Scalable multi-electrode microbial electrolysis cells for high electric current and rapid organic removal

Microbial electrolysis cells (MECs) can be used to produce hydrogen gas from wastewater. A novel multi-electrode stack design was proposed and examined under various operating conditions to maximize electric current in MECs without precious metal catalysts. For the cathode in the electrode stack, stainless steel mesh generated higher electric current than activated carbon cloth. The electric current density increased in proportion to the number of electrode pairs as the maximum current density was 520 A m−3 in MEC-10 (10 electrode pairs), 270 A m−3 in MEC-5 (5 electrode pairs), and 45 A m−3 with a single electrode pair. The stacked MEC was not ideal for fed-batch operation due to the short inter-electrode distance (∼2 mm); consequently, continuous-recycle and -flow operation resulted in the high electric current generation. During continuous-flow operation, individual electrodes in MEC-10 and MEC-5 showed a variation in electric current capacity (0.9-2.7 mA for 0.6 mL min−1). The COD (chemical oxygen demand) removal rate increased from 45.7 to 128.8 mg-COD L−1 h−1 with increasing flow rate from 0.1 to 0.6 mL min−1. These findings indicate that the stacked multi-electrode design can magnify the current generation and COD removal rate in MECs.