Degradation of sulfonamide antibiotics and a structurally related compound by chlorine dioxide: Efficiency, kinetics, potential products and pathways

Sulfonamides (SAs) detected in all kinds of environmental water matrix may cause potential risk for aquatic environment and organisms. In this research, the oxidation of three SAs of sulfamethoxazole (SMX), sulfadiazine (SD) and sulfaguanidine (SGD), and a structurally related compound of 4-methylsulfonylaniline (MSA) by chlorine dioxide (ClO2) was investigated to identify removal efficiency, kinetics, potential products and pathways. At pH 7.0, the highest removal rates of 99.36 %, 100 % and 97.29 % were acquired for SMX, SD and SGD at the initial ClO2 concentration of 50 μM, while that of MSA was only 48.25 %. The difference among three SAs and MSA can be explained by structural influences of substituent attached to the sulfonyl amido-nitrogen. The reactions of SMX, SD and SGD with ClO2 followed the second-order kinetic model (R2 greater than 0.98) with the apparent second-order rate constants range of 5.60 × 102 to 2.73 × 103 M−1 s−1 at pH 7.0 and 25 ℃. The reaction rates were highly dependent on the pH and the trend of activation energy was SGD > SMX > SD at pH 7.0. Products evaluation indicated that the main potential degradation pathways of three SAs were the cleavage of SN and SC bonds, deamination and hydroxylation of aniline group. The sulfonyl amido-nitrogen and aniline amino-nitrogen were prone to be attacked by ClO2. Aniline and sulfanilic acid were found to be the common products of three SAs degradation. The results suggest that ClO2 has the potential to serve as a chemical oxidant for removing sulfonamides in practical water treatment conditions.