Effluent Chemical Oxygen Demand Research Articles

Influence of organic loading rate on integrated bioreactor treating hypersaline mustard wastewater.

Mustard tuber wastewater is characterized by high salinity and high organic content that is potentially detrimental to the biological treatment system and affects the treatment efficiency accordingly. The experiment used the integrated bioreactor to reduce much of the organics in mustard tuber wastewater, and found the influence of organic loading rate on effluent chemical oxygen demand (COD) and phosphate (PO4 (3-) -P). Results showed that under the condition of 10-15°C, 6mg/L of dissolved oxygen, the reduction value of COD removal rate in anaerobic and aerobic area was 14.5% and 31.7% when the organic loading rate increased from 2.0 to 4.0kg COD/m(3) /day. Therefore, an integrated bioreactor should take 2.0kg COD/m(3) /day organic loading rate in mustard wastewater treatment if the effluent is expected to meet the third level of "Integrated Wastewater Discharge Standard" (GB 8978-1996).

Effect of the mixing ratio during co-treatment of landfill leachate and sewage with a combined stripping and reversed A2/O process

In this study, pilot-scale tests were conducted to evaluate the effect of volumetric mixing ratio of landfill leachate to sewage on the performance of the combined ammonia stripping and reversed anaerobic/anoxic/oxic (A2/O) process for co-treatment of landfill leachate and municipal sewage. Stripping, as pre-treatment, could significantly remove ammonia nitrogen (NH3-N) and total nitrogen (TN) by 55% and 52%, respectively. Moreover, chemical oxygen demand (COD) was slightly reduced by 6.8%, and little total phosphorus (TP) was removed. The subsequent reversed A2/O process appeared to be highly influenced by the volumetric mixing ratio of leachate to sewage. Typically, the effluent COD, NH3-N, TN and TP increased with the increasing ratio from 1:30 to 1:15, namely, the increasing fraction of leachate. Over the all tested mixing ratio range, the effluent COD and NH3-N were satisfied with the primary B standards of Chinese Discharge Standard of Pollutants for municipal waste water treatment plant (GB18918-2002). The standards different from the primary A standards for water reuse are used for discharge into the most surface water bodies in China. However, TN and TP would exceed the primary B standard levels at a mixing ratio of 1:15 or greater. These findings suggest that an appropriate volumetric mixing ratio should be carefully selected to ensure the performance of the reversed A2/O process.

Grey water treatment by the slanted soil system with unsorted soil media

This study evaluated the performance of unsorted soil media in the slanted soil treatment system, in terms of removal efficiency in suspended solids (SS), chemical oxygen demand (COD), linear alkylbenzene sulphonate (LAS) and Escherichia coli, and lifetime until clogging occurs. Unsorted soil performed longer lifetime until clogging than sorted fine soil. Removal of SS, COD, and LAS also performed same or better level in unsorted soil than fine soil. As reaction coefficients of COD and LAS were described as a function of the hydraulic loading rate, we can design a slanted soil system according to the expected hydraulic loading rate and the targeted level of COD or LAS in effluent. Regarding bacteria removal, unsorted soil performed sufficient reduction of E. coli for 5 weeks; however, the removal process occurred throughout all four chambers, while that of fine soil occurred in one to two chambers.

Comparative evaluations of organic matters and nitrogen removal capacities of integrated vertical-flow constructed wetlands: Domestic and nitrified wastewater treatment

Two groups of integrated vertical-flow constructed wetland (IVCW) microcosms were established for treating two types of representative wastewater: domestic and nitrified wastewater under two loading rates (LRs) over about two years. Their removal capacities of organic substance and nitrogen as well as the effects of loading rate (LR), outflow temperature and dissolved oxygen (DO) concentration were investigated and compared. Efficient chemical oxygen demand (COD) eliminations were achieved by the IVCWs, with the mass removal rates increasing linearly with the increasing LRs strongly, achieving average value of 56.07 g m−2 d−1 at the highest loading rate. Nevertheless, the effluent COD concentrations also increased, with the average value exceeding Class I A discharge standard (< 50 mg L−1) for municipal wastewater treatment plants in China at the highest loading rate. Greater total nitrogen (TN) mass removal rates but lower efficiencies were obtained at the high LR for both types of wastewater, and better removal was achieved for nitrified wastewater (NW) in comparison to domestic wastewater (DW), probably due to the prevailing anoxic conditions inside the IVCW beds restricted nitrification process of DW. The influences of LR, temperature and DO on COD removal were slight, but all remarkable on TN reduction. As compared to DO, temperature was more crucial for nitrogen removal, and the temperature dependence coefficient for TN removal of low LR of NW was significantly greater than others.

Treatment of oil-water emulsion from the machinery industry by Fenton's reagent.

An oil-water emulsion from the machinery industry was treated using Fenton's reagent. The objective was to reduce the high chemical oxygen demand (COD) of this waste stream so that it would meet the COD effluent limit of Chinese Standard JS-7740-95. The optimal [H2O2]/[Fe2+] ratio for COD removal was 3. An orthogonal experimental design was developed based on the optimal [H2O2]/[Fe2+] ratio to evaluate the significance of four parameters relevant to the treatment process, namely, H2O2 dosage, initial pH, oxidation time and coagulation pH. The influence of the four parameters on COD removal efficiency decreased as follows: H2O2 dosage>oxidation time>coagulation pH>initial pH. The COD removal efficiency was further investigated based on the most important single-factor parameter, which was H2O2 dosage, as discovered in the orthogonal test. A well-fitted empirical correlation was obtained from the single-factor analysis and up to 98% COD removal was attained using 50 mM H2O2. Using the doses and conditions identified in this study, the treated oil-water emulsion can be discharged according to Chinese Standard JS-7740-95.

Comparative study on response of thiocyanate shock load on continuous and fed batch anaerobic-anoxic-aerobic sequential moving bed reactors

A comparative study on response of a toxic compound thiocyanate (SCN－) was carried out in continuous and fed batch moving bed reactor systems. Both systems had three sequential anaerobic, anoxic and aerobic reactors and operated at same hydraulic retention time. Feed SCNwas first increased from 600 mg/L to 1,000 mg/L for 3 days (shock 1) and then from 600 to 1,200 mg/L for 3 days (shock 2). In anaerobic continuous reactor, increase of effluent COD (chemical oxygen demand) due to shock load was only 2%, whereas in fed batch reactor it was 14%. In anoxic fed batch reactor recovery was partial in terms of SCN-, phenol, COD and NO₃--N and NO₂--N removals and in continuous reactor complete recovery was possible. In both systems, inhibition was more significant on aerobic reactors than anaerobic and anoxic reactors. In aerobic reactors ammonia removal efficiency deteriorated and damage was irreversible. Present study showed that fed batch reactors showed higher substrate removal efficiency than continuous reactors during regular operation, but are more susceptible to toxic feed shock load and in nitrifying reactor damage was irreversible.

Treating low carbon/nitrogen (C/N) wastewater in simultaneous nitrification-endogenous denitrification and phosphorous removal (SNDPR) systems by strengthening anaerobic intracellular carbon storage

A novel simultaneous nitrification denitrification and phosphorous removal-sequencing batch reactor (SNDPR-SBR) enriched with PAOs (phosphorus accumulating organisms), DPAOs (denitrifying PAOs), and GAOs (glycogen accumulating organisms) at the ratio of 2:1:1 was developed to achieve the simultaneous nutrient and carbon removal treating domestic wastewater with low carbon/nitrogen ratio (≤3.5). The SNDPR system was operated for 120 days at extended anaerobic stage (3 h) and short aerobic stage at low oxygen concentration (2.5 h) with short sludge retention time (SRT) of 10.9 d and hydraulic retention time (HRT) of 14.6 h. The results showed that at the stable operating stage, the average effluent chemical oxygen demand (COD) and PO43−–P concentrations were 47.2 and 0.2 mg L−1, respectively, the total nitrogen (TN) removal efficiency was 77.7%, and the SND efficiency reached 49.3%. Extended anaerobic stage strengthened the intracellular carbon (mainly poly-β-hydroxybutyrate, PHB) storage, efficiently utilized the organic substances in wastewater, and provided sufficient carbon sources for denitrification and phosphorus uptake without external carbon addition. Short aerobic stage at low oxygen concentration (dissolved oxygen (DO): 1 ± 0.3 mg L−1) achieved a concurrence of nitrification, endogenous denitrification, denitrifying and aerobic phosphorus uptake, and saved about 65% energy consumption for aeration. Microbial community analysis demonstrated that P removal was mainly performed by aerobic PAOs while N removal was mainly carried out by denitrifying GAOs (DGAOs), even though DPAOs were also participated in both N and P removal.

The performance of fluidized bed solar photo Fenton oxidation in the removal of COD from hospital wastewaters

In this study, fluidized bed solar photo Fenton process was adopted for the treatment of hospital wastewater with an objective of improving the biodegradability and reducing the chemical oxygen demand (COD) of wastewater. The optimal conditions were observed at pH 3, Fe2+ dosage of 5 mM, H2O2 dosage of 50mM and silica carrier amount of 40 g/L. Under such conditions, the maximum COD removal was 98% at a hydraulic retention time of 90 min. The enhancement of biodegradability, evaluated in terms of BOD5/COD ratio increased from 0.16 to 0.7. It was also observed that in fluidized bed solar photo Fenton process, the COD efficiency was 92% whereas in solar photo Fenton process the COD removal efficiency was 67% at 60 min. The effluent COD and total suspended solid concentrations were found to be 30 mg/L, which met the requirements of the discharge standard.

Modeling of effluent quality parameters in a submerged membrane bioreactor with simultaneous upward and downward aeration treating municipal wastewater using hybrid models

This research was an effort to develop hybrid multilayer perceptron and radial basis function artificial neural network–genetic algorithm (MLPANN-GA and RBFANN-GA) models to accurately predict effluent biochemical oxygen demand (BOD), chemical oxygen demand (COD), total nitrogen (TN), and total phosphorus (TP) in a submerged membrane bioreactor. The input variables of the networks were influent BOD, influent COD, influent TN or influent TP, sludge retention time (SRT), mixed liquor suspended solid, membrane permeability, and transmembrane pressure. Training procedures of all effluent quality parameters were successful for both the MLPANN-GA and RBFANN-GA models. The training and testing models showed an almost perfect match between the experimental and predicted values. Based upon the statistical analysis, results indicated that there is a very little difference between predicted and experimental values of the effluent BOD, COD, TN, and TP. The predicted and experimental values of the effluent concentrations gave a very low root mean squared error and a high coefficient of determination very close to one demonstrated high accuracy of these models to predict output variables. It became clear that the models based on the genetic algorithm (GA) were much better than those models without GA from the viewpoint of the achievement of an accurate prediction of the effluent BOD, COD, TN, and TP. The results indicated that the accuracy of all models increased when GA was applied to neural networks. The mean average error for the hybrid models varied from 3 to 8%.

Biological nutrient removal of gallic acid processing wastewater by combined expanded granular sludge bed and bio-contact oxidation under mesophilic conditions

The biological treatment of gallic acid processing wastewater (GAPW) was carried out with laboratory-scale 30-L expanded granular sludge bed (EGSB) and 60-L bio-contact oxidation (BCO) reactors. The temperatures of the EGSB and bio-contact oxidation reactors were maintained under mesophilic conditions of 35 and 32°C, respectively. The effluent chemical oxygen demand (COD), total nitrogen, total phosphorus, gallic acid levels, and pH values of both the EGSB and bio-contact oxidation reactors, and redox potential of the EGSB were monitored. When the influent COD concentration was 3,000 mg L−1 and the organic loading rate (OLR) was 17.5 kg COD (m3 d)−1, the removal efficiency of COD by the EGSB and bio-contact oxidation reactors was 87.021%. The removal efficiencies of nitrogen, phosphorus, and gallic acid were 70.822, 58.116, and 63.407%, respectively. The redox potential in the EGSB varied between −320 and −350 mV. The effluent pH increased either in the EGSB or the bio-contact oxidation reactor. Both reactors were resistant to shock loading. The results of our study provided a theoretical basis for the biological treatment of GAPW.

Hydrolytic acidification via rumen microorganisms and aerobic MBR to reduce contaminants in pulping midcourse wastewater

Experiments on microbial degradation with hydrolytic acidification–aerobic (membrane bioreactor) MBR process were conducted to treat the pulping midcourse wastewater (PMW) with chemical oxygen demand (COD) concentration of 1,182 mg/L, chromaticity of 327 PCU, and TSS concentration of 153 mg/L. Rumen micro-organisms (RM) were used in the hydrolytic acidification process. The experimental results demonstrated that the hydrolytic–aerobic process could raise the biodegradability of the PMW, the VFA concentration could reach 200 mg/L, and the acidification rate was 24%; the effluent COD could reach 96 mg/L, the chromaticity 80 PCU, and the TSS 15 mg/L. These results suggested that hydrolytic acidification via RM and aerobic MBR could be a promising way for effective disposal of puling midcourse wastewater.

Modeling of organic substrate transformation in the high-rate activated sludge process.

This study describes the development of a modified activated sludge model No.1 framework to describe the organic substrate transformation in the high-rate activated sludge (HRAS) process. New process mechanisms for dual soluble substrate utilization, production of extracellular polymeric substances (EPS), absorption of soluble substrate (storage), and adsorption of colloidal substrate were included in the modified model. Data from two HRAS pilot plants were investigated to calibrate and to validate the proposed model for HRAS systems. A subdivision of readily biodegradable soluble substrate into a slow and fast fraction were included to allow accurate description of effluent soluble chemical oxygen demand (COD) in HRAS versus longer solids retention time (SRT) systems. The modified model incorporates production of EPS and storage polymers as part of the aerobic growth transformation process on the soluble substrate and transformation processes for flocculation of colloidal COD to particulate COD. The adsorbed organics are then converted through hydrolysis to the slowly biodegradable soluble fraction. Two soluble substrate models were evaluated during this study, i.e., the dual substrate and the diauxic models. Both models used two state variables for biodegradable soluble substrate (SBf and SBs) and a single biomass population. The A-stage pilot typically removed 63% of the soluble substrate (SB) at an SRT <0.13 d and 79% at SRT of 0.23 d. In comparison, the dual substrate model predicted 58% removal at the lower SRT and 78% at the higher SRT, with the diauxic model predicting 32% and 70% removals, respectively. Overall, the dual substrate model provided better results than the diauxic model and therefore it was adopted during this study. The dual substrate model successfully described the higher effluent soluble COD observed in the HRAS systems due to the partial removal of SBs, which is almost completely removed in higher SRT systems.

Peroxone mineralization of chemical oxygen demand for direct potable water reuse: Kinetics and process control

Mineralization of organics in secondary effluent by the peroxone process was studied at a direct potable water reuse research treatment system serving an occupied four-bedroom, four bath university residence hall apartment. Organic concentrations were measured as chemical oxygen demand (COD) and kinetic runs were monitored at varying O3/H2O2 dosages and ratios. COD degradation could be accurately described as the parallel pseudo-1st order decay of rapidly and slowly-oxidizable fractions, and effluent COD was reduced to below the detection limit (<0.7 mg/L). At dosages ≥4.6 mg L−1 h−1, an O3/H2O2 mass ratio of 3.4–3.8, and initial COD <20 mg/L, a simple first order decay was indicated for both single-passed treated wastewater and recycled mineral water, and a relationship is proposed and demonstrated to estimate the pseudo-first order rate constant for design purposes. At this O3/H2O2 mass ratio, ORP and dissolved ozone were found to be useful process control indicators for monitoring COD mineralization in secondary effluent. Moreover, an average second order rate constant for OH oxidation of secondary effluent organics (measured as MCOD) was found to be 1.24 × 107 ± 0.64 × 107 M−1 S−1. The electric energy demand of the peroxone process is estimated at 1.73–2.49 kW h electric energy for removal of one log COD in 1 m3 secondary effluent, comparable to the energy required for desalination of medium strength seawater. Advantages/disadvantages of the two processes for municipal wastewater reuse are discussed.

Removal of Refractory Organics from Biologically Treated Landfill Leachate by Microwave Discharge Electrodeless Lamp Assisted Fenton Process

Biologically treated leachate usually contains considerable amount of refractory organics and trace concentrations of xenobiotic pollutants. Removal of refractory organics from biologically treated landfill leachate by a novel microwave discharge electrodeless lamp (MDEL) assisted Fenton process was investigated in the present study in comparison to conventional Fenton and ultraviolet Fenton processes. Conventional Fenton and ultraviolet Fenton processes could substantially remove up to 70% of the refractory organics in a membrane bioreactor treated leachate. MDEL assisted Fenton process achieved excellent removal performance of the refractory components, and the effluent chemical oxygen demand concentration was lower than 100 mg L−1. Most organic matters were transformed into smaller compounds with molecular weights less than 1000 Da. Ten different polycyclic aromatic hydrocarbons were detected in the biologically treated leachate, most of which were effectively removed by MDEL-Fenton treatment. MDEL-Fenton process provides powerful capability in degradation of refractory and xenobiotic organic pollutants in landfill leachate and could be adopted as a single-stage polishing process for biologically treated landfill leachate to meet the stringent discharge limit.

Adaptive neuro-fuzzy inference-based modeling of a full-scale expanded granular sludge bed reactor treating corn processing wastewater

In this study, an adaptive neuro-fuzzy inference system ANFIS including five process variables, such as influent chemical oxygen demand, influent flow rate, influent total Kjeldahl nitrogen, effluent volatile fatty acids and effluent bicarbonate, was described to predict the effluent chemical oxygen demand load from a full-scale expanded granular sludge bed reactor EGSBR treating corn processing wastewater. The proposed ANFIS model was conducted by applying hybrid learning algorithm and the model performance was tested by the means of distinct test data set randomly selected from the experimental domain. The ANFIS-based predictions were also validated using various descriptive statistical indicators, such as root mean-square error, index of agreement, the factor of two, fractional variance, proportion of systematic error, etc. The lowest root mean square error RMSE = 0.03655 and the highest determination coefficient R2 = 0.958 were achieved with the subtractive clustering of a first-order Sugeno type fuzzy inference system. ANFIS predicted results were compared with the outputs of multiple nonlinear regression analysis-based models derived in the scope of the present work. Statistical performance indices computed for the testing data set proved that the developed ANFIS-based model exhibited a very good precision in predicting the effluent chemical oxygen demand, load for the EGSBR system. Due to high capability of the ANFIS model in capturing the dynamic behavior and non-linear interactions, it was demonstrated that a complex system, such as anaerobic digestion, could be easily modeled.

Performance Evaluation of the Horizontal Subsurface Flow Constructed Wetland with Ipomoea Aquatica Plant for Rural Domestic Wastewater Treatment

In this study, the performance treatment of horizontal subsurface flow constructed wetland (HSFCW) was evaluated. The HSFCW built as a tertiary treatment process after the biological reactors to improve the effluent quality. The HSFCW system was operated with different hydraulic loading rates (HLRs) ranged from 0.15 to 0.333 m3/ (m2.d) to assess their influence on removal efficiency. During the system operation time, the average temperature was ranged of 22.3 to 31.2 °C and pH ranges was 7.3 – 8.1. The Ipomoea aquatica (Chinese spinach) planted into HSFCW system and the growth parameters during the experimental operation observed. The Ipomoea aquatica growth parameters such as the plant height, a fresh and dry weights were monitored and measured. The influent and effluent of chemical oxygen demand (COD), ammonium nitrogen (NH4-N), total nitrogen (TN) and total phosphorus (TP) were examined. The removal efficiency for all parameters showed decreased with an increase in HLR from 0.15 to 0.333 m3/ (m2.day). The results demonstrated that the average removal efficiency of the COD, NH4-N, TN and TP during system operation is 52.9%, 64.6%, 58.2% and 72.8% respectively. These results confirm that the HSFCW has a good efficient in treatment and can be used for the nutrients and organic matter removal from the domestic wastewater.

Comparative study on the treatment of raw and biologically treated textile effluents through submerged nanofiltration

Raw and biologically treated textile effluents were submerged filtrated using lab-fabricated hollow fiber nanofiltration membrane with a molecular weight cut-off of about 650g/mol. Permeate flux, chemical oxygen demand (COD) reduction, color removal, membrane fouling, and cleaning were investigated and compared by varying the trans-membrane pressure (TMP) and volume concentrating factor (VCF). It was found that both raw and biologically treated textile effluents could be efficiently treated through submerged nanofiltration. The increase of TMP resulted in a decline in water permeability, COD reduction, color removal, and flux recovery ratio, while the increase of VCF resulted in both increased COD reduction and color removal. Under the TMP of 0.4bar and VCF of 5.0, fluxes of 1.96 and 2.59l/m2h, COD reductions of 95.7 and 94.2%, color removals of 99.0, and 97.3% and flux recovery ratios of 91.1 and 92.9% could be obtained in filtration of raw and biologically treated effluents, respectively. After filtration, the COD and color contents of the raw effluent declined sharply from 1780 to 325mg/l and 1.200 to 0.060Abs/cm, respectively, while for the biologically treated effluent, they decreased from 780 to 180mg/l and 0.370 to 0.045Abs/cm, respectively.

Multi‐objective optimisation for design and operation of anaerobic digestion using GA‐ANN and NSGA‐II

AbstractBACKGROUNDDue to the complexity of nonlinear and biochemical phenomena involved in anaerobic wastewater treatment units, efficient operation and control is limited and difficult. The objective of this study was to implement a new multi‐objective control strategy to simultaneously optimise the effluent chemical oxygen demand (CODeff) and the biogas flow rate (Qgas) in an anaerobic bioreactor using non‐dominated sorting genetic algorithms‐II (NSGA‐II) and genetic algorithm–artificial neural network (GA‐ANN). The novel approach considered two operational objectives, i.e. control of the effluent quality and control of the maximum production rate of biogas, and took advantage of the difference between the dynamics of the liquid and gas phases using variables from both phases.RESULTSBased on the relatively lower values for the mean square error, the root mean square normalised error, and the mean absolute percentage error, as well as higher values for the correlation coefficient, GA‐ANN models achieve better performances than ANN models. Based on GA‐ANN and NSGA‐II, a more flexible and precise optimisation process was allowed, and an optimal balance between effluent quality and biogas flow rate of the anaerobic bioreactor can be achieved.CONCLUSIONThe proposed GA‐ANN models were shown to be capable of dynamically predicting CODeff and Qgas. Meanwhile the optimisation system developed may offer a useful tool for simulation, design, control and optimisation of anaerobic biodigesters. © 2014 Society of Chemical Industry

The combined effects of COD/N ratio and nitrate recycling ratio on nitrogen and phosphorus removal in anaerobic/anoxic/aerobic (A2/O)-biological aerated filter (BAF) systems

The combined effects of chemical oxygen demand (COD) to total nitrogen ratio (COD/N) and nitrate recycling ratio (R) on simultaneous nitrogen, phosphorus, and COD removal were studied in a laboratory-scaled anaerobic/anoxic/aerobic (A2/O)-biological aerated filter (BAF) system. Variation in the COD/N ratio alone had no noticeable effect on COD removal and nitrification, with the effluent COD concentration of 37mg/L and ammonium concentration below the detection level. However, low COD/N ratio (3.0) with high R (200–600%) deteriorated the total nitrogen (TN) removal due to insufficient carbon source and oxygen presence (dissolved oxygen concentration: 0.31–0.72mg/L) in the anoxic zones of A2/O. At the COD/N ratio of 4.0, the TN removal efficiency steadily increased from 66% to 81% when R was increased from 100% to 400%, but decreased to 70% at the highest R (600%). At the high COD/N ratio of 5.5, the TN removal efficiency increased from 68% to 90% with R increasing from 100 to 600%. The phosphorus release amounts in the anaerobic zone of the A2/O increased from 16.2mg/L to 55mg/L with the COD/N ratio increasing from 3.0 to 5.5. Low COD/N ratios (3.0 and 4.0) had little effect on phosphorus removal, while high COD/N ratio (5.5) caused the phosphorus release in sedimentation tanks due to the residual carbon in effluent.

Analysis of the effects of ultrasound irradiation over effluent quality and membrane integrity in flat sheet microfiltration MBR systems

Membrane fouling is one of the main problems regarding the performance of membrane bioreactors (MBRs) and it constitutes an important impediment to the increasing application of this technology. One of the most promising alternative cleaning methods is ultrasound irradiation and for that reason, in this study, the performance of four pilot-scale MBR modules using flat sheet microfiltration membranes working in parallel was evaluated and compared with a conventional MBR system. In these modules, sonication at different frequencies (20, 25, 30 and 40 kHz) and powers (100, 200, 300 and 400 W) was simultaneously applied during the filtration process and parameters such as total suspended solids (TSS) and volatile suspended solids activated sludge concentrations and effluent chemical oxygen demand (COD) concentration, turbidity, viscosity, colour or particle size distribution were analyzed. Moreover, operational parameters such as temperature or TMP were also evaluated, and scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR) analyses were carried out once the membranes were replaced. Although parameters such as effluent COD concentration, absorbance at 254 nm, colour at 436 nm, viscosity and activated sludge TSS did not show significant differences at different US frequencies, other parameters such as effluent turbidity or particle size distribution reached values too high compared with those obtained for the effluent from the microfiltration MBR system, especially at lower frequencies (20 kHz) and higher powers (400 W). Moreover, SEM images demonstrated that membrane integrity was negatively affected especially at these conditions and membrane pore size was enlarged due to sonication.