Insights into regulating influent nitrogen load to restore autotrophic nitrogen removal performance of a two-stage reactor

Abstract

To better understand performance recovery and its mechanism, after the deterioration of an anaerobic ammonia oxidation (anammox) process, experiments were conducted in a UASB reactor. A two-stage anammox reaction was conducted in the reactor, and long-term continuous operation was conducted for 202 d. The mechanism of performance recovery was studied by adjusting the total nitrogen (TN) concentration and hydraulic retention time (HRT) of the influent. The results showed that after the long-term continuous operation, the TN removal efficiency decreased from 88.22 % before deterioration to 11.68 %, and then recovered to 80.63 %. The nitrogen loading rate decreased from 2.25 kg-N/m3/d before deterioration to 0.26 kg-N/m3/d and then recovered to 2.79 kg-N/m3/d. Nitrogen removal load (NRR) decreased from 1.98 kg-N/m3/d to 0.26 kg-N/m3/d before deterioration and recovered to 2.25 kg-N/m3/d. Microbial diversity was analyzed by high-throughput sequencing. During the operation, the dominant anammox strains changed from Candidatus Kuenenia (24.19 %) before deterioration to Candidatus Brocadia (11.90 %) after recovery. The influent TN concentration and HRT were the key factors that affected performance recovery. Reducing the influent TN concentration and shortening the HRT can effectively avoid the inhibition of anammox by the substrate and enable the rapid recovery of nitrogen removal performance. As the microorganisms in the reactor recovered their activity through enrichment, the influent TN gradually increased, and produced NRR higher than the pre-deterioration level, so the reactor performance was fully restored. This study provides a scientific support for recovering the two-stage anammox process performance after deterioration.