Influence of catholyte pH and temperature on hydrogen production from acetate using a two chamber concentric tubular microbial electrolysis cell

Microbial electrolysis cells (MECs) could be integrated with dark fermentative hydrogen production to increase the overall system yield of hydrogen. The influence of catholyte pH on hydrogen production from MECs and associated parameters such as electrode potentials (vs Ag/AgCl), COD reduction, current density and quantity of acid needed to control pH in the cathode of an MEC were investigated. Acetate (10 mM, HRT 9 h, 24 C, pH 7) was used as the substrate in a two chamber MEC operated at 600 mV and 850 mV applied voltage. The effect of catholyte pH on current density was more significant at an applied voltage of 600 mV than at 850 mV. The highest hydrogen production rate was obtained at 850 mV, pH 5 amounting to 200 cm3stp/lanode/day (coulombic efficiency 60%, cathodic hydrogen recovery 45%, H2 yield 1.1 mol/mol acetate converted and a COD reduction of 30.5%). Within the range (18.5-49.4 C) of temperatures tested, 30 C was found to be optimal for hydrogen production in the system tested, with the performance of the reactor being reduced at higher temperatures. These results show that an optimum temperature (approximately 30 C) exists for MEC and that lower pH in the cathode chamber improves hydrogen production and may be needed if potentials applied to MECs are to be minimised.