Spent mushroom substrates recycled as solid-liquid mixed carbon sources: Inducing concurrent denitrification and anammox in a membrane-less microbial fuel cell

Spent mushroom substrates (SMSs) were recycled as solid-liquid mixed carbon sources in a single chamber microbial fuel cell (SC-MFC) to investigate nitrogen removal and electricity generation performances as well as explore the corresponding mechanisms. The leaching experiments showed that the release rate of COD was as high as 59.75 mg/(g·d) for the first stage but it declined sharply to 0.3 mg/(g·d) for the second stage, and denitrification performance relied on COD released from SMS at the beginning. A pH of 6.5, a solid-liquid ratio of 1:100 and an electrode distance of 3 cm were deemed as the optimum operating conditions of SC-MFC. For the long-term operation of SC-MFC, the total nitrogen removal efficiency exceeded 50 % and the average voltage output attained 153 mV. Microbial diversity indicated that the anode enriched hydrolyzing bacteria, fermentation bacteria and electricigens, whereas the cathode was found to be predominated by denitrifying bacteria and anammox microorganisms, suggesting nitrate was mainly removed in the cathodic area. The membrane-less structure and SMS as substrates mutually created a special environment that induced concurrent denitrification and anammox. Our results can provide useful information for understanding the mechanisms of using SMS as solid-liquid carbon sources for simultaneous nitrogen removal and electricity generation.