Membrane Fouling In Membrane Bioreactor Research Articles

Study on efficiency and mechanism of ultrasonic controlling membrane fouling in ceramic membrane bioreactors.

In recent years, ceramic membranes have been increasingly used in membrane bioreactors (MBRs). However, membrane fouling was still the core issue restricting the large-scale engineering application of ceramic MBRs. As a novel and alternative technology, ultrasonic could be used to control membrane fouling. This research focused on the efficiency and mechanism of ultrasonic controlling membrane fouling in ceramic MBRs. The results showed that ultrasonic reduced the sludge concentration in MBR, and the average particle size of sludge was always in a high range. The sludge activity of the system was stable at 6-9 (mg O2·(g MLSS·h)-1), indicating that ultrasonic did not destroy the activity of microorganisms in the system. The extracellular polymer substance (EPS) of the ultrasonic group was slightly higher than that of the control group, while the soluble microbial product (SMP) content was relatively stable. The ceramic membrane of the ultrasonic group has a partial retention effect on the organic components. The application of ultrasonic slowed down the decrease of the hydrophilicity of the ceramic membrane. The main pollutants on the membrane surface exist in the form of aromatic and heteroaromatic rings, alkynes, and so forth. Ultrasonic removes the amide substances from the membrane surface. Membrane fouling resistance is mainly due to membrane pore blockage, accounting for 75.53%. PRACTITIONER POINTS: Enrich the research on the mechanism of ultrasonic technology in membrane fouling control. The MBR can still operate normally with ultrasonic applied. The time for the ceramic membrane to reach the fouling end point is 2.4 times that without ultrasonic. The main cause of membrane fouling was pore blocking, accounting for 75.53%.

Effect of Membrane Pore Size on Membrane Fouling of Corundum Ceramic Membrane in MBR.

Ceramic membrane has emerged as a promising material to address the membrane fouling issue in membrane bioreactors (MBR). In order to optimize the structural property of ceramic membrane, four corundum ceramic membranes with the mean pore size of 0.50, 0.63, 0.80, and 1.02 μm were prepared, which were designated as C5, C7, C13, and C20, respectively. Long-term MBR experiments showed that the C7 membrane with medium pore size experienced the lowest trans-membrane pressure development rate. Both the decrease and increase of membrane pore size would lead to more severe membrane fouling in the MBR. It was also interesting that with the increase of membrane pore size, the relative proportion of cake layer resistance in total fouling resistance was gradually increased. The content of dissolved organic foulants (i.e., protein, polysaccharide and DOC) on the surface of C7 was quantified as the lowest among the different ceramic membranes. Microbial community analysis also revealed the C7 had a lower relative abundance of membrane fouling associated bacteria in its cake layer. The results clearly demonstrated that ceramic membrane fouling in MBR could be effectively alleviated through optimizing the membrane pore size, which was a key structural factor for preparation of ceramic membrane.

The impact of sunlight on fouling behaviors and microbial communities in membrane bioreactors

Membrane fouling is a significant obstacle to applying membrane bioreactors (MBRs) for wastewater treatment. Here we report the impact of sunlight irradiation on membrane fouling, biopolymers, signal molecules, and microbial communities in MBRs. The degradation of signal molecules, which induce membrane biofouling, occurred through solar photolysis in batch tests. However, MBR sludge exposed to sunlight exhibited different biological behaviors creating more soluble microbial products (SMP) and signal molecules (particularly autoinducer-2). Cell lysis and deflocculation occurred when the MBR mixed liquor was exposed to sunlight. MBR fouling rates coincided with the temporal concentration profiles of SMP and signal molecules. Sunlight caused drastic changes in the MBR microbial community, stimulating the preferential growth of specific bacteria (e.g., Deinococcus Runella, Flavitalea, Glaiimonas, and Rurimicrobium). The nonmetric multidimensional scaling analysis of the MBR community structures with and without sunlight irradiation showed two distinct microbial community clusters and their reversibility. Network analysis based on Spearman's rank correlations revealed that with sunlight irradiation, fouling rates had significant positive connections with SMP proteins and the Flavitalea genus. The findings of this study demonstrate that sunlight is a considerable factor affecting membrane fouling and microbial ecology in MBRs, needing shade for fouling mitigation and sustainable operation.

Unveiling the residual membrane foulants in full-scale MBR plant after chemically enhanced backwash: Insights into microbe-associated compounds

Membrane fouling is a main bottleneck that limits the stable operation of membrane bioreactors (MBRs). However, the nature of residual foulants over frequent chemical cleaning remain elusive. Herein, we collected fouled membranes from a large-scale MBR with the treatment capacity of 200, 000 m3/d and explored the culprit for the key components resistant to chemically enhanced backwash. During 155 days of operation, transmembrane pressure increasing highly linked to the characteristics of membranes and bio-cakes. Fourier-transform infrared microscopy deciphered that a part of polyvinylpyrrolidone in the structure of polyvinylidene fluoride hollow fiber membrane was removed by NaOCl after chemical backwash. The stubborn uronic acids were mostly responsible for irreversible fouling due to pore constriction and the resistance to NaOCl. The fouling-related genera f_Rhodocyclaceae and f_Anaerolineaceae prevailed in the bio-cakes. According to the network analysis, the negative and competitive interactions on the bio-cake contributed more to severe membrane fouling than the positive and cooperative interactions. The keystone taxa c_WS6 (Dojkabacteria) and c_Deltaproteobacteria, which involved in secreting polysaccharides and hydrolyzing refractory matters, accelerated the accumulation of organic foulants. Our findings help to elucidate the key contributors to membrane fouling and anti-cleaning in full-scale MBR, which provide new insights for future fouling control.

Research of BP Neural Network Based on GA-WOA Algorithm Optimization in MBR Membrane Pollution Simulation

For the membrane fouling problem faced by the MBR (Membrane Bio-Reactor) system, an intelligent model is constructed to predict the membrane fouling. The BP neural network has strong self-learning, self-adaptive and generalization capabilities and is widely used in the prediction of MBR membrane pollution, but membrane fouling is a complex dynamic process, which is difficult to simulate accurately by classical mathematical models. Aiming at this problem, the GA-WOA hybrid algorithm was introduced to optimize the BP neural network, and the MBR membrane fouling prediction model was constructed. The simulation results show that the BP neural network model optimized by GA-WOA hybrid algorithm is more suitable and accurate than that optimized by whale optimization algorithm in predicting MBR membrane fouling.

Membrane fouling behavior in membrane bioreactors for nitrogen-deficient wastewater pretreated by ammonium ion exchange

Nitrogen is a critical element closely related to the synthesis of cellular membrane fouling behaviors in membrane bioreactors (MBRs). In this study, a novel pretreatment process by coupling chemically enhanced primary treatment (CEPT) with ammonia nitrogen ion exchange and regeneration (AIR) was proposed to analyze their influences on sludge properties and membrane fouling in MBRs. The MBRs with CEPT and AIR pretreatment obtained the effluent with chemical oxygen demand (COD) and ammonium nitrogen (NH4+-N) levels comparable to the conventional anoxic/aerobic MBR, but with much lower concentrations of total nitrogen (≤3.0 mg/L) and total phosphorous (≤0.15 mg/L). CEPT and AIR remarkably removed particles and soluble proteins from the influent, prohibited EPS secretion by 62.9–79.1% and elevated viscoelasticity of EPS, and thus alleviated membrane fouling. Membrane foulant in the experimental MBRs had unstable EPS structures easily detached, and low biofilm roughness to prevent the adsorption of organic matters. Nitrogen load had significantly positive correlations with EPS contents, viscoelasticity of EPS, and the total filtration resistance. The nitrogen-deficient condition enriched quorum quenching bacteria and microbes surviving retarding EPS production, and inhibited the overgrowth of filamentous bacteria. Therefore, nitrogen separation from wastewater in advance can effectively alleviate membrane fouling and improve pollutant removal in MBRs.

Feasibility of implementing quorum quenching technology to mitigate membrane fouling in MBRs treating phenol-rich pharmaceutical wastewater: Application of Rhodococcus sp. BH4 and quorum quenching consortium

This study aimed to implement quorum quenching (QQ) to mitigate membrane fouling in membrane bioreactors (MBRs) treating phenol-rich pharmaceutical wastewater using Rhodococcus sp. BH4 and isolated QQ consortium (QQcs) from activated sludge. Neither BH4 nor QQcs impacted the removal efficiency of chemical oxygen demand (COD) (>94%), phenol (>99%), and ammonium (>99%), indicating that QQ did not have adverse impact on treatment performance. In addition, both BH4 and QQcs effectively retarded membrane fouling, which could be attributed to the reduction of soluble microbial products (SMP). Interestingly, the TMP increase was delayed 68.7% by Rhodococcus sp. BH4, while 31.3% was achieved by QQcs. This difference may be due to the relatively higher degradation for short- and medium-chain N-acyl-homoserine lactones (AHLs) by BH4 compared to the QQcs. Furthermore, the possible presence of quorum sensing (QS) bacteria within QQcs also could have contributed to the less effective fouling control than that of BH4.

Study of membrane fouling mechanism during the phenol degradation in microbial fuel cell and membrane bioreactor coupling system

This study evaluated the feasibility of phenol degradation in microbial fuel cell (MFC) and membrane bioreactor (MBR) coupling system, and explored the mechanism of MBR membrane fouling. Four aspects were researched in open and closed circuit conditions: the degradation capacity of the coupling system, the increase of trans-membrane pressure (TMP), and the adhesion of phenol degradation products and microorganisms on the membrane. The results showed that the degradation of phenol and COD in the closed circuit coupling system was higher than that in the open circuit. The micro-electric field can inhibit the growth of TMP and keep dodecamethylcyclohexasiloxane away from the membrane, meanwhile can also reduce the abundance and species diversity of microorganisms. Nevertheless, the micro-electric field could not completely eliminate the membrane fouling due to the fact that the phenol degradation product of ethanethiol, microorganisms of Proteobacteria and Actinobacteria were more favorable on the membrane.

Effect of Operating Conditions on Membrane Fouling in Pilot-Scale MBRs; Filaments Growth, Diminishing Dissolved Oxygen and Recirculation Rate of the Activated Sludge.

This is the first study that examines the effect of operating conditions on fouling of Membrane Bio-Reactors (MBRs), which treat municipal wastewater in field conditions, with specific regard to the controlled development of filamentous microorganisms (or filaments). The novelty of the present work is extended to minimize the dissolved oxygen (DO) in recirculated activated sludge for improving the process of denitrification. For this purpose, two pilot-scale MBRs were constructed and operated in parallel: (i) Filament-MBR, where an attempt was made to regulate the growth of filaments by adjustment of DO, the Food-to-Microorganisms (F/M) ratio and temperature, and (ii) Control-MBR, where a gentle stirring tank was employed for the purpose of zeroing the DO in the recycled sludge. Results showed that low temperature (<15 °C) slightly increased the number of filaments in the Filament-MBR which, in turn, decreased the Trans-Membrane Pressure (TMP). As the Soluble Microbial Products (SMP) and the colloids are considered to be the basic foulants of membranes in MBR systems, specific attention was directed to keep their concentration at low values in the mixed liquor. The low F/M ratio in the aeration tanks which preceded the membrane tank was achieved to keep the SMP proteins and carbohydrates at very low values in the mixed liquor, i.e., less than 6 mg/L. Moreover, as a result of the low recirculation rate (2.6∙Qin), good aggregation of the produced excess sludge was achieved, and low concentration of colloids with a size ≤50 nm (nearly the membranes’ pore size used for filtration/separation) was measured, accounted for maximum 15% of the total colloids. Additionally, the increase in filamentous population at the Filament-MBR contributed to the further reduction of colloids in the mixed liquor at 7.9%, contributing beneficially to the reduction of TMP and of membrane fouling. The diminishing of DO in the recirculated sludge improved denitrification, and resulted in lower concentrations of Ν-NO3− and TN in the effluent of the Control-MBR. Furthermore, the recirculation rate of Qr = 2.6∙Qin, in comparison with Qr = 4.3∙Qin, resulted in improved performance regarding the removal of N-NH4+. Finally, high organics removal and ammonium nitrification was observed in the effluent of both pilots, since COD and Ν-ΝH4+ concentrations were generally in the range of 10–25 mg/L and <0.1 mg/L, respectively.

Pharmaceutical wastewater treatment using polypropylene membranes incorporated with carboxylated and PEG‐grafted nanodiamond in membrane bioreactor (MBR)

AbstractThe aim of this work is to prepare polypropylene (PP) membrane by embedding carboxylated(‐COOH) and also polyethylene glycol(‐PEG) functionalized nanodiamond to improve membrane hydrophilicity and decline membrane fouling in pharmaceutical wastewater treatment. Porosity, contact angle, mechanical strength, field emission scanning electron microscopy (FESEM) and membrane pure water permeation analysis were performed for the characterization of the membranes. The membranes with 0.75 wt.% of nanoparticles introduced the highest water flux, porosity and mechanical strength. The performance of PP, PP/ND‐COOH (0.75 wt.%) and PP/ND‐PEG (0.75 wt.%) membranes was studied in a lab‐scale membrane bioreactor (MBR). COD removal was more than 91% in all cases. It was found that antifouling characteristics, membrane resistance (Rm) and specific cake layer resistance (α) of nanocomposite membranes were better than of neat PP membrane. PP/ND‐PEG (0.75 wt.%) membrane exposed highest hydrophilicity and maximum critical flux and anti‐fouling characteristics. The results indicated that embedding nanodiamond in PP membrane can reduce membrane fouling in MBR.

Data-Driven Intelligent Warning Method for Membrane Fouling.

Membrane fouling has become a serious issue in membrane bioreactor (MBR) and may destroy the operation of the wastewater treatment process (WWTP). The goal of this article is to design a data-driven intelligent warning method for warning the future events of membrane fouling in MBR. The main novelties of the proposed method are threefold. First, a soft-computing model, based on the recurrent fuzzy neural network (RFNN), was proposed to identify the real-time values of membrane permeability. Second, a multistep prediction strategy was designed to predict the multiple outputs of membrane permeability accurately by decreasing the error accumulation over the predictive horizon. Third, a warning detection algorithm, using the state comprehensive evaluation (SCE) method, was developed to evaluate the pollution levels of MBR. Finally, the proposed method was inserted into a warning system to complete the predicting and warning missions and further tested in the real plants to evaluate its efficiency and effectiveness. Experimental results have verified the benefits of the proposed method.

Aerobic granular sludge (AGS) scouring to mitigate membrane fouling: Performance, hydrodynamic mechanism and contribution quantification model

Aerobic granular sludge (AGS) has been proven to have a low fouling potential in membrane bioreactor (MBR). Nevertheless, AGS scouring effect on mitigating membrane fouling remains poorly investigated. The main objective of this study is to examine AGS-MBR performance, to reveal the AGS scouring mechanism and quantify its contribution rate to membrane fouling mitigation, from the views of theory and experiment. Above all, AGS-MBR exhibited a low fouling rate ((transmembrane pressure (TMP) kept below 20 kPa) without membrane cleaning and a higher removal of organics and nutrients than conventional MBR during 80 days’ sludge granulation process. Then, flocculent sludge (FS) with various AGS ratios was applied to simulate the sludge granulation phase. When AGS ratio increased from 0% to 100%, the permeate flux gradually elevated from 40.0 L m−2h−1 to 92.9 L m−2h−1, and fouling resistance decreased from 9.0 × 10−12m−1 to 3.9 × 10−12m−1 benefiting from the loose structure and high porosity of AGS fouling layer. Meanwhile, the scouring effect produced by AGS on the membrane fouling mitigation was investigated. Based on the momentum conservation, a new hydrodynamic model was developed to explain the scouring mechanism of AGS. The scouring stress, proportional to the total amount of AGS depositing on the membrane surface, effectively reinforced the collision between AGS and FS, and reduced their deposition on the membrane surface by friction with the membrane; thus it was further conducive to membrane fouling mitigation. Moreover, a novel contribution quantification model was proposed for analyzing the contribution rate of AGS scouring effect to mitigate membrane fouling. AGS scouring possessed a significant contribution rate (39.9%) for fouling mitigation, compared with AGS structure (50.3%) and hydraulic stress (9.7%). In final, this study provides an in-depth understanding to mitigate the MBR membrane fouling by the unique advantages of sludge granulation.

Effects of sulfate on activated sludge characteristics and membrane fouling in membrane bioreactor treating penicillin wastewater

Treating penicillin wastewater is receiving more and more attention, because penicillin has strong anti-oxidant, anti-degradation and strong inhibitory effect on microbial growth. Membrane bioreactor (MBR) with stable and superior performance, has been used in the treatment of pharmaceutical wastewater. In this paper, effects of sulfate on activated sludge and membrane fouling in MBR treating penicillin wastewater were investigated. The results showed MBR could guarantee excellent effluent in the chemical oxygen demand (COD) and ammonia nitrogen (NH4+-N) removal. However, sulfate reduced the biodegradability of wastewater due to the changes in microbial species and the inhibition of microbial metabolic activity. Difference in the transmembrane pressure (TMP) indicated that sulfate made membrane fouling more serious. Colloids which exacerbated the clogging of the membrane pores and the formation of a dense cake layer, were the major contributor to membrane fouling.

Combined Effect of Colloids and SMP on Membrane Fouling in MBRs.

Membrane fouling investigations in membrane bioreactors (MBRs) are a top research issue. The aim of this work is to study the combined effect of colloids and soluble microbial products (SMPs) on membrane fouling. Two lab-pilot MBRs were investigated for treating two types of wastewater (wwt), synthetic and domestic. Transmembrane pressure (TMP), SMP, particle size distribution and treatment efficiency were evaluated. Chemical Oxygen Demand (COD) removal and nitrification were successful for both kinds of sewage reaching up to 95–97% and 100%, respectively. Domestic wwt presented 5.5 times more SMP proteins and 11 times more SMP carbohydrates compared to the synthetic one. In contrast, synthetic wwt had around 20% more colloids in the mixed liquor with a size lower than membrane pore size (<400 nm) than domestic. Finally, the TMP at 36 days reached 16 kPa for synthetic wwt and 11 kPa for domestic. Therefore, synthetic wwt, despite its low concentration of SMPs, caused severe membrane fouling compared to domestic, a result that is attributed to the increased concentration of colloids. Consequently, the quantity of colloids and possibly their special characteristics play decisive and more important roles in membrane fouling compared to the SMP—a novel conclusion that can be used to mitigate membranes fouling.

A Review on the Mechanism, Impacts and Control Methods of Membrane Fouling in MBR System.

Compared with the traditional activated sludge process, a membrane bioreactor (MBR) has many advantages, such as good effluent quality, small floor space, low residual sludge yield and easy automatic control. It has a promising prospect in wastewater treatment and reuse. However, membrane fouling is the biggest obstacle to the wide application of MBR. This paper aims at summarizing the new research progress of membrane fouling mechanism, control, prediction and detection in the MBR systems. Classification, mechanism, influencing factors and control of membrane fouling, membrane life prediction and online monitoring of membrane fouling are discussed. The research trends of relevant research areas in MBR membrane fouling are prospected.

Research on Operation Efficiency and Membrane Fouling of A2/O-MBR in Reclaimed Water Treatment.

Taking the public building domestic wastewater as an example, the combination of the MBR (membrane bioreactor) process and the traditional A2/O (anaerobic-anoxic-oxic) process was established and analyzed in terms of the removal effect of the pollutants, the impact of the microbial community changes on the process, the MBR membrane fouling, the cleaning methods, and the cleaning performance. The results indicated that the effluent water quality of the domestic wastewater treated with the A2/O-MBR process was stable and met the emission requirement to the natural water body. There was good microbial diversity in raw water, the anaerobic tank, the anoxic tank, the aerobic MBR tank and the disinfection tank, and the aerobic MBR tank has a wide variety of aerobic microorganisms, which elevates the removal of organics and the nitrification of ammonia nitrogen and ensures the qualification of nitrogen and phosphorus indexes of the system effluent water. For the fouled membrane, the surface of the contaminated membrane was covered by macromolecular contaminants, causing the membrane flux to drop, and after different cleaning methods to the membrane were compared, it was discovered that the combined use of cleaning agents had better effects than the single ones, and the cleaning method of sodium hydroxide followed by hydrochloric acid showed the best effect, achieving a membrane flux restoration ratio above 80% after cleaning.

Application of radial basis function artificial neural network to quantify interfacial energies related to membrane fouling in a membrane bioreactor

Efficient quantification of interfacial energy related with membrane fouling represents the primary interest in membrane bioreactors (MBRs) as interfacial energy determines foulant layer formation. In this study, radial basis function (RBF) artificial neural networks (ANNs) with five related factors as input variables were applied to quantify interfacial energy with randomly rough membrane surface. It was found that, RBF ANNs could well capture the complex non-linear relationships between the related factors and interfacial energy. RBF ANN quantification showed high regression coefficient and accuracy, suggesting its high capacity to quantify interfacial energy. Compared to at least one-week time consumption of the advanced extensive Derjaguin-Landau-Verwey-Overbeek (XDLVO) approach, quantification by RBF ANNs only took several seconds for a same case, indicating the high efficiency of RBF ANNs. Moreover, the abilities of RBF ANNs can be further improved. The robust RBF ANNs proposed paved a new way to study membrane fouling in MBRs.

Membrane fouling caused by lipopolysaccharides: A suggestion for alternative model polysaccharides for MBR fouling research

Polysaccharides were identified as key foulants in membrane bioreactors (MBRs) in previous studies. Polysaccharides used for MBR fouling research should represent real foulants, and alginate and dextran have often been used as model polysaccharides. However, their properties are not necessarily similar to those of polysaccharides that actually cause membrane fouling in MBRs. In recent studies, it was shown that polysaccharides causing membrane fouling in MBRs had the structures of lipopolysaccharides (LPSs), which are components of the cell wall of gram-negative bacteria. In the present study, therefore, membrane fouling caused by commercially available LPSs was investigated and was compared with that caused by model polysaccharides. In a series of batch filtration tests using four different microfiltration (MF) and ultrafiltration (UF) membranes, regardless of the membrane used, LPSs caused more severe membrane fouling than did alginate or dextran when they were filtered under the condition of the same organic carbon concentration. The properties of LPSs were found to be considerably different from those of alginate and dextran. In particular, affinity of LPS to PVDF polymer assessed by quartz crystal microbalance (QCM) mass measurement was remarkably high, and it would account for the severe fouling caused by LPSs. In experiments with filtering of mixtures of the model polysaccharides and a biomass suspension collected from a pilot-scale MBR, which were conducted to mimic the sudden increase in dissolved polysaccharides in real MBRs, LPS induced significant irreversible fouling, while alginate and dextran did not. The results obtained in this study clearly demonstrated high fouling potential of LPSs. Use of LPSs in future MBR fouling studies is therefore recommended.

Novel insights into membrane fouling caused by gel layer in a membrane bioreactor: Effects of hydrogen bonding

Gel layer formation in some cases directly determines membrane fouling extent in membrane bioreactors (MBRs). While hydrogen bonding interactions extensively exist in gelling foulants and sludge suspension, their exact roles in fouling remain unveiled. Filtration results in this study showed that, specific filtration resistance (SFR) of a gel layer formed in the MBR was as high as 2.06 × 1019 m−1·kg−1 at 20 °C, and moreover, SFR of both the real gel and model gel (Poly(N-isopropylacrylamide) (PNIPAM)) decreased with temperature. Fourier-transform infrared spectroscopy (FTIR) analysis indicated that gel samples were abundant of good hydrogen bonding donors/acceptors to form hydrogen bonding, and hydrogen bonding strength decreased with temperature. From viewpoint of free energy, mathematical models depicting roles of hydrogen bonding were proposed. For the first time, contribution level of hydrogen bonding effects to total gel SFR was quantified to be around 20%. These results offered in-depth insights into membrane fouling in MBRs.

Ceramic membrane fouling by dissolved organic matter generated during on-line chemical cleaning with ozone in MBR

Ceramic membrane bioreactor (MBR) has attracted increasing interest due to its high flux, long membrane life-span and excellent resistance to hash operation conditions. Although ozone has been used for chemical cleaning of ceramic membranes, it is still unclear about the role of dissolved organic matter (DOM) generated during on-line chemical cleaning with ozone in the development of membrane fouling in ceramic MBR. This study clearly revealed that the released DOM could considerably induce irreversible membrane fouling, and humic acid like-substances (HAL) with molecular weight (MW) of about 500 Da were mainly responsible for the observed membrane fouling. A strong positive relationship existed between the membrane fouling rate of supernatant and the rejection level of HAL, evidenced by a high correlation coefficient (R2) of 0.99. Meanwhile, the results also showed that biopolymers with MW greater than 10 kDa were easily rejected by the ceramic membranes used, leading to the development of membrane fouling. However, the high ozone concentration helped to reduce the generation of biopolymers. The organic fractions with MW less than 500 Da in the DOM (e.g. building blocks, low-MW acid and low-MW neutrals) could pass through the ceramic membranes used, i.e. their contributions to the observed membrane fouling could be considered insignificant. Consequently, it appeared from this study that membrane fouling associated with the DOM generated by ozone during on-line chemical cleaning should not be ignored in the design and operation of ceramic MBR towards long-term process sustainability.