Recovery process of polyurethane-enhanced Anammox for the treatment of ammonia nitrogen leached from rare earth tailings: Removal performance, structure changes and biodiversity evolution

Anaerobic ammonia oxidizing bacteria (AnAOB) exhibit low resistance to environmental disturbances. The high concentration of ammonia nitrogen leached form rare earth ore (REO) tailings poses a significant challenge to the industrial application of Anammox. In this study, polyurethane was employed as an enhancing material to resist the high ammonia nitrogen concentration inhibition for Anammox. The nitrogen removal performance, structural morphology, and microbial community changes during the recovery process were explored. The results showed that the immobilized Anammox was restored after almost 53 d of recovery strategy with nitrogen removal rate(NRR) of 1.55±0.027 kgN∙m-3∙d-1. The stoichiometric ratio was close but slightly below theoretical value due to other nitrogen conversion of bacteria. The morphology of immobilized Anammox was cauliflower-like shape containing functional AnAOB and other coexisting bacteria combined with extracellular polymeric substances (EPS). Due to the adhesion of EPS, polyurethane could enrich more AnAOB. The ratio of protein (PN)/polysaccharides (PS)<1 was obtained due to the better compatibility between PS and polyurethane filler. The abundance of anammox bacteria Planctomycetota increased from 15.27% to 64.46%, mainly consisting of Unclassified_Brocadiaceae and Candidatus_Kuenenia with close relationship.