An Efficient Way for Nitrifying Bacteria Enrichment with Coal Ash: Nitrification and Microbial Community

In this study, five different fillers: coal ash, fiber-ball, polypropylene, ceramic, and polyhedron empty ball were used for cultivating nitrifying bacteria by increasing influent ammonia concentration gradually in sequencing batch reactors (SBRs). The results of ammonia removal performance showed that the reactor with coal ash has the highest NH₄ ⁺-N removal rate all the time. The ammonia removal rate of it averagely reached ≥ 95% under the condition of hydraulic retention time (HRT), dissolved oxygen (DO), pH was 12 h, 4.5 ± 0.5 mg/L, 7.5–8.5, respectively, even when the ammonia nitrogen loading reached 1000 mg/L. MiSeq Highthrough sequence was used for analyzing microbial community. The results revealed that obvious variation have occurred among the reactors after 48 days of operation; however, Nitrosomonas was enriched in large amount and became the dominant genus except in the reactor with polypropylene. Compared with other carriers, coal ash can enrich more nitrifying bacteria, the cell biomass of Nitrosomonas increased from 12.25 to 384.18 mg/L, which was 5.5 times more than the negative control. The use of coal ash as filler realizes the enrichment of a large amount of nitrifying bacteria in a short period, which guarantees a highly efficient nitrification.