Optimization of sequential chemical coagulation - electro-oxidation process for the treatment of an industrial textile wastewater

In this study, the sequential Chemical Coagulation-Electro-Oxidation (CC-EO) process was proposed as an alternative for the treatment of an industrial textile wastewater. Complete characterization of the effluent was made in the terms of its organic load (Total Organic Carbon (TOC), Chemical Oxygen Demand (COD), Biological Oxygen Demand (BOD5)), biodegradability (BOD5/COD ratio) and solids content (total solids and turbidity). For CC, the jar test was used to determine both the most favorable dosage of coagulant and pH of the process (i.e., 600 mg/L of Al2(SO4)3 at pH of 9.3). CC let to remove ca. 93% of turbidity, 53% of COD and 24% of TOC. It also increased BOD5/COD ratio of raw textile wastewater from 0.16 to 0.27. Next, CC effluent was treated by EO. Its performance was optimized using Box-Behnken experimental Design and Response Surface Methodology. The following EO optimal conditions were found: current density = 15 mA/cm2, conductivity = 4.7 mS/cm and pH = 5.6. At these conditions, the sequential CC-EO process removed 100% of color, 93.5% of COD, and 75% of TOC after 45 min of electrolysis with an estimated operating cost of 6.91 USD/m3. Moreover, the CC-EO process yield a highly oxidized (Average Oxidation State, AOS = 2.3) and biocompatible (BOD5/COD >0.4) effluent. © 2018 Elsevier Lt