The mitigation effect of free ammonia and free nitrous acid on nitrous oxide production from the full-nitrification and partial-nitritation systems

Abstract

The potentials of using endogenous free ammonia (FA) and free nitrous acid (FNA) as nitrous oxide (N2O) mitigators were investigated in treatment of both mainstream and sidestream wastewater. Although the N2O emission factor of a sidestream partial-nitritation (PN) reactor (averaged 1.70 % ± 0.39 %, n = 30) was about 2.4 times higher than a mainstream full-nitrification (FN) reactor (averaged 0.72 % ± 0.24 %, n = 30) (P < 0.01), one-hour exposure of PN sludge to 1.5 mg HNO2-N/L FNA could virtually abolish N2O emission. As for FN sludge, both 45 mg NH3-N/L FA and 0.015 mg HNO2-N/L FNA successfully mitigated N2O production at varying dissolved oxygen (DO) levels (50 % vs 61 %), while 1.5 mg HNO2-N/L FNA not only reduced more N2O (92 %) but also altered the N2O dependency on DO. Both FNA and FA sludge treatment were effective N2O mitigation strategies with FNA toward the end of carbon neutrality and FA being more economically appealing (2 % cost saving).