Anaerobic membrane distillation bioreactors for saline organic wastewater treatment: Impacts of salt accumulation on methanogenesis and microbial community

Anaerobic membrane distillation bioreactor (AnMDBR), which possesses several distinctive advantages such as high-quality water production, desalination and methanogenesis, shows enormous potential in saline organic wastewater (SAOW) treatment. However, salt accumulation in the reactor may deactivate anaerobic organisms and impede methanogenesis. In this work, effects of salt accumulation were comprehensively investigated regarding pollutant removal performance and methanogenesis in AnMDBRs over a 30-d operation. The investigative influent salinity was in the range of 0.0-2.0 %. The results demonstrated that AnMDBR achieved excellent chemical oxygen demand (COD) rejection (> 97 %) in the stabilization phase regardless of influent salinity. Moreover, the methane production was as high as 267 mL/gCOD, when the influent salinity did not exceed 1.0 %. When the influent salinity increased to 2.0 %, the methane production was significantly restricted, because salt stress altered the microbial community, resulting in a more sensitive and fragile ecosystem. Thermophilic and halophilic bacteria genera (Bacillus and Caproiciproducens) were selectively enriched in AnMDBR, promoting short-chain fatty acids generation. Meanwhile, these bacteria severely suppressed methanogenic archaea Methanosarcina, leading to an 80 % reduction in species abundance compared to a robust reactor. Furthermore, the salt stress inactivated key enzymes (mtr and mcr), disrupting methanogenic metabolism.