Boosting conversion of waste activated sludge to methane during anaerobic digestion via facilitating direct interspecies electron transfer with glycerol

Possibility of boosting conversion of waste activated sludge to methane via facilitating direct interspecies electron transfer with glycerol was explored. Methane yields with 5 %/8 % glycerol were 1.18/1.31 folds higher than that without glycerol. After removing methane yields from glycerol, methane yields with 5 %/8 % glycerol was still 17 %/19 % higher than that without glycerol. Electron transfer coefficients for charge/discharge in sludge with 8 % glycerol were 1.12/1.39 folds higher than that without glycerol. Analysis of conductivity-temperature responses found that conductivity of sludge with 8 % glycerol exhibited an exponential increase when temperature was declined, similar to that with 8 % ethanol. However, conductivity of sludge with 8 % glycerol was one order of magnitude higher than that with 8 % ethanol. Electrochemical Fourier transform infrared spectra showed that reversible changes of bands associated with c-type cytochrome in sludge with 8 % glycerol were more intense than that with 8 % ethanol. Analysis of microbial communities showed that glycerol feeding increased the abundance of Methanospirillum hungatei JF-1, and specially enriched Tangfeifania diversioriginum, Syntrophomonas zehnderi OL-4 and Trichococcus pasteurii. These results indicated that glycerol feeding facilitated the better direct interspecies electron transfer than ethanol feeding that had been previously documented during anaerobic digestion of waste activated sludge.