Model-Based Evaluation of N_2O Production Pathways in the Anammox-Enriched Granular Sludge Cultivated in a Sequencing Batch Reactor

摘要

A mechanistic model was developed as an extension of the Activated Sludge Model No. 1 to describe three nitrous oxide (N_(2)O) production pathways in a laboratory-scale anammox-enriched granular sequencing batch reactor. Heterotrophic denitrification and two processes mediated by ammonia oxidizing bacteria (AOB), that is, ammonia (NH_(4)~(+)) oxidation via hydroxylamine (NH_(2)OH) and autotrophic denitrification, were considered. A systematic model calibration and validation protocol was developed to obtain a unique set of kinetic parameters in the extended model. The dynamic nitrate (NO_(3)~(–)), nitrite (NO_(2)~(–)), NH_(4)~(+) and N_(2)O behaviors were accurately predicted (R~(2) ≥ 0.81) under five different nitrogen loading conditions. The predicted N_(2)O production factor ranged from 1.7 to 2.9%. The model-based analysis also revealed the dominant N_(2)O production mechanisms in terms of the actual process conditions, that is, NH_(4)~(+) oxidation via NH_(2)OH when only NH_(4)~(+) was supplied, heterotrophic denitrification when only NO_(2)~(–) was supplied, and a shift of the dominant mechanism when a mixture of NH_(4)~(+) and NO_(2)~(–) was supplied.