Advanced electrocoagulation using aluminum electrodes supported by persulfate for the treatment of a high-strength wastewater

Abstract

In this study, the treatment of leachate nanofiltration (NF) concentrate, which is high-strength wastewater, by advanced electrocoagulation (EC) was investigated. The EC process, in which aluminum electrodes were used, was enhanced by persulfate (PS) addition (EC-PS). First, the control experiments were conducted then the operating parameters of the process were optimized by the Box-Behnken design. Process variables were PS dose, applied current, initial pH, and reaction time while chemical oxygen demand (COD), total organic carbon (TOC), UV254, and color removal were the system responses. COD, TOC, UV254, and color removal efficiencies by the validation studies performed under optimized conditions (PS dose: 0.590 g/L; applied current: 0.710 A; initial pH: 5, and reaction time: 31.4 min) were 62.6%, 54.3%, 74.2%, and 88.0%, respectively. Based on the degree of effect on COD and TOC removal, statistical analysis parameters can be listed as linear, quadratic, and interactive from higher to lower one. The linear parameters can be listed as initial pH, applied current, reaction time, and PS dose according to the level of their effect on removal efficiencies. Quenching experiments showed that sulfate and hydroxyl radicals work together in the process while hydroxyl radicals were more effective. The specific energy consumption and total cost of the process under optimized operating conditions were 1.90 kWh/kg COD and 1.40 $/m3 respectively. By obtaining the spectrum of the sludge formed under optimum process conditions by Fourier Transform Infrared Spectroscopy analysis, the characteristics of the sludge were determined and Al hydroxides and hydrocarbons were present in the sludge.