Hydrogen production with effluent from an anaerobic baffled reactor (ABR) using a single-chamber microbial electrolysis cell (MEC)

Abstract

In the process of fermentative bio-hydrogen production, organic matter is degraded into volatile fatty acids and ethanol, and consequently thermodynamic constraints prevent the further spontaneous reactions. Moreover, the anaerobic baffled reactor (ABR) with the advantage of phase separation could realize the acetic acid accumulation via acid-producing bacteria. The microbial electrolysis cell (MEC) could convert the acetic acid into hydrogen furthermore. Considering this, the ABR coupled with MEC has been operated to strengthen the hydrogen production. This study was designed regarding orthogonal experiments to operate the four-compartment ABR with a hydraulic retention time (HRT) = 24 h, influent COD ∼ 4600 mg/L, temperature = 35 ± 1 °C, and discovered the optimal parameters with pH = 7, C/N = 44, and 2-bromoethanesulfonate (BES) concentration = 20 mmol/L to achieve the high acetic acid accumulation of effluent. The single-chamber membranless MEC with carbon anode and Ni-catalyst stainless steel cathode (liquid volume = 85 mL) fed with the ABR effluent with applied voltage = 0.6 V and electric conductivity = 7.45 mS/cm, achieved 99.0 ± 0.3% total COD removal efficiency, 1.31 ± 0.04 m3H2/m3d hydrogen production, 2.78 ± 0.11 mLH2/mgCOD hydrogen yield and 138.63 ± 3.11% electrical energy efficiency. Therefore the ABR-MEC system could overcome the “fermentation barrier” to achieve higher hydrogen production and organic matter degradation.