In order to obtain compact plants and to assure a greater treatment reliability, fixed film reactors have been developed. This biofiltration has been applied and proved for over a decade for carbon removal. Today, new applications appear in nitrogen and phosphate removals, which are able to respond to the upgrading of aging waste water treatment plants. Full scale plant results are presented in nitrification. The use of two stages of biofilm reactors (C + N) permits high effluent quality. Chemical phosphate removal and denitrification results obtained on pilot tests are also discussed. Some plants are now been built with such processes.

The VEAS concept, in Oslo, which includes four steps of fixed film reactors is discussed as an example of this present upgrading tendency.

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