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.

Enhanced methanogenic degradation and membrane fouling associated with protein-EPS by extending sludge retention time in a high-solid anaerobic membrane bioreactor treating concentrated organic sludge

The improvement of organic sludge destruction efficiency and methanogenic performance is a key concern during anaerobic digestion toward maximum energy recovery. In this study, a high-solid anaerobic membrane bioreactor (AnMBR) was operated continuously for the treatment of organic sludge from Japanese small-scale collective wastewater treatment facility (Johkasou), and digestion efficiency was enhanced by the optimizing solid retention time (SRT). Degradation efficiency of the substrate improved from 36 % to 52 % and the biogas yield was enhanced from 0.37 to 0.51 L/g-VSfed when the SRT was extended from 30 to 60 d. The net energy yield of AnMBR at SRT 60 days was 9.83 kJ/g-VSfed, and the corresponding energy sufficiency ratio was 181 %, indicating that SRT extension could enhance substrate destruction with significant energy recovery potential. However, a long SRT is characterized by high mixed liquor total solids (MLTS), small particle size, high extracellular polymeric substances content, and poor filterability, which exert detrimental effects on membrane operation. Membrane fouling was effectively controlled by regulating the flux at a sustainable rate. The low fouling region and transition region of operating flux were determined as 0.21-4.6 L/m2/h (LMH) and 1.5-5.7 LMH, respectively, when MLTS was 25-50 g/L, and the main contributors to membrane fouling were high protein fractions and small sludge flocs. The current study proposes a promising method to promote digestion efficiency and provided adequate guidance for membrane operation at super-high MLTS by presenting practical engineering applications of AnMBRs in solid waste treatment.

Optimization of membrane filtration and cleaning strategy in a high solid thermophilic AnMBR treating food waste

Anaerobic membrane bioreactor is advantageous over traditional processes for food waste treatment, i.e. short retention time, high loading rate, and particulate clean permeate. However, establishing a sustainable membrane filtration is a long-standing challenge because of its high viscosity and solids concentration characteristics. Therefore, this study investigated the changes in the membrane permeability before and after the cleaning during a 130-day thermophilic anaerobic experiment. Results show that the AnMBR system could maintain high stability even under a short HRT of 10 days and OLR of 9.0 kg-COD/(m3·d) with low volatile fatty acid of 50 mg/L. The membrane filtration deteriorates with the concurrence of a sharp increase of viscosity when the volatile solids reached 23 g/L. A critical flux was achieved at 5.5 L/(m2·h) under optimized operation conditions, membrane filtration/relaxing ratio with less than 4:1 at a hydraulic retention time of 15 d. Membrane fouling can be removed by soaking the membrane in NaClO (1 g/L, 15 h) and citric acid (2 g/L, 2 h). Conclusively, this work provides insight to establish the operation strategy for a thermophilic AnMBR treating food waste.

Electroactive biocake layer-driven advanced removal of dissolved organic matter at membrane interface of anaerobic electrochemical membrane bioreactor

The bio-cake layer is one of the most negative effects during water and wastewater filtration, but its potential behoof of biodegradation is poorly understood. In this study, we activated and reconstructed the bio-cake by using the carbon nanotube membrane (25 cm2 area, 17 LMH flux) as the anode in an anaerobic membrane bioreactor (AnMBR), and investigated its positive role in advanced removal of dissolved organic matter from up-flow anaerobic sludge bed unit (3 L/d) when treating synthetic municipal wastewater. At the anodic membrane interface, the enhanced biodegradation was proved to dominate the DOM reduction (contribution >40%), controlling the effluent COD as low as 19.2 ± 2.5 mg/L. Bio-cake characterizations suggested that the positive potential induced electroactive improvement, cell viability boost, and metabolic optimization. Metatranscriptomic analyses revealed that anode respiratory out-compete methanogenesis, forwarding a synergetic metabolism between enriched fermenters like Proteiniphilum sp. and exoelectrogens like Geobacter sp. Thus, electroactive bio-cake not only accelerated the decomposition of inside foulants to maintain the high flux, but also efficiently intercepted flow-through DOM due to reduced mass-transfer limitations and enhanced metabolic activity. An ordered, non-clogging, and potentially functional "cell filter" was established to achieve a win-win situation between fouling control and effluent improvement, which is promising to upgrade the AnMBR technology for maximizing the sustainable regeneration in future wastewater treatment.

Bioaugmentation of the green alga to enhance biogas production in an anaerobic hollow-fiber membrane bioreactor

Anaerobic membrane reactors (AnMBRs) offer an alternative wastewater treatment system, presenting both reclamation of value through biogas production, and efficient treatment of recalcitrant contaminants such as antibiotics from wastewater. The effects of bioaugmentation with the green alga Haematococcus pluvialis on anaerobic treatment of pharmaceutical wastewaters, alleviating membrane biofouling, biogas production and impact on the indigenous microbial communities were evaluated using AnMBRs. The outputs of the bioreactor experiments revealed that bioaugmentation strategies with the green alga increased removal of chemical oxygen demand by 12% and delayed membrane fouling by 25% and increased biogas production by 40%. Furthermore, bioaugmentation with the green alga led to a significant change in relative abundance of archaea and the main methanogenesis pathway shifted from Methanothermobacter to Methanosaeta, accompanied by their respective syntrophic bacteria.

Direct ammonium recovery from the permeate of a pilot-scale anaerobic MBR by biochar to advance low-carbon municipal wastewater reclamation and urban agriculture

The rapidly evolving global climate change has an unprecedented impact sustainable water supply, but also challenges and water shortage global food security. In such a dynamic situation, this study explored direct recovery of ammonium from the effluent of a pilot-scale anaerobic membrane bioreactor (AnMBR) treating actual municipal wastewater via biochar adsorption, while the use of produced ammonium-loaded biochar for urban agriculture was also demonstrated. Results showed that modified biochar could remove almost all ammonium in the pilot AnMBR permeate at an empty bed contact time of 30 mins. Results showed that ammonium extracted from the ammonium-loaded biochar could promote the germination of Daikon radish seeds. It was further observed that the fresh weight of Pak Choi (a typical leafy vegetable) planted in the soils augmented with the ammonium-loaded biochar was 42.5 g per vegetable versus 18.5 g per vegetable in the control, indicating a 130 % of increase in the Pak Choi productivity. In addition, the Pak Choi in grown the ammonium-loaded biochar augmented soils appeared to be much bigger with larger leaves compared to the control. It was also worth to note that the ammonium-loaded biochar could significantly stimulate the root development of Pak Choi, i.e., 20.7 cm over 10.5 cm obtained in the control. More importantly, the amount of carbon emission reduced through returning ammonium-loaded biochar to urban agriculture could offset the treatment process-associated direct and indirect carbon emission.

Chemically and biologically driven carbon transformation flow in MSW leachate treated by a high-solids anaerobic membrane bioreactor system

Carbon transformation is important for an anaerobic process but is often overlooked when using an anaerobic membrane bioreactor (AnMBR). Material flow in an AnMBR treating calcium-rich MSW leachate was thus quantitatively investigated to illustrate how chemical and biological factors affect carbon transformation. The results show that a remarkable amount of carbon in the leachate was degraded, with 50.1% of it should be converted into CH₄ and 37.7% of it into CO₂. However, a much smaller value of 40.6% and 14.2% were experimentally obtained. Chemical analysis indicated that the precipitation of calcium carbonate captured 1.23 g/day of carbon. At the same time, about 23.2 g/L HCO₃^- and 16.6 mg/L CH₄ (both as carbon) were dissolved in the liquid. Those features facilitated the high CH₄ (74%) content in biogas. A carbon transformation model was therefore established and showed carbon flow into the gas, liquid, and solid phases, respectively. Carbon existed in biogas, permeate, and discharged sludge was also obtained.

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.

Methanogenic treatment of dairy wastewater: A review of current obstacles and new technological perspectives

Methanogenic treatment can effectively manage wastewater in the dairy industry. However, its treatment efficiency and stability are problematic due to the feature of wastewater. This review comprehensively summarizes the dairy wastewater characteristics and reveals the mechanisms and impacts of three critical issues in anaerobic treatment, including ammonia and long-chain fatty acid (LCFA) inhibition and trace metal (TM) deficiency. It evaluates current remedial strategies and the implementation of anaerobic membrane bioreactor (AnMBR) technology. It assesses the use of nitrogen-removed effluent return to dilute the influent for solving protein-rich dairy wastewater treatment. It explores the methodology of TM addition to dairy wastewater in accordance with microbial TM content and proliferation. It analyzes the multiple benefits of applying high-solid AnMBR to lipid-rich influent to mitigate LCFA inhibition. Finally, it proposes a promising low-carbon treatment system with enhanced bioenergy recovery, nitrogen removal, and simultaneous phosphorus recovery that could promote carbon neutrality for dairy industry wastewater treatment.

Performance of Anaerobic Membrane Bioreactor (AnMBR) with Sugarcane Bagasse Ash-based Ceramic Membrane treating Simulated Low-strength Municipal Wastewater: Effect of Operation Conditions

This study assesses the performance of waste sugarcane bagasse ash (SBA)-based ceramic membrane in anaerobic membrane bioreactor (AnMBR) treating low-strength wastewater. The AnMBR was operated in sequential batch reactor (SBR) mode at hydraulic retention time (HRT) of 24 h, 18 h, and 10 h to understand the effect on organics removal and membrane performance. Feast-famine conditions were also examined to evaluate system performance under variable influent loadings. An average removal of >90% chemical oxygen demand (COD) was obtained at each HRT and starvation periods up to 96 days did not significantly affect removal efficiency. However, feast-famine conditions affected extracellular polymeric substances (EPS) production and consequently the membrane fouling. EPS production was high (135 mg/g MLVSS) when the system was restarted at 18 h HRT after shutdown (96 days) with corresponding high transmembrane pressure (TMP) build-up; however, the EPS content stabilized at ~60-80 mg/g MLVSS after a week of operation. Similar phenomenon of high EPS and high TMP was experienced after other shutdowns (94 and 48 days) as well. Permeate flux was 8.8±0.3, 11.2±0.1 and 18.4±3.4 L/m² h at 24 h, 18 h and 10 h HRT, respectively. Filtration-relaxation (4 min - 1 min) and backflush (up to 4 times operating flux) helped control fouling rate. Surface deposits (that significantly attributed to fouling) could be effectively removed by physical cleaning, resulting in nearly complete flux recovery. Overall, SBR-AnMBR system equipped with waste-based ceramic membrane appears promising for treatment of low-strength wastewater with disruptions in feeding.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s11270-023-06173-3.

Enhancement of struvite generation and anti-fouling in an electro-AnMBR with Mg anode-MF membrane module

Severe membrane fouling and the inability to remove/recover nitrogen and phosphorus are bottlenecks of anaerobic membrane bioreactors (AnMBRs) for large-scale application in wastewater treatment. Herein, an electrochemical AnMBR with a Mg anode-membrane module (electro-AnMBR) was built and showed good performance in terms of membrane fouling mitigation and nutrient recovery during sewage treatment. Compared with the traditional AnMBR, membrane fouling in the electro-AnMBR was reduced by up to 30%. The application of an electric field decreased the zeta potential, viscosity, and EPS concentration of the sludge-water liquor in the electro-AnMBR, which could improve the cake layer structure and thus enhance water permeability. Meanwhile, 26% of NH₄⁺ and 48% of PO₄^3- co-precipitated with Mg²⁺ generating from the sacrificial Mg anode and were recovered as struvite deposited onto cathode in the electro-AnMBR. Hydrogen evolution provided a relatively alkaline pH environment, resulting in struvite electrodeposition on the graphic cathode, which partly separated the formed struvite from the sludge with a purity of 77%. In the electro-AnMBR, the electrochemical reactions provided alkalinity and effectively inhibited anaerobic acidification. The applied voltage of 0.6 V reduced the relative abundance of methanosaeta, but increased that of methanosarcina, which is also beneficial for the membrane anti-fouling.

Biofouling control potential of quorum quenching anaerobes in lab-scale anaerobic membrane bioreactors: Foulants profile and microbial dynamics

Indigenously isolated anaerobes encoding four quorum quenching (QQ) enzymes were applied in immobilized- and bioaugmented forms for their implications on membrane foulants, microbial taxa, and biofouling control. Two identical anaerobic membrane bioreactors (AnMBRs) with different immobilizing media, i.e. silica-alginate (AnMBR-Si) and hollow fiber-alginate (AnMBR-Hf), were sequentially operated for two conventional and three QQ based phases. The synergistic addition of QQ anaerobes in free cells and the immobilized form prolonged the membrane filtration operation by 172 ± 29% and 284 ± 12% in AnMBR-Si and AnMBR-Hf, respectively. Biocake with low surface coverage was prominent during QQ application compared to conventional phases. Despite the better control of AHLs (3OC6-, C6-, 3OC8, C8, and C10-HSL) and AI-2 at various points of QQ phases, the QQ consortium could not maintain a low concentration of signals for longer period. Therefrom, quenching of targeted signal molecules instigate the dominance of microbial species bearing non-targeted quorum sensing mechanism. The QQ significantly altered the biofilm-forming community in mixed liquor, while the members with robust signal transduction systems became dominant to counteract the QQ mechanism and were the ultimate cause of biofouling. The improved methane content in biogas and increased methanogens composition during QQ phases demonstrated the synergism of exogenous and immobilized QQ as the most viable option for long-term AnMBR operation.

Anaerobic membrane bioreactor for carbon-neutral treatment of industrial wastewater containing N, N-dimethylformamide: Evaluation of electricity, bio-energy production and carbon emission

The feasibility of anaerobic membrane bioreactor (AnMBR) for the treatment of N, N-dimethylformamide (DMF)-containing wastewater was theoretically compared with the conventional activated sludge (CAS) process in this study. The electricity consumption and expenditure, bio-energy production and CO₂ emission were investigated using the operational results of a lab-scale AnMBR operated in a long-term operation. The AnMBR was capable of producing bio-methane from wastewater and generated 3.45 kWh/m³ of electricity as recovered bio-energy while the CAS just generated 1.17 kWh/m³ of electricity from the post-treatment of excessive sludge disposal. The large quantity of bio-methane recovered by the AnMBR can also be sold as sustainable bioresource for the use of household natural gas with a theoretical profit gain of 29,821 US$/year, while that of the CAS was unprofitable. The AnMBR was also demonstrated to significantly reduce the carbon emission by obtaining a theoretical negative CO₂ production of -2.34 kg CO₂/m³ with the recycle of bio-energy while that for the CAS was 4.50 kg CO₂/m³. The results of this study demonstrate that the AnMBR process has promising potential for the carbon-neutral treatment of high-strength DMF-containing wastewater in the future.

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.

Material mass balance and elemental flow analysis in a submerged anaerobic membrane bioreactor for municipal wastewater treatment towards low-carbon operation and resource recovery

The anaerobic membrane bioreactor (AnMBR) has gained huge attention as a municipal wastewater (MWW) treatment process that combined high organics removal, a low sludge yield and bioenergy recovery. In this study, a 20 L AnMBR was set up and operated steadily for 70 days in temperate conditions with an HRT of 6 h and a flux of 12 LMH for the treatment of real MWW, focusing on the behavior of the major elements (C, N, P and S) from an elemental balance perspective. The results showed that the AnMBR achieved more than 85 % COD removal, a low sludge yield (0.081 gVSS/gCOD_removed) and high methane production (0.31 L-CH₄/gCOD_removed) close to the theoretical value. The elemental flow analysis revealed that the AnMBR converted 77 % of the influent COD to methane (57 % gaseous and 20 % dissolved) and 6 % of the COD for sludge production. In addition, the AnMBR converted 34 % of the total carbon to energy-generated carbon, and only 3 % was in the form of CO₂ in the biogas for further upgradation, which was in line with the concept of carbon neutrality. Since little nitrogen or phosphorus were removed, the permeate was nutrient-rich and further treatment to recover the nutrients would be required. This study illustrates the superior performance of the AnMBR for MWW treatment with a microscopic view of elemental behavior and provides a reference for implementing the mainstream AnMBR process in carbon-neutral wastewater treatment plants.

Highly selective butyric acid production by coupled acidogenesis and ion substitution electrodialysis

Selective production of carboxylic acids (CAs) from mixed culture fermentation remains a difficult task in organic waste valorization. Herein, we developed a facile and sustainable carbon loop strategy to regulate the fermentation micro-environment and steer acidogenesis towards selective butyric acid production. This new ion substitution electrodialysis-anaerobic membrane bioreactor (ISED-AnMBR) integrated system demonstrated a high butyric acid production at 11.19 g/L with a mass fraction of 76.05%. In comparison, only 1.04 g/L with a mass fraction of 30.56% was observed in the uncoupled control reactor. The carbon recovery reached a maximum of 96.09% with the assistance of ISED. Inorganic carbon assimilation was believed to be an important contributor, which was verified by ¹³C isotopic tracing. Microbial community structure shows the dominance of Clostridia (80.16%) in the unique micro-environment (e.g., pH 4.80-5.50) controlled by ISED, which is believed beneficial to the growth of such fermentative bacteria with main products of butyric acid and acetic acid. In addition, the emergence of chain elongators such as Clostridium sensu stricto 12 was observed to have a great influence on butyric acid production. This work provides a new approach to generate tailored longer chain carboxylic acids from organic waste with high titer thus contributing to a circular economy.

The relationship between quorum sensing dynamics and biological performances during anaerobic membrane bioreactor treatment

Anaerobic membrane bioreactors (AnMBRs) enhance carbon neutrality with biomethane recovery from wastewater; however, microbial signaling, which may affect biological performances, was poorly understood. Here, we thus evaluate quorum sensing (QS) dynamics while monitoring acyl-homoserine lactones (AHLs) and autoinducer-2 (AI-2) levels during long-term AnMBR operations after sludge inoculation. Significant organic removal and methane production were achieved with the reactor startup. Signal molecule levels varied with transient organic loading rates, depending on their types. A starving condition may cause an increase in short- and medium-chain AHLs and AI-2. Biopolymers, biosolids, volatile fatty acids, and alkalinity levels had positive correlations with short- and medium-chain AHLs and AI-2, whereas methane production had positive correlations with long-chain AHLs. The principal component analysis of QS signal composition and biological performance data explains their interconnectivity. The findings of this study help to understand that QS signals regulate metabolic pathways in addition to microbial group behaviors.

Anaerobic membrane bioreactors for pharmaceutical-laden wastewater treatment: A critical review

Pharmaceuticalsare a diverse group of chemical compounds widely used for prevention and treatment of infectious diseases in both humans and animals. Pharmaceuticals, either in their original or metabolite form, find way into the wastewater treatment plants (WWTPs) from different sources. Recently, anaerobic membrane bioreactors (AnMBR) has received significant research attention for the treatment of pharmaceuticals in various wastewater streams. This review critically examines the behaviour and removal of a wide array of pharmaceuticals in AnMBR with primary focus on their removal efficiencies and mechanisms, critical influencing factors, and the microbial community structures. Subsequently, the inhibitory effects of pharmaceuticals on the performance of AnMBR and membrane fouling are critically discussed. Furthermore, the imperative role of membrane biofouling layer and its components in pharmaceuticals removal is highlighted. Finally, recent advancements in AnMBR configurations for membrane fouling control and enhanced pharmaceuticals removal are systemically discussed.

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.

Seasonal and annual energy efficiency of mainstream anaerobic membrane bioreactor (AnMBR) in temperate climates: Assessment in onsite pilot plant and estimation in scaled-up plant

The seasonal and annual energy efficiency of mainstream anaerobic membrane bioreactor (AnMBR) was first assessed in an onsite pilot plant (15 m³/d) and then estimated in a scaled-up plant (10,000 m³/d) in temperate climates (15-25 °C). It was found that the annual net electricity demand was 0.100 and 0.090 kWh/m³, and the annual net energy (electricity + heat) demand was -0.158 and -0.309 kWh/m³ under the dissolved methane recovery condition and the non-recovery condition, respectively, demonstrated that the application of mainstream AnMBR in temperate climates is electricity saving and energy positive. The energy efficiency of the AnMBR decreased with temperature drop due to the reduction of methane production, and the increase in biogas sparging to mitigate membrane fouling. Since approximately 26.7%-39.7% of input COD remained in sludge, attention should be paid to recovering this potential energy to improve the overall energy performance of the mainstream AnMBR plants in future.

Fate and removal of emerging contaminants in anaerobic fluidized membrane bioreactor filled with thermoplastic gel as biofilm support

The Anaerobic Fluidized Membrane Bioreactor (AnFMBR) is a membrane-based hybrid technology that can overcome the limitations of conventional anaerobic sewage treatment. Although previous studies have demonstrated excellent performance in the removal of conventional organic pollutants, further research into the removal paths of emerging contaminants (ECs) under various operating conditions is required for proper design and development of the AnFMBR technology. Regarding this, the fate of four ECs in a lab-scale AnFMBR filled with thermoplastic gel for biofilm growth was investigated under various Hydraulic Retention Time (HRT) conditions. When the HRT was 13 h, diclofenac and 17β-estradiol were efficiently removed at 93% and 72% respectively. Even after an HRT reduction to 6.5 h, the system was still able to maintain high ECs removals (74% for diclofenac and 69% for 17β-estradiol). However, irrespective of HRT operational condition, smaller removals of 17a-ethinylestradiol (37-52%) were observed, while only marginal removals of amoxicillin were achieved (5-29%). Biotransformation was attributed as the main route for ECs removal. The results obtained in this study indicate that the membrane-based hybrid AnFMBR can be used to treat the target ECs without influence on anaerobic process. The technology had better removal efficiency for diclofenac and 17β-estradiol. However, the AnFMBR system exhibits high variability in EC removal and low capacity for amoxicillin removal, implying that a combination of other processes is still required to properly avoid the release of these contaminants into the environment.

Double-stage membrane-assisted anaerobic digestion process intensification for production and recovery of volatile fatty acids from food waste

The potential of organic waste streams (i.e., food waste) for the sustainable production of precursor chemicals such as volatile fatty acids (VFAs) using anaerobic digestion (AD) has received significant attention in the present days. AD-derived VFAs have great market appeal if the challenges with their recovery and purification from the complex AD effluent is overcome. In this study, a microfiltration immersed membrane bioreactor (MBR) was used for the production of VFAs from food waste and simultaneously in-situ recovery of VFAs. The MBR set-up was applied for 98 days, with a maximum yield of 0.2 gVFA/gVS_added at an organic loading rate (OLR) of 4 g VS/L/d. The recovered permeate was then subjected to further purification using a side stream ultrafiltration unit. It was found that the removal rates of total solids (TS), total suspended solids (TSS), dissolved solids (DS), volatile solids (VS) and volatile suspended solids (VSS) were above 70-80% in both membranes (10 kDa and 50 kDa), and Phosphorus (P), Total Kjeldahl Nitrogen (TKN), chemical oxygen demand (COD), and NH₄₊-N were also removed partially. Particularly, VFAs concentration (above 6 g/L) was higher for 10 kDa at pH 5.4 in ultrafiltered solution and permeate flux decline was higher for 10 kDa at pH 5.4. These results are also supported by the measurement of UV-Vis spectra of the solution and visual appearance, providing a promising approach towards building a VFAs-based platform.

Pilot plant demonstration of temperature impacts on the methanogenic performance and membrane fouling control of the anaerobic membrane bioreactor in treating real municipal wastewater

A 5,000-L anaerobic membrane bioreactor (AnMBR) fed with actual municipal wastewater was employed to study the impact of temperature drops on methanogenic performance and membrane fouling. With temperature dropped from 25 °C to 15 °C, the methane yield decreased from 0.244 to 0.205 NL-CH₄/g-COD_removal and the dissolved methane increased from 29% to 43%, resulted in the methanogenic performance reduced by 25%. The membrane rejection offset the deteriorated anaerobic digestion at low temperatures and ensured the stable COD removal efficiency of 84.5%-90.0%. The synergistic effects of the increased microbial products and viscosity and the residual inorganic foulants aggravated the membrane fouling at lower temperatures. As the organic fouling was easily removed by NaClO, the inorganics related to the elements of S, Ca and Fe were the stubborn membrane foulants and required the enhanced acid membrane cleaning. These findings obtained under the quasi-practical condition are expected to promote the practical applications of mainstream AnMBR.

A review on anaerobic membrane bioreactors for enhanced valorization of urban organic wastes: Achievements, limitations, energy balance and future perspectives

Sustainable urban development is threatened by an impending energy crisis and large amounts of organic wastes generated from the municipal sector among others. Conventional waste management methods involve greenhouse gas (GHG) emission and limited resource recovery, thus necessitating advanced techniques to convert such wastes into bioenergy, bio-fertilizers and valuable-added products. Research and application experiences from different scale applications indicate that the anaerobic membrane bioreactor (AnMBR) process is a kind of high-rate anaerobic digester for urban organic wastes valorization including food waste and waste sludge, while the research status is still insufficiently summarized. Through compiling recent achievements and literature, this review will focus on the following aspects, including AnMBR treatment performance and membrane fouling, technical limitations, energy balance and techno-economic assessment as well as future perspectives. AnMBR can enhance organic wastes treatment via complete retention of functional microbes and suspended solids, and timely separation of products and potential inhibitory substances, thus improving digestion efficiency in terms of increased organics degradation rates, biogas production and process robustness at a low footprint. When handling high-solid organic wastes, membrane fouling and mass transfer issues can be the challenges limiting AnMBR applications to a wet-type digestion, thus countermeasures are required to pursue extended implementations. A conceptual framework is proposed by taking various organic wastes disposal and final productions (permeate, biogas and biosolids) utilization into consideration, which will contribute to the development of AnMBR-based waste-to-resource facilities towards sustainable waste management and more economic-environmental benefits output.

Sodium hypochlorite induced inhibition in anaerobic digestion and possible approach to maintain methane fermentation performance

Since sodium hypochlorite (NaClO), a commonly used chemical to deal with membrane fouling, is toxic to microorganisms, it is a major concern in the membrane cleaning process. In this study, the concentration-dependent effects of NaClO (0-9 g/L) on the biodegradation performance and microbial activity were investigated via batch experiments. The methane production (obtained approximately 140 mL) and microbial community revealed by principal coordinates analysis were almost unaffected when the NaClO concentration ranged between 0 and 3 g/L. A follow-up batch experiment was conducted and revealed that the microbial products could help protect or recover the activity of anaerobic microorganisms at a high NaClO concentration of 10 g/L. Additionally, correlation analysis was used to investigate the associations between the 15 major bacterial genera. Moreover, the microbial analysis results indicated that the top 10 operational taxonomic units most affected by NaClO were primarily coryneform and filamentous bacteria.

Primary and A-sludge treatment by anaerobic membrane bioreactors in view of energy-positive wastewater treatment plants

Energy-rich sludge can be obtained from primary clarifiers preceding biological reactors. Alternatively, the incoming wastewater can be sent to a very-high-loaded activated sludge system, i.e., a so-called A-stage. However, the effects of applying an A-stage instead of a primary clarifier, on the subsequent sludge digestion for long-term operation is still unknown. In this study, biogas production and permeate quality, and filterability characteristics were investigated in a lab-scale anaerobic membrane bioreactor for primary sludge and A-stage sludge (A-sludge) treatment. A higher specific methane yield was obtained from digestion of A-sludge compared to primary sludge. Similarly, specific methanogenic activity was higher when the anaerobic membrane bioreactor was fed with A-sludge compared to primary sludge. Plant-wide mass balance analysis indicated that about 35% of the organic matter in wastewater was recovered as methane by including an A-stage, compared to about 20% with a primary clarifier.

Enriched autoinducer-2 (AI-2)-based quorum quenching consortium in a ceramic anaerobic membrane bioreactor (AnMBR) for biofouling retardation

This study is the first to enrich a facultative QQ consortium for AI-2-based quorum sensing (QS) disruption (FQQ2) and discover its quorum quenching (QQ) performance in an anaerobic membrane bioreactor (AnMBR) for membrane fouling retardation. Herein, FQQ2 was enriched by the enrichment culture using 4,5-dihydroxy-2,3-pentanedione (DPD) followed by anaerobic screening. FQQ2 was composed of various facultative AI-2-based QQ microorganisms including Acinetobacter, Comamonas, Stenotrophomonas, and FQQ2 was capable to degrade 96.96% of DPD in 9 h. More importantly, FQQ2 prolonged membrane filtration operation by an average of 3.72 times via reduction of DPD in the AnMBR treating domestic wastewater (p ≤ 0.05). QQ was implicated to reduce the content of proteins and carbohydrates of the extracellular polymeric substances (EPS) of suspended biomass by 24.16% and 10.39%, respectively, and concentration of proteins of the soluble microbial products (SMP) by 18.77%. Parallel factor (PARAFAC) modelling of excitation-emission matrix (EEM) demonstrated that QQ could reduce the content of fulvic acid-like and humic acid-like substances, aromatic proteins and soluble-microbial-by-product-like proteins of the EPS (p ≤ 0.05) and abate the content of soluble-microbial-by-product-like proteins in the SMP (p ≤ 0.05). The lower EPS content of suspended biomass could be rendered with the reduced relative abundance of AI-2-regulated Christensenellaceae;g-, Hyphomicrobium, Leucobacter and Microbacterium by 48.48%, 76.56%, 64.78% and 59.26%, respectively, and QQ led to the reduction of the relative abundance of Christensenellaceae;g- and Leucobacter in the cake layer by 31.07% and 51.43%, respectively. Moreover, quantity of organics as well as planktonic microorganisms in the supernatant decreased in presence of FQQ2 (p ≤ 0.05). Of note, markedly lower relative abundance of AI-2-regulated Sulfurovum in supernatant by 97.74% resulted in its lower abundance of cake layer. Intriguingly, in the presence of QQ, methane production was statistically enhanced by 62.5% (p ≤ 0.05). It was closely linked to the decrease of sulfate reduction (p ≤ 0.05), which resulted from 37.93% lower abundance of sulfate-reduction Desulfomonile in the suspended biomass (p ≤ 0.05). Collectively, this study sheds lights on the development of AI-2-based QQ for biofouling control in AnMBRs.

Seasonal temperatures impact on the mass flows in the innovative integrated process of anaerobic membrane bioreactor and one-stage partial nitritation-anammox for the treatment of municipal wastewater

A pilot-scale anaerobic membrane bioreactor (AnMBR) integrated with a one-stage partial nitritation-anammox (PN/A) reactor was operated for the treatment of municipal wastewater (MWW) at seasonal temperatures of 15-25 °C. The removal efficiencies of COD and total nitrogen (TN) were always > 90% and > 75% respectively. The methanogenesis and PN/A were identified as the primary removal pathways of COD and TN, respectively, and were suppressed at low temperatures. With the temperature dropped from 25 °C to 20 °C to 15 °C, the methane-accounted COD decreased from 63.1% to 59.6% to 48.4%, and the PN/A-accounted TN decreased from 58.1% to 51.7% to 45.3%. The AnMBR and PN/A mutually complement each other in this combined process, as the AnMBR removed 8.5%-16.1% of TN by sludge entrainment and the PN/A reactor removed 2.6%-3.4% of COD by denitrification and aerobic oxidation. These results highlighted the strong feasibility of applying the AnMBR-PN/A process to the treatment of MWW in temperate climate.

Predicting membrane fouling in a high solid AnMBR treating OFMSW leachate through a genetic algorithm and the optimization of a BP neural network model

Anaerobic membrane bioreactors are a promising technology in the treatment of high-strength wastewater; however, unpredictable membrane fouling largely limits their scale-up application. This study, therefore, adopted a backpropagation neural network model to predict the membrane filtration performance in a submerged system, which treats leachate from the organic fraction of municipal solid waste. Duration time, water yield flow, influent COD, pH, bulk sludge concentration, and the ratio of ΔTMP to filtration time were selected as input variables to simulate membrane permeability. The membrane pressure slightly increased by 1.1 kPa within 62 days of operation. The results showed that the AnMBR membrane filtration performance was acceptable when treating OFMSW leachate under a flux of 6 L/(m²·h). The model results indicated that the sludge concentration largely determined the membrane fouling with a contribution of 33.8%. Given the local minimization problem in the BP neural network process, a genetic algorithm was introduced to optimize the simulation process, and the relative error of the results was reduced from 5.57% to 3.57%. Conclusively, the artificial neural network could be a useful tool for the prediction of an AnMBR that is so far under development.

Application of deep learning for predicting the treatment performance of real municipal wastewater based on one-year operation of two anaerobic membrane bioreactors

In this study, data-driven deep learning methods were applied in order to model and predict the treatment of real municipal wastewater using anaerobic membrane bioreactors (AnMBRs). Based on the one-year operating data of two AnMBRs, six parameters related to the experimental conditions (temperature of reactor, temperature of environment, temperature of influent, influent pH, influent COD, and flux) and eight parameters for wastewater treatment evaluation (effluent pH, effluent COD, COD removal efficiency, biogas composition (CH₄, N₂, and CO₂), biogas production rate, and oxidation-reduction potential) were selected to establish the data sets. Three deep learning network structures were proposed to analyze and reproduce the relationship between the input parameters and output evaluation parameters. The statistical analysis showed that deep learning closely agrees with the AnMBR experimental results. The prediction accuracy rate of the proposed densely connected convolutional network (DenseNet) can reach up to 97.44%, and the single calculation time can be reduced to within 1 s, suggesting the high performance of AnMBR treatment prediction with deep learning methods.

Encapsulation technology for decentralized brewery wastewater treatment: A small pilot experiment

The feasibility of implementing encapsulation technology for the biological anaerobic treatment of high-strength wastewater was investigated. The small pilot-scale wastewater treatment process, deployed at a local brewery, consisted of a 4-L fermenting first-stage reactor containing alginate-encapsulated fermenting microorganisms and a 30-L methanogenic second-stage reactor containing alginate-encapsulated anaerobic digester sludge (CH4E reactor). A parallel second-stage 30-L anaerobic membrane bioreactor (AnMBR) was operated for comparison. The first-stage reactor produced 40.4 ± 47.3% more volatile fatty acids than present in the influent wastewater. The CH4E reactor stared rapidly, with an off-gas methane content >60% after 14 days. It took >1 month for the AnMBR to achieve this performance. Nevertheless, the CH4E reactor performance declined relative to the AnMBR over time. This was thought to be a result of encapsulant leakage and the encapsulation of a non-ideal initial community. Further optimization is needed, but encapsulation shows promise for small-footprint anaerobic biological treatment applications.

The first pilot-scale demonstration of the partial nitritation/anammox-hydroxyapatite process to treat the effluent of the anaerobic membrane bioreactor fed with the actual municipal wastewater

Recently, it was reported that for synthetic low-strength wastewater, the excellent nitrogen removal rate (NRR) accompanied with phosphorus removal could be achieved through the partial nitritation/anammox (PNA)-hydroxyapatite (HAP) process. Thus, this research further investigated the performance of the pilot-scale PNA-HAP process treating the effluent of an anaerobic membrane bioreactor (AnMBR) fed with the actual municipal wastewater. The results showed that with the hydraulic retention time of 4.0 h, the influent ammonium concentration ranging from 36.0 to 41.0 mg/L, and the BOD₅ ranging from 6.3 to 12.7 mg/L, the average NRR and the nitrogen removal efficiency was 0.13 kg/m³/d and 63.38%, respectively. The specific activity test of sludge confirmed that the PNA process was the main nitrogen metabolism pathway. The effluent nitrate and the BOD₅ were almost zero, indicating the existence of denitrification activity in reactor. Given that the oxygenation condition, the heterotrophic organic matter oxidization activity also occurred in reactor. The sludge analysis confirmed the phosphate formation in sludge. Thus, in the reactor, four kinds of biological activities and chemical crystallization occurred harmoniously in sludge. From the mixed liquid volatile suspended solid of 2.4 g/L and the low distribution range of granule size, it was obvious that the sludge had a high dispersity. Based on the well settling ability of sludge during the operation, it was inferred that there was a close bond between biomass and HAP in sludge, which was helpful to enhance the settleability of sludge granule. Besides, the phosphorus-containing sludge was suitable as the fertilizer. In all, this study demonstrated that the PNA-HAP process is an ideal alternative treating the effluent of the AnMBR process in the municipal wastewater treatment.

Dynamic anaerobic membrane bioreactor coupled with sulfate reduction (SrDMBR) for saline wastewater treatment

This study investigated organic removal performance, characteristics of the membrane dynamics, membrane fouling and the effects of biological sulfate reduction during high-salinity (1.0%) and high-sulfate (150 mgSO₄^2--S/L) wastewater treatment using a laboratory-scale upflow anaerobic sludge bed reactor integrated with cross-flow dynamic membrane modules. Throughout the operational period, dynamic membrane was formed rapidly (within 5-10 min) following each backwashing cycle (21-16 days), and the permeate turbidity of <5-7 NTU was achieved with relatively high specific organic conversion (70-100 gTOC/kgVSS·d) and specific sulfate reduction (50-70 gSO₄^2--S/kgVSS·d) rates. The sulfide from sulfate reduction can be reused for downstream autotrophic denitrification. 16S rRNA gene amplicon sequencing revealed that the microbial communities enriched in the sludge were different than those accumulated on the dynamic layer. Overall, this study demonstrates that the anaerobic dynamic membrane bioreactor coupled with sulfate reduction (SrDMBR) shows promising applicability in saline wastewater treatment.

Microbial characteristics in anaerobic membrane bioreactor treating domestic sewage: Effects of HRT and process performance

Two anaerobic membrane bioreactors (AnMBRs) equipped with different membrane pore size (0.4 or 0.05 µm) were operated at 25˚C and fed with domestic wastewater. The hydraulic retention time (HRT) of the reactors was shortened. The microbial communities of the two AnMBRs were investigated by 16S rRNA gene amplicon sequencing to see the effects of HRT. The predominant Archaea was an aceticlastic methanogen Methanosaeta. The composition of hydrogenotrophic methanogens changed with the HRTs: the population of Methanobacterium was higher for longer HRTs, whereas the population of unclassified Methanoregulaceae was higher for shorter HRTs. The Anaerolineae, Bacteroidia and Clostridia bacteria were dominant in both of the reactors, with a combined relative abundance of over 55%. The relative abundance of Anaerolineae was proportional to the biogas production performance. The change in the population of hydrogenotrophic methanogens or Anaerolineae can be used as an indicator for process monitoring. The sum of the relative abundance of Anaerolineae and Clostridia fluctuated slightly with changes in the HRT in both AnMBRs when the reactor was stably operated. The co-occurrence analysis revealed the relative abundance of the operational taxonomic units belonging to Anaerolineae and Clostridia was functionally equivalent during the treatment of real domestic sewage. A principal coordination analysis revealed that the changes in the microbial community in each reactor were consistent with the change of HRT. In addition, both the HRT and the stability of the process are important factors for maintaining microbial community structures.

Enhancing the performance of thermophilic anaerobic digestion of food waste by introducing a hybrid anaerobic membrane bioreactor

The thermophilic anaerobic digestion of food waste was a long-term challenge for maintaining process stability. A hybrid submerged anaerobic membrane bioreactor (AnMBR), integrating 27%(v/v) polyurethane sponge as fixed carriers were therefore investigated at (50 ± 2) °C. The organics removal efficiencies, COD mass balance, and membrane filtration performance were investigated in a 75-days continuously operated experiment. The results showed that methane production reached 0.31 L/(kg·COD) under an organic loading rate of 7.3 kg·COD/(m³·d). The low concentration of total volatile fatty acids of 247 ~ 274 mg/L and a high proportion of Methanosarcina (>97%) represented the high stability of the thermophilic process. Approximately 21% of biomass grew on the carriers in the hybrid AnMBR and induced a much lower suspended solids concentration and viscosity of bulk sludge. Noticeable lower trans-membrane pressure was consequently observed. The affecting factors identified by PCA analysis proved the advantages of the hybrid AnMBR for alleviating membrane fouling formation.

Chemical oxygen demand and nitrogen transformation in a large pilot-scale plant with a combined submerged anaerobic membrane bioreactor and one-stage partial nitritation-anammox for treating mainstream wastewater at 25 °C

A novel municipal wastewater treatment process towards energy neutrality and reduced carbon emissions was established by combining a submerged anaerobic membrane bioreactor (SAnMBR) with a one-stage partial nitritation-anammox (PN/A), and was demonstrated at pilot-scale at 25 °C. The overall COD and BOD₅ removal efficiencies were 95.1% and 96.4%, respectively, with 20.3 mg L^-1 COD and 5.2 mg L^-1 BOD₅ remaining in the final effluent. The total nitrogen (TN) removal efficiency was 81.7%, resulting 7.3 mg L^-1 TN was discharged from the system. The biogas yield was 0.222 NL g^-1 COD _removed with a methane content range of 78-81%. Approximately 90% of influent COD was removed in the SAnMBR, and 70% of influent nitrogen was removed in the PN/A. The denitrification which occurred in the PN/A enhanced overall COD and nitrogen removal. The successful operation of this pilot-scale plant indicates the SAnMBR-PN/A process is suitable for treating real municipal wastewater.

The NEWgeneratorTM non-sewered sanitation system: Long-term field testing at an informal settlement community in eThekwini municipality, South Africa

Globally, there is a dire need for a new class of advanced non-sewered sanitation systems (NSSS) to provide onsite wastewater treatment that is capable of meeting stringent discharge or reuse criteria. These systems need to be simple to operate and maintain, reliable, and resilient to unreliable electrical service. The NEWgenerator (NG) is a compact, automated, solar-powered wastewater treatment system comprised of three major treatment processes: anaerobic membrane bioreactor (AnMBR), nutrient capture system (NCS) with ion exchange and carbon sorption, and electrochlorination (EC). The NG system operated at an informal settlement community in South Africa over a 534 d period, treating high-strength blackwater (BW) and yellow water (YW) from a public toilet facility. Over three test stages (BW, BW + YW, BW) that included several periods of dormancy, the NG system was able to provide a high level of removal of total suspended solids (97.6 ± 3.1%), chemical oxygen demand (94.5 ± 5.0%), turbidity (96.3 ± 9.7%), color (92.0 ± 10.5%), total nitrogen (82.1 ± 24.0%), total phosphorus (43.0 ± 22.1%), E. coli (7.4 ± 1.5 LRV, not detected in effluent), and helminth ova (not detected in effluent). The treatment levels met most of the ISO 30500 NSSS standard for liquid effluent and local water reuse criteria. A series of maintenance events were successfully conducted onsite over the 534 d field trial: two membrane cleanings, two NCS regenerations, and granular activated carbon replacement. Desludging, a major pain point for onsite sanitation systems, was unnecessary during the field trial and thereby not performed. The AnMBR performed well, removing 94.5 ± 5.0% of the influent COD across all three stages. The high COD removal rate is attributed to the sub-micron separation provided by the ultrafiltration membrane. The NCS was highly efficient at removing total nitrogen, residual COD and color, but the regeneration process was lengthy and is a topic of ongoing research. The EC provided effective disinfection, but frequent prolonged run cycles due to power supply and water quality issues upstream limited the overall system hydraulic throughput. This extended field trial under actual ambient conditions successfully demonstrated the feasibility of using advanced NSSS to address the global water and sanitation crises.

Important effects of temperature on treating real municipal wastewater by a submerged anaerobic membrane bioreactor: Removal efficiency, biogas, and microbial community

A submerged anaerobic membrane bioreactor (SAnMBR) was used in the treatment of real municipal wastewater at operation temperatures ranging from 15 °C to 25 °C and hydraulic retention time (HRT) of 6 h. The treatment process was evaluated in terms of organic removal efficiency, biogas production, sludge growth and membrane filtration. During long-term operation, the SAnMBR achieved chemical oxygen demand removal efficiencies of about 90% with a low sludge yield (0.12-0.19 g-VSS/g-COD_rem) at 20-25 °C. Approximately 1.82-2.27 kWh/d of electric energy was generated during the wastewater treatment process at 20-25 °C, 0.67 kWh/d was generated at 15 °C. The microbial community analysis results showed that microbial community was dominated by aceticlastic methanogens, coupled by hydrogenotrophic methanogens and a very small quantity of methylotrophic methanogens. It was also shown that the stabilization of the microbial community could be attributed to the carbohydrate-protein degrading bacteria and the carbohydrate degrading bacteria.

Temperature and immigration effects on quorum sensing in the biofilms of anaerobic membrane bioreactors

Quorum sensing (QS), a microbial communication mechanism modulated by acyl homoserine lactone (AHL) molecules impacts biofilm formation in bioreactors. This study investigated the effects of temperature and immigration on AHL levels and biofouling in anaerobic membrane bioreactors. The hypothesis was that the immigrant microbial community would increase the AHL-mediated QS, thus stimulating biofouling and that low temperatures would exacerbate this. We observed that presence of immigrants, especially when exposed to low temperatures indeed increased AHL concentrations and fouling in the biofilms on the membranes. At low temperature, the concentrations of the main AHLs observed, N-dodecanoyl-L-homoserine lactone and N-decanoyl-L-homoserine lactone, were significantly higher in the biofilms than in the sludge and correlated significantly with the abundance of immigrant bacteria. Apparently low temperature, immigration and denser community structure in the biofilm stressed the communities, triggering AHL production and excretion. These insights into the social behaviour of reactor communities responding to low temperature and influx of immigrants have implications for biofouling control in bioreactors.

Efficient recovery of phosphorus and sulfur from Anaerobic Membrane Bioreactor (AnMBR) permeate using chemical addition of iron and evaluation of its nutrient availability for plant uptake

Anaerobic membrane bioreactors (AnMBRs) represent an emerging environmental biotechnology platform with the potential to simultaneously recover water, energy, and nutrients from concentrated wastewaters. The removal and beneficial capture of nutrients from AnMBR permeate has yet to be fully explored, therefore this study sought to foster iron phosphate recovery through a tertiary coagulation process, as well as characterize the recovered nutrient product (RNP) and assess its net phosphorus release, diffusion, and availability for plant uptake. One of the primary goals of this study was to optimize the dose of the coagulant, ferric chloride, and coagulant aid, aluminum chlorohydrate (ACH), for continuous application to the coagulation-flocculation-sedimentation (CFS) unit of an AnMBR pilot plant treating municipal wastewater, through controlled bench-scale jar tests. Anaerobic systems present unique challenges for nutrient capture, including high, dissolved hydrogen sulfide concentrations, along with settleability issues. The addition of the coagulant aid increases settleability, while enhancing phosphorus removal by up to 20%, decreasing iron demand. Water quality analysis indicated that a variety of factors affect nutrient capture, including the COD (chemical oxygen demand) concentration of the permeate and the limiting coagulant dose. COD >200 mg/L was shown to decrease the phosphorus removal efficiency by up to 15%. A combination of inductively coupled plasma optical emission spectrometer (ICP-OES) elemental analysis, inductively coupled plasma mass spectrometer (ICP-MS) elemental analysis, scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray absorption near-edge structure (XANES) spectroscopy analysis was used to characterize the P-rich RNP which revealed a 2.58% w/w phosphorus content and the lack of a well-defined crystalline structure. Detailed studies on resin extractable phosphorus to assess the plant uptake potential also demonstrated that iron-based P-rich RNPs may not be an effective fertilizer product, as they can act as a phosphorus sink in some agricultural systems instead of a source.

Artificial intelligence modeling to predict transmembrane pressure in anaerobic membrane bioreactor-sequencing batch reactor during biohydrogen production

The complex nature of wastewater treatment has led to search for alternative strategies such as different artificial intelligence (AI) techniques to model the various operational parameters. The present work is aimed at predicting the transmembrane pressure (TMP) as a key operational parameter in the case of anaerobic membrane bioreactor-sequencing batch reactor (AnMBR-SBR) during biohydrogen production using the adaptive neuro-fuzzy inference systems (ANFIS) and artificial neural network (ANN). In both the models, organic loading rates (OLR) ranging from 0.5 to 8.0 g COD/L/d, effluent pH (3.6-6.9), mixed liquor suspended solid (4.6-21.5 g/L) and mixed liquor volatile suspended solid (3.7-15.5 g/L) were used as the input parameters to test TMP as an output parameter. The ANFIS model was trained using the hybrid algorithms for TMP prediction. The higher prediction performance was obtained by using the Gauss membership function with four membership numbers. A back-propagation algorithm was also employed for the feed forward training of ANN model; the best structure was a Levenberg-Marquardt training algorithm with nine neurons in the hidden layer. By employing ANFIS and ANN models, relatively a good prediction of TMP was obtained with the R² values of 0.93 and 0.88, respectively while the calculated mean square error for TMP in the ANFIS model (7.3 × 10^-3) was lower than that of ANN model (8.02 × 10^-3). The higher R² and lower MSE values for the ANFIS model exhibited a better TMP prediction performance than the ANN model. Finally, it was observed that in the sensitivity analysis of ANN model, OLR was the most important input parameter on the variation of TMP.

Antifouling potential and microbial characterization of an electrochemical anaerobic membrane bioreactor utilizing membrane cathode and iron anode

Serious membrane fouling limits the application of anaerobic membrane bioreactors (AnMBRs) in sewage treatment. Herein, a novel electrochemical AnMBR (eAnMBR) was established by integrating electrocoagulation and a conductive membrane into an AnMBR. Compared with the traditional AnMBR, TP average removal rate increased by 24.97% and the membrane service cycle extended by 109.68% in the eAnMBR. Low extracellular polymeric substance concentration and large floc size were found in the mixed liquid of the eAnMBR due to the combined effect of coagulation and electric field, which induced a porous and hydrophilic cake layer, resulting in excellent water permeation capabilities. Additionally, the conductive membrane cathode effectively suppressed membrane fouling by the electrostatic repulsion and gas scouring. In the eAnMBR, the presence of an electric field and iron ions enriched the diversity of the microbial community, which may improve the adaptation of biochemical systems to environmental changes.

Attached-growth configuration outperforms continuously stirred tank anaerobic membrane bioreactors in alleviating membrane biofouling

Biofouling impedes the performance of anaerobic membrane bioreactors (AnMBR). Two reactors, one as an up-flow attachment-growth AnMBR (UA-AnMBR) configuration, and the other, as a continuously stirred AnMBR (CS-AnMBR) were evaluated for differences in membrane fouling rate. TMP increment in UA-AnMBR was slower than CS-AnMBR, although both reactors had similar COD removal efficiency (ca. > 96%). Slower fouling rate for UA-AnMBR was related to lower total and viable cells, and thereby microbial activity compared to that in CS-AnMBR. Acinetobacter and Methanobacterium that played keystone roles in anaerobic biofilm formation were not consistently prevalent on the membranes connected to UA-AnMBR. This is in contrast to both Acinetobacter and Methanobacterium consistently prevalent on the membranes connected to CS-AnMBR. The findings suggest that UA-AnMBR can alleviate membrane biofouling through changes in microbial activity and profile dynamics, and would be a suitable reactor configuration to adopt to achieve an efficient AnMBR for municipal wastewater treatment.

Advanced near-zero waste treatment of food processing wastewater with water, carbon, and nutrient recovery

A near-zero waste treatment system for food processing wastewater was developed and studied. The wastewater was treated using an anaerobic membrane bioreactor (AnMBR), polished using an outdoor photobioreactor for microalgae cultivation (three species were studied), and excess sludge was treated using hydrothermal carbonization. The study was conducted under arid climate conditions for one year (four seasons). The AnMBR reduced the total organic carbon by 97%, which was mostly recovered as methane (~57%) and hydrochar (~4%). Microalgal biomass productivity in the AnMBR effluent ranged from 0.25 to 0.8 g·L^-1·day^-1. Nitrogen (N) and phosphorous (P) uptake varied seasonally, from 18 to 45 mg·L^-1·day^-1 and up to 5 mg·L^-1·day^-1, respectively. N and P mass balance analysis demonstrated that the process was highly efficient in the recovery of nitrogen (~77%), and phosphorus (~91%). The performance of the microalgal culture changed among seasons because of climatic variation, as a result of variation in the wastewater chemistry, and possibly due to differences among the microalgal species. Effluent standards for irrigation use were met throughout the year and were achieved within two days in summer and 4.5 days in winter. Overall, the study demonstrated a near-zero waste discharge system capable of producing high-quality effluent, achieving nutrient and carbon recovery into microalgae biomass, and energy production as biogas and hydrochar.

The use of UV/H2O2 to facilitate removal of emerging contaminants in anaerobic membrane bioreactor effluents

Effluent from anaerobic membrane bioreactor (AnMBR) contains ammonia and would require post-polishing treatment before it can be disinfected by chlorine. However, additional post-treatment steps to remove nutrients offset the energetic benefits derived from anaerobic fermentation. The use of chlorine or ozone also promotes concerns associated with disinfection byproducts. This study evaluates UV/H₂O₂ as a potential strategy suited for the removal of pharmaceutical compounds as well as antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) from AnMBR effluent. Our findings indicate that 10 mg/L H₂O₂ and 61.5 mJ/cm² of UV fluence are able to achieve a 4-log removal of both Escherichia coli PI7 and Klebsiella pneumoniae L7. However, a higher fluence of 311 mJ/cm² with the same amount of H₂O₂ would be required to achieve >90% removal of atenolol, carbamazepine and estrone. The removal of the pharmaceutical compounds was driven by the hydroxyl radicals generated from H₂O₂, while UV exposure governed the inactivation of ARB and ARGs. UV/H₂O₂ increased overall mutagenicity of the treated wastewater matrix but did not result in any changes to the natural transformation rates. Instead, UV significantly reduced natural transformation rates by means of DNA damage. Overall, UV/H₂O₂ could be the ideal final disinfection strategy for AnMBR effluent without requiring additional post-treatment prior disinfection.

One-year operation of a 20-L submerged anaerobic membrane bioreactor for real domestic wastewater treatment at room temperature: Pursuing the optimal HRT and sustainable flux

A 20 L hollow-fiber submerged anaerobic membrane bioreactor (SAnMBR) was used to treat real domestic wastewater at 25 °C with hydraulic retention times (HRTs) ranging from 4 to 12 h. The process performance was evaluated by organic removal efficiency, biogas production, sludge yield, and filtration behaviors during one-year's operation. For HRTs ranging between 6 and 12 h, the AnMBR showed good organic removal efficiency with chemical oxygen demand (COD) and biochemical oxygen demand (BOD) removal efficiencies of about 89% and 93%, respectively. The biogas yield was 0.26 L-gas/g-COD_fed, with approximately 80% methane content, and the sludge yield was 0.07-0.11 g-VSS/g-COD_rem. While at an HRT of 4 h, with the higher wastewater treatment capacity and organic loading rate (OLR), the biogas production was lower (0.17 L-gas/g-COD_fed), and the sludge production was higher (0.22 g-VSS/g-COD_rem). The organic removal performance (COD 84% and BOD 89%) at HRT of 4 h was acceptable due to the effective separation effect of the membrane filtration process. According to COD balance analysis, the low biogas yield and high sludge yield at HRT of 4 h were due to insufficient biodegradation under an OLR of 2.05 g-COD/L-reactor/d. Theoretical calculations based on Henry's law indicate that the ideal methane content in the biogas should be 82-85% when the operational temperature was 25 °C. To achieve a high flux and sustainable AnMBR operation, the impact of mixed liquor suspended solid (MLSS) and gas sparging velocity (GSV) on the filtration performance was analyzed. The critical flux increased with increase in the GSV from 24.2 to 174.3 m/h, but decreased with increase in the MLSS concentration from 8.2 to 20.2 g/L. Therefore, decreasing fouling rate to 0.8-1.2 kPa/d by efficiently controlling GSV and MLSS, sustainable operation could be achieved at a flux of 0.34 m/d.

Biochar addition supports high digestion performance and low membrane fouling rate in an anaerobic membrane bioreactor under low temperatures

The enhancement effects of biochar to an anaerobic membrane bioreactor (AnMBR) treating sewage at low temperatures was investigated in this study through analyzing organics removal, digestion performance, mixed liquor properties, membrane resistance, and foulant compositions. The chemical oxygen demand (COD) removal efficiency and the COD converted to methane rate increased by more than 12.5% at 10 °C, mainly because of the promotion of biochar to volatile fatty acids degradation. Although biochar caused higher dissolved organic matter (DOM) concentration in the AnMBR, it improved the filtration property of the bulk sludge and absorbed the hydrophobic DOM. The decreased filtration resistance assisted by biochar leads to a prolonged membrane operation duration over 200%. Surface foulants, especially cake foulants, were largely mitigated by the enhanced scouring intensity of mixed liquor at the membrane surface, and hence, decreasing the cake/gel foulants ratio.

The materials flow and membrane filtration performance in treating the organic fraction of municipal solid waste leachate by a high solid type of submerged anaerobic membrane bioreactor

The anaerobic digestion of leachate from organic fraction of municipal solid waste (OFMSW) is a long-standing challenge. A submerged anaerobic membrane bioreactor (AnMBR) embedding three flat sheet membrane was therefore continuously operated for 63 days to investigate the materials flow and membrane performance. The results obtained show that approximately 90% COD was removed and 86% was converted into methane under an OLR of 5.6 kgCOD/m³·d corresponding to a HRT of 10 days. Under the high solid condition (34.5-61.1 g/L total solids in AnMBR) and flux of 5 and 6 LMH, the membranes was operated practically at constant trans-membrane pressure (TMP). When the membrane was operated at a high flux of 7 LMH the TMP rapid increase occurred in 22 h resulting in a non-recoverable permeability. A sustainable flux was thus identified. This study demonstrated the feasibility of AnMBR treating OFMSW leachate under high solid condition with high flux.

Robustness of granular activated carbon-synergized anaerobic membrane bioreactor for pilot-scale application over a wide seasonal temperature change

A novel granular activated carbon-synergized anaerobic membrane bioreactor (GAC-AnMBR), consisted of four expanded bed anaerobic bioreactors with GAC carriers and a membrane tank, was established in pilot scale (10 m³/d) to treat real municipal wastewater (MWW) at ambient temperature seasonally fluctuating from 35 to 5 °C. It showed sound organic removal over 86% with the permeate COD less than 50 mg/L even at extremely low temperatures below 10 °C. COD mass balance analysis revealed that membrane rejection (with a contribution rate of 10%-20%) guaranteed the stable organic removal, particularly at psychrophilic temperature. The methane yield was over 0.24 L CH_{4 (STP)}/g COD _removed at mesophilic temperature and 0.21 L CH_{4 (STP)}/g COD _removed at 5-15 °C. Pyrosequencing of microbial communities suggested that lower temperature reduced the abundance of the methane producing bacteria, but the methane production was enhanced by selectively enriched Methanosaeta, syntrophic Syntrophobacter and Smithella and exoelectrogenic Geobacter for direct interspecies electron transfer (DIET) on the additive GAC. Compared with previously reported pilot-scale AnMBRs, the GAC-AnMBR in this study showed better overall performance and higher stability in a wide temperature range of 5-35 °C. The synergistic effect of GAC on AnMBR guaranteed the robustness of GAC-AnMBR against temperature, which highlighted the applicational potential of GAC-AnMBR, especially in cold and temperate climate regions.

Long term performance of a pilot scale anaerobic membrane bioreactor treating beet molasses based industrial wastewater

Baker's yeast industries (BYI) generate highly polluted effluents, especially vinasse from yeast separators, with very high chemical oxygen demand (COD), nitrogen, sulphate and salts, mainly potassium and calcium. Anaerobic treatment is the most commonly applied method for treating BYI wastewaters. However, it is quite challenging to obtain a high performance due to the difficulties in biomass retention. Moreover, it does not provide compliance with COD and color discharge limits when used as a sole treatment process. In this context, a pilot scale anaerobic membrane bioreactor, which provides excellent biomass retention, was operated to investigate its treatment performance for vinasse from a BYI. The reactor achieved a COD removal between 48% and 92% up to a volumetric load of 10 kg COD m³ d^-1. A specific methane production of 0.37 m³ CH₄ kg^-1 COD_removed was observed in the study. On the other hand, passage of inert organic compounds through membrane deteriorated permeate quality and treatment efficiency. High alkalinity and pH led to the accumulation of calcium precipitates, which reduced volatile solids fraction of sludge and biomass activity in the reactor. The present study showed the operational challenges and potential drawbacks of AnMBR systems for BYI wastewater treatment. The experience gained in the pilot system can be utilized in the design and operation of full scale AnMBRs for high strength industrial effluents.