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

Synergic treatment of domestic wastewater and food waste in an anaerobic membrane bioreactor demo plant: Process performance, energy consumption, and greenhouse gas emissions

Ambient operation and large-scale demonstration have limited the implementation and evaluation of anaerobic membrane bioreactors (AnMBRs) for low-strength wastewater treatment. Here, we studied these issues at an AnMBR demo plant that treats domestic wastewater and food waste together at ambient temperatures (7-28 °C). At varied hydraulic retention times (HRTs, 8-42 h), the AnMBR achieved a COD removal efficiency and biogas production of 80.4% ± 3.9% and 66.5 ± 9.4 NL/m3-Influent, respectively. Moreover, a stable high membrane flux of 14.4 L/m2/h was reached. The electric energy consumption for the AnMBR operation was 0.269-0.433 kW·h/m3, and 49.4%-91.3% could be compensated by the electric energy produced from methane production. At an HRT of 10 h, the AnMBR system demonstrated an impressively low net electric energy consumption of merely 0.05 kW·h/m3, resulting in a net greenhouse gas emission of 0.015 CO2-eq/m3, cutting 85% compared to the conventional activated sludge process. Achievements in this study provide key parameters for the ambient operation of AnMBR and demonstrate that AnMBR is an energy-saving and low-carbon solution for low-strength wastewater treatment.

CO2 removal from biogas improved stable treatment of low-alkalinity municipal wastewater using anaerobic membrane bioreactor

This study addressed a less-reported issue: the insufficient alkalinity encountered when anaerobic membrane bioreactors (AnMBRs) are used to treat municipal wastewater (MWW). In the present study, a 20-L AnMBR was initiated at an MWW treatment plant. During the initial startup, a continuous decrease in pH was observed. Through the analyses of the balance between HCO3-/CO2 in the biogas and alkalinity in the reactor, the cause of pH instability was determined to be that the alkalinity could not balance the acidity induced by the continuous dissolution of CO2 from biogas in the liquid phase. Therefore, this study employed the in-situ removal of CO2 from biogas using soda lime to reduce the CO2 partial pressure, thereby achieving stable control of the pH in the reactor. This study provides valuable experience and technical support for anaerobic processes for treating low-alkalinity MWW in the future applications.

Innovative high-performance and energy-positive Co-treatment of organic kitchen waste and domestic wastewater using a fluidized bed ceramic membrane bioreactor

The aim of the study was to efficiently treat organic kitchen waste (FW) and domestic wastewater (DWW) together in an anaerobic fluidized bed bioreactor equipped with a ceramic membrane (AnFCMBR) through a sustainable approach considering energy recovery. The system operated continuously for 519 days at room temperature, and different filtration fluxes (1.7 and 5 L/m2/h), hydraulic retention times (HRTs) (22 h and 7 h), and organic loading rate (OLRs) (0.46, 1.52, 3.42, 6.08 kg/m3.d) were tested. The amount of organic matter in DWW may be insufficient for feasible gas production, but this challenge can be resolved through the addition of food waste. Influent chemical oxygen demand (COD) of 500 ± 143 mg/L gradually increased to 2000 ± 196 mg/L by increasing the portion of FW. The COD removal ranged from 92 to 98% throughout the study, with the membrane and the cake layer contributing 5-8% to the performance. Average supernatant SMP and EPS concentrations increased from 5 ± 1 to 45 ± 5 mg COD/L and from 54 ± 7 to 254 ± 26 mg COD/g VSS, respectively, when the highest amount of FW was added to the synthetic wastewater. This significant increase in SMP and EPS concentrations due to the addition of FW negatively impacted the filtration performance. SRF and CST values also increased with rising OLR, especially with the supplementation of synthetic wastewater with FW. After FW started to be mixed with DWW, the methane production increased approximately 5.5 times. With the use of AnFCMBR for the co-treatment of FW and DWW, it is possible to achieve energy-positive treatment with high-quality effluent that can be reused for various applications, such as irrigation. The methane produced provided 12 times more energy than was needed to operate the bioreactor. This is the first study evaluating the co-treatment of FW and DWW in AnFCMBR under varying operational parameters.

Iron Recycle-Driven Organic Capture and Sidestream Anaerobic Membrane Bioreactor for Revolutionizing Bioenergy Generation in Municipal Wastewater Treatment

The practicality of intensifying organic matter capture for bioenergy recovery to achieve energy-neutral municipal wastewater treatment is hindered by the lack of sustainable methods. This study developed innovative processes integrating iron recycle-driven organic capture with a sidestream anaerobic membrane bioreactor (AnMBR). Iron-assisted chemically enhanced primary treatment achieved elemental redirection with 75.2% of chemical oxygen demand (COD), 20.2% of nitrogen, and 97.4% of phosphorus captured into the sidestream process as iron-enhanced primary sludge (Fe-PS). A stable and efficient biomethanation of Fe-PS was obtained in AnMBR with a high methane yield of 224 mL/g COD. Consequently, 64.1% of the COD in Fe-PS and 48.2% of the COD in municipal wastewater were converted into bioenergy. The acidification of anaerobically digested sludge at pH = 2 achieved a high iron release efficiency of 96.1% and a sludge reduction of 29.3% in total suspended solids. Ultimately, 87.4% of iron was recycled for coagulant reuse, resulting in a theoretical 70% reduction in chemical costs. The novel system evaluation exhibited a 75.2% improvement in bioenergy recovery and an 83.3% enhancement in net energy compared to the conventional system (primary sedimentation and anaerobic digestion). This self-reliant and novel process can be applied in municipal wastewater treatment to advance energy neutrality at a lower cost.

Development and modeling of an integrated fixed-film activated sludge (IFAS) system for simultaneous nitrogen and carbon removal from an industrial estate wastewater

The potential of an integrated fixed film activated sludge (IFAS) bioreactor for developing simultaneous aerobic and anoxic micro-zones under continuous aeration regime to promote carbon and nitrogen removal from Faraman industrial estate wastewater was evaluated in the present research. The effects of three independent variables on carbon and nitrogen removal were assessed. Overall, the optimum condition with 94 %, 77 %, and 2 NTU of COD (chemical oxygen demand) removal, Total nitrogen (TN) removal, and effluent turbidity has been specified with hydraulic retention time (HRT) of 11 h, air flow rate (AFR) of 3.5 L/min, and filling ratio (FR) of 50 %. To assess the stability of treating processes in the system, the IFAS system was operated in this optimal condition. Moreover, the simulation of the bioreactor was accomplished via calibration and verification of GPS-X model. GPSX simulation results and experimental data were compared using an independent sample T-test, which the T-test result confirmed that there was no significant difference between them.

Dominant factors analyses and challenges of anaerobic digestion under cold environments

With the development of fermentation technology and the improvement of efficiency, anaerobic digestion (AD) has been playing an increasingly primary role in waste treatment and resource recovery. Temperature is undoubtedly the most important factor because it shapes microbial habitats, changes the composition of the microbial community structure, and even affects the expression of related functional genes. More than half of the biosphere is in a long-term or seasonal low-temperature environment (<20 °C), which makes psychrophilic AD have broad application prospects. Therefore, this review discusses the influencing factors and enhancement strategies of psychrophilic AD, which may provide a corresponding reference for future research on low-temperature fermentation. First, the occurrence of AD has been discussed. Then, the adaptation of microorganisms to the low-temperature environment was analyzed. Moreover, the challenges of psychrophilic AD have been reviewed. Meanwhile, the strategies for improving psychrophilic AD are presented. Further, from technology to application, the current situation of psychrophilic AD in pilot-scale tests is described. Finally, the economic and environmental feasibility of psychrophilic AD has been highlighted. In summary, psychrophilic AD is technically feasible, while economic analysis shows that the output benefits cannot fully cover the input costs, and the large-scale practical application of psychrophilic AD is still in its infancy. More research should focus on how to improve fermentation efficiency and reduce the investment cost of psychrophilic AD.

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.

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.

Insights on pretreatment technologies for partial nitrification/anammox processes: A critical review and future perspectives

For almost 20 years, partial nitrification-anammox (PN/A) has been the subject of intensive study and development. Pretreatment of wastewater for PN/A is crucial because the inhibitory substances in the influent may reduce the performance of PN/A. In this review, the current PN/A pretreatment technologies are comprehensively summarized. The selection of pretreatment technology for PN/A depending on the source of the wastewater and its main characteristics (high-strength wastewater or municipal wastewater, organic matters, suspended solids). Comparison of pretreatment technologies through multiple perspectives including wastewater characteristics, the objectives of the wastewater treatment (treating requirement, energy and resource recovery demand), reactor configuration of PN/A. Based on the discussion, two integrated processes, HRAS + one-stage PN/A and advanced AD + two-stage PN/A, are recommended as the preferred processes for treating municipal wastewater and wastewater with a high-strength ammonium, respectively. This review aims to provide guidance for future research and development of PN/A.

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.

In-situ membrane fouling control and performance improvement by adding materials in anaerobic membrane bioreactor: A review

Anaerobic membrane bioreactor (AnMBR) is a promising treatment technique for various types of wastewaters, and is preferred over other conventional aerobic and anaerobic methods. However, membrane fouling is considered a bottleneck in AnMBR system, which technically blocks membrane pores by numerous inorganics, organics, and other microbial substances. Various materials can be added in AnMBR to control membrane fouling and improve anaerobic digestion, and studies reporting the materials addition for this purpose are hereby systematically reviewed. The mechanism of membrane fouling control including compositional changes in extracellular polymeric substances (EPSs) and soluble microbial products (SMPs), materials properties, stimulation of antifouling microbes and alteration in substrate properties by material addition are thoroughly discussed. Nonetheless, this study opens up new research prospects to control membrane fouling of AnMBR, engineered by material, including compositional changes of microbial products (EPS and SMP), replacement of quorum quenching (QQ) by materials, and overall improvement of reactor performance. Regardless of the great research progress achieved previously in membrane fouling control, there is still a long way to go for material-mediated AnMBR applications to be undertaken, particularly for materials coupling, real scale application and molecular based studies on EPSs and SMPs, which were proposed for future researches.

Self-forming electroactive dynamic membrane for enhancing the decolorization of methyl orange by weak electrical stimulation

An electroactive dynamic membrane (EADM), which enabled simultaneous solid-liquid separation and contaminants removal, has been developed by electrostimulation using domestic wastewater as inoculum. Results showed that both the control dynamic membrane (CDM), without electrical stimulation, and the EADM systems exhibited stable removal performance with chemical oxygen demand (COD), and a robustness in responding to a fluctuating organic load. With the introduction of a weak electrical field, the EADM transmembrane pressure (TMP) was significantly reduced (0.02 kPa/d) compared with the control (0.20 kPa/d). In the treatment of methyl orange (MO), the EADM system achieved a decolorization efficiency of 85.87 %, much higher than the control dynamic membrane (CDM) system (58.84 %), which can be attributed to electrical stimulation and H₂ production on cathode. Microbial analysis has established that electrostimulation enriched the electroactive bacteria in the dynamic biofilm, and shaped the microbial structure, with improved contaminant removal. The results of this study highlight the potential of regulating the microbial community and creating a beneficial biofilm as a dynamic layer to facilitate contaminant removal.

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.

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.

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.

Methane production from peroxymonosulfate pretreated algae biomass: Insights into microbial mechanisms, microcystin detoxification and heavy metal partitioning behavior

This study investigated the methane production potential of algal biomass by anerobic digestion with the addition of peroxymonosulfate (PMS), the removal of microcystin were analyzed and discussed. The microcystin concentration in the collected algal sludge was 1.20 μg/L in the liquid phase and 1393 μg/g in the algal sludge before anaerobic fermentation. The microcystin concentration decreased to 0.20-0.35 μg/L in the liquid phase and 4.16-11.51 μg/g in the sludge phase after 60 days of digestion. The initial PMS dose and residue microcystin concentration could be simulated with a logarithmic decay model (R² > 0.87). Anaerobic digestion could recover energy from algal source in the form of methane gas, which was not affected in the presence of microcystin, and the microcystin removal rate was >99%. Digestion decreased the total contents of Cd and Zn in the liquid phase and increased the total contents of Cr and Pb in the liquid phase. The microbial community and function prediction results indicated that the PMS0.1 system had the highest methane production, which was attributed to the high abundance of Mechanosaeta (40.52%). This study provides insights into microbial mechanisms, microcystin detoxification and the heavy metal partitioning behavior of the algal biomass during methane production.

Anaerobic dynamic membrane bioreactors for synthetic blackwater treatment under room temperature and mesophilic conditions

Two anaerobic dynamic membrane bioreactors (AnDMBRs) were set up for the treatment of synthetic blackwater at room temperature (20-25 °C) and mesophilic conditions for 180 days with progressively increased organic loading rates(OLR). Despite dynamic membranes (DM), organics removal at room temperature was similar to removal within the mesophilic conditions of the reactor, with some disparities in methane production. A dense sludge filtration layer was more likely to be formed on the DM at room temperature, resulting in a faster membrane fouling. Microbial community analysis revealed that microorganisms had higher richness and lower diversity at room temperature, which was beneficial to the growth of Actinobacteriota, especially Propioniciclava. This comparative study discusses the feasibility of operating an AnDMBR under room temperature conditions versus mesophilic conditions. This analysis provides novel insights into future large-scale attempts to treat blackwater at room temperature.

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.

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.

Role of microparticles in membrane fouling from acidogenesis to methanogenesis phases in an anaerobic baffled reactor

Microparticles (0.45-10 μm) have been recognized as key foulants in anaerobic membrane bioreactors (AnMBRs). However, their characteristics and fouling behaviors are often understood in single-stage and completely mixed reactors, failing to elucidate the occurrence of microparticles in the multi-stage anaerobic bioprocess. Here, a lab-scale anaerobic baffled reactor with four compartments (C1-C4) was employed to explore the composition and fouling potential of microparticles in different compartments. Photometric analysis showed that the microparticles had an increasing percentage in the total organics of the top supernatant but a decreasing concentration from C1 to C4. Long-term filtration and dead-end filtration tests revealed that the top supernatant in C1 had much higher fouling potential than those in C2-C4. The supernatant microparticles significantly accumulated in the cake layers for each compartment (68-95% of the total organics), particularly the fraction of 1-5 μm, and the fouling rate was positively correlated with the biomass accumulation rate. Based on reactor performance and 16S rRNA gene sequences, a significant bio-phase separation occurred between C1 (acidogenesis) and C2-C4 (methanogenesis). And hydrolytic and fermentative bacteria in the family Veillonellaceae, Streptococcaceae, and Enterobacteriaceae were dominant in the supernatant microparticles, particularly in C1, which had a positive correlation with the fouling rate and biomass accumulation rate. These above results all revealed that the microparticles in the acidogenesis phase had higher fouling potential. In summary, our results suggest that the tactic of pre-hydrolysis and acidification with feedstocks and constructing AnMBRs by coupling with multi-phase anaerobic bioprocesses and membrane units could be beneficial to fouling control.

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.

Anaerobic Membrane Bioreactors for Municipal Wastewater Treatment: A Literature Review

Currently, there is growing scientific interest in the development of more economic, efficient and environmentally friendly municipal wastewater treatment technologies. Laboratory and pilot-scale surveys have revealed that the anaerobic membrane bioreactor (AnMBR) is a promising alternative for municipal wastewater treatment. Anaerobic membrane bioreactor technology combines the advantages of anaerobic processes and membrane technology. Membranes retain colloidal and suspended solids and provide complete solid–liquid separation. The slow-growing anaerobic microorganisms in the bioreactor degrade the soluble organic matter, producing biogas. The low amount of produced sludge and the production of biogas makes AnMBRs favorable over conventional biological treatment technologies. However, the AnMBR is not yet fully mature and challenging issues remain. This work focuses on fundamental aspects of AnMBRs in the treatment of municipal wastewater. The important parameters for AnMBR operation, such as pH, temperature, alkalinity, volatile fatty acids, organic loading rate, hydraulic retention time and solids retention time, are discussed. Moreover, through a comprehensive literature survey of recent applications from 2009 to 2021, the current state of AnMBR technology is assessed and its limitations are highlighted. Finally, the need for further laboratory, pilot- and full-scale research is addressed.

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.

Hydrophilic porous materials provide efficient gas-liquid separation to advance hydrogen production in microbial electrolysis cells

Preventing methane evolution is a key issue to guarantee stable hydrogen production in microbial electrolysis cell (MEC). In this study, low-cost hydrophilic porous materials, such as non-woven cloth (NWC) and polyvinylidenedifluoride (PVDF), were investigated as alternatives to proton exchange membrane (PEM) in MEC. The MEC with a NWC (NWC-MEC) improved the current density and hydrogen production rate (HPR) of 262.5±10 A m^-3 and 2.5±0.2 m³ m^-3 d^-1, respectively, due to its lower pH gradient (0.37) and ion transport resistance (0.9±0.1 mΩ m²). Hydrogen production in NWC-MEC (from 2.5 to 2.1 m³ m^-3 d^-1) and PVDF-MEC (from 2.2 to 2.0 m³ m^-3 d^-1) showed more stable performance compared to PEM-MECs (from 2.2 to 1.6 m³ m^-3 d^-1) during 30 days of operation. Moreover, results of anodic microbial community analysis indicate that the growth of methanogens of NWC-MEC and PVDF-MEC was effectively inhibited in 30 days.

Promoting direct interspecies electron transfer and acetoclastic methanogenesis for enhancing anaerobic digestion of butanol octanol wastewater by coupling granular activated carbon and exogenous hydrogen

Butanol octanol wastewater (BOW) generated from syngas conversion of coal contained abundant toxic organic pollutants. Anaerobic digestion is a promising technology for BOW, but abundant toxic substances would inhibit the activity of anaerobic microorganisms. Granular activated carbon (GAC) and exogenous hydrogen (EH₂) were employed to enhance anaerobic digestion of BOW. The results indicated that methane production increased to 289.55 ± 17.43 mL CH₄/g COD in EH₂/GAC group, which was 1.07, 2.04, and 1.98 times of that in GAC, EH₂, and control groups, respectively. In EH₂/GAC group. The relative abundance of Geobacter and Methanosaeta increased rapidly to 25.36% and 52.81%, respectively, and the relative abundance of Clostridium was 9.78%. The underlying mechanism might be that GAC promoted the enrichment of Geobacter, and EH₂ changed metabolic mechanism of Clostridium, stimulating the enrichment of Methanosaeta. Direct interspecies electron transfer was promoted by EH₂/GAC, thus improving the methane production rate of BOW.

Novel insights into the anaerobic digestion of propionate via Syntrophobacter fumaroxidans and Geobacter sulfurreducens: Process and mechanism

The accumulation of volatile fatty acids, particularly propionic acid, significantly inhibits the efficiency of the anaerobic digestion system. In propionate degradation metabolism, the unfavorable thermodynamics of syntrophic reactions, strict ecological niche of syntrophic priopionate oxidizing bacteria, and slow metabolic rate of methanogens are regarded as major limitations. In this study, Geobacter sulfurreducens was co-cultured with Syntrophobacter fumaroxidans in bioelelectrochemical cells to analyze the propionate degradation process, impact factor, mechanism metabolic pathways, and electron transfer comprehensively. The results revealed that the syntroph S. fumaroxidans and syntrophic partner G. sulfurreducens achieved more efficient propionate degradation than the control group, comprising S. fumaroxidans and methanogens. Moreover, the carbon resource concentration and pH were both significantly correlated with propionate degradation (P < 0.01). The results further confirmed that G. sulfurreducen strengthened the consumption of H₂ and acetate via direct interspecific electron transfer in propionate degradation. These findings indicate that G. sulfurreducens plays an unidentified functional role in propionate degradation.