Optimizing continuous-flow electrocoagulation–flotation for municipal wastewater through low-current recirculation and pulsed-current operation

Electrocoagulation–flotation (ECF) is a promising pretreatment technology for municipal wastewater (MWW), but high energy demand, operating costs, electrode passivation, and variability in reactor design constrain its wider application. This study evaluated two operational strategies for real MWW using the same reactor: semi-continuous sequential-pass effluent recirculation at 12 A/m 2 and continuous-flow direct pulsed-current (DPC) operation at 80 A/m 2 (10 min on/5 min off). Two- and three-pass recirculation were compared with single-pass direct-current (DC) operation at 40 and 80 A/m 2 , while DPC was compared with DC at 80 A/m 2 . Two-pass recirculation at 12 A/m 2 provided the most favorable balance between treatment performance and resource consumption, achieving 78% total chemical oxygen demand removal and 85% total phosphorus removal with near-unity Faradaic efficiency. Relative to DC at 40 A/m 2 , operating cost, energy consumption, and iron (Fe) consumption decreased by 39%, 47%, and 34%, respectively; corresponding reductions relative to DC at 80 A/m 2 were 74%, 86%, and 69%. Energy demand, Fe consumption, and operating cost for two-pass recirculation at 12 A/m 2 were 0.144 kWh/m 3 , 0.062 kg/m 3 , and 0.234 €/m 3 , respectively. At 80 A/m 2 , DPC reduced energy consumption, Fe consumption, operating cost, and dry-sludge production by 74%, 32%, 53%, and 76.7%, respectively. Excitation–emission matrix fluorescence spectroscopy, parallel factor analysis, and fluorescence indices indicated selective removal and changes in residual fluorescent dissolved organic matter (DOM) composition. These strategies enhanced ECF resource efficiency at bench scale; however, further pilot-scale validation involving additional independent replicates and comprehensive characterization of electrode passivation and sludge is required.