Effectiveness of fenton's reagent in the treatment of textile effluent

Abstract

Textile industry is one of the largest consumers of water and consequently, one of the largest producers of wastewater among all industries in Bangladesh. Dyeing and finishing are two important steps involved of man-made or natural fibers to the desired permanent colors and processing of the fibers into final commercial products. Textile wastewater from dyeing and finishing processes has been a serious environmental threat for years. This wastewater, with high Chemical Oxygen Demand (COD) and a strong dark color, is classified as a high strength wastewater. Moreover, textile wastewater exhibit low BOD to COD ratios indicating their nonbiodegradable nature. The discharge of this type of wastewater without any type of treatment brings about considerable adverse impacts on the receiving water bodies and thus demands for an efficient treatment process. Textile wastewater is usually treated by conventional methods such as chemical coagulation, biological oxidation and activated carbon adsorption. However, these conventional methods suffer from a few limitations or drawbacks related to cost, efficiency and sludge generation. The limitations of conventional methods can be overcome by using Fenton‘s reagent. In present study, textile effluents were collected from two different sections like cotton dyeing and finishing; then its characterization was done. The aim of the work was mainly to investigate the efficiency of the Fenton‘s processes for the removal of COD, color and Turbidity from a real textile wastewater. The Fenton‘s process employs ferrous ions and hydrogen peroxide H2O2 under acidic pH conditions. The experimental variables studied include doses of iron salts and hydrogen peroxide, oxidation time, pH for oxidation and coagulation. The COD, color and turbidity removal reached a maximum of 97.2%, 96.8% and 84.8% respectively at a reaction time of 20 minutes under low doses of H2O2 and Fe2+ for cotton dyeing effluent. At optimized conditions 85.7% reduction in color, 99.8% reduction in turbidity and 99.9% reduction in COD is obtained for finishing effluent. Optimum dose of hydrogen peroxide was 2.0 ml/500 ml and 1.5 ml/500 ml for cotton dyeing and finishing effluent, respectively. Optimum dose of ferrous sulphate was 1.0 gm/500 ml and 0.5 gm/500ml for cotton dyeing and finishing effluent, respectively. Maximum removal occurred in the 20 minutes reaction time for cotton dyeing effluent and 30 minutes reaction for finishing effluent. The tested parameters after Fenton‘s process met the standard of Bangladesh environmental conservation rules for disposing of treated effluent into sewerage system. In this study optimum pH was found to be 4.0 and 6.0 respectively for oxidation and coagulation for both samples. It is observed that at an extremely low and high pH, removal efficiency decreased. COD was removed primarily by Fenton‘s coagulation, rather than by Fenton‘s oxidation. In this study Fenton process is found technically effective for the treatment of finishing effluent as compared to dyeing effluent.