High concentration of ammonia sensitizes the response of microbial electrolysis cells to tetracycline

•High ammonia nitrogen reduced the tetracycline (TC) degradation capacity of MEC.•High ammonia nitrogen sensitized the response of anode respiring bacteria to TC.•TC and high ammonia nitrogen synergically reduced anode bio-activity and biomass.•The ARGs were closely related to microbial communities and MGE (intI1) in MEC.•The presence of MPs may lead to the risk of ARGs spreading to the environment. Microbial electrolysis cell (MEC) is a promising technology for effective energy conversion of wastewater organics to biogas. Yet, in swine wastewater treatment, the complex contaminants including antibiotics may affect MEC performance, while the high ammonia concentration might increase this risk by increasing cell membrane permeability. In this work, the responses of MECs on tetracycline (TC) with low and high ammonia loadings (80 and 1000 mg L–1) were fully investigated. The TC of 0 to 1 mg L–1 slightly improved MEC performance in current production and electrochemical characteristics with low ammonia loading, while TC ≥ 4 mg L–1 started to show negative effects. Generally, the high ammonia loading sensitized MECs to TC concentration, inducing the current and COD removal of MECs to sharply decline with TC ≥ 0.5 mg L–1. The positive effect of high ammonia loading on MEC due to conductivity increase was counteracted with TC ≥ 1 mg L–1. The co-contamination of TC and ammonia significantly decreased the bioactivity and biomass of anode biofilm. Although the high concentration of co-existing TC and ammonia inhibited MEC performance, the reactors still obtained positive energy feedback. The network analyses indicated that the effluent suspension contributed much to antibiotic resistance gene (ARG) transmission, while the microplastics (MPs) in wastewater greatly raised the risks of ARGs spreading. This work systematically examined the synergetic effects of TC and ammonia and the transmission of ARGs in MEC operation, which is conducive to expediting the application of MECs in swine wastewater treatment. [Display omitted]