N2O production in a single stage nitritation/anammox MBBR process

12
10
091014 Continously operation, DO 1.0 (mg/l)
4.5
3.75
N₂O (µmol/l)
8
6
4
2
3
2.25
1.5
0.75
DO (mg/l)
N₂O
(µmol/l)
DO
(mg/l)
0
0
0 20 40 60 80
Time (min)
Figure 4. Concentration profiles of N 2O and O 2 during measurement at continuous aeration with
DO ~1.0 mg/l.
As seen in Figure 4 N2O is only accumulating for the first 5-6 minutes of the unaerated
period then there is a short time span when production and N2O flows leaving the
reactor are in equilibrium. The N2O concentration measured in the water phase is
decreasing before aerations starts again which have not been noticed in any of the
former cases. Initial N2O production is below 2% of reduced inorganic nitrogen and
maximum production is also very low.
Conclusions
Conclusions that can be made from the experiments are summarised below:
• The single stage nitritation/anammox system produced significant amounts of
N2O with a minimum production of 2% of removed inorganic nitrogen.
• Operating the MBBR at intermittent aeration with a DO of ~3 mg/l gave the
highest N2O production with initial and maximum productions of 6-11% and 10-
30% respectively.
• Smaller amounts of N2O were produced by the partial/nitritation anammox
system during continuous operation at DO in the interval 1-1.5 mg/l. The initial
N2O production was found to be 2-3% and the maximum N2O production
corresponded to 2-6%.
• When the MBBR was exposed to a longer period of anoxic conditions both
ammonium oxidation and N2O production ceased.
• The absolute number on overall N2O production for an operation mode (based on
the measurements of N2O accumulating during the anoxic phase) could be both
overestimated or underestimated and should therefore be used as a comparative
tool.
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