Biological nitrate removal in a laboratory-scale slow sand filter

Abstract

This research evaluated removal of nitrates from drinking waters in a slow sand filter (SSF). Batch experiments were per - �ormed to determine optimum carbon to NO �-N (C/N) ratio for the filtration experiments. The filter column was filled with filter sand of an effective diameter of 0.5 mm and uniformity coefficient of 1.23. The filter was operated at filtration rates of between 0.02 to 0.120 m/h and 0.01 to 0.25 m/h with concentrations of 22.6 and 45.2 mg NO �-N/ℓ, respectively, and effluent samples of the SSF were taken at 6 depths of 10, 15, 20, 40, 60, 80 cm, and the bottom. Optimum C/N ratio was found to be 1.5 when using ethanol in batch tests when the removal efficiencies of NO �-N and C were higher than 90%. Although increasing filtration rates decreased NO �-N removal, effluent NO�-N concentration at the effluent port of the SSF was lower than the limit value. Most o � the NO�-N removal was carried out at the upper layer of (10 cm) the filter bed.

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