Insight into the performance and microbial community profiles of magnetite-amended anaerobic digestion: Varying promotion effects at increased loads.

Abstract In current study, the enhancement effect of magnetite on anaerobic digestion was evaluated at increased organic loading rate (OLR) from 1.6 to 25.6 kg COD·m-3·d-1. The supplement of magnetite enhanced the methane yield by 7%-483% accompanied with faster VFAs conversion. Microbial analysis suggested the varied enhancing effect achieved at different OLRs was attributed to different syntrophic interactions triggered by magnetite. More specially, an electroactive syntropy was established between Trichococcus with Methanobacterium at OLR lower than 6.4 kg COD·m-3·d-1, while with the OLR increase, more acid fermentative bacteria (Propionimicrobium, Syner-01) were enriched and further enhanced methanogenesis in a syntrophic way with Methanosaeta. Overall, the incorporation of magnetite was a promising approach to achieve efficient anaerobic digestion, OLR was also critical factor affecting the methanogenesis and should be carefully regulated in future application.