Abstract: How may the price of electrochemical treatment be decreased? It is a serious issue that prevents the widespread use of electrochemical technology in the electroplating of heavy metal-containing wastewater. In this work, a heavy metal-containing electroplating wastewater treatment system called a photovoltaic-powered sinusoidal alternating current coagulation system was developed. Computational fluid dynamics was used to grasp the fluid flow and mass transfer mixing in the electrocoagulation reactor. Response surface methodology based on Box-Behnken design was applied to optimize the combination of three important operating parameters (time, current density and initial pH) and applied to the treatment of actual wastewater for one month. The feasibility and mechanism of adsorption of heavy metals (Ni2+, Zn2+ and Cu2+) by nano-iron sol were discussed. The results revealed that when c0(Ni2+) = c0(Zn2+) = c0(Cu2+) = 50 mg×dm-3, cCl- = 100 mg×dm-3, pH0 = 10, j = 1.3 A×m-2, t = 85 min, the removal efficiency (Re) of Ni2+, Zn2+ and Cu2+ were 98.4%, 99.1%, and 99.3%, respectively, and the energy consumption was 0.105 kWh×m-3. The energy consumption and operating cost of sinusoidal alternating current coagulation mode were 37.13% and 64.86% lower than those of direct current coagulation mode, respectively. The removal efficiency of real wastewater treatment could still be maintained at more than 99%, and the effluent met the national discharge standard (GB 31574-2015). The main mechanisms of heavy metal ion removal are cathodic reduction, alkaline precipitation and adsorption. The photovoltaic-powered sinusoidal alternating current coagulation system achieves ultra-low cost treatment of heavy metal wastewater. This work provides a very economical and environmentally friendly strategy for the development and industrial application of new electrocoagulation technologies.
Keywords: Photovoltaic power supply; Sinusoidal alternating current electrocoagulation; Electroplating wastewater; Operating costs; Removal mechanism
