Effects of adsorbents and copper(II) on activated sludge microorganisms and sequencing batch reactor treatment process

Wastewater treatment systems employing simultaneous adsorption and biodegradation processes have proven to be effective in treating toxic pollutants present in industrial wastewater. The objective of this study is to evaluate the effect of Cu(II) and the efficacy of the powdered activated carbon (PAC) and activated rice husk (ARH) in reducing the toxic effect of Cu(II) on the activated sludge microorganisms. The ARH was prepared by treatment with concentrated nitric acid for 15 h at 60-65 degrees C. The sequencing batch reactor (SBR) systems were operated with FILL, REACT, SETTLE, DRAW and IDLE modes in the ratio of 0.5:3.5:1:0.75:0.25 for a cycle time of 6 h. The Cu(II) and COD removal efficiency were 90 and 85%, respectively, in the SBR system containing 10 mg/l Cu(II) with the addition of 143 mg/l PAC or 1.0 g PAC per cycle. In the case of 715 mg/l ARH or 5.0 g ARH per cycle addition, the Cu(II) and COD removal efficiency were 85 and 92%, respectively. ARH can be used as an alternate adsorbent to PAC in the simultaneous adsorption and biodegradation wastewater treatment process for the removal of Cu(II). The specific oxygen uptake rate (SOUR) and kinetic studies show that the addition of PAC and ARH reduce the toxic effect of Cu(II) on the activated sludge microorganisms.     

Effect of trace amounts of polyacrylamide (PAM) on long-term performance of activated sludge

This study aims at evaluating the impacts of PAM addition on activated sludge performance. Four lab-scale sequencing batch reactors (SBRs), each with a working volume of 3L, were investigated with different PAM concentrations. Experiments were conducted with varying organic loading rate and the sludge volume index (SVI), particle size, zeta potential, specific oxygen uptake rate (SOUR), mixed liquor suspended solids (MLSS), COD and ammonium removal efficiency were monitored over a 105-day period. The results showed that all of the PAM addition not only improved the removal efficiencies of COD and ammonium, but also exhibited some advantages on sludge performance. It was found that the sludge performance of settling property, flocculation and microbial activity increased with increasing concentration of PAM. However, high level of PAM (1mg/L) led to the formation of large amounts of loose-structure flocs, which eliminated dissolved oxygen transfer and caused the sludge disintegration, resulting in bad settleability and lower microbial activity. In this way, when the dosage of PAM was 0.1mg/L, the sludge had the best settling property and activity.     

Improving the performance of sequencing batch reactor (SBR) by the addition of zeolite powder

Two types of operation means "SBR reactor alone (control reactor)" and "adding zeolite powder into SBR reactor (test reactor)" were used to treat municipal wastewater. The test results revealed that zeolite powder addition could improve the activity of the activated sludge. It was investigated the specific oxygen utilization rate (SOUR) of the tested zeolite sludge were about double times that of the control activated sludge, and the nitrification rate and settling property of zeolite-activated sludge were both improved. Due to the combination of zeolite adsorption for NH(4)(+)-N and enhanced simultaneous nitrification and de-nitrification (SND), a higher nitrogen removal was observed in test reactor compared to the control reactor, and the addition of zeolite powder is helpful to inhabit sludge bulking. In addition, through long-term parallel shock load test, it was found that the zeolite powder addition could enhance the ability of activated sludge in resisting the shock load of organics and ammonium. Compared to the control activated sludge, zeolite powder added activated sludge could remove COD, NH(4)(+)-N, TN and TP significantly in a shorter cycle time. At the same operational time period, the test SBR could treat wastewater quantity 1.22 times that treated in control SBR.     

Ultrasonic reduction of excess sludge from the activated sludge system

Sludge treatment has long become the most challenging problem in wastewater treatment plants. Previous studies showed that ozone or chlorine effectively liquefies sludge into substrates for bio-degradation in the aeration tank, and thus reduces the excess sludge. This paper employs ultrasound to reduce the excess sludge from the sequential batch reactor (SBR) system. Partial sludge was disintegrated into dissolved substrates by ultrasound in an external sono-tank and was then returned to the SBR for bio-degradation. The results showed that ultrasound (25kHz) effectively liquefied the sludge. The most effective conditions for sludge reduction were as following: sludge sonication ratio of 3/14, ultrasound intensity of 120kW/kgDS, and sonication duration of 15min. The amount of excess sludge was reduced by 91.1% to 17.8mg/(Ld); the organic content and settleability of sludge in the SBR were not impacted. The chemical oxygen demand (COD) removal efficiency was 81.1%, the total nitrogen (TN) removal efficiency was 17-66%, and high phosphorus concentration in the effluent was observed.     

Elimination of Cu(II) toxicity by powdered waste sludge (PWS) addition to an activated sludge unit treating Cu(II) containing synthetic wastewater

Copper(II) ion toxicity onto activated sludge organisms was eliminated by addition of powdered waste sludge (PWS) to the feed wastewater for removal of Cu(II) ions by biosorption before biological treatment. The synthetic feed wastewater containing 14 or 22 mgl(-1) Cu(II) was mixed with PWS in a mixing tank where Cu(II) ions were adsorbed onto PWS and the mixture was fed to a sedimentation tank to separate Cu(II) containing PWS from the feed wastewater. The activated sludge unit fed with the effluent of the sedimentation tank was operated at a hydraulic residence time (HRT) of 10h and sludge age (SRT) of 10 days. To investigate Cu(II), COD and toxicity removal performance of the activated sludge unit at different PWS loadings, the system was operated at different PWS loading rates (0.1-1 gPWSh(-1)) while the Cu(II) loading rate was constant throughout the operation. Percent copper, COD and toxicity removals increased with increasing PWS loading rate due to increased adsorption of Cu(II) onto PWS yielding low Cu(II) contents in the feed. Biomass concentration in the aeration tank increased and the sludge volume index (SVI) decreased with increasing PWS loading rate due to elimination of Cu(II) from the feed wastewater by PWS addition. PWS addition to the Cu(II) containing wastewater was proven to be effective for removal of Cu(II) by biosorption before biological treatment. Approximately, 1 gPWSh(-1) should be added for 28 mgCuh(-1) loading rate for complete removal of Cu(II) from the feed wastewater to obtain high COD removals in the activated sludge unit.     

Mathematical modeling of copper(II) ion inhibition on COD removal in an activated sludge unit

A mathematical model was developed to describe the Cu(II) ion inhibition on chemical oxygen demand (COD) removal from synthetic wastewater containing 15 mg l(-1) Cu(II) in an activated sludge unit. Experimental data obtained at different sludge ages (5-30 days) and hydraulic residence times (HRT) (5-25 h) were used to determine the kinetic, stoichiometric and inhibition constants for the COD removal rate in the presence and absence of Cu(II) ions. The inhibition pattern was identified as non-competitive, since Cu(II) ion inhibitions were observed both on maximum specific substrate removal rate (k) and on the saturation constant (Ks) with the inhibition constants of 97 and 18 mg l(-1), respectively, indicating more pronounced inhibition on Ks. The growth yield coefficient (Y) decreased and the death rate constant (b) increased in the presence of Cu(II) ions due to copper ion toxicity on microbial growth with inhibition constants of 29 and 200 mg l(-1), respectively indicating more effective inhibition on the growth yield coefficient or higher maintenance requirements. The mathematical model with the predetermined kinetic constants was able to predict the system performance reasonably well especially at high HRT operations.     

Unhairing effluents treated by an activated sludge system

Leather tannery effluents are a source of severe environmental impacts. In particular, the unhairing stage, belonging to beamhouse processes, generates a significantly toxic, alkaline wastewater with high concentrations of organic matter, sulphides, suspended solids and salts. The objective of this work was to evaluate the biodegradability and toxicity of diluted unhairing wastewater after being treated by an activated sludge (AS) system. The biomass activity of the AS was also evaluated. The AS system was fed for 180 days with diluted unhairing effluent. The operation strategy increased the organic load rate (OLR) from 0.23 to 2.98 g COD/l per day while the HRT was variable until operation day 113, when the HRT was near 1.1 days. Results show that when the organic load rate was lower than 2 g COD/l per day, the biological oxygen demand (BOD5) efficiency was 99%, whereas the chemical oxygen demand (COD) was around 80%. The reactor operation was stable until 2 g COD/l per day. For higher values, the system was less efficient (COD and BOD5 removal rate lower than 40%) and the relation of food/micro-organisms (F/M) was higher than 0.15. Biomass evaluations through oxygen utilisation coefficients show that the specific oxygen uptake rate (SOUR) decreased from 1.11 to 0.083 g O2/g MLVSS per day, in the same way the endogenous oxygen coefficient decreased from 0.77 to 0.058 per day. The reduction of biomass activity (measured as oxygen respiration) could be attributable to the inorganic compound content (ammonia and chloride) in the unhairing effluent. Also, the bioassays with Daphnia magna and Daphnia pulex showed that with these compounds, only between 24 and 31% of the toxicity of the aerobic-treated effluent can be removed. On the other hand, ultrafiltration (UF) analysis indicated that a COD fraction is recalcitrant to the aerobic treatment, principally those above 10,000 Da (around 55% of total unhairing influent COD).     

An OUR-based approach to determine the toxic effects of 2,4-dichlorophenoxyacetic acid in activated sludge

This study uses the oxygen uptake rate (OUR) measurement to measure toxicity effects of 2,4-dichlorophenoxyacetic acid (2,4-D) on activated sludges fed with the wastewater from a small domestic wastewater treatment plant and peptone-based synthetic wastewater. Two 2l lab-scale batch reactors were run in parallel with the same F/M ratios (0.4 mg COD per mg VSS per day) to assess the inhibition effects of 2,4-D concentrations between 25 and 75 mg l(-1) considering at least a 100% dilution rate, as compared with a pesticide industry effluent containing 20,000-40,000 mg l(-1) COD, reaches a central treatment plant. It was noted that the OUR was decreased to 15 and 30%, respectively, when adding 75 mg l(-1) of 2,4-D to the domestic and synthetic reactors. Meanwhile, the addition of 25 plus 50 mg l(-1) of 2,4-D in sequence to the domestic wastewater reactor did not significantly affect the OUR profile. The OUR-based inhibition definition has been used in this research since the OUR methods have been frequently used and cited in the literature to study toxicity effects. However, the origin of the sludge used in the testing is also important. Synthetic wastewater may simulate the toxicity studies but with a higher response than actual systems, since the microorganisms are considerably becoming substrate-selective.     

Catalytic ozonation of p-chlorobenzoic acid by activated carbon and nickel supported activated carbon prepared from petroleum coke

The aim of this research was to investigate catalytic activity of petroleum coke, activated carbon (AC) prepared from this material, Ni supported catalyst on activated carbon (Ni/AC) in the ozonation of aqueous phase p-chlorobenzoic acid (p-CBA). Activated carbon and Ni/AC catalyst were characterized by XRD and SEM. The presence of petroleum coke did not improve the degradation of p-CBA compared to ozonation alone, but it was advantageous for p-CBA mineralization (total organic carbon, TOC, reduction), indicating the generation of highly oxidant species (*OH) in the medium. The presence of either activated carbon or Ni/AC considerably improves TOC removal during p-CBA ozonation. Ni/AC catalyst shows the better catalytic activity and stability based on five repeated tests during p-CBA ozonation. During the ozonation (50 mg/h ozone flow rate) of a 10 mg/L p-CBA (pH 4.31), it can be more mineralized in the presence of Ni/AC catalyst (5.0 g/L), TOC removal rate is over 60% in 60 min, 43% using activated carbon as catalyst, only 30% with ozonation alone.     

Biodegradation of 4-CP in an activated sludge reactor: effects of biosurfactant and the sludge age

The biosurfactant's effect on the biodegradation of 4-chlorophenol (4-CP) in the existence of glucose was researched under the circumstances of using unacclimated culture and various sludge ages. The removal efficiencies of chemical oxygen demand (COD) and 4-CP, the growth of biomass and specific substrate removal rates were examined under various operating conditions. When 150 mg/l concentration of 4-CP was applied, glucose and 4-CP degraded in the same period in the unacclimated bioreactors where biosurfactant was added. Nevertheless, the COD removal in the control reactor noticeably decreased and when compared with reactors which biosurfactant was added, a longer period was needed for the degradation of 4-CP in this reactor. While the complete removal of 4-CP in the control reactor eventuated on the 14th day, in the reactor which 2xcritical micelle concentration (CMC) was added the complete removal of 4-CP eventuated on the end of the 1st day. These results showed that addition of biosurfactant reduced the transient time before the steady-state. COD and 4-CP removal performances were improved by increasing the sludge age. No difference in system performance was observed at high sludge ages in the absence and presence of biosurfactant. However, the performance of the system in the presence of biosurfactant was satisfactory even at low sludge ages. That is, the system should be operated either at high sludge ages (>15 days) in the absence of biosurfactant or at low sludge ages (<15 days) in the presence of surfactants.     

Mathematical modelling of 4-chlorophenol inhibition on COD and 4-chlorophenol removals in an activated sludge unit

A mathematical model was developed for an activated sludge unit treating 4-chlorophenol (4-CP) containing synthetic wastewater composed of diluted molasses, urea, KH(2)PO(4) and MgSO(4) with COD and 4-CP contents of 2500 and 500 mg l(-1), respectively. The model included 4-CP inhibition on COD and 4-CP removals. Experimental data obtained at different hydraulic residence times (HRT=5-30h) and sludge ages (SRT, 3-30 days) were used to estimate the kinetic and inhibition constants for COD and 4-CP removal rates. 4-CP inhibition on COD removal was negligible while the inhibition on 4-CP removal was significant. The specific rate constant (k), saturation constant (K(s)) for COD oxidation were found to be 2.64 day(-1) and 559 mg l(-1), respectively. A similar model was used for 4-CP oxidation in the activated sludge unit and the constants were found to be k'=1.44 day(-1), K'(s)=25.7 mgl(-1), K"(CP)=559 mg l(-1),and K(I,CP)=17 mg l(-1). Increases in death rate constant because of 4-CP inhibition was also quantified and the inhibition constants were determined for both COD and 4-CP removals. Model predictions with the estimated kinetic constants were in good agreement with the experimental data. Developed model can be used to estimate the performance of an activated sludge unit treating 4-CP containing wastewater under the specified experimental conditions.     

Kinetic responses of activated sludge to individual and joint nickel (Ni(II)) and cobalt (Co(II)): An isobolographic approach

The effects of Ni(II) and Co(II) on the activated sludge growth rate have been assessed for a batch growth system, for a range of concentrations between 0 and 320 mg L(-1). The activated sludge was not acclimatized to the above metallic species, while a synthetic rich growth medium was used as substrate throughout out the experimental trials. Ni(II) and Co(II) have been found to stimulate microbial growth at concentrations approximately below 27 and 19 mg L(-1), with maximum stimulation concentrations 10 and 5 mg L(-1), respectively. The lethal concentrations (zero growth) for both species have been found to lie between 160 and 320 mg L(-1), with Co(II) identified as more potent growth inhibitor compared to Ni(II). The behaviour of activated sludge was also tested at the presence of three Ni(II) and Co(II) quotas, at various concentrations (75%Ni-25%Co (w/w), 50%Ni-50%Co (w/w) and 25%Ni-75%Co (w/w)). All the mixtures stimulated more drastically the activated sludge growth at relatively small concentrations, compared with the stimulation of equal concentrations of single species, whilst they also acted as more potent inhibitors at relatively high concentrations. Based on the isobole method, the data indicated that Ni(II) and Co(II) acted synergistically at the increasing stimulation and at the intoxication zones, whilst an antagonistic relation determined at the decreasing stimulation zone. Under the light of the present study, it is obvious that interactions (particularly synergism) between different metallic species should be taken into account in the methodologies used to establish criteria for tolerance levels in the environment.     

COD, para-chlorophenol and toxicity removal from para-chlorophenol containing synthetic wastewater in an activated sludge unit

Chlorinated phenolic compounds present in some chemical industry wastewaters cause severe toxic effects on the organisms and often are resistant to biological degradation. Synthetic wastewater containing different concentrations of para-chlorophenol (4-chlorophenol, 4-CP) was biologically treated in an activated sludge unit for COD, 4-CP and toxicity removal. Effects of feed 4-CP concentration on COD, 4-CP, toxicity removals and on sludge volume index were investigated at a constant sludge age of 20 days and hydraulic residence time (HRT) of 25 h. Resazurin method based on dehydrogenase activity was used for determination of the toxicity of the feed and effluent wastewater. COD and 4-CP removals were not affected by the presence of 4-CP in the wastewater up to feed 4-CP concentration of 925 mg l(-1) because of almost complete degradation of 4-CP yielding lower than 50 mg l(-1) 4-CP in the aeration tank. Percent COD, 4-CP and toxicity removals decreased and the effluent COD, 4-CP and toxicity levels increased with further increases in the feed 4-CP concentrations above 925 mg l(-1) because of inhibitory concentrations of 4-CP in the reactor. Biomass concentration in the aeration tank decreased and the sludge volume index (SVI) increased with feed 4-CP concentrations above 925 mg l(-1) resulting in lower COD and 4-CP removal rates. The rates of COD and 4-CP removals indicated substrate (4-CP) inhibition for the feed 4-CP concentrations above 925 mg l(-1) corresponding to the reactor 4-CP of above 200 mg l(-1). The system should be operated at the feed 4-CP concentrations of less than 900 mg l(-1) (4-CP(R) < 200 mg l(-1)) in order to obtain high rates and extents of COD, 4-CP and toxicity removals at a sludge age of 20 days and HRT of 25 h.     

Biodegradation of total organic carbons (TOC) in Jordanian petroleum sludge

Biodegradation is cost-effective, environmentally friendly treatment for oily contaminated sites by the use of microorganisms. In this study, laboratory experiments were conducted to establish the performance of bacterial isolates in degradation of organic compounds contained in oily sludge from the Jordanian Oil Refinery plant. As a result of the laboratory screening, three natural bacterial consortia capable of degrading total organic carbons (TOC) were prepared from isolates enriched from the oil sludge. Experiments were conducted in Erlenmeyer flasks under aerobic conditions, with TOC removal percentage varied from 0.3 to 28% depending on consortia type and concentration. Consortia 7B and 13B exhibited the highest TOC removal percentage of 28 and 22%, respectively, before nutrient addition. TOC removal rate was enhanced after addition of nutrients to incubated flasks. The highest TOC reduction (43%) was estimated after addition of combination of nitrogen, phosphorus and sulphur to consortia 7B.

A significant variation (P < 0.005) was obser0ved between the effect of consortia type and concentration on TOC% reduction. No significant variation was observed between incubation at 10 and 18 days in TOC% reduction. This is the first report concerning biological treatment of TOC by bacteria isolated from the oil refinery plants, where it lays the ground for full integrated studies recommended for the degradation of organic compounds that assist in solving sludge problems.     

Effect of operating parameters on color and COD removal performance of SBR: sludge age and initial dyestuff concentration

Effect of sludge and initial dyestuff concentration on color and COD removal performance of anaerobic-aerobic sequential batch reactor was investigated. Remazol Red RR a vinylsulphonyl (VS) and monochlortriazine (MCT), reactive azo dye was used in the study. Sludge age was varied between thetaC=12 days and thetaC=30 days and dyestuff concentration was between D0=50 and D0=500 mg l(-1). The maximum color and COD removal was obtained as 95% and 70% for D0=60 mg l(-1) and COD0=800 mg l(-1) at 15 days sludge retention time, respectively, and no further improvement was observed when sludge age was increased to 30 days. The main color removal phase in this operation system was the anaerobic phase. Because, the color removal efficiency was already above 95% under anaerobic condition and therefore, the contribution of aerobic phase to color removal was negligible. Increasing dyestuff concentration did not significantly affect the decolorization. It was possible to obtain over 90% dyestuff removal even at D0=500 mg l(-1). SBR system reduces 1000 mg l(-1) initial COD concentrations to about 400 mg l(-1) for dyestuff concentration up to 150 mg l(-1). COD removal efficiency decreased from 70% to 60% by increasing initial dyestuff concentration from 100 to 500 mg l(-1). The results indicated that dyestuff and COD are mainly used by anaerobic organisms and aeration does not improve the performance of SBR system.     

An investigation of heavy metal biosorption in relation to C/N ratio of activated sludge

The effect of C/N ratio of activated sludge on heavy metal biosorption was investigated. Three sets of semi-continuous reactors with different feed C/N ratios (9, 21 and 43 mg COD/mg TKN) were set up. Sorption equilibrium tests have indicated that the biosorptive capacity of activated sludge was highly dependent on metal species and the C/N ratio. The increase in C/N ratio resulted in an increase in the Cd(II) sorption capacity of activated sludge whereas it decreased the Cu(II) sorption capacity. As for Zn(II), a different behavior was observed such that, the highest and lowest capacities have occurred at C/N ratio of 21 and 43, respectively. For Ni(II) biosorption, isotherm tests produced greatly scattered data; so, it was not possible to obtain any plausible result to indicate the relationship between maximum adsorptive capacity and C/N ratio. The accompanying release of Ca(II) and Mg(II) ions and also carbohydrates into the solution during biosorption have indicated that ion exchange mechanism was involved however, was not the only mechanism during the sorption process.     

Adsorption of nickel(II) from aqueous solution onto activated carbon prepared from almond husk

Activated carbon was prepared from almond husk by activating without (MAC-I) and with (MAC-II) H(2)SO(4) at different temperatures. The ability of the activated carbon to remove nickel(II) ions from aqueous solutions by adsorption has been investigated under several conditions such as pH, carbonisation temperature of husk, initial concentration of metal ions, contact time, and adsorbent concentration. Optimal conditions were pH 5.0, the carbonisation temperature of 700 degrees C, 50 min of contact time and adsorbent concentration of 5 g/l. The results indicate that the effective uptake of Ni(II) ions was obtained by activating the carbon, prepared from almond husk at 700 degrees C, through the addition of H(2)SO(4). The removal of Ni(II) were found to be 97.8% at initial concentration of 25mg/l and the adsorbent concentration of 5 g/l. When the adsorbent concentration was increased up to 40 g/l, the adsorption density decreased from 4.89 to 0.616 mg/g for MAC-II. In the isotherm studies, the experimental adsorption data fitted reasonably well the Langmuir isotherm for both MAC-I and MAC-II.     

Landfill leachate treatment using powdered activated carbon augmented sequencing batch reactor (SBR) process: optimization by response surface methodology

In this study, landfill leachate was treated by using the sequencing batch reactor (SBR) process. Two types of the SBR, namely non-powdered activated carbon and powdered activated carbon (PAC-SBR) were used. The influence of aeration rate and contact time on SBR and PAC-SBR performances was investigated. Removal efficiencies of chemical oxygen demand (COD), colour, ammoniacal nitrogen (NH(3)-N), total dissolved salts (TDS), and sludge volume index (SVI) were monitored throughout the experiments. Response surface methodology (RSM) was applied for experimental design, analysis and optimization. Based on the results, the PAC-SBR displayed superior performance in term of removal efficiencies when compared to SBR. At the optimum conditions of aeration rate of 1L/min and contact time of 5.5h the PAC-SBR achieved 64.1%, 71.2%, 81.4%, and 1.33% removal of COD, colour, NH(3)-N, and TDS, respectively. The SVI value of PAC-SBR was 122.2 mL/g at optimum conditions.     

Removal of heavy metal ions by iron oxide coated sewage sludge

The municipal sewage sludge was modified with iron oxide employed in metal ions removal. The surface modification method was proposed and the effect of parameters in the preparation was studied. The iron oxide coated sludge had higher surface area, pore volume and iron content, compared to uncoated sludge. The suitable conditions for removal of Cu(II), Cd(II), Ni(II) and Pb(II) ions from solutions were investigated using batch method. The suitable pH value in the extraction was 7 for adsorption of Cd(II) and Ni(II), 6 for Cu(II) and 5 for Pb(II) ions. The presence of NaNO(3), Ca(NO(3))(2) and Na(2)SO(4) in metal solution in the concentration of 0.01 M and 0.50 M could reduce the removal efficiency. The adsorption isotherms for the adsorption of the metal ions were defined by Langmuir relation. The maximum adsorption capacity of the iron oxide coated sludge for Cu(II), Cd(II), Ni(II) and Pb(II) was 17.3, 14.7, 7.8 and 42.4 mg g(-1), respectively. The adsorption kinetics for every metal ions followed pseudo-second order model. The metal removal from wastewater by iron oxide coated sludge was also demonstrated.     

Optimization of polyhydroxybutyrate (PHB) production by excess activated sludge and microbial community analysis

In this study, a high value-added and biodegradable thermoplastic, polyhydroxybutyrate (PHB), was produced by excess activated sludge. The effects of the nutritional condition, aeration mode, sodium acetate concentration and initial pH value on PHB accumulation in the activated sludge were investigated. The maximum PHB content and PHB yield of 67.0% (dry cell weight) and 0.740gCODgCOD(-1) (COD: chemical oxygen demand), respectively, were attained by the sludge in the presence of 6.0gL(-1) sodium acetate, with an initial pH value of 7.0 and intermittent aeration. The analysis of the polymerase chain reaction (PCR)-denaturing gradient-gel-electrophoresis (DGGE) sequencing indicated that the microbial community of the sludge was significantly different during the process of PHB accumulation. Three PHB-accumulating microorganisms, which were affiliated with the Thauera, Dechloromonas and Competibacter lineages, were found in the excess activated sludge under different operating conditions for PHB accumulation.