Microbial community analysis in a long-term membrane-less microbial electrolysis cell with hydrogen and methane production

• CH4 was produced in a single-chamber MEC despite using 2-bromoethanesulfonate (BES).
• Methanogenesis was not inhibited despite 100 mM of BES in the media.
• H2-oxidizing Methanobrevibacter sp. represented 97% of total Archaea in the cathode.
• Homoacetogenesis increased when methanogenesis decreased at 200 mM of BES.
• Development of BES adaptation could explain the experimental data.

A single-chamber microbial electrolysis cell (MEC) aiming at hydrogen production with acetate as sole carbon source failed due to methanogenesis build-up despite the significant amount of 2-bromoethanesulfonate (BES) dosage, 50 mM. Specific batch experiments and a thorough microbial community analysis, pyrosequencing and qPCR, of cathode, anode and medium were performed to understand these observations. The experimental data rebuts different hypothesis and shows that methanogenesis at high BES concentration was likely due to the capacity of some Archaea (hydrogen-oxidizing genus Methanobrevibacter) to resist high BES concentration up to 200 mM. Methanobrevibacter, of the Methanobacteriales order, represented almost the 98% of the total Archaea in the cathode whereas Geobacter was highly abundant in the anode (72% of bacteria). Moreover, at higher BES concentration (up to 200 mM), methanogenesis activity decreased resulting in an increase of homoacetogenic activity, which challenged the performance of the MEC for H2 production.