N2O production in a single stage nitritation/anammox MBBR process

Denitrification produces alkalinity and pH is generally raised by the process. pH
optimum is ranging from 7-9 depending on local conditions (Henze et al., 1997).
Cell synthesis in the anammox reaction is increasing pH and the process is active in a pH
range from 6.5-9 with an optimum around 8 (Egli et al., 2001).
2.2.4 Substrate
Nitrifying, denitrifying and anammox bacteria are all dependent on different substrates
for energy and cellular growth as discussed above. The ability to utilise their substrate
varies between bacterial species. This implies that a species with high affinity for its
substrate will be better at utilising the substrate at low concentration and therefore
outcompete species with lower affinity for the substrate. The half saturation constant,
which is the substrate concentration when the growth rate is half of maximum, is often
used to compare how well adapted different microorganisms are to their substrates.
The half saturation constant or Ks value for ammonium oxidisers in a nitrifying biofilm
airlift reactor was found to correspond to a NH4-N concentration of 11 mg/l. And the
microorganisms were inhibited by NH4-N concentrations of 3300 ±1400 mg/l. (Carvallo
et al., 2002)
Denitrification rate and capacity is very dependent on available organic carbon source.
External carbon sources like methanol, ethanol and acetic acid are readily biodegradable
and give much higher denitrification rates than denitrification with organic compounds
found in the waste water (Ødegaard, 1993).
Anammox bacteria have high affinity for their substrates ammonia and nitrite, the Ks
values are below chemical detection level (