Rapid start-up of single-stage nitrogen removal using anammox and partial nitritation (SNAP) process in a sequencing batch biofilm reactor (SBBR) inoculated with conventional activated sludge

The long initiation period of the single-stage nitrogen removal using the anammox and partial nitritation (SNAP) process is a major hindrance to its practical application. In this study, the SNAP process was initiated in a sequencing batch biofilm reactor (SBBR) inoculated with conventional activated sludge within 46 days when the ammonium removal efficiency (ARE) and total nitrogen removal efficiency (TNRE) reached 86.9% and 76.8%, respectively. After the 46 days, ARE of 93.7 +/- 2.8% and TNRE 77.5 +/- 2.3% were achieved. The rapid initiation of the SNAP process could be attributed to biomass retention provided by biofilm and regulation of parameters including dissolved oxygen (DO), pH, temperature, organic matter, inorganic carbon (IC), free ammonium (FA), and free nitrite acid (FNA). The microbial analysis suggested that microbial richness of biomass increased while the microbial diversity reduced during the initiation of the SNAP process. Nitrosomonas and Candidatus Brocadia were the main ammonium oxidizing bacteria (AOB) and anammox bacteria (AnAOB), respectively, and were found to be enriched. Nitrospira was the main nitrite oxidizing bacteria (NOB) and relative abundance of it was decreased. The heterotrophic denitrification established rapidly and then gradually declined during the start-up of the SNAP process.