The growth process of the cake layer and membrane fouling alleviation mechanism in a MBR assisted with the self-generated electric field

Sludge bound-EPS solubilization enhance CH4 bioconversion and membrane fouling mitigation in electrochemical anaerobic membrane bioreactor: Insights from continuous operation and interpretable machine learning algorithms

Bound extracellular polymeric substances (EPS) are complex, high-molecular-weight polymer mixtures that play a critical role in pore clogging, foulants adhesion, and fouling layer formation during membrane filtration, owing to their adhesive properties and gelation tendencies. In this study, a novel electrochemical anaerobic membrane bioreactor (EC-AnMBR) was constructed to investigate the effect of sludge bound-EPS solubilization on methane bioconversion and membrane fouling mitigation. During the 150-days' operation, the EC-AnMBR demonstrated remarkable performance, characterized by an exceptionally low fouling rate (transmembrane pressure (TMP) < 4.0 kPa) and high-quality effluent (COD removal > 98.2 %, protein removal > 97.7 %, and polysaccharide removal > 98.5 %). The highest methane productivity was up to 38.0 ± 3.1 mL/Lreactor/d at the applied voltage of 0.8 V with bound-EPS solubilization, 107.6 % higher than that of the control stage (18.3 ± 2.4 mL/Lreactor/d). Morphological and multiplex fluorescence labeling analyses revealed higher fluorescence intensities of proteins, polysaccharides, total cells and lipids on the surface of the fouling layer. In contrast, the interior exhibited increased compression density and reduced activity, likely attributable to compression effect. Under the synergistic influence of the electric field and bound-EPS solubilization, biomass characteristics exhibited a reduced propensity for membrane fouling. Furthermore, the bio-electrochemical regulation enhanced the electroactivity of microbial aggregates and enriched functional microorganisms, thereby promoting biofilm growth and direct interspecies electron transfer. Additionally, the potential hydrogenotrophic and methylotrophic methanogenesis pathways were enhanced at the cathode and anode surfaces, thereby increasing CH₄ productivity. The random forest-based machine learning model analyzed the nonlinear contributions of EPS characteristics on methane productivity and TMP values, achieving R² values of 0.879 and 0.848, respectively. Shapley additive explanations (SHAP) analysis indicated that S-EPSPS and S-EPSPN were the most critical factors affecting CH₄ productivity and membrane fouling, respectively. Partial dependence plot analysis further verified the marginal and interaction effects of different EPS layers on these outcomes. By combining continuous operation with interpretable machine learning algorithms, this study unveils the intricate impacts of EPS characteristics on methane productivity and membrane fouling behaviors, and provides new insights into sludge bound-EPS solubilization in EC-AnMBR.

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.

In situ cleaning of foulants by gas scouring on the membrane-electrode in an electro-membrane bioreactor

Low-maintenance membrane cleaning is essential for the stable operation of membrane bioreactors. This work proposes an in-situ electrical-cleaning method using an electro-MBR. When the applied bias was transiently increased, the membrane flux recovered rapidly because of the scouring effect from gas evolution reactions. The exfoliation of the cake layer induced by gas scouring played a major role in mitigating membrane fouling, recovering the transmembrane pressure (TMP) by 88.6 % under optimal conditions. Membrane modules did not require replacement during the operation period due to the efficacy of electrical cleaning, with the TMP varying between 37.5 % and 62.5 % of the ultimate pressure requiring change of the membrane modules. Despite the increase in power consumption of 0.66 Wh·m-3 due to the additional applied bias, there was no need for chemical additives or manual maintenance. Therefore, the electrical cleaning method enhanced the service life and reduced the maintenance costs of the electro-MBR.

Impacts of electric field-magnetic powder coupled membrane bioreactor on phenol wastewater treatment: Performance, synergistic mechanism, antibiotic resistance genes, and eco-environmental benefit evaluation

A novel electric field-magnetic powder coupled membrane bioreactor (EM-MBR) was constructed, which was superior on improvement of phenol treatment performance and sludge characteristics, and mitigation of membrane fouling. EM-MBR enhanced the phenol degradation via the improvement activity of phenol degrading enzymes. The EPS contents and SVI of EM-MBR were significantly reduced by 49.3 % and 58.7 % than that of the conventional MBR, respectively. Moreover, EM-MBR successfully reduced fouling rate by 57.0 %, delaying the membrane resistance. The EPS contents were positively correlated with the SVI and fouling rate, implying that the sludge settleability was strengthened by improving the properties of EPS with the assistance of electromagnetic, thus mitigating the membrane fouling. Microbial co-occurrence network demonstrated that EM-MBR enriched phenol-degrading and EPS-degrading genera correlated to Fe redox cycle. Furthermore, the activation of the antioxidant system in the EM-MBR resulted in the suppression of reactive oxygen species (ROS) generation, consequently impeding the dissemination of antibiotic resistance genes (ARGs). Co-occurrence patterns of MGEs and ARGs revealed that intercellular binding facilitated by ist and Integrase may account for the horizontal transfer of ARGs. The reduction of unit capital costs (15.63 %), running costs (53.00 %), and total average carbon emissions (15.18 %) indicated that EM-MBR was environmentally beneficial.

Performance analysis of microbial fuel cell - membrane bioreactor with reduced graphene oxide enhanced polypyrrole conductive ceramic membrane: Wastewater treatment, membrane fouling and microbial community under high salinity

The application of membrane bioreactor (MBR) in high salinity wastewater treatment was mainly hindered by membrane fouling. Microbial fuel cell (MFC)-MBR coupling system was established to alleviate membrane fouling and save energy. Reduced graphene oxide/polypyrrole ceramic membrane (rGO/PPy CM) with high conductivity and stability was innovatively placed in MFC-MBRs as both cathode and filter, with PPy CM, rGO/PPy CM and CM placed in other reactors. MFC-MBR (rGO/PPy) and MFC-MBR (PPy) achieved higher pollutant removal efficiencies (90.73 % and 90.45 % for TOC, 87.22 % and 86.56 % for NH4+-N, respectively) and superior anti-fouling performance (1.86 and 1.93 kPa/d for average membrane fouling rates) than both conventional MBRs (CMBRs). The stable voltage generation was around 287 and 242 mV, respectively. Through high throughput sequencing, electric field showed a positive correlation with the abundance and activity of most dominant phylum (Bacteroidetes, Chloroflexi, Actinobacteria, and Firmicutes) and functional genes (amoA, hao, narG, napA, nirK, norB, and nosZ), thereby improving pollutant removal efficiency. The higher conductivity of rGO/PPy CM resulted in enhanced electric field intensity, leading to superior performance of anti-fouling and pollutant removal. This study inventively explored the effects of conductive membrane property on electricity generation performance, microbial community, pollutant removal and membrane fouling, providing theoretical support for the selection of electrode materials in MFC-MBR.

Research progress of electrically-enhanced membrane bioreactor (EMBR) in pollutants removal and membrane fouling alleviation

Membrane bioreactor (MBR), as a biological unit for wastewater treatment, has been proven to have the advantages of simple structure and high pollutant removal rate. However, membrane fouling limits its wide application, and it is crucial to adopt effective membrane fouling control methods. As a new type of membrane fouling control technology, electrically-enhanced MBR (EMBR) has attracted more interest recently. It uses the driving force of electric field to make pollutants flocculate or move away from the membrane surface to achieve the purpose of inhibiting membrane fouling. This paper expounds the configuration of EMBR in recent years, including the location of membrane components, the way of electric field application and the selection of electrode and membrane materials, and provides the latest development information in various aspects. The enhanced effect of electric field on the removal of comprehensive and refractory pollutants is outlined in detail. And from the perspective of sludge properties (EPS, SMP, sludge particle size, zeta potential and microbial activity), the influence of electric field on sludge characteristics and the relationship between the changes of sludge properties in EMBR and membrane fouling are discussed. Moreover, the electrochemical mechanisms of electric field alleviating membrane fouling are elucidated from electrophoresis, electrostatic repulsion, electroflocculation, electroosmosis, and electrochemical oxidation, and the regeneration and stability of EMBR are assessed. The existing challenges and future research directions are also proposed. This review could provide theoretical guidance and further studies for subsequent topic, and promoting the wide engineering applications of EMBR.

Study on the performance and mechanism of bio-electrochemical system to mitigate membrane fouling in bioreactors

To alleviate membrane fouling, a membrane of the membrane bioreactor was directly used as the anode of the bio-electrochemical system. On the 14th day, the control group had blocked, while the experimental group with a current of 0.44 mA, the increase in ΔTMP was only 2.2 kPa. The polysaccharide and protein concentrations in the open-circuit group were 4.2 and 2.9 times higher than those in the closed-circuit group, respectively. Three-dimensional fluorescence spectroscopy and gas chromatography mass spectrometry showed that most of the deposition in the control group contained high-molecular-weight compounds, especially long-chain ester derivatives, phenols, and complex hydrocarbons, whereas the experimental group was the opposite. Therefore, current (electrons) can change the composition of the cake layer. High-throughput sequencing indicated that a significantly higher abundance of electroactive microorganisms on the experimental than control group. Two-dimensional correlation spectroscopy showed that electrons promote the degradation of polysaccharides, thereby alleviating membrane fouling.

Performance enhancement, membrane fouling mitigation and eco-friendly strategy by electric field coupled membrane bioreactor for treating mariculture wastewater

An eco-friendly strategy for mariculture wastewater treatment using an electric field attached membrane bioreactor (E-MBR) was evaluated and compared with a conventional membrane bioreactor (C-MBR). The removal efficiencies of total nitrogen (TN) and chemical oxygen demand (COD) increased significantly and the membrane fouling rate reduced by 44.8% in the E-MBR. The underlying mechanisms included the enriched nitrifiers and denitrifiers, the enhanced salinity-resistance, the increased activities and upregulated genes of key enzymes involved in nitrification and denitrification for improving the performance of mariculture wastewater treatment, and the enriched extracellular polymeric substance (EPS)-degrading genera, the downregulated EPS biosynthesis genes, the repressed biofilm-forming bacteria, the enhanced zeta potential absolute value and the generated H₂O₂ for membrane fouling mitigation by electrical stimulation. Compared with the C-MBR, the energy consumption, carbon emissions, and nitrogen footprint were reduced. These findings provide novel insights into mariculture wastewater treatment using an applied electric field.

Efficient use of electrons in a double-anode microbial fuel cell-biofilm electrode reactor self-powered coupled system for degradation of azo dyes

A coupled system consisting of a double-anode microbial fuel cell (MFC) unit and a biofilm electrode reactor (BER) has been applied to degrade the azo dye reactive brilliant red X-3B. In this system, the MFC effluent was used as the input of the BER. The MFC preliminarily degraded X-3B while generating electricity, and the BER obtained electrons from the MFC through the external circuit to continue degrading pollutants without the need for an external power supply. The X-3B removal efficiency was 41.93% higher in the coupled system than the control when the X-3B concentration was 3000 mg/L. The analysis of intermediate products showed that the azo bond of X-3B broke in the MFC, generating a large number of complex intermediates such as anthraquinones, which were further degraded into simple organic compounds in the BER. Meanwhile, the abundance of microbial taxa related to the degradation of refractory organics in the MFC was high, as was that of microbial taxa related to the degradation of simple organics in the BER. Furthermore, the abundance of microorganisms related to power generation in the MFC increased. These results provided an efficient strategy for improving electron utilization efficiency in the coupling system of bioelectrochemical system.

Biodegradation performance and anti-fouling mechanism of an ICME/electro-biocarriers-MBR system in livestock wastewater (antibiotic-containing) treatment

Livestock wastewater is an important reservoir of antibiotic resistance genes (ARGs) and antibiotic residues. Membrane fouling is one of the most challenging problems confining the operation and application of membrane bioreactor (MBR). In this work, a novel iron-carbon micro-electrolysis (ICME)/electro-biocarriers-MBR system was established to explore the performance of pollutant removal and anti-fouling for an actual livestock wastewater. A light-weight porous ceramsite (bulk density 0.98 g/cm³) was used as the MBR biocarriers. The electrons generated from iron corrosion in the ICME tank traveled through external wires to the stainless steel membrane modules of MBR and the protons were transferred from the MBR tank to the ICME tank through a salt bridge, thus producing a spontaneous electric field. Under the optimized conditions, the system exhibited chemical oxygen demand removal of 76.0%, total suspended solids removal of 100%, antibiotic removal of 86.4%, NH₄⁺-N removal of 91.1%, and ARGs reduction of 6-8 orders of magnitude. The quality of the final effluent can reach the national Class I-A discharge criteria. Adding ceramsite could not only effectively improve biodegradation performance but also alleviate membrane fouling through the migration and enrichment of microbial flora to the ceramsite. The self-generated electric field had no significant improvement effect on pollutant removal, but exhibited good anti-membrane fouling behavior which could be ascribed to (i) oxidization of membrane foulants by the electrochemical products (such as H₂O₂ and •OH radicals), and (ii) electrostatic repulsion of negatively charged foulants and bacterial cells. The bacterial community structure and diversity were studied using high-throughput pyrosequencing, and the results demonstrated the roles of electric field and biocarriers in enrichment of anti-fouling communities and repulsion of biofouling-creating communities.

Effect of addition sites on bioaugmentation of tea polyphenols-NZVI/PE composite packing: Nitrogen removal efficiency and service life

Although efficient improvement of the nitrogen removal from wastewater by adding iron was achieved in wastewater process, the influence mechanism of addition sites is unclear. The study was based on the A/O-MBR treating simulated domestic wastewater, and tea polyphenol-nano zero-valent iron/polyethylene packing (TP-NZVI/PE) was added into the anoxic tank, aerobic tank and membrane effluent end of the process, respectively. The effect of the different addition sites on the nitrogen removal performance of A/O-MBR was investigated. Combine with the corrosion rate of NZVI on the packing surface to optimize TP-NZVI/PE addition site. The enhancement mechanism of TP-NZVI/PE under different addition site was explored through the calculation of the materials balance (carbon, nitrogen, phosphorus). The results showed that the pollutant removal of A/O-MBR was significantly increased with the TP-NZVI/PE added. In particular, the TP-NZVI/PE was added into the aerobic tank, and the pollutant removal rate was increased 31.71% (TN) and 53.00% (total phosphorus), respectively. Meanwhile, the service life of TP-NZVI/PE in the aerobic tank was 66 days. The anti-oxidation and dispersion of NZVI was improved with the encapsulation of tea polyphenols and support of packing, and it also played a certain slow-release effect, so that the service life of NZVI was further prolonged in aerobic condition. Combined with the material balance analysis, the result showed that the environmental structure made diversity in the aerobic tank by added the TP-NZVI/PE, and the simultaneous nitrification and denitrification process was achieved. The dependence of the denitrification process on the carbon source was greatly reduced. Besides, it promoted the adsorption and chemical precipitation process of the system for phosphor pollutant and achieved the denitrifying phosphorus removal performance.

Simultaneous shortcut nitrification and denitrification in a hybrid membrane aerated biofilms reactor (H-MBfR) for nitrogen removal from low COD/N wastewater

The residues of nitrogen contaminants due to insufficient organic carbon sources in sewage has always been the main problem faced by wastewater treatment plants in the process of nitrogen removal. In this study, simultaneous shortcut nitrification and denitrification (SND) was achieved in the hybrid membrane aerated biofilm reactor (H-MBfR) for treating low COD/N ratio (∼x223C 4: 1) wastewater. The effects of the aeration pressure and the influent COD/N ratio in H-MBfR were investigated and further optimized by the response surface methodology (RSM). By controlling the dissolved oxygen to achieve SND, the removal efficiencies of NH₄⁺-N, COD and TN of low COD/N ratio wastewater reached maximum values of 95.52%, 96.61% and 72.23%, respectively. Microbial community analysis showed that the influent COD/N ratio had an obvious influence on the microbial community structure. In particular, ammonia oxidizing bacteria (AOB) and denitrifying bacteria had a good commensalism when the COD/N ratio was 4.3. Compared to control reactor, the analysis of membrane bio-fouling showed that H-MBfR has a lower amount of extracellular polymeric substance (EPS) on membrane and a low concentration of MLSS in bulk liquid, which is helpful for the longer-term operation of H-MBfR.

Effects of different Ca2+ behavior patterns in the electric field on membrane fouling formation and removal of trace organic compounds

The effects of Ca²⁺ on membrane fouling and trace organic compounds (TrOCs) removal in an electric field-assisted microfiltration system were investigated in the presence of Na⁺ alone for comparison. In the electric field, negatively charged bovine serum albumin (BSA) migrated towards the anode far away from the membrane surface, resulting in a 42.9% transmembrane pressure (TMP) reduction in the presence of Na⁺ at 1.5 V. In contrast, because of the stronger charge shielding of Ca²⁺, the electrophoretic migration of BSA was limited and led to a neglectable effect of the electric field (1.5 V) on membrane fouling. However, under 3 V applied voltage, the synergistic effects of electrochemical oxidation and bridging interaction between Ca²⁺ and BSA promoted the formation of denser settleable flocs and a thinner porous cake layer, which alleviated membrane fouling with a 64.5% decrease in TMP and nearly 100% BSA removal. The TrOCs elimination increased with voltage and reached 29.4%-80.4% at 3 V. The electric field could prolong the contact between TrOCs and strong oxidants generated on the anode, which enhanced the TrOCs removal. However, a stronger charge shielding ability of Ca²⁺ weakened the electric field force and thus lowered the TrOCs removal.

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∙Q_in), 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 Q_r = 2.6∙Q_in, in comparison with Q_r = 4.3∙Q_in, 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.

Biological-based control strategies for MBR membrane biofouling: a review

Membrane bioreactor (MBR) technology has been paid extensive attention for wastewater treatment because of its advantages of high effluent quality and minimized occupation space and sludge production. However, the membrane fouling is always an inevitable problem, which causes high operation and maintenance costs and prevents the wide use of MBR technology. The membrane biofouling is the most complicated and has relatively slow progress among all types of fouling. In recent years, many membrane biofouling control methods have been developed. Different from the physical or chemical methods, the biological-based strategies are not only more effective for membrane biofouling control, but also milder and more environment-friendly and, therefore, have been increasingly employed. This paper mainly focuses on the mechanism, unique advantages and development of biological-based control strategies for MBR membrane biofouling such as quorum quenching, uncoupling, flocculants and so on. The paper summarizes the up-to-date development of membrane biofouling control strategies, emphasizes the advantages and promising potential of biological-based ones, and points out the direction for future studies.

Degradation of organic pollutants by intimately coupling photocatalytic materials with microbes: a review

With the rapid development of industry and agriculture, large amounts of organic pollutants have been released into the environment. Consequently, the degradation of refractory organic pollutants has become one of the toughest challenges in remediation. To solve this problem, intimate coupling of photocatalysis and biodegradation (ICPB) technology, which allows the simultaneous action of photocatalysis and biodegradation and thus integrates the advantages of photocatalytic reactions and biological treatments, was developed recently. ICPB consists mainly of porous carriers, photocatalysts, biofilms, and an illuminated reactor. Under illumination, photocatalysts on the surface of the carriers convert refractory pollutants into biodegradable products through photocatalytic reactions, after which these products are completely degraded by the biofilms cultivated in the carriers. Additionally, the biofilms are protected by the carriers from the harmful light and free radicals generated by the photocatalyst. Compared with traditional technologies, ICPB remarkably improves the degradation efficiency and reduces the cost of bioremediation. In this review, we introduce the origin and mechanisms of ICPB, discuss the development of reactors, carriers, photocatalysts, and biofilms used in ICPB, and summarize the applications of ICPB to treat organic pollutants. Finally, gaps in this research as well as future perspectives are discussed.

Evaluation of the fouling potential of sludge in a membrane bioreactor integrated with microbial fuel cell

This study focused on the fouling characteristics evaluation of the sludge in a membrane bioreactor integrated with microbial fuel cell (MFC-MBR) to reveal the mechanisms of membrane fouling mitigation. The filtration of soluble microbial products (SMPs) in MFC-MBR showed lower flux decline rate than those in the control system (C-MBR). Based on the extended Derjaguin-Landau-Verwey-Overbeek analysis, decreases in free energies of adhesion between the SMPs and clean membrane or SMP-fouled membrane were observed in MFC-MBR. When approaching the clean membrane or SMP-fouled membrane, the SMPs in MFC-MBR had to overcome a higher energy barrier compared to those in C-MBR, indicating the inhibition of adsorption of SMPs on the membrane surface in MFC-MBR. Additionally, sludge flocs in MFC-MBR exhibited lower hydrophobicity and were less negative surface charged in comparison to those in the C-MBR. In MFC-MBR, the sludge flocs approaching the clean membrane, SMP-fouled membrane and cake layer all experienced higher energy barriers and lower secondary energy minimums compared to those in C-MBR, exhibiting the lower potential of cake layer formation. These results confirmed that decreases of the fouling potentials of SMPs and sludge flocs were essential for the membrane fouling mitigation in the MFC-MBR.

Self-generated electric field to suppress sludge production and fouling development in a membrane bioreactor for wastewater treatment

Compared with conventional sludge reduction techniques, electric field assisted membrane bioreactor (MBR) is a cost-effective technology with low power consumption. In this study, spontaneous electric field without extra power supply was introduced into the MBR for wastewater treatment to complete the in situ sludge reduction and membrane fouling mitigation. A novel spontaneous electric field membrane bioreactor (SEF-MBR) equipped with Cu-nanowires (Cu-NWs) conductive microfiltration membrane as cathode was established by using baffles to form anaerobic and aerobic tanks. SEF-MBR 1 with external resistance of 500 Ω maintained a highest electric field intensity of 1.25 mV/cm. Compared with Control-MBR, the reduction of mixed liquor suspended solids (MLSS) growth rate, extracellular polymeric substances (EPS) growth rate, total cell number and water content of SEF-MBR 1 reached 50.0%, 43.0%, 37.1% and 6.4%, respectively. After 43 days operation, SEF-MBR 1 obtained the minimum MLSS concentration and sludge volume, which were 29.9% and 83.8% lower than that of it in Control-MBR. The total biovolume of the contaminants (i.e., EPS and cells) on the membrane surface of SEF-MBR 1 was 68.8% lower than that of Control-MBR. SEF-MBR 1 exhibited a better performance with a lower membrane fouling rate (0.58 kPa/d) than Control-MBR (1.09 kPa/d). Economic analysis showed that a total of 148.1 kWh/m³ of electric energy was saved in the SEF-MBR 1. This technology reduced the sludge production in the sewage biological treatment process, which realized the sludge reduction had a positive impact on the membrane fouling mitigation.