Inducing high nitrite accumulation via modulating nitrate reduction power and carbon flux with Thauera spp. selection

Partial-denitrification (PD, NO3--N → NO2--N) is emerging as a promising approach for application of anaerobic ammonium oxidation (anammox) process. In this study, stable PD with high nitrite (NO2--N) accumulation was achieved by modulating nitrate (NO3--N) reduction activity and carbon metabolism. With the influent NO3--N increasing from 30 to 200 mg/L, specific NO3--N reduction rates (rno3) were significantly improved, corresponding to the nitrate-to-nitrite transforming ratio (NTR) increasing rapidly to 80.0% within just 70 days. The required COD/NO3--N decreased from 4.5 to 2.0 and the carbon flux was more shared in NO3--N reduction to NO2--N. Notably, Thauera spp. as core denitrifying bacteria was highly enriched with the relative abundance of 70.5%∼82.1% despite different inoculations. This study provided a new insight into inducing high NO2--N accumulation and promoting practical application of anammox technology.