Less energy and material consumption in an electrocoagulation system using AC waveform instead of DC for nickel removal: Process optimization through RSM

Abstract

This study pursues two major aims, first, to compare the electrocoagulation (EC) system for Ni2+ removal from aqueous solution using direct current (DC) versus alternating current (AC), and second, to optimize the process for each mode. For this purpose, four variables, viz., current density, initial nickel concentration, initial pH of the solution, and reaction time, alongside three responses, namely remaining nickel, energy consumption, and electrode (aluminum) consumption, were considered. Accordingly, 30 experiments designed by the response surface methodology (RSM) based on the central composite design (CCD) were carried out for each type of current. The statistical analysis revealed that the quadratic models proposed by the Design Expert are reliable to predict the outcomes. As quantitative results for the DC and AC modes, the average amount of the remaining nickel was 44.06 and 43.91 mg/L, energy consumption was 34.9 and 29.2 kWh/kg Ni removed, and electrode consumption was 2.3 and 1.2 kg Al/kg Ni removed, respectively. Thus, the transition from conventional DC to AC waveform coagulation led to a more than 16% reduction in energy consumption and approximately 47% depletion in electrode consumption.