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The objective of this research is focused to evaluate the effectiveness of a denitrifying filter system for the tertiary effluent polishing process. Operational results from the laboratory-scale denitrifying filter using sand media of 90 cm depth showed that a successful application largely depended on the design of filtration rate, amount ofexternal carbon source supplied, and bumping operation. A deterioration of SS quality in the final effluent was caused by the reduced empty bed detention time (EBDT) due to the increase of filtration rate. Up to 96% of NO3-N removal efficiency was consistently achieved by the addition of methanol as a carbon source and with EBDT ofless than 18 minutes. It is noticed that the production of low SS effluent from the denitrifying filter largely depended on the bumping operation. The frequent bumping operation was a major source of SS washout from the filter. The negative effect of the bumping operation inthe single-stage filter was minimized by the design of the shallow bed 2-stage filter system. Although the denitrification rate at 10 deg.C was reduced to 4.8 mg NO3-Nremoved/grVSS/hr,a practical level of nitrate removal would be achieved by appropriate design. (c) 1997 IAWQ. Published by Elsevier Science Ltd. [ABSTRACT FROM AUTHOR]