Wet air oxidation of aqueous dichlorvos pesticide over catalytic copper-carbon nanofiberous beads

Abstract

Aqueous dichlorvos (DDVP) pesticide, an emerging organic contaminant from abundantly agricultural uses, was degraded by catalytic wet air oxidation (CWAO) over the activated carbon bead (∼0.8 mm) supported copper (Cu)-dispersed carbon nanofiber (CNF) catalyst. The catalyst was shown to be adequately effective in oxidizing the aqueous organics, attributed to the combined effects of a highly active (Cu) metal dispersed in a large specific area containing porous (carbon) substrate and the chemically active CNFs grown over the beads, increasing the exposure of the metal catalyst to the surrounding water via the tip-growth. The batch tests showed 100% degradation in ∼3 h for 150 ppm DDVP concentration at the catalyst-dose of 0.5 g/L at 200 °C and 25 bar. Initial oxidation of the highly active Cuo into monovalent and divalent Cu resulted in the generation of OH radicals as an oxidant for DDVP. The DDVP molecule was gradually degraded into the small molecular organic acids, namely, dichlorovinyl alcohol and dimethyl phosphate, which were mineralized into CO2, H2O and the PO43−, Cl− heteroatom ions. Bacterial tests performed on the reaction intermediates against Escherichia coli revealed the treated water to be less toxic than its parental form. The study indicated CWAO using the prepared catalytic Cu-CNF-dispersed-carbon beads to be a promising technique for the remediation of pesticide contaminated wastewater.