High-rate partial nitritation as a pretreatment of anammox process

In this study, a laboratory-scale partial nitrification reactor (PN reactor) was used to treat high-ammonia-nitrogen wastewater, by changing the influent NH₄⁺-N conversion rate as the main operating strategy, to investigate the upper limit of its NH₄⁺-N conversion rate (ACR) and explore its feasibility as an anammox pre-process. During the experiment, PN reactor was successfully activated in only 10 days. The PN reactor reached the highest ACR value of approximately 10.24 kg N/(m³ · day) when the influent ACR was 16.57 kg N/(m³ · day), and the ammonia conversion efficiency (ACE) was 61.78% at this time. The ratio of [NO₂^--N]_Eff/[NH₄⁺-N]_Eff was approximately 1.37 which was close to the theoretical ratio of 1.32. And feasibility exploration experiment proved that it was feasible to use this PN reactor as a pre-process of anammox. The PCR-DGGE results showed that the dominant phylum and genus in the reactor during the ACR experiment were Proteobacteria and Nitrosomonas, respectively. With the increase in the ACR, the relative concentration of Nitrosomonas sp. G1 increased from 15 to 40%. This indicates that its abundance is directly correlated with the increase in the ACR. High-throughput sequencing showed that increasing the ACR of the PN reactor greatly reduced the diversity and abundance of the system microbial community structure and changed the dominant phylum and genus; however, the stability of the system was not disrupted. High-throughput sequencing experiments showed that the abundance value of nitrosation enzymes accounted for 91.62%, which was positively correlated with the expression of nitrification genes in the genus Nitrosomonas.