Performance evaluation of an anoxic/oxic activated sludge system: effects of mean cell residence time and anoxic hydraulic retention time

A laboratory investigation has been undertaken to asses the effects of two operating parameters, mean cell residence time (MCRT) and anoxic hydraulic retention time (HRT), on the performance of an anoxic/oxic activated sludge system. The performance of the system was evaluated in terms of its COD, nitrogen, and biomass characteristics. An activated sludge system is capable of producing a better effluent, in terms of COD and nitrogen characteristics, when it is operated in an anoxic/oxic fashion. A longer MCRT and an adequate anoxic HRT are desirable in the operation of an anoxic/oxic activated sludge system. For the wastewater used in this investigation, the anoxic/oxic unit was capable of producing an effluent with the following characteristics when it was operated at MCRT = 20 days, total system HRT = 10 h, and anoxic HRT = 3-5 h: COD = 15 mg/L; VSS = 10 mg/L; TKN = 1.30 mg/L; NH(3) - N = 0.60 mg/L; and NO(2) + NO(3) - N = 5.0 mg/L. A uniform distribution of biomass is achievable in an anoxic/oxic activated sludge system because of the intensive recirculation/convection maintained. The provision of an anoxic zone in the aeration tank promotes a rapid adsorption of feed COD into the biomass without an immediate utilization for cell synthesis. This, in turn, results in a high microbial activity and a lower observed biomass yield in the system. A tertiary treatment efficiency is achievable in an anoxic/oxic activated sludge system with only secondary treatment operations and costs. A conventional activated sludge system can be easily upgraded by converting to the anoxic/oxic operation with minor process modifications.     

Kinetic modeling of aerobic biodegradation of high oil and grease rendering wastewater

Batch scale activated sludge kinetic studies were undertaken for the treatment of pet food wastewater characterized by oil and grease concentrations of up to 21,500 mg/L, COD and BOD concentrations of 75,000 and 60,000 mg/L, respectively as well as effluent from the batch dissolved air flotation (DAF) system. The conducted kinetics studies showed that Haldane Model fit the substrates and biomass data better than Monod model in DAF-pretreated wastewater, while the modified hydrolysis Monod model better fit the raw wastewater kinetic data. For the DAF pretreated batches, Haldane Model kinetic coefficients k, K(S), Y and Ki values of 1.28-5.35 g COD/g VSS-d, 17,833-23,477 mg/L, 0.13-0.41 mg VSS/mg COD and 48,168 mg/L, respectively were obtained reflecting the slow biodegradation rate. Modified hydrolysis Monod model kinetic constants for the raw wastewater i.e., k, K(S), Y, and K(H) varied from 1-1.3 g COD/g VSS-d, 5580-5600 mg COD/l, 0.08-0.85 mg VSS/mg COD, and 0.21-0.66 d(-1), respectively.     

Excess sludge reduction induced by Tubifex tubifex in a recycled sludge reactor

Sludge reduction in a conventional activated sludge (CAS) process combined with a recycled sludge reactor where Tubifex tubifex (one of Oligochaeta) was inoculated was investigated in this study. The results showed sludge production could be reduced through T. tubifex's predation on sludge in the recycled sludge reactor. The sludge reduction rate of T. tubifex (R) was from 0.18 to 0.81 mg-VSS mg-Tubifex(-1) d(-1). The sludge reduction capacity of the recycled sludge reactor E was from 650 to 1080 mg-VSS L(-1) d(-1). The optimum density of T. tubifex was 2500 mg L(-1) and the optimum sludge recycled ratio was 1. The existence of T. tubifex did not affect COD and NH(4)(+)-N removals in the process, but led to a slight decrease in TP removal. SVI almost did not change when the T. tubifex density was lower than 3300 mg L(-1). The LC50 values on T. tubifex of copper and ammonia were 2.5 and 880 mg L(-1), respectively, both of which were higher than those on Aeolosoma hemprichi.     

The effect of Ni(II) on properties of bulking activated sludge and microbial analysis of sludge using 16S rDNA gene

This study investigated the effect of nickel on properties and microbial community of bulking activated sludge when 60-240 mg/L Ni(II) was dosed continuously in a sequencing batch reactor (SBR) over 350 days. Results showed that 120 mg/L nickel did not significantly inhibited removal of organic pollutant by activated sludge. However, the system was completely upset when 240 mg/L Ni(II) was dosed. Improvement of settling and dewatering ability was also observed with the addition of Ni(II). In addition, investigations by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) of 16S rDNA of bacteria strain demonstrated that Ni(II) significantly affected microbial community of bulking activated sludge, judging from the elimination of original species and emergence of possible new nickel-resistant bacteria. The effect of nickel on shift of microbial community was an important cause resulted in the improvement of sludge properties in this bulking activated sludge system.     

Treatment of oilfield wastewater containing polymer by the batch activated sludge reactor combined with a zerovalent iron/EDTA/air system

Laboratory-scale experiments were conducted in order to evaluate the performance of a novel treatment process for oilfield wastewater based on combining chemical oxidation, performed by a zerovalent iron (ZVI), ethylenediamine tetraacetic acid (EDTA) and air process, with biological degradation, carried out in a batch activated sludge reactor. The influence of some operating variables was studied. The results showed that the optimum pretreatment conditions were 150 mg/L EDTA, 20 g/L ZVI, and a 180-min reaction time, respectively. Under these conditions, removal efficiencies for hydrolyzed polyacrylamide (HPAM), total petroleum hydrocarbons (TPH), and chemical oxygen demand (COD) were 66%, 59%, and 45%, respectively. During the subsequent 40 h of bioremediation, the concentrations of HPAM, TPH, and COD were decreased to 10, 2 and 85 mg/L, respectively. At the end of experiments, the total removal efficiencies of HPAM, TPH, and COD were 96%, 97% and 92%, respectively.     

Decolorization of 1-amino-4-bromoanthraquinone-2-sulfonic acid in bioaugmented membrane bioreactor

Decolorization of 1-amino-4-bromoanthraquinone-2-sulfonic acid (ABAS) in a Sphingomonas xenophaga-augmented membrane bioreactor was investigated. The results showed that sequencing bioaugmented membrane bioreactor (SMBR) could run stably for 60 days. During the process, over 99% ABAS (570 mg/L) was decolorized and 60% COD was removed. Moreover, the yellow intermediate produced in continuous operation mode was not detected in SMBR. It was probably a dimer resulting from the autoxidation of 2-amino-3-hydroxy-5-bromobenzenesulfonic acid. Ribosomal intergenic sequence analysis (RISA) of the sludge in SMBR suggested that bioaugmentation resulted in large decrease or increase of certain population and Strain QYY can persist in SMBR. The biomass of membrane surface in SMBR could be further divided into a cake layer and a dense layer. The former is mainly composed of coccus, bacillus and filamentous bacteria, which is different from suspended sludge flocs with predominant bacillus.     

Characteristics of the bioreactor landfill system using an anaerobic-aerobic process for nitrogen removal

A sequential upflow anaerobic sludge blanket (UASB) and air-lift loop sludge blanket (ALSB) treatment was introduced into leachate recirculation to remove organic matter and ammonia from leachate in a lab-scale bioreactor landfill. The results showed that the sequential anaerobic-aerobic process might remove above 90% of COD and near to 100% of NH4+ -N from leachate under the optimum organic loading rate (OLR). The total COD removal efficiency was over 98% as the OLR increased to 6.8-7.7 g/l d, but the effluent COD concentration increased to 2.9-4.8 g/l in the UASB reactor, which inhibited the activity of nitrifying bacteria in the subsequent ALSB reactor. The NO3- -N concentration in recycled leachate reached 270 mg/l after treatment by the sequential anaerobic-aerobic process, but the landfill reactor could efficiently denitrify the nitrate. After 56 days operation, the leachate TN and NH4+ -N concentrations decreased to less than 200 mg/l in the bioreactor landfill system. The COD concentration was about 200 mg/l with less than 8 mg/l BOD in recycled leachate at the late stage. In addition, it was found that nitrate in recycled leachate had a negative effect on waste decomposition.     

Bioaugmented sulfur-oxidizing denitrification system with <Emphasis Type="Italic">Alcaligenes defragrans</Emphasis> B21 for high nitrate containing wastewater treatment

The performance of enriched sludge augmented with the B21 strain of Alcaligenes defragrans was compared with that of enriched sludge, as well as with pure Alcaligenes defragrans B21, in the context of a sulfur-oxidizing denitrification (SOD) process. In synthetic wastewater treatment containing 100–1,000 mg NO₃⁻-N/L, the single strain-seeded system exhibited superior performance, featuring higher efficiency and a shorter startup period, provided nitrate loading rate was less than 0.2 kg NO₃⁻-N/m³ per day. At nitrate loading rate of more than 0.5 kg NO₃⁻-N/m³ per day, the bioaugmented sludge system showed higher resistance to shock loading than two other systems. However, no advantage of the bioaugmented system over the enriched sludge system without B21 strain was observed in overall efficiency of denitrification. Both the bioaugmented sludge and enriched sludge systems obtained stable denitrification performance of more than 80% at nitrate loading rate of up to 2 kg NO₃⁻-N/m³ per day.     

Treatment of tomato processing wastewater by an upflow anaerobic sludge blanket-anoxic-aerobic system

The main objective of this study is to assess the achievability of stringent discharge criteria i.e. BOD(5)<15 mg/L, TSS<15 mg/L and NH(4)-N<1mg/L during the treatment of tomato processing wastewater with COD of 2800-15,500 mg/L, BOD(5) of 1750-7950 mg/L, TKN of 48-340 mg/L and NH(4)-N of 21-235 mg/L. Two treatment systems, a UASB-aerobic system and a UASB-anoxic-aerobic system were tested. Furthermore due to alkalinity deficiency, in the raw wastewater, the study explored varying UASB effluent recirculation flowrates to the UASB influent to reduce additional alkalinity requirements. The UASB-anoxic-aerobic system was effective in treating tomato canning wastewater at an overall HRT of 1.75 days while achieving 98.5% BOD(5), 95.6% COD, 84% TSS and 99.5% NH(4)-N removal producing effluent BOD(5), COD, TSS, NH(4)-N, TKN, NO(2)-N, NO(3)-N and PO(4)-P of 10, 70, 15, 0.5, 3, 0, 60 and 4 mg/L, respectively. The biogas yield was 0.43 m(3)/kg COD removed.     

Effect of nitrogen limitation on enrichment of activated sludge for PHA production

Polyhydroxyalkanoates (PHA) are good candidates to plastics because of their material properties similar to conventional plastics and complete biodegradability. The use of activated sludge can be a cheaper alternative to pure cultures for PHA production. In this study, effect of nitrogen limitation during acclimatization period of biomass on production of polyhydroxyalkanoate was investigated. Activated sludge was selected in two sequencing batch reactors operated with and without nitrogen limitation. Batch tests were performed to examine polymer productions of activated sludges acclimatized to different nitrogen regimes. Responses of biomass to different organic loading rates, organic acids, and carbon to nitrogen (C/N) ratios were studied by determining specific polymer storage rate, polymer storage yield, and sludge polymer content of biomasses. Results obtained from batch experiments showed that concentrations of polymer accumulated by two different sludges increased directly with initial substrate concentration. Observed highest polymer yields for the biomasses enriched with and without nitrogen deficiency were 0.69 g COD PHA g(-1) COD S and 0.51 g COD PHA g(-1) COD S, and corresponding polymer contents of biomasses were 43.3% (g COD PHA g(-1) COD X) and 38.3% (g COD PHA g(-1) COD X), respectively. Polymer yields for both biomasses decreased with substrate shift however, biomass enriched with nitrogen deficiency adapted well to acetate-propionate mixture. The results presented in this study showed that polymer storage ability of biomass was improved more under dynamic conditions with nitrogen deficiency when compared to that without nitrogen deficiency. Limiting ammonia availability during batch experiments also caused higher polymer production by suppressing growth, as well as during enrichment of biomass.     

Role of phosphorus in activated sludge

Monod's kinetic model was used to correlate the specific growth rate of mixed activated sludge with the limiting substrate of phosphorus for both batch and continuous-flow culture systems. In the batch reactor system, the specific growth rate varied from 0.092 to 0.617 h(-1) and the saturation constant changed from 25.5 to 117.5 when the COD: P ratio was controlled within the range of 10 to 788 and at the temperature 25+/- 0.5 degrees C. An inverse relationship between specific growth rate and cell yield was found. the maximum specific growth rate and the saturation constant obtained from this study were equal to 0.64 h(-1) and 0.378mg/L, respectively. In the completely mixed continuous-flow culture system, it was found that the substrate utilization, biological solids production, and sludge composition were markedly affected by the source of phosphorus available in the wastewater. The phosphorus-limited activated sludge is normally high in carbohydrate content and low in protein content. Also, sludge organisms growth under the severely restricted phosphorus condition usually possess a large capsule. These capsulated carbohydrate-like substances can be converted to cellular protein if the source of phosphorus is added. The values of cell yield in the continuous-flow activated sludge system are predictable by the use of kinetic constants that are generated from batch culture studies.     

Simultaneous sludge reduction and nutrient removal (SSRNR) with interaction between Tubificidae and microorganisms: a full-scale study

A symbiotic ecosystem between Tubificidae and microorganisms was established at a full-scale wastewater treatment plant (WWTP). In this ecosystem Tubificidae were inoculated, and then adhered to the outer layers of carrier materials in an oxidation tank. During the long-term treatment of sewage volumes of 20,000 m(3)d(-1), the excess sludge production rate was reduced from 0.21 to 0.051 kg m(-3) and sludge settleability was significantly improved. When the influent concentrations of COD, NH(4)(+)-N, PO(4)(-)-P, and SS were in the ranges of 130.0-459.0 mg L(-1), 14.2-27.5 mg L(-1), 1.6-7.0 mg L(-1), and 60.0-466.0 mg L(-1), respectively, the COD and SS removal efficiency was increased by 8.7% and 13.6% within the symbiotic system compared to the control without Tubificidae. In addition, NH(4)(+)-N and phosphorus removal efficiency can also be improved. The results showed that both sludge reduction and nutrient removal were enhanced simultaneously significantly within the system utilizing the symbiotic interactions of Tubificidae and microorganisms.     

Monitoring the impact of bioaugmentation on the start up of biological phosphorus removal in a laboratory scale activated sludge ecosystem

The acclimatisation of activated sludge to enhanced biological phosphorus removal (EBPR) conditions requires a period of about 40–100 days but its output remains hazardous. The impact of bioaugmentation on the start-up of a laboratory scale EBPR sequencing batch reactor was evaluated by process parameters measurement and microbial community dynamics monitoring using 16S rDNA targeted polymerase chain reaction-single strand conformation polymorphism electrophoresis (PCR-SSCP). Bioaugmentation: (1) speeded up the installation of good and stable EBPR in the bioaugmented reactor by about 15 days; (2) correlated with the transient enrichment of the sludge in the added microbial populations; and (3) favoured the long-term enrichment of the sludge in the phosphorus-accumulating organism (PAO) Candidatus Accumulibacter phosphatis. However, despite a lag time period, the control non-bioaugmented reactor ended up with comparable reactor parameters and microbial community evolution, suggesting that the same PAO populations were already present from the beginning in the original non-P-accumulating seed sludge. The potential of a true installation of the added microbial populations within the bioaugmented reactor compared to their substitution by indigenous similar populations is discussed. Competition between PAOs and the antagonistic glycogen accumulating organism Candidatus Competibacter phosphatis is also highlighted during EBPR start-up.     

Bioaugmentation as a Tool To Protect the Structure and Function of an Activated-Sludge Microbial Community against a 3-Chloroaniline Shock Load

Bioaugmentation of bioreactors focuses on the removal of xenobiotics, with little attention typically paid to the recovery of disrupted reactor functions such as ammonium-nitrogen removal. Chloroanilines are widely used in industry as a precursor to a variety of products and are occasionally released into wastewater streams. This work evaluated the effects on activated-sludge reactor functions of a 3-chloroaniline (3-CA) pulse and bioaugmentation by inoculation with the 3-CA-degrading strain Comamonas testosteroni I2 gfp. Changes in functions such as nitrification, carbon removal, and sludge compaction were studied in relation to the sludge community structure, in particular the nitrifying populations. Denaturing gradient gel electrophoresis (DGGE), real-time PCR, and fluorescent in situ hybridization (FISH) were used to characterize and enumerate the ammonia-oxidizing microbial community immediately after a 3-CA shock load. Two days after the 3-CA shock, ammonium accumulated, and the nitrification activity did not recover over a 12-day period in the nonbioaugmented reactors. In contrast, nitrification in the bioaugmented reactor started to recover on day 4. The DGGE patterns and the FISH and real-time PCR data showed that the ammonia-oxidizing microbial community of the bioaugmented reactor recovered in structure, activity, and abundance, while the number of ribosomes of the ammonia oxidizers in the nonbioaugmented reactor decreased drastically and the community composition changed and did not recover. The settleability of the activated sludge was negatively influenced by the 3-CA addition, with the sludge volume index increasing by a factor of 2.3. Two days after the 3-CA shock in the nonbioaugmented reactor, chemical oxygen demand (COD) removal efficiency decreased by 36% but recovered fully by day 4. In contrast, in the bioaugmented reactor, no decrease of the COD removal efficiency was observed. This study demonstrates that bioaugmentation of wastewater reactors to accelerate the degradation of toxic chlorinated organics such as 3-CA protected the nitrifying bacterial community, thereby allowing faster recovery from toxic shocks.     

Effect of effluent recycling and shock loading on the biodegradation of complex phenolic mixture in hybrid UASB reactors

This study describes the feasibility of anaerobic treatment of synthetic coal wastewater using four identical 13.5L (effective volume) bench scale hybrid up flow anaerobic sludge blanket (HUASB) reactors (R1, R2, R3 and R4) under mesophilic (27+/-5 degrees C) conditions. Synthetic coal wastewater with an average chemical oxygen demand (COD) of 2240 mg/L and phenolics concentration of 752 mg/L was used as substrate. Effluent recirculation was employed at four different effluent to feed recirculation ratios (R/F) of 0.5, 1.0, 1.5 and 2.0 for 100 days to study the effect of recirculation on the performance of the reactors. Phenolics and COD removal was found to improve with increase in effluent recirculation. An effluent to feed recycle ratio of 1.0 resulted in maximum removal of phenolics and COD. Phenolics and COD removal improved from 88% and 92% to 95% each, respectively. The concentration of volatile fatty acids in the effluent was lower than the influent when effluent to feed recirculation was employed. Effect of shock loading on the reactors revealed that phenolics shock load up to 2.5 times increase in the normal input phenolics concentration in the form of continuous shock load for 4days did not affect the reactors performance irreversibly.     

Methane emission potential and increased efficiency of a phytoremediation system bioaugmented with Bacillus firmus XJSL 1-10

Horizontal subsurface flow constructed wetland mesocosms (HSSCW) designed to treat municipal waste water were bioaugmented with Bacillus firmus XJSL 1-10. The efficiencies of the three HSSCW mesocosms (non-vegetated HSSCW, Schoenoplectus validus HSSCW and Bambusa vulgaris HSSCW) were assessed. Bioaugmentation not only enhanced the efficiency of the phytoremediation system but also reduced methane emission from an average of 51.3 mg/m2/d to 21.6 mg/m2/d in Schoenoplectus validus HSSCW and from an average of 1708 mg/m2/d to 1473 mg/m2/d in Bambusa vulgaris HSSCW. Each of the three types of bioaugmented HSSCWs showed higher purification efficiency with respect to the removal of BOD and NH4-N than the non-bioaugmented HSSCWs. The performance enhancement was most significant in bioaugmented Schoenoplectus validus HSSCW mesocosm with 48.8 and 44.8% lower BOD, and NH4-N, respectively than the non-bioaugmented HSSCW.     

Bioaugmentation as a tool to protect the structure and function of an activated-sludge microbial community against a 3-chloroaniline shock load

Bioaugmentation of bioreactors focuses on the removal of xenobiotics, with little attention typically paid to the recovery of disrupted reactor functions such as ammonium-nitrogen removal. Chloroanilines are widely used in industry as a precursor to a variety of products and are occasionally released into wastewater streams. This work evaluated the effects on activated-sludge reactor functions of a 3-chloroaniline (3-CA) pulse and bioaugmentation by inoculation with the 3-CA-degrading strain Comamonas testosteroni I2 gfp. Changes in functions such as nitrification, carbon removal, and sludge compaction were studied in relation to the sludge community structure, in particular the nitrifying populations. Denaturing gradient gel electrophoresis (DGGE), real-time PCR, and fluorescent in situ hybridization (FISH) were used to characterize and enumerate the ammonia-oxidizing microbial community immediately after a 3-CA shock load. Two days after the 3-CA shock, ammonium accumulated, and the nitrification activity did not recover over a 12-day period in the nonbioaugmented reactors. In contrast, nitrification in the bioaugmented reactor started to recover on day 4. The DGGE patterns and the FISH and real-time PCR data showed that the ammonia-oxidizing microbial community of the bioaugmented reactor recovered in structure, activity, and abundance, while the number of ribosomes of the ammonia oxidizers in the nonbioaugmented reactor decreased drastically and the community composition changed and did not recover. The settleability of the activated sludge was negatively influenced by the 3-CA addition, with the sludge volume index increasing by a factor of 2.3. Two days after the 3-CA shock in the nonbioaugmented reactor, chemical oxygen demand (COD) removal efficiency decreased by 36% but recovered fully by day 4. In contrast, in the bioaugmented reactor, no decrease of the COD removal efficiency was observed. This study demonstrates that bioaugmentation of wastewater reactors to accelerate the degradation of toxic chlorinated organics such as 3-CA protected the nitrifying bacterial community, thereby allowing faster recovery from toxic shocks.     

Treatment of saline municipal wastewater using hybrid growth system

Background

In this study, a hybrid treatment system (Fluidized Bed positioned in a biological reactor of an Activated Sludge process) was used to treat saline domestic wastewater. The performance of the mentioned hybrid system was compared with the conventional activated sludge. A pilot study was conducted, and Chemical Oxygen Demand (COD), Electrical Conductivity (EC), Total Dissolved Solids (TDS) and pH were measured to investigate treatment efficiency. Three saline wastewater samples with salt concentrations of 0.5, 1, and 1.5 % and detention times of 2, 4 and 6 h were loaded into both rectors of hybrid system and activated sludge.

Results

The results showed that Chemical Oxygen Demand (COD) removals at salt concentrations of 0.5, 1, 1.5 % were equal to 80, 71, 48.5 for the hybrid system and 62, 47.7, 26.5 for the activated sludge system respectively. Likewise, similar results obtained for other contamination indices indicating the superiority of the hybrid system in comparison to activated sludge system. Moreover, another advantage of the hybrid system was that the activated sludge needed sludge returning while sludge returning was not required in the hybrid system. In addition, by loading fixed rate of air into both systems, dissolved oxygen concentration in the hybrid reactor is higher than the conventional reactor.

Conclusions

Therefore, the hybrid system had a significantly higher efficiency than conventional reactor to treat saline domestic wastewater.

     

微生物烟气脱硫中硫酸盐还原阶段的限制性因素及其影响

【目的】利用硫酸盐还原菌(SRB)厌氧活性污泥进行烟气脱硫,探索硫酸盐生物还原的最适条件及重金属离子对硫酸盐生物还原的影响,以提高硫酸盐还原阶段的效率。【方法】对取自污水处理厂的SRB厌氧活性污泥进行高浓度硫酸盐胁迫驯化。分析生物脱硫过程中SRB厌氧污泥还原硫酸盐的限制性因素及影响。【结果】在最适生长条件下(pH 6.5,32°C),经驯化获得的SRB厌氧活性污泥有较强的硫酸盐还原能力。Fe2+的适量添加对硫酸盐还原有一定促进作用。SRB厌氧污泥还原硫酸盐的ThCOD/SO42-最适值为3.00,ThCOD=3.33为最适理论化学需氧量,硫酸盐还原率可达72.15%。SRB厌氧污泥还原硫酸盐反应体系中抑制SRB活性的硫化物浓度为300 mg/L。Pb2+和Ni2+在较低的浓度下(1.0 mg/L和2.0 mg/L)对硫酸盐的还原产生较强的抑制作用,而Cu2+在稍高的浓度下(8.0 mg/L)显示出明显的抑制作用。【结论】经驯化,SRB厌氧活性污泥显示出较强的硫酸盐还原能力,具有应用于工业烟气生物脱硫的潜力。去除重金属离子Pb2+、Ni2+和Cu2+可有效解除对硫酸盐生物还原作用的抑制。     

Preliminary studies on continuous chromium(VI) biological removal from wastewater by anaerobic-aerobic activated sludge process

The long-term continuous chromium(VI) removal from synthetic wastewater affected by influent hexavalent chromium (Cr(VI)) and glucose concentrations were studied with an anaerobic-aerobic activated sludge process. It was observed that before activated sludge was acclimated, the chromium in the effluent increased immediately as the influent chromium increased. However, both Cr(VI) and total chromium (TCr) in the effluent significantly decreased after acclimation. In the acclimated activated sludge, the chromium removal efficiency was 100% Cr(VI) and 98.56% TCr at influent Cr(VI) levels of 20 mg/day, 100% Cr(VI) and 98.92% TCr at influent Cr(VI) levels of 40 mg/day, and 98.64% Cr(VI) and 97.16% TCr at influent Cr(VI) levels of 60 mg/day. The corresponding effluent Cr(VI) and TCr concentrations were 0 and 0.012 mg/l, 0 and 0.018 mg/l, and 0.034 mg/l and 0.071 mg/l, respectively. When the influent glucose increased from 1125 to 1500 mg/l at influent Cr(VI) dosage of 60 mg/day, the Cr(VI) and TCr removal efficiency with the acclimated activated sludge improved from 98.64% and 97.16% to 100% and 98.48%, respectively, and the chromium concentration in the effluent decreased from 0.034 mg/l of Cr(VI) and 0.071 mg/l of TCr to 0 (Cr(VI)) and 0.038 mg/l (TCr). The effluent COD and turbidity was around 40 mg/l and 0, respectively, after the activated sludge was acclimated. Further studies showed that after the activated sludge was acclimated, its specific dehydrogenases activity (SDA) and protein contents increased. The SDA and protein increased respectively 15% and 10% when influent Cr(VI) increased from 20 to 60 mg/day.