The Photocatalytic Degradation of Priority Pollutants

Abstract

Industrial development is pervasively connected with the disposal of number of toxic pollutants. Nonbiodegradable Pollutants present in wastewater is a point of major concern in many countries. Some of these pollutants require a high priority of treatment for development of water quality criteria and effluent limitation guidelines because they are frequently found in wastewater such type of pollutants are referred to as priority pollutants. Therefore, it becomes imperative to completely degrade these pollutants which cannot be completely degraded by well established techniques like conventional wastewater treatment methods. The main objective of destructive oxidation processes is to mineralize organic contaminants, i.e., convert them to carbon dioxide, water and the oxidised inorganic anions of any heteroatoms present. These processes frequently include the addition of oxidizing agents in the presence of a Catalyst or UV light. These types of processes are collectively called as Advanced oxidation processes (AOP’s). The principal mechanism of AOP’s function is the generation of highly reactive free radicals. TiO2 has been demonstrated to be excellent catalyst and its behaviour is well documented in the literature. In order to meet international standards treatment of industrial wastewater containing pollutants is mandatory. The attention is being given to alternative photocatalytic oxidation processes for wastewater treatment. Taking all these facts into consideration, in the present study, 2-nitroaniline was chosen as a model compound. Photo degradation of 2-nitroaniline 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 2-nitroaniline compound has been investigated in terms of change in color by measuring absorbance and reduction in COD. Various process parameters like catalyst dose, pH, effect of UV/solar, initially pollutant concentration was 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 photocatalytic degradation of various priority pollutants and aniline and its derivatives 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 2-nitroaniline compound and real effluent have been presented in fourth chapter. In the case of 2-nitroaniline (25ppm), TiO2 dose was optimized to be 4g/l, at operating pH of 2.0 with UV intensity of 25 W/m2. In case of 2-nitroaniline 89.5% and 98.9% degradation 6 was achieved in UV at 282nm and 411nm and 93% and 99.3% degradation was achieved at 282nm and 411nm in solar light under the optimized parameters. While the treatment of real effluent yields COD reduction from 80 to 8.4 mg/l in UV and 80mg/l to 5.6mg/l in solar at 282nm and 60mg/l to 2mg/l in UV and 60 to 1mg/l in solar at 411nm was observed. The results of photo degradation of 2-nitroaniline showed that heterogeneous photo catalytic 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. The results depict that solar light can be effectively used for the degradation of 2-nitroaniline and this will help in the economical viability of the process at industrial scale.