Dynamic modelling of nitrous oxide emissions from three Swedish sludge liquor treatment systems

Abstract

Abstract:The objective of this paper is to model the dynamics and validate the results of nitrous oxide (N 2 O) emissions from three Swedish full-scale nitrifying/denitrifying, nitritation and anammox systems treating anaerobic digester sludge liquor. The Activated Sludge Model No. 1 is extended in order to describe N 2 O production by both heterotrophic and autotrophic bacteria. In addition, mass transfer equations are implemented to characterize the dynamics of N 2 O in the water and the gas phases. The biochemical model is simulated for two hydraulic patterns: 1) a sequencing batch reactor (SBR); and, 2) a moving-bed biofilm reactor (MBBR). Preliminary results show that the calibrated model is partly capable of reproducing the behaviour of N 2 O as well as the nitritation/nitrification/denitrification dynamics. However, the results emphasize that more work is required before N 2 O emissions from sludge liquor treatment plants can be generally predicted with certainty by simulations. Continued efforts should focus on determining the switching conditions for different N 2 O formation pathways and, if full-scale data is used, modelling of the measurement devices might improve the conclusions that can be drawn.

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