Higher impact resistance and lower antibiotic resistance genes proliferation rate in shortcut nitrification-denitrification process under long-term antibiotics selection pressure

Abstract

Shortcut nitrification–denitrification (SCND) has been widely concerned due to its high nitrogen removal efficiency and low operating cost. However, little information is available on the fate of antibiotic resistance genes (ARGs) in SCND process. This study investigates the dynamics of nitrogen removal and ARGs between SCND and full nitrification–denitrification (FND) under long-term selective pressure conditions of tetracycline and sulfadiazine. The study explores the response patterns of extracellular polymers, microbial activity, and microbial community. Results show that the SCND process exhibits 9.14% higher extracellular polymers and 119.07% higher respiratory activity than FND process, resulting in better TN removal performance (67.16% vs. 49.24%) and stronger impact resistance. Compared to Phase I (0 µg/L) and Phase II (100 µg/L), the relative abundance of total ARGs experienced a sharp increase in Phase III (500 µg/L). The SCND process maintains a lower total ARGs abundance than the FND process in water phase. Specifically, in phase III, the relative abundance of intI1 and ARGs in the FND process are 0.04–2.1 logs and 0.66–1.60 logs higher than that of the SCND process in sludge and water phases, respectively. More denitrifying microbes (>40%) are enriched in the SCND process, while it changes to hydrolytic acidification bacteria (>20%) in the FND process. The Partial Least Squares Path Modeling reveals that microbial community and microbial activity play a crucial role in ARGs transmission, with microbial activity exerting greater influence. Additionally, potential pathogenic bacteria including Clostridium, Gemnobacter, Klebsiella, Enternobacter, Aeromonas, Burkholderia are identified, and SCND over FND process shows better inhibition effect on potential pathogenic bacteria proliferation (0.022% vs 0.080%). This study provides new insights into removing traditional pollutants and ARGs simultaneously from wastewater treatment system.