Enhanced degradation of tetracycline hydrochloride by microwave-activated sulfites: Influencing factors and mechanisms

Sulfite (SO32−) has garnered widespread attention for its ability to produce free radicals and environmentally friendly properties. In this work, the mechanism and feasibility of the microwave (MW) activated sulfite system for the removal of tetracycline hydrochloride (TCH) were investigated. The removal efficiency, reaction kinetics, and influencing factors of the MW/SO32− were explored. The identification of active substances and the reaction mechanism of the MW/SO32− system were further analyzed. The results showed that MW could activate sulfite effectively and the reaction process followed the pseudo-first-order kinetic. MW/SO32− achieved a 97.8 % degradation of TCH within 15 min. The influencing factors experiments showed that increasing the initial pH promoted the degradation of TCH. According to the results of EPR and free radical quenching experiments, the degradation of TCH by the MW/SO32− system had both free radical (SO3·−, SO5·−, SO4·−, and O2·−) and non-free radical pathway (1O2) reactions. The degradation pathways of TCH mainly included hydroxylation, removal reaction, ring-opening reaction, and oxidation reaction. Evaluation with the T.E.S.T system found that the ecological risk of TCH was reduced after MW/SO32− treatment. The use of microwaves as sulfite activation method was shown to be a new alternative to promote the rapid degradation of emerging organic pollutants.