Persulfate activation by Fe3O4-doped biochar synthesized from Fenton sludge and sewage sludge for enhanced 1-H-1,2,4-triazole degradation

A novel composite biochar synthesized from Fenton sludge (FS) and sewage sludge (SS) was employed to catalyze persulfate for the removal of 1-H-1,2,4-triazole (TZ). The optimized conditions for the synthesis and operating process were identified through response surface methodology as follow: SS/FS mass ratio = 5:1, catalyst dosage = 0.9 g L−1 and PDS concentration = 0.5 g L−1. The removal efficiencies of TZ, TOC and organic nitrogen were found to be as high as 97.6%, 80.33% and 100%, respectively, with the addition of Fe3O4-doped biochar in persulfate catalytic system. Besides, Fe3O4-doped biochar exhibited superior stability and tolerance to wide range of pH (2–12), temperature (15–45 °C) and co-existing substrate. The reactive oxygen species, which resulted in the catalytic degradation of TZ followed the order of SO4∙− > ∙OH > O2∙− > 1O2, were identified by electron spin resonance and quenching tests. It demonstrated that the radical pathway accomplished with non-radical pathway contributed to the enhanced degradation of TZ, which was further identified by electrochemical experiments. Moreover, the possible degradation pathway of TZ was ascertained and proposed through DFT calculation and LC-MS analysis. These findings illustrated that the novel magnetic biochar would be a promising persulfate catalyst for the treatment of refractory organic matters. In addition, it also provided a new alternative method for the resource utilization of FS and SS.