Enhancing anaerobic digestion in anaerobic integrated floating fixed-film activated sludge (An-IFFAS) system using novel electron mediator suspended biofilm carriers.

Suspended biofilm carriers mediating direct interspecies electron transfer (DIET)-based syntrophic metabolism is a promising strategy to enhance anaerobic digestion and methane production by associating the advantages of conductive suspended biofilm carriers and anaerobic integrated floating fixed-film and activated sludge (An-IFFAS) process. However, the current knowledge of DIET using conductive suspended biofilm carrier is still limited. In this study, novel electron mediator suspended biofilm carriers had been prepared by introducing a series of graphite powders (3 wt%, 5 wt% and 7 wt%) into high-density polyethylene (HDPE), and applied in An-IFFAS reactors. Results showed that An-IFFAS reactors filled with graphite-modified carriers could enhance the degradation of organic matters and the production of methane significantly in comparison with the control reactor filled with conventional HDPE carriers at organic loading rates (OLRs) of 5.9–23.7 kg COD/m3/d. Microbial analysis proved that 7 wt% graphite-modified carrier improved approximately 4.2% abundance of Geobacter and 7.3% abundance of electrotrophic methanogens (Methanothrix) that exchange electron via DIET comparing with that of HDPE carriers, respectively. These findings demonstrated that electron mediator suspended biofilm carrier was able to potentially proceed DIET and enhance the efficiency of anaerobic digestion and recover CH 4 -related energy. Image 1 • Electron mediator carrier had the capability of AD-enhancing. • Electron mediator carrier-filled reactors gained higher methane productivity. • More Geobacter and electrotrophic methanogens were enriched in electron mediator carrier reactors. • Graphite established DIET on the surface of novel carriers. [ABSTRACT FROM AUTHOR]