N2O production in a single stage nitritation/anammox MBBR process

6. Conclusions
The following conclusions concerning, process performance of the laboratory MBBR,
produced N2O and evaluation of the NO2-N biosensor can be made:
• 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.
• From results of mixing with N2 gas during the anoxic period it cannot be said
with certainty that the N2O production is the same during aeration and anoxic
phase. 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.
• It was not possible to replace conventional methods for determination of NO2-N
concentrations with the NO2-N biosensor since stable operation of the sensor
could not be obtained at all times.
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