Efficient elimination of sulfadiazine in an anaerobic denitrifying circumstance: Biodegradation characteristics, biotoxicity removal and microbial community analysis

Sulfadiazine (SDZ) is widely used in clinical treatment, livestock husbandry and aquaculture as an antibacterial agent, resulting in environmental risks. In this work, batch experiments were conducted to investigate the characteristics of SDZ biodegradation and reaction mechanisms in a nitrate anaerobic denitrifying system for the first time. The results showed that 98.52% of the SDZ, which had an initial concentration of 50 mg L−1, was degraded after 70 h, indicating that the removal efficiency of SDZ in anaerobic denitrifying system was 55.27% higher than that in anaerobic system. Furthermore, LC-MS-MS analysis confirmed that SDZ could be degraded into 16 byproducts via 3 main degradation pathways that contained 6 different reactions. After analyzing the microbial communities of the reactor, the denitrifying bacteria and desulfurizing bacteria Desulforhabdus, Ignavibacterium, SBR1031_norank, Nocardioides, etc. were highly associated with the removal of SDZ in the system. The biological toxicity test of the effluent indicated that the remaining organic matter and inorganic matter of the effluent could provide nutrients for E. coli and promote its growth. In other words, anaerobic denitrifying systems are highly efficient, simple and environmentally friendly, and have an impressive prospect in the biodegradation of sulfonamide antibiotics.