N2O production in a single stage nitritation/anammox MBBR process

Appendix A
Calculation of concentrations in calibration solutions for N2O and NO2-
N microsensors
During calibration of the microsensors solutions with known concentration of N2O and
NO2-N are used from the start. The volume in the calibration chamber is known and the
final concentration for each calibration step is also known. The initial volume that has to
be added to get the correct concentration in the calibration solution is obtained with:
(A.1)
where:
Mi = the initial molar concentration mol/l, Vi = the initial volume (l), Mf = the final molar
concentration mol/l and Vf = the final volume (l).
The initial volume is then added in each calibration step until the final concentration is
reached.
Equilibrium nitrous oxide concentrations at different temperatures and salinities are
obtained from the nitrous oxide sensor users manual. The saturated water solution is
prepared from distilled water at 20 °C corresponding to an equilibrium N2O
concentration of 27.05mmol/l or ~1.2 g/l. 2 µM (88 µg/l )N2O was added in each step to
perform a five point calibration up to 10 µM, (440 µg/l ). See Table A1 for calculated
initial volume, (Vi), of saturated N2O solution added to the calibration chamber, Mi, Mf,
and Vf are also given in the table.
A stock solution with a NO2-N concentration of 5 g/l NO2-N was used for calibration of
the biosensor. 2 mg/l NO2-N was added in each step to perform a five point calibration
up to 10 mg/l NO2-N. See Table A1 for calculated initial volume of NO2-N stock solution
added to the calibration chamber, Mi, Mf, and Vf are also given in the table.
Table A1. Parameters used to calculate the volume of concentrated N 2O and NO 2-N solutions that
has to be added during the calibration procedure of the sensors, calculated values for V i is also
shown.
N2O calibration solution NO2-N calibration solution
Mi 27.05∙10 -3 mol/l Mi 5∙10 -3 g/l
Mf 2∙10 -6 mol/l Mf 2∙10 -3 g/l
Vf 0.300 L Vf 0.300 l
Vi 22∙10 -6 L Vi 120∙10 -6 l
22 µl 120 µl
63