Degradation of pesticides present in tomato rinse water by direct photolysis and UVC/H2O2: optimization of process conditions through sequential Doehlert design

Abstract

The degradation of three pesticides, azoxystrobin (AZO), difenoconazole (DFZ), and imidacloprid (IMD), commonly found in the tomato rinse water, was studied through UVC (251-257 nm) and UVC/H2O2 photolysis. The results showed that direct photolysis follows pseudo-first-order kinetics, with total AZO and IMD removals within 15 min, using 21.8 and 28.6 W m-2, respectively, while the highest percentage of DFZ degradation was 51.7% at 28.6 W m-2 UVC. The estimated quantum yields were 0.572, 0.028, and 0.061 mol Einstein-1 for AZO, DFZ, and IMD, respectively. With regard to UVC/H2O2, total pesticide removal was achieved after 10 min, while optimal treatment conditions in relation to the pesticide removal rates, estimated through the sequential Doehlert design, were about [H2O2]0 = 130 mg L-1 and 26 W m-2. Cytotoxicity and genotoxicity assays carried out with Allium cepa, for real industrial tomato rinse water sampled from washing belts did not show abnormalities during cell division, with total pesticides degradation after 15 min, demonstrating the potential application of the UVC/H2O2 process as a viable localized treatment with a focus on the possible reuse of treated water.