Oxidative removal of sulfadiazine using synthetic and natural manganese dioxides

Studies on oxidation kinetics of sulfadiazine (SDZ) using δ−MnO2 (birnessite) and natural MnO2 are limited. Reaction order at different SDZ speciation was determined based on the effects of initial H+, MnO2 and SDZ concentrations using initial rate method, which would be useful to determine the optimum pH and MnO2 concentration. Birnessite and natural MnO2 with different physico-chemical properties such as BET surface area, pHPZC, d-spacing, and crystal size similarly showed good efficiencies in oxidizing neutral SDZ (pH 5) and anionic SDZ (pH 8). Activation energy (Ea) and thermodynamic parameters indicated the similar oxidation efficiencies in the temperature range of 10–40°C. The S⁢O2−
4 was produced from the SDZ oxidation coupled to the reduction of MnO2 to Mn2+. The effect of co-solute ciprofloxacin (CIP) on the oxidation kinetics of SDZ was also studied. The rates of SDZ oxidation by both birnessite and natural MnO2 were reduced by the presence of CIP due to competition in oxidation between SDZ and CIP. The SDZ was more rapidly oxidized than CIP in both single- and bi-solute systems, as indicated by the presence of CIP intermediate, whereas the intermediate of SDZ was not detected.