Degradation of sulfamethazine in water in thermally activated persulfate process

Abstract

BackgroundThe thermally activated persulfate (TAP) process was utilized to degrade sulfamethazine in water. MethodsThe effects of temperature, Na2S2O8 dosage, initial concentration of sulfamethazine, and the presence of salt (NaCl and NaNO3) and natural organic matter (humic acid) on the degradation of sulfamethazine in the TAP process were studied. Significant FindingsThe degradation of sulfamethazine in the TAP process was closely fitted by a pseudo-first-order kinetic model. At pH 6, the degree and rate of degradation of sulfamethazine at 70 °C considerably surpassed those at 40 °C with diverse Na2S2O8 dosages. At 70 °C and pH 6, raising the Na2S2O8 dosage from 1 mM to 8 mM increased the degree and rate of degradation of sulfamethazine; but excess Na2S2O8 (16 mM) limited them. However, lower temperatures eliminated this limitation. The degree and rate of degradation of sulfamethazine were higher at 70 °C and pH 6 when the initial concentration of sulfamethazine was lower. The Arrhenius equation was utilized to calculate the apparent activation energy at diverse Na2S2O8 dosages. The apparent activation energy for the degradation of sulfamethazine increased from 91 kJ/mol to 150 kJ/mol as the Na2S2O8 dosage was raised from 1 mM to 8 mM. However, the apparent activation energy for the degradation of sulfamethazine was reduced to 120 kJ/mol as the Na2S2O8 dosage was raised further to 16 mM. Radical quenching tests indicate that the most important radical in the degradation of sulfamethazine at 70 °C and pH 6 was SO4•−. At 70 °C and pH 6, the presence of salt (NaCl and NaNO3) and humic acid (HA) exhibited various influences on the degradation of sulfamethazine. The degree of degradation of sulfamethazine (10 mg/L) in the TAP process (70 °C and pH 6) reached 100% at 3 min at an Na2S2O8 dosage of 8 mM with a corresponding rate constant of 1.4003 min−1. Accordingly, the TAP process can be utilized in the effective treatment of sulfamethazine-contaminated water.