30% phosphorus . Results suggest that phosphorus removal in activated sludge might be due not only to PAO, but also by EPS acting as a phosphorus reservoir . Extraction of EPS from two different activated sludge plants yielded different amounts of EPS, which, in combination with SEM-EDS, may shed light on different phosphate uptake abilities of different activated sludges. Water Sci Technol, 2001, 43(3), 77 - 84 Performance of triple ditch: effects of duration and periodic operation programs; Ma LM et al.; The periodic variation of operation states in triple ditch (BIO-DENITRO process) was investigated in a pilot-scale and a full-scale triple ditch treating raw wastewater containing 70% petrochemical wastewater and 30% domestic wastewater . Mathematical models describing the periodic variation of activated sludge concentrations in each ditch were proposed based on theoretical analysis and were verified in the pilot-scale and full-scale triple ditches respectively . The existence of optimal cycle time and time arrangement of periodic operation programs were demonstrated and discussed according to the mathematical models and the experimental results of the pilot-scale triple ditch operated in four different stages . Four rulers determining the duration and operation programs are suggested. Water Sci Technol, 2001, 43(3), 35 - 43 Using the flexibility index to compare batch and continuous activated sludge processes; Hopkins LN et al.; This paper considers the question of which is better: the batch or the continuous activated sludge processes? It is an important question because dissension still exists in the wastewater industry as to the relative merits of each of the processes . A review of perceived differences in the processes from the point of view of two related disciplines, process engineering and biotechnology, is presented together with the results of previous comparative studies . These reviews highlight possible areas where more understanding is required . This is provided in the paper by application of the flexibility index to two case studies . The flexibility index is a useful process design tool that measures the ability of the process to cope with long term changes in operation. Water Sci Technol, 2001, 43(3), 323 - 30 SBR technology in Germany--an overview; Teichgraber B et al.; The SBR technology is applied in about 1.3% of the wastewater treatment plants (WWTP) in Germany . This caused the German Association for the Water Environment (ATV) to prepare the guideline ATV-M 210 to represent the state of the art for this type of WWTPs in Germany . The basic design parameters were derived from the standard ATV-A 131 for activated sludge plants to prepare a basis for the comparison of alternatives . In Bavaria numerous small WWTPs utilize SBR technology . Operational experiences show that these plants require specifically trained personnel . The plants produce effluents comparable to those of continuous flow plants in every respect . Hence the choice of system can be based on economic criteria. Water Sci Technol, 2001, 43(3), 215 - 22 Simulation and applications of a novel modified SBR system for biological nutrient removal; Wu W et al.; Dynamic simulation and applications of a novel, continuous-fed, constant level modified sequencing batch reactor for biological nutrient removal are presented . The underlying mathematical model and practical applications of the simulation are discussed . Case studies are presented to illustrate the applications as well as the flexibility of the system in meeting different wastewater treatment requirements . Operation experience from full-scale wastewater treatment plant demonstrates the reliability, ease of operation and high efficiency of the system . Average BOD5, total nitrogen, total phosphorus and TSS removals of 97, 81, 88 and 94% are achieved respectively on an annual basis with little operator attention . Consistently high waste activated sludge concentrations are demonstrated, averaging approximately 20,000 mg/L. Water Sci Technol, 2001, 43(3), 131 - 8 Performance of an SBR-plant for advanced nutrient removal, using septic sludge as a carbon source; Morling S; The Tjustvik SBR-plant outside Stockholm, Sweden has been in operation for four years . The plant has to meet stringent effluent standards, BOD7 < 10 PPM, total N < 15 PPM and total P < 0.3 PPM . The plant is a typical two reactor SBR-plant, sized for about 15,000 inhabitants . During the first year of operation there were difficulties in meeting the P consent level . The difficulties were linked to a deficit of available organic carbon and a secondary phosphorus release . The problem was solved with the addition of septic sludge, in an amount equivalent to about 10,000 to 15,000 inhabitants with respect to the BOD-load . The altered operation resulted in a very stable and good effluent quality from the plant that has been maintained ever since, giving typical discharge levels as follows: BOD7, < 3 mg/l; Total-P, < 0.15 mg/l; Total-N, < 7 mg/l; NH4-N, < 1 mg/l . The change of process saved the community from a major investment in a separate treatment facility for the septic sludge . The stabilisation degree of the waste activated sludge is sufficient to by pass the anaerobic digestion for the time being . In the beginning, the SBR-process stability played an unwanted role during start up as it maintained a secondary phosphorus release for a considerable time . Later the process stability became an asset as the varying loads from the septic sludge addition were handled with very good results. Water Sci Technol, 2001, 43(3), 1 - 8 Monitoring of the microbial community of a sequencing batch reactor bioaugmented to improve its phosphorus removal capabilities; Dabert P et al.; The acclimatisation of an activated sludge to enhanced biological phosphorus removal conditions was followed after and without bioaugmentation with a low amount of phosphorus-accumulating sludge . Phosphorus removal yields were monitored by conventional analytical methods and microbial communities evolutions were followed by a finger printing molecular technique (PCR-SSCP) . While the benefit of the bioaugmentation seems real at the level of the reactor parameters, bioaugmentation speeded up the installation of good and stable phosphorus removal yield, the establishment of the inoculated microbial community in the bioaugmented reactor is still unclear . Both the bioaugmented and the control microbial communities evolved in a similar way to end up with apparently comparable populations . At the time of the experiment, the results suggest that the microbial community inoculated for the bioaugmentation did not establish in the reactor but compensated for phosphorus accumulation until the acclimatisation of an endogenous microbial community arose. J Environ Sci Health A Tox Hazard Subst Environ Eng, 2001, 36(1), 101 - 15 Activated sludge immobilization using the PVA-alginate-borate method; An M et al.; The PVA-alginate-borate method was used successfully to immobilize activated sludge . The optimum polyvinyl alcohol (PVA) concentration in the immobilized sludge was determined to be 10-12.5% . A minimal alginate of 1% in the beads was needed to prevent bead agglomeration . If the pH of the saturated boric acid was adjusted to 7.0 prior to allowing droplets of the mixture of PVA, alginate and sludge to enter the solution, a high level of sludge activity could be maintained in the beads formed . During the continuous operation of a fluidized bed reactor, with hydraulic retention time (HRT) in the range of 24-3 h (BOD loading from 0.176 to 0.766 kg/d/m3) and an aeration rate at 1.0 L/min, more than 90% of BOD5, NH4(+)-N and TKN were removed . The immobilized sludge exhibited satisfactory mechanical stability without apparent breakage. Water Sci Technol, 2001, 43(2), 51 - 8 Changes in the organic composition of wastewater during biological treatment as studied by NMR and IR spectroscopies; Dignac MF et al.; Despite its importance, relatively little is known about the composition and fate of wastewater organic matter (OM) in treatment plants . Monitoring the chemical changes in OM during activated sludge treatment can improve our knowledge of the processes involved in the biological elimination of OM . Direct chemical analyses of treated water OM typically account for about 20% of the OM, and structural information was obtained in this study using Nuclear Magnetic Resonance (NMR) and Fourier Transform Infrared (FTIR) spectroscopic techniques . Distinct changes in the OM during wastewater biological treatment were underlined . 13C and 1H NMR showed that aromatic carbons were minor constituents of the samples . Alkyl chains exhibited a more highly branched character in treated water, as compared to long chain aliphatic carbons present in wastewater . Carboxyl signals in the 13C NMR spectrum of wastewater could be due to peptide bonds in proteins, whereas in the treated water spectrum, this signal could be related to the presence of non-proteinaceous nitrogen . Besides the non-degraded compounds, treated water OM could contain recondensation products of simple molecules . Their refractory character probably derives from their complex structures rather than from particular chemical functions, as suggested by the lack of fundamental differences in the chemical structures of wastewater and treated water OM. Water Sci Technol, 2001, 43(2), 355 - 62 Comparison of dye wastewater treatment by normal and anoxic + anaerobic/aerobic SBR activated sludge processes; Panswad T et al.; In this research, the effects of different color intensities, anoxic + anaerobic times and types of substrate on color removal effectiveness were studied using 16-litre bench scale sequencing batch reactor (SBR) anoxic + anaerobic/aerobic models . The systems were fed with a synthetic wastewater containing 500 mg/l of COD, 50 mg/l of N, 15 mg/l of P along with 10, 40 and 80 mg/l of reactive diazo Remazol Black B dye . The anoxic + anaerobic/aerobic periods were 0/11 (normal aerobic SBR), 2/9, 4/7 and 8/3 hours, respectively . The color removal occurred mainly under the anaerobic environment, while a slight attenuation was noticed under the aerobic condition . A better decolorization could be achieved with a longer anoxic + anaerobic period . The sodium acetate was a slightly better co-substrate for the color removal than glucose . The decolorization efficiency dwindled as the fed dye concentration increased, but the overall color removal leaned in the opposite direction . The phosphorus removal of the anoxic + anaerobic/aerobic systems was outstanding, whereas only 50% removal was achieved for the aerobic process . A dye concentration of up to 80 mg/l did not have any significant impact on the performance of the polyphosphate accumulating organisms (PAOs) . The removal of organic carbon and TKN was comparable among all experiments regardless of system configurations, color intensities and types of substrate. Water Sci Technol, 2001, 43(1), 99 - 106 Characterization of microbial community in an activated sludge process treating domestic wastewater using quinone profiles; Hu HY et al.; The dynamics of microbial community structure of activated sludges in a small-scale domestic wastewater treatment process were examined using a novel approach of quinone profiles . The composition and content of quinones in the activated sludges were analyzed monthly over a period of one year . More than 4 types of ubiquinones and 12 types of menaquinones were observed in the activated sludges, with the dominant quinones being ubiquinone (UQ)-8, menaquinone (MK)-7, followed by UQ-10, MK-8 and MK-6 . The total quinone contents in the activated sludges varied from 0.93 to 2.68 mumol per gram of particle organic carbon . The molar ratio of ubiquinones to menaquinones (UK/MK) changed from 0.38 to 0.98, indicating that anaerobic bacteria dominated the microbial community of the activated sludges examined . The ratio of UQ/MK varied similar to that of dissolved oxygen in the bulk . The microbial diversity of the activated sludges calculated from the quinone compositions was 13.4-16.8 . The diversity of menaquinones was much higher than that of ubiquinones, and increased slightly with increasing temperature . The microorganisms containing menaquinones appear to be sensitive to the change in temperature than those containing ubiquinones. Water Sci Technol, 2001, 43(1), 91 - 8 16S rRNA in situ probing for the determination of the family level community structure implicated in enhanced biological nutrient removal; Mudaly DD et al.; Knowledge of a discrete physiological group capable of excess biological phosphate removal (EBPR) remains unclear . Consequently, microbial community analysis of an enhanced continuous laboratory-scale activated sludge process displaying a strong EBPR mechanism was conducted . Unit design was configured upon the three-stage Phoredox process and characterization of the activated sludge bacterial community was carried out using fluorescent in situ hybridization (FISH) techniques . Fixed activated sludge samples were hybridized with fluorescently labeled oligonucleotide probes targeting the following bacterial phylogenetic divisions: a kingdom level probe specific for all bacteria (EUB338); family level probes specific for the alpha, beta and gamma subclasses of the class Proteobacteria; Gram positive bacteria with a high (G + C) DNA content (GPBHGC) or Actinobacteria; the Cytophaga-Flavobacterium (CF) subclass within the Cytophaga-Flavobacterium-Bacteriodes division; and genus level probes specific for Pseudomonas spp., Aeromonas spp., and Acinetobacter spp . Bacterial predominance between the anaerobic, anoxic and aerobic zones of the EBPR sludge were comparable and appeared as follows; beta (22%), alpha (19%), gamma (17%), GPBHGC (11%) and CF (8%) . The incidence of Acinetobacter spp . appeared to be generally low with counts amounting to < 9% of the total bacterial count . A population shift in the alpha Proteobacteria subclass was evident between the non-nutrient removal seed sludge and the EBPR sludge, implicating this group in EBPR . The overall results indicate that the beta and alpha Proteobacteria can be metabolically functional in EBPR processes and reiterate the functional misconception of Acinetobacter spp . in EBPR systems. Water Sci Technol, 2001, 43(1), 83 - 90 Biolog for the determination of microbial diversity in activated sludge systems; van Heerden J et al.; In this study, different carbon source profiles were generated by inoculating Biolog GN microwell plates, with different dilutions of microbial communities from a number of activated sludge systems . This led to the successful generation of patterns reflecting diversity and evenness in the different systems . The high number of substrates utilized at the lower dilutions (10(-1) and 10(-2)) indicated a high microbial diversity in the community, but not necessarily evenness of each species . Evenness of each species was reflected upon further dilution . Our results indicated differences in the microbial community composition amongst some of the activated sludge systems studied . These differences were not specifically related to phosphate removing and non phosphate removing systems. Water Sci Technol, 2001, 43(1), 321 - 6 Removal of organics from wastewater using a novel biological hybrid system; al-Sharekh HA et al.; This paper summarizes the results obtained using the hybrid aerated submerged fixed-film (HASFF) process . HASFF is an innovative system comprising a four-compartment reactor having an array of fixed ceramic plates maintained under diffused aeration to support attached biomass, with activated sludge recycle to promote suspended growth in the reactor . Wastewater from a municipal treatment plant was fed to the reactor and its activated sludge was used for recycling in the hybrid system . Four pilot units were operated in the plant at various hydraulic retention times, HRTs (2, 4, 6 and 8 h), using primary-settled wastewater under organic loading rates up to 0.7 g BOD/gMLTVS . d . Data obtained showed that the overall BOD percentage removal efficiencies were consistently above 94.0% at all HRTs including the 2 hours while the COD percentage removal efficiencies ranged between 65.7-76% . The effluent's mean filtered BOD concentration ranged between 4.5-7.5 mg/l whereas the mean filtered COD concentration ranged between 70.0-89.6 mg/l . Increasing the hydraulic loading rate by four-folds from 0.08 to 0.32 m3/m2.d had a minor effect on the unit's BOD and COD percentage removal efficiencies indicating a robust biological process that is resilient to hydraulic shock loads, thereby offering a viable upgrading option. Water Sci Technol, 2001, 43(1), 173 - 80 Microbial storage products, biomass density, and settling properties of enhanced biological phosphorus removal activated sludge; Schuler AJ et al.; The relationships between bacterial storage products, density, and settling characteristics were determined in a laboratory-scale sequencing batch reactor (SBR) enhanced biological phosphorus removal (EBPR) system . Both long-term and single anaerobic-aerobic cycle variations in these properties were studied . Increased polyphosphate (PP) content of the biomass during long-term operation resulted in improved sludge volume index (SVI) values . End-aerobic phase (after phosphate (P) uptake) SVI values were consistently lower than end-anaerobic phase (after P release) values . Neither filamentous nor slime bulking were evident by microscopic observations . Biomass density increased at a rate of 1.2 mg/L per each 1% increase in biomass P content . End-aerobic phase samples had an average 25% higher buoyant density than end-anaerobic phase samples; which was attributed to aerobic P uptake . Biomass density was negatively correlated with SVI values, and SVI values increased sharply at low biomass density . A mathematical model developed by Mas et al . (1985) was modified to predict total cell density based on literature values of PP, glycogen (GLY), and poly-b-hydroxybutyrate (PHB) densities . Model predictions were in good agreement with experimental results, although improved measurement of PP density is required to improve model predictions. Water Sci Technol, 2001, 43(1), 165 - 72 Transformation of lipids in activated sludge; Dueholm TE et al.; Transformation of lipids in activated sludge treatment plants is of interest for two reasons: lipids contribute 30-40% of the chemical oxygen demand (COD) in wastewater, and they may stimulate the growth of filamentous microorganisms in nutrient removal activated sludge plants . The transformation of lipids was investigated under aerobic and anoxic conditions by measuring the oxygen and nitrate uptake rates (OUR and NUR) . The maximal OUR and NUR of long-chain fatty acid was found to be at the same level as acetate indicating that long-chain fatty acid was as easily consumable . However, the adsorption of long-chain fatty acid to surfaces of sludge flocs made it difficult to determine initial uptake rates of long-chain fatty acids . It was not possible to describe the hydrolysis rate of triacylglyceride by OUR and NUR to long-chain fatty acids because the hydrolysis rate was very slow . For a better description of the processes involved in transformation of lipids, a conceptual model was suggested . The processes in the suggested model were the adsorption/desorption of both triacylglyceride, and long-chain fatty acid onto surfaces of sludge flocs, hydrolysis of triacylglyceride by lipases and the uptake of long-chain fatty acid by bacteria under various conditions . The model can be helpful to structure design and evaluation of activated sludge experiment with lipids. Water Sci Technol, 2001, 43(1), 123 - 30 Stress protein expression in domestic activated sludge in response to xenobiotic shock loading; Bott CB et al.; Using the Western blot immunochemical analysis method, the heat shock protein, GroEL, was found to be either induced or repressed in activated sludge microorganisms exposed to a range of xenobiotics . At the EC25 concentration, pentachlorophenol (PCP), cadmium, nickel, 2,4-dichloroaniline, benzoquinone, 2,4-dinitrophenol, and 1,1,1-trichloroethane all rapidly induced measurable GroEL expression, even though the time-dependent response for each of these compounds was somewhat varied . Toluene and hydroquinone resulted in repression of GroEL expression to levels below that measured in the control mixed liquor . For PCP concentrations at or exceeding the EC25, there was a significant and consistent increase in effluent volatile suspended solids from activated sludge sequencing batch reactors relative to unstressed controls . These preliminary results indicate that stress proteins may serve as sensitive and rapid indicators of toxicity which can adversely impact treatment process performance in activated sludge systems. Water Res, 2001 Jun, 35(9), 2277 - 85 Storage and degradation of poly-beta-hydroxybutyrate in activated sludge under aerobic conditions; Dircks K et al.; This research analyses the accumulation and degradation of poly-beta-hydroxybutyrate (PHB) in experiments with pulse addition of acetate to samples of activated sludge from pilot-plant and full-scale wastewater treatment plants . The experiments are divided into two periods: a feast period defined as the time when acetate is consumed and a famine period when the added acetate has been exhausted . In the feast period the significant process occurring is the production of PHB from acetate . The produced PHB is utilised in the famine period for production of glycogen and biomass . According to modelling results approximately 90% of the total potential growth occurs in the famine period utilising the stored PHB . The degradation rate for PHB in the famine period is found to be dependent on the level of PHB obtained at the end of the feast period . It was found that multiple order kinetics gives a good description of the rate of PHB degradation . The examined sludge of low SRT origin is found to degrade PHB faster than long SRT sludge at high fractions of PHB . The observed yield of glycogen on PHB in the famine period is in the range of 0.22-0.33 g COD/g COD depending on the SRT . The storage pool of glycogen in the examined sludge is more slowly degraded than PHB (COD/COD/h). Water Res, 2001 Jun, 35(9), 2137 - 44 Effect of pump shear on the performance of a crossflow membrane bioreactor; Kim JS et al.; The influences of pumping shear on the performance of a crossflow membrane bioreactor (MBR) were investigated . To compare the intensity of pumping shear, two types of pumps (a centrifugal pump and a rotary one) were used in turn to recirculate mixed liquor . Rotary pump system imposed much stronger shear to microbial floc than centrifugal one and resulted in severe floc breakage . Colloidal particles and organics were liberated from microbial floc by shear and caused rapid loss of membrane permeability by the formation of dense cake layers on the surface of membrane . Recirculation of mixed liquor with a rotary pump gradually increased the soluble COD in the bioreactor and deteriorated microbial activity . After 7 days' operation, specific oxygen uptake rate (SOUR) of microorganisms in rotary pump system reduced to 78%, of initial condition . With a centrifugal pump, however, buildup of soluble COD was not observed and change in microbial activity was negligible . Sludge yield in MBR process was lower than that (0.4-0.5 g MLVSS gCOD(-1)) reported in a conventional activated sludge process: 0.3 g MLVSS gCOD(-1) for the centrifugal pump system and 0.2 g MLVSS gCOD(-1) for the rotary pump system. Biochem, Eng . J. . 2001 Jul, 8(1), 9 - 18 Removal of mixtures of acetaldehyde and propionaldehyde from waste gas in packed column with immobilized activated sludge gel beads; Ibrahim MA et al.; The removal of mixed acetaldehyde and propionaldehyde as a model of the binary contaminants in waste gas was studied in the packed column containing the immobilized activated sludge gel beads together with the hollow plastic balls developed for the removal of a single aldehyde in the previous work . The rate of each aldehyde biodegradation by the gel beads in the aldehydes mixture was expressed by the Michaelis-Menten type rate equation with an inhibitory term due to the other coexistent aldehyde . The kinetic parameters involved were found to be the same as those determined previously for biodegradation of a single aldehyde . A model for prediction of removal of each aldehyde in the packed column was developed assuming that each aldehyde dissolved in the aqueous phase within the gel bead was biodegraded according to the above rate equation with no mass transfer effect . The packed column was stable and efficient for removal of the binary aldehydes mixture with a very low pressure drop for gas flow due to a reduced gel beads bed compaction by the hollow plastic balls . Removal of each aldehyde decreased with increasing the inlet aldehyde concentrations since each biodegradation rate itself appro