Natural tourmaline activated peracetic acid for efficient degradation of sulfadiazine: Reaction mechanisms and catalyst reusability

Peracetic acid (PAA) has received extensive attention in the water treatment due to its high oxidation potential and low toxicity of by-products. In this study, natural non-toxic mineral tourmaline (TM) was used to activate PAA to remove sulfadiazine (SDZ). The TM/PAA system could remove 92 ​% SDZ in 120 ​min. The radical analysis confirmed the co-existence of both free radical and non-free radical degradation pathways in the TM/PAA system, indicating that singlet oxygen (1O2) and acetyl(per)oxy radicals (CH3C(O)O· and CH3C(O)OO·) were the main reactive oxygen species. The Fe2+/Fe3+ ratio on the TM surface decreased during the degradation of SDZ due to Fe2+ consumption. The effect of water matrix on SDZ removal indicated that Cl−, SO42− and NO3− posed little effect on SDZ removal, while CO32− inhibited SDZ removal by affecting pH. Particularly, humic acid (HA) slightly promoted SDZ removal. Ten by-products of SDZ were identified by HPLC-MS/MS, and four possible transformation pathways (SO2 detachment, S–N breakage, amino acid oxidation, and hydroxylation) were proposed. TM was recycled five times and the removal of SDZ remained above 85 ​%, confirming its excellent reusability. This work indicates the TM/PAA system is of great potential for the application on the organic contaminant removal.