Source identification of nitrous oxide on autotrophic partial nitrification in a granular sludge reactor

Abstract

Emission of nitrous oxide (N 2 O) during biological wastewater treatment is of growing concern since N 2 O is a major stratospheric ozone-depleting substance and an important greenhouse gas. The emission of N 2 O from a lab-scale granular sequencing batch reactor (SBR) for partial nitrification (PN) treating synthetic wastewater without organic carbon was therefore determined in this study, because PN process is known to produce more N 2 O than conventional nitrification processes. The average N 2 O emission rate from the SBR was 0.32 ± 0.17 mg-N L -1 h -1 , corresponding to the average emission of N 2 O of 0.8 ± 0.4% of the incoming nitrogen load (1.5 ± 0.8% of the converted NH 4 + ). Analysis of dynamic concentration profiles during one cycle of the SBR operation demonstrated that N 2 O concentration in off-gas was the highest just after starting aeration whereas N 2 O concentration in effluent was gradually increased in the initial 40 min of the aeration period and was decreased thereafter. Isotopomer analysis was conducted to identify the main N 2 O production pathway in the reactor during one cycle. The hydroxylamine (NH 2 OH) oxidation pathway accounted for 65% of the total N 2 O production in the initial phase during one cycle, whereas contribution of the NO 2 -reduction pathway to N 2 O production was comparable with that of the NH 2 OH oxidation pathway in the latter phase. In addition, 3 spatial distributions of bacteria and their activities in single microbial granules taken from the reactor were determined with microsensors and by in situ hybridization. Partial nitrification occurred mainly in the oxic surface layer of the granules and ammonia-oxidizing bacteria were abundant in this layer. N 2 O production was also found mainly in the oxic surface layer. Based on these results, although N 2 O was produced mainly via NH 2 OH oxidation pathway in the autotrophic partial nitrification reactor, N 2 O production mechanisms were complex and could involve multiple N 2 O production pathways.

Nitrous oxide emission in autotrophic partial nitritation system: Macro- and microanalyses

“…The N 2 O emission quantity per cycle varied from 3.33 to 7.76 mg (5.98 mg on average), accounting for 0.556%e1.29% (0.997% on average) of influent nitrogen. Fluctuation of the N 2 O emission quantity was also observed by Rathnayake et al (19). It might be due to fluctuation of airflow and hydraulic flow rates.…”

Nitritation and N2O Emission in a Denitrification and Nitrification Two-Sludge System Treating High Ammonium Containing Wastewater

“…When the aeration rate was above 0.6 L/min, the N2O emission factor was below 1%, while when the nitrifier activity was low, it reached the highest ratio of 26.1%. Rathnayake et al [4] reported that the N2O emission factors to the influent NH4-N loading rate or to the removal of NH4-N during nitritation were 0.8% and 1.5%, respectively. However, Desloover et al [3] found that the N2O emission factor was in the range of 5.1%-6.6%.…”

“…If external organic carbon is dosed for denitrification, the operating cost will increase significantly. Therefore, novel processes, such as SHANRON, short-cut nitrification and anaerobic ammonium oxidation, and so on, have been developed to treat high ammonium containing wastewater [3,4]. The prerequisite of these processes is to achieve short-cut nitrification, namely nitritation (nitrifying ammonium to nitrite rather than nitrate).…”

Nitrous oxide emissions from an aerobic granular sludge system treating low-strength ammonium wastewater

“…After that, most of these studies have focused on the emissions of N 2 O in partial nitrification aerobic granular sludge systems for treating high strength ammonium wastewater (13e15). The relative contributions of the three pathways (hydroxylamine oxidation, nitrifier denitrification and heterotrophic denitrification) to N 2 O emissions in these systems were also quantitatively examined (9,15). The removal of nitrogen via nitrite is energy-and costefficient compared to conventional processes over nitrate.…”