Effect of oxidation on nitro-based pharmaceutical degradation and trichloronitromethane formation

Nitro-based compounds are the direct precursors of trichloronitromethane during chlorination disinfection. Two nitro-based pharmaceuticals ranitidine and nizatidine were selected as model compounds to assess the effect of oxidation on the removal of nitro-based pharmaceuticals, as well as the reduction of their trichloronitromethane formation potentials (TCNMFPs). The four oxidants were ozone (O-3), chlorine (Cl-2), chlorine dioxide (ClO2) and potassium permanganate (KMnO4). The changes in pharmaceuticals and their TCNMFPs during oxidation using various oxidants and dosages were quantified. The relationships between oxidation product structures and TCNMFP changes were also analyzed. The results showed that oxidation with Cl-2 and KMnO4 were more effective than ClO2 and O-3 in removing the nitro based pharmaceuticals. Meanwhile, decreased TCNMFPs by KMnO4 oxidation but increased TCNMFPs by Cl-2, ClO2 and O-3 oxidation were observed. The results of product analysis indicated that chlorine transfer products had higher TCNMFPs, while oxygen transfer products made little contribution to TCNMFPs after oxidation. In addition, one possible reaction pathway leading TCNMFP increase was that chloronitromethane or nitromethane, which was a better TCNM precursor, formed when double bond was attacked by oxidants. (C) 2015 Published by Elsevier Ltd.