Nitrate is an undesirable component of several foods. A typical case of contamination with high nitrate contents is whey concentrate, containing nitrate in concentrations up to 25 l. The microbiological removal of nitrate by Paracoccus denitrificans under formation of harmless nitrogen in combination with a cell retention reactor is described here. Focus lies on the resource-conserving design of a micro bat denitrification process. Two methods are compared. The application of polyvinyl alcohol-immobilized cells, which can he applied several times in whey feed, is compared with the implementation of a two step denitrification system. First, the whey concentrate's nitrate is removed by ion exchange and subsequently the eluent regenerated by microorganisms under their retention by crossflow filtration. Nitrite and nitrate concentrations were determined by reflectometric color measurement with a commercially available Reflectoquant (R) device. Correction factors for these media had to be determined. During the pilot development, bioreactors from 4 to 250 mg.L-1 and crossflow units with membrane areas from 0.02 to 0.80 m(2) were examined. Based on the results of the pilot plants, a scaling for the exemplary process of denitrifying 1,000 tons per day is discussed. (C) 2010 American Institute of Chemical Engineers Biotechnol. Prog., 26: 756-762, 2010