N2O production in a single stage nitritation/anammox MBBR process

4.4 NO2-N biosensor
The biosensor was used to register changes in NO2-N online during measurements of
N2O production. The purpose was both to examine NO2-N concentration changes in the
anammox process and to see if it was possible to replace the traditional NO2-N analysis
with Dr Lange kit (LCK 342/341). Two typical measurement occasions where the
biosensor has been used are shown here in . All concentrations profiles achieved
through measurements made with the biosensor can be found in appendix C, the sensor
was not in use during measurements of N2O production 14-15 of September. The reason
for not using the sensor was that there were problems in achieving a stable sensor signal
during calibration and the biochamber had to be exchanged.
Figure 21 shows the obtained NO2-N concentrations from online measurements with the
biosensor and from grab samples analysed with Dr Lange’s method, LCK 342, during a
prolonged unaerated measurement period.
DO, NO₂-N (mg/l)
10
9
8
7
6
5
4
3
2
1
0
0.00 50.00 100.00 150.00 200.00
Time (min)
NO₂-N
biosensor
(mg/l)
NO₂-N LCK
342
(mg/l)
Figure 21. NO 2-N concentration profiles obtained with biosensor and with Dr Lange’s method, LCK
342, during prolonged unaerated measurement.
As can be seen in Figure 21 there was a difference in concentrations obtained from the
two different measurement methods. The concentration of NO2-N registered by the
biosensor is 2-3 mg/l higher than NO2-N concentrations obtained from grab samples
analysed with LCK 342. Even if NO2-N concentrations registered with the biosensor
were higher than concentrations obtained from analysis with LCK 342 both methods
showed the same trends in NO2-N concentration profiles during the measurement.
Figure 22 shows the result from online measurements with the biosensor compared to
grab samples analysed with LCK 342 from a measurement occasion when the MBBR was
operated at continuous aeration at a DO level of ~1.5 mg/l. The NO2-N concentrations
obtained from both methods correlated much better during this measurement. The
deviation in NO2-N concentrations was below 1 mg/l during this measurement and the
concentration profile given from the two methods correlates well.
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