Chemical and electrochemical coagulation processes as a tertiary treatment for residual phosphate removal from domestic wastewater: effect of operating parameters and calculation of operating cost

Abstract

In this study, we aimed to compare the treatment efficiency and techno-economic analysis of chemical coagulation (CC) and electrocoagulation (EC) processes for residual phosphate (PO43--P) removal from a secondary domestic wastewater treatment plant. The effect of two different coagulants (FeCl3 and alum) and different pH values was evaluated in the CC process. On the other hand, the effect of different metal scrap anodes (Fe, Al, and hybrid Fe + Al), applied current (i = 0.1-0.4 A), and charge loading (q = C L-1 or F m-3) were evaluated in the EC process. In the CC process, the highest removal efficiency of 99.7% PO43--P was obtained with 0.5 kg FeCl3 m-3 and pH = 7.5. However, in the EC process, the highest removal efficiency of 99.9% PO43--P was obtained with Fe scrap anodes under optimum conditions (EC time = 15 min, i = 0.4 A, and q = 6 C L-1 or 3.73 F m-3). The removal capacity and metal/PO43--P molar ratios in the CC process were calculated as 85.7 mg PO43--P g-1 Fe and 19.8 mol mol-1 for FeCl3, and 218.9 mg PO43--P g-1 Al and 7.7 mol mol-1 for alum, respectively. On the other hand, the EC process was calculated as 85.0 mg PO43--P g-1 Fe and 20.0 mol mol-1 for Fe scrap, 132.5 mg PO43--P g-1 Al and 26.6 mol mol-1 for Al scrap, and 84.1 mg PO43--P g-1 Fe + Al and 13.6 mol mol-1 for Fe + Al scrap, respectively. At the end of the study, total operating costs ($ per m3 and $ per kg PO43--P) were calculated for both processes. The results of the study showed that using Fe scrap anodes with the EC process for PO43--P removal results in higher removal efficiencies and lower operating costs.