Removal of nutrients and emission of nitrous oxide during simultaneous nitrification, denitrification and phosphorus removal process with metal ions addition

The impacts of metal ions (Cu2+ and Fe3+) on nutrients removal and nitrous oxide (N2O) emission during the simultaneous nitrification, denitrification and phosphorus removal (SNDPR) process were evaluated and the mechanism was further investigated. Results showed that both Cu2+ and Fe3+ addition at moderate concentrations enhanced nitrogen removal by reinforcing the denitrification process. The long-term addition of Fe3+ weakened the removal of phosphorus by 2.3%-11.7%, due to the suppression of polyphosphate-accumulating organisms (PAOs) growth and activity. N2O production and emission factor decreased greatly by the addition of Cu2+. This decrease was caused by the enhancement of nitrite reductase and N2O reductase (N2OR) activities. On the contrary, Fe3+ addition at moderate concentrations stimulated the N2O production. Fe3+ enhanced the nitric oxide reductase (NOR) and increased the NOR/N2OR ratio, leading to the accumulation of N2O. Moreover, addition of Fe3+ caused a reduction in polyhydroxyalkanoates synthesis at the anaerobic stage and renforced glycogen-accumulating organisms (GAOs) activity instead of PAOs activity, resulting in increased N2O accumulation. Addition of high concentrations of metal ions (5 mg/L Cu2+ and 60 mg/L Fe3+ in this study) suppressed the nutrients removal and stimulated the N2O production, partly due to the inhibition of the bacterial activity.