Reaction Kinetics of Immobilized-Cell Denitrification. II: Experimental Study

Laboratory experiments were conducted to characterize the performance of an immobilized-cell denitrification process treating nitrate-contaminated groundwater and to provide supporting data for the validation of a quasi-steady state model based on half-order reaction kinetics. The treatment process consists of laboratory-scale, plug-flow reactors packed with biocatalyst particles. Pseudomonas denitrificans (American Type Culture Collection 13867), a heterotrophic denitrifier, was cultured and immobilized in calcium alginate particles. Ethanol was used as the source of organic carbon. Thirty concentration profiles were obtained at four levels of nitrate concentration and at three ranges of flow rate. An analysis of the nitrate and nitrite concentration profiles suggested that a half-order reaction rate model could be used to describe the reduction of both nitrate and nitrite. The half-order reaction rate constants for nitrate and nitrite reduction were dependent on the age of the biocatalyst particles and the nitrate loading history. The validity of the half-order denitrification model was satisfactorily tested with experimental data. As illustrated by preliminary calculations, the immobilized-cell denitrification process is feasible for practical applications, particularly for small drinking water systems.