Abstract: Electromethanogenesis of degrading organics has great potential in bioenergy (CH₄) production, wastewater treatment, groundwater bioremediation, soil and sediment bioremediation. Enriching biocathode with high activity is currently one of the prominent problems to deal with for its development. The cathodic biofilms in glucose-fed SCMMEC exhibited electroactivity. This suggested that wastewater containing glucose could directly be used to enrich biocathode through SCMMEC. Two microbial biocathodes had current density (compared to the geometric surface area of the electrode) of 0.59 A/m² and 0.62 A/m² under 0.8 V applied cell voltage, respectively. However, relative to the bioanode activity, their electroactivity was still lower. They were the current-limiting electrodes in the system. The current with fed-batch mode operation suggested that possible redox mediators or suspended cells did not affect the biocathode electroactivity upon the medium complete replacement. With the medium containing 6 mM phosphate, the biocathode electroactivity showed no difference at day 62 and 153 under 0.8 V. However, the biocathode electroactivity decreased at day 275. Ions concentrating and salt precipitation due to long-term one direction polarization with DC power lead to the activity loss.

Key words: methanogenic biocathode, electroactivity, single chamber, membraneless microbial electrolysis cell, current-limiting electrode, one direction polarization