In situ startup of a full-scale combined partial nitritation and anammox process treating swine digestate by regulation of nitrite and dissolved oxygen

[Display omitted] •Regulation of DO and NO2−-N is the key to start up the CPNA process quickly.•Deficiency of nitrite is the limiting factor in conversion from partial nitritation to Anammox.•The rapid growth of Anammox bacteria was realized with stable nitrite supply of by dosing NaNO2.•Rapid startup of a full-scale CPNA reactor was realized with conventional activated sludge. A challenge during the startup of the combined partial nitritation and anammox process is how to balance dissolved oxygen control and nitrite accumulation for converting partial nitritation into anammox, maintaining stable partial nitritation and promoting growth of anammox bacteria. An innovative regulation strategy of nitrite dosing and dissolved oxygen control in this study was developed to achieve the rapid startup of a full-scale combined partial nitritation and anammox reactor within 77 days and the total nitrogen removal rate of reactor was 0.097 kg N/kgMLSS·d−1, and the activity and gene copy concentration of anammox bacteria reached 0.307 kg N/kgMLVSS·d−1 and 7.79 × 109 copies/gMLVSS, respectively. Microbial community analysis revealed that Candidatus_Kuenenia and Nitrosomonas were the dominant nitrogen transformation bacteria with an abundance of 2.49% and 14.86%, respectively. This study offers a new method for rapid startup and spreading application of the full-scale anammox process.