Oxidation of sulfonamides, macrolides, and carbadox with free chlorine and monochloramine

The oxidation of 10 antibiotics-carbadox, erythromycin-H2O, roxithromycin, sulfadimethoxine, sulfamerazine, sulfamethazine, sulfamethizole, sulfamethoxazole, sulfathiozole, and tylosin during chlorination and monochloramination in laboratory and surface waters was investigated to identify kinetics and treatment effectiveness. A kinetic model that incorporates pH-based speciation of both oxidant species and sulfonamide antibiotics was developed and validated. Specific rate constants for the individual ionic species were developed for the dominant reactant pairs. Liquid chromatography/mass spectrometry, preceded by solid phase extraction, was used to analyze antibiotics in kinetic experiments. With experimental conditions of 25 °C and reaction times of up to 2 h, an initial concentration of 1 mg/L of free chlorine removed an average of 88 percent of the antibiotics over a pH range of 6.1–9.1. Monochloramine was less effective at typical drinking water dosage concentrations of 3 mg/L, with average removals of 35, 10, and 0 percent at a pH of 6.1, 7.6, and 9.1, respectively.