Degradation of ciprofloxacin by manganese(III) intermediate: Insight into the potential application of permanganate/bisulfite process

Permanganate could be activated by bisulfite to generate soluble Mn(III) which can oxidize organic contaminants rapidly. However, a lot of concerns need to be addressed for the application of permanganate/bisulfite (PM/BS) process. Taking ciprofloxacin as a target contaminant, the influence of pH, temperature and co-existing solutes on the degradation of organic contaminant in PM/BS process was systematically investigated. The PM/BS process oxidized ciprofloxacin with k_obs 2.18–6.27 orders of magnitude larger than other oxidation processes under various reaction conditions and thus stood out. Ciprofloxacin present in real waters can be degraded effectively in the PM/BS process and the co-existing solutes have less inhibiting effect at lower pH and lower ciprofloxacin concentration. Bromate less than 5 µg/L was generated in PM/BS process even in the presence of 1000 µg/L bromide and thus bromate generation in PM/BS process was not a concern. The residual manganese species could be easily removed by aeration from real waters. The degradation products of ciprofloxacin in PM/BS process were identified and the plausible reaction pathways were proposed. Although the quinolone core structure in degradation products remained unattacked, bacterial growth inhibition bioassays and genotoxic experiments showed that the PM/BS treated ciprofloxacin samples displayed negligible cytotoxic and genotoxic potency.