Electrocoagulation flotation as a municipal wastewater (pre-)treatment technology: Effect of weather conditions and current density

Abstract

Electrocoagulation (EC) is a promising compact alternative technology, despite its viability in municipal wastewater treatment (MWWT) is currently challenged by its energy-intensive and batch-mode operation. This study introduces an innovative continuous electrocoagulation flotation (ECF) design for MWWT. ECF shows promising pollutant removal efficiencies, with identical results using both iron (Fe) and aluminum (Al) anodes. At a current density (CD) of 120 A/m2, it achieved significant removals: 90% tCOD, 98% TP, 94% TSS, 60% BOD5, and 40% TN. Designed ECF is proposed as a pre-treatment step due to limited TN removal. The study investigated optimal ECF performance under varying weather conditions using CD ranges of 40, 80, and 120 A/m2. Both Fe and Al ECF outperformed in treating rainy weather (RW) and dry weather (DW) municipal wastewater (MWW). However, Al anode's super-faradaic behavior resulted in higher residual concentrations in effluent, (i.e., an average of 6.53–33.7 mg/L), and operational costs compared to Fe ECF. Optimized Fe ECF setting needs to be changed depending in the weather variation. Fe ECF achieved high removal rates for tCOD (94%) and TP (95%) in RW MWW at a low CD of 40 A/m2. Comparative to this, the optimum CD for treated DW MWW was between 40 and 80 A/m2, removing tCOD (71–73%) and TP (85–95%). Specifically, at these conditions, the operational expenses were respectively 0.47 ± 0.03 €/m3 (RW MWW), and 0.37 ± 0.02 €/m3 to 0.81 ± 0.04 €/m3 (DW MWW). Moreover, ECF enables resource recovery and a circular economy through anaerobic sludge digestion, with Fe ECF generating more biogas than Al.