N2O production in a single stage nitritation/anammox MBBR process

stricter it might lead to elevated emissions of nitrous oxide from the biological removal
processes. It is therefore of great importance to design and operate these processes to
minimise the emissions of nitrous oxide to the atmosphere.
Wastewater treatment plants using biologic treatment processes for nutrient removal
are producing excessive sludge giving rise to ammonium rich effluent from the
anaerobic sludge digestion. This internal wastewater stream is recombined with the
influent of the treatment plant and corresponds to 15-20% of the total nitrogen load of
the wastewater treatment plant (Fux et al., 2003). In the early 1990s a new biological
treatment process for nitrogen removal through anaerobic ammonium oxidation
(anammox) was discovered by research teams in Holland, Germany and Switzerland
(Mulder et al., 1995, Hippen et al., 1997, Siegrist et al., 1998). The technology has turned
out to be suitable for treatment of reject waters and other problematic wastewaters
with a low COD/N ratio and high ammonium concentrations. The bacteria performing
the microbial conversion of nitrite into dinitrogen gas are strict anaerobe autotrophs
and the process has the potential to replace conventional nitrification/denitrification of
recirculated high strength ammonium streams within the wastewater treatment plant
(Strous et al., 1997). No additional carbon source is needed, the oxygen demand is
reduced by 50% in the nitrifying step and the aeration can thereby be strongly reduced
(Jetten et al., 2001, Fux et al., 2002). This means that the process offers an opportunity to
decrease the carbon footprint of the wastewater treatment plant in terms of saving
possibilities of both additional carbon source and power consumption (Jetten et al.,
2004). Further advantages with the anammox process is that the production of surplus
sludge is minimized and that high volumetric loading rates can be obtained resulting in
reduced operational and investment costs (Abma et al., 2007). However there are
doubts that the process could produce significant amounts of N2O gas with negative
environmental impacts detracting the process advantages.
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