Janez Vrtovšek*, Milenko Roš*

*National Institute of Chemistry, PO BOX 660, Hajdrihova 19, SI-1001 Ljubljana, Slovenia
E-mail: janez.vrtovsek@ki.si

Absrtract
This study demonstrated the feasibility of a fixed-bed reactor system with a specific biomass support material for groundwater treatment. The denitrification rate increased up to a maximal value of 1.3 gNO₃-N·m^-2·day^-1 with increasing nitrogen loading rate. Kinetic analysis of the system confirmed a half-order denitrification kinetic region in the NO_x-N concentration range from 0.25 mg·L^-1 to 16 mg·L^-1, with the half-order reaction coefficient k_1/2 of 0.35 g^0.5·m^-0.5·day^-1 when the carbon source was in excess. Under the experimental conditions, drinking water quality was achieved at a nitrogen loading lower than 1.9 g NO₃-N·m^-2·day^-1 with an influent COD/N ratio of 3.7 if acetate was used as the carbon source. The system is fairly robust; it can be operated in a simple manner at low hydraulic loadings without recirculation flow and without backwashing.

Key words: biofilm reactor, denitrification, external carbon substrate, groundwater, kinetics