Studies on the Photocatalytic Degradation of Dye and Textile Wastewater

Abstract

The release of dyes into the receiving water bodies is deleterious, not only because of their color, but also because they are not easily degraded by aerobic bacteria and forms toxic compounds under the action of anaerobic bacteria. Therefore, it becomes imperative to completely degrade these organic compounds before their discharge. Such pollutants cannot be completely degraded by well established techniques like coagulation, flocculation, precipitation, adsorption, membrane separation, aerobic biological treatment. The incapability of conventional wastewater treatment methods to effectively remove such pollutants leads to explore the new, efficient and cost effective treatment systems. In order to meet stringent environmental regulations, the latest development is the oxidation of these biorecalcitrant organic compounds. These radicals have high oxidizing power superior to other usual oxidants and results in complete degradation. The methods are called advanced oxidation processes (AOP’s). AOP’s include homogenous and heterogeneous photocatalytic processes, however the latter being more promising technique for the degradation of organic pollutants. Photocatalytic process relies on the activation of semiconductor results in the generation of electrons and holes. This hole can react with water to produce hydroxyl radical which results in series of redox reaction to destroy the pollutants. TiO2 has been demonstrated to be excellent catalyst and its behavior is well documented in the literature. Many studies have been reported for the use of photocatalyst in the transformation of dyes into simpler end products but the work on photocatalytic degradation of reactive dyes in literature is limited as compared to other dyes. Although the strong potential of photocatalytic process for wastewater treatment is widely recognized but its technical development at industrial scale is not met with much success due to its high operating cost. Taking all these facts into consideration, in the present study, Procion Blue (PB) dye and effluent was collected from textile mill. Photo degradation of PB dye was performed in specially designed reaction vessel in the photoreactor equipped with UV tubes and constant stirring of solution was ensured at constant temperature. Experiments were performed in slurry mode in both UV and solar light at optimized condition. The degradation of dye and textile effluent has been investigated in terms of change in color by measuring absorbance, reduction in COD and solid content. Various process parameters like catalyst dose, pH, concentration of oxidant, initially pollutant concentration were varied and their effects have been analyzed. The work done has been presented in four chapters. After introducing the problem and its content in the first chapter, the study begins with the literature review on photocatalyic degradation of various dyes and textile effluents in the second chapter. In the third chapter, experimental materials and methods have been discussed in detail. Results and their discussion of photocataytic degradation of model dye compound and real effluent has been presented in fourth chapter. In the case of PB dye (25ppm), TiO2 dose was optimized to be 500 mg/l, at operating pH of 4.0 along with oxidant concentration of 300 mg/l at UV intensity of 25 W/m2. In case of textile wastewater, parameters optimized were pH 4.0, catalyst dose of 2.5g/l and oxidant concentration of 900 mg/l. In case of PB dye 82% degradation was achieved in solar light and 89 % in UV light at the optimized parameter, While the treatment of real effluent yields COD reduction from 1250 to 340 mg/l, TDS reduction from 5770 to 2370 mg/l and color reduction from 890 PCU to 180 PCU after 4 hrs of UV treatment. In solar photocatalysis, COD was reduced from 1250 to 260, TDS from 5770 to 1920, Color from 890 PCU to 202 PCU and more than 80% degradation was achived after 5 hrs of treatment. The results of photo degradation of dye and textile mill wastewater showed that heterogeneous photocatalytic could be used as efficient and environmental friendly technique for the complete degradation of recalcitrant organic pollutants which will increase the chances for the reuse of wastewater. The investigations demonstrate the importance of selecting the optimal degradation parameters for practical applications of this operation.