Gamma irradiation of pharmaceutical compounds, nitroimidazoles, as a new alternative for water treatment

The main objectives of this study were: (1) to investigate the decomposition and mineralization of nitroimidazoles (Metronidazole [MNZ], Dimetridazole [DMZ], and Tinidazole [TNZ]) in waste and drinking water using gamma irradiation; (2) to study the decomposition kinetics of these nitroimidazoles; and (3) to evaluate the efficacy of nitroimidazole removal using radical promoters and scavengers. The results obtained showed that nitroimidazole concentrations decreased with increasing absorbed dose. No differences in irradiation kinetic constant were detected for any nitroimidazole studied (0.0014-0.0017 Gy(-1)). The decomposition yield was higher under acidic conditions than in neutral and alkaline media. Results obtained showed that, at appropriate concentrations, H2O2 accelerates MNZ degradation by generating additional HO center dot; however, when the dosage Of H2O2 exceeds the optimal concentration, the efficacy of MNZ degradation is reduced. The presence of t-BuOH (HO center dot radical scavenger) and thiourea (HO center dot, H-center dot and e(aq)(-) scavenger) reduced the MNZ irradiation rate, indicating that degradation of this pollutant can take place via two pathways: oxidation by HO center dot radicals and reduction by e(aq)(-) and H-center dot. MNZ removal rate was slightly lower in subterranean and surface waters than in ultrapure water and was markedly lower in wastewater. Regardless of the water chemical composition, MNZ gamma irradiation can achieve i) a decrease in the concentration of dissolved organic carbon, and ii) a reduction in the toxicity of the system with higher gamma absorbed dose. (C) 2009 Elsevier Ltd. All rights reserved.