A new moving bed biofilm reactor (MBBR) has been developed in Norway. The biomass is attached to carrier elements that move freely along with the water in the reactor. It has been demonstrated that existing, high loaded, activated sludge plants can easily be upgraded to nitrogen removing MBBR plants. With chemically enhanced mechanical treatment, full scale tests showed that 80-90% total nitrogen could be removed in a MBBR plant at a total empty bed hydraulic retention time (HRT) of 2.6 hours. The plant was operated in the post-denitrification mode, using methanol as an external carbon source.

Internationally, phosphorus limitation in nitrification of municipal wastewater has been given little attention. However, pre-precipitation of low alkalinity wastewater normally results in phosphate concentrations significantly below 0.10 mg PO4-P/l. Tests have been carried out for tertiary nitrification in rotating biological contactors (RBCs), with different influent phosphorus concentrations. These tests showed that tertiary nitrification in biofilm reactors was clearly phosphate limited at influent concentrations below approximately 0.15 mg PO4-P/l. This means that with todays practice, extension of Scandinavian chemical treatment plants with downstream biofilm reactors for nitrogen removal (i.e. nitrification and post-denitrification) will be hampered by phosphorus limitation in the biological stages. Actions to increase the phosphate concentrations in these biological reactors must be taken.

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