Sulfamethoxazole oxidation in secondary treated effluent using Fe(VI)/PMS and Fe(VI)/H2O2 processes: Experimental parameters, transformation products, reaction pathways and toxicity evaluation

Sulfamethoxazole (SMX), a bacteriostatic sulfonamide antibiotic, has been detected in various aquatic ecosystems, which is a serious environmental concern. The main objective of this research was to assess the usage of Fe(VI)/PMS and Fe(VI)/H2O2 oxidation for SMX removal from an aqueous media. A series of experiments were accomplished to investigate the effect of various environmental parameters including initial concentration of SMX, contact time, pH and molar ratio of oxidants for both processes. The SMX transformation products (TPs) formed in Fe(VI)/PMS system were detected using LC-MS-MS and possible oxidation pathways were suggested. Complete removal of SMX was achieved using Fe(VI)/PMS system at SMX concentration of 2.2 mg/L and pH= 5 after contact time of 25 min, while the degradation efficiency of 70.81% was observed by Fe(VI)/H2O2 at SMX= 2 mg/L, pH= 3 and contact time of 90 min. Kinetic studies showed that the SMX oxidation using both processes followed first-order kinetics. The S–N bond cleavage, the benzene ring opening and hydroxylation are the predominant SMX degradation pathways. The ECOSAR simulation program showed that some TPs were more toxic than SMX in terms of acute and chronic toxicity. Daphnia was also found to be the most susceptible organism to SMX and its TPs. This paper offers new insights into the use of an effective and appropriate method for the treatment of SMX polluted municipal wastewater plant effluent.