Application of Side-Stream Bio-Electrochemical Module to Quickly Reactivate Process Performances in Deteriorated Bench-Scale Anaerobic Digestion of Food Waste

This study evaluated a bench-scale side-stream bio-electrochemical anaerobic digestion (SBEAD) system for rapid reactivation of deteriorated food-waste anaerobic digestion (AD) and benchmarked it against internal-electrode bio-electrochemical AD (BEAD). At an organic loading rate (OLR) of 4.0 kg-COD/m3/d, AD deteriorated (Volatile fatty acids (VFAs) > 6000 mg/L and a pH drop) and methane yield declined to 0.12 L-CH4/g-COD. In contrast, BEAD maintained performance at the same OLR, sustaining a methane yield of 0.25 ± 0.02 L-CH4/g-COD and a COD removal of 77.3 ± 4.5%. Within 20 days of converting the deteriorated AD into SBEAD, VFAs decreased to 4387 mg/L and pH recovered from 6.61 to 7.35, while COD removal and methane yield increased to 64.8% and 0.21 L-CH4/g-COD. At OLR 7.0 kg-COD/m3/d, SBEAD sustained high performance (COD removal 75.2 ± 3.6%, methane yield 0.25 ± 0.01 L-CH4/g-COD), whereas BEAD deteriorated with impaired internal mixing (VFAs 9500 mg/L, pH < 6.39, COD removal 44.0% and methane yield 0.11 L-CH4/g-COD). Despite additional recirculation energy, higher OLR tolerance may reduce required digester volume and capital cost, thereby improving overall cost efficiency. Future development and validation of operational strategies are expected to further improve the practicality and efficiency of the SBEAD system for full-scale implementation.