Responsiveness extracellular electron transfer (EET) enhancement of anaerobic digestion system during start-up and starvation recovery stages via magnetite addition.

Two up-flow anaerobic sludge blanket (UASB) reactors (RM with 10 g Fe L-1 magnetite, RB without magnetite) feeding with synthetic wastewater were built to investigate the effect of magnetite addition on anaerobic digestion (AD) performance during start-up and starvation recovery stages. With the magnetite addition, the COD removal efficiency and biogas production during the two stages were enhanced, and the recovery time of RM was shortened by about 50%. The reduced synthesis of riboflavin and heme c along with enhanced sludge conductivity of RM indicated that magnetite could replace their roles for efficient extracellular electron transfer (EET), which favors the growth of anaerobes. Microbial community analysis showed that potential syntrophic partners like Syntrophaceae and Methanothrix were enriched in RM during the recovery stage, and the performance was improved with quick responsiveness. Results demonstrated that addition of conductive materials like magnetite could improve the stability and restorability of AD process efficiently.