Degradation of sulfamethazine in sewage sludge mixture by gamma irradiation

• Gamma irradiation was effective in removing SMT from sludge mixture.
• SMT removal efficiency from sludge mixture reached 98% at a dose of 2.5 kGy.
• 93–97% of SMT was observed in the supernatant.
• Sludge activity decreased by 85–98% with increasing dose from 1.0 to 5.0 kGy.
• Addition H2O2 exhibited synergetic effect on SMT degradation by gamma irradiation.

The gamma-irradiation-induced degradation of antibiotics sulfamethazine (SMT) in sludge mixture was investigated. The results showed that gamma irradiation was effective in removing SMT from contaminated sludge mixture. With an initial SMT concentration of 10 mg/L, the SMT removal efficiency reached 65% at 1.0 kGy and increased to 98% at 2.5 kGy. The SMT degradation rate was lower in the sludge mixture than that in pure water. The pseudo first-order kinetic constant of SMT degradation in pure water was 2.3 times higher than that in the sludge mixture. Analysis of the SMT concentrations in the supernatant and sludge residue revealed that 93–97% of SMT was observed in the supernatant and the detected SMT in the sludge residue was 168±29, 147±4, and 87±9 μg/g dry weight following irradiation at doses of 0, 1.0 and 2.5 kGy, respectively. The sludge solubilization slowly increased from 1.5% to 3.5% with increasing dose from 1.0 to 5.0 kGy, while the sludge activity decreased by 85–98%. Addition of H2O2 exhibited a synergetic effect on the degradation of SMT, with the pseudo first-order kinetic constant k increasing by around 25%.