Insights into the effects of bio-augmentation on the granule-based anammox process under continuous oxytetracycline stress: Performance and microflora structure

Abstract Three up-flow anaerobic sludge blanket bioreactors treating wastewater containing 2 mg L−1 oxytetracycline (OTC) were used to examine the enhancement of bio-augmentation (BA) tactics on the resistance and resilience of the anammox performance. The BA tactics were carried out by the BA-addition and BA-exchange modes, and the optimized mode was first proposed. The results showed that prior to OTC suppression, excellent anammox performance was observed in the reactors, with a total nitrogen removal efficiency (TNRE) above 92.0% and a nitrogen removal rate (NRR) greater than 3.3 kg N m−3 d−1. Upon inhibition by continuous OTC, the NRR decreased to 2.0 ± 0.6 kg N m−3 d−1 without BA assistance, 2.3 ± 0.6 kg N m−3 d−1 for BA-addition mode assistance and 2.8 ± 0.3 kg N m−3 d−1 for the BA-exchange mode one. Redundancy analysis indicated that BA mode regulation may maintain system stability by microbial communities gradual acclimation and thus functional bacteria to be potential antibiotic resistance species is the main reason for performance stabilization. Our findings elucidate for the first time that the BA-exchange mode is feasible to remit 2 mg L−1 OTC-stressed anammox performance.