Improving hydrogen production in microbial electrolysis cells through hydraulic connection with thermoelectric generators

Using alternative power sources to drive hydrogen production in microbial electrolysis cells (MECs) is important to implementation of MEC technology. Herein, thermoelectric generators (TEG) were to power MECs using simulated waste heat. With the MEC anolyte as a cold source for TEG, current generation of the MEC increased to 2.46 ± 0.06 mA and hydrogen production reached 0.14 m³ m⁻³ d^-1, higher than those of the TEG-MEC system without hydraulic connection (1.16 ± 0.07 mA and 0.07 ± 0.01 m³ m⁻³ d^-1). A high recirculation rate of 30 mL min^-1 doubled both current generation and hydrogen production with 10 mL min^-1, benefited from a stronger cooling effect that increased the TEG voltage output. However, the optimal recirculation rate was determined as 20 mL min^-1 because of comparable performance but potentially less energy requirement. Reducing anolyte hydraulic retention time to 4 h has increased hydrogen production to 0.25 ± 0.05 m³ m⁻³ d^-1 but decreased organic removal efficiency to 69 ± 2%. Adding three more TEG units that captured more heat energy further enhanced hydrogen production to 0.36 m³ m⁻³ d^-1. Those results have demonstrated a successful integration of TEG with MEC through both electrical and hydraulic connections for simultaneous wastewater treatment and energy recovery.