Improvement of the performance of simultaneous nitrification denitrification and phosphorus removal (SNDPR) system by nitrite stress

Abstract

This study investigated a new way to improve the performance of simultaneous nitrification denitrification and phosphorus removal (SNDPR) system by regularly changing the anaerobic/micro-aerobic/anoxic mode to the anaerobic/anoxic mode with 30 mg/L of nitrite dosing. The results indicated that the removal efficiency of total inorganic nitrogen and PO43−-P was improved from 75.44% and 85.14% to 98.89% and 98.17%, respectively. And the good performance of the SNDPR showed a long-time sustainability when the C/N ratio was 5. The results of microbial community illustrated that the abundance of the main nitrite-oxidizing bacteria (NOB), Nitrospira sp., dropped from 5.71% to 0.85% and the abundance of denitrifying polyphosphate-accumulating organisms (DPAOs), Pseudomonas sp. and Acinetobacter sp., increased by 5 times after nitrite stress. The high level of nitric oxide (NO) and free nitrite acid produced by addition of nitrite strongly suppressed the undesired organisms NOB and ordinary heterotrophic denitrifying organisms, and promoted the enrichment of DPAOs. The NO accumulated in the nitrite denitrification process could inhibit NOB and promote AOB. This study revealed that NO plays an important role in regulating the microbial community in the SNDPR system.