Modeling Nitrous Oxide Production during Biological Nitrogen Removal via Nitrification and Denitrification: Extensions to the General ASM Models

Abstract

Nitrous oxide (N(2)O) can be formed during biological nitrogen (N) removal processes. In this work, a mathematical model is developed that describes N(2)O production and consumption during activated sludge nitrification and denitrification. The well-known ASM process models are extended to capture N(2)O dynamics during both nitrification and denitrification in biological N removal. Six additional processes and three additional reactants, all involved in known biochemical reactions, have been added. The validity and applicability of the model is demonstrated by comparing simulations with experimental data on N(2)O production from four different mixed culture nitrification and denitrification reactor study reports. Modeling results confirm that hydroxylamine oxidation by ammonium oxidizers (AOB) occurs 10 times slower when NO(2)(-) participates as final electron acceptor compared to the oxic pathway. Among the four denitrification steps, the last one (N(2)O reduction to N(2)) seems to be inhibited first when O(2) is present. Overall, N(2)O production can account for 0.1-25% of the consumed N in different nitrification and denitrification systems, which can be well simulated by the proposed model. In conclusion, we provide a modeling structure, which adequately captures N(2)O dynamics in autotrophic nitrification and heterotrophic denitrification driven biological N removal processes and which can form the basis for ongoing refinements.

Evaluating two concepts for the modelling of intermediates accumulation during biological denitrification in wastewater treatment

“…Nitrate reduction consists 46 of four consecutive reduction steps, with nitrite (NO2 -), nitric oxide (NO) and nitrous oxide 47 (N2O) as three obligatory intermediates (Zumft 1997). Each reduction step is catalysed by 48 one or more specific enzymes, including nitrate reductase (Nar), nitrite reductase (Nir), NO 49 is increasingly recognised that N2O accumulation should also be modelled, especially due to 75 its detrimental influence on the atmosphere (Ni et al 2011). It has been proposed to achieve 76 this goal through modelling denitrification as a four-step process, using NO3 -, NO2 -, NO, and as a separate and independent oxidation-reduction reaction (Figure 1-a), and reaction-specific 89 kinetics are applied.…”

“…It has been proposed to achieve 76 this goal through modelling denitrification as a four-step process, using NO3 -, NO2 -, NO, and as a separate and independent oxidation-reduction reaction (Figure 1-a), and reaction-specific 89 kinetics are applied. Many of the multiple step denitrification models have adopted such 90 structure (e.g., Ni et al (2011), Schulthess and Gujer (1996). …”

Evaluation of Greenhouse Gas Emissions from a Continuous Activated Sludge Process under Power Saving Conditions

“…The NH 4 + concentration in Run 2 hardly increased during the first 2 h of Phase II, meaning that AOB oxidized NH 4 + to NO 2 -soon after the DO concentration became 0 mg/L. Ni et al (2011) have reported that NO 2 -can be used as an electron acceptor instead of O 2 when DO concentration is low. The first 2 h compared with the rest of the time in Phase II, accumulation of NH 4 + was completely quenched.…”

Mathematical modeling of simultaneous carbon-nitrogen-sulfur removal from industrial wastewater

“…Parameter identifiability was revealed by analyzing the 95% confidence intervals of the individual parameter estimate and the joint confidence regions for different parameter combinations [35]. conditions.…”