Activated Sludge Bioreactor Research Articles

Zinc-induced antibiotic resistance in activated sludge bioreactors

Increased levels of bacterial resistance to antibiotics noted in recent decades poses a significant obstacle to the effective treatment and prevention of disease. Although overuse of antibiotics in agriculture and medicine is partially responsible, environmental exposure to heavy metals may also contribute to antibiotic resistance, even in the absence of antibiotics themselves. In this study, a series of eight lab-scale activated-sludge reactors were amended with Zn and/or a suite of three antibiotics (oxytetracycline, ciprofloxacin, and tylosin), in parallel with unamended controls. Classical spread-plating methods were used to assess resistance to these compounds in culturable bacteria over 21 weeks. After seven weeks of general acclimation and development of baseline resistance levels (phase 1), 5.0 mg/L Zn was added to half of the reactors, which were then operated for an additional 7 weeks (phase 2). For the final seven weeks (phase 3), two of the Zn-amended reactors and two of the control reactors were amended with all three antibiotics, each at 0.2 mg/L. Zn amendment alone did not significantly change resistance levels at the 95% confidence level in phase 2. However, tylosin resistance increased significantly during phase 3 in the Zn-only reactors and resistance to all three antibiotics significantly increased as a consequence of combined Zn+antibiotic amendments. Ambient dissolved Zn levels in the reactors were only 12% of added levels, indicating substantial Zn removal by adsorption and/or precipitation. These results show that sub-toxic levels of Zn can cause increased antibiotic resistance in waste treatment microbial communities at comparatively low antibiotic levels, probably due to developed cross-resistance resulting from pre-exposure to Zn.

Formaldehyde Removal from Air by a Biodegradation System

A biodegradation system was used for the treatment of formaldehyde-polluted air. Air pressure dropped 12 mm water in the trickling biofilter during the experiment of about 4 months. In the range 20-300 mg m(-3) influent formaldehyde, this biodegradation system obtained 4.0-40.0 mg h(-1) degradation capacity, with 100%-66.7% degradation efficiency. The amount of formaldehyde degraded by the trickling biofilter was more than that by the activated sludge bioreactor below 200 mg m(-3) influent gaseous formaldehyde while the amount by the trickling biofilter was less than that by the activated sludge bioreactor over 200 mg m(-3) influent gaseous formaldehyde.

Investigation of bacterial diversity in membrane bioreactor and conventional activated sludge processes from petroleum refineries using phylogenetic and statistical approaches.

Bacterial diversity of two distinct wastewater treatment systems, conventional activated sludge (CAS) and membrane bioreactor (MBR), of petroleum refineries were investigated through 16S rRNA gene libraries. Sequencing and phylogenetic analysis showed that the bacterial community composition of sludge samples was distinct between the two wastewater treatment systems. MBR clones belonged predominantly to Class Betaproteobacteria, represented mainly by genera Thiobacillus and Thauera, whereas CAS clones were mostly related to Class Alphaproteobacteria, represented by uncultured bacteria related to Order Parvularculales. Richness estimators ACE and Chao revealed that the diversity observed in both libraries at the species level is an underestimate of the total bacterial diversity present in the environment and further sampling would yield an increased observed diversity. Shannon and Simpson diversity indices were different between the libraries and revealed greater bacterial diversity for the MBR library, considering an evolutionary distance of 0.03. LIBSHUFF analyses revealed that MBR and CAS communities were significantly different at the 95% confidence level (P< or =0.05) for distances 0< or =D< or =0.20. This work described, qualitatively and quantitatively, the structure of bacterial communities in industrial-scale MBR and CAS processes of the wastewater treatment system from petroleum refineries and demonstrated clearly differentiated communities responsible for the stable performance of wastewater treatment plants.

Distribution of &lt;I&gt;Nitrobacter&lt;/I&gt; and &lt;I&gt;Nitrospira&lt;/I&gt; Communities in an Aerobic Activated Sludge Bioreactor and their Contributions to Nitrite Oxidation

An analysis of nitrite-oxidizing bacteria in the activated sludge process of a full-scale partially nitrifying wastewater treatment plant revealed Nitrospira and Nitrobacter averaged 10 13 cells·L -1 and 10 12 cells·L -1 , respectively. Correlation coefficients linking shifts in NOB community to operational or environmental variables illustrated Nitrospira were negatively correlated to nitrite (r = -0.45, P<0.01), while Nitrobacter showed no significant relationship to nitrite (P=0.1017). Nitrospira was negative correlation to DO (r = -0.46, P<0.01) and positively correlated to temperature (r = 0.59, P<0.0001). However, Nitrobacter was positively correlated to DO (r = 0.38, P<0.01) and HRT (R = 0.33, P<0.05), as well as negatively correlated to temperature (r = -0.49, P<0.001) suggesting niche adaptations within the NOB community. The positive association between Nitrobacter and DO supports a selective advantage over Nitrospira in completely nitrifying plants. Given the operational schematic at this WWTP, Nitrospira contributed more to nitrification than Nitrobacter in this WWTP.

Respirometric evaluation of side-stream treatment of reject water as a source of nitrifying bacteria for main-stream activated sludge bioreactors

A laboratory-scale bioreactor study was conducted to characterize differences in nitrification function in main-stream reactors due to bioaugmentation from side-stream reactors treating reject water. The objective was to evaluate how configuration of a suspended growth side-stream bioreactor impacts nitrification function in the main-stream bioreactor. A bioaugmentation effect was not observed in main-stream reactors operated at warm temperatures. Complete oxidation of ammonia to nitrate was observed in the bioaugmented and control main-stream reactors although nitrite accumulation was observed in each case. Furthermore, respirometry did not reveal superior kinetics in bioaugmented reactors operated at warm temperatures. At cold temperatures bioaugmentation may have stabilized ammonia oxidation in main-stream reactor B2 bioaugmented from a PFR side-stream. Complete ammonia oxidation was observed for most of cold period of operation in the main-stream bioreactor B2. Furthermore, respirometry revealed a higher rate of ammonia oxidation and more stable nitrite oxidation compared with the control bioreactor.

Ammonia‐oxidizing communities in a highly aerated full‐scale activated sludge bioreactor: betaproteobacterial dynamics and low relative abundance of Crenarchaea

Ammonia-oxidizing bacteria (AOB) have long been considered key to the removal of nitrogen in activated sludge bioreactors. Culture-independent molecular analyses have established that AOB lineages in bioreactors are dynamic, but the underlying operational or environmental factors are unclear. Furthermore, the contribution of ammonia-oxidizing archaea (AOA) to nitrogen removal in bioreactors has not been studied. To this end, we investigated the abundance of AOA and AOB as well as correlations between dynamics in AOB lineages and operational parameters at a municipal wastewater treatment plant sampled weekly over a 1 year period. Quantitative PCR measurements of bacterial and archaeal ammonia monooxygenase subunit A (amoA) genes revealed that the bacterial homologue predominated by at least three orders of magnitude in all samples. Archaeal amoA was only detectable in approximately 15% of these samples. Using terminal restriction fragment length polymorphism analysis, we monitored AOB lineages based on amoA genes. The Nitrosomonas europaea lineage and a novel Nitrosomonas-like cluster were the dominant AOB signatures, with a Nitrosospira lineage present at lower relative abundance. These lineages exhibited strong temporal oscillations, with one becoming sequentially dominant over the other. Using non-metric multidimensional scaling and redundancy analyses, we tested correlations between terminal restriction fragment length polymorphism profiles and 20 operational and environmental parameters. The redundancy analyses indicated that the dynamics of AOB lineages correlated most strongly with temperature, dissolved oxygen and influent nitrite and chromium. The Nitrosospira lineage signal had a strong negative correlation to dissolved oxygen and temperature, while the Nitrosomonas-like (negative correlations) and N. europaea lineages (positive correlations) were inversely linked (relative to one another) to influent nitrite and chromium. Overall, this study suggests that AOA may be minor contributors to ammonia oxidation in highly aerated activated sludge, and provides insight into parameters controlling the diversity and dominance of AOB lineages within bioreactors during periods of stable nitrification.

A liquid chromatography-electrospray ionization-tandem mass spectrometry study of ethanolamines in high salinity industrial wastewaters

The detection and quantitation of four ethanolamines, tris(2-hydroxyethyl)amine (triethanolamine, TEA), N, N-bis(2-hydroxyethyl)methylamine (methyldiethanolamine, MDEA), N-(2-aminoethyl)ethanolamine (AEA), and N, N-diethylethanolamine (DEA), were achieved in wastewaters from two aerobic activated sludge bioreactors located in an industrial wastewater treatment plant. The streams had salt concentrations of approximately 3% and 7% by weight in Reactor 1 and Reactor 2, respectively. The use of liquid chromatography-electrospray ionization-tandem mass spectrometry avoided the need for some sample preparation steps such as extraction, concentration, and derivatization. Ion suppression in the electrospray, attributable to the presence of sodium clusters, was attenuated by a 10-fold dilution of the wastewaters with acetonitrile. A matrix-matched calibration model averted other potential interferences. For the compounds analyzed in selected reaction monitoring mode (TEA, MDEA, and DEA), the calibration curves presented linearity in a range of 10–1000 μg/L with corresponding detection limits ranging from 2 to 11 μg/L, depending upon the specific analyte and aqueous matrix. AEA was calibrated in selected ion monitoring mode (100–1000 μg/L), with corresponding detection limits in the two wastewaters of 74.6 and 85.3 μg/L, respectively. Overall good precision (<10%) and accuracy (97–110%) were achieved for both matrices, which fell within-laboratory reproducibility. Finally, the amines were introduced into six mixed liquor samples from both reactors and quantified following the reported protocol. Again, recoveries were close to 100% with a relative standard deviation of less than 10% in all cases.

Metabolism studies of diclofenac and clofibric acid in activated sludge bioreactors using liquid chromatography with quadrupole – time-of-flight mass spectrometry

Summary Two environmentally relevant pharmaceuticals, the non-steroidal antiinflammatory drug, diclofenac and the pharmacologically active metabolite of several serum triglyceride-lowering pharmaceuticals, clofibric acid, were subjected to microbiological transformation in activated sludge bioreactors, and the production of breakdown products was studied. For separation, detection and identification of diclofenac’s metabolites a UPLC-(+)ESI-QqToF-MS was employed, which enabled the detection of seven transformation products of diclofenac, all including the diagnostic fragment ion at m/z 214. The chemical structure of one metabolite was proposed, which was produced by dehydratation and lactame formation. Further investigations revealed additional two metabolites, which were isomeric structures with an elemental composition C13H10NCl2; however, their chemical structures were not completely resolved. In addition, another biodegradation product showed an abundant fragment ion at m/z 295, the elemental composition of which was confirmed with a high degree of certainty as C14H11NO2Cl2. The biodegradation of clofibric acid revealed one metabolite in the (-)ESI-QqToF chromatogram, 4-chlorophenol, which is known to exhibit a higher toxicity than the parent compound. This study confirms that further research is needed on the formation of stable metabolites both during wastewater treatment and in the environment. It also highlights the need for parallel toxicity testing. In addition, this study suggests that more needs to be known about the environmental fate of pharmaceuticals so that we are able to provide a comprehensive risk assessment.

Enhanced treatment of waste frying oil in an activated sludge system by addition of crude rhamnolipid solution

The presence of high-strength oil and grease (O&G) in wastewater poses serious challenges for environment. Addition of surfactant into the activated sludge bioreactor is feasible in reducing high concentrations of O&G via enhancing its bioavailability. In this paper, an aqueous biosurfactant solution of rhamnolipid as a cell-free culture broth of Pseudomonas aeruginosa zju.um1 was added into a batch of aerobic activated sludge system for treatment of the waste frying oil. This treatment was conducted on both bench and pilot-scales, whereas the removal efficiency of frying oil was determined by analyzing the residue concentration of O&G and chemical oxygen demand (COD). In the presence of varying concentrations of rhamnolipid from 22.5 mg/L to 90 mg/L, aerobic treatment for 30 h was enough to remove over 93% of O&G while this biodegradability was only 10% in the control system with the absence of rhamnolipids. The equivalent biodegradability was similarly obtained on COD under addition of rhamnolipid. Compared with bench studies, a higher treatment efficiency with the presence of rhamnolipids was achieved on a pilot-scale of activated sludge system, in which a short time of 12 h was required for removing approximately 95% of O&G while the control treatment attained a low efficiency of 17%. Finally, foaming and biodegradability of rhamnolipids in activated sludge system were further examined in the whole treatment process. It seems that the addition of rhamnolipid-containing culture broth showed great potential for treatment of oily wastewater by activated sludge.

Enhanced atrazine removal using membrane bioreactor bioaugmented with genetically engineered microorganism

Bioaugmentation with genetically engineered microorganisms (GEMs) in a membrane bioreactor (MBR) for enhanced removal of recalcitrant pollutants was explored. An atrazine-degrading genetically engineered microorganism (GEM) with green fluorescent protein was inoculated into an MBR and the effects of such a bioaugmentation strategy on atrazine removal were investigated. The results show that atrazine removal was improved greatly in the bioaugmented MBR compared with a control system. After a start-up period of 6 days, average 94.7% of atrazine was removed in bioaugmented MBR when atrazine concentration of influent was 14.5 mg/L. The volumetric removal rates increased linearly followed by atrazine loading increase and the maximum was 65.5 mg/(L·d). No negative effects were found on COD removal although carbon oxidation activity of bioaugmented sludge was lower than that of common sludge. After inoculation, adsorption to sludge flocs was favorable for GEM survival. The GEM population size initially decreased shortly and then was kept constant at about 104–105 CFU/mL. Predation of micro-organisms played an important role in the decay of the GEM population. GEM leakage from MBR was less than 102 CFU/mL initially and was then undetectable. In contrast, in a conventionally activated sludge bioreactor (CAS), sludge bulking occurred possibly due to atrazine exposure, resulting in bioaugmentation failure and serious GEM leakage. So MBR was superior to CAS in atrazine bioaugmentation treatment using GEM.

Effects of different hydraulic models on predicting longitudinal profiles of reactive pollutants in activated sludge reactors

This paper presents effects of dispersion on predicting longitudinal ammonia concentration profiles in activated sludge bioreactor located at "Wschod" WWTP in Gdansk. The aim of this study was to use the one-dimensional advection-dispersion Equation (ADE) to simulate the flow conditions (based on the inert tracer concentrations in selected points) and longitudinal profile of reactive pollutant (based on the ammonia concentration profiles in selected points). The simulation results were compared with the predictions obtained using a traditional "tanks-in-series" (TIS) approach, commonly used in designing biological reactors. The use of dispersion coefficient calculated from an empirical formula resulted in substantial differences in the tracer concentration distributions in two sampling points in the bioreactor. Simulations using the one-dimensional ADE and TIS model, with the nitrification rate incorporated as the source term, revealed that the hydraulic model plays a minor role compared to the biochemical transformations in predicting the longitudinal ammonia concentration profiles.

Optimization of phenol degradation in a combined photochemical–biological wastewater treatment system

A UV/H 2O 2 process and an activated sludge bioreactor were integrated to achieve a cost-effective process of aqueous degradation of phenol. By applying the two-step Haldane approach for the activated sludge bioreactor and a validated kinetic model for the UV/H 2O 2 process, an integrated model was developed for the phenol degradation in a combined photochemical–biological system. In this study, a kinetic model was employed to study the effects of different parameters in the combined photochemical–biological system, where the optimum conditions in terms of retention time and cost were determined. Three penalized objective functions were developed to find the best operating conditions including the minimization of the retention time, the power consumption, and the total cost. The least retention time for this system was determined to be 99 h and the optimal electrical energy consumption occurred at a photochemical retention time of 15 h with the biological retention time of 92 h. Total cost for different retention times was calculated demonstrating the fact that the incurred cost by the photochemical unit was considerably higher than that of the biological unit; however, the minimum total cost was evaluated to occur at 15.5 h of photochemical retention time and 90 h of biological retention time.

Biogenic H2SO4 corrosion of concrete in oxygen activated sludge bioreactors

Significant concrete corrosion has occurred within the headspace of a pure oxygen activated sludge treatment (OAS) bioreactor treating pulp and paper mill effluent. Bioreactor input effluent solutions were characterized and compared to identify the process conditions most likely responsible for the biogenic H2SO4 corrosion and the damage mechanism. The results suggest that dissolved hydrogen sulfide (H2S), total reduced sulfur (TRS), or both, when stripped from the effluent during biotreatment, are the critical factors required to sustain corrosion. Anaerobic activity within the primary clarifier has been identified as the likely root source of dissolved TRS in primary clarified TMP/newsprint effluent. Changing, or improving control of, TMP/newsprint primary clarifier operating conditions to minimize septicity may be the best way to tackle the problem.

DEVELOPMENT OF A 4-MEASURABLE STATES ACTIVATED SLUDGE PROCESS MODEL DEDUCED FROM THE ASM1

The Activated Sludge Model No.1 (ASMI) allows the prediction of organic matter degradation, nitrification and denitrification in the activated sludge bioreactors using thirteen states variables. This paper deals with modal reduction procedure applied to the ASM1, that followed by physical considerations about the process allows the development of a 4-state variables model which is still able to describe the nonlinear behavior of bioreactors in the Activated Sludge Process (ASP). Furthermore, coupling the reduced bioreactor model with a simplified model for the secondary settler (as the Takacs model), the overall ASP behavior is deduced.

Development of the wastewater reclamation and reusing system with a submerged membrane bioreactor combined bio-filtration

Recently there have been many wastewater treatment processes combining different units of process to improve the dissolving and suspension of pollutants in water. The submerged membrane bioreactor (SMBR) system uses a membrane that can produce high quality water for reusing with minimal land demand, instead of using secondary clarifier as biological treatment, sand filters, ozonation, GAC or disinfection processes as a tertiary treatment. For the development of the bio-filter membrane bioreactor (BMB) system as a submerged membrane bioreactor in this study the new wastewater treatment system will consist of a rapid bio-filter clarifier, a bioreactor and a hollow fiber membrane and plate membrane, to help find the optimal process to meet the regulations for reused water. This study was performed to evaluate the BMB reusing system, made up of a rapid bio-filter clarifier, an activated sludge bioreactor and a membrane module. The rapid bio-filter clarifier replaced a conventional primary sedimentation and removed SS, BOD and COD to 40, 20, and 20%, while the turbidity and color were removed by 30 and 10% respectively. This means that the rapid bio-filter clarifier having an HRT value 5.2 min can replace the conventional primary sedimentation of the HRT value of 1.5–2.5 h. Also the BMB reusing system could achieve the effluent quality of BOD < 5 mg/L, COD < 10 mg/L, turbidity < 0.5 NTU, and color < 20 unit respectively, and total coliforms did not appear. This means this system can meet water quality standard for water reusing systems. The flux of the plate membrane and hollow Fiber membrane were 120–140 L/m 2 h bar and 60–90 L/m 2 h bar; much more water could permeate the plate type membrane than hollow fiber type membrane. Plus the total resistance of hollow fiber type membrane was higher than plate type membrane.

A Review and Assessment of Emerging Technologies for the Minimization of Excess Sludge Production in Wastewater Treatment Plants

This paper focuses on the most promising technologies, available for full-scale applications, aimed to the on-site reduction of the excess sludge produced in municipal wastewater treatment plants. New techniques are added to the conventional stages of wastewater treatment, both integrated in the activated sludge bioreactors or applied as pretreatment for the enhancement of anaerobic digestion. A concise review about the alternatives based on physical, chemical or biological mechanisms is described. The present work highlights the efficiency of two such techniques, sonolysis and alkaline thermolysis integrated on the return flow from the secondary settler into the activated sludge bioreactors. The investigation on the effect of sonolysis and alkaline thermolysis on activated sludge samples was carried out by evaluating the COD concentration released in soluble and colloidal form and biodegradability measured by respirometry. The physicochemical treatments of sludge have several advantages (easy management, stability in performances and flexibility), but are associated with high operational costs that often limit the wide-scale applications. The application of hybrid methods, that couple almost two techniques for the enhancement of efficiency with respect to a single one, could optimise the sludge reduction, giving a significant saving in energy consumption for large-scale operations, but further research is needed.

Occurrence of Ammonia-Oxidizing Archaea in Wastewater Treatment Plant Bioreactors

We report molecular evidence that ammonia-oxidizing archaea (AOA) occur in activated sludge bioreactors used to remove ammonia from wastewater. Using PCR primers targeting archaeal ammonia monooxygenase subunit A (amoA) genes, we retrieved and compared 75 sequences from five wastewater treatment plants operating with low dissolved oxygen levels and long retention times. All of these sequences showed similarity to sequences previously found in soil and sediments, and they were distributed primarily in four major phylogenetic clusters. One of these clusters contained virtually identical amoA sequences obtained from all five activated sludge samples (from Oregon, Wisconsin, Pennsylvania, and New Jersey) and accounted for 67% of all the sequences, suggesting that this AOA phylotype may be widespread in nitrifying bioreactors.

Characterization of Thiobacillus thioparus isolated from an activated sludge bioreactor used for hydrogen sulfide treatment

To compare Thiobacillus thioparus population dynamics in a control and a test activated sludge (AS) bioreactor, used for hydrogen sulfide (H(2)S) degradation. Denaturing gradient gel electrophoresis (DGGE) was used to confirm the presence of T. thioparus, and real-time PCR was used to quantify the level of this bacterium in the AS samples. The DGGE analysis showed a band for T. thioparus in all samples, with the band being more prominent in the test sample with H(2)S diffusion. It also showed that although a change occurred in the diversity of the microbial population in the test sludge after 6 weeks of H(2)S diffusion, the microbial community structure of the test and control was still similar. Thiobacillus thioparus-specific PCR primers confirmed that 50% of the isolates from both the test and control bioreactors were T. thioparus. The thiobacilli population became more efficient at degrading the diffused H(2)S. This increase in efficiency was confirmed by a significant increase in the number of isolates from the test sludge compared with those from the control sludge, when they were grown in a thiosulfate-rich liquid medium. It was concluded that the use of AS process for H(2)S removal encourages the population of T. thioparus to increase even at times when the total biomass concentration shows a decrease. The research results give an insight into the dynamics of the microbial population in an AS pilot plant used in a dual role, to treat the wastewater and H(2)S.

Characterization of soluble microbial products (SMP) derived from glucose and phenol in dual substrate activated sludge bioreactors

Soluble microbial products (SMP) generated by activated sludge cultures receiving a mixed feed of phenol and glucose were characterized with respect to molecular weight (MW) distribution, octanol-water partition coefficient (K(ow)), and Microtox toxicity. Short-term batch reactor tests using 14C-labeled substrates were performed to collect SMP derived from each substrate, while long-term tests were performed with SMP accumulated over multiple feed cycles using fed-batch reactors receiving non-labeled substrates. Yield of SMP in the batch tests, 10%-20% for phenol and 2%-5% for glucose, differed for each substrate and was independent of initial concentration. The MW distribution (MWD) of SMP was independent of feed composition, and was bimodal in the < 1 kDa and 10-100 kDa MW ranges for phenol-derived SMP and predominantly < 1 kDa for glucose-derived SMP. In the non-labeled tests, the fraction of SMP of MW > 100 kDa increased with the proportion of glucose in the feed. The K(ow) of phenol-derived SMP was higher compared to glucose-derived SMP, indicating that the phenol-derived SMP were more hydrophobic. This was particularly true at an acidic pH, where the K(ow) was 4.2 +/- 1.0 for phenol-derived SMP versus 0.13 +/- 0.13 for glucose-derived SMP. Toxicity testing indicated that phenol-derived SMP, exerting a mean Microtox inhibition of 1%, were less toxic than phenol itself, and showed little correlation between toxicity and concentration. However, glucose-derived SMP were generally more toxic than glucose itself (a non-toxic substrate), and the toxicity increased linearly with the concentration of SMP.

Stability Analysis of an Activated Sludge Bioreactor at a Petrochemical Plant at Different Temperatures

The Mexican petrochemical industry, Morelos S.A. de C.V. is one of the biggest and most important petroleum industries in Mexico and in Latin America. It has an activated sludge system to treat its wastewater flow, which is about 7000m3/d. The wastewater contains volatile organic carbon substances classified as toxic. The old surface aeration system was changed for fine bubble diffusers; however, one major drawback of the new aeration system is that the temperature in the bioreactor has increased due to the compression of the air, which at the compressor exit reaches up to 85oC. This effect produces a temperature in the aerated bioreactor of 32oC during the fall, whereas in the spring and summer, the bioreactor temperature reaches higher values than 40oC. The high temperatures reduce the microorganisms’ activity and cause higher volatilization rates of volatile compounds, among other effects, which affect the performance of the biological treatment. In this work we performed a stability analysis at different equilibrium points in different scenarios of temperatures, recycle flowrate and wastage flowrate. The eigenvalues of the state matrix of dynamical model of the petrochemical wastewater treatment were evaluated. The model describes the effect of the temperature on the soluble and volatile pollutants removal rate, heterotrophic organism growth rate, oxygen uptake rate and biomass concentration in the settler. The model was obtained from tests that were done in laboratory reactors with 14 L of capacity, which were operated at different temperatures (from 30oC to 45oC), with the same conditions as the actual system. Simulations were done based on the model obtained manipulating the operation variables Qw and Qr. The stability analysis was also done to the reactor without recycle (Qr = 0 m3/d). In all the cases the stability analyses was performed. The stripping of VOC´s is an important process of COD removal at high operation temperatures.