Comparison of the dynamic responses of different anammox granules to copper nanoparticle stress: Antibiotic exposure history made a difference.

Two types of anaerobic ammonium oxidation (anammox) seed sludge were selected to evaluate their responses to copper nanoparticles (CuNPs) exposure. Antibiotic-exposed anammox granules (R) were more likely to be inhibited by 5.0 mg L CuNPs than the normal anammox granules (C). The nitrogen removal efficiency (NRE) of C decreased by 9.00% after two weeks of exposure to CuNPs, whereas that of R decreased by 20.32%. Simultaneously, the abundance of Candidatus. Kuenenia decreased by 27.65% and 36.02% in C and R under CuNPs stress conditions, respectively. Generally, R was more susceptible to CuNPs than C. The correlation analysis indicated that the horizontal transfer of antibiotic resistance genes and copA triggered by intI1 facilitated the generation of multiresistance in the anammox process. Moreover, the potential multiresistance mechanism of anammox bacteria was hypothesized based on previous results. The results will generate new ideas for the treatment of complex wastewater using the anammox process.