Synergistic electrocoagulation–precipitation process using magnesium electrodes for denim wastewater treatment: Bifunctional support electrolyte effect

Abstract

The textile industry is one of the most polluting activities since its processes handle >8000 different types of chemical products. It consumes a significant volume of water, for example, a denim dying process requires from 30 to 50 L/kg. The goal of this study was to determine the synergistic effect of the electrocoagulation–chemical precipitation treatment (EC–CP) on real textile wastewater from the denim industry. MgCl2, CaCl2, and MgSO4 were tested for CP, and CaCl2 exhibited the best results: 77, 76, and 77 % of COD, color, and turbidity were removed, respectively. EC batch treatment was performed with an anode of Mg and a cathode of Fe at a pH of 4.5, treatment time was 29 min, and current density 144.7 A/m2 (1.7 A). The optimal conditions were obtained by using a Box–Behnken model, with removal efficiencies of 93, 87, and 93 % for COD, color, and turbidity, respectively. The main contribution and conclusion of this work were the bifunctional effect of the electrolyte (CaCl2) improves the conductivity and precipitates the pollutants. The Mg anode removes efficiently the organic matter and the nutrients (N and P) by complexation, the synergistic EC–CP achieved removal efficiencies were 91, 93, and 94 % for COD, color, and turbidity, respectively. The energetic costs for EC and EC–CP treatments were 1.82 and 0.25 US$/m3, respectively.