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Waterborne illnesses are a growing concern among health and regulatory agencies worldwide. The United States Environmental Protection Agency has established several rules to combat the contamination of water supplies by cryptosporidium oocysts, however, the detection and study of cryptosporidium oocysts is hampered by methodological and financial constraints. As a result, numerous surrogates for cryptosporidium oocysts have been proposed by the scientific community and efforts are underway to evaluate many of the proposed surrogates. The purpose of this review is to evaluate the suitability of aerobic bacterial spores to serve as a surrogate for cryptosporidium oocysts in identifying contaminated drinking waters. To accomplish this we present a comparison of the biology and life cycles of aerobic spores and oocysts and compare their physical properties. An analysis of their surface properties is presented along with a review of the literature in regards to the transport, survival, and prevalence of aerobic spores and oocysts in the saturated subsurface environment. Aerobic spores and oocysts share many commonalities with regard to biology and survivability, and the environmental prevalence and ease of detection make aerobic spores a promising surrogate for cryptosporidium oocysts in surface and groundwater. However, the long-term transport and release of aerobic spores still needs to be further studied, and compared with available oocyst information. In addition, the surface properties and environmental interactions of spores are known to be highly dependent on the spore taxa and purification procedures, and additional research is needed to address these issues in the context of transport., (Published by Elsevier Ltd.)

The challenge of energy generation from biodegradation of recalcitrant organics in microbial fuel cells (MFCs) is mainly attributed to their persistence to degradation under anaerobic condition in anode chamber of MFCs. In this work, we demonstrated that electricity generation from aniline, a typical recalcitrant organic matter under anaerobic condition was remarkably facilitated by employing oxygen into bioanode of MFCs. By exposing bioanode to air, electrons of 47.2 ± 6.9 C were recovered with aniline removal efficiency of 91.2 ± 2.2% in 144 h. Limited oxygen supply (the anodic headspace was initially filled with air and then closed) resulted in the decrease of electrons recovery and aniline removal efficiency by 52.5 ± 9.4% and 74.2 ± 2.1%, respectively, and further decline by respective 64.3 ± 4.5% and 82.7 ± 1.0% occurred under anaerobic condition. Community analysis showed that anode biofilm was predominated by several aerobic aniline degrading bacteria (AADB) and anode-respiration bacteria (ARB), which likely cooperated with each other and finally featured the energy recovery from aniline. Cyclic voltammetry indicated that anodic bacteria transferred electrons to anode mainly through electron shuttle. This study provided a new sight to acquaint us with the positive role of oxygen in biodegradation of recalcitrant organics on anode as well as electricity generation., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Numerous studies have shown that the efficacy of ultraviolet (UV) disinfection can be hindered by the presence of particles that can shield microorganisms. The main objective of this study was to determine to what extent natural particulate matter can shield indigenous spores of aerobic spore-forming bacteria (ASFB) from UV rays. The extent of the protective shielding was assessed by comparing the inactivation rates in three water fractions (untreated, dispersed and filtered on an 8 microm membrane) using a collimated beam apparatus with a low-pressure lamp emitting at 254 nm. Levels of inactivation were then related to the distribution and abundance of particles as measured by microflow imaging. Disinfection assays were completed on two source waters of different quality and particle content. A protocol was developed to break down particles and disperse aggregates (addition of 100mg/L of Zwittergent 3-12 and blending at 8000 rpm for 4 min). Particle size distribution (PSD) analysis confirmed a statistically significant decrease in the number of particles for diameter ranges above 5 microm following the dispersion protocol and 8 microm filtration. The fluence required to reach 1-log inactivation of ASFB spores was independent of particle concentration, while that required to reach 2-log inactivation or more was correlated with the concentration of particles larger than 8 microm (R(2)>0.61). Results suggest that natural particulate matter can protect indigenous organisms from UV radiation in waters with elevated particle content, while source water with low particle counts may not be subject to this interference.

A knowledge of the decay rates of autotrophic bacteria is important for reliably modeling nitrification in activated sludge plants. The introduction of nitrite to activated sludge models also requires the separate determination of the kinetics of ammonia- and nitrite-oxidizing bacteria. Batch experiments were carried out in order to study the effects of different oxidiation-reduction potential conditions and membrane separation on the separate decay of these bacteria. It was found that decay is negligible in both cases under anoxic conditions. No significant differences were detected between the membrane and conventional activated sludge. The aerobic decay of these two types of bacteria did not diverge significantly either. However, the measured loss of autotrophic activity was only partly explained by the endogenous respiration concept as incorporated in activated sludge model no. 3 (ASM3). In contrast to nitrite-oxidizing bacteria, ammonia-oxidizing bacteria needed 1-2 h after substrate addition to reach their maximum growth rate measured as a maximum OUR. This pattern could be successfully modeled using the ASM3 extended by enzyme kinetics. The significance of these findings on wastewater treatment is discussed on the basis of the extended ASM3.

Cryptosporidium and Giardia represent a major microbiological issue for drinking water production from surface water. As their monitoring through a treatment process is rather tedious and as low-concentration goals should be reached for drinking water, aerobic spore-forming bacteria (ASFB) have been studied as an indicator microorganism for a drinking water treatment plant using surface water. The results reveal that monitoring naturally occurring ASFB better highlights daily achievable performances and identifies unusual process events for global disinfection, for both physical and chemical treatment steps in a multi-barrier drinking water treatment plant. Advantages of ASFB over usual process parameters are that these microorganisms are more sensitive to process fluctuations. The use of ASFB also showed that the efficiency of ozone disinfection is not as significantly influenced by the water temperature as reported, despite similar or higher CT values applied during warmer periods. Thus, the disinfection of resistant microorganisms with ozone can also be an efficient process at lower water temperature. ASFB have been shown to be a conservative indicator for Cryptosporidium and Giardia up to a 1st stage filtration and the ASFB Log removals can be used to estimate Log removals for Cryptosporidium and Giardia: compared to ASFB, the Log removals for Cryptosporidium or Giardia are at least equal or 50% higher, respectively. Thus, the monitoring of ASFB along a drinking water treatment process could be a useful tool for performing risk analysis for parasites such as Cryptosporidium and Giardia, and would further allow integration of daily variability into a risk analysis.

Temperature changes can influence biological processes considerably. To investigate the effect of temperature changes on the conversion processes and the stability of aerobic granular sludge, an aerobic granular sludge sequencing batch reactor (GSBR) was exposed to short-term and long-term temperature changes. Start-up at 8 degrees C resulted in irregular granules that aggregated as soon as aeration was stopped, which caused severe biomass washout and instable operation. The presence of COD during the aerobic phase is considered to be the major reason for this granule instability. Start-up at 20 degrees C and lowering the temperature to 15 degrees C and 8 degrees C did not have any effect on granule stability and biomass could be easily retained in the system. The temperature dependency of nitrification was lower for aerobic granules than usually found for activated sludge. Due to decreased activity in the outer layers of granules at lower temperatures, the oxygen penetration depth could increase, which resulted in a larger aerobic biomass volume, compensating the decreased activity of individual organisms. Consequently the denitrifying capacity of the granules decreased at reduced temperatures, resulting in an overall poorer nitrogen removal capacity. The overall conclusion that can be drawn from the experiments at low temperatures is that start-up in practice should take place preferentially during warm summer periods, while decreased temperatures during winter periods should not be a problem for granule stability and COD and phosphate removal in a granular sludge system. Nitrogen removal efficiencies should be optimized by changes in reactor operation or cycle time during this season.

Pre-treatment of sisal pulp prior to its anaerobic digestion was investigated using an activated sludge mixed culture under aerobic conditions in batch bioreactors at 37 degrees C. The progression of aerobic pre-treatment of the residue in relation to the activities of some extracellular hydrolytic enzymes in the slurry was monitored. The highest activity of hydrolytic enzymes was obtained at 9 h of pre-treatment. Filter paper cellulase had a maximum activity of 0.90 IU/ml, while carboxymethyl cellulase, amylase and xylanase were produced to a maximum of about 0.40 IU/ml. The methane yield obtained after anaerobic digestion of the pre-treated pulp ranged between 0.12 and 0.24 m3 CH4/kg VS added. The highest and lowest values were obtained for 9 and 72 h of pre-treatment, respectively. Nine hours of pre-treatment of sisal pulp prior to anaerobic digestion demonstrated a 26% higher methane yield when compared to the sisal pulp without pre-treatment. The consortia of microorganisms in activated sludge demonstrated a useful potential in the production of hydrolases acting on major macromolecules of sisal pulp. The fact that a correlation was observed between high enzyme activity and high methane yield at 9 h of aerobic pre-treatment suggests that such a short pre-treatment period could be an alternative option for increasing solubilization of sisal pulp and promoting methane productivity.

An integrated anaerobic-aerobic fixed-film pilot-scale reactor with arranged media was fed during 166 days with slaughterhouse wastewater. Operation temperature was 25 degrees C and the anaerobic-aerobic volume ratio was decreased from 4:1 to 3:2 and finally to 2:3. Overall organic matter removal efficiencies of 93% were achieved for an average organic loading rate of 0.77 kg COD/m3 d, and nitrogen removal efficiencies of 67% were achieved for nitrogen loading rates of 0.084 kg N/m3 d. The high internal recirculation associated to the air-lift effect linked to the aeration of a part of the reactor section caused high mixing between the anaerobic and aerobic zones, so that most organic matter was removed aerobically. The nitrification process achieved an efficiency of 91% for nitrogen loads of 0.15 kg N/m3 d when the anaerobic-aerobic volume ratio was 2:3 and was limited by dissolved oxygen concentration below 3 mg/l. The influence of the heterotrophic biomass growing in the outer biofilm was checked. Denitrification only implied the 12-34% of the total nitrogen removal and was limited by dissolved oxygen concentration in the anaerobic zone above 0.5 mg/l caused by the mixing regime. Most removed nitrogen was employed in synthesis of heterotrophic bacteria.

A mixed microbial culture degraded a mixture of benzoate (863 mg/L), 3-chlorobenzoate (3-CB) (69.7 mg/L), and pyruvate (244 mg/L) under denitrifying conditions in a chemostat. Biodegradation under denitrifying conditions was stable, complete (effluent concentrations below detection limits), and proceeded without the production of toxic intermediates like chlorocatechols. The addition of oxygen at mass input rates of 6.2%, 15.5%, and 43.9% of the mass input rate of chemical oxygen demand (COD) (337 mg COD/h) did not induce the synthesis of aerobic biodegradation pathways and thus did not disrupt biodegradation. Rather, the oxygen was used as a terminal electron acceptor, displacing a stoichiometric amount of nitrate, leading to microaerobic conditions (dissolved oxygen concentration <0.050 mg/L) in which oxygen utilization and denitrification occurred simultaneously. The reduction of nitrate occurred fully to N(2) gas with no accumulation of nitrite, nitrous oxide, or nitric oxide, although the ability of the culture to transfer electrons to the nitrogen oxides decreased as the oxygen input was increased. The anoxic benzoate uptake capability was unaffected by the increase in oxygen addition, but the anoxic 3-CB uptake capability increased, as did the level of benzoyl-CoA reductase in the cells.

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

In-situ pilot studies of aerobic cometabolism were conducted to evaluate the injection of toluene-vapor and air into TCE-contaminated aquifer. Delivery of primary substrate (toluene) in a vapor state with air enhanced the growth of indigenous toluene-utilizing bacteria that would degrade TCE by aerobic cometabolism. Meanwhile, delivering toluene in a vapor state effectively reduced potential clogging near the injection points due to excessive microbial growth, which was observed in the field when the injection of neat toluene was employed. Over 90% removal of TCE was achieved with primary substrate (toluene) degraded to a concentration below 10 microg/L.

Quantification of the oxygen fluxes in the sewer system is at present the optimal methodology to obtain information about the influence of sewers on transformations and mass balances in the urban drainage system. However, the relative and absolute values of these fluxes are practically unknown. In this work, the oxygen fluxes were quantified experimentally in a full-scale aerobic main sewer. The sewer biofilm respiration was determined with an in situ flow cell, a method that has not been used before in the sewer. The surface reaeration was determined with a gas tracer method based on the inert, non-radio-active and non-toxic gas tracer sulphur hexafluoride. In addition, the wastewater biomass respiration rate was measured. The validity of the applied methods was verified with redundant oxygen balances over a 2-km-long section. Measurement campaigns under different hydrodynamic conditions showed that the relative contribution of the biofilm, the wastewater, the reaeration and the in- and outflow with the water, all contributed significantly. However, the absolute contributions varied extensively and depended especially on the discharge. The COD conversion in the sewer could be estimated from the aerobic activity. The aerobic total degradation in the study reach was 3%. However, when extrapolated to the entire sewer net of the catchment area with 5000 PE, the COD conversion was estimated as high as 30% of the dissolved COD during the night. This indicates that the wastewater composition at the treatment plant will be strongly affected by the sewer system.

Alachlor (2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide) is a moderately toxic herbicide that is frequently found in agriculturally impacted surface waters. To assess primary mechanism(s) that affect its fate in aquatic systems, two field experiments were performed using large mesocosms (n=39) and smaller microcosms with and without microbial inhibitors (n=16). The mesocosm experiment tested the effect of fertility conditions on alachlor fate, assessing alachlor disappearance over time under oligotrophic (total phosphorus (TP) <12 microg/L) through hypereutrophic (TP>80 microg/L) water conditions. Whereas, the microcosm experiment assessed alachlor fate in the presence of microbial inhibitors that selectively blocked eubacterial (chloroamphenicol, streptomycin, and penicillin combined), eukaryotic (cycloheximide), and universal (all inhibitors) microbial activity. First-order alachlor transformation rate coefficients ranged from 0.006 to 0.042 day(-1) when microbial inhibitors were not present (half-lives from 16 to 122 days) with the highest rates occurring in hypereutrophic waters. Statistics indicated that mean TP, and universal and eubacterial small sub-unit rRNA level most closely correlated with transformation rate. Further, the inhibitor study indicated that alachlor transformation was biotic (>90%), but that high transformation rates only occurred when eubacterial and eukaryotic domains were both metabolically active. Our results confirm that alachlor transformation is primarily biotic; however, efficient biotransformation only occurs when both major microbial domains in aerobic systems are active.

A combination of two fixed-film bioreactors (FFB) with arranged media, the first anaerobic and the second aerobic, connected in series with recirculation was fed continuously for 133 days with wastewater from a poultry slaughterhouse. Oxidation of the organic carbon compounds and nitrification were carried out in the aerobic FFB and methanogenesis and denitrification were performed in the anaerobic FFB. The average organic loading rate was 0.39 kg COD/m3d and 92% removal efficiencies of organic matter were achieved. COD-removal occurred mainly in the anaerobic FFB, increasing when the recirculation ratio rose from 1 to 6 due to the increase in the anoxic denitrification. The influence of the C/N ratio of the raw wastewater over the proportion in which the COD-removal was carried out by oxidation in the aerobic FFB, methanogenesis or denitrification in the anaerobic FFB was studied. When the volume of the aerobic FFB became smaller than that of the anaerobic one the fraction of organic matter removed in the anaerobic FFB increased, but also the ratio between the respective volumetric rates (rCODan/rCODae) increased. High recirculation and low C/NO-N ratio in the anaerobic FFB feed favoured the denitrification to the detriment of the methanogenic process. Regarding nitrogen removal for nitrogen applied loads around 0.064 kg TKN/m3d the removal efficiency was of 95%, which decreased to 84% for 0.14 kg TKN/m3d. The stability of the nitrification process was the controlling factor of the nitrogen removal. High ammonia concentration caused by high recirculation ratio, specially when the aerobic FFB volume was smaller, caused nitrification inhibition which destabilised the system.

The effects of temperature variations on aerobic biological wastewater treatment were evaluated with respect to treatment efficiency, solids discharges, sludge physicochemical properties and microbiology. The effects of controlled temperature shifts (from 35 degrees to 45 degrees C; from 45 degrees to 35 degrees C) and periodic temperature oscillations (from 31.5 degrees C to 40 degrees C, 6-day period, for 30 days) were assessed in 4 parallel, lab-scale sequencing batch reactors (SBRs) that treated pulp and paper mill effluent. Overall, the temperature shifts caused higher effluent suspended solids (ESS) levels (25-100 mg/L) and a decrease (up to 20%) in the removal efficiencies of soluble chemical oxygen demand (SCOD). Lower ESS levels were triggered by a slow (2 degrees C/day) versus a fast (10 degrees C/12h) temperature shift from 35 degrees to 45 degrees C, but the SCOD removal efficiencies decreased similarly in both cases (from 66+/-3% and 65+/-2% to 49+/-3% and 51+/-3%). Temperature oscillations caused an increased deterioration of the sludge settleability [high sludge volume indices (SVI); low zone settling velocities (ZSV)], high ESS levels and lower SCOD removals. The temperature transients were associated with poor sludge settleability (SVI>100 mL/g MLSS, ZSV<1 cm/min), more negatively charged sludge (up to -0.35+/-0.03 meq/g MLSS), increased filament abundance (approximately 4 to 4.5, subjective scale equivalent to very common), and decreased concentrations of protozoa and metazoa (25,000-50,000 microorganisms/mL sludge). The controlled, periodic temperature oscillations had a slight impact on SCOD removal efficiency (5% decrease), and did not seem to select for robust microorganisms that withstood the temperature shift. Sludge deflocculation and filament proliferation caused by these temperature transients may explain the higher ESS levels.

Bacterial strains 1CX and SAD4i--previously isolated from the mixed liquor of a municipal sewage treatment plant--are capable of degrading the azo dye Acid Orange 7 (AO7) and sulfanilic acid, respectively. A rotating drum bioreactor (RDBR), operating under continuous flow and nutrient conditions designed to simulate the effluent from a dye manufacturing plant, was seeded with strains 1CX and SAD4i, forming a biofilm capable of degrading AO7 and sulfanilic acid. In addition, an RDBR containing a pre-existing biofilm capable of degrading AO7, but not sulfanilic acid, was seeded with strain SAD4i alone. Strain SAD4i was incorporated into the existing biofilm and degraded the sulfanilic acid resulting from the degradation of AO7 by indigenous members of the biofilm. The ability to seed a bioreactor with bacterial strains capable of degrading azo dyes, and resulting by-products, in a mixed microbial community suggests that this process could have commercial applications.

The selection of filamentous bacteria is often assumed to be associated with specific microbial properties such as growth rate, substrate uptake rate, substrate affinity and potential for substrate storage. In this study we aimed to verify some of these factors. Sequencing batch reactor (SBR) systems were used to scale-down aerobic activated sludge systems with an aerobic selector. Adding acetate in different aerobic feeding periods allowed us to simulate a variable relative size of aerobic selector with different bulk liquid substrate concentrations. The experiments showed that as expected, the aerobic fill time ratio (FTR(ox)) and the corresponding feast period, which can be assumed similar to contact time in an aerobic selector, had a strong effect on the sludge settleability. Promoting a strong substrate gradient in the SBR (FTR(ox)<5.4%) resulted in good sludge settleability (SVI<120mLg(-1)). Whenever acetate was added in a limiting rate (FTR(ox)>6.2%), a condition in which the acetate concentration in the reactor was always very low, the sludge settleability decreased (SVI>150mLg(-1)). Sludge settleability could be improved by changing the feeding strategy to a pulse feed. The maximum specific acetate uptake rate and poly beta-hydroxybutyrate (PHB) production rate of bad settling sludge, including bulking sludge, was similar to well-settling sludge, which is not in accordance with the general assumptions that well settling sludge have a higher maximal substrate uptake rate and better storage capacities. An alternative hypothesis for the development of filamentous structures in biological flocs has been formulated. It is hypothesized that bulking sludge originates from the presence of substrate gradients in sludge aggregates. Whereas at low bulk liquid substrate concentration filamentous bacteria give easier access to the substrate at the outside of the flocs and thereby proliferate, at high bulk liquid substrate concentration there is no substrate advantage for filamentous organisms and smooth bacterial structures predominate. In this hypothesis there is no need for an intrinsic difference in kinetic parameters between floc and filamentous bacteria. Where presence of filamentous bacteria is related to process conditions, the presence of a specific filament is likely due to presence of a specific limiting substrate.

This study makes a comparison between the nitrification performance of TNCU-I (a combined activated sludge-rotating biological contactor process) and A2O systems by the use of a pilot plant and batch experiments. The nitrifier abundance in both systems was determined, using cloning-denaturing gradient gel electrophoresis (DGGE) and fluorescent in-situ hybridization (FISH), to investigate the role of rotating biological contactor in the TNCU-I process. The stability of the nitrification performance and the specific nitrification rate were found to be greater in TNCU-I system than in the A2O system. RBC biofilm promoted nitrifying activity that contributed to the nitrification performance, especially at a low SRT. By using the cloning-DGGE method, the genera Nitrosospira and Nitrospira were found to be present in all the samples, while the genus Nitrosomonas was observed only in the TNCU-I RBC biofilm. In addition, the proportions of ammonia oxidizer in the TNCU-I RBC biofilm, the TNCU-I activated sludge and the A2O activated sludge were 11.4%, 13.2%, and 4.1%, respectively, higher than the nitrite oxidizer fractions of 3.3%, 5.7% and 2.1%, respectively, according to the cloning-DGGE method. On the other hand, the proportions of ammonia oxidizers in the afore-mention materials were 10.3%, 13.7%, and 5.2%, higher than the nitrite oxidizer fractions of 2.5%, 3.6% and 2.3%, according to the FISH experiments. This implies that the proportion of ammonia oxidizer in the TNCU-I process was 3.2 and 2.6 times that in the A2O process, determined by the cloning-DGGE and FISH methods, respectively. These amounts are also close to the ammonia oxidization rate of 2.9 times. All the data show that RBC added to the aerobic zone of TNCU-I process would increase the nitrifier abundance and enhance the nitrification performance of the system.

As input to the steady state design and kinetic simulation models for the activated sludge system, the correct value for the heterotroph anoxic yield is essential to provide reliable estimates for the system denitrification potential. This paper examines activated sludge anoxic yield values in the literature, and presents experimental data quantifying the value. In the literature, in terms of the structure of ASM1 and similar models, theoretically it has been shown that the anoxic yield should be reduced to approximately 0.79 the value of the aerobic yield. This theoretical value is validated with data from corresponding aerobic OUR and anoxic nitrate time profiles in a batch fed laboratory scale long sludge age activated sludge system treating municipal wastewater. The value also is in close agreement with values in the literature measured with both artificial substrates and municipal wastewater. Thus, it is concluded that, in ASM1 and similar models, for an aerobic yield of 0.67mg COD/mg COD, the anoxic yield should be about 0.53 mg COD/mg COD. Including such a lower anoxic yield in ASM1 and similar models will result in a significant increase in denitrification potential, due to increased denitrification with wastewater RBCOD as substrate. In terms of the structure of ASM3, for the proposed substrate storage yields and the aerobic yield of 0.63 mg COD/mg COD, experimental data indicate that the corresponding anoxic yield should be about 0.42 mg COD/mg COD. This is significantly lower than the proposed value of 0.54 mg COD/mg COD, and requires further investigation.

A sequencing batch reactor (SBR) was operated in the conventional anaerobic-aerobic mode for enhanced biological phosphate removal (EBPR) using acetate as the sole substrate. Results showed that, however, the reactor was unable to remove phosphate from wastewater. The sludge containing 1.65% of phosphate did not exhibit the typical characteristics of polyphosphate-accumulating organisms (PAO) or glycogen-accumulating organisms (GAO). Phylogenetic analysis, based on 16S rDNA sequences of individual microorganisms, showed that the microbial community of this acetate-degrading sludge was closely related to Comamonas testosteroni (43.8% of total population) of beta-1-proteobacteria, Zoogloea resiniphila (25.0%) of beta-2-proteobacteria, and Xanthomonas maltophilia (19.8%) of gamma-proteobacteria. Results of this study imply that GAO might not be the sole group of bacteria responsible to the deterioration of phosphate removal efficiency in an EBPR reactor.

The treatment of domestic sewage at low temperature of 13 degrees C was investigated in a two-step system consisting of an anaerobic filter (AF) +an anaerobic hybrid (AH) reactor operated at different hydraulic retention times (HRTs). The AF reactor was efficient in the removal of suspended COD, viz. 81%, 58% and 57% at an HRT of, respectively, 4, 2 and 3 h. For optimisation of the removal of suspended COD and dissolved COD, an HRT of 4 + 4 h is required for the AF + AH system. For additional optimisation of colloidal COD removal, the AH reactor needs an HRT of 8 h. The AF + AH system operated at an HRT of 4 + 8 h at 13 degrees C provided a high removal efficiency for all COD fractions. The achieved total COD removal was as high as 71% which is similar to values found in tropical areas. Moreover, 60% of the removed COD was converted to methane.

Conventional biological wastewater treatment plants do not easily degrade the dyes and polyvinyl alcohols (PVOH) in textile effluents. Results are reported on the possible advantages of anaerobic/aerobic cometabolism in sequenced redox reactors. A six phase anaerobic/aerobic sequencing laboratory scale batch reactor was developed to treat a synthetic textile effluent. The wastewater included PVOH from desizing and an azo dye (Remazol Black). The reactor removed 66% of the applied total organic carbon (load F: M 0.15) compared to 76% from a control reactor without dye. Colour removal was 94% but dye metabolites caused reactor instability. Aromatic amines from the anaerobic breakdown of the azo dyes were not completely mineralised by the aerobic phase. Breakdown of PVOH by the reactor (20-30%) was not as good as previous reports with entirely aerobic cultures. The anaerobic cultures were able to tolerate the oxygen and methane continued to be produced but there was a deterioration in settlement.

The organic fraction of municipal solid waste (OFMSW) should be utilised by means of biological methods. The biodegradation of solid wastes can be intensified owing to application of the bioreactors. Estimation of the optimum values of the organic load is one of the most important tasks for the aerobic biodegradation processes. The kinetic model of biological oxidation of the organic wastes has been presented in this paper. The experiments were carried out in batch 6-l working volume stirred tank bioreactors at constant temperature of 25 degrees C. Initial total solids have been at the levels of 15, 19, 34, 55 and 66 g l(-1). The kinetics of microbial decomposition of organic substances was described by means of an unstructured model. The satisfactory time courses for substrate chemical oxygen demand in the solid (CODs) and liquid phase (CODL) and biomass concentration (RNA) have been achieved. Also, the influence of the initial TS on the kinetics of the biodegradation process was investigated and the optimum value of initial TS for this type of processes was estimated at 34-55 g l(-1).

For many years, calorimetric measurements have been used for understanding, modelling, controlling, and optimising chemical reactions. Calorimetry could be as well utilised to investigate biological processes, which however, involve very small amount of heat and therefore require very sensitive instruments. For this purpose, a Mettler Toledo RCI (Reaction calorimeter) was modified, changing both hardware and software, increasing its resolution up to 5 10m W/l. Such sensitivity allows the monitoring of aerobic and anoxic processes. This paper points out the excellent agreement between calorimetric and respirometric data, obtained simultaneously under aerobic conditions using activated sludge from a lab-scale scale reactor. Heat production rate can be directly converted in oxygen uptake rate by means of a correlation factor, whose value is approximately the same for all aerobic respiratory metabolisms. Taking into account this factor, calorimetric data were introduced in a chemical oxygen demand based model and processed for the estimation of kinetic parameters of heterotrophic biomass. Aerobic heterotrophic, denitrifying, and autotrophic nitrifying activity were determined by specific calorimetric tests. The effect of potentially toxic or inhibitory substances on the activity of all microbial communities was as well pointed out in these measurements.

Aerobic granular sludge was cultivated in an intensely mixed sequencing batch airlift reactor (SBAR). A COD loading of 2.5 kg Acetate-COD/(m3 d) was applied. Granules developed in the reactor within one week after inoculation with suspended activated sludge from a conventional wastewater treatment plant. Selection of the dense granules from the biomass mixture occurs because of the differences in settling velocities between granules (fast settling biomass), and filaments and flocs (slow settling biomass). At 'steady state' the granules had an average diameter of 2.5 mm, a biomass density of 60g VSS/I of granules, and a settling rate of > 10 m/h. The biomass consisted of both heterotrophic and nitrifying bacteria. The reactor was operated over a long period during which the granular sludge proved to remain stable. The performance of the intermittently fed SBAR was compared to that of the continuously fed biofilm airlift suspension reactor (BASR). The most importance difference was that the density of the granules in the SBAR was much higher than the density of the biofilms in the BASR. It is discussed that this could be due to the fact that the SBAR is intermittently fed, while the BASR is continuously fed.

Aerobic treatment of municipal waste water in a membrane bioreactor was studied for 535 d. Apart from sampling, sludge was retained completely by a submerged hollow fibre membrane with a pore-size of 0.2 microm. The pilot plant comprised an anoxic zone to enable denitrification. The maximum liquid hold-up of the plant was 3.9 m3. In this study the reactor performance and the stability of the process and the membrane capacity were investigated. A stable flux of 181 m(-2)h(-1) could be realised with a mean transmembrane pressure difference of 0.3bar with air-bubbling and backflushing the membrane and cleaning it in place every two months for one or two hours. For about 140d, a flux of 271 m(-2)h(-1) was achieved, but cleaning became necessary more often. The hydraulic retention time (HRT) varied between 10.4 and 15.6h. Accordingly the volumetric loading rate was between 1.1 and 1.7kg CODm(-3)d(-1). No inoculum was used. The mixed liquor suspended solids (MLSS) concentration gradually increased to 18-20g MLSSl(-1). The feed to microorganism (F/M) ratio varied according to the operation conditions but decreased against a value of 0.07 kg COD kg(-1) MLSSd(-1). Treatment performance was very stable and on a high level. The COD was reduced by 95%. Nitrification was complete and up to 82% of the total nitrogen could be denitrified.

Activated sludge inocula taken from five different wastewater treatment plants were grown aerobically under laboratory conditions on mineral salts medium containing either glucose or skimmed milk powder as carbon source. Cultures showed increases of between 50% and 143% in levels of phosphate uptake from the medium when the growth pH was 5.5 rather than 7.5. Of 100 individual sludge microbial isolates studied, 34 demonstrated such acid-stimulated luxury phosphate uptake; the optimum pH for the process was shown to lie between 5.0 and 6.5. Enhanced phosphate removal by these isolates was accompanied by increases of between 2 and 10.5-fold in their polyphosphate content; this was visualised as intracellular inclusions. Acid-stimulated luxury phosphate uptake by environmental microorganisms is a previously-unrecognised phenomenon that may have application in novel technologies for nutrient removal from wastewaters.

Degradation of Aroclor 1242 was studied in granular biofilm reactors with limited aeration. An aerobic biphenyl degrader, Rhodococcus sp. M5, was used to supplement a natural bacterial population present in a "bioaugmented" reactor, while the "non-bioaugmented" reactor only contained natural granular sludge. The bioaugmentation, however appeared to have no effect on the reactor performance. Aroclor measurements showed its disappearance in both reactors with only 16-19% of Aroclor recovered from the reactor biomass and effluent. Simultaneously, a chlorine balance indicated that dechlorination occurred at a specific rate of 1.43 mg PCB (g volatile suspended solids)(-1) d(-1), which was comparable to the observed rate of Aroclor disappearance. Intermediates detected in both reactors were biphenyl, benzoic acid, and mono-hydroxybiphenyls. This suggests that a near-complete mineralization of Aroclor can be achieved in a single-stage anaerobic/aerobic system due to a combination of reductive and oxidative degradation mechanisms.