Synergetic promotion of direct interspecies electron transfer for syntrophic metabolism of propionate and butyrate with graphite felt in anaerobic digestion

Direct interspecies electron transfer (DIET) was considered to replace interspecies H-2 transfer to enhance syntrophic metabolism during the anaerobic digestion. The graphite felt with excellent electrical conductivity was added into a semi-continuous reactor as a conducive material, strengthening DIET in enhancing the degradation of propionate and butyrate. The final average CH4 production rate increased by 19.1% and 16.7%, respectively, during the propionate and butyrate degradation. Microbial community analysis revealed that the relative abundance of the microflora that could participate in DIET, like Geobacter, Methanosaeta and Methanosarcina species, was greatly improved in the presence of graphite felt. Further experiments showed that the high H-2 partial pressure had no obvious effect on the degradation of propionate and butyrate in the graphite felt-supplement reactors.