Aspartame affects methane yield and enhances transmission of antibiotic resistance genes during anaerobic digestion of sludge

Aspartame (ASP) is a widely used artificial sweetener, yet recent studies have shown that ASP have potential toxic effect. ASP is also detected in sludge, however, the influence of ASP on the performance of sludge anaerobic digestion and the fate of antibiotic resistance genes (ARGs) have not been thoroughly investigated. Under stress of 0, 0.5, 5and 50 mg/L ASP, cumulative methane production was 181.7, 167.0, 154.0 and 140.8 mlCH4/g VSS, respectively. ASP inhibited the dissolution and conversion of organic matter in sludge. Sequencing data revealed a decline in the abundance of functional microorganisms compared to control, such as hydrolytic-acidifying bacteria and methanogens, potentially attributed to increased intracellular reactive oxygen species and damaged cell membranes caused by ASP addition. Specifically, 50 mg/L ASP reduced the total abundance of methanogens by 59.40 % compared to control. Concurrently, alterations in microbial communities along with an increase in Tn916 and intI1 were observed, increasing the abundance of ARGs. The total abundance of five ARGs peaked at 1.43E+ 12 copies/g at 5 mg/L ASP, representing 139 % of the control. This research contributes valuable insights into the alterations in anaerobic digestion caused by ASP, emphasizing the potential risks in the overall environmental system.