Kinetic aspects and identification of by-products during the ozonation of bitertanol in agricultural wastewaters

The degradation of bitertanol by ozone treatment is investigated. Solutions of bitertanol (8.4 μg mL^?1) were prepared either by dissolution of the standard or by dilution of Gaucho Blé seed loading solution and then ozonated under different conditions. Evolution of the concentrations of bitertanol and its ozonation by-products in both solutions was monitored by HPLC–UV as a function of the treatment time for a concentration of 100 g m^?3 of ozone in the inlet gas. Bitertanol degradation was found to follow a pseudo-first order reaction in both cases. However, the rate of the reaction in diluted seed loading solution was much lower (0.19 vs. 0.27 min^?1 in standard solution) and was close to the reaction rate observed in the presence of a radical scavenger, tert-butanol (0.11 min^?1). Thus, it may be suggested that additives present in the seed loading solution may play the role of radical scavengers. Study of ozone concentration in the inlet gas (from 25 to 100 g m^?3) showed that ozone degradation is also a first-order reaction with respect to ozone. Four ozonation by-products were highlighted, collected and identified by HPLC coupled with an ion trap mass spectrometer using positive electrospray ionization mode. A degradation pathway of bitertanol was finally proposed.