Fouling In Membrane Bioreactors Research Articles

Mitigation of Membrane Fouling in Membrane Bioreactors Using Granular and Powdered Activated Carbon: An Experimental Study

This experimental study explores the mitigation of membrane fouling in membrane bioreactors (MBRs) through the combined use of granular activated carbon (GAC) and powdered activated carbon (PAC). The research assesses the impact of these materials on the fouling resistance, critical flux, and permeate quality using various mixed liquor suspended solids concentrations and carbon dosages. The results indicate that the GAC-PAC combination significantly reduces the total filtration resistance, particularly the cake layer resistance, by 11.7% to 13.6% compared to setups without activated carbon or with the individual carbon types. The study also reveals that this combination decreased the fouling rate by 15% to 24% at critical flux steps, demonstrating substantial improvements in fouling mitigation and operational efficiency. Furthermore, the GAC-PAC combination, which produces an adsorption process, enhances the permeate quality, achieving the near-complete removal of organic matter, total nitrogen, and turbidity, with total phosphorus removal reaching 99%. These findings demonstrate that the combined use of GAC and PAC not only reduces membrane fouling but also improves the overall MBR performance, making it a viable strategy for enhancing the efficiency of wastewater treatment processes.

Mechanisms and Strategies of Advanced Oxidation Processes for Membrane Fouling Control in MBRs: Membrane-Foulant Removal versus Mixed-Liquor Improvement.

Membrane bioreactors (MBRs) are well-established and widely utilized technologies with substantial large-scale plants around the world for municipal and industrial wastewater treatment. Despite their widespread adoption, membrane fouling presents a significant impediment to the broader application of MBRs, necessitating ongoing research and development of effective antifouling strategies. As highly promising, efficient, and environmentally friendly chemical methods for water and wastewater treatment, advanced oxidation processes (AOPs) have demonstrated exceptional competence in the degradation of pollutants and inactivation of bacteria in aqueous environments, exhibiting considerable potential in controlling membrane fouling in MBRs through direct membrane foulant removal (MFR) and indirect mixed-liquor improvement (MLI). Recent proliferation of research on AOPs-based antifouling technologies has catalyzed revolutionary advancements in traditional antifouling methods in MBRs, shedding new light on antifouling mechanisms. To keep pace with the rapid evolution of MBRs, there is an urgent need for a comprehensive summary and discussion of the antifouling advances of AOPs in MBRs, particularly with a focus on understanding the realizing pathways of MFR and MLI. In this critical review, we emphasize the superiority and feasibility of implementing AOPs-based antifouling technologies in MBRs. Moreover, we systematically overview antifouling mechanisms and strategies, such as membrane modification and cleaning for MFR, as well as pretreatment and in-situ treatment for MLI, based on specific AOPs including electrochemical oxidation, photocatalysis, Fenton, and ozonation. Furthermore, we provide recommendations for selecting antifouling strategies (MFR or MLI) in MBRs, along with proposed regulatory measures for specific AOPs-based technologies according to the operational conditions and energy consumption of MBRs. Finally, we highlight future research prospects rooted in the existing application challenges of AOPs in MBRs, including low antifouling efficiency, elevated additional costs, production of metal sludge, and potential damage to polymeric membranes. The fundamental insights presented in this review aim to elevate research interest and ignite innovative thinking regarding the design, improvement, and deployment of AOPs-based antifouling approaches in MBRs, thereby advancing the extensive utilization of membrane-separation technology in the field of wastewater treatment.

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%.

MAO-DBN based membrane fouling prediction

Due to the complexity of the factors influencing membrane fouling in membrane bioreactors (MBR), it is difficult to accurately predict membrane fouling. This paper proposes a multi-strategy of integration aquila optimizer deep belief network (MAO-DBN) based membrane fouling prediction method. The method is developed to improve the accuracy and efficiency of membrane fouling prediction. Firstly, partial least squares (PLS) are used to reduce the dimensionality of many membrane fouling factors to improve the algorithm’s generalization ability. Secondly, considering the drawbacks of deep belief network (DBN) such as long training time and easy overfitting, piecewise mapping is introduced in aquila optimizer (AO) to improve the uniformity of population distribution, while adaptive weighting is used to improve the convergence speed and prevent falling into local optimum. Finally, the prediction of membrane fouling is carried out by utilizing membrane fouling data as the research object. The experimental results show that the method proposed in this paper can achieve accurate prediction of membrane fluxes, with an 88.45% reduction in RMSE and 87.53% reduction in MAE compared with the DBN model before improvement. The experimental results show that the model proposed in this paper achieves a prediction accuracy of 98.61%, both higher than other comparative models, which can provide a theoretical basis for membrane fouling prediction in the practical operation of membrane water treatment.

Synergistic algal/bacterial interaction in membrane bioreactor for detoxification of 1,2-dichloroethane-rich petroleum wastewater

The study addressed the challenge of treating petroleum industry wastewater with high concentrations of 1,2-dichloroethane (1,2-DCA) ranging from 384 to 1654 mg/L, which poses a challenge for bacterial biodegradation and algal photodegradation. To overcome this, a collaborative approach using membrane bioreactors (MBRs) that combine algae and bacteria was employed. This synergistic method effectively mitigated the toxicity of 1,2-DCA and curbed MBR fouling. Two types of MBRs were tested: one (B-MBR) used bacterial cultures and the other (AB-MBR) incorporated a mix of algal and bacterial cultures. The AB-MBR significantly contributed to 1,2-DCA removal, with algae accounting for over 20% and bacteria for approximately 49.5% of the dechlorination process. 1,2-DCA metabolites, including 2-chloroethanol, 2-chloro-acetaldehyde, 2-chloroacetic acid, and acetic acid, were partially consumed as carbon sources by algae. Operational efficiency peaked at a 12-hour hydraulic retention time (HRT) in AB-MBR, enhancing enzyme activities crucial for 1,2-DCA degradation such as dehydrogenase (DH), alcohol dehydrogenase (ADH), and acetaldehyde dehydrogenase (ALDH). The microbial diversity in AB-MBR surpassed that in B-MBR, with a notable increase in Proteobacteria, Bacteroidota, Planctomycetota, and Verrucomicrobiota. Furthermore, AB-MBR showed a significant rise in the dominance of 1,2-DCA-degrading genus such as Pseudomonas and Acinetobacter. Additionally, algal-degrading phyla (e.g., Nematoda, Rotifera, and Streptophyta) were more prevalent in AB-MBR, substantially reducing the issue of membrane fouling.

Enhanced total nitrogen removal and membrane fouling control by increasing biomass in MBR equipped with ceramic membrane

Simultaneous nitrification and denitrification (SND) is an efficient method to remove nitrogen in municipal wastewater treatment. However, low dissolved oxygen (DO) concentrations are generally required, leading to serious membrane fouling in membrane bioreactors (MBRs). This study aimed to clarify the synergistic effect of biomass and DO on nitrogen removal and membrane fouling. To achieve this goal, four submerged MBRs equipped with ceramic membranes were operated with different biomass (mixed liquor suspended solids (MLSS)) concentrations (3 000 mg/L, 5 000 mg/L, 7 500 mg/L, and 12 000 mg/L) under various DO concentrations (2.0 mg/L, 1.0 mg/L, and 0.5 mg/L). As a result, increasing biomass in the MBRs enhanced total nitrogen (TN) removal via SND, and excellent TN removal efficiencies of 60.7% and 75.8% were obtained using the MBR with an MLSS concentration of 12 000 mg/L and DO concentrations of 2.0 mg/L and 1.0 mg/L. However, a further decrease in DO deteriorated TN removal due to the inhibition of nitrification. Moreover, high MLSS concentrations were beneficial to membrane fouling control for ceramic membranes in MBRs. The lowest transmembrane pressure development rate was observed for the MBR with an MLSS concentration of 12 000 mg/L. High biomass offset the adverse effect of DO decrease on membrane fouling to some extent, and improved the stability of the reactor. Therefore, biomass might be an important parameter for membrane fouling reduction in ceramic MBRs. Overall, optimal biomass and DO concentrations for TN removal were identified, providing useful information for the successful operation of MBRs with efficient TN removal and membrane fouling control.

Membrane reciprocation and quorum quenching: An innovative combination for fouling control and energy saving in membrane bioreactors

Membrane bioreactors (MBRs) play a crucial role in wastewater treatment, but they face considerable challenges due to fouling. To tackle this issue, innovative strategies are needed. This study investigated the effectiveness of membrane reciprocation and quorum quenching (QQ) to control fouling in MBRs. The study compared MBRs using membrane reciprocation (30 rpm) and QQ (injecting media containing 100 or 200 mg/L BH4) with conventional MBRs employing different air-scouring intensities. The results demonstrated that combining membrane reciprocation (30 rpm) with QQ (200 mg/L BH4) significantly extended the service time of MBRs, making it approximately six times longer than conventional methods. Moreover, this approach reduced physically reversible resistance. The reduction in signal molecules related to biofouling due to QQ showcased its critical role in controlling biofouling, even under high shear caused by membrane reciprocation. However, the impact of QQ on microbial community structure appeared relatively insignificant when compared to factors such as operation time, aeration intensity, and membrane reciprocation. By combining membrane reciprocation and QQ, the study achieved a remarkable 81 % energy saving compared to extensive aeration (103 s−1 in velocity gradient), in addition to the extended service time. Importantly, this combined antifouling approach did not negatively affect microbial characteristics and wastewater treatment, emphasizing its effectiveness in MBRs. Overall, the findings of this study offer valuable insights for developing synergistic fouling control strategies in MBRs, significantly improving the energy efficiency of the wastewater treatment process.

Employing low dissolved oxygen strategy to simultaneously improve nutrient removal, mitigate membrane fouling, and reduce energy consumption in an AAO-MBR system: Fine bubble or coarse bubble?

The high energy consumption associated with aeration, which is a widely used hydrodynamic method to mitigate membrane fouling in membrane bioreactors (MBR), poses a significant challenge to the widespread application of aerated MBR. In this study, low dissolved oxygen was applied to optimize the overall performance and reduce energy consumption in an anaerobic-anoxic-aerobic MBR (AAO-MBR) under fine and coarse bubble aeration conditions. Coarse bubble aeration exhibited better membrane fouling control, but induced releasing more proteins and polysaccharides in mixed liquor than that in fine bubble aeration. Coarse bubble aeration resulted in a decrease in the relative abundance of function bacteria, and there was a corresponding drop in enzymes involved in the nitrogen and phosphorus pathways. Furthermore, the average total specific energy demand (0.45 ± 0.02 kW·h/d) and total carbon emissions (0.32 ± 0.01 kg/d) of coarse bubble aeration was remarkably higher than that of fine bubble aeration (0.35 ± 0.01 kW·h/d and 0.25 ± 0.02 kg/d). Our results demonstrate that the fine bubble aeration in low dissolved oxygen-based AAO-MBR can optimize the overall performance and reduce energy consumption, thereby making it a more viable option for the wastewater treatment.

Construction of synthetic anti-fouling consortia: fouling control effects and polysaccharide degradation mechanisms

The physical states and chemical components of bulk sludge determine the occurrence and development of membrane fouling in membrane bioreactors. Thus, regulation of sludge suspensions can provide new strategies for fouling control. In this study, we used “top-down” enrichment to construct a synthetic anti-fouling consortium (SAC) from bio-cake and evaluate its roles in preventing membrane fouling. The SAC was identified as Massilia-dominated and could almost wholly degrade the alginate solution (1,000 mg/L) within 72 h. Two-dimensional Fourier transformation infrared correlation spectroscopy (2D-FTIR-CoS) analysis demonstrated that the SAC induced the breakage of glycosidic bond in alginates. The co-cultivation of sludge with a low dosage of SAC (ranging from 0 to 1%) led to significant fouling mitigation, increased sludge floc size, and decreased unified membrane fouling index value (0.55 ± 0.06 and 0.11 ± 0.05). FTIR spectra and X-ray spectroscopy analyses demonstrated that the addition of SAC decreased the abundance of the O-acetylation of polysaccharides in extracellular polymeric substances. Secondary derivatives analysis of amide I spectra suggested a strong reduction in the α-helix/(β-sheet + random coil) ratio in the presence of SAC, which was expected to enhance cell aggregation. Additionally, the extracellular secretions of SAC could both inhibit biofilm formation and strongly disperse the existing biofilm strongly during the biofilm incubation tests. In summary, this study illustrates the feasibility and benefits of using SAC for fouling control and provides a new strategy for fouling control.

Effect of free nitrous acid on extracellular polymeric substances production and membrane fouling in a nitritation membrane bioreactor

The membrane bioreactor (MBR) with nitritation based nitrogen removal processes has attracted growing interest in recent years, although membrane fouling in the nitritation MBR is a challenging issue. In this study, the inhibitory effect of free nitrous acid (FNA) on microbial extracellular polymeric substances (EPS) production and membrane fouling in a nitritation MBR was investigated. Results showed that EPS played a critical role in the biofouling process, and EPS production was affected by FNA concentration. As FNA concentration increased from 5.10 × 10−3 mg N/L to 1.34 × 10−2 mg N/L, protein (PN) and polysaccharide (PS) contents increased from 8.20 to 60.28 mg/g VSS and 4.74–30.46 mg/g VSS, respectively. However, when FNA concentration was 1.48 × 10−2 mg N/L, PN and PS reduced by 20.0% and 10.9%, respectively, indicating that the higher FNA concentration could reduce EPS production. The EPS reduction could be attributed to reduction in the loosely bound (LB) and tightly bound (TB) EPS but not the soluble microbial products (SMP). It was further revealed that higher FNA concentrations up to 1.48 × 10−2 mg N/L consequently mitigate trans-membrane pressure (TMP) rate in terms of dTMP/dt by 25.5% in the nitritation MBR. High throughput sequencing analysis revealed that the increase in FNA led to enrichment of Nitrosomonas but reduction in heterotrophic bacteria. This study showed that the appropriate FNA concentration affected EPS production and hence membrane fouling, leading to the possibility of membrane fouling mitigation by in-situ generated FNA in the nitritation MBR.

Sewage-derived substances and dead microbial cells cause gel biofilm formation in membrane bioreactors treating real sewage

Gel fouling is frequently reported as one of the biggest obstacles in membrane bioreactors (MBRs) and is observed under unstable conditions. However, the mechanism and the cause of gel fouling are unknown. In this study, gel fouling was induced and compared with normal fouling (cake fouling) in MBR to identify the source of the substances and microorganisms which form the basis of the gel biofilm. Two anoxic/oxic MBRs were operated under changing and stable sludge loading rate (SLR) to induce gel and cake fouling, respectively. As SLR increased from 0.07 to 0.11 kg-COD/kg-MLSS, transmembrane pressure increased rapidly, and a gel biofilm formed on the membrane surface. By contrast, a cake biofilm was developed under stable SLR of 0.07 kg-COD/kg-MLSS with slow transmembrane pressure increase. Excitation-emission matrix-parallel factor analysis indicated that simple aromatic proteins and soluble microbial byproduct-like substances in the filtered supernatant were efficiently removed in both reactors; however, proteins and polysaccharides accumulated in the supernatant with flocs. Scanning electron microscopy analysis revealed that the gel biofilm had a cloud-like structure, with aggregates of filamentous bacteria and microcolonies. The gel biofilm had a thick dead-cell layer and a small number of dispersed live cells, whereas the cake biofilm had a three-dimensional structure of live and dead cells. In the context of the microbial community in gel biofilms, sewage-derived bacteria, such as Campylobacteria and Clostridia, were highly dominant, and the microbial community resembled more sewage than activated sludge. These results indicate that the accumulation of sewage-derived substances and dead microorganisms might have formed gel biofilm in the MBR.

Fouling mitigation in membrane bioreactors by nanobubble-assisted backwashing

Widespread application of membrane bioreactors (MBRs) is still difficult because of the problem of membrane fouling, which increases operational and maintenance costs. A novel approach to mitigate fouling in MBRs, nanobubble-assisted backwashing (NBB), is presented in this paper. Nanobubbles generated in this study had an average diameter of about 150 nm, and some of the nanobubbles could pass through the pores of microfiltration (MF) membranes used for MBRs. Therefore, nanobubbles introduced from the permeate side during backwashing might exhibit cleaning effects for membranes since applications of nanobubbles for cleaning of various materials such as protein-coated gold electrodes and stainless steel have been reported. The effectiveness of NBB was compared with that of tap water backwashing (TWB) and chemically enhanced backwashing (CEB) using 50 ppm NaClO. Experiments were carried out by using three bench-scale MBRs installed at a local wastewater treatment plant. The three MBRs were operated in parallel with identical operating conditions except for backwashing conditions. Polyethylene glycol (PEG) granular materials were inserted in each membrane tank to scour the membrane surface. Regardless of the variation of the feed, NBB always exhibited better cleaning performance than TWB, and the cleaning efficiency of NBB was sometimes comparable to that of CEB. The degree of reversible fouling observed with TWB was 424 % higher than that with NBB, indicating that NBB is much more effective than TWB for the control of reversible fouling. It was also found that NBB could mitigate irreversible fouling even in the absence of a thick protective layer on the surface of the membrane. It was attempted to reveal the mechanism by which NBB enhances the cleaning effect by carrying out comprehensive analysis of the distribution of filtration resistance, mixed liquor suspension and the fouling layer. Significant changes in microbial activity of the mixed liquor suspension and sludge properties in the MBRs were not observed when NBB was carried out. The results of the analysis suggested that NBB made the structure of the fouling layer more porous, possibly facilitating the removal of the fouling layer from the membrane.

Comparison of NaOH and NaOCl on-line chemical enhanced backwash on membrane fouling of high flux membrane bioreactor treating sewage

Different physio-chemical and biological methods have been applied to reduce membrane fouling and to maintain the flux of membrane bioreactor (MBR). Periodic chemically enhanced backwash (CEB) has been recently developed and displayed good performance to recover the membrane permeability. However, the comparative effect of on-line CEB (using NaOCl and NaOH) on fouling mitigation and the effluent quality of MBR was poorly known. This study aimed to evaluate the changes in membrane resistance, membrane fouling and the effluent quality with and without CEB in MBR to reveal the effect of different NaOCl and NaOH concentrations. Lab-scale MBR treating sewage at high flux were operated for 8 min continuously at a flux of 20 L/(m2.h) followed by a backwash duration of 30 s. In reference MBR permeate (without chemical) was used as a backwash solution. The study found that MBR with CEB has higher operational time and lower fouling rates than reference MBR. Overall, backwash with NaOH increased the run-time by 29% – 45% compared to the control MBR, and backwash with NaOCl increased run-time from 34% to 61% compared to the control MBR. NaOCl was significantly more effective by 7% – 28% compared to NaOH in fouling reduction at different concentrations. CEB has no significant (p > 0.05) effect on the removal efficiencies of different pollutants. The chemical oxygen demand removal efficiencies varied between 82 and 84%. The removals of total kjeldahl nitrogen (50 – 54%) and total phosphorus (45 – 52%) were lower due to the short solids and hydraulic retention time. This study highlights the potential of periodic CEB and concentrations of chemicals on MBR fouling and provides insights into potential approaches for mitigating this issue in MBR systems.

The positive roles of influent species immigration in mitigating membrane fouling in membrane bioreactors treating municipal wastewater

The influence of influent species immigration (ISI) on membrane fouling behaviors of membrane bioreactors (MBRs) treating municipal wastewater remains elusive, leading to an incomprehensive understanding of fouling ecology in MBRs. To address this issue, two anoxic/aerobic MBRs, which were fed with raw (named MBR-C) and sterilized (MBR-E) municipal wastewater, were operated. Compared with the MBR-E, the average fouling rate of the MBR-C was lowered by 30% over the long-term operation. In addition, the MBR-E sludge had significantly higher unified membrane fouling index and biofilm formation potential than the MBR-C sludge. Considerably larger flocs size and lower soluble microbial products (SMP) concentrations were observed in the MBR-C than in the MBR-E. Moreover, the 16S rRNA gene sequencing results showed that highly diverse and abundant populations responsible for floc-forming, hydrolysis/fermentation and SMP degradation readily inhabited the influent, shaping a unique microbial niche. Based on species mass balance-based assessment, most of these populations were nongrowing and their relative abundances were higher in the MBR-C than in the MBR-E. This suggested an important contribution of the ISI on the assemblage of these bacteria, thus supporting the increased flocs size and lowered SMP concentrations in the MBR-C. Moreover, the SMP-degrading related bacteria and functional pathways played a more crucial role in the MBR-C ecosystem as revealed by the bacterial co-occurrence network and Picrust2 analysis. Taken together, this study reveals the positive role of ISI in fouling mitigation and highlights the necessity for incorporating influent wastewater communities for fouling control in MBR plants.

Monitoring of MBR fouling properties by filtration resistance and zeta potential measured for both filtration and backwashing directions

Membrane Bioreactor (MBR) being the promising and sustainable technology, will be highly in demand in future. To monitor the inline status of fouling, in order to make the process more economical, novel fouling monitoring indexes based on the differences in filtration properties between the filtration direction and backwashing direction were developed. The module clogging and fouling properties were monitored by direct visual observation of filtration surface, filtration resistance and zeta potential for both directions in a lab scale MBR using alumina tubular microfiltration membrane having pore size of 0.2 μm. The optimal clearance size of flow channel in membrane module for avoiding clogging by sludge cake was determined at 5 mm by the visual observation. The filtration resistance for filtration direction, RF, increased steeply in later stage of operation while that for backwashing direction, RB, showed a gradual increasing throughout operation. This difference between RF and RB was elucidated by a model where the sludge cake behaves like a “check valve”. The analysis of cleaning experiments of fouled membrane with the resistance in series model also supported the model of the sludge cake behavior and showed that the resistance caused by sludge cake, Rcake, dominated RF and had no impact on RB. This analysis also showed that Rcake and the resistance caused by macromolecule adsorption, Radsorption, which are important factors for recognizing fouling status, can be evaluated from RF and RB, which are easy to monitor during operation, without cleaning experiments. The zeta potential also depended on the measurement direction and showed a decreasing trend with the increase in filtration resistance.

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.

Effect of starch-coated magnetic particles on treatment performance and membrane fouling in membrane bioreactor for low carbon/nitrogen municipal wastewater treatment

Membrane bioreactor (MBR) is an attractive sewage treatment technology but the major weakness remains in membrane fouling. Nowadays, magnetic activated sludge process with magnetic particle addition has been extensively investigated for membrane fouling mitigation due to the excellent magnetic bio-effect. However, the bioeffect is still limited and further study to enhance the fouling control is needed. Herein, the starch-coated magnetic particles (MsP) were fabricated and utilized to alleviate membrane fouling and enhance the treatment performance for low carbon/nitrogen municipal wastewater treatment. The MsP addition in MBR can effectively mitigate the membrane fouling which might be due to the magnetic bio-effect and enhanced bioflocculation, leading to the lower soluble microbial product (SMP) concentration from 17.3 ± 1.7 to 13.1 ± 0.7 mg L−1, higher microbial dehydrogenase activity from 234.65 ± 11.21 to 430.57 ± 39.48 mgTF gVSS−1h−1, bigger sludge particle size and more extracted extracellular polymer substances (EPS) secretion in the bulk sludge. Additionally, MsP particle can facilitate to form an aerobic and anoxic microenvironment, which is conducive to improve the nitrogen removal for low carbon/nitrogen municipal wastewater treatment. Microbial diversity analyses revealed that MsP addition enriched Flavobacterium sp, leading to more EPS secretion and therefore enhance the hydrophobic property and aggregation ability of sludge flocs to mitigate membrane fouling. Rhodobacter sp was also accumulated, indicating better denitrification process for total nitrogen removal. This study provided evidence for the efficiency of adding MsP to MBR in order to suppress membrane fouling and improve nitrogen removal for low carbon/nitrogen municipal wastewater treatment.

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.

High propensity of membrane fouling and the underlying mechanisms in a membrane bioreactor during occurrence of sludge bulking

While sludge bulking often occurring in activated sludge processes generally leads to serious membrane fouling in membrane bioreactors (MBR), the underlying causes are still unclear. In this study, fouling behaviors of a MBR operated at stages of normal and sludge bulking were compared, and the fouling mechanisms of the different behaviors were explored. It was found that, the MBR could be stably operated in normal stage without membrane cleaning for about 60 days, whereas, daily membrane cleaning had to be carried out when operated in sludge bulking stage. The bulking sludge possessed a rather high specific filtration resistance (SFR) of about 1.36×1014 m·kg−1, which is over 5.33 times than that of the normal sludge. A series of characterizations demonstrated that the bulking sludge had rather lower dewaterability, smaller particle size, higher fractal dimension, higher viscosity, abundant filamentous bacteria and different functional groups of extracellular polymer sustains (EPS). It was suggested that microbial community transition was responsible for the occurrence of sludge bulking, further affecting membrane fouling. Based on these characterizations, it was reported that adhesion propensity (indicated by the thermodynamic interaction) of the bulking sludge to the membrane surface is about 3.6 times than that of the normal sludge. It was proposed that, extra force should be provided to offset a chemical potential gap caused by foulant layer structure transition during sludge bulking in order to sustain filtration of the bulking sludge, resulting in extremely high SFR. This study offered deep thermodynamic mechanisms of MBR fouling during occurrence of sludge bulking.