Studies on the Solar Assisted Advanced Oxidative Treatment of Procion Blue Dye

Abstract

The textile industry consumes considerable amounts of water during the dyeing and finishing operations. Considering both volumes discharged and effluent composition, the wastewater generated by the textile industry is rated as one of the most polluting among all industrial sectors. About 1–20% of the total world production of dyes is lost during the dyeing process and is released in the textile effluents. The release of these colored wastewaters in the environment is a considerable source of non-aesthetic pollution and eutrophication and can originate dangerous byproducts through oxidation, hydrolysis, or other chemical reactions taking place in the wastewater phase. Reactive dyes represent approximately 12% of the worldwide production of the commercialized synthetic dyes used. They are extensively used in the textile industry, fundamentally due to the capacity of their reactive groups to bind to textile fibers by covalent bond formation. This characteristic facilitates the interaction with the fiber and reduces energy consumption. The fixation efficiency of reactive dyes ranges between 60% and 90%. Consequently, substantial amounts (about 20%) of unfixed dyes are released in the wastewater, which causes major environmental problems. In view of the carcinogenic or mutagenic character of some reactive dyes, the deleterious effect of the color in the receiving waters, and the customary resistance of the effluents to biological degradation, the necessity of investigating new alternatives for the adequate treatment of this kind of residues are evident. The conventional technologies currently used to degrade the color of the dye-contaminated water include primary (adsorption, flocculation), secondary (biological methods), and chemical processes (chlorination, ozonization). However, these techniques are non-destructive, since they only transfer the non-biodegradable matter into sludge, giving rise to a new type of pollution, which needs further treatment. Advanced oxidation processes (AOPs) employing heterogeneous catalysis has emerged as potential destructive technology leading to the total mineralization of most of organic pollutants. Taking all these facts into consideration, in the present study, Procion Blue HERD (PB) dye was collected from textile mill. Photo degradation of PB dye was performed in specially designed reaction vessel and constant stirring of solution was ensured. Experiments were performed in slurry mode in both UV and solar light at optimized condition. The degradation of dye has been investigated in terms of change in color by measuring absorbance. 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 five chapters. After introducing the problem in first chapter and giving brief account regarding treatment technologies in second chapter, the study begins with the literature review on photocatalyic degradation of various dyes in the third chapter. In the fourth chapter, experimental materials and methods have been discussed in detail. Results and their discussion of solar photocatalytic degradation of PBH dye compound in fifth chapter. In the case of PB dye (25mg/L), TiO2 dose was optimized to be 0.5 g/L, at operating pH of 4 along with oxidant concentration of 0.3 M (H2O2) .However with ZnO, parameters optimized were catalyst dose of 0.375g/L, pH 8 with oxidant concentration of 0.2M In case of PBH dye 86.23% degradation was achieved in solar light using TiO2 (0.5g/L and pH 4) and with ZnO 97.61% degradation was achieved. With the addition of oxidant degradation rate increased in case of TiO2 (86.94%) and there was reduction in degradation time with the addition of oxidant that was from 75 min to 45 min. with both catalysts. The results of solar photo degradation of dye showed that solar photocatalysis using ZnO could be used as efficient and environmental friendly technique for degradation of PBH dye.