Abstract
N2O emission in the anaerobic ammonium oxidation (anammox) process is of growing concern. In this study, effects of substrate concentrations on N2O emissions were investigated in an anammox reactor. Extremely high N2O emissions of 1.67 % were led by high NH4-N concentrations. Results showed that N2O emissions have a positive correlation with NH4-N concentrations in the anammox reactor. Reducing NH4-N concentrations by recycling pump resulted in decreasing N2O emissions. In addition, further studies were performed to identify a key biological process that is contributed to N2O emissions from the anammox reactor. Based on the results obtained, Nitrosomonas, which can oxidize ammonia to nitrite, was deemed as the main sources of N2O emissions.
Highlights
Nitrogen removal (NR) is an important component of wastewater treatment
At a constant HRT, the influent NH4-N and NO2-N concentrations were further increased to 100.4 and 124.8 mg L−1, respectively, and effluent NH4-N and NO2-N concentrations initially were a little higher, but both soon decreased to below 8 mg L−1 over a 3-day period. These results indicated that the seed anammox sludge could adapt quickly to changes in nitrogen loading rate (NLR)
On day 24, the influent NH4-N and NO2-N concentrations were increased to 145.0 and 176.4 mg L−1, respectively, which were the highest levels used in this study
Summary
Nitrogen removal (NR) is an important component of wastewater treatment. Biological nitrogen removal (BNR) is often preferred to other non-biologic processes due to its high efficiency and energy conservation characteristics. The anammox process operates under anaerobic conditions where nitrite is used as an electron acceptor by anammox bacteria for oxidation of ammonia to nitrogen gas (N2) (Kuenen 2008). By using this new technology, only 50 % of the source ammonium needs to be oxidized to nitrite. This means that the oxygen requirement is reduced to about 75 % of the traditional BNR process. Research has generally shown that N2 is the end product of the anammox process (Jetten et al 2005); high N2O emission from Anammox processes have been reported (Kampschreur et al 2009b). Genetic analysis using the 16S rRNA gene was employed to characterize the microbial population of the anammox granules
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