Behaviors and Mechanism of Color, COD, and Silica Removals in the Electrocoagulation of Batik Wastewater Using Waste Aluminum Electrodes

Abstract

Batik wastewater contains organic dyes, waxes, silicate, etc. that are environmentally problematic. Two plain waste aluminum cans were used as electrodes in a batch electrocoagulation (EC) process to remove color, chemical oxygen demand (COD), and silica from batik wastewater. Response surface methodology based on the central composite design was used to demonstrate the dependence of removal efficiency on four key process variables and possible interactions between them. The models were statistically evaluated and conditions for optimized color, COD, and silica removals were verified experimentally. Relatively stronger effects of current density were detected while interactions could be observed on the effects of pH with current density or process time. The floatation of silica scum resulted in increased removal and deviation from the model. The optimal operating conditions were achieved at a current density of 29.91 mA/cm2, an initial pH of 4.51, a reaction time of 24.93 min, and a NaCl dosage of 1.03 g/L that resulted in 88.13 ± 0.51%, 70.50 ± 3.17%, and 100.00 ± 0.00% removals of color, COD, and silica, respectively. The color, COD and pH of the batik wastewater were also reduced to 33 ADMI, 100 mg/L and 6.62 to meet the respective discharge standard limits. Silica content toughened the flocs and increased their buoyancy by strongly interacting with gas bubbles to float to the surface. EC was demonstrated to be an effective and cost-effective treatment technology for the treatment of batik wastewater.