Sunlight-Assisted Photo-Fenton Process for Removal of Insecticide from Agricultural Wastewater

Abstract

Pesticides and insecticides are harmful and toxic organic chemicals that are used for controlling pests and insects in agriculture, thereby considered as necessary evil. Agricultural wastewater, contaminated with such toxic pesticides, pollutes surface and groundwater. Pesticides are able to reach surface waters either directly or indirectly via the discharge of agricultural drainage water from treated land and via runoff after application on hard surfaces (Leu et al. 2004). Organophosphorus pesticides are produced in mass and are widely used in the developing country. 2,2 dichlorovinyl dimethyl phosphate, commonly referred as Dichlorvos (Fig. 2.1) is an organophosphorous insecticide, which is highly toxic, non-biodegradable and difficult to remove by conventional methods. During 2006–2010 period, consumption of Dichlorvos in India was 5833 metric tons. Due to its fairly good solubility [~10 g.L⁻¹ (at 20 °C)] in water (WHO 1978, 1994) it is highly mobile in aquatic environment. Various technologies and processes have been proposed for the treatment of pesticide-contaminated waters. Some conventional techniques including flocculation, filtration and adsorption of activated carbon are only based on a phase transfer of the pollutant. These treatment procedures are either of high cost or a source of secondary pollution due to sludge formation: therefore, there is a need to seek better alternatives (Evgenidou et al. 2005). Advanced oxidation processes (AOPs) are attractive methods for the treatment of wastewaters containing refractory organics due to their efficiency to oxidize a great variety of organic contaminants by the generation of highly reactive hydroxyl radicals (OH•) (Espulgas et al. 2002). Many pollutants, including pesticides, pharmaceuticals and dyes can be completely mineralised by AOP as reported in the works of Chiron et al. (2000), Perez-Estrada et al. (2005) and Lucas and Peres (2006). Heterogeneous photocatalysis using titanium dioxide (TiO₂) and solar/UV radiation, combined with hydrogen peroxide (H₂O₂), and homogeneous processes such as Fenton (Fe²⁺/H₂O₂) and photo-Fenton (Fe²⁺/H₂O₂/UV/sunlight) reactions are proved to be useful techniques for the treatment of pesticide-contaminated wastewater. There are different ways to produce HO•, among which solar photo-Fenton process is one of the most efficient ones for the treatment of contaminated wastewater (Malato et al. 2002; Oller et al. 2006; Maldonado et al. 2007; Ortega-Liébana et al. 2012; Klamerth et al. 2013).