Hydrogen gas can be produced by electrohydrogenesis in microbial electrolysis cells (MECs) at greater yields than fermentation and at greater energy efficiencies than water electrolysis. It has been assumed that a membrane is needed in an MEC to avoid hydrogen losses due to bacterial consumption of the product gas. However, high cathodic hydrogen recoveries (78 ± 1% to 96 ± 1%) were achieved in an MEC despite the absence of a membrane between the electrodes (applied voltages of 0.3 < Eap < 0.8 V; 7.5 mS/cm solution conductivity). Through the use of a membrane-less system, a graphite fiber brush anode, and close electrode spacing, hydrogen production rates reached a maximum of 3.12 ± 0.02 m3 H2/m 3 reactor per day (292 ± 1 A/m3) at an applied voltage of Eap = 0.8 V. This production rate is more than double that obtained in previous MEC studies. The energy efficiency relative to the electrical input decreased with applied voltage from 406 ± 6% (E ap = 0.3 V) to 194 ± 2% (Eap = 0.8 V). Overall energy efficiency relative to both Esp and energy of the substrate averaged 78 ± 4%, with a maximum of 86 ± 2% (1.02 ± 0.05 m3 H2/m3 day, Eap = 0.4 V). At Eap = 0.2 V, the hydrogen recovery substantially decreased, and methane concentrations increased from an average of 1.9 ± 1.3% (Eap = 0.3-0.8 V) to 28 ± 0% of the gas, due to the long cycle time of the reactor. Increasing the solution conductivity to 20 mS/ cm increased hydrogen production rates for Eap = 0.3-0.6 V, but consistent reactor performance could not be obtained in the high conductivity solution at Eap > 0.6 V. These results demonstrate that high hydrogen recovery and production rates are possible in a single chamber MEC without a membrane, potentially reducing the costs of these systems and allowing for new and simpler designs.
All Science Journal Classification (ASJC) codes
- Environmental Chemistry