Degradation of ethylenethiourea pesticide metabolite from water by photocatalytic processes

Abstract

In this study, photocatalytic (photo-Fenton and H₂O₂/UV) and dark Fenton processes were used to remove ethylenethiourea (ETU) from water. The experiments were conducted in a photo-reactor with an 80 W mercury vapor lamp. The mineralization of ETU was determined by total organic carbon analysis, and ETU degradation was qualitatively monitored by the reduction of UV absorbance at 232 nm. A higher mineralization efficiency was obtained by using the photo-peroxidation process (UV/H₂O₂). Approximately 77% of ETU was mineralized within 120 min of the reaction using [H₂O₂]₀ = 400 mg L⁻¹. The photo-Fenton process mineralized 70% of the ETU with [H₂O₂]₀ = 800 mg L⁻¹ and [Fe²⁺] = 400 mg L⁻¹, and there is evidence that hydrogen peroxide was the limiting reagent in the reaction because it was rapidly consumed. Moreover, increasing the concentration of H₂O₂ from 800 mg L⁻¹ to 1200 mg L⁻¹ did not enhance the degradation of ETU. Kinetics studies revealed that the pseudo-second-order model best fit the experimental conditions. The k values for the UV/H₂O₂ and photo-Fenton processes were determined to be 6.2 × 10⁻⁴ mg L⁻¹ min⁻¹ and 7.7 × 10⁻⁴ mg L⁻¹ min⁻¹, respectively. The mineralization of ETU in the absence of hydrogen peroxide has led to the conclusion that ETU transformation products are susceptible to photolysis by UV light. These are promising results for further research. The processes that were investigated can be used to remove pesticide metabolites from drinking water sources and wastewater in developing countries.

Keywords:

• Pesticide metabolites
• ethylenethiourea
• photo-Fenton reaction
• degradation
• mineralization
• photocatalytic processes
• advanced oxidation process