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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. [Display omitted] [ABSTRACT FROM AUTHOR]

The anaerobic membrane bioreactor (AnMBR) has potential as a low-cost wastewater treatment process with the benefit of energy production. However, to ensure satisfactory treatment performance, an AnMBR is operated at a relatively high temperature currently. Research focused on the operation of the AnMBR at low temperature is significant since the energy required for heating is an impediment to the application of AnMBRs for municipal wastewater treatment. Hence, in this study, a constant low-temperature (15 °C) AnMBR was evaluated for the treatment of real municipal wastewater with hydraulic retention times (HRTs) in the range of 6–24 h. During the long-term experiment, a chemical oxygen demand (COD) removal efficiency of approximately 90.5% was obtained with a sludge yield below 0.13 g-VSS/g-COD rem at HRTs of 16 and 24 h. The amount of energy generated was theoretically calculated based on biogas production, with a high of 0.62 kWh/t. The energy balance analysis showed that the AnMBR process can be energy positive under the optimal operational conditions investigated. Membrane filtration performed well during operation at 15 °C with HRTs ranging between 12 and 24 h, while it was compromised at the extremely short HRT of 6 h. In this study, the effectiveness of optimizing the conditions on the performance of the AnMBR operating at low temperature was confirmed, along with the potential for energy recoverability under those conditions. [Display omitted] • AnMBR for mainstream municipal wastewater treatment was evaluated at 15 °C. • COD removal of 90.5% with sludge yield <0.13 g-VSS/g-COD rem was obtained. • Mass balance and energy balance was evaluated in the HRTs ranged 6–24 h. • Energy positive operation can be achieved at 15 °C low temperature when HRT at 16 h. • Flux up to 0.225 m/d was obtained via enhanced GSV and sludge concentration control. [ABSTRACT FROM AUTHOR]

[Display omitted] • Real municipal wastewater was treated at 15–25 °C by a SAnMBR at HRT 6 h. • COD removal efficiencies of 90% and BOD removal efficiencies of 92% were obtained. • Electric energy could generate 2.27 kWh/d from biogas in a 10000 m3/d plant. • Trans-membrane pressure and fouling risks were high under the low temperature. • Populations of functional microbes had significant relations with the temperature. 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. [ABSTRACT FROM AUTHOR]

The application of anaerobic membrane bioreactor (AnMBR) process for low-carbon and sustainable municipal wastewater (MWW) treatment is still hindered by membrane fouling and dissolved methane issues, while optimizing operational mode for efficient fouling mitigation and modelling the liquid-gaseous phase equilibrium of multicomponent biogas are still not well understood. To address this gap, a 20-L submerged AnMBR was operated for the treatment of real MWW over a 200 d operation period, divided into three phases according to the variations of operational flux (5, 8 and 11 L/m2h) and intermittent filtration mode (filtration to relaxation time (F/R) ratios of 3:1, 4:1, 5:1 and 9:1). The AnMBR showed a stable COD removal (∼85%), satisfactory methane production (∼0.07 LCH 4 /L-wastewater), and a high methane content of 80% regardless of filtration mode. A theoretical model was successfully developed to simulate the liquid-gaseous phase equilibrium of the multicomponent biogas, which can quantitatively predict the origin and phase distribution of biogas with high accuracy and also determine the saturation index of dissolved methane in the range of 0.8–1.1. At low-flux conditions (5 and 8 LMH), the transmembrane pressure (TMP) remained at low values of 0.5–1.0 kPa, and was not affected by changed F/R ratios. However, at the higher flux of 11 LMH, the TMP increase was obvious at F/R ratios of 3:1 and 9:1, and larger than that at F/R ratios of 4:1 and 5:1. A higher instantaneous flux and shorter relaxation time resulted in substantial irreversible fouling caused by a high-flux induced drag force and insufficient detachment of foulants, while periodical in-situ chemical cleaning allowed a sustainable operation with irreversible fouling successfully mitigated. The results recommended optimized filtration mode for cost-effective fouling control and highlighted the importance of dissolved methane management, which are expected to support large-scale AnMBR implementations for mainstream MWW treatment towards low fouling operation and efficient bioenergy recovery. [Display omitted] • The AnMBR showed a low TMP and high permeability operation at a long-term scale. • AnMBR achieved excellent organics removal and biogas generation (80% CH 4 content). • Dissolved methane accounting for 30% of total methane yield should be well managed. • Biogas phase-equilibrium phenomenon was accurately simulated by a developed model. • Effects of operation mode regarding intermittent filtration and flux were discussed. [ABSTRACT FROM AUTHOR]

• 5 m3 large-scale AnMBR realized effluent COD < 50 mg L-1 and BOD 5 < 10 mg L-1. • COD and BOD 5 removal over 90% with biogas recovered by 0.25–0.27 L g−1 removed COD. • An auto-control grille system facilitated AnMBR by removing large-size impurities. • 60%-64% of influent COD converted to methane and 20%-26% of that converted to MLSS. • Hollow fiber membrane realized an average flux of 0.35 m d-1 at a △TMP of 23.5 kPa. The aim of this work was to demonstrate the operation of a large pilot-scale submerged anaerobic membrane bioreactor (5.0 m3) for biogas production from municipal wastewater at ambient temperature of 25 °C. To the best of our knowledge, this is the largest one-stage submerged AnMBR that has ever been reported. This AnMBR realized a hydraulic retention time (HRT) of 6 h and a treatment capacity of 20 m3 d-1, obtaining excellent effluent quality with COD removal efficiency over 90% and BOD 5 removal over 95%. The biogas yield of the AnMBR was 0.25–0.27 L g−1 removed COD and 0.09–0.10 L L-1 raw wastewater. The methane content of the biogas was at the range of 75%-81%. The COD and nitrogen mass balance were also identified based on long-term operation. The hollow-fiber membrane module realized a flux of 2.75–17.83 LMH. An online backwash chemical cleaning system helped to lower the transmembrane pressure timely. [ABSTRACT FROM AUTHOR]