Characterization of methane production and microbial community shifts during waste activated sludge degradation in microbial electrolysis cells

• Methane production was enhanced by MECs fed with alkali-pretreated WAS.
• Efficient sludge reduction was achieved compared with open circuit controls.
• Pyrosequencing revealed the occurrence of hydrogenotrophic methanogenesis.
• The shift of microbial community resulted in methane increase in MECs.

Microbial electrolysis cell (MECs) were investigated as a promising technology to manage waste activated sludge (WAS) reduction and bio-methane generation. The effect of WAS concentration on the MECs performance was discussed. At the optimal concentration of 15 g COD/L, maximum methane yield of MECs fed with alkaline pretreated WAS (A-WAS) were achieved with the value of 77.13 ± 2.52 L CH4/kg-COD on Day 3, which had been improved by 1.5-fold compared with MECs fed with raw WAS (R-WAS), while that was negligible in open circuit controls. Efficient sludge reduction was also obtained in terms of TCOD, total protein, TSS and VSS removal. Pyrosequencing revealed the dominance of exoelectrogen Geobacter and hydrogen-producing bacteria Petrimonas in MECs fed with WAS. Methanocorpusculum with the capacity of methane generation using CO2 and H2 also showed overwhelming dominance (96.01%). The large proportions of Petrimonas and Methanocorpusculum indicated the occurrence of hydrogenotrophic methanogenesis in our methane-producing MECs.