Activated Sludge Concentration Research Articles

Promoting mechanism of nitrogen removal by Fe3O4 magnetic particles during the start-up phase in sequencing batch reactor.

In this paper, a magnetic sequencing batch reactor (SBR) was constructed, and the influence rule of magnetic particle dosing performance of denitrification was investigated. The diversity, structure, and potential functions of the microbial community were comprehensively explored. The results showed that the particle size and the dosage of Fe3O4 magnetic particles were the main parameters affecting the sedimentation performance of activated sludge. The start-up phase of the SBR reactor with Fe3O4 magnetic particles was 5days less than the control. Moreover, total nitrogen removal efficiency during the start-up phase was improved, with the maximum value reaching 91.93%, surpassing the control by 9.7% with the Fe3O4 dosage of 1.2g L-1. In addition, the activated sludge concentration and dehydrogenase activity were improved, compared to the control. High-throughput sequencing showed that the denitrifying bacterium Saccharimonadales dominated the reactor and was enriched by magnetic particles. According to predicted functions, the abundance of genes for denitrification increased with the addition of magnetic particles, suggesting the capacity of nitrogen removal was enhanced in the microbial community. Overall, the Fe3O4 magnetic particles provide great potential for enhanced wastewater nitrogen removal.

Study on activated sludge composition and concentration setting for increasing COD efficiency in dairy industry wastewater

The dairy industry’s wastewater is the pollution problems that must be concerned. Since dairy wastewater tends to be easily biodegradable, the commonly wastewater treatment technology is biological treatment. The efficiency of reducing COD in the aeration tank of PT. AN was about 39.54% compared to the theoretical that can be achieved until 90%. Therefore, this research objective was to improve the efficiency of COD reduction in the aerobic-activated sludge process of PT. AN. The research was done by laboratory experimental method with variations of the concentration and type of the activated sludge applied, also variations in Bacillus cereus bacteria addition. The performance was measured by the COD reduction efficiency after 9-hour aeration and 3-hour sedimentation. The result showed that by increasing 100% of the activated sludge concentration, the process could increase the COD reduction from 20.3% to 49.8%. The 50:50 combination of existing activated sludge and other activate sludge taken from non-dairy industry’s WWTP got worse result, with the COD reduction from 20.3% to 15.9 %. The better result was shown by Bacillus cereus bacteria addition, the COD reduction can achieve 67.0% with 4.7 % bacteria addition and 97.0% COD reduction can be achieved with 9% bacteria addition.

Feasibility Study of Using Excess Sludge Fermentation Broth as a Co-Metabolic Carbon Source for 2,4,6-Trichlorophenol Degradation

Excess sludge fermentation is a commonly employed method for carbon sources in wastewater treatment plants, but its use as a carbon source for chlorophenol removal has been relatively underexplored. In this study, a laboratory-scale sludge fermentation SBR (FSBR) was integrated with a 2,4,6-trichlorophenol (2,4,6-TCP) degradation SBR (DSBR), resulting in a stable removal of 2,4,6-TCP without the need for external carbon sources. In this coupled system, the concentrations of volatile fatty acids in FSBR remained constant, with acetic acid, propionic acid, butyric acid, and valeric acid concentrations reaching 322.04 mg COD/L, 225.98 mg COD/L, 274.76 mg COD/L, and 149.58 mg COD/L, respectively, and the acid production efficiency increased to 88.40%. Throughout the 110-day operational period, the activated sludge concentration in the DSBR was consistently maintained at 3021 ± 110 mg/L, and the sludge SVI remained stable at 70 mL/g. The maximum amount of 2,4,6-TCP removed reached 240.13 mg/L within a 12 h operating cycle. The use of excess sludge fermentation can completely replace commercial carbon sources for 2,4,6-TCP removal, leading to cost savings in chlorophenol treatment and broadening the applicability of this technology.

The impact of solid/floc holdup on oxygen transfer in a rotating hollow fiber membrane bioreactor under endogenous conditions.

A set of oxygen transfer experiments in clean water and three different activated sludge concentrations were conducted with fine and coarse bubble aeration in a rotating hollow fiber membrane bioreactor to observe the impact of different rotational speeds on the oxygen transfer rate. The results showed that with increasing membrane rotational speed, the oxygen transfer coefficient enhanced while the α-factor showed similar values at comparable sludge concentrations and solid/floc holdups. The highest improvement rates occurred during the experiments with coarse bubble aeration at 50 rpm and the lowest specific airflow rate. The solid/floc holdup appears to universally impact oxygen transfer depletion regardless of what reactor type, diffuser setup and membrane rotational speed were used in the wastewater experiments.

Impact of Naproxen on Wastewater Biological Treatment: Focus on Reactor Performance and Mechanisms

Pharmaceutical contamination has emerged as a significant environmental concern; yet, the impact and underlying mechanisms of widely detected naproxen (NPX) on wastewater biological treatment remain poorly understood. To address this knowledge gap, this study investigates the influence of NPX on biological nutrient removal in wastewater treatment under mesophilic conditions, and elucidates the associated mechanisms. The results demonstrate that NPX concentrations below 0.05 mg/L have no significant effect on the removal of pollutants and nutrients in wastewater, whereas the concentrations exceeding 0.5 mg/L hinder the removal of both chemical oxygen demand (COD) and nutrients, with a more pronounced inhibitory effect observed at higher NPX doses. When the concentration of NPX was 2.0 mg/L, the removal efficiency of COD, NH4+-N and phosphate decreased to 81.2~83.6%, 82.5~84.2% and 80.2~82.6%, respectively, which was much lower than that of the blank. Furthermore, NPX leads to a decrease in activated sludge concentration and organic matter content within the sludge. Additionally, NPX promotes the secretion of extracellular polymeric substances (EPS). Periodic investigations reveal that NPX inhibits the biosynthesis of intracellular polymer polyhydroxyalkanoate (PHA), thereby reducing energy production during later stages of degradation. Enzyme activity analysis indicates that high NPX concentrations suppress the activity of key enzymes associated with biological nitrogen and phosphorus removal. These findings provide theoretical insights for the treatment of NPX-containing wastewater using activated sludge processes.

Biologically recovered polyhydroxyalkanoates (PHA) as novel biofilm carrier for Acid Orange 7 decolourization: Statistical optimization of physicochemical and biological factors

The incorporation of biofilm process in activated sludge process is beneficial in enhancing treatment performance. In this study, biologically recovered polyhydroxyalkanoates (PHA) were explored as an eco-friendly alternative to conventional materials as the biofilm carrier. The PHA was shaped in a pellet form, melt-fused and added as a biofilm carrier in a moving bed biofilm reactor (MBBR). From the scanning electron microscopy image, biofilm was successfully developed on the PHA pellets, with a biofilm thickness of 236 μm. Modeling and optimization were conducted using response surface methodology (RSM) in predicting the AO7 decolourization efficiency and first-order kinetics in the integrated biofilm and suspended activated sludge processes. The interaction effects of three factors of suspended activated sludge concentration (2000–6000 mg/L), PHA pellet packing volume (1–20 %) and initial AO7 concentration (1–20 mg/L) on AO7 decolourization were studied. The AO7 decolourization efficiency and kinetics were well described using the respective reduced quadratic regression models. The analysis showed that the AO7 decolourization was significantly affected by the suspended activated sludge concentration and the PHA pellet packing volume. Under the optimum conditions (5100 mg/L suspended sludge, 10 mg/L initial AO7 and 20 vol% of PHA pellets), the maximum AO7 decolourization efficiency and rate constant were 96.44 % and 0.3550 h−1, respectively. The high bioactivity of attached activated sludge at a low packing volume demonstrated the potential of the biologically recovered PHA as a biocarrier in retaining a high biomass concentration with a low space requirement.

Tetrabromobisphenol A (TBBPA) generation and removal paths analysis in printed circuit board (PCB) industrial wastewater: Lab-scale investigations

With the rapid development of printed circuit board (PCB) industry, the problem of the release of tetrabromobisphenol A (TBBPA) during PCB manufacturing processes was recognized and harmful to the receiving water body. In this study, TBBPA generation paths, fates in industrial wastewater in the PCB manufacturing processes were analyzed. Gas chromatograph-mass spectrometer (GC-MS) scanning results showed that the raw materials including solder mask ink, character ink and dry film mainly contained TBBPA. The PCB fabrication procedures, mainly including development, etching, stripping of inner layer manufacturing process, and pattern plating, tin-plating of outer layer manufacturing process, and development during the forming and surface treatment process would introduce TBBPA into wastewater. Flocculation and activated sludge process (ASP) that were commonly used for industrial wastewater treatment were selected to assess their removal capability for TBBPA in the wastewater, both which could remove more than 80% TBBPA. Low pH below 7, increased PAC and PAM dosages, and proper dosing during the slow-stirring stage could enhance the TBBPA removal of flocculation-sedimentation process. The ASP removes TBBPA mainly by the path of adsorption. High activated sludge concentration, low pH, medium-temperature and limited competitive adsorbates (NH4+, Cu2+) were beneficial to remove TBBPA by the ASP.

Humic acid removal and microbial community function in membrane bioreactor

A membrane bioreactor with humic acid substrate (MBR-H) was operated to investigate organic removal and membrane performance. Approximately, 60% of chemical oxygen demand removal was observed in MBR-H. The biosorption capacity reached to the maximum value of 29.2 mg g−1 in the experiments with various activated sludge concentrations and the amount adsorbed on the newly produced microbes was limited. To understand key functions of microorganisms in the biodegradation of humic acid, the microbial community was examined. The dominant phylum was changed from Actinobacteria at the raw sludge to Proteobacteria at the MBR-H. Especially, great increases of β-, γ-, and δ-Proteobacteria in the MBR-H indicated that those class of Proteobacteria played a vital role in humic acid removal. Investigation at the genus level showed enrichment of Stenotrophobacter in the MBR-H, which indicated the presence of metabolites in the proposed humic substance degradation pathway. In addition, the bacteria producing extracellular polymeric substances were increased in the MBR-H. Substantial variation of microbial community function was occurred in the MBR to degrade humic acid. Operational parameters in MBRs might be sought to maintain water permeability and to obtain preferable condition to evolution of microbial consortia for degradation of the refractory organic matter.

3D MODELING OF BIOLOGICAL WASTEWATER TREATMENT IN AERATION TANK

Purpose. The main purpose of the article is to develop a 3D CFD model for modeling the process of biological wastewater treatment in an aeration tank. Methodology. For mathematical modeling of the process of biological wastewater treatment in the reactor, taking into account the flow hydrodynamics, geometric shape of the aeration tank, convective-diffusion transfer of the substrate and activated sludge, a 3D CFD model was built. The model is based on the three-dimensional equation of motion of an ideal liquid and the equation of mass conservation for the substrate, activated sludge. The field of sewage flow rate in the aeration tank is calculated based on the velocity potential equation. The process of biological transformation of the substrate is calculated on the basis of the Monod model. The splitting scheme was used for numerical integration of the equations of convective-diffusion transfer of activated sludge and substrate. The splitting is carried out in such a way to take into account the transfer of substrate (activated sludge) in only one direction at each step of splitting. The calculation of the unknown value of the substrate (activated sludge) concentration is carried out according to an explicit scheme. The Richardson method is used to numerically integrate the three-dimensional equation for the velocity potential, and the unknown value of the velocity potential is calculated by an explicit formula. Euler's method is used for numerical integration of equations describing the process of substrate transformation and change in activated sludge concentration (Monod model). Findings. The software implementation of the constructed 3D CFD model is carried out. A description of the structure of the developed software package is provided. The results of a computer experiment to study the process of wastewater treatment in an aeration tank with additional elements are presented. Originality. A new multifactor 3D CFD model has been developed, which allows quick assessing the efficiency of biological treatment in an aeration tank. Practical value. The constructed 3D CFD model can be used to analyze the efficiency of the aeration tank under different operating conditions at the stage of sketch design of wastewater treatment systems.

Phenol and p-nitrophenol biodegradations by acclimated activated sludge: Influence of operational conditions on biodegradation kinetics and responding microbial communities

This study aims to evaluate the influence of operational factors (i.e. substrate concentration, activated sludge concentration and acclimation concentration) and the microbial communities of activated sludge on the aerobic biodegradation of phenol and p-nitrophenol (PNP). During the biodegradation process, the phenol or PNP biodegradation and activated sludge growth kinetics were determined and the interaction effects of the operational factors on the kinetics were assessed. The phenol biodegradation kinetics was well described by zero-order model (R2 > 0.813). At low phenol concentration (< 200 mg/L), the biodegradation rate can be enhanced by increasing activated sludge concentration and acclimation concentration. From the specific oxygen uptake rate (SOUR) analysis, lower SOUR values for PNP relative to phenol suggests higher toxicity of PNP, with inhibition detected above 50 mg/L for both phenol and PNP. In view of the inadequacy of zero-order equation for PNP biodegradation, the kinetic data was fitted into Haldane equation that incorporate the inhibitory effect. From the results, the value of critical PNP concentration was observed to increase at higher acclimation concentration, indicating the attenuation of inhibitory effects on PNP-acclimated activated sludge. For microbial growth, only the factor of acclimation concentration greatly affected the growth kinetics, in which the Ks/Ki ratio was greatly reduced when the acclimation concentration was doubled. Lastly, potential degrading strains of Acinetobacter sp. USM, Rhodococcus sp. USM1 and Caballeronia sp. USM2, were successfully isolated from the acclimated activated sludge. From the results of dioxygenase genes amplification, the phenol degradation mechanism was identified following ortho fission pathway.

Consistency of batch anaerobic digestion process of high and low activated sludge concentrations to the interference of sodium benzoate as preservative material

Anaerobic digestion resulted best performance in degradation of organic materials. Degradation of the organic materials was stated as complete by the formation of methane, carbon dioxide etc. (or biogas) as the final product of degradation. Food or beverages products utilized preservative agents in order to prolong the expired date. Sodium benzoate is the most common of preservative agent which can be used for both food and beverages. This experiments were pointed out to observe the effect of high and low activated sludge to the formation of biogas. Research was conducted in some batch mode reactor systems employing high and low of activated sludge (80% and 20% of volume) and solution concentration of sodium benzoate volume. The activated sludge used was 12 g MLSS/L. Concentrations of sodium benzoate used were 400, 600, and 800 mg/L. Product of biogas samples was measured every two days for 60 days of experiment. The results showed that the volume ratio of activated sludge and sodium benzoate of 80% able to reduce the interference of sodium benzoate and for 20% was not able to produce biogas where the load of sodium benzoate influenced the production of biogas.

DISOLVED OXYGEN PERFORMANCE IN DEGRADATION OF TOTAL PETROLEUM HYDROCARBONS BY EX SITE ACTIVATED SLUDGE

Contamination of soil by the activities of exploration, production and disposal of oil waste into the environment causes serious damage to the environmental ecosystem, the target of processing by the activated sludge as a model for remediation of petroleum contaminated site. Optimization of oxygen supply becomes special attention in aerobic bioprocess for optimizing the growth of microorganisms to degrade total petroleum hydrocarbons. Thus, the study was focused on determining the performance of dissolved oxygen in degradation of total petroleum hydrocarbons by ex situ activated sludge. The research used biological methods (bioremediation), with the ratio of contaminated soil to water was 20:80%(w/v) and a soil size 40/50 mesh. The degradation process was carried out with 15% and 20% (v/v) activated sludge put into the bioreactor slurry with a capacity of 4 liters and stirring was 90 rpm at a temperature of 30oC as well as aeration and nutrient injection into the bioreactor. TPH analysis was measured by the gravimetric method. The results obtained showed that the performance of dissolved oxygen increased well in the bioreactor slurry at 15% (v/v) and 20% (v/v) activated sludge concentrations was 3.31–8.57 mg/L and 3.5–8.21 mg/L respectively, which had an impact on the level of TPH degradation, namely from 18,000 µg/g to 2870 µg/g and 18,000 µg/g to 1970 µg/g during the 49 days remediation period. In general, activated sludge shows good performance throughout the remediation period.

A Comparative Study of Conventional Aerator and Microbubble Generator in Aerobic Reactors for Wastewater Treatment

Aeration in aerobic reactor for wastewater treatment has an important role in determining its performance. In this case, sufficient oxygen supply with good mixing is necessary to guarantee a good pollutant biodegradation. However, biodegradation is not the only parameter to consider when designing an aerator, energy consumption and cost also have important roles. In this study, a conventional air diffuser (CAD) and a low-cost microbubble generator (MBG) were compared in a 400-L reactor for two aerobic wastewater treatment process configurations, i.e. suspended culture and attached culture (with pumice stones). Dissolved oxygen (DO) concentration throughout the reactor was initially investigated with tap water. Results indicated that the maximum DO which could be obtained for the two type of aerators were almost similar, in the range of 7.7 to 7.9 mg/L. But the lowest values are different, i.e. 5.6 mg/L for CAD and 6.8 mg/L for MBG, showing that homogeneity was better for MBG. This might be due to smaller bubble sizes produced by MBG which were able to stay inside the liquid for a longer time. Afterward, comparison of the two aerators were performed for aerating activated aerobic sludge. Without pumice stones, DO concentration for MBG and CAD was almost similar, but for MBG, lower values were found in the bottom of the tank indicating the higher activated sludge concentration. When using pumice stones, MBG again shows its superiority indicated by a higher DO values reaching 6.4 mg/L, compared to 5.6 mg/L for the CAD. These results revealed the promising potential of MBG as a low-cost aerator to be used in aerobic reactor for wastewater treatment with attached culture.

Studies on a new stainless steel mesh dynamic membrane for wastewater treatment.

In this study an innovative dynamic membrane bioreactor (DMBR) was implemented from a stainless-steel mesh filter, which was used as a support material, and activated sludge used as an adsorption and filtration interface containing particulate organics. This work indicated that DMBR can achieve rapid solid-liquid pollutants separation. The activated sludge in the aeration tank quickly formed a thin dynamic membrane layer on the filter. The layer was automatically regenerated as the sludge traveled through the reactor. The experimental results for the new DMBR showed good biodegradability in sewage treatment when the activated sludge concentrations ranged between 3000 and 7000mg/L. Excellent adsorption and filtration performance were also achieved. This dynamic membrane layer significantly improved the effluent quality. The average removal rates were 92.2% and 91.5% for Chemical Oxygen Demand (COD) and Total Phosphorus (TP), respectively. The sewage treatment index was better than the current standard activated sludge process.

Dairy Wastewater Treatment Using Membrane Bioreactor

The paper presents the results of scientific researches in the field of biomembrane treatment of dairy products industry enterprises wastewater. Practical experiments confirmed the possibility of reducing the inhibition degree of the process of biological treatment of dairy products industry wastewater, which has been physically and chemically purified, by increasing the concentration of active sludge. This effect can be achieved while using membrane bioreactor technology (MBR). The experiments also showed that if dairy plants wastewater is pre-treated with coagulants and flocculants, specific speed of biocontamination oxidation decreases in 1, 2-2, 3 times at BODfull = 250 mg/l in comparison with the initial wastewater. It happens because of substrate inhibition rate of biochemical reactions. The identified dependencies show that it is advisable to exclude the stage of reagent flotation before the biological treatment of dairy products industry wastewater. It can reduce costs of using a large number of expensive reagents and simplify the technological scheme. During the experiments dairy plants wastewater was taken as a model. Later, the researchers used real wastewater and confirmed the main kinetic constants and coefficients for calculations of biological purification plants. These results are as follows: temperature constant χ, grad−1, for aerobic heterotrophic conversion – 0,079-0,091, for nitrification – 0.096; for denitrification – 0.13. Coefficients of inhibition by active sludge φ metabolic products amounted to (l/g): for organic substances oxidation by BODfull – 0,39-0,54; for nitrification – 0.19, for denitrification – 0.22; active reaction of the environment corresponding to the highest rate of oxidation of organic substances pHopt – 6.9 at pH-constant 150. The maximum specific speed of organic substances oxidation r’max is 82,5-101,1 mg/(g × h), the Michaelis constant Km – 15 mg/l. The maximum specific speed of nitrification r’max is 1.49 mg/(g × h), the Michaelis constant Km is 0.12 mg/l, the constant of inhibition a is 43. The maximum specific speed of denitrification r’max is 10.8 mg/(g × h), the Michaelis constant Km is 3.5 mg/l. The calculated values of kinetic coefficients and constants make it possible to calculate membrane bioreactors of sewage treatment plants of dairy industry to the specified degree of purification. The estimated annual economic effect for “Pestravskiy” diary plant of the Samara region equaled 4 mln. rub/year (at 2017 values).

Production Biomethane from Palm Oil Mill Effluent (POME) with Truncated Pyramid Digester in Fed Batch System

Palm oil mill effluent (POME) production in Indonesia is estimated around 63 million ton/year [1]. Therefore it is a potential source of contamination when it directly discharged into the river. Even though, POME will be as raw resource biogas production. The aims of this research were to know the effect of fermentation time toward biogas production in truncated pyramid digester. The study was done in three combinations of feedstock with POME concentrations of 90, 80, and 70% and activated sludge concentrations of 10, 20, and 30%. A mixture of POME and activated sludge at 6 L/minutes for 30 days were fed into the digester. The result showed the fermentation time gave significant effect toward biogas production in the truncated pyramid digester. All combinations showed the upward trend in the volume of biogas during fermentation. The highest quantity of biomethane in biogas was 25% mol that the active microbes were added to POME in the ratio 1: 9 in a fed-batch system.

Self-forming dynamic membrane formed on mesh filter coupled with membrane bioreactor at different sludge concentrations

This study attempted to evaluate the process of self-forming dynamic membrane formation on mesh filter in membrane bioreactor with a two-stage method of batch (agitation) and continues (aeration) stage at different sludge concentrations. Four concentrations of activated sludge including 6+-0.4, 8+-0.5, 10+-0.3, 14+-0.3 g/L were used to demonstrate the optimal concentration of sludge for treating municipal wastewater and reducing fouling in dynamic membrane bioreactor. The formation time and effluent turbidity were decreased in the batch stage when increasing the activated sludge concentration. The minimum values of formation time and effluent turbidity were 14 min and 43 NTU for the optimum mixed liqueur suspended solids of 8+-0.5 g/L, respectively. To improve operational condition and fouling reduction in the aeration stage, critical fluxes were measured for all concentrations by flux-step method. With increasing the sludge concentration, the relevant critical fluxes reduced. The optimum subcritical flux of 30 L/m2/h was applied as operating flux in the second stage. The maximum COD removal efficiency of 98% was achieved by the concentration of 8+-0.5 g/L. Compressibility index of self-forming dynamic membrane and transmembrane pressure trend remained somewhat constant until the optimal concentration of 8+-0.5 g/L and thereafter they increased steeply.

Current Trends in Biological Wastewater Treatment

Abstract Waste water treatment plants are complex systems consisting of construction, hydro-mechanical, electrical, monitoring and automation equipment. Monitoring activities emphasize that the processes are dynamic; wastewater quality at the entering point of treatment plant varies in a wide range. Treatment technologies adopted must reduce major pollutants; that involves nitrification-denitrification processes and biological and chemical reduction of phosphorus through mechanical-chemical-biological treatment pathways. Increasing the activated sludge concentration in a wastewater treatment plant is an effective method by altering the process dynamics and by reducing the produced sludge volume. There are proposed and discussed in terms of technical and cost efficiency different technological wastewater treatment schemes. In Romania, wastewater treatment plants and sewage systems operating involve processes based on the new systems overrated, there is mandatory to diminish quantities in water supply systems and to exclude improperly working of wastewater pre-treatment stations. Those operations impose technological measures ensuring efficient functioning regardless the service conditions.

Performance and microbial community analysis of an algal-activated sludge symbiotic system: Effect of activated sludge concentration.

It was focused on the effect of different sludge concentrations on the performances of an algal-activated sludge symbiotic system in terms of wastewater treatment, algal-activated sludge characteristics and community structure. The results showed that the highest nutrient removal efficiencies were obtained in the reactor R2 with soluble chemical oxygen demand (sCOD), ammonia nitrogen (NH4+-N) and phosphate (PO43- -P) removal efficiencies of (90.6±2.3)%, (97.69±2.6)% and (83.81±2.3)%, respectively. Further investigation exhibited that sludge concentration has a great effect on the dissolved oxygen (DO) concentration, the pH, the growth of algae and the extracellular polymeric substance (EPS) production, which resulted in influencing the settleability and the performance of symbiotic system. The denaturing gradient gel electrophoresis (DGGE) analysis demonstrated that the sludge concentration had a selective power for particular members of algae. Meantime, the stimulated algal population would selectively excite the members of bacteria benefited for the formation of algal-bacterial consortia. The variation of microbial compositions, which was influenced by the different sludge concentrations, might be ultimately responsible for the different treatment performances.

Concentration of active sludge in the aeration reactors

The purpose of the paper was to study the dehydrogenase activity (DHA) of activated sludge in aeration tank. The article describes a change in enzyme activity, (dehydrogenase activity of sludge-DHA) of activated sludge while various time of aeration as well as various dose in sludge of aeration tank. Assessment changes enzyme activity were done on two indicators - on DHAor. (original dehydrogenase activity of sludge) and DHAH2O (dehydrogenase sludge activity with tap water). In the first case - DHA with the actual substrate, in the second case - DHA with poorly concentrated substrate. The work was performed on a pilot installation consisting of four models of aeration tanks blocked with sedimentation tanks, on a real city waste water. Working doses of sludge in biological wastewater treatment process was ranged from 2 to 6 g/l, time of aeration in aeration tanks changed from 3.5. up to 0.8 hours. Experimental studies have shown that regardless of the size of working sludge dose in aeration tank character of changes DHA or and DHAH2O is identical.