N2O production in a single stage nitritation/anammox MBBR process

Figure 2. Illustration of anammox bacteria. (Adapted from van Niftrik et al., 2004).
Anammox bacteria are extremely slow growers, their doubling time has been found to
11 days in activated sludge (Strous et al., 1999). However it might be possible to
increase this doubling rate with optimal operation conditions since other researchers
have found a much shorter doubling rate of 3.6-5.4 days for anammox bacteria in a upflow
fixed-bed biofilm column reactor (Tsushima et al., 2007).
The microbial processes and chemical reactions of nitrification, denitrification and
anammox are summarized in Table 1.
Table 1. Microbial processes and chemical reactions taking part in the nitrogen cycle showed in
Figure 1.
Energy yield
ΔG ̊’ eq.
Process
Chemical reaction
+
kJ/mol NH 4
Nitritation: NH 1.5O NO 2H H O -271 (2.1.1)
Nitratation: NO 0.5O
NO -72.8 (2.1.2)
Nitrification: NH 2O NO 2H H O - (2.1.3)
Denitrification: NO org. carbon N 2CO
-
(2.1.4)
Anammox: NH
NO N 2H O -358.8 (2.1.6)
2.2. Environmental factors
Dissolved oxygen, temperature, pH, substrate concentrations and turbulence are abiotic
conditions that are of great importance for the growth and survival of the microbiology
in a wastewater treatment system.
2.2.1 Dissolved oxygen
Depending on the electron donor in the respiratory chain of the microorganism can be
limited or inhibited by either to low or to high DO concentrations. It is the oxygen
concentration within the biofilm experienced by the bacteria that is of importance for
the wellness of the organism (Henze et al., 1997).
Nitrifying bacteria utilising oxygen as electron donor are sensitive for too low oxygen
concentrations and are limited by DO concentrations