Establishment and optimization of partial nitrification/anammox/partial nitrification/anammox (PN/A/PN/A) process based on multi-stage ammonia oxidation: Using response surface method as a tool

The presence of nitrite-oxidizing bacteria (NOB) when treating low-strength ammonia wastewater was a challenge in the application of the PN/A process. The partial nitrification/ANAM-MOX/partial nitrification/ANAM-MOX (PN/A/PN/A) process based on multiple oxidations of ammonia was proposed to solve this problem. The influence of independent variables such as nitrite concentration was analyzed based on the response surface method (RSM). The model showed that nitrite concentration has an adverse impact on ammonia removal efficiency and nitrite accumulation rate. The model provided optimal parameters for the PN/A/PN/A process: the dissolved oxygen concentration was 0.60 mg/L, and the cycle duration was 90 min. Advanced nitrogen removal was achieved by maintaining the nitrite concentration below 10.0 mg/L. The nitrogen removal efficiency was 81.44 +/- 4.15 %, and the nitrogen removal rate was 0.18 +/- 0.02 kg N/(m(3).d). Potential functions of microorganisms were analyzed by functional annotation of prokaryotic taxa (FAPROTAX) and the correlation network analysis was performed.

Automated summary

This study proposes a new PN/A/PN/A process to address the challenge of nitrite-oxidizing bacteria in treating low-strength ammonia wastewater. The influence of nitrite concentration on ammonia removal efficiency and nitrite accumulation rate is analyzed using a model. The study provides optimal parameters for the PN/A/PN/A process and achieves advanced nitrogen removal by controlling the nitrite concentration below a certain threshold.