N2O production in a single stage nitritation/anammox MBBR process

2.5.4 Deamox
Deamox (denitrifying ammonium oxidation) combines the anammox process with
autotrophic denitrification utilising sulphide as an electron donor for production of
nitrite from nitrate. The Deamox reactor can therefore be used in the treatment process
of wastewaters containing organic bound nitrogen and SO4 2− (Kalyuzhnyi et al., 2006).
The organic nitrogen content in these wastewaters firstly has to be anaerobic
mineralised before nitrification can proceed. If the Deamox process is utilised not all
effluent water from the anaerobic mineralisation reactor has to be nitrified, it can
instead be partially fed to the Deamox reactor. Anammox activity is stimulated by the
denitrifying conditions in the Deamox reactor and since nitrite concentrations are kept
low the process is not thought to produce unwanted emissions of NOx-gases (Kalyuzhnyi
et al., 2006). Since sulphide rich waters are not common in municipal wastewater
treatment the Deamox process has been further developed utilising volatile fatty acids
as a more widespread electron donor for the partial denitrification (Kalyuzhnyi et al.,
2008).
2.5 N2O emissions from wastewater treatment
It has been known for decades that N2O is produced both as an intermediate and end
product in the metabolism of microorganisms performing nitrification and
denitrification processes (Hooper, 1968, Poth and Focht, 1986, Firestone et al., 1979).
Until recently, anammox activity has not been believed to produce any N2O, however
Kartal et al., (2007) have shown that anammox bacteria produces small amounts of N2O
as a result of detoxification of NO which is an intermediate in the anammox process.
Variable temperature and loading rates of inorganic nitrogen compounds, low pH,
alternating aerobic and anaerobic conditions together with growth rate and microbial
composition are parameters that have great influence on N2O emissions from a
wastewater treatment plant (Kampschreur et al., 2008 b). N2O production as a
consequence of these environmental conditions during nitrification and denitrification
will be described in the chapter 2.5.1-2.5.2.The possibility of chemical N2O production in
wastewater treatment is shortly described in 2.4.3. Table 2 gives molecular weight of
N2O and the water solubility both in mol/l and g/l.
Table 2. Physical properties of N 2O
Property:
Unit:
Molecular weight 44.0 g/mol
Water solubility (0 salinity at 20 ̊C)
27.05∙10 − 3 mol/l
1.19 g/l
18