Biological denitrification applied to a marine closed aquaculture system

The denitrification of marine effluents was tested using a technology involving immobilized denitrifying bacteria on granular material. To ensure efficient denitrification, an organic carbon addition was needed. The denitrification rate was quantified in the pilot-unit working as a batch fermentor. A first order kinetic model according to the nitrate nitrogen concentration was found and the rate coefficient is an increasing function of the TOC/N(NO−3) ratio, with an optimum ratio of 1 g g−1. Smaller values led to a nitrite production which was nevertheless oxidized in the treatment line; higher values could lead to the appearance of toxic sulphides. Working on stationary hydraulic loads, the treatment capacity of the unit was about 2.4 kgN(NO−3) m−3 j−1. It was necessary to wash the packing once every 3 days. The malfunctioning of the unit could be avoided by the oxidation-reduction potential control.