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[Display omitted] • Applying electric field suppressed membrane fouling rate of AnMBR. • Applying electric field decreased the deposition of organic foulants on membrane. • Contribution of electrophoresis to membrane fouling suppression was quantified. • Applying electric field improved mixed liquor filterability of AnMBR. • Mechanism of mixed liquor filterability improvement was analyzed. Anaerobic membrane bioreactor (AnMBR) is a promising technology for wastewater treatment. However, membrane fouling as an inevitable challenge restricts its application. Recently novel membrane fouling control technology by applying electric field in AnMBR showed its economics and effectiveness. Nevertheless, the mechanism of fouling suppression is still unclear, limiting the development of this technology. In this study, electro-AnMBR was constructed. Long-term running showed that applying electric field of 0.5 V suppressed the membrane fouling evolution rate by nearly 23% and reduced the organic foulants on membrane by nearly 10%. To clarify the mechanism of fouling suppression, the contribution of electrophoresis to membrane fouling suppression was quantified by theoretical calculation for the first time. Results showed that electrophoresis was approximately equivalent to backwash with a flux of 0.56 L/(m2·h). Besides, impact of electric field on mixed liquor filterability of AnMBR was first investigated by dead-end filtration. Results presented that electric field reduced the filtration resistance of mixed liquor by nearly 77%. Then mixed liquor properties analysis, electrochemical oxidation simulation tests and metagenomic analysis revealed that electric field might improve mixed liquor filterability by bioelectrochemical oxidation. Finally, novel mechanism of electric field suppressed membrane fouling was elucidated, including electrophoresis to drive off the foulants and mixed liquor filterability improvement. This study might contribute to better understanding for membrane fouling control by applying electric field in AnMBR, and was meaningful for technical development. [ABSTRACT FROM AUTHOR]

Nitrite-dependent anaerobic methane-oxidizing (n-damo) process has a promising prospect in anaerobic wastewater treatment, utilizing methane as the sole electron source to remove nitrite. However, the metabolic activity of n-damo bacteria is too low for practical application. This study aimed to stimulate n-damo process by introducing conductive nano-magnetite and/or electron shuttle anthraquinone-2,6-disulfonate (AQDS), and also set a comparative treatment of adding insulated ferrihydrite. The results showed that the nitrite reduction rate was enhanced the most significantly in treatment with nano-magnetite, approximately 1.6 times higher than that of the control without any supplement. While ferrihydrite application showed an adverse effect on n-damo process. The well-known aerobic methane oxidizer Methylomonas spp. was found to be enriched under n-damo condition with the supplementation of nano-magnetite and/or AQDS, but abundance of n-damo bacteria did not exhibit significant increase. It was hypothesized that Methylomonas spp. could be survived under anaerobic n-damo condition using oxygen produced by n-damo bacteria for the self-growth, and the nitrite reduction could be promoted through the enhancement of microbial interspecies electron transfer triggered by the introduction of conductive materials. It opens a new direction for the stimulation of n-damo activity, which needs more evidences to verify the hypothetic mechanism. • Nano-magnetite and/or AQDS stimulated the nitrite reduction of n-damo process. • Stimulation depended on acceleration of electron transfer via conductive materials. • N-damo pmoA and nod genes kept constant among different treatments. • Methylomonas was selectively enriched via nano-magnetite and/or AQDS. • A novel synergistic relationship of n-damo bacteria and Methylomonas was proposed. [ABSTRACT FROM AUTHOR]

Biogas sparging is one of the most commonly used strategies for membrane fouling control in anaerobic membrane bioreactors (AnMBR). However, as a cost-effective sparging pattern, high/low alternate sparging mode was seldom studied, not to mention at a quantitative level. In this study, we systematically assessed the impacts of various parameters of gas sparging (intensity, duration and interval/frequency) on membrane fouling characteristics, on the basis of orthogonal tests coupled with statistical analysis of variance and covariance. The specific gas demand in the high-intensity phase (SGD H) was identified as the key factor impacting the overall fouling rate and stagewise rate constants (K p ' and K c ' for pore blocking and cake layer stages respectively) with negative correlation. The product of SGD H and time, i.e. the accumulative gas amount in the high-intensity phase (Q H), was identified as the key factor affecting foulant layer reversibility (η) and specific resistance (α), with logarithmic models established in terms of log Q H versus log η and log α. The validity and robustness of the quantitative models with definite physical meaning were evaluated via Monte Carlo simulation of the regression. The underlying mechanisms were explained from the perspective that hydrodynamic conditions influence mixed liquor and foulant properties (particle size distribution, microbial products amount and component) and, hence, affect fouling rates and foulant layer properties, with a panorama of the interrelated factors and properties delineated by multivariate analysis. This study is expected to provide a quantitative basis for the design of gas sparging conditions, under which sustainable operation of AnMBR could be achieved with the lowest energy consumption. Image 1 • SGD H was the key factor impacting overall and stagewise apparent fouling rate. • The overall and stagewise fouling rate constants had negative correlation with SGD H. • Q H was the key factor affecting foulant layer reversibility and specific resistance. • Reversibility increased and specific resistance decreased with increasing Q H. • Hydrodynamic conditions affect fouling by altering MLSS and foulant properties. [ABSTRACT FROM AUTHOR]

• ZVI showed its versatility for improving the performances of AnMBR. • Applying ZVI enhanced COD and TP removal, H 2 S removal. • Applying ZVI without electric field suppressed membrane fouling. • The occurrences of the iron ions in AnMBR were studied. • Iron ions releasing rate of ZVI is vital parameter for enhanced performances. Comprehensive insight into the long-term impact of applying zero valent iron (ZVI) in anaerobic membrane reactor (AnMBR) was conducted here. ZVI showed its versatility for enhancing the performances of AnMBR including COD and TP removal, H 2 S removal and membrane fouling suppression in this study, and the iron ions releasing rate of ZVI had great influence on the enhancing performances. Two iron ions releasing states were used including "with electric field" and "without electric field". Applying electric field could boost iron ions releasing rate by 12 times here. COD removal rate increased by 3% via coagulation effect with and without electric field. H 2 S in biogas was decreased from >500 ppm to <60 ppm via the formation of FeS precipitation with and without electric field. Applying ZVI with electric field increased the removal rate of TP by 50% via the formation of Fe 3 (PO 4) 2 , but applying ZVI without electric field did not change the TP removal due to the insufficient iron ions. Utilizing ZVI without electric field suppressed the membrane fouling rate by 20% via the improvement of mixed liquor filterability, however utilizing ZVI with electric field accelerated the membrane fouling rate by 17 times due to the formation of dense Fe-enriched fouling layer with server inorganic and organic fouling. This study provided a novel approach to improve the performances of AnMBR by utilizing versatile ZVI. Meanwhile, this study enclosed that the iron ions releasing rate of ZVI is vital technical parameter for its application. [ABSTRACT FROM AUTHOR]