New insight into the membrane fouling of anaerobic membrane bioreactors treating sewage: Physicochemical and biological characterization of cake and gel layers

Recovering nutrients and unblocking the cake layer of an electrochemical anaerobic membrane bioreactor

The sustainable development strategy shifts water treatment from pollution removal to resource recovery. Here, an electrochemical resource-recovery anaerobic membrane bioreactor (eRAnMBR) that employed a magnesium plate and conductive membrane as dual anodes is presented and shows excellent performance in carbon, nitrogen, and phosphorus recovery, as well as 95% membrane anti-fouling. The Mg2+ released alters the physicochemical properties of sludge, unblocking the cake layer, and recovers ammonium and phosphate, yielding 60.64% purity and 0.08 g d-1 struvite deposited onto cathode to be separated from sludge. The enhanced direct interspecies electron transfer, along with hydrogen evolution and alkalinity increase due to the electrochemical reactions, significantly increase methane yield and purity (93.97%) of the eRAnMBR. This increased internal energy can cover the additional electricity and electrode consumption. This integrated eRAnMBR reactor boasts the benefits of short process, low maintenance, and low carbon footprint, introducing a concept for the next generation of wastewater treatment.

Anaerobic dynamic membrane bioreactor treating sulfamethoxazole wastewater: advantages of dynamic membrane and its fouling mechanism

Discharge of improperly treated sulfamethoxazole (SMX) wastewater seriously threats environmental security and public health. Anaerobic dynamic membrane bioreactors (AnDMBRs) technology would be cost-effective for SMX wastewater treatment, considering its low cost and satisfactory treatment efficiency. The performance of AnDMBR, though demonstrated to be excellent in treating many types of wastewaters, was for the first time investigated for treating SMX wastewater. Particular efforts were devoted to elucidating the advantages of dynamic membrane (DM) and the governing mechanism responsible for DM fouling with the presence of SMX. The threshold SMX concentration for AnDMBR was found to be 90 mg/L and the AnDMBR exhibited excellent removal efficiency of COD (90.91 %) and SMX (88.95 %) as well as satisfactory acute toxicity reduction rate (88.84 %). It was noteworthy that the DM made indispensable contributions to the removal of COD (14.26 %) and SMX (22.20 %) as well as the acute reduction of toxicity (25.81 %). The presence of SMX significantly accelerated DM fouling mainly by increasing its specific resistance, which was attributed to the increased content of small particles, high-valence metal ions and EPS content (mainly hydrophobic proteins), resulting in a denser DM structure with lower porosity. Besides, the biofouling-related bacteria (Firmicutes) was found to be enriched in the DM with the presence of SMX.

Activating Biocake Communities Retards Jumps of Transmembrane Pressure in Membrane Bioreactors

Sudden jump of transmembrane pressure (TMP) in membrane bioreactors (MBRs), associated with abrupt aggravation of membrane fouling, limits practical applications of MBRs and calls for effective mitigation strategies. While the TMP jump is generally related to the bacterial activity of biocakes, the mechanisms underlying the TMP jump remain unclear. Herein, we conducted various backwash protocols with different nutrient (e.g., nitrate and sodium acetate) loadings on fouled membranes in MBRs to reveal the critical role of bacterial activity of biocakes for the TMP jump. The filtration tests showed a lower TMP jump rate for the membrane backwashed with a nutrient solution (a mixture of 180 mg/L NaNO3 and 200 mg/L NaAc, averaged at 1.40 kPa/d) than that backwashed with tap water (averaged at 3.56 kPa/d), implying that TMP jump could be efficiently mitigated by providing sufficient nutrients to biocake bacteria. The characterization of biocakes showed that high-nutrient solution backwash considerably increased bacterial viability and activity, while considerably reducing biomolecule accumulation on membranes. The keystone taxa (e.g., g_Aeromonas and o_Chitinophagaceae) in the network of nutrient-enriched biocake communities were involved in nitrate reduction and biomolecule degradation. Ecological null model analyses revealed that the deterministic manner mainly shaped biocake communities with high-nutrient availability. Overall, this study highlights the significance of the bacterial activity of biocakes for TMP development and provides potential alternatives for controlling membrane fouling.

Effectiveness of cloth media filters on mitigating membrane fouling in anaerobic filter membrane bioreactors

Membrane fouling is a persistent challenge that has impeded the broader application of anaerobic membrane bioreactors (AnMBRs). To mitigate membrane fouling, between the outlet of the UASB anaerobic bioreactor and the PVDF membrane to form the anaerobic filter membrane bioreactor (AnFMBR) system. Through comprehensive experiments, the optimal pore size for cloth filters was determined to be 50 μm. A comprehensive assessment over 140 days of operation shows that the novel AnFMBR had significantly greater resistance to membrane pollution than the traditional AnMBR. The AnFMBR system membrane tank exhibited lower mixed liquor suspended solid and mixed liquor volatile suspended solid concentrations, smaller sludge particle sizes, increased hydrophilicity of sludge flocs, and optimized microbial community distribution compared to those of conventional AnMBRs. The total solids foulant accumulation rate in the AnMBR was 5.1 g/m2/day, while in the AnFMBR, the rate was 2.4 g/m2/day, marking a 53.7 % decrease in fouling rate for the AnFMBR compared with the AnMBR. This decrease indicates that integrating the filtration assembly significantly lowered the rate of solid foulant accumulation on the membrane surface, primarily by controlling the buildup of solid foulants in the cake layer, thereby alleviating membrane fouling. AnFMBR compared to AnMBR, the membrane fouling rate halved, effectively doubled the interval between membrane cleaning from seven days, as observed in the AnMBR system, to fourteen days. These findings underscore the potential of integrating cloth media filters into AnMBRs to improve operational efficiency, economic viability, and sustainability.

Removal of RNA viruses from swine wastewater using anaerobic membrane bioreactor: Performance and mechanisms

The effective removal of viruses from swine wastewater using anaerobic membrane bioreactor (AnMBR) is vital to ecological safety. However, most studies have focused only on disinfectants, whereas the capabilities of the treatment process have not been investigated. In this study, the performance and mechanism of an AnMBR in the removal of porcine hepatitis E virus (HEV), porcine kobuvirus (PKoV), porcine epidemic diarrhea virus (PEDV), and transmissible gastroenteritis coronavirus (TGEV) are systematically investigated. The results show that the AnMBR effectively removes the four viruses, with average removal efficiencies of 1.62, 3.05, 2.41, and 1.34 log for HEV, PKoV, PEDV and TGEV, respectively. Biomass adsorption contributes primarily to the total virus removal in the initial stage of reactor operation, with contributions to HEV and PKoV removal exceeding 71.7 % and 68.2 %, respectively. When the membrane is fouled, membrane rejection dominated virus removal. The membrane rejection contribution test shows the significant contribution of membrane pore foulants (23-76 %). Correlation analysis shows that the surface characteristics and size differences of the four viruses contribute primarily to their different effects on biomass adsorption and membrane rejection. This study provides technical guidance for viral removal during the treatment of high-concentration swine wastewater using an AnMBR.

Biogas upgrading and membrane anti-fouling mechanisms in electrochemical anaerobic membrane bioreactor (EC-AnMBR): Focusing on spatio-temporal distribution of metabolic functionality of microorganisms

Electrochemical anaerobic membrane bioreactor (EC-AnMBR) by integrating a composite anodic membrane (CAM), represents an effective method for promoting methanogenic performance and mitigating membrane fouling. However, the development and formation of electroactive biofilm on CAM, and the spatio-temporal distribution of key functional microorganisms, especially the degradation mechanism of organic pollutants in metabolic pathways were not well documented. In this work, two AnMBR systems (EC-AnMBR and traditional AnMBR) were constructed and operated to identify the role of CAM in metabolic pathway on biogas upgrading and mitigation of membrane fouling. The methane yield of EC-AnMBR at HRT of 20 days was 217.1 ± 25.6 mL-CH4/g COD, about 32.1 % higher compared to the traditional AnMBR. The 16S rRNA analysis revealed that the EC-AnMBR significantly promoted the growth of hydrolysis bacteria (Lactobacillus and SJA-15) and methanogenic archaea (Methanosaeta and Methanobacterium). Metagenomic analysis revealed that the EC-AnMBR promotes the upregulation of functional genes involved in carbohydrate metabolism (gap and kor) and methane metabolism (mtr, mcr, and hdr), improving the degradation of soluble microbial products (SMPs)/extracellular polymeric substances (EPS) on the CAM and enhancing the methanogens activity on the cathode. Moreover, CAM biofilm exhibits heterogeneity in the degradation of organic pollutants along its vertical depth. The bacteria with high hydrolyzing ability accumulated in the upper part, driving the feedstock degradation for higher starch, sucrose and galactose metabolism. A three-dimensional mesh-like cake structure with larger pores was formed as a biofilter in the middle and lower part of CAM, where the electroactive Geobacter sulfurreducens had high capabilities to directly store and transfer electrons for the degradation of organic pollutants. This outcome will further contribute to the comprehension of the metabolic mechanisms of CAM module on membrane fouling control and organic solid waste treatment and disposal.

Synergistic effects of biochar addition and filtration mode optimization on mitigating membrane fouling in high-solid anaerobic membrane bioreactors

In this study, a high-solid anaerobic membrane bioreactor was established for treating food waste, and membrane fouling rates were regulated through multivariate modulation. The anaerobic membrane bioreactor operated stably at a high organic loading rate of 28.75 gCOD/L/d achieved a methane production rate of 8.03 ± 0.61 L/L/d. Experimental findings revealed that the most effective control of membrane fouling was achieved at a filtration- relaxation ratio (F/R) of 10/90 s. This indicates that a higher relaxation frequency provided improved the mitigation of membrane fouling. Compared with single F/R modulation, the combined modulation of biochar and F/R provided enhanced control over membrane fouling. Moreover, the addition of biochar altered the sludge properties of the reactor, thereby preventing the formation of a dense cake layer. Additionally, biochar enhanced the sheer force of the fluid on the membrane surface and facilitated the separation of pollutants during the relaxation stage, thereby contributing to improved control of membrane fouling.

Deciphering the behavior and potential mechanism of biochar at different pyrolysis temperatures to alleviate membrane biofouling

Biofouling limits applications of membrane technology in wastewater treatment, but dosing additives to membrane tanks is an effective method to alleviate biofouling. In this study, biochar derived from corncob and pyrolyzed at 300, 500, and 700°C was dosed to determine the underlying anti-biofouling mechanism. The effects of the biochar on the membrane properties and foulant behavior were systematically investigated. The results showed that biochar delayed the occurrence of the fouling transition (0.5-3.0 h), and decreased the flux decline rate, thus achieving a higher water flux (3.1-3.7 times of the control group). Biochar altered membrane surface properties, and increased the membrane surface charge, roughness, and hydrophilicity, which all contributed to higher membrane permeability. Moreover, adding biochar reduced the number of foulants in the fouling layer, particularly protein substances. The flux model fit and the XDLVO theory further revealed the mitigating effect of biochar on membrane biofouling. At the initial intermediate-blocking stage, the effect of biochar on membrane fouling was determined by its properties, and adsorption capacity to the foulants, BC500 presented the best mitigation performance. At the later cake-filtration stage, the role of biochar in membrane fouling was strongly associated with protein content in the fouling layer, and the minimum rate of flux decline occurred in BC300. This study promotes the understanding and development of biochar to alleviate membrane biofouling.

Insight into the effects and mechanism of cellulose and hemicellulose on anaerobic digestion in a CSTR-AnMBR system during swine wastewater treatment

The cellulose and hemicellulose content in swine wastewater significantly affected the performance of a continuous stirred tank reactor-anaerobic membrane bioreactor (CSTR-AnMBR). When the influent content of cellulose and hemicellulose was controlled at 3.88 ± 0.89 and 9.72 ± 2.05 g/L, respectively, the CSTR-AnMBR showed a low methane yield (0.04-0.06 L CH₄/g COD) at both HRT of 12 d and HRT 30 d. The functional microbes preferred to use the freshly added degradable COD, and the decomposition of refractory COD was paused. Meanwhile, the AnMBR unit was troubled by rapidly growing membrane fouling. The trans-membrane pressure increased with a rate of 1.63 kPa/d (HRT = 12d), and 0.99 kPa/d (HRT = 30 d) exacerbated the reactor performance. In high cellulose and hemicellulose-containing environments, the cellulolytic and hemicellulolytic microbes, including Bacteroidetes and Proteobacteria, were stimulated to a certain extent. In addition, cellulose and hemicellulose up-regulated the gene expression for sugar and amino acid metabolism, decreasing the abundance of metabolism related to methane production. When the influent content of cellulose and hemicellulose decreased to 0.62 ± 0.12 and 0.77 ± 0.30 g/L, respectively, the system's performance was significantly improved, microorganisms produced less low-molecular-weight soluble microbial products, which also reduced membrane fouling risk. This study provides significant guidance for treating livestock manure with the CSTR-AnMBR system.

New insights into membrane fouling during direct membrane filtration of municipal wastewater and fouling control with mechanical strategies

Direct membrane filtration (DMF) technology achieves energy self-sufficiency through carbon recovery and utilization from municipal wastewater. To control its severe membrane fouling and improve DMF technology, targeted research on fouling behaviour and mechanisms is essential. In this study, a DMF reactor equipped with a flat-sheet ceramic membrane was conducted under three scenarios: without control, with intermittent aeration, and with periodic backwash. This system achieved efficient carbon concentration with chemical oxygen demand below 50 mg/L in permeate. Membrane fouling was dominated by intermediate blocking and cake filtration. And reversible external resistance accounted for over 85 % of total resistance. Predominant membrane foulants were free proteins, whose deposition underlies the attachment of cells and biopolymers. Backwash decreased the fouling rate and increased fouling layer porosity by indiscriminately detaching foulants from the membrane surface. While aeration enhanced the back transport of large particles and microbial activity, causing a relatively thin and dense fouling layer containing more microorganisms and β-d-glucopyranose polysaccharides, which implies a higher biofouling potential during long-term operation. In addition, aeration combined with backwash enhanced fouling control fivefold over either one alone. Therefore, simultaneous operation of backwash and other mechanical methods that can provide shear without stimulating aerobic microbial activity is a preferred strategy for minimizing membrane fouling during DMF of municipal wastewater.

New insight in algal cell adhesion and cake layer evolution in algal-related membrane processes: Size-fractioned particles, initial foulant seeds and EDEM simulation

A clear understanding of algal cell adhesion and cake layer evolution in algal-related membrane processes (ARMPs) is urgently required to mitigate the membrane fouling. In this study, the effect of microparticles (10 μm-30 μm), subvisible particles (0.45 μm-10 μm), and ultrafine particles (50 kDa-0.45 μm) on the membrane fouling were explored based on the filtration performance through Hermia models, thermodynamic analysis, and simulation of extended discrete element method (EDEM). The results illustrated that microparticles played an important role in algal cell aggregation and the formation of initial clusters. Intermediate blocking fouling occurred when filtrating the subvisible particle, which facilitated internal adhesion and enhanced biofilm formation. In addition, the interfacial attractive force for the initial algal adhesion was obviously increased when the membrane surfaces were in high concentration of protein and polysaccharide. Moreover, the EDEM simulation demonstrated that subsequent particles, particularly the particles with small sizes, preferred to occupy the spaces among the previously deposited particles. This study provided new insights into the contributions of size-fractioned particles to initial fouling and their influence on the successive adhesion of other contaminants.

Enhanced energy production and biological treatment of swine wastewater using anaerobic membrane bioreactor: Fouling mechanism and microbial community

This study aimed to reveal the membrane fouling mechanisms during anaerobic membrane bioreactor (AnMBR) operation for swine wastewater treatment under different organic loading rates (OLR). Results showed that AnMBR could achieve high pollutant removal (71.9-83.6 %) and energy recovery (0.18-0.23 L-CH₄/g-COD) at an OLR range of 0.25-0.5 g-COD/g-VSS.d, realizing energy production. However, higher OLR would aggravate the membrane fouling due to accumulation of fine sludge particles, organic foulants, and extracellular polymeric substances (EPS) on cake layer. Based on the high-throughput sequencing, microbial communities significantly changed and fouling-causing bacteria (e.g. Pseudomonas, Methanosarcina and Methanothrix) enriched in the cake layer at higher OLR conditions, leading to lower membrane permeability. Backwash can effectively remove the cake layer from the membrane surface and recover membrane permeability. The present study provides important information about membrane fouling and microbial information that could have significant impact on large-scale AnMBR application.

Application of moving bed biofilm reactor - nanofiltration - membrane bioreactor with loose nanofiltration hollow fiber membranes for synthetic roxithromycin-containing wastewater treatment: Long-term performance, membrane fouling and microbial community

The present study operated the novel moving bed biofilm reactor-nanofiltration-membrane bioreactor (MBBR-NF-MBR) with loose polyamide NF membranes for the first time to treat roxithromycin (ROX) wastewater. Results showed that both MBBR-NF-MBRs achieved superior COD removal of 98.4% and 97.2% and excellent removal of ROX at 74.1% and 65.5%, respectively. The main membrane fouling mechanism was reversible fouling caused by the combination of abundant polysaccharides, proteins and Ca-P precipitates, which could be effectively removed by acidic cleaning. Sorption and biodegradation were the main removal routes of ROX in MBBR. Partial retention of loose NF membrane contributed to microbial metabolism and increased microbial diversity, especially the genera Hyphomicrobium in attached biofilm, which was reasonable for ROX removal. The cleavage of cladinose, demethylation, phosphorylation and β-oxidation in macrolactone ring were the main biotransformation reactions of ROX. This study provides novel insights for micropollutants wastewater treatment by using loose NF membrane in MBR.

Biochar enhances the biotransformation of organic micropollutants (OMPs) in an anaerobic membrane bioreactor treating sewage

The removal of emerging organic micropollutants (OMPs) in anaerobic membrane bioreactors (AnMBRs) has garnered considerable attention owing to the rapid development of AnMBR technology and the increased environmental risk caused by OMP discharge. We investigated the removal efficiency of 22 typical OMPs from sewage being treated in an AnMBR, and implemented and evaluated an upgrading strategy by adding biochar. The average removal efficiency of OMPs was only 76.8% due to hydrophilic OMPs containing electron-withdrawing groups (ketoprofen, ibuprofen, diclofenac, and carbamazepine) being poorly removed. Biochar addition (5.0 g/L) promoted the removal of recalcitrant OMPs by 45%, leading to an enhanced removal efficiency of 88.7%. Although biochar has a high adsorption capacity to different OMPs, the biotransformation rather than sorption removal efficiency of 13 of the 22 OMPs was largely enhanced, suggesting that adsorption-biotransformation was the main approach by which biochar enhances the OMP removal. Biotransformation test and microbial analysis revealed that the enrichment of species (Flavobacterium, Massilia, Acinetobacter, and Cloacibacterium) involved in OMP biotransformation on biochar contributed largely to the enhanced biotransformation removal efficiency of OMPs. In this way, the enhanced electron transfer activity and syntrophic metabolism between hydrogenotrophic methanogens and species that oxidize acetate to H₂/CO₂ on biochar jointly contributed to the stable CH₄ production and OMP biotransformation. This study provides a promising strategy to enhance the OMP removal in AnMBRs and improves our understanding of the underlying mechanism of biochar-amended OMP removal in anaerobic treatment systems.

Contrasting behaviors of pre-ozonation on ceramic membrane biofouling: Early stage vs late stage

Pre-ozonation coupled with ceramic membrane filtration has been widely used to alleviate membrane fouling. However, information on the efficiency and underlying mechanism of pre-ozonation in the evolution of ceramic membrane biofouling is limited. Herein, filtration experiments with a synthesis wastewater containing activated sludge were conducted in a cross-flow system to evaluate the effects of pre-ozonation on ceramic membrane biofouling. Results of flux tests show that pre-ozonation aggravated biofouling at the early stage, but alleviated the biofouling at the late stage. In situ FTIR spectra show that the aggravated biofouling with pre-ozonation was mainly caused by the enhanced complexation between phosphate group from DNA and Al₂O₃ surface and the increased rigid of proteins' structure. At the early stage, more severe pore blockage further substantiated the higher permeate resistance. By contrast, more dead cells were observed on membrane surface at the late stage, indicating the prevention of biofouling development after long-term pre-ozonation. Additionally, the structures and compositions of cake layers at the early and late stages exhibited considerable differences accompanied by the variation in microbial community with the evolution of biofouling. Therefore, this work demonstrates the effectiveness of pre-ozonation in biofouling in long-term operation and provides mechanistic insights into the evolution of biofouling on ceramic membrane.

Interface behavior and removal mechanisms of human pathogenic viruses in anaerobic membrane bioreactor (AnMBR)

Effective removal of human pathogenic viruses is an indispensable yet rarely studied aspect for sustainable treatment of domestic wastewater by anaerobic membrane bioreactor (AnMBR). In this study, the interface behaviors and removal mechanisms of norovirus genogroup I (GI), genogroup II (GII), and rotavirus A from domestic wastewater was systematically investigated in a one-stage AnMBR. On average, norovirus GI, GII and rotavirus were reduced by 4.64, 5.00, and 2.31 logs, respectively. Viruses tended to be transferred to larger-sized suspended solids from sewage influent to the mixed liquor, and the weight-specific concentration of the virus in >100 μm particles of the mixed liquor was significantly higher than that of sewage, indicating a particle scale-dependent affinity with the virus. In-series membrane filtration test showed the main contribution of the membrane retention, which was dominated by the bio-cake layer and the pristine membrane, while the membrane and associated pore foulants can retain viruses in a filtration resistance-efficient way. An unsteady-state mass balance model revealed that free viruses in the bulk liquid of AnMBR were minimally attached to the cake layer but mainly retained by the membrane and pore foulants (>99%). In addition, despite the small virus decay rates in the mixed liquor, the associated contribution increased with run time due to the prolonged sludge retention time. These insights into virus behaviors and removal mechanisms may provide novel regulation strategies for enhanced virus removal by AnMBR.

Gravity-driven high flux filtration behavior and microbial community of an integrated granular activated carbon and dynamic membrane bioreactor for domestic wastewater treatment

A gravity-driven dynamic membrane bioreactors (DMBR) with GAC addition (G-DMBR) was operated under constant pressure filtration mode (using 20 cm water head) for real domestic wastewater treatment. During the stable operation period, the treatment performance, DM filtration behavior and mechanism as well as microbial properties were studied and compared with a control DMBR (C-DMBR). Both DMBRs showed stable removal of chemical oxygen demand (COD) and ammonia (NH₄⁺-N) with average removal rates over 88% and 98%, respectively. GAC addition effectively enhanced dynamic membrane (DM) permeability with a stable flux of 17 to 65 L/m²h, which was approximately four times higher than that in the C-DMBR without GAC addition. Filtration resistance analysis indicated the DM formation can be divided to three stages: the formation of the initial DM layer, the development of mature DM layer and dynamic equilibrium stage of the DM layer. Filtration model analysis illustrated that added GAC could be the skeleton of the DM, resulting in a more porous and incompressible DM layer. Additionally, microbial community analysis revealed that in the G-DMBR several fouling-causing phyla including Proteobacteria reduced while other phyla preferring attached growth such as Bacteroidetes and Gemmatimonadetes increased. Thus, adding GAC to the DMBR can be an effective strategy for achieving stable and high-flux operation by modifying DM properties and regulating DM formation process and structure.

Oak-inspired anti-biofouling shape-memory unidirectional scaffolds with stable solar water evaporation performance

Biomimetic porous materials have contributed to the enhancement of solar-driven evaporation rate in interfacial desalination and clean water production. However, due to the presence of numerous microbes in water environment, biofouling should occur inside porous materials to clog the channels for water transfer, resulting in obvious inhibition of the solar-driven evaporation efficacy in long-term use. To prevent and control biofouling in porous materials for solar-driven evaporation, a facile and environment-friendly design is required in real application. Oak wood possesses vertically aligned channels for transpiration and polyphenol compounds with antimicrobial activity. In this work, inspired by the oak wood, we developed an anti-biofouling shape-memory chitosan scaffold with unidirectional channels and tannic acid coating (oak-inspired scaffold). The shape-memory property facilitated rapid decoration with oak-inspired photothermal and anti-biofouling coating inside the scaffold, respectively, which also promotes the material durability by avoiding the external force-induced permanent structure failure. More importantly, the oak-inspired tannic acid coating not only prevented bacterial adhesion and colonization, but also inhibited fungal interference. They were subjected to a microbe-rich environment, and after 3 days, the evaporation rates of the untreated chitosan scaffolds were obviously decreased to 1.24, 1.16 and 1.19 kg m^-2 h^-1 for C. albicans, S. aureus and E. coli, respectively, which were only 65.6, 61.4 and 63.0% of original performance (1.89 kg m^-2 h^-1). In comparison, the oak-inspired scaffold exhibited a high solar-driven water evaporation rate after incubation in microbial suspensions (1.80, 1.70 and 1.75 kg m^-2 h^-1 for C. albicans, S. aureus and E. coli after 3 days) and lake water (1.74 kg m^-2 h^-1 after one month). The bioinspired anti-biofouling scaffolds maintain as high as 86.7-91.8% of the solar-driven water evaporation ability after exposure to a microbe-rich environment, which is conducive to develop a biomimetic long-term durable structure in water treatment.

Virus removal during sewage treatment by anaerobic membrane bioreactor (AnMBR): The role of membrane fouling

Anaerobic membrane bioreactor (AnMBR) is a low-energy and promising solution for sewage treatment. During the treatment, the fouled membrane of AnMBR is recognized as an important barrier against pathogenic viruses. Here, the role of membrane fouling of an AnMBR at room temperature in the virus removal was investigated using MS2 bacteriophage as a virus surrogate. Results revealed that the virus removal efficiency of AnMBR was in the range of 0.2 to 3.6 logs, gradually increasing with the course of AnMBR operation. Virus removal efficiency was found to be significantly correlated with transmembrane pressure (R²=0.92, p<0.01), especially in the rapid fouling stage, indicating that membrane fouling was the key factor in the virus removal. The proportion of virus decreased from 52.03% to 15.04% in the membrane foulants when membrane fouling was aggravating rapidly, yet increased from 0.74% to 21.52% in the mixed liquor. Meanwhile, the permeate flux dramatically dropped. These imply that the primary rejection mechanism of virus by membrane in the slow fouling stage is the virus adsorption onto membrane, while the sieving effect is the main reason in the rapid fouling stage. Ex-situ virus rejection test unveiled that the cake layer was the main contributor to the overall virus rejection, while the greatest resistance-specific virus rejection was provided by the organic pore blocking. This paper provides operation strategies to balance enhanced virus removal and high permeate flux by regulating the membrane fouling process.

Enhanced methane production coupled with livestock wastewater treatment using anaerobic membrane bioreactor: Performance and membrane filtration properties

The present study introduced a new method for enhanced biomethane production and pollution control of swine wastewater (SW) using anaerobic membrane bioreactor (AnMBR). Results confirmed 35 °C as the optimum temperature for enhanced anaerobic digestion which resulted in relatively higher methane production rate and potential. In AnMBR system, robust pollutants removal and conversion rate were achieved under various hydraulic retention time (HRT) ranging from 20 to 10 days, while the highest methane yield (0.24 L/g-COD_removed) and microbial activity (6.65 mg-COD/g-VSS·h) were recorded at HRT of 15 days. Reduction of HRT to 10 days resulted in serious membrane fouling due to accumulation of extracellularpolymericsubstances(EPS) and cake layer on the membrane. However, cake layer as the dominant membrane foulant could be effectively removed through periodic physical backwash to recover the membrane permeability. Overall, the suggested AnMBR is a promising technology to enhance SW treatment and energy recovery.

Polymer Surface Dissection for Correlated Microscopic and Compositional Analysis of Bacterial Aggregates during Membrane Biofouling

Multispecies biofilms are a common limitation in membrane bioreactors, causing membrane clogging, degradation, and failure. There is a poor understanding of biological fouling mechanisms in these systems due to the limited number of experimental techniques useful for probing microbial interactions at the membrane interface. Here, we develop a new experimental method, termed polymer surface dissection (PSD), to investigate multispecies assembly processes over membrane surfaces. The PSD method uses photodegradable polyethylene glycol hydrogels functionalized with bioaffinity ligands to bind and detach microscale, microbial aggregates from the membrane for microscopic observation. Subsequent exposure of the hydrogel to high resolution, patterned UV light allows for controlled release of any selected aggregate of desired size at high purity for DNA extraction. Follow-up 16S community analysis reveals aggregate composition, correlating microscopic images with the bacterial community structure. The optimized approach can isolate aggregates with microscale spatial precision and yields genomic DNA at sufficient quantity and quality for sequencing from aggregates with areas as low as 2000 μm², without the need of culturing for sample enrichment. To demonstrate the value of the approach, PSD was used to reveal the composition of microscale aggregates of different sizes during early-stage biofouling of aerobic wastewater communities over PVDF membranes. Larger aggregates exhibited lower diversity of bacterial communities, and a shift in the community structure was found as aggregate size increased to areas between 25,000 and 45,000 μm², below which aggregates were more enriched in Bacteroidetes and above which aggregates were more enriched with Proteobacteria. The findings demonstrate that community succession can be observed within microscale aggregates and that the PSD method is useful for identification and characterization of early colonizing bacteria that drive biofouling on membrane surfaces.

Biological mechanism of alleviating membrane biofouling by porous spherical carriers in a submerged membrane bioreactor

In this study, porous spherical carriers were fixed around the hollow fiber membrane module to mitigate membrane biofouling. Two MBRs (R1 without carriers, R2 with carriers) were operated for 31 days under identical operating conditions to investigate the effects of the carriers on the reactor performances, the production of extracellular polymeric substances (EPS), the level of N-acyl-homoserine lactones (AHLs), and the microbial communities. The results showed that the presence of carriers in MBR was conducive to nitrogen removal and decreased the total membrane filtration resistance by about 1.7 times. Slower transmembrane pressure (TMP) rise-up, thinner bio-cakes, lower EPS production, and fewer tryptophan and aromatic proteins substances on the membrane surface were observed in R2. The polysaccharides secretion of EPS in bio-cakes was mainly regulated by C4-HSL and 3OC6-HSL in the presence of carriers. The microbial community analysis revealed that carriers addition reduced the relative abundance of EPS and AHL producing bacteria in the membrane bio-cakes and enriched the accumulation of functional bacteria conducive to nutrient removal in the mixed liquor. This study provided an in-depth understanding for the application of porous spherical carriers to alleviate membrane biofouling.