A hybrid electrocoagulation and filtration system using waste Fe scrap for enhancing organic matter recovery and biogas production from wastewater

Conventional chemically enhanced primary treatment and standalone electrocoagulation (EC) face limitations associated with chemical demand, sludge production, and sacrificial electrode consumption. To address these challenges, a hybrid electrocoagulation and filtration (h-EC/F) system was developed using waste iron scrap as both the electrode and filter medium. Response surface methodology was used to optimize operating conditions based on pollutant removal and recovered sludge characteristics. Under the optimal conditions of 6.01 V and 1.72 h, the system achieved removal efficiencies of 78.0% for total chemical oxygen demand, 59.5% for soluble chemical oxygen demand, 83.8% for suspended solids, 24.4% for total nitrogen, and 89.3% for total phosphorus. The recovered sludge had a ratio of volatile solids (VS) to total solids of 62.9% and exhibited a higher biochemical methane potential than that of conventional primary sludge. During a 105-day continuous anaerobic digestion experiment, the organic loading rate (OLR) was increased from 1 to 4 kg-VS/m 3 /d. At the highest OLR, the anaerobic reactor fed with conventional primary sludge experienced process failure accompanied by substantial volatile fatty acid (VFA) accumulation, whereas the reactor fed with h-EC/F sludge maintained stable methane production, pH, and alkalinity. Microbial community analysis revealed differences in bacterial composition and a higher relative abundance of Methanosarcina thermophila in the h-EC/F sludge reactor. The coexistence of acetoclastic and hydrogenotrophic methanogens was consistent with the consumption of fermentation products and the limited accumulation of VFAs. These findings support the integration of primary organic matter recovery with stable anaerobic methane production using the h-EC/F system.