Responses of nitrogen removal, microbial community and antibiotic resistance genes to biodegradable microplastics during biological wastewater treatment

Biodegradable plastics decompose more easily into microplastics (MPs) as alternatives to traditional plastics. However, the effects of biodegradable microplastics (BMPs) on the aerobic biological treatment process in activated sludge need further investigation. This study compared the effects of three BMPs (Polylactic acid (PLA), Polyhydroxyalkanoate (PHA) and Polybutylene succinate (PBS)) with 1, 10 and 50 mg/L on nitrogen removal, microbial community and antibiotic resistance genes (ARGs) in activated sludge . The results demonstrated that 10 and 50 mg/L PHA and 50 mg/L PLA enhanced specific nitrate and specific nitrite reduction rates, promoting total nitrogen removal. The positive effects on denitrification-related functional genes (such as napA, nirK, nirS ) were also identified. Additionally, 10 mg/L PLA and PHA stimulated the production of loosely bound extracellular polymeric substances (EPS). However, 50 mg/L PLA and PHA decreased the tightly and loosely bound EPS contents. The response of nitrogen removal and EPS were attributed to the shifts of dominant bacteria abundance including Bacteroidota, Chloroflexi and Acidobacteriota. Moreover, PHA and PLA promoted the abundance of ARGs and intI1 in activated sludge, particularly at high concentrations. However, PBS did not affect the nitrogen removal, EPS and microbial communities. The results might shed light on the influence of BMPs on activated sludge. • High concentrations of PHA and PLA promoted denitrification and nitrogen removal. • PLA and PHA affected the functional genes involved in the denitrification. • 10 mg/L PLA and PHA stimulated EPS secretion, while 50 mg/L BMPs inhibited. • PLA and PHA enhanced ARGs and intI1 abundance, especially at 50 mg/L concentration. • 50 mg/L PLA and PHA induced more ARGs-hosting bacteria in activated sludge.