Persulfate activation by sulfide-modified nanoscale iron supported by biochar (S-nZVI/BC) for degradation of ciprofloxacin

Antibiotics ciprofloxacin pollution has become a major problem in the aqueous environment. Advanced oxidation processes (AOP) have been recognized as promising technology to treat wastewater contaminated by antibiotics. In this study, biochar-supported sulfided nanoscale zero- valent iron (S-nZVI/BC) was employed as a catalyst to activate persulfate (PS) to remove the ciprofloxacin (CIP). The effects of S/Fe molar ratio, PS dosage, initial pH value and CIP concentration, and coexisting anion were investigated. Results showed that S-nZVI/BC exhibited excellent performance in removing CIP when combined with PS. S-ZVI/BC with an S/Fe mole ratio of 0.25 exhibited the highest CIP removal efficiency. CIP could be efficiently removed when the initial solution pH ranged from 2.5 to 8.5, and chloride was found to have a negative effect on degradation. The batch experimental data agreed well with the pseudo-second-order model. Radical scavenger studies revealed that SO4− and HO were the crucial reactive species, which contributed to the high CIP degradation performance. A possible degradation pathway was proposed with the elimination of the piperazine ring based on the LC-MS analysis. Moreover, the catalytic ability of S-nZVI/BC could be maintained at 87% after five turnovers. In all, this study indicates that S-nZVI/BC is an ideal catalyst for PS activation for antibiotics treatment.