Effect of calcium peroxide pretreatment on the remediation of sulfonamide antibiotics (SMs) by Chlorella sp

Highlights: • Dose of 0.05–0.1 g CaO₂/g biomass removed 60% of the spiked sulfonamide antibiotics. • CaO₂ pretreatment increased cometabolism of sulfonamides 10 to 20%. • Bioassimilation removed 24% sulfadiazine and sulfamethazine, and 38% sulfamethoxazole. • Ring cleavage, hydroxylation and pterin-related conjugation metabolites were detected. • Peroxidase is a micropollutants-specific enzyme for sulfonamides cometabolism. This study investigated the effect of CaO₂ pretreatment on sulfonamide antibiotics (SMs) remediation by Chlorella sp. Results showed that a CaO₂ dose ranging from 0.05 to 0.1 g/g biomass was the best and led to higher SMs removal efficacy 5–10% higher than the control. The contributions made by cometabolism and CaO₂ in SMs remediation were very similar. Bioassimilation could remove 24% of sulfadiazine (SDZ) and sulfamethazine (SMZ), and accounted for 38% of sulfamethoxazole (SMX) remediation. Pretreatment by CaO₂ wielded a positive effect on microalgae. The extracellular polymeric substances (EPS) level of the CaO₂ pretreatment microalgae was three times higher when subjected to non-pretreatment. For the long-term, pretreatment microalgae removed SMs 10–20% more than the non-pretreatment microalgae. Protein fractions of EPS in continuous operation produced up to 90 mg/L for cometabolism. For bioassimilation, SMX intensity of the pretreatment samples was 160-fold less than the non-treatment one. It indicated the CaO₂ pretreatment has enhanced the biochemical function of the intracellular environment of microalgae. Peroxidase enzyme involved positively in the cometabolism and degradation of SMs to several metabolites including ring cleavage, hydroxylation and pterin-related conjugation.