N2O production in a single stage nitritation/anammox MBBR process

laboratory system might be underestimated. If calibrations have been performed with
an unsaturated N2O solution this will give rise to overestimated N2O productions from
the partial nitritation/anammox MBBR. As pointed out by Kampschreur et al., (2009)
changing environmental conditions might lead to higher N2O emissions and short term
laboratory scale measurements might therefore give over estimated N2O emissions.
Since the anammox process needs less resources and produces less CO2 than common
nitrogen removal, anammox has been pointed out as a more environmental friendly
alternative (Fux and Siegrist, 2004). Kuenen and Robertson, (1994) are calling attention
to that wastewaters in the Netherlands generally have a nitrogen content between 40-60
mg/l, each person produces about 150 l/d which gives a nitrogen production of 2.2 kg
nitrogen per person and year and that even a small N2O production corresponding to
0.1% of the nitrogen concentration will result in significant N2O emissions. Considering
that the MBBR process has been found to produce N2O corresponding to a minimum of
2% of removed inorganic nitrogen it has to be further examined whether this single
stage anammox process is more environmental friendly than common nitrogen removal
processes. Even if rather high N2O production was obtained in this study, experiences in
pilot scale trials with similar operation modes has given N2O production as low as 0.2 %
of removed inorganic nitrogen (Christensson, 2010). Additional research is needed to
determine if the N2O production from a full scale process would be as high as the
production found from the laboratory MBBR system. It also has to be determined which
bacteria that are responsible for producing N2O, whether the relatively high N2O
emissions found from the laboratory MBBR are due to biofilm structure with oxygen
pore conditions. Amounts of N2O emissions have to be further evaluated in correlation
to process operation and performance. A single stage biofilm system might not be the
best solution for the partial nitritation anammox process if this process design always
gives rise to high N2O emissions.
5.3 Measurements with NO2-N biosensor
The biosensor gave results that correlated very well with concentrations obtained with
LCK 342 at some occasions and the fluctuations in NO2-N concentration measured with
the biosensor always showed the same trends as achieved with LCK 342. However the
NO2-N biosensor did not give reliable results at all times in use and could never replace
LCK 342 for determination of NO2-N concentrations during this master thesis work.
Some measurements performed with the biosensor recorded much higher NO2-N
concentrations than obtained with the Dr. Lange kit. This was probably due to electric
disturbances that caused electric migration which is the transport of a charged body in
an electric field. Kjær et al., (1999), have shown that this phenomenon can be used to
force negatively charged NO3 − ions over the semi permeable membrane of the
biochamber increasing the ion sensitivity by a factor of more than 10.000. The electric
disturbances can have been caused by other laboratory equipment or since the ground
channel on the backside of the piccoameter was used. This ground port has another
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