N2O production in a single stage nitritation/anammox MBBR process

To enable efficient nutrient removal the hydraulic conditions should prevent the buildup
of a laminar layer and the contact surface between water phase and biofilm should be
as large as possible (Metcalf & Eddy, I. 2003).
2.5 System configurations for nitrogen removal by anammox
Nitrogen removal by anammox can be implemented either as a two stage or one stage
system. 50% of the influent ammonium is oxidised to nitrite by nitrifying bacteria in
both cases. In a two stage system this conversion takes place in a nitritation reactor
followed by an anammox reactor where the oxidation of ammonium into dinitrogen gas
with nitrite takes place. In single stage technology both processes takes place in the
same reactor (Abma et al., 2007). Since the anammox process was discovered by
different research teams and in slightly diverse environments the system configurations
evolved have been given different names but are in practice quite similar. Main
differences are reactor configuration and operational mode. Some of the available
anammox processes are shortly described in this chapter.
2.5.1 Sharon/Anammox
A Sharon (single reactor system for high rate ammonium removal over nitrite)
reactor followed by an anammox reactor is a possible system configuration to achieve
nitrogen removal with anammox bacteria. The Sharon process is used to nitrify 50% of
the influent ammonium to nitrite. The effluent from the Sharon reactor is then used as
feed for the anammox reactor where nitrite and ammonium is converted to elemental
nitrogen, see Figure 5, (Stowa, 2009).
Figure 5. Sharon/Anammox process scheme.
To achieve partial nitrification to only 50% the Sharon reactor is operated in a manner
that benefits the ammonium oxidizers, washing out the nitrite oxidizers from the system
(van Dongen et al., 2001). This is obtained by operation above 25 ̊C, keeping the sludge
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