The application of N isotope tracer in differentiating denitrification, anammox and DNRA during anammox start-up by adding calcium nitrate.

Denitrification, anaerobic ammonium oxidation (anammox) and dissimilatory reduction of nitrate to ammonium (DNRA) are important forms of nitrogen transformation process. The addition of calcium nitrate induces the coupling of denitrification, anammox and DNRA in the malodorous sediment, which accelerates the start-up of anammox process. However, conventional detection methods are difficult to differentiate the above-mentioned nitrogen transformation processes. A modified N isotope tracer technology was used to quantitatively differentiate each N-removal contribution of denitrification, anammox and DNRA in this research, which is of great significance for ascertaining the coupling relationship among denitrification, anammox and DNRA induced by calcium nitrate.•A modified N isotope tracer technology was used to quantitatively differentiate denitrification, anammox and DNRA.•N isotope tracer results indicated that the contribution of anammox to total nitrogen increased by 20% approximately.