Redox mediator, microaeration, and nitrate addition as engineering approaches to enhance the biotransformation of antibiotics in anaerobic reactors

The present work assessed some engineering approaches, such as the addition of the redox mediator anthraquinone-2,6-disulfonate (AQDS) (50 and 100 mu M), microaeration (1 mL air min(-1)), and nitrate (100-400 mg L-1), for enhancing the biotransformation of the antibiotics sulfamethoxazole (SMX) and trimethoprim (TMP) (200 mu g L-1 each) in anaerobic reactors operated at a short hydraulic retention time (7.4 h). Initially, very low removal efficiencies (REs) of SMX and TMP were obtained under anaerobic conditions (similar to 6%). After adding AQDS, the anaerobic biotransformation of these antibiotics significantly improved, with an increase of approximately 70% in the REs with 100 mu M of AQDS. Microaeration also enhanced the biotransformation of SMX and TMP, especially when associated with AQDS, which provided REs above 70%, particularly for TMP (similar to 91% with 1 mL air min(-1) and 50 mu M of AQDS). Concerning nitrate, the higher the added concentration, the higher the REs of the antibiotics (similar to 86% with 400 mg L-1). Therefore, all the assessed approaches were demonstrated to be very effective in improving the limited biotransformation of SMX and TMP in anaerobic reactors, ensuring REs comparable to those found in higher-cost wastewater treatment technologies, such as conventional activated sludge, membrane bioreactors, and hybrid processes.

Automated summary

The study found that engineering approaches such as the addition of AQDS, microaeration, and nitrate can significantly enhance the biotransformation of sulfamethoxazole and trimethoprim in anaerobic reactors, ensuring removal efficiencies comparable to higher-cost wastewater treatment technologies.