4.2. Nitrogen
In most RAS systems, nitrogen is removed by a combination
of moving bed and fixed bed nitrification reactors and, in some
cases, additional denitrification reactors (Losordo et al., 1999). The
nitrification process in RAS is hampered by the level of organic matter entering the bio-filters (Eding et al., 2006). As a result, both
autotrophic and heterotrophic bacteria are growing in the reactors. The challenge is to enable nitrification reactors to work as
chemo-autotrophic as possible, e.g., by minimizing the organic carbon (OC) in the influent of the nitrification reactor. Therefore, major
objectives for research are: