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

A novel Anaerobic Cathodic Dynamic Membrane Bioreactor (AnCDMBR) for efficient mitigating fouling and recovering bioenergy from municipal wastewater

Concerns regarding membrane fouling and suboptimal bioenergy recovery have constrained the implementation of anaerobic membrane bioreactor (AnMBR) for treating low-strength municipal wastewater. This study presents a novel anaerobic cathodic dynamic membrane bioreactor (AnCDMBR) designed to address these challenges. A self-formed cathodic dynamic membrane (CDM) on inexpensive carbon cloth was developed to function as both a membrane and biocathode to achieve dual-function effects of mitigating membrane fouling and accelerating organics conversion. Compared with common dynamic membrane (1.52 kPa/d) and commercial membranes (7.52 kPa/d), the developed CDM presented a significantly reduced fouling rate (1.02 kPa/d), exhibiting the potential as a substitute for high-cost conductive membranes. Furthermore, efficient and stable biomethanation occurred in AnCDMBR with a superior methane yield rate of 0.26 L-CH4/g-COD (CH4 content > 95 %), which was 1.42 times higher than the control, linked to the higher activities of microbial metabolism and methanogenic-related key enzymes. Further analysis revealed that electrostimulation-induced niche differentiation of microbiota regulated interspecies interactions between electroactive microorganisms and complex anaerobic digestion microbiomes, facilitating organic matter conversion to methane and leading to superior bioenergy recovery. This study offered a new strategy for effectively mitigating fouling and recovering bioenergy from low-strength wastewater, potentially expanding the application of AnMBRs.

Study on membrane fouling mechanisms and mitigation strategies in a pilot-scale anaerobic membrane bioreactor (P-AnMBR) treating digestate

Anaerobic Membrane Bioreactor (AnMBR) are employed for solid-liquid separation in wastewater treatment, enhancing process efficiency of digestion systems treating digestate. However, membrane fouling remains a primary challenge. This study operated a pilot-scale AnMBR (P-AnMBR) to treat high-concentration organic digestate, investigating system performance and fouling mechanisms. P-AnMBR operation reduced acid-producing bacteria and increased methane-producing bacteria on the membrane, preventing acid accumulation and ensuring stable operation. The P-AnMBR effectively removed COD and VFA, achieving removal rates of 82.3 % and 92.0 %, respectively. Higher retention of organic nitrogen and lower retention of ammonia nitrogen were observed. The membrane fouling consisted of organic substances (20.3 %), predominantly polysaccharides, and inorganic substances (79.7 %), primarily Mg ions (10.1 %) and Ca ions (4.5 %). To reduce the increased transmembrane pressure (TMP) caused by fouling (a 10.6-fold increase in filtration resistance), backwash frequency experiment was conducted. It revealed a 30-min backwash frequency minimized membrane flux decline, facilitating recovery to higher flux levels. The water produced amounted to 70.3 m³ over 52 days. The research provided theoretical guidance and practical support for engineering applications, offering practical insights for scaling up P-AnMBR.

Multi-omics analysis reveals the mechanisms by which C6-HSL enhances the resistance of typical functional bacteria in activated sludge to low-temperature stress

Signaling molecules, particularly acyl-homoserine lactones (AHLs), can enhance microbial activity under low-temperature stress. However, the specific mechanisms underlying this effect remain unclear. This study identified a typical activated sludge functional bacterium that is sensitive to low temperatures and regulated by hexanoyl-L-homoserine lactone (C6-HSL), a representative of AHLs. It elucidates how C6-HSL modulates the bacterium's resistance to low-temperature stress. Experimental results indicated that C6-HSL significantly increased the levels of adenosine triphosphate (ATP), superoxide dismutase (SOD), peroxidase (POD) and glutathione peroxidase (GSH-Px) in strain LB-001 under low-temperature stress, while also decreasing the levels of reactive oxygen species (ROS). Additionally, C6-HSL markedly repaired the damage to cell membrane structure caused by low-temperature stress. At the genetic level, C6-HSL upregulated the expression of 20 key genes related to energy metabolism, antioxidation, and fatty acid synthesis. At the metabolic level, C6-HSL increased the levels of metabolites related to energy metabolism and antioxidation, boosted the content of unsaturated fatty acids, and reduced the content of saturated fatty acids. This study utilized C6-HSL and low-temperature induction in conjunction with 16S microbial diversity sequencing, genomics, transcriptomics, and metabolomics. These methods were employed to elucidate the molecular mechanisms by which exogenous C6-HSL regulates the resistance of activated sludge microbial communities to low-temperature stress. This research lays the foundation for the application of AHLs and cell communication in wastewater biological treatment, fostering deeper exploration and further innovation in related academic research.

The effect of temperature on fouling in anaerobic membrane bioreactor: SMP- and EPS-membrane interactions

Biofouling is the main challenge in the operation of anaerobic membrane bioreactors (AnMBRs). Biofouling strongly depends on temperature; therefore, we hypothesize that the interactions and viscoelastic properties of soluble microbial products (SMP) and extracellular polymeric substances (EPS) vary with temperature, consequently influencing membrane permeability. This study compares the performance of an AnMBR operated at a similar permeate flux at two temperatures. The transmembrane pressure (TMP) rose rapidly after 5 ± 2 days at 25 °C but only after 18 ± 2 days at 35 °C, although the reactor's biological performance was similar at both temperatures, in terms of the efficiency of dissolved organic carbon removal and biogas composition, which were obtained by changing the hydraulic retention time. Using confocal laser scanning microscopy (CLSM), a higher biofilm amount was detected at 25 °C than at 35 °C, while quartz crystal microbalance with dissipation (QCM-D) showed a more adhesive, but less viscous and elastic EPS layer. In situ optical coherence tomography (OCT) of an ultra-filtration membrane, fed with the mixed liquor suspended solids (MLSS) at the two temperatures, revealed that while a higher rate of TMP increase was obtained at 25 °C, the attachment of biomass from MLSS was markedly less. Increased EPS adhesion to the membrane can accelerate TMP increase during the operation of both the AnMBR and the OCT filtration cell. EPS's reduced viscoelasticity at 25 °C suggests reduced floc integrity and possible increased EPS penetration into the membrane pores. Analysis of the structures of the microbial communities constituting the AnMBR flocs and membrane biofilms reveals temperature's effects on microbial richness, diversity, and abundance, which likely influence the observed EPS properties and consequent AnMBR fouling.

Anaerobic membrane bioreactors for municipal wastewater: Progress in resource and energy recovery improvement approaches

Anaerobic membrane bioreactor (AnMBR) offer promise in municipal wastewater treatment, with potential benefits including high-quality effluent, energy recovery, sludge reduction, and mitigating greenhouse gas emissions. However, AnMBR face hurdles like membrane fouling, low energy recovery, etc. In light of net-zero carbon target and circular economy strategy, this work sought to evaluate novel AnMBR configurations, focusing on performance, fouling mitigation, net-energy generation, and nutrients-enhancing integrated configurations, such as forward osmosis (FO), membrane distillation (MD), bioelectrochemical systems (BES), membrane photobioreactor (MPBR), and partial nitrification-anammox (PN/A). In addition, we highlight the essential role of AnMBR in advancing the circular economy and propose ideas for the water-energy-climate nexus. While AnMBR has made significant progress, challenges, such as fouling and cost-effectiveness persist. Overall, the use of novel configurations and energy recovery strategies can further improve the sustainability and efficiency of AnMBR systems, making them a promising technology for future sustainable municipal wastewater treatment.

A robust, low-temperature, closed-loop anaerobic system for high-solid mixed farm wastes: advancing agricultural waste management solutions in Canada

This study investigates the effectiveness of low-temperature (20 ± 1 °C) anaerobic digestion (AD) for two organic multiple farm substrate combinations: Set 1 comprising chicken manure (CM), dairy manure (DM), and waste corn silage (CS) and Set 2 comprising CM, DM, pig manure (PM), and CS. Inoculum adaptation steps were carried out using CM and CM+DM for Set 1 and Set 2, respectively. Over three consecutive operating cycles spanning 245 days with increasing organic loads, 4.3 and 2.8 g VS L-1 d-1 for Sets 1 and 2 during Cycles 1 to 5.1 and 4.6 g VS L-1 d-1for Sets 1 and 2 during Cycle 3, a closed-loop two-stage liquid-solid AD system was employed, with performance assessed via stability ratios of short-chain volatile fatty acids and alkalinity. Results demonstrate that mono-digestion of CM with adapted inoculum yielded the highest biogas production of 424 ± 4 L over 77 days, indicating superior performance by Set 1 during Phase I, whereas a similar performance was observed during Phase 2, where Sets 1 and 2 exhibited highest specific methane yields of 0.233 ± 0.028 and 0.262 ± 0.004 L g-1 VSfed, respectively, over 68 days. Analysis of heavy metal concentrations in digestates revealed a significant decrease compared to initial raw substrate concentrations, highlighting their role as nutrients for microbial growth. This study, the first of its kind, highlights the potential of low-temperature AD systems to manage diverse organic residues/byproducts and offers insights into effective performance monitoring without compromising system integrity.

Elimination of methylmercury production potential in excessive sludge in wastewater treatment plants by sulfur addition

Mercury ions (Hg(II)) in wastewater can accumulate and transform into the highly neurotoxic methylmercury (MeHg) in activated sludge. The release of MeHg can have severe environmental consequences, making the treatment of MeHg-contaminated sludge a pressing concern. In this study, we found that all the collected activated sludge samples, from different wastewater treatment plants in four cities, had the potential for Hg methylation. The Hg-methylating capacity reached a maximum level of 0.70-0.92 μg/g volatile suspended solids after 48 h of exposure to 5 μg/L Hg(II) and showed an average MeHg production rate of 4.8±0.5%. Accordingly, a sludge treatment method involving the addition of elemental sulfur (S0) for a short-term or long-term duration (3 or 180 days, respectively) was proposed. The results demonstrated that this treatment approach effectively mitigated and potentially eliminated MeHg formation by simultaneously reducing Hg bioavailability and Hg-methylating bioactivity. We found that bioavailable Hg(II) ions were converted to a secondary phase similar to insoluble HgS after S0 addition treatment, leading to a decrease in Hg bioavailability in sludge. The enhancement of Hg and extracellular polymeric substances (EPS) complexation via the increasing amount of thiol groups in EPS also reduced the Hg bioavailability after the long-term treatment. Furthermore, the long-term S0 addition significantly reduced the abundance of Hg-methylators with hgcA gene and promoted the growth of Hg-reducers with merA gene, which ensured the complete elimination of MeHg production potential of the excessive activated sludge. Our findings demonstrated that the proposed S0-addition sludge treatment is a promising and safe biotechnology for treating Hg-contaminated sludge. This approach has the potential to contribute significantly to the mitigation of MeHg pollution within environmental contexts.

Propidium monoazide - polymerase chain reaction reveals viable microbial community shifts in anaerobic membrane bioreactors treating domestic sewage at low temperature

An anaerobic membrane bioreactor (AnMBR) treated domestic sewage at 15 °C under different hydraulic retention time (HRT) conditions (6, 12, 16, and 24 h). Propidium monoazide (PMA)-PCR excluded microorganisms without intact cell membranes, focusing on the viable microbial community in anaerobic digestion. The results showed that the 6-hour HRT had poor treatment performance: low chemical oxygen demand removal efficiency (below 80%) and high mean trans-membrane pressure and flux (15 kPa and 9.4 L/(m2 h)). Comparatively, PMA-PCR combined with next-generation sequencing improved the identification of microbial changes compared to conventional 16S rRNA gene sequencing. HRT influenced microorganisms in the hydrolysis and acid-production stages, including carbohydrate-degrading bacteria such as Bifidobacterium and Prevotella 1. Remarkably, a comparison with an AnMBR at 25 °C showed Proteobacteria to be the main cause of membrane fouling in the low-temperature AnMBR, with most operational taxonomic units negatively correlated with HRT and solids retention time.

Insights into effects of operating temperature on the removal of pharmaceuticals/pesticides/synthetic organic compounds by membrane bioreactor process

In this study, the removal efficiency and mechanism of 8 kinds of typical micropollutants by membrane bioreactor (MBR) at different temperatures (i.e. 15, 25 and 35 °C) were investigated. MBR exhibited the high removal rate (>85%) for 3 kinds of industrial synthetic organic micropollutants (i.e. bisphenol A (BPA), 4-tert-octylphenol (TB) and 4-n-nonylphenol (NP)) with similar functional groups, structures and high hydrophobicity (Log D > 3.2). However, the removal rates of ibuprofen (IBU), carbamazepine (CBZ) and sulfamethoxazole (SMX) with pharmaceutical activity showed great discrepancy (i.e. 93%, 14.2% and 29%, respectively), while that of pesticides (i.e. acetochlor (Ac) and 2,4-dichlorophenoxy acetic acid (2,4-D) were both lower than 10%. The results showed that the operating temperature played a significant role in microbial growth and activities. High temperature (35 °C) led to a decreased removal efficiency for most of hydrophobic organic micropollutants, and was also not conducive for refractory CBZ due to the temperature sensitivity. At lower temperature (15 °C), a large amount of exopolysaccharides and proteins were released by microorganisms, which caused the inhibited microbial activity, poor flocculation and sedimentation, resulting in the polysaccharide-type membrane fouling. It was proved that dominant microbial degradation of 61.01%-92.73% and auxiliary adsorption of 5.29%-28.30% were the main mechanisms for micropollutant removal in MBR system except for pesticides due to the toxicity. Therefore, the removal rates of most micropollutants were highest at 25 °C due to the high activity sludge so as to enhance microbial adsorption and degradation.

Impact of sandwich-type composite anodic membrane on membrane fouling and methane recovery from sewage sludge and food waste via electrochemical anaerobic membrane bioreactor

Membrane fouling presents a big challenge for the real-world implementation of anaerobic membrane bioreactors (AnMBRs) in digesting high-solid biowastes. In this study, an electrochemical anaerobic membrane bioreactor (EC-AnMBR) with a novel sandwich-type composite anodic membrane was designed and constructed for controlling membrane fouling whilst improving the energy recovery. The results showed that EC-AnMBR produced a higher methane yield of 358.5 ± 74.8 mL/d, rising by 12.8% compared to the AnMBR without applied voltage. Integration of composite anodic membrane induced a stable membrane flux and low transmembrane pressure through forming an anodic biofilm while total coliforms removal reached 97.9%. The microbial community analysis further provided compelling evidence that EC-AnMBR enriched the relative abundance of hydrolyzing (Chryseobacterium 2.6%) bacteria and methane-producing (Methanobacterium 32.8%) archaea. These findings offered new insights into anti-biofouling performance and provided significant implications for municipal organic waste treatment and energy recovery in the new EC-AnMBR.

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.

Anaerobic recalcitrance in wastewater treatment: A review

Anaerobic treatment is applied as an alternative to traditional aerobic treatment for recalcitrant compound degradation. This review highlighted the recalcitrant compounds in wastewaters and their pathways under aerobic and anaerobic conditions. Forty-one recalcitrant compounds commonly found in wastewater along with associated anaerobic removal performance were summarized from current research. Anaerobic degradability of wastewater could not be appropriately evaluated by BOD/COD ratio, which should only be suitable for determining aerobic degradability. Recalcitrant wastewaters with a low BOD/COD ratio may be handled by anaerobic treatments after the adaption and provision of sufficient electron donors. Novel indicator characterizing the anaerobic recalcitrance of wastewater is called for, essential for emergent needs to resource recovery from high-strength recalcitrant wastewater for fulfilling appeals of circular bioeconomy of modern societies.

Process characteristics and energy self-sufficient operation of a low-fouling anaerobic dynamic membrane bioreactor for up-concentrated municipal wastewater treatment

Up-concentration of municipal wastewater using physico-chemical methods can effectively enrich organic matter, facilitating subsequent anaerobic digestion of up-concentrated wastewater for enhanced methanogenesis at reduced energy consumption. An anaerobic dynamic membrane bioreactor (AnDMBR) assisted with biogas-sparging was developed to treat up-concentrated municipal wastewater, focusing on the effects of operating temperature and hydraulic retention time (HRT) as well as COD mass balance and energy balance. The COD removal stabilized at about 98 % over the experimental period, while gaseous and dissolved methane contributed 43-49 % and 2-3 % to the influent COD reducing greenhouse gas emissions. The formed dynamic membrane exists mainly as a heterogeneous cake layer with a uneven distribution feature, ensuring the stable effluent quality. Without adopting any physico-chemical cleaning, the transmembrane pressure (TMP) maintained at a low range (2.7 to 14.67 kPa) with the average TMP increasing rate of 0.089 kPa/d showing a long-term low-fouling operation. Increasing the concentration ratio, the methane production rate decreased from 0.18 to 0.15 L CH₄/gCOD likely due to the accumulation of particulate organics. Microbial community analysis indicated the predominant methanogenic pathway shifted from hydrogenotrophic to acetoclastic methanogenesis in response to the temperature change. Net energy balance (0.003-0.600 kWh/m³) can be achieved only under room temperature (25 °C) rather than mesophilic conditions (36 °C).

Applications of submerged and staged membrane systems for pollutant removal from effluents and mechanism studies - a review

Membrane based filtration is one of the promising technologies for rehabilitation of wastewater streams for reuse and recycle. Many advancements have emerged with the use of novel materials and innovative integrated technologies. The present investigation focuses on the treatment methods based on submerged and stages systems of membranes for water purification. Ceramic, polymeric and mixed matrix type of membranes fabricated for specific type of effluents, their modification methods for accelerating the rejection efficiency, permeability, durability, stability and antifouling properties are detailed in this review. Graphene oxide is the most considered membrane material for adsorption purposes as it exhibits larger surface area, abundant functional groups contain oxygen and has good supply of ligands which is responsible in metal adsorption as it enhances electrostatic interaction by bonding metal ions with graphene oxide nanosheets. Energy derivation in terms of biogas production was also reported in some integrated methods. In many cases, embedded nanomaterial matrices yielded maximum efficiencies in both the submerged and staged operations. However, submerged type of membranes are reported more than the staged type due to simpler configuration with relatively lesser equipment, operational and maintenance issues. In treatment of a low strength wastewater, aluminum oxide based membrane in fluidized bed assembly was reported to yield promising results with reduced power requirement.

Energy-Efficient AnMBRs Technology for Treatment of Wastewaters: A Review

In recent years, anaerobic membrane bioreactor (AnMBRs) technology, a combination of a biological reactor and a selective membrane process, has received increasing attention from both industrialists and researchers. Undoubtedly, this is due to the fact that AnMBRs demonstrate several unique advantages. Firstly, this paper addresses fundamentals of the AnMBRs technology and subsequently provides an overview of the current state-of-the art in the municipal and domestic wastewaters treatment by AnMBRs. Since the operating conditions play a key role in further AnMBRs development, the impact of temperature and hydraulic retention time (HRT) on the AnMBRs performance in terms of organic matters removal is presented in detail. Although membrane technologies for wastewaters treatment are known as costly in operation, it was clearly demonstrated that the energy demand of AnMBRs may be lower than that of typical wastewater treatment plants (WWTPs). Moreover, it was indicated that AnMBRs have the potential to be a net energy producer. Consequently, this work builds on a growing body of evidence linking wastewaters treatment with the energy-efficient AnMBRs technology. Finally, the challenges and perspectives related to the full-scale implementation of AnMBRs are highlighted.

Enhanced organic degradation and biogas production of domestic wastewater at psychrophilic temperature through submerged granular anaerobic membrane bioreactor for energy-positive treatment

This study deals with the conversion of organic matter into methane at ambient temperature, during anaerobic digestion of domestic wastewater combined with a submerged ultrafiltration membrane with no gas-sparging. A one-stage submerged granular anaerobic membrane bioreactor (G-AnMBR) and a control anaerobic digester (UASB type) were operated during four months, after 500 days of biomass acclimatization to psychrophilic and low loading rate conditions. Membrane barrier led to the retention of biomass, suspended solids and dissolved and colloidal organic matter which greatly enhanced total COD (tCOD) removal (92.3%) and COD to methane conversion (84.7% of tCOD converted into dissolved and gaseous CH4). G-AnMBR overcame the usual long start-up period and led to a higher sludge heterogeneity, without altering the granular biomass activity. The feasibility of the G-AnMBR without gas-sparging was also assessed and the net positive energy balance was estimated around + 0.58 kWh.m^-3.

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.

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.

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.

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.

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.

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

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

Integrated anaerobic and algal bioreactors: A promising conceptual alternative approach for conventional sewage treatment

Conventional sewage treatment applying activated sludge processes is energy-intensive and requires great financial input, hampering widespread implementation. The introduction of anaerobic membrane bioreactors (AnMBR) followed by an algal reactor growing species of commercial interest, may present an alternative, contributing to the envisaged resource recovery at sewage treatment plants. AnMBRs can be applied for organic matter removal with energy self-sufficiency, provided that effective membrane fouling management is applied. Haematococcus pluvialis, an algal species with commercial value, can be selected for ammonium and phosphate removal. Theoretical analysis showed that good pollutant removal, positive financial output, as well as a significant reduction in the amount of hazardous activated sludge can be achieved by applying the proposed process, showing interesting advantages over current sewage treatment processes. Microbial contamination to H. pluvialis is a challenge, and technologies for preventing the contamination during continuous sewage treatment need to be applied.

Operation of Submerged Anaerobic Membrane Bioreactors at 20 °C: Effect of Solids Retention Time on Flux, Mixed Liquor Characteristics and Performance

Four flat-sheet submerged anaerobic membrane bioreactors ran for 242 days on a simulated domestic wastewater with low Chemical Oxygen Demand (COD) and high suspended solids. Organic loading was maintained around 1.0 g COD L−1 day−1, while solids retention time (SRT) was varied from 20–90 days. This was achieved at a constant membrane flux, maintained by adjusting transmembrane pressure (TMP) in the range 1.8–9.8 kPa. Membrane fouling was assessed based on the required TMP, with mixed liquors characterised using capillary suction time, frozen image centrifugation and quantification of extracellular polymeric substances (EPS). SRT had a significant effect on these parameters: fouling was least at an SRT of 30 days and highest at 60 days, with some reduction as this extended to 90 days. Operation at SRT < 30 days showed no further benefits. Although operation at a short SRT was optimal for membrane performance it led to lower specific methane productivity, higher biomass yields and higher effluent COD. Short SRT may also have accelerated the loss of essential trace elements, leading to reduced performance under these conditions. A COD-based mass balance was conducted, including both biomass and methane dissolved in the effluent.