Enhanced antibiotic removal in a nitrifying sludge system by ammonia-oxidizing bacteria and heterotrophs

Nitrifying system is a promising alternative for the removal of numerous antibiotics. However, the respective contribution of ammonia-oxidizing bacteria (AOB) and heterotrophs for antibiotic degradation in nitrifying sludge system remain unclear. In this study, a nitrifying sludge system for treating sulfamethoxazole (SFX) containing wastewater was developed. The mechanisms of SFX removal were investigated under varying SFX concentrations (0.1, 1, 5 and 10 mg/L). The results showed that AOB (Nitrosomonas) played a major role in SFX degradation in nitrifying sludge system (> 50%). The relatively poorer SFX degradation performance at higher concentration corresponding to pharmaceutical wastewater (10 mg/L) was attributed to the inhibition of AOB, which was further confirmed at molecular and enzyme levels. In addition, heterotrophic bacteria (Thauera, Azoarcus, Thermomonas, Ferribacterium, Flavobacterium, and Brevundimonas) with potential degradation ability and antibiotic resistance were also involved in SFX degradation, second only to AOB. This study sheds new light on the important contribution of heterotrophic bacteria and ARGs to the biodegradation of antibiotics in a ni-trifying sludge system.

Automated summary

This study revealed that ammonia-oxidizing bacteria (AOB) are the main contributors to antibiotic degradation in nitrifying sludge systems, while heterotrophic bacteria also play a significant role, especially at higher concentrations. The inhibition of AOB at high concentrations and the involvement of heterotrophic bacteria in antibiotic degradation were confirmed through molecular and enzyme analysis, shedding new light on the complex mechanisms of antibiotic removal in nitrifying sludge systems.