Two-Phase Improves Bio-Hydrogen and Bio-Methane Production of Anaerobic Membrane Bioreactor from Waste Activated Sludge with Digestate Recirculation

Abstract

The recirculated two-phase anaerobic digestion (R-TPAD) equipped with two conventional continuous stirred tank reactors (CSTR) usually shows poor water quality, unideal energy recovery effectiveness and low richness of methanogens in methanogenic phase. In this study, a new R-TPAD composed of CSTR and anaerobic membrane reactor (AnMBR) was constructed to treat waste activated sludge (WAS) for renewable energy recovery (H2 and CH4), and the potential influence of recirculation ratio (R) on start-up time, long-term performance, membrane fouling behaviors, microbial community evolution and shift, and energy recovery efficiencies was investigated systematically. Result showed that the R-TPAD produced high H2 and CH4 yields of around 6.1 ± 1.6 and 67.9 ± 4.6 mL/g COD/d, respectively at R0.2, with the corresponding COD removal of up to 98.5%. During the whole process, no obvious membrane fouling occurred and transmembrane pressure was lower than -3.3 kPa. 16s rRNA gene analysis further revealed that the synergistic introduction of membrane system and recirculation promoted the proliferation of fatty acids-producing and organics-degrading bacteria (i.e. Coprothermobacteraeota, Bacteroidetes, etc.) in AP and CH4-producing methanogens (i.e. Methanobacterium, Methanosaeta, etc.) in MP, thus accelerating the hydrolysis-acidification-methanation steps of sludge. This positive effect maintained the highest diversity and the dynamic balance of microorganisms in the hybrid process. Energy balance estimation indicated that the R-TPAD with R0.2 can increase by 77.9% net energy output compared to the TPAD without recirculation. This study will provide basic data for the long-term management of biological waste and push forward a wider application of R-TPAD technology in future.

Keywords: Two-phase anaerobic digestion, Recirculation ratio, Hydrogen, methane, Microbial community