Anaerobic Membrane Bioreactor System Research Articles

Synchronised removal of nitrogen and sulphate from rubber industrial wastewater by coupling of Sulfammox and sulphide-driven autotrophic denitrification in anaerobic membrane bioreactor.

Global rubber industry, growing 4-6 % annually with 13.76 million Mt of rubber produced in 2019, significantly impacts the economy. This study explores coupling sulfate-dependent ammonium oxidation (Sulfammox) and sulfide-driven autotrophic denitrification (SDAD) within an anaerobic membrane bioreactor (AnMBR) to treat high-strength natural rubber wastewater. Over 225 days, the AnMBR system achieved maximal chemical oxygen demand (COD), total nitrogen (TN), ammonium nitrogen (NH4+-N), and sulfate sulfur (SO42--S) removal efficiencies of 58 %, 31 %, 13 %, and 45 %, respectively. TN is predominantly removed through Sulfammox (accounting for 49 % of NH4+-N removal), SDAD, and conventional denitrification pathways. Sulfate removal is achieved via Sulfammox (responsible for 43 % of SO42--S removal), and Dissimilatory sulfate-reducing (DSR) processes (contributing 57 % of SO42--S removal). Microbial analysis identified Desulfovibrio and Sulfurospirillum as key microbes, while metagenomic analysis highlighted crucial sulfur and nitrogen cycling pathways. The findings support Sulfammox and SDAD as promising eco-friendly strategies for treating ammonia- and sulfate-rich industrial wastewater.

Improving organic and nutrient removal efficiencies in seafood processing wastewater using anaerobic membrane bioreactor (AnMBR) integrates with anoxic/oxic (AO) processes

Wastewater from seafood processing is a significant source of pollution, containing many harmful organic and inorganic compounds such as proteins, lipids, carbohydrates, nitrogen and phosphorus. This study investigated the enhancement of organic and nutrient removal efficiencies in seafood processing wastewater by integrating an Anaerobic Membrane Bioreactor (AnMBR) with an anoxic/oxic (AO) processes. A pilot-scale system was constructed with a capacity of 0.5 m3/day directly at the factory operated continuously, featuring an AnMBR process with a 24-hour hydraulic retention time (HRT) and an AO process with HRT values and internal recycle changes. The AnMBR system exhibited consistent and high-performance biochemical oxygen demand (COD) elimination, approximately 80 ± 5 %. However, this system demonstrated low-efficiency removal of total nitrogen (TN) at about 20 ± 5 %, and total phosphorus (TP) 15 ± 5 %, under organic loading rates (OLR) of 0.6 to 1.3 kg-COD/(L·d). The AO process was then continually employed to improve the treatment efficacy (at HRT, 5 h in the anoxic phase, and 8.3 h in the oxic phase, at a recycling rate of 300 %) resulting in the final post-treatment concentrations of COD 27–41 mg/L (removal 98.3 ± 0.3 %), TN 12–25 mg/L (90 ± 2 %), and TP 18 ± 2 mg/L (35 ± 5 %). The performance of the integrated AnMBR-AO system met the established Vietnamese discharge standards for seafood processing wastewater, as outlined in QCVN 11-MT: 2015/BTNMT.

Performance of a recirculated biogas-sparging anaerobic membrane bioreactor system for treating synthetic swine wastewater containing sulfadiazine antibiotic

Anaerobic Membrane Bioreactor (AnMBR) is an efficient system for treating synthetic swine wastewater (SW). However, the presence of antibiotics in SW discourages the activity of microorganisms, resulting in less pollutants removal and biogas production. In this paper, a recirculated biogas-sparging anaerobic membrane bioreactor system was used to treat swine wastewater containing sulfadiazine (SDZ). The effects of different concentrations of SDZ on the AnMBR system’s performance were explored, in terms of pollutant removal, biogas production, membrane fouling and microbial community. Results indicated that the larger concentration of SDZ triggered a strong suppression in the system’s performance. When treating 1.0 mg/L SDZ, the biogas-sparging AnMBR system achieved about 77 % COD removal and 0.23 L/g CODremoved biogas production, which without SDZ fell to 21 % COD being removed and dropped biogas production by 30 %. As well, the presence of SDZ (1.0 mg L) increased by about half the amount of soluble microbial product (SMP) and extracellular polymeric substances (EPS) with lower protein/polysaccharide ratio and reduced sludge particle size by 49 %. Meanwhile, microbial community analysis revealed that the abundance of Firmicutes increased while Chloroflexi diminished. These jointly contributed to a shorter membrane fouling cycle declining from the initial 23 d to 7 d. Furthermore, the shift from acetoclastic methanogens to hydrogenotrophic methanogens resulted in less methane production due to the presence of SDZ, while the hydrogenotrophic methanogen Methanobacterium promoted the degradation of SDZ. The work showed AnMBR can effectively treat swine wastewater containing antibiotics and provides basis for practical application.

Life cycle assessment of AnMBR technology for urban wastewater treatment: A case study based on a demo-scale AnMBR system

This study aims at assessing the environmental performance of a projected full-scale anaerobic membrane bioreactor (AnMBR) treating urban wastewater (UWW) at ambient temperature. To this aim, data from an AnMBR demonstration plant equipped with commercially available equipment, including industrial hollow fiber and degassing membranes, was used for projecting a full-scale facility. The use of real operation data allows to obtain robust results that contribute to improve the knowledge of the environmental performance of this technology, pointing out its strengths and the challenges that still need to be addressed. Life cycle assessment (LCA) was applied by means of Ecoinvent data base and ReCiPe2016 methodology considering 1 kg of removed COD as functional unit. Additionally, sensitivity and uncertainty analysis were conducted. Energy balance showed AnMBR performing as energy producer (net energy surplus up to −0.688 kWh·kg CODrem−1) and carbon sink (emissions credit up to 0.223 kgCO2eq·kgCODrem−1). Results also showed energy recovery, heavy metals in sludge, dissolved methane in the effluent, and effluent nutrient content as the most important aspects affecting LCA outcome. Construction phase affected some impact categories significantly (e.g., 51–71% in mineral resource scarcity, 18–27% in fossil resource scarcity, 21–28% in water consumption), therefore its exclusion should be carefully evaluated. CHP efficiency, dissolved methane recovery, filtration productivity, membrane scouring, reactor mixing, HRT and SRT appeared most influencing parameters. Finally, actions leading to increase the recovery and valorization of dissolved methane and/or of nutrients through, for instance, fertigation, improve the environmental performance of AnMBR for UWW treatment.

Effect of Hydraulic retention time on performance of anaerobic membrane bioreactor treating slaughterhouse wastewater

Slaughterhouse wastewater is a major environmental concern in many Vietnamese cities due to its high organic content and unpleasant odor. This study aimed to evaluate performance of a submerged flat sheet Anaerobic membrane bioreactor (AnMBR) system at different hydraulic retention time (HRT, 8–48 h) treating wastewater from a slaughterhouse in Hanoi City (Vietnam) at ambient temperature. The wastewater characteristics were as follows: chemical oxygen demand (COD) of 910 ± 171 mg/L; suspended solids (SS) of 273 ± 139 mg/L; and total nitrogen (T-N) of 115 ± 31 mg/L. The AnMBR system achieved high removal efficiencies for SS (99%) and COD (>90%) at an optimum HRT of 24 h. The biomethane yield reached 0.29 NL CH4/g CODinf. Importantly, the system maintained stable operation without flux decay and membrane fouling. HRT longer than 24 h could offer the better effluent quality without an increase in transmembrane pressure (TMP); however, it led to a lower methane production rate. Shorter HRT of 8–12 h caused a high TMP over −10 kPa, posing a risk for membrane fouling and biomass loss during cleaning, thus resulting in a low methane production. Our results suggest that AnMBR can be a reliable technology for wastewater treatment, reuse and energy recover from slaughterhouse wastewater in Vietnam and other similar climate countries.

Evaluation of anaerobic membrane bioreactor treating dairy processing wastewater: Elemental flow, bioenergy production and reduction of CO2 emission

The management of dairy processing wastewater (DPW) must address water pollution while delivering renewable energy and recovering resources. A high-rate anaerobic membrane bioreactor (AnMBR) was investigated for treating DPW, and the system was evaluated in terms of elemental flow, nutrient recovery, energy balance, and reduction of CO2 emission. The AnMBR system was superior in terms of both methanogenic performance and efficiency of bioenergy recovery in the DPW treatment, with a high net energy potential of 51.4–53.2 kWh/m3. The theoretical economic values of the digestate (13.8 $/m3) and permeate (4.1 $/m3) were assessed according to nutrient transformation and price of mineral fertilizer. The total CO2 emission equivalent in the AnMBR was 44.7 kg CO2-eq/m3, with a significant reduction of 54.1 kg CO2-eq/m3 compared to the conventional process. The application of the AnMBR in the DPW treatment is a promising approach for the development of carbon neutrality and a circular economy.

Life cycle costing of AnMBR technology for urban wastewater treatment: A case study based on a demo-scale AnMBR system

This study aims at assessing the economic performance of a projected full-scale anaerobic membrane bioreactor (AnMBR) for urban wastewater (UWW) treatment at ambient temperature. To this aim, data from an AnMBR demonstration plant (industrial prototype, TRL 6) was used, which was operated for 3 years treating real UWW, allowing gathering a robust set of information for scaling-up to full scale. The obtained results revealed that reactor mixing (0.056–0.124 kWh·kgCODrem-1; 34–57%), and membrane scouring (0.048–0.120 kWh·kgCODrem-1; 22–48%) were the main contributors to the total energy demand; while net energy productions between 0.210 and 0.645 kWh·kgCODrem-1 were achieved. Capital expenditure was highly influenced by UF membranes (€0.029–0.073 kgCODrem-1; 31–49%), combined heat and power technology for energy recovery (€0.012–0.023 kgCODrem-1; 8–24%), and reactor construction (€0.07–0.014 kgCODrem-1; 8–13%); while the main contributors to operating expenditure were energy requirements (€0.042–0.069 kgCODrem-1; 41–46%), membrane replacement (€0.011–0.028 kgCODrem-1; 9–17%), and discharge fee (€0.010–0.020 kgCODrem-1; 9–12%). Total annualized costs showed high variability, between €− 0.003 and 0.188 kgCODrem-1. Results presents AnMBR as a competitive technology for UWW treatment compared to conventional aerobic technologies (e.g., CAS). Membrane fouling control; hydraulic retention time; biogas requirements for reactor mixing and membrane stirring; and energy recovery efficiency were identified as key parameters for improving economic sustainability of AnMBR technology.

Performance evaluation and energy potential analysis of anaerobic membrane bioreactor (AnMBR) in the treatment of simulated milk wastewater

An anaerobic membrane bioreactor (AnMBR) was employed as primary treatment unit for anaerobic treatment of simulated wastewater to produce high effluent quality. A lab scale hollow fiber membrane was used to scrutinize the performance of AnMBR as a potential treatment system for simulated milk wastewater and analyze its energy recovery potential. The 15 L bioreactor was operated continuously at mesophilic conditions (35 °C) with a pH constant of 7.0. The membrane flux was in the range of 9.6–12.6 L/m2. h. The different organic loading rates (OLRs) of 1.61, 3.28, 5.01, and 8.38 g-COD/L/d, of simulated milk wastewater, were fed to the reactor and the biogas production rate was analyzed, respectively. The results revealed that the COD removal efficiencies of 99.54 ± 0.001% were achieved at the OLR of 5.01 gCOD/L/d. The highest methane yield was found to be at OLR of 1.61 gCOD/L/d at HRT of 30 d with the value of 0.33 ± 0.01 L-CH4/gCOD. Moreover, based on the analysis of energy balance in the AnMBR system, it was found that energy is positive at all the given HRTs. The net energy production (NEP) ranged from 2.594 to 3.268 kJ/gCOD, with a maximum NEP value of 3.268 kJ/gCOD at HRT 10 d HRT. Bioenergy recovery with the maximum energy ratio, of 4.237, was achieved with an HRT of 5 d. The study suggests a sizable energy saving with the anaerobic membrane process.

An integrated leachate bed reactor – anaerobic membrane bioreactor system (LBR-AnMBR) for food waste stabilization and biogas recovery

This study developed an integrated LBR – AnMBR system for efficient stabilization and biogas recovery from food waste (FW) at room temperatures (21–22 °C). First, the leachate recirculation rate (4.4–13.2 L/h) was optimized to maximize hydrolysis and acidification yields. The maximum hydrolysis yield of 551 gSCOD/kg VSadded was achieved at recirculation rate of 13.2 L/h. The VFA concentrations in the FW leachate was as high as 12.5–16.0 g/L, resulting in a high acidification of 468 g CODVFA/kg VS. The solubilized FW was further stabilized by feeding the leachate to AnMBR. Different hydraulic (HRT) and solids retention times (SRT) were tested to achieve high COD removal and methane yields. High COD removal of 86 ± 3% was obtained in the AnMBR at HRT of 13 and SRT of 75 days. High biogas recovery of about 850 kWh per ton FWtreated was achieved along with high quality of AnMBR permeates containing low COD concentration but advantageously high concentration of nutrients (NH4+-N 317–403 mg/L, total phosphate 23–213 mg/L) without any particulates, which can be reused for landscape or liquid fertilizer.

Long-term comparison of pilot UASB and AnMBR systems treating domestic sewage at ambient temperatures

The upflow anaerobic sludge blanket (UASB) reactor and the anaerobic membrane bioreactor (AnMBR) are leading candidates for high-rate anaerobic treatment of domestic wastewater. The objective of this study was to perform a long-term comparison on the treatment of domestic sewage by the UASB and AnMBR systems at pilot scale at ambient temperature conditions and relate this to full-scale performance from a range of domestic strength UASB reactors. Analysis of overall operation indicated that the pilot reactor was more likely to be effective in removing solids (and less effective in soluble COD) than full-scale reactors, but that both had comparable performance ranges (i.e., from very effective, to very ineffective). Analyzing both UASB and AnMBR pilot plants treating the same wastewater, it can be concluded that both systems could achieve comparable performance (the UASB for very short periods), with COD removal efficiencies of more than 90%. However, the UASB could only achieve this performance for weeks at a time with good solids retention and long (>15 h) hydraulic retention time (HRT). This performance in general was not sustainable. For the UASB, the average COD removal at 15-h HRT was approximately 50%, with a significant reduction in performance as the hydraulic loading increased (which effectively reduced the HRT). Conversely, the AnMBR system produced exceptional COD removal at an HRT of 9 h. Considering this, the sustained volumetric methane production (per volume of reactor) was approximately 4 times that in the AnMBR than in the UASB system.

Pollutant Removal and Energy Recovery from Swine Wastewater Using Anaerobic Membrane Bioreactor: A Comparative Study with Up-Flow Anaerobic Sludge Blanket

Due to its high content of organics and nutrients, swine wastewater has become one of the main environment pollution sources. Exploring high-efficient technologies for swine wastewater treatment is urgent and becoming a hot topic in the recent years. The present study introduces anaerobic membrane bioreactor (AnMBR) for efficient treatment of swine wastewater, compared with up-flow anaerobic sludge blanket (UASB) as a traditional system. Pollutant removal performance, methanogenic properties, and microbial community structures were investigated in both reactors. Results showed that by intercepting particulate organics, AnMBR achieved stable and much higher chemical oxygen demand (COD) removal rate (approximately 90%) than UASB (around 60%). Due to higher methanogenic activity of anaerobic sludge, methane yield of AnMBR (0.23 L/g-COD) was higher than that of UASB. Microbial community structure analysis showed enrichment of functional bacteria that can remove refractory organic matter in the AnMBR, which promoted the organics conversion processes. In addition, obvious accumulation of acetotrophic and hydrotrophic methanogens in AnMBR system was recorded, which could broaden the organic matter degradation pathways and the methanogenesis processes, ensuring a higher methane yield. Through energy balance analysis, results concluded that the net energy recovery efficiency of AnMBR was higher than that of UASB system, indicating that applying AnMBR for livestock wastewater treatment could not only efficiently remove pollutants, but also significantly enhance the energy recovery.

In-situ biogas upgrading with H2 addition in an anaerobic membrane bioreactor (AnMBR) digesting waste activated sludge

Biological in-situ biogas upgrading is a promising approach for sustainable energy-powered technologies. This method increases the CH4 content in biogas via hydrogenotrophic methanogenesis with an external H2 supply. In this study, an anaerobic membrane bioreactor (AnMBR) was employed for in-situ biogas upgrading. The AnMBR was operated in semi-batch mode using waste activated sludge as the substrate. Pulsed H2 addition into the reactor and biogas recirculation effectively increased the CH4 content in the biogas. The addition of 4 equivalents of H2 relative to CO2 did not lead to appreciable biogas upgrading, although the acetate concentration increased significantly. When 11 equivalents of H2 were introduced, the biogas was successfully upgraded, and the CH4 content increased to 92%. The CH4 yield and CH4 production rate were 0.31 L/g-VSinput and 0.086 L/L/d, respectively. In this phase of the process, H2 addition increased the acetate concentration and the pH because of CO2 depletion. Compared with a continuously-stirred tank reactor, the AnMBR system attained higher CH4 content, even without the addition of H2. The longer solid retention time (100 d) in the AnMBR led to greater degradation of volatile solids. Severe membrane fouling was not observed, and the transmembrane pressure remained stable under 10 kPa for 117 d of continuous filtration without cleaning of the membrane. The AnMBR could be a promising reactor configuration to achieve in-situ biogas upgrading during sludge digestion.

Influence of the Sludge Retention Time on Membrane Fouling in an Anaerobic Membrane Bioreactor (AnMBR) Treating Lipid-Rich Dairy Wastewater.

This study evaluated the effects of sludge retention time (SRT) on the membrane filtration performance of an anaerobic membrane bioreactor (AnMBR) fed lipid-rich synthetic dairy wastewater. The membrane filtration performance was evaluated in two AnMBR systems operated at two different SRTs, i.e., 20 and 40 days. For the AnMBR operated at 40 days, SRT exhibited worse membrane filtration performance characterized by operational transmembrane pressures (TMP) exceeding the maximum allowed value and high total resistances to filtration (Rtotal). The sludge in the two reactors evaluated at the different SRTs showed similar sludge filterability properties. However, the sludge in the reactor operated at 40 days SRT was characterized by exhibiting the highest concentrations of: (i) total suspended solids (TSS), (ii) small-sized particles, (iii) extracellular polymeric substances (EPS), (iv) soluble microbial products (SMP), (v) fats, oils and grease (FOG), and (vi) long-chain fatty acids (LCFA). The cake layer resistance was the major contributor to the overall resistance to filtration. The high TSS concentration observed in the AnMBR systems apparently contributed to a less permeable cake layer introducing a negative effect on the membrane filtration performance.

A Novel and Green Method for Turning Food Waste into Environmentally-Friendly Organic Deicing Salts: Enhanced VFA Production through AnMBR

In order to improve the production efficiency of volatile fatty acids (VFAs) by anaerobic fermentation of food waste and reduce the cost for the production of organic deicing salt (ODS), ceramic microfiltration (MF) membrane separation was applied in the conventional food waste fermenter to build an anaerobic membrane bioreactor (AnMBR). Results showed that the maximum VFA concentration in AnMBR was up to 55.37 g/L. Due to the fact that the MF membrane could realize in situ separation of VFAs, the recovery of VFAs could reach 95.0%; 66.6% higher than that of traditional fermentation reactors. After the application of the MF membrane, more than 20.0% of soluble COD, 40.0% of proteins, and 50.0% of polysaccharides were retained and more than 90.0% of VFAs could be transferred in a timely fashion in the AnMBR system. In addition, the enrichment effect of the MF membrane enhanced enzymatic activities such as protease, α-Glucosidase and acetate kinase, and increased the abundance of some important bacteria for organic acid generation such as Amphibacter, Peptoniphilus and Halomonas, which made a significant contribution to the yield of VFAs. After concentration, evaporation and crystallization, the melting efficiency of obtained ODS can reach more than 90.0% in chloride salts, which was 112.0% of commercial calcium magnesium acetate (CMA). When compared to chloride salts and CMA, ODS was more environmentally-friendly as it can reduce the corrosion of carbon steel and concrete significantly. This study created a new way of converting food waste into a high-value organic deicing agent, realizing the resource utilization of solid waste and reducing the production cost of organic deicing agents.

Hybrid Anaerobic Membrane Bioreactor System for Treatment and Reuse of Potato Processing Wastewater

Hybrid Anaerobic Membrane Bioreactor System for Treatment and Reuse of Potato Processing Wastewater

Unveiling the characterization and development of prokaryotic community during the start-up and long-term operation of a pilot-scale anaerobic membrane bioreactor for the treatment of real municipal wastewater

The anaerobic membrane bioreactor (AnMBR) is a promising sustainable process and technology for the treatment of municipal wastewater from the perspective of carbon neutrality. In this study, a large pilot-scale AnMBR was constructed and the microbial community development of the anaerobic digested sludge in the AnMBR was determined during the treatment of municipal wastewater. The AnMBR system was conducted for 217 days during a long-term operation with the feed of real municipal wastewater. The characterization and dynamics of the microorganisms revealed that a stable prokaryotic community was gradually achieved. In the community of methane-producing archaea (or methanogens), the acetotrophic methanogen Methanosaeta was significantly enriched at an ambient temperature of 25 °C with an overwhelming relative abundance in the entire community. The abundance of Methanosaeta was even higher than the most abundant bacterial phyla Chloroflexi, Firmicutes, Proteobacteria and Bacteroidetes. This phenomenon is quite different from that found in other typical anaerobic systems. The massive enrichment of methanogens is the key to maintaining stable methane production in the treatment of municipal wastewater by the AnMBR. The interspecies cooperation of major functional bacterial groups including protein/carbohydrate/cellulose-degrading (genera Anaerovorax, Aminomonas, Levilinea, Flexilinea and Ruminococcus etc.), sulfate-reducing (Desulfovibrio and Desulfomicrobium etc.) and syntrophic (Syntrophorhabdus and Syntrophus etc.) bacteria with acetotrophic and hydrogenotrophic archaea enhances the stability of reactor operation and help to acclimate the entire prokaryotic community to the characteristics of real municipal wastewater.

Tapping the energy potential from wastewater by integrating high-rate activated sludge process with anaerobic membrane bioreactor

Advances in wastewater treatment have pushed forward new developments for energy recovery from wastewater. Integrating high-rate activated sludge process (HRAS) with anaerobic membrane bioreactor (AnMBR) is promising towards energy-positive rather than energy-consuming wastewater management. In this study, the overall performance of the lab-scale HRAS-AnMBR system was investigated under different operating conditions through experimental and modeling investigations. The decrease in sludge retention time (SRT) from 2 to 0.5 days of the HRAS process could improve chemical oxygen demand (COD) capture efficiency by up to 43%, realizing an overall COD recovery of 30% with methane production of 0.25 L/g COD. Simulation results further confirmed that the overall performance highly depended on dissolved oxygen, solid retention time, and influent composition. More importantly, there could be a trade-off between carbon capture and effluent quality in the HRAS process with different operating conditions. The findings of this study indicate that the integrated process has potential for energy recovery while multiple operating parameters in the HRAS process should be overall considered to maximize the energy recovery potential and improve the effluent quality of the integrated HRAS and AnMBR system.

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-CODremoved) 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.

Performance of Alternating-Current-Enhanced Anaerobic Membrane Bioreactor: Membrane Fouling, Wastewater Treatment, and CH4 Production

An alternating current (ac)-enhanced (+1.0 V/–1.2 V) anaerobic membrane bioreactor system was constructed (AC-AnMBR) with conductive carbon nanotubes hollow-fiber membranes (CHFMs) as the basic separation unit and electrode, simultaneously. Compared with the other two anaerobic membrane bioreactors polarized by anodic direct current (dc) (+1.0 V, A-AnMBR) and cathodic dc (−1.2 V, C-AnMBR), the membrane fouling was obviously mitigated based on the always lower transmembrane pressure. Meanwhile, the cake layer on CHFM from AC-AnMBR (∼15.7 μm) was thinner than those from C-AnMBR (∼22.8 μm) and A-AnMBR (∼35.7 μm) after 40 days of operation. In AC-AnMBR, a barrier of electrostatic repulsion force around membranes with −1.2 V hindered the negatively charged pollutants (mainly extracellular polymeric substances) deposited on the membranes’ surface. Then, the electrochemical oxidation provided by positively charged membranes would play a role in oxidizing or mineralizing pollutants for deep fouling removal. Two alternating effects reduced the adhesion of living bacteria, eventually causing a bacterial detachment from membrane surface at the same time. Additionally, AC-AnMBR showed a more than 90% effluent COD removal rate. The CH4 production could stabilize at 210 mL/L·day (COD ∼ 1500 mg/L) in AC-AnMBR and C-AnMBR, about higher 10 mL/L·day than that in A-AnMBR.

Considering the Prospect of Utilizing Anaerobic Membrane Biofouling Layers Advantageously for the Removal of Emerging Contaminants

Membrane biofilm formation has traditionally been perceived as a wholly negative occurrence in membrane filtration-based wastewater treatment systems due to its resultant effect on transmembrane pressure and energy expenditure. This is the case for both membrane bioreactor (MBR) systems, generally, and anaerobic membrane bioreactors (AnMBRs), specifically. Insight gained through recent research, however, has revealed a potentially positive aspect to biofouling in AnMBR systems—namely, the improved removal of certain emerging contaminants (both microbial and chemical) from wastewater that would not otherwise be retained by the microfiltration/ultrafiltration membranes that are commonly used. Although the exact reasons behind this are not yet understood, the biofilm-specific anaerobic microbial communities that develop on membrane surfaces may play a key role in the phenomenon. Mechanisms of biofouling development in AnMBRs have recently been proven distinctly different from those that govern fouling in aerobic MBR systems. Based on these differences, it may be possible to devise operational strategies that promote the development of anaerobic biofilms on membranes while also minimizing transmembrane pressure increases. If achievable, this would serve as a sustainable basis for reducing the release of emerging contaminants such as organic micropollutants (OMPs) and antibiotic resistance genes (ARGs) with treated wastewater effluents.