Effect of C/N ratio on the denitrifying enzymes activity and global warming potential

The greenhouse gases generated in the wastewater treatment process based on heterotrophic denitrification technology have become a dilemma between water environment protection and carbon emission reduction. Therefore, balancing the removal of nitrate pollutants and greenhouse gas emissions has become a key issue in "green denitrification". Based on the insufficient research of previous studies on C/N and global warming potential (GWP) in denitrification systems, this study constructed a series of batch experiments with different initial C/N to analyze their impact on the denitrifying enzymes specific activity concentration and the GWP caused by GHGs emissions. This study indicates that when the initial C/N is below 6.82, it leads to a decrease in the nitrous oxide reductase specific activity concentration by 0.11∼12.45 %, but an increase in the nitric oxide reductase specific activity concentration by 5.96∼22.01 %. In addition, when the initial C/N was between 2.34 ∼ 6.82, the GWP caused by every complete reduction of 1 mg NO - 3 -N has a better cost-effectiveness, with 0.09 ∼ 0.13 mmol CO 2 -eq/mg NO - 3 -N. Overall, the results of the study provide a reference for balancing the nitrate removal and the GWP caused by GHGs emission in wastewater treatment. • The GWP caused by denitrification can as low as 0.09 mmol CO 2 -eq/mg NO - 3 -N. • The denitrification with C/N higher than 2.34 was beneficial for reducing GWP. • The N 2 O reductase activity can be reduced by 12.45 % with insufficient organic. • A low initial C/N will significantly increase the proportion of N 2 O emissions.