Abstract
Sustainable wastewater treatment has been attracting increasing attentions over the past decades. However, the production of nitrous oxide (N2O), a potent GHG, from the energy-efficient granule-based autotrophic nitrogen removal is largely unknown. This study applied a previously established N2O model, which incorporated two N2O production pathways by ammonia-oxidizing bacteria (AOB) (AOB denitrification and the hydroxylamine (NH2OH) oxidation). The two-pathway model was used to describe N2O production from a granule-based partial nitritation (PN) reactor and provide insights into the N2O distribution inside granules. The model was evaluated by comparing simulation results with N2O monitoring profiles as well as isotopic measurement data from the PN reactor. The model demonstrated its good predictive ability against N2O dynamics and provided useful information about the shift of N2O production pathways inside granules for the first time. The simulation results indicated that the increase of oxygen concentration and granule size would significantly enhance N2O production. The results further revealed a linear relationship between N2O production and ammonia oxidation rate (AOR) (R2 = 0.99) under the conditions of varying oxygen levels and granule diameters, suggesting that bulk oxygen and granule size may exert an indirect effect on N2O production by causing a change in AOR.
Highlights
During past years, an innovative technology based on shortcut nitrification and anaerobic ammonium oxidation offers a superior alternative to conventional processes in WWTPs, saving 30–40% of the overall costs due to a significantly lower oxygen (O2) demand, minimized external carbon requirements and sludge yield[16]
It is of great interest to investigate the N2O production and the shift of pathways in granule-based partial nitritation (PN) reactor as well as inside aerobic granules using the two-pathway N2O model
The validity and applicability of the N2O model were tested by comparing simulations with process data from a lab-scale granular PN sequencing batch reactor (SBR) and isotopic data on pathway contributions
Summary
An innovative technology based on shortcut nitrification (partial nitritation, PN) and anaerobic ammonium oxidation (anammox) offers a superior alternative to conventional processes in WWTPs (i.e. nitrification-denitrification), saving 30–40% of the overall costs due to a significantly lower oxygen (O2) demand, minimized external carbon requirements and sludge yield[16]. The previously-established two-pathway N2O model incorporating both AOB denitrification and NH2OH oxidation pathways[26] was applied to describe the N2O production in granule-based PN reactor.
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