Competing electrons with humic and protein-like substances via direct interspecies electron transfer during anaerobic digestion of waste activated sludge with glycerol

Alcohol feeding had been recognized as an effective strategy for boosting methane production during anaerobic digestion of waste activated sludge (WAS). However, the mechanisms were curtly attributed to the promotion of direct interspecies electron transfer (DIET). Anaerobic digestion of WAS with a series of concentrations of glycerol were conducted. When eliminated methane production from glycerol, the remaining methane production was still 15−32 % higher than that without glycerol. However, the differences in the efficiency of volatile solid removal as well as concentration of short-chain fatty acids among all the digesters were not significant. Microbial communty analysis showed that addition of glycerol increased abundance of Methanothrix soehngenii GP6 that was capable of participating in DIET and sugar/amino acid-fermenting bacteria (Fastidiosipila sanguinis and Brevefilum fermentans). Electrochemical Fourier transform infrared spectra and electron transfer coefficient showed that addition of glycerol increased electron transfer efficiencies of digestates, and the gaps were further widened with the increase in the concentration of glycerol. Conversely, addition of glycerol lowered electron transfer efficiencies of humic and protein-like substances extracted from digestates. These results suggested the potential mechanisms on competing electrons with humic and protein-like substances via DIET for high-efficiency methane production from WAS with glycerol.