3.2.2. Microbial community composition
At the genus level, the community structure on the different membranes was similar, but the abundance of the genus was different (Fig. 5A). Genera belonging to Proteobacteria (Pseudomonas, Thiopseudomonas, Marinobacterium, Arcobacter, Sulfurospirillum, Rhodopseudomonas, Desulfobulbus, Pusillimonas, Advenella), Firmicutes (Saccharofermentans and Tissierella), Bacteroidetes (Proteiniphilum), and Synergistetes (Aminobacterium) were the dominant taxa on the membrane surface.
Proteobacteria is mostly anaerobic or facultative anaerobic gram-negative bacteria. It was widely distributed on the membrane surface, and the percentages in ES-OsMFC, NW-OsMFC and TFC-OsMFC were 40.11%, 47.21% and 68.11%, respectively. Many studies had shown that Proteobacteria exists extensively in MFC anodes [34–36], thus key genera are discussed in details below.
Pseudomonas is a heterotrophic bacterium under the γ-proteobacteria class, which uses organic matter as a energy source for anaerobic respiration . Pseudomonas accounted for 6%, 13.56%, and 20.55% in the NW-OsMFC, ES-OsMFC, and TFC-OsMFC, respectively, and thus was speculated to be the major electroactive bacteria in the OsMFCs. It could also be seen from Fig. S3 that Pseudomonas was most abundant on the three membranes. Pham et al. found that Pseudomonas produced phenazine compounds for electron shuttling and improved MFC performance in mixed cultures. The abundance of Marinobacterium in the TFC-OsMFC (4.42%) was relatively higher than in the NW-OsMFC (1.14%) and ES-OsMFC (2.04%). Marinobacterium has been reported to be halophiles [39, 40]. Because the catholyte was 1 mol/L NaCl, the forward osmosis would cause reversely transported salts. The landfill leachate also contained a certain salinity, resulting in high salinity of the anolyte. Arcobacter belongs to the ε-proteobacteria class whose bioelectrochemical activity has been reported [41, 42].The percentage of Arcobacter in ES-OsMFC (9.54%) was higher than in NW-OsMFC (6.01%) and TFC-OsMFC (0.35%). This might be one of the reasons why ES-OsMFC had a better power generation effect (Fig. 2). Fedorovich et al.  found that Arcobacter butzleri ED-1 was an electrogenic microorganism that could efficiently use acetate as a carbon source. Due to the presence of Saccharofermentans in OsMFCs, the organic matter is degraded into acetic acid, which leads to better growth of Arcobacter. Rhodopseudomonas belongs to the α-proteobacteria class, is a Gram-negative bacterium,which secretes a phenolic electron mediator with weak electrical energy and uses various carbon as an energy source to generate electricity [43–47]. Rhodopseudomonas in NW-OsMFC, ES-OsMFC and TFC-OsMFC were 3.8%, 4.43% and 2.86%, respectively. Thiopseudomonas as a denitrifying bacteria  showed a percentage of 1.58%, 1.57% and 10.05% in NW-OsMFC, ES-OsMFC and TFC-OsMFC, respectively.
Firmicutes have been reported to utilize complex organic matter to produce electricity . The abundance of Firmicutes in the ES-OsMFC, NW-OsMFC and TFC-OsMFC were 28.85%, 24.23% and 11.80%, respectively, probably due to the presence of complex high organic in landfill leachate. In this phylum, Saccharofermentans are known to perform hydrolysis, fermentation, and acetogenesis . Its abundance in NW-OsMFC, ES-OsMFC and TFC-OsMFC were 3.34%, 3.58% and 2.24%, respectively.
Pseudomonas , Arcobacter  and Rhodopseudomonas  are commonly found in bioelectrochemical systems and are speculated to be the main electrogenic bacteria in the OsMFCs. However, some well-known electroactive microorganisms (e.g., Anaeromusa , Dechlormonas, Geobacter , and etc.) were been found in this study, probably because the salt in the catholyte passed through the membranes and caused high anode salinity. In addition, landfill leachate as an anode substrate has a complex composition and high toxicity that may be inhibitory to those microorganisms.