Study of Electrocoagulation and Combined Electrocoagulation-Oxidation Processes for Dye Removal

Abstract

Dyeing and finishing are the two most important processes usually applied in textile manufacturing industries. These two processes generate considerable amount of wastewater, which may contain high color, suspended solids (SS), pH, temperature, biological oxygen demand (BOD), chemical oxygen demand (COD), and low biodegradability. However, the major problem is strong color wastes that are lost after the dyeing process up to 50%. The discharge of dyeing wastewater into streams and rivers causes several problems. Therefore, it is necessary to treat dye wastewater before discharged into water. The purpose of this study was to investigate the effects of the operating parameters, such as pH, treatment time, and current density on COD removal from synthetic water sample prepared by dissolving Brilliant Cresyl Blue dye in distilled water. Better COD removal was observed with increasing current density. It was found that for current density equal to 14.53 mA/cm2 (with 5.5 A current) with four electrodes gave better result as compared to 9.25 mA/cm2 and 11.88 mA/cm2. It was possible to bring the residual COD in the treated water within the permissible limit in 75 minutes of electrolysis time. pH 6 was found to be appropriate for the treatment. The comparison of COD removal by EC alone and with EC and oxidation combined was carried out. Hydrogen peroxide was used as oxidant. The results showed that the COD removal efficiency increased from 87% to 97% with 1.5 ml/l of H2O2 dose and from 87% to 94% with 1.0 ml/l of H2O2 dose. This increased COD removal results due the formation of hydroxyl radicals. Also, the treatment time decreased from 90 min to 60 min in case of combined process.