Process contribution evaluation for COD removal and energy production from molasses wastewater in a BioH₂–BioCH₄–MFC-integrated system

In this study, a three-stage-integrated process using the hydrogenic process (BioH₂), methanogenic process (BioCH₄), and a microbial fuel cell (MFC) was operated using molasses wastewater. The contribution of individual processes to chemical oxygen demand (COD) removal and energy production was evaluated. The three-stage integration system was operated at molasses of 20 g-COD L⁻¹, and each process achieved hydrogen production rate of 1.1 ± 0.24 L-H₂L⁻¹day⁻¹, methane production rate of 311 ± 18.94 mL-CH₄L⁻¹day⁻¹, and production rate per electrode surface area of 10.8 ± 1.4 g m⁻²day⁻¹. The three-stage integration system generated energy production of 32.32 kJ g-COD⁻¹and achieved COD removal of 98 %. The contribution of BioH₂, BioCH₄, and the MFC reactor was 20.8, 72.2, and, 7.0 % of the total COD removal, and 18.7, 81.2, and 0.16 % of the total energy production, respectively. The continuous stirred-tank reactor BioH₂at HRT of 1 day, up-flow anaerobic sludge blanket BioCH₄at HRT of 2 days, and MFC reactor at HRT of 3 days were decided in 1:2:3 ratios of working volume under hydraulic retention time consideration. This integration system can be applied to various configurations depending on target wastewater inputs, and it is expected to enhance energy recovery and reduce environmental impact of the final effluent.