Biotech

• “… designed an upflow single-chamber microbial electrolysis cell (MEC) by placing the cathode on the top of the MEC and carried out a program to track the fate of H2 and electron equivalents in batch experiments.” ¹

Researchers from the Center for Environmental Biotechnology, Biodesign Institute at Arizona State University, in Tempe, Arizona, USA; have presented an article titled: “Fate of H2 in an upflow single-chamber microbial electrolysis cell using a metal-catalyst-free cathode.”

The researchers from Tempe, Arizona, have also noted:

• “When the initial acetate concentration was 10 mM in batch-evaluation experiments lasting 32 h, the cathodic conversion efficiency (CCE) from coulombs (i.e., electron equivalents in current from the anode to the cathode) to H2 was 98 +/- 2%, the Coulombic efficiency (CE) was 60 +/- 1%, the H2 yield was 59 +/- 2%, and methane production was negligible.”
• “However, longer batch reaction time (approximately 7 days) associated with higher initial acetate concentrations (30 or 80 mM) led to significant H2 loss due to CH4 accumulation: up to 14 +/- 1% and 16 +/- 2% of the biogas at 30 and 80 mM of acetate, respectively.”
• “Quantitative PCR proved that no acetoclastic methanogens were present, but that hydrogenotrophic methanogens (i.e., Methanobacteriales) were present on both electrodes.”
• “The hydrogenotrophic methanogens decreased the CCE by diverting H2 generated at the cathode to CH4 in the upflow single-chamber MEC.”
• “In some experiments, the CE was greater than 100%.”
• “The cause was anode-respiring bacteria oxidizing H2 and producing current which recycled H2 between the cathode and the anodes, increasing CE to over 100%, but with a concomitant decline in CCE, despite negligible CH4 formation.”

(1) Lee HS, Torres CI, Parameswaran P, Rittmann BE: Fate of H2 in an upflow single-chamber microbial electrolysis cell using a metal-catalyst-free cathode. Environ Sci Technol. 2009 Oct 15;43(20):7971-6.