A review on nitrous oxide (N 2 O) emissions during biological nutrient removal from municipal wastewater and sludge reject water

Abstract

Nitrous oxide (NO) is an important pollutant which is emitted during the biological nutrient removal (BNR) processes of wastewater treatment. Since it has a greenhouse effect which is 265 times higher than carbon dioxide, even relatively small amounts can result in a significant carbon footprint. Biological nitrogen (N) removal conventionally occurs with nitrification/denitrification, yet also through advanced processes such as nitritation/denitritation and completely autotrophic N-removal. The microbial pathways leading to the NO emission include hydroxylamine oxidation and nitrifier denitrification, both activated by ammonia oxidizing bacteria, and heterotrophic denitrification. In this work, a critical review of the existing literature on NO emissions during BNR is presented focusing on the most contributing parameters. Various factors increasing the NO emissions either per se or combined are identified: low dissolved oxygen, high nitrite accumulation, low chemical oxygen demand to nitrogen ratio, slow growth of denitrifying bacteria, uncontrolled pH and temperature. However, there is no common pattern in reporting the NO generation amongst the cited studies, a fact that complicates its evaluation. When simulating NO emissions, all microbial pathways along with the potential contribution of abiotic NO production during wastewater treatment at different dissolved oxygen/nitrite levels should be considered. The undeniable validation of the robustness of such models calls for reliable quantification techniques which simultaneously describe dissolved and gaseous NO dynamics. Thus, the choice of the N-removal process, the optimal selection of operational parameters and the establishment of validated dynamic models combining multiple NO pathways are essential for studying the emissions mitigation.

Effects of free nitrous acid treatment conditions on the nitrite pathway performance in mainstream wastewater treatment

“…In the NH2OH oxidation pathway, N2O is produced as a by-product during the oxidation of NH2OH (an intermediate of NH4 + oxidation) to NO2 -. In the nitrifier denitrification pathway, N2O is formed from sequential reductions from NO2to nitric oxide (NO) and to N2O (Massara et al, 2017). Site-preference analysis is a promising isotope technology that has recently been applied to WWTP for quantifying the N2O production contributions from the NH2OH oxidation and nitrifier denitrification pathways (Duan et al, 2017;Toyoda et al, 2017).…”

Evaluation of the Nitrous Oxide Emission Reduction Potential of an Aerobic Bioreactor Packed with Carbon Fibres for Swine Wastewater Treatment

“…In these strategies, operators select the optimal operational conditions such as aeration rate and DO. Wastewater treatment operates at an optimal combination of pH 7 and water temperature of 20 • C. It uses models to predict the N 2 O hotspots [8]. Santín also reported that it is important to control the DO for N 2 O reduction [9].…”

Energy use and challenges in current wastewater treatment plants

“…Moreover, N 2 O has also been identified as an intermediate of denitrification by autotrophic or heterotrophic bacteria (Shapleigh, 2013). Many factors including dissolved oxygen concentration, nitrite concentration, and COD/N ratio, etc., may affect N 2 O emission during municipal wastewater treatment (Massara et al, 2017).…”