Nitrogen removal performance and microbial community structure in the start-up and substrate inhibition stages of an anammox reactor

In this study, the nitrogen removal performance and microbial community structure were investigated during the start-up, instability, and recovery stages of an anaerobic ammonium oxidation (anammox) reactor loaded with compound carriers (shale ceramsite and suspended ball carrier). The results indicated that the anammox reactor successfully started up on 116th d when the nitrogen loading rate (NLR) reached 0.72 ± 0.05 kg N m−3 d−1. The anammox reactor ran well with free ammonia (FA) at 13.65 ± 2.69 mg/L and free nitrous acid (FNA) at 39.49 ± 10.95 μg/L, indicating that its tolerance for FA and FNA was higher than that of granular sludge anammox reactors. The anammox system was inhibited when FA and FNA reached 29.65 mg/L and 77.02 μg/L, respectively. The tolerance of anammox bacteria towards FA and FNA decreased after this inhibition. The nitrogen removal performance could be efficiently recovered by decreasing the influent substrate concentration and increasing the hydraulic retention time (HRT). Candidatus Brocadia and Candidatus Jettenia, two genus-level anammox bacteria, were detected in this reactor using a high-throughput sequencing technique. After high substrate shock, the abundance of Candidatus Brocadia decreased while that of Candidatus Jettenia increased, which might be due to the competition between Candidatus Jettenia and Candidatus Brocadia. The relationships between anammox communities and operational factors were investigated via redundancy analysis (RDA), which showed that FA was the principal factor affecting the microbial community structure during the operation stage.