Kinetics of ozonation of typical sulfonamides in water

To investigate the kinetic rate constants ozone and hydroxyl radicals towards two groups of antimicrobials -sulfadiazine (SD) and sulfamethoxazole (SMX).

The solute consumption method was used to detect the rate constants of ozone alone with sulfadiazine and sulfamethoxazole, and tertiary butanol was selected as a scavenging agent and pH was adjusted to 2.5 by adding orthophosphate buffers (OB); and the competition kinetics studying methodwith nitrobenzene as a reference was applied to measure the rate constants of hydroxyl radicals towards sulfadiazine and sulfamethoxazole, and pH was adjusted to 7.0 by adding OB.

The rate constants of SD and SMX with ozone alone were 261 mol(-1) · dm(3) · s(-1) and 303 mol(-1) · dm3 · s(-1) by calculating in low reaction system. The rate constants of hydroxyl radicals with SD and SMX were 2.2×1010 mol(-1) · dm(3) · s(-1) and 2.7×1010 mol(-1) · dm(3) · s(-1), respectively. Moreover, the rate constants of hydroxyl radicals with SMX were found to have increased from 3.6×109 mol(-1) · dm(3) · s(-1) to 2.8×1010 mol(-1) · dm(3) · s(-1) with pH value rising from 5.0 to 7.8.

SMX and SD are both refractory to ozone oxidation alone, and are liable to be degraded by hydroxyl radicals, and the rate constants of SMX with the hydroxyl radical slightly increases with pH rise.