UASB Treatment of Tapioca Starch Wastewater

Feasibility of the upflow anaerobic sludge blanket (UASB) process was investigated for the treatment of tapioca starch industry wastewater. After removal of suspended solids by simple gravity settling, starch wastewater was used as a feed. Start-up of a 21.5-L reactor with diluted feed of approximately 3,000 mg∕L chemical oxygen demand (COD) was accomplished in about 6 weeks using seed sludge from an anaerobic pond treating tapioca starch wastewater. By the end of the start-up period, gas productivity of 4–5 m3/m3r?day was obtained. Undiluted supernatant wastewater with a COD concentration of 12,000–24,000 mg∕L was fed during steady-state reactor operation at an organic loading rate of 10–16 kg COD/m3r?day. The upflow velocity was maintained at 0.5 m∕h with a recirculation ratio of 4:1. COD conversion efficiencies >95% and gas productivity of 5–8 m3/m3r?day were obtained. These results indicated that removal of starch solids from wastewater by simple gravity settling was sufficient to obtain satisfactory performance of the UASB process.     

Simultaneous Nitrogen and Phosphorus Removal from High-Strength Industrial Wastewater Using Aerobic Granular Sludge

Aerobic granular sludge technology was applied to the simultaneous nitrogen and phosphorus removal from livestock wastewater that contains high concentrations of nitrogen and phosphorus (TN: 650?mg/L; TP: 125?mg/L). A lab-scale sequencing batch reactor was operated in an alternating anaerobic/oxic/anoxic denitrification mode. Granular sludge was first formed using synthetic wastewater. When livestock wastewater was diluted with tap water, the shape and settleability of aerobic granular sludge were maintained even though livestock wastewater contained suspended solids. Simultaneous nitrification, denitrification, and phosphate uptake were observed under an aerobic condition. However, when nondiluted livestock wastewater was used, the diameter of granular sludge and the denitrification efficiency under an oxic condition decreased. When the concentrations of nitrogen and phosphorus in wastewater increased, hydraulic retention time (HRT) increased resulting in a decrease in selection pressure for granular sludge. Therefore, the sustainment of granular sludge was difficult in livestock wastewater treatment. However, by applying a new excess sludge discharge method based on Stokes’ law, the shape of granular sludge was maintained in spite of the long HRT (7.5?days). To select large granular sludge particles, excess sludge was discharged from the upper part of settled sludge because small particles localized there after settling. Finally, excellent nitrogen and phosphorus removal was accomplished in practical livestock wastewater treatment. The effluent concentrations of NH4–N, NOx–N, and PO4–P were <0.1, 1.4, and 1.2?mg/L, respectively.     

Pharmaceutical wastewater treatment using an anaerobic/aerobic sequencing batch biofilter

The performance of a sequencing batch biofilter integrating anaerobic/aerobic conditions in one tank to treat a pharmaceutical wastewater effluent was studied. A pilot reactor, packed with a porous volcanic stone (puzzolane) was used in the study. The reactor operated as a sequencing batch biofilter, SBB, with reaction times varying for the anaerobic stage from 8 to 24 h and for the aerobic one from 4 to 12 h. The volume of exchange was from 16 to 88%. The pharmaceutical wastewater contained organic chemicals including phenols and o-nitroaniline, a concentration of organic matter that varied from 28,400 to 72,200 mg/L (as total COD), 280 to 605 mg N-NH4/L. and 430 to 650 mg SST/L. In order to acclimatize the microorganisms to the industrial wastewater, the organic load was increased stepwise from 1 to 7.7 kg COD/m3/d. The adequate time was obtained when the removal efficiency of COD reached 80%, or more. Maximal removal loads, associated to high removal efficiencies (95-97% as COD), varied from 4.6 to 5.7 kg COD/m3/d. Under these conditions color removal was 80% as Pt-Co units. Microtox analysis was performed to the wastewater and to the anaerobic and aerobic stages. It was observed that the aerobic stage was the responsible for wastewater detoxification. Results showed that the anaerobic/aerobic SBB was able to treat efficiently initial concentrations of the raw effluent up to 28,400 mg COD/L.     

Treatment of High-Strength Pharmaceutical Wastewater and Removal of Antibiotics in Anaerobic and Aerobic Biological Treatment Processes

Anaerobic and aerobic treatment of high-strength pharmaceutical wastewater was evaluated in this study. A batch test was performed to study the biodegradability of the wastewater, and the result indicated that a combination anaerobic-aerobic treatment system was effective in removing organic matter from the high-strength pharmaceutical wastewater. Based on the batch test, a pilot-scale system composed of an anaerobic baffled reactor followed by a biofilm airlift suspension reactor was designed. At a stable operational period, effluent chemical oxygen demand (COD) from the anaerobic baffled reactor ranged from 1,432 to 2,397?mg/L at a hydraulic retention time (HRT) of 1.25 day, and 979 to 1,749?mg/L at an HRT of 2.5 day, respectively, when influent COD ranged from 9,736 to 19,862?mg/L. As a result, effluent COD of the biofilm airlift suspension reactor varied between 256 and 355?mg/L at HRTs of from 5.0 to 12.5 h. The antibiotics ampicillin and aureomycin, with influent concentrations of 3.2 and 1.0?mg/L, respectively, could be partially degraded in the anaerobic baffled reactor: ampicillin and aureomycin removal efficiencies were 16.4 and 25.9% with an HRT of 1.25 day, and 42.1 and 31.3% with HRT of 2.5 day, respectively. Although effective in COD removal, the biofilm airlift suspension reactor did not display significant antibiotic removal, and the removal efficiencies of the two antibiotics were less than 10%.     

SBR System for Phosphorus Removal: Linear Model Based Optimization

Using a linear model, an optimization scheme for a sequencing batch reactor (SBR) system for phosphorus removal was investigated. The objective was to minimize energy consumption by reducing the aeration cycle time (tair), while meeting the permit requirement (monthly average PO3?4 of 0.5 mg P∕L). Based on the model prediction and error feedback information, the proposed scheme controlled the SBR system well both in the simulation and the real application by adjusting the tair to meet the effluent PO3?4 constraint. Mismatch between the model prediction and the measured data was compensated for. In the simulation, the average aeration cycle time was calculated to be 2.8 h, while in the real system it was 3.5 h. The actual optimized system provided excellent removal of phosphorus, COD, and ammonia with efficiencies of 93% (7.4 to 0.5 mg P∕L), 90% (420 to 43 mg COD∕L), and 98% (22.1 to 0.4 mg N∕L), respectively. However, the effluent nitrate concentrations were relatively high (10 mg N∕L), due to a slower endogenous nitrate respiration rate.     

Low-Strength Wastewater Treatment with Combined Granular Anaerobic and Suspended Aerobic Cultures in Upflow Sludge Blanket Reactors

Combined cultures were developed from anaerobic granular and suspended aerobic cultures in three upflow sludge blanket reactors aerated at 10?mL air/min 4?h/day (R2), every other day (R3), and 24?h/day (R4). The use of combined cultures was found to be advantageous compared to the anaerobic granules for the treatment of low-strength wastewaters. During municipal wastewater treatment at influent 5-day biochemical oxygen demand (BOD5) concentration of 53–118?mg/L (hydraulic retention time: 0.75?day), combined cultures in R2, R3, and R4 exhibited average BOD5 removal efficiencies of 52, 75, and 76%, respectively. The use of these cultures might be proposed as an alternative for municipal wastewater treatment due to their advantages such as achievement of required discharge standards, prevention of biomass loss/settleability problems unlike activated sludge systems and possible methanogenic activity, as well as high settling characteristics comparable to those of anaerobic granules.     

Combined Anaerobic/Aerobic Secondary Municipal Wastewater Treatment: Pilot-Plant Demonstration of the UASB/Aerobic Solids Contact System

Anaerobic pretreatment followed by aerobic posttreatment of municipal wastewater is being used more frequently. Recent investigations in this field using an anaerobic fluidized bed reactor/aerobic solids contact combination demonstrated the technical feasibility of this process. The investigation presented herein describes the use of a combined upflow anaerobic sludge bed (UASB)/aerobic solids contact system for the treatment of municipal wastewater and attempts to demonstrate the technical feasibility of using the UASB process as both a pretreatment unit and a waste activated sludge digestion system. The results indicate that the UASB reactor has a total chemical oxygen demand removal efficiency of 34%, and a total suspended solids removal efficiency of about 36%. Of the solids removed by the unit, 33% were degraded by the action of microorganisms, and 4.6% accumulated in the reactor. This low solids accumulation rate allowed operating the UASB reactor for three months without sludge wasting. The long solids retention time in this unit is comparable to the one normally used in conventional sludge digestion units, thus allowing the stabilization of the waste activated sludge returned to the UASB reactor. Particle flocculation was very poor in the UASB reactor, and therefore, it required postaeration periods of at least 100?min to proceed successfully in the aerobic unit. Polymer generation, which is necessary for efficient biological flocculation, was practically nonexistent in the anaerobic unit; therefore, it was necessary to maintain dissolved oxygen levels greater than 1.5?mg/L in the aerobic solids contact chamber for polymer generation to proceed at optimum levels. Once these conditions were attained, the quality of the settled solids contact chamber effluent always met the 30?mg BOD/L, 30?mg SS/L secondary effluent guidelines.     

Formation of Aerobic Granules with Domestic Sewage

The use of aerobic granules in wastewater treatment can reduce the land area that is needed for the treatment of sewage. Until now granulation has been mainly studied using artificial wastewater. Studying the possibility of forming aerobic granules on domestic sewage in a sequencing batch reactor was a logical step in the scaling-up process and development of this technology. Therefore, aerobic granulation was studied using presettled sewage as influent. After 20?days of operation at high chemical oxygen demand (COD) loading heterogeneous aerobic granular structures were observed, with a sludge volume index after 10?min settling of 38?mL?g?1 and an average diameter of 1.1?mm. Applying a high COD load was found to be a critical factor for the formation of aerobic granules on this type of influent. Therefore short cycle times and concentrated wastewater are preferred to form granules in a sequencing batch reactor when low strength wastewater is used. The nutrient removal was not optimized in this study.     

Biodegradation of Phenol with Wastewater as a Cosubstrate in Upflow Anaerobic Sludge Blanket

Anaerobic degradation of phenol mixed with a readily degradable synthetic wastewater (DSWW) as a cosubstrate was studied in a 12?L upflow anaerobic sludge blanket reactor at 30±2°C over a period of 632?days. DSWW was prepared by diluting sugar cane based molasses. The biomass was acclimatized to high phenol concentration by gradually decreasing the DSWW chemical oxygen demand (COD) of 4,000?mg/L. Feed made up of phenol COD and DSWW COD in the ratio of 7:3 (phenol concentration = 1,176?mg/L) was successfully treated at a hydraulic retention time (HRT) of 12?h and organic loading rate (OLR) of 8?g?COD/L?day. Phenol removal ranged from 99.9 to 84% at phenol COD varying from 10 to 70% in the feed. During the entire operation, COD removal varied from about 74 to 91.3%. The influent COD was distributed into CH4–COD ( ～ 72%), effluent COD ( ～ 17%), and sludge and unaccounted COD ( ～ 11%). The process failure occurred at 4:1 phenol COD: DSWW COD. Specific methanogenic activity of granular sludge exhibited uniform activity up to phenol COD of 70%. The performance of the reactor could not be maintained beyond 70% phenol COD even by reducing the sludge loading rate, increasing HRT, or decreasing OLR.     

Biotransformation of Carbon Tetrachloride and Anaerobic Granulation in a Upflow Anaerobic Sludge Blanket Reactor

Carbon tetrachloride (CT) in a synthetic wastewater was effectively degraded in a 2?l upflow anaerobic sludge blanket reactor during the granulation process by increasing the chemical oxygen demand (COD) and CT loadings. The effect of operational parameters such as influent CT concentrations, COD, CT loading, food to mass (F/M) ratio, and specific methanogenic activity (SMA) were also detected during granulation. Over 97% of CT was removed at 37°C, at a COD loading rate of 10?g/L?day. Chemical oxygen demand and CT removal efficiencies of 92 and 88% were achieved when the reactor was operating at CT and COD loading rates of 17.5?mg/L?day and 12.5?g/L?day, respectively. This corresponds to an hydraulic retention time of 0.28?day and an F/M ratio of 0.57?g?COD/g?volatile?suspended?solids?(VSS)?day. In 4?weeks, the seed sludge developed the CT degrading capability that was not very sensitive to shocks. The granular sludge cultivated had a maximum diameter of 2.5?mm and SMA of 1.64?g?COD/g?VSS?day. Glucose biodegradation by CT acclimated anaerobic granules was expressed with competitive inhibition. However the competitive inhibition was not significant since the competitive inhibition coefficient (Ki) was as high as 18.72?mg/L. Kinetic coefficients of k (maximum specific substrate utilization rate), Ks (half velocity coefficient), Y (growth yield coefficient), and b (decay coefficient) were determined as 0.6/day, 1.1?mg/L, 0.23?g?VSS/g glucose-COD, and 0.01/day, respectively, based on growth substrate glucose–COD during CT biotransformation. The CT was treated via biodegradation and this contributed to 89% of the total removal. The removal contributions from biomass adsorption, abiotic transformation, and volatilization were negligible. Adsorption and volatilization accounted for only 0.8 and 0.5% of the total removal, respectively.     

Simultaneous Removal of Nitrogen and Phosphorous from Municipal Wastewater Using Continuous-Flow Integrated Biological Reactor

A pilot-scale experiment was carried out to study the simultaneous removal of nitrogen and phosphorous from municipal wastewater by an innovative continuous-flow integrated biological reactor (CIBR) process. A three-phase separator was used in the CIBR process, which not only saved energy consumption of sludge returning, but also solved the sludge–gas separating problem. The optimal working condition was 2?h aeration, 1?h agitation, and 1?h settling, with an energy consumption of 0.23?kW?h/m3. The average removal of chemical oxygen demand (COD), ammonia nitrogen (NH4+–N), total nitrogen (TN), and total phosphorus (TP) under the optimal conditions were 72.87, 75.23, 61.25, and 68.25%, respectively. The distributing rules of dissolved oxygen, pH, mixed liquid suspended solid, COD, NH4+–N, NO3?–N, TN, and TP in each phase of CIBR was studied. It was indicated that the appropriate condition was created for the simultaneous removal of nitrogen and phosphorus in the integrated reactor. The study demonstrated the feasibility of using CIBR process for simultaneous removal of nitrogen and phosphorus at the average temperature 12.2°C.     

Using Polyphosphate Buffering to Treat Phosphorus-Deficient Wastewater

The suitability of the anaerobic/aerobic process was investigated for treating phosphorus-deficient wastewaters with highly variable influent chemical oxygen demand (COD) loading patterns to produce consistently low effluent P levels. During laboratory-scale experiments, two sequencing batch reactors (SBRs), one anaerobic/aerobic (AnA) and the other completely aerobic (CA), received transient influent COD loading patterns that simulated (No. 1) daily COD loading fluctuations and (No. 2) low weekend COD loading, each for a period of approximately 6?months. The AnA SBR produced lower effluent soluble P concentrations than the CA SBR during loading pattern No. 1 (0.5 versus 1.2?mgP/L). During loading pattern No. 2, both SBRs allowed effluent acetate breakthrough, following the low weekend COD loading period, and the P removal in the AnA SBR gradually deteriorated. The AnA process has the potential to produce lower effluent P levels than the CA process during transient loading periods due to the P release and uptake characteristics associated with the polyphosphate-accumulating metabolism. Extended periods of low COD loading can however cause a loss of P removal.     

Effects of Sodium Chloride on the Performance of a Sequencing Batch Reactor

In this study, we investigated the effects of sodium chloride (concentrations ranging from 0?to?60?g/L) on the performance of sequencing batch reactors (SBRs) using a microbial culture developed from a domestic sewage treatment plant. The lab-scale SBRs were fed with synthetic wastewater (acetate as the organic substrate) containing either sodium chloride solution or seawater to ensure consistency in feed composition. It was found that sodium chloride concentrations of up to 10?g/L stimulated substrate removal. The organic removal efficiency decreased from 96%, when no sodium chloride was added, to 86% when 60?g/L of sodium chloride was introduced into the influent wastewater. Effluent turbidity increased significantly when the sodium chloride concentration in the wastewater was equal to or above 30?g/L even though the sludge volume index (SVI) decreased. The increase in effluent turbidity could be caused by the release of nondissolved cellular components due to plasmolysis of microorganisms as observed by scanning electron microscopy. Experiments involving seawater (with 20?g/L total dissolved solids) showed that organic removal efficiency improved from 87 to 95% while effluent turbidity and SVI values were lowered when the loading rate parameter (Li) was lowered from 0.6?to?0.3?mg total chemical oxygen demand (mg?VSS?day). Optical microscopy and scanning electron microscopy indicated morphological changes in the microbial population. From this study, it was concluded that microbial culture from domestic wastewater facilities could be acclimated in a SBR to treat wastewater containing sodium chloride concentrations of up to 60?g/L.     

Improved Anaerobic Degradation of Phenol with Supplemental Glucose

In this study, phenol degradation was investigated, with and without glucose as a cosubstrate, in batch and continuous studies. The two 2-L lab upflow anaerobic sludge blanket reactors were operated at a constant hydraulic retention time of 12 h with a gradual stepwise increase in phenol concentration from 105 to 1,260 mg∕L. Batch studies showed that a 1,000-mg∕L glucose supplement provided the fastest phenol removal and sludge acclimation. The effect of the glucose supplement was assessed based on microbial acclimation and granulation, phenol degradation, and resistance to shock loading. The reactor with the 1,000-mg∕L glucose supplement had a shorter start-up and granulation period (4 months, compared to 7 months for the reactor without glucose supplement), larger granule size (2.76 mm, compared to 1.77 mm), and higher phenol removal efficiency under steady-state operation at 6-kg phenol-COD∕L?day (98% compared to 88%). The reactor with the glucose supplement also exhibited a higher resistance to shock load or temperature change and faster recovery than the reactor without a glucose supplement.     

Short-Term Effects of Wastewater Biodegradability on Biological Phosphorus Removal

A steady-state laboratory-scale sequencing batch reactor process for biological phosphorus removal (BPR) was developed, and the influence of wastewater biodegradability on BPR was studied in batch tests. Biodegradability was expressed in this work as the readily biodegradable fraction of wastewater COD (rbCOD) present in the mixed liquor after the anaerobic stage of the anaerobic/oxic cycle of the BPR process. The rbCOD fraction was changed by varying the organic composition of synthetic wastewater (different carbohydrates were used: saccharose, cellobiose, starch, and cellulose) or varying the anaerobic retention time (1.25, 4, 9, and 24 h) when only one kind of low biodegradable synthetic wastewater (starch composed) was used. A clear positive trend was observed between rbCOD and anaerobic P release, but such a clear relationship was not observed with BOD5 measurements. Soluble carbohydrates allowed a BPR mechanism, but particulate carbohydrates seemed to cause nonbiological P removal. An increase in anaerobic retention time improved rbCOD concentrations up to 50%, approximately, and P removal, but excessive retention times, >9 h, should be used to reach good BPR results.     

SBR System for Phosphorus Removal: ASM2 and Simplified Linear Model

An SBR (sequencing batch reactor) system was evaluated for nutrient removal. The system is capable of removing 95% of influent PO3?4, or from 6.7 to 0.4 mg P∕L, with the addition of acetate of 120–150 mg COD∕L in the feed solution (primary effluent). Nitrification was also achieved within the preset aeration cycle time in reducing the effluent ammonia level from 16.3–19.8 mg N∕L to 0.2–0.3 mg N∕L. However, denitrification was incomplete due to a slower endogenous nitrate respiration rate in the idle period, resulting in an effluent nitrate level of 7–8 mg N∕L. A linear version of the ASM2 (Activated Sludge Model No. 2) was developed to model the performance of an SBR system for nutrient removal. The developed model appropriately predicts the dynamic behavior of the SBR system with respect to phosphate release∕uptake, nitrification, ammonification, and denitrification. Compared with the full ASM2, the calibration of model parameters and model simulation require less computational time for practical implementation of the linear model into a process control system for the SBR.     

Effect of Carbon Source on PCE Dehalogenation

A laboratory study using the upflow anaerobic sludge blanket reactor for treating high-strength wastewater containing tetrachloroethene (PCE) was carried out to study the effect of carbon source, recycle, and shock loading on dehalogenation of PCE and process performance. The PCE was dehalogenated to trichloroethylene, cis-1,2-dichloroethylene, vinyl chloride, and ethylene. During the study on the effect of carbon source, the PCE and COD removal up to 97% and biogas production of 0.518–0.47 m3∕kg CODrem with methane content up to 66% were achieved under steady-state operating conditions. An increase in the influent COD from 2,000 to 4,000 mg∕L did not show any improvement in the PCE removal. Recycling of effluent at 50% showed the decrease in COD removal and increase in the effluent concentration of dichloroethylene and vinyl chlorides. Around 1–3.5% of influent PCE stripping to biogas was observed. It was observed that methanol has the stimulatory effect on the dehalogenation of PCE. A shock loading study showed that the upflow anaerobic sludge blanket reactor could assimilate 1.5–2 times the original PCE concentration (50 mg∕L) without much effect on the process performance.     

Improved Anaerobic Process Efficiency Using Mesophilic and Thermophilic Elutriated Phased Treatment

An innovative anaerobic digestion elutriated phased treatment (ADEPT) has been evaluated at mesophilic (M-ADEPT) (35°C) and thermophilic (T-ADEPT) (55°C) temperatures in which the organic loading rate (OLR) was increased until reactor failure (pH<5.5). Single-stage continuously stirred tank reactors (CSTRs) at both temperatures were also operated as controls (M-CSTR for 35°C and T-CSTR for 55°C). The T-CSTR failed at an OLR of 7.4 g volatile solid (VS)/L?day and the M-CSTR at an OLR of 10 g VS/L?day while the M-ADEPT continued until an OLR of 18 g VS/L?day and the T-ADEPT reached an OLR of 24 g VS/L?day before system failure. The T-CSTR produced the poorest effluent quality as manifested by high propionate concentrations (1,500–2,500 mg/L) while both M-ADEPT and T-ADEPT produced much better quality of effluent with propionate concentrations below 100 mg/L. Thus it appears that the T-ADEPT design may solve effluent quality problems associated with normally high propionate concentrations produced during thermophilic anaerobic digestion. Superior effluent quality, reduced reactor volume requirements, more stable methanogenesis due to the extended solids retention time, and uncoupling of the methanogen wasting from the refractory sludge wasting process resulted in stable and efficient processing at both temperatures for the innovative ADEPT design. Because the higher amounts of volatile fatty acids produced in the acid elutriation phase of the ADEPT system can be a favorable carbon source for biological nutrient removal in wastewater treatment plants, this positive aspect should be considered in future applications of the ADEPT system.     

2,4,6 Tri-Chlorophenol Containing Wastewater Treatment Using a Hybrid-Loop Bioreactor System

A hybrid-loop bioreactor system consisting of a packed column biofilm and an aerated tank bioreactor with an effluent recycle was used for biological treatment of 2,4,6 tri-chlorophenol (TCP) containing synthetic wastewater. The effects of sludge age (solids retention time) on chemical oxygen demand (COD), TCP, and toxicity removal performance of the system were investigated for sludge ages between 5 and 30?days, while the feed COD (2600±100?mg?L?1), TCP (370±10?mg?L?1), and the hydraulic residence time (25?h) were constant. Percent TCP, COD, and toxicity removals increased with increasing sludge age resulting in nearly complete COD, TCP, and toxicity removal at sludge ages above 20?days. Biomass concentrations in the packed column and in the aeration tank increased with increasing sludge age resulting in low reactor TCP concentrations, and therefore, high TCP, COD, and toxicity removals. More than 95% of COD, TCP, and toxicity removal took place in the packed column reactor. Volumetric rates of TCP and COD removal increased due to increasing biomass and decreasing effluent TCP and COD concentrations with increasing sludge age. The specific rate of TCP removal was maximum (120?mg?TCP?gX?1?day?1) at a sludge age of 20?days. TCP inhibition was eliminated by operation of the system at sludge age above 20?days to obtain nearly complete COD, TCP, and toxicity removal.     

Activated Carbon Addition to an Activated Sludge Model Reactor for Color Removal from a Cotton Textile Processing Wastewater

Color removal from cotton textile processing wastewater by addition of powdered activated carbon (PAC) into a lab-scale activated sludge system was examined. The activated sludge system was continuously operated in different sludge ages (SRTs) and hydraulic retention times (HRTs). SRT = 30?d and HRT = 1.6?d operation resulted in up to 36% color removal and 94% COD removal. PAC was added 100, 200, and 400 mg/L into the activated sludge system under these operating conditions. The results indicated that 100 mg/L PAC was sufficient to remove the maximum color measured (up to 50 m?1) from the wastewater. The addition of PAC did not affect chemical oxygen demand (COD) removal significantly. Oxygen uptake rate (OUR) tests were also performed to investigate the microbial activities controlling the system performance. The average OUR was 74.1 mg/L/h without PAC addition while it was 70 mg/L/h with PAC addition. Adsorbable organic halogens of the effluent wastewater decreased from 400 to 50 μg/L with the addition of PAC. Toxicity dilution factor decreased from 2 to 1.5 with the PAC addition into the activated sludge system.