Nitric oxide and nitrous oxide production in anaerobic/anoxic nitrite-denitrifying phosphorus removal process: effect of phosphorus concentration.

Abstract

Nitric oxide (NO) and nitrous oxide (N2O) production in biological nutrient removal has been studied widely due to the strong negative effects on the environment. Nitrite-denitrifying phosphorus removal (N-DPR), as a significant source of NO and N2O production, has received great attention. However, the mechanism of NO and N2O production at different phosphorus concentrations is not well understood. Therefore, this study was conducted to investigate the effect of phosphorus concentration on pollutant removal, as well as NO and N2O production during the N-DPR process. The results showed that the phosphorus removal efficiency was improved with the increase of phosphorus concentration, which is caused by the enrichment of denitrifying phosphorus accumulating organisms (DPAOs) at high phosphorus concentration. High NO production was observed at phosphorus concentration of 0.5 mg L-1, which is mainly attributed to the slow recovery of reductase activity and low abundance of DPAOs. The maximal N2O accumulation of 31.45 mg L-1 was also achieved at phosphorus concentration of 0.5 mg L-1. The possible reason is that fewer poly-β-hydroxyalkanoates (PHAs) were synthesized by glycogen accumulating organisms (GAOs) at low phosphorus concentration, which could intensify the electron competition among different reductases. In addition, free nitrous acid (FNA) inhibition was another significant reason for high N2O production.