Effect of Alcaligenes faecalis on nitrous oxide emission and nitrogen removal in three phase fluidized bed process

Recent advances in nitrous oxide production and mitigation in wastewater treatment

Nitrous oxide (N₂O) emitted from wastewater treatment plants has caused widespread concern. Over the past decade, people have made tremendous efforts to discover the microorganisms responsible for N₂O production, elucidate metabolic pathways, establish production models and formulate mitigation strategies. The ultimate goal of all these efforts is to shed new light on how N₂O is produced and how to reduce it, and one of the best ways is to find key opportunities by integrating the information obtained. This review article critically evaluates the knowledge gained in the field within a decade, especially in N₂O production microbiology, biochemistry, models and mitigation strategies, with a focus on denitrification. Previous research has greatly deepened the understanding of the N₂O generation mechanism, but further efforts are still needed due to the lack of standardized methodology for establishing N₂O mitigation strategies in full-scale systems. One of the challenges seems to be to convert the denitrification process from a net N₂O source into an effective sink, which is recommended as a key opportunity to reduce N₂O production in this review.

Nitrogen removal in a wastewater treatment plant through biofilters: nitrous oxide emissions during nitrification and denitrification

In order to estimate N(2)O emissions from immersed biofilters during nitrogen removal in tertiary treatments at urban wastewater treatment plants (WWTPs), a fixed culture from the WWTP of "Seine Centre" (Paris conurbation) was subjected to lab-scale batch experiments under various conditions of oxygenation and a gradient of methanol addition. The results show that during nitrification, N(2)O emissions are positively related to oxygenation (R (2) = 0.99). However, compared to the rates of ammonium oxidation, the percentage of emitted N(2)O is greater when oxygenation is low (0.5-1 mgO(2) L(-1)), representing up to 1% of the oxidized ammonium (0.4% on average). During denitrification, the N(2)O emission reaches a significant peak when the quantity of methanol allows denitrification of between 66% and 88%. When methanol concentrations lead to a denitrification of close to 100%, the flows of N(2)O are much lower and represent on average 0.2% of the reduced nitrate. By considering these results, we can estimate, the emissions of N(2)O during nitrogen removal, at the "Seine Centre" WWTP, to approximately 38 kgN-N(2)O day(-1).