Evaluation of Fenton’s Oxidation for Treatment of Selected Paint Emulsions and its Residual Toxicity in Water

Abstract

Due to increasing water scarcity, recycle and reuse of wastewater is increasingly pertinent. Paint manufacturing industries emit enormous quantity of wastewater. This wastewater contains high Chemical Oxygen Demand (COD) and turbidity. Advanced oxidation process is increasingly recognized as an appropriate method among the chemical methods to reduce the toxicity of paint wastewater. In this study, the degradation of mixture of three different emulsion samples in water is investigated using laterite soil heated to 800°C as heterogeneous catalyst by Fenton-like oxidation process. Optimisation of different factors such as pH, H2O2 and catalyst concentration is done with the Design Expert 11 software using Central Composite Design (CCD), to evaluate their effects on COD removal efficiencies of the synthetically prepared paint wastewater. A remarkable result found was that the treatment efficiency of 98% was achieved for the mixture of emulsions with and without the addition of H2O2. The laterite calcined at 800°C could produce in-situ •OH radicals in the acidic pH which initiated the Fenton’s reaction due to the bimetallic action of Fe3+ and Al3+ in the solution. Thereby, this experimental analysis provides an important breakthrough for treatment of paint industry wastewater, where it can overcome the disadvantages of using H2O2 and conventional Fenton process. The laterite calcined at 800°C is found to be remarkably stable and reusable and also it produced very less amount of sludge compared to conventional process. The remarkable property of the green synthesized heterogeneous catalyst particles (LSFeNP(TC)) using laterite extract and Terminalia catappa leaf extract made the catalyst wonderfully working in reducing the COD of paint wastewater upto 85% efficiency without an external oxidizing agent such as H2O2, and acid, thus reducing the cost of process and increasing the environmental sustainability. Although the reduction in chemical oxidation generally reduces toxicity, high efficiency of organic component breakdown does not always result in a drop in toxicity to a tolerable level. Hence, toxicity reduction studies for industrial effluent are required. Therefore, proxy tests, such as the use of indicator bacteria, have the potential to provide insights for toxicological studies of (treated) wastewater. Having reviewed various methods and indicators adopted for toxicity analysis of AOP treated wastewater, the toxicity of treated paint wastewater was studied by bacterial growth inhibition test using Bacillus subtilis and seed germination test using mung bean (Vigna radiata) and Bengal gram (Cicer arietinum). The results showed that the wastewater is completely toxic free for the growth of indicator bacteria treated with LS 800 catalyst but it shows 38% inhibition for LSFeNP(TC) due to the presence of FeOCl. This indicates that the heterogeneous Fenton’s oxidation using laterite as catalyst is an effective AOP in reducing the toxicity of paint wastewater. The finding reported in this research is significant because it proves laterite soil, which is abundantly available in tropical regions, to be an efficient catalyst for Fenton’s Oxidation treatment of paint wastewater by considerable reduction in the sludge, which opens up further scope for treatment of other similar industrial effluents in tropical regions.