Methanogenesis performance and microbial characteristics in An-IFFAS process filled with conductive suspended carriers at ambient temperature

Direct interspecies electron transfer (DIET) has been proven to be established efficiently on conductive suspended carriers, and thus enhances methane production at thermophilic condition. However, the methanogenesis performance and relevant microbial characteristics in the anaerobic integrated floating-film activated sludge (An-IFFAS) reactor filled with conductive suspended carriers when feeding different substrates at ambient temperature are still unclear. In this study, An-IFFAS was fed by different substrates including ethanol, sodium propionate, glucose, sucrose and starch at ambient temperature (11.7-23.6 degrees C). The experimental An-IFFAS reactor always exhibited significant advantages in COD removal (removal efficiency increased by 9.73 +/- 4.36%) and methane production (methane production rate increased by 72.6 +/- 49.1%) compared with the control reactor filled with conventional carriers regardless of the feeding substrate types. Abundant nano-wire structures were observed on conductive carriers, implying potential DIET pathway. The abundance of syntrophic electroactive bacteria (Smithella, Syntrophobacter, Thauera, Pseudomonas) and methanogens (Methanobacterium, Methanosaeta) increased by 3.79 and 4.08 times respectively on the novel carriers. Besides, the hydrolytic acidification bacteria (Endomicrobium, Treponema, Lentimicrobium) and hydrogen-producing acetogens (Acinetobacter) were enriched. This study provides a reference for DIET establishment and enhanced anaerobic digestion performance at ambient temperature.