Underground water pollution by nitrates has become alarming in Algeria. A survey carried out revealed that the nitrate concentration is in continual increase. For example, in water samples from the Mitidja plain in 2004, the nitrates concentration (175 mg/l) doubled compared to that found in 2002. Considering their dramatic effects on environment, human health, physicochemical and biological processes of nitrate removal are widely used in domestic treatment and industrial wastewaters. Biological denitrification enables transformation of oxidized nitrogen compounds by a wide spectrum of heterotrophic bacteria into harmless nitrogen gas with accompanying carbon removal. Based on its price and availability, methanol is the most commonly used as an additional carbon source for bacterial denitrification. The study investigated the valorisation of a vegetable residue as a carbon source (olive pits) in water treatment using the denitrification process. In batch tests with the suspended vegetable biomass, the parameters were studied which influence the denitrification process: biomass concentration, initial nitrate concentration, initial pH, temperature and particle size. The results obtained for complete denitrification showed that 5 00 mg/l of N-NO3-/l were removed within 7 days, the most effective pH values are between 5.95 and 7.91, and an increase of temperature accelerates the process. The effect of the initial concentration influences the kinetics reaction but not the removal. The effect of particle size showed that a fine dimension gives better denitrification because of the importance of the surface area of fine particles.