Microbial community shift and functional genes in response to nitrogen loading variations in an anammox biofilm reactor

A lab-scale anaerobic ammonium oxidation (anammox) biofilm reactor was operated to explore the impact of free ammonia (FA) and free nitrous acid (FNA) on the anammox process with nitrogen loading rate (NLR) increasing from 0.1 to 0.5 g/L.d with identical pH of 7.8. When influent NLR was less than 0.4 g/L.d, total inorganic nitrogen (TIN) removal efficiency maintained around 80% on average. When the NLR increased to 0.5 g/L.d, TIN removal efficiency sharply reduced to 66%. It was revealed that Candidates Brocadia and Candidates Kuenenia were the main anammox genera in this study. When NLR raised from 0.1 to 0.5 g/L.d, together with FA from 4.44 to 20.23 mg/L and FNA from 5.00 to 22.69 mu g/L, the dominant anammox genus showed a shift from Candidates Kuenenia to Candidates Brocadia. The highest anammox community abundance of 25.3% and maximum absolute abundances of anammox-related functional genes were observed at NLR of 0.3 g/L.d, together with 12.88 mg/L FA and 14.58 mu g/L FNA.