To preserve organic materials in the sludge required for denitrification, a study was made with a contact process. The contactor, when operated with a short retention time (30 min), gave incomplete metabolism of organic matter. With 64% of the influent soluble COD (SCOD) was adsorbed to activated sludge within 30 min. The specific mass of organic matter uptaken was 55 mg SCOD/g Mixed Liquor Suspended Solids that enhanced the denitrification efficiency up to 63% in the following denitrification step.