Effects of Hydraulic Retention Time on the Performance and Microbial Communities of a High-Load Partial Nitrification Reactor

A high-load partial nitrification reactor (HLPNR) was operated to treat high-ammonia wastewater by varying the hydraulic retention time (HRT). The associated shifts in the microbial community were analyzed using PCR-DGGE and high-throughput sequencing. The results indicated that the reactor achieved a maximum nitrogen loading rate (NLR) of 10.14 kg·N/(m3·d) at an HRT of 1.5 h, with a nitrite accumulation rate (NAR) of 86%. PCR-DGGE analysis revealed Proteobacteria and Nitrosomonas as the dominant phylum and genus, respectively, whose relative abundances varied significantly with HRT. Specifically, the relative abundance of Nitrosomonas sp. G1 increased from 15% to 40%, indicating that the abundances of Proteobacteria and Nitrosomonas were directly related to the load of the HLPNR. High-throughput sequencing revealed a marked decline in both the diversity and abundance of the HLPNR’s microbial community under conditions of reducing load. The dominant genus changed; however, the stability of the HLPNR was not destroyed. It can be inferred that the stability of the HLPNR primarily depended on the enrichment of key functional bacteria rather than on the overall microbial community composition.