Hydrogen production from buffer-free anaerobic fermentation liquid of waste activated sludge using microbial electrolysis system

Anaerobic fermentation liquid from waste activated sludge with a rich content of organics and phosphate ions is a promising source of carbon and electrolytes for MECs. The effects of three different electrolytes, including phosphate buffer solution (PBS), bicarbonate buffer solution (BBS), and sodium chloride (NaCl), on the performance of an MEC fed with sludge fermentation liquid (SFL) were compared under conditions of similar conductivity. The production yield of hydrogen was 0.92 mL mg^-1 COD in an MEC with NaCl, which performed similarly with yields of 1.03 mL mg^-1 with BBS and 1.04 mL mg^-1 with PBS. The COD removal efficiencies exceeded 50% in all three groups. Although the energy efficiency of 108% with NaCl was lower than that with PBS (121%), the self-buffering system had advantages regarding cost and environment-friendly application over both PBS and BBS. Comparable performance could be obtained in an MEC with NaCl by adjusting the conductivity using SFL as a carbon source and buffer solution.