Effect of microalgae addition on sulfonamide removal and antibiotic resistance gene dissemination in leachate sludge

Abstract

Sulfonamide antibiotics (SAs) cannot be sufficiently removed from the conventional biological leachate systems. So far, it remained unclear how microalgae addition impacted SA removal and the spread of antibiotic resistance genes (ARGs) in leachate nitrification sludge (PNS). In this study, Scenedesmus obliquus and indigenous PNS were used to construct a variety of microalgal-bacterial symbiotic systems with various sludge proportions (100%, 99%, 97%, and 95%). The removal performance of 3 SAs including sulfadiazine (SDZ), sulfamethoxazole (SMX), and trimethoprim (TMP), and the dissemination of ARGs (sul1, sul2, and sul3), were investigated in batch experiments for 10 days under illumination. The results showed that the treatments with 99% and 97% leachate sludge had the highest biodegradation efficiencies of SDZ and SMX. In contrast, the highest removal of TMP was observed in the pure leachate sludge groups, indicating that TMP removal was dominated by the leachate sludge. Additionally, the higher abundances of the target ARGs and the mobile genetic element (Intl1) on day 10 indicated the potential enrichment of ARGs by horizontal gene transfer across all treatment groups. Furthermore, the higher addition of microalgae stimulated the horizonal gene transfer of ARGs. These findings will improve our understanding of the antibiotic contamination control in leachate sludge treatment systems.