Effectiveness of mill scale on the decomposition of dye ingredients for the treatment of textile effluent

Abstract

Wastewater effluent from textile dying plants is one of the major pollutants to the environment. Traditional chemical, physical and biological processes for treating textile dye wastewaters involve high cost, require high energy and generate secondary pollution during the treatment process. These dyestuffs resist biodegradation and are barely removed from effluents using conventional wastewater treatments. Recently there has been considerable interest in the utilization of advanced oxidation processes (AOPs) for the complete destruction of dyes. AOPs are based on generation of reactive species such as hydroxyl radicals that oxidizes a broad range of organic pollutants quickly and non-selectively. AOPs include photocatalysis systems such as combination of semiconductors and light, and semiconductors and oxidants. In the present study the photocatalytic degradation of two commercial dyes (liquid waste) Methylene Blue (MB) and Reactive Orange 4 (RO4) with the help of mill scale (another solid waste generated in steel plants) using AOP was investigated. Photocatalytic activity of mill scale (iron oxide) was also studied. An attempt has been made to study the effect of process parameters through amount of catalyst, concentration of dye, amount of oxalic acid and amount of hydrogen peroxide and light source (UV/ solar illumination) on photocatalytic degradation of MB and RO4. The experiments were carried out by varying amount of catalyst (0.1-1.3 g/100mL), initial concentration of dye (MB = 0.01–0.1 mM/100mL and RO4 = 0.05-0.25mM/100mL), oxalic acid concentration (0.5-3.0mM/100mL for MB and 1mM for RO4), hydrogen peroxide concentration (1-4mL/100mL for MB and 1-2 mL/100mL for RO4). The optimum catalyst dose was found to be 0.8g and 0.3 g/100mL for MB and RO4 respectively in presence of hydrogen peroxide and UV illumination upon using oxalic acid (1mM), is used optimum catalytic condition was obtained 0.5 g/100ml for MB and in the case of RO4 maximum degradation obtained for 0.02g/100mL solution but further research is required to find out optimum value. The performance of photocatalytic system employing mill scale and UV light was observed to be better than that with mill scale and solar system. However, as an alternative energy sources photo-Fenton process could be an economic alternative when using solar light.