Elucidating microalgae-mediated metabolism for sulfadiazine removal mechanism and transformation pathways

Sulfadiazine (SDZ) as a typical sulfonamide antibiotic is commonly detected in wastewater, and its removal mechanism and transformation pathways in microalgae-mediated system remain unclear. In this study, the SDZ removal through hydrolysis, photodegradation, and biodegradation by Chlorella pyrenoidosa was investigated. Higher superoxide dismutase activity and biochemical components accumulation were obtained under SDZ stress. The SDZ removal efficiencies at different initial concentrations were 65.9-67.6%, and the removal rate followed pseudo first-order kinetic model. Batch tests and HPLC-MS/MS analyses suggested that biodegradation and photodegradation through the reactions of amine group oxidation, ring opening, hydroxylation, and the cleavage of S-N, C-N, C-S bond were dominant removal mechanisms and pathways. Characteristics of trans-formation products were evaluated to analyze their environmental impacts. High-value products of lipid, car-bohydrate, and protein in microalgae biomass presented economic potential of microalgae-mediated metabolism for SDZ removal. The findings of this study broadened the knowledge for the microalgae self-protection from SDZ stress and provided a deep insight into SDZ removal mechanism and transformation pathways.

Automated summary

This study investigated the removal mechanism and transformation pathways of sulfadiazine (SDZ), a typical sulfonamide antibiotic commonly found in wastewater, through hydrolysis, photodegradation, and biodegradation by Chlorella pyrenoidosa. The results showed that under SDZ stress, higher superoxide dismutase activity and accumulation of biochemical components were obtained. The SDZ removal efficiencies ranged from 65.9% to 67.6% at different initial concentrations, and the removal rate followed a pseudo first-order kinetic model. Batch tests and HPLC-MS/MS analyses suggested that biodegradation and photodegradation, through reactions such as amine group oxidation, ring opening, hydroxylation, and cleavage of S-N, C-N, C-S bonds, were the dominant removal mechanisms and pathways.