Water Science & Technology Vol 55 No 1-2 pp 9–17 © IWA Publishing 2007 doi:10.2166/wst.2007.025

Nitrification and denitrification in partially aerated biological aerated filter (BAF) with dual size sand media

J.H. Ha and S.K. Ong

A 104-mm (4-inch) diameter pilot-scale biological aerated filter (BAF) with a media depth of 2.5 m (8.3 feet) was operated with an anaerobic, anoxic and oxic zone at a temperature of 23°C. The medium for the anaerobic and anoxic zones was 10 mm diameter sand while the medium for the oxic zone was 5 mm diameter sand. The influent sCOD and total nitrogen concentrations in the feedwater were approximately 250 mg/L and 35 mg N/L, respectively. sCOD removal at optimum hydraulic retention time (HRT) of 3 h with recirculation rates of 100, 200 and 300% in the column was above 96%. Nitrification was found to be more than 96% for 3 h HRT at 200 and 300% recirculation. Total nitrogen removal was consistent at more than 80% for 4 and 6 h HRT at 300% recirculation. For 3 h HRT and 300% recirculation, total nitrogen removal was approximately 79%. The ammonia loading rates for maximum ammonia removed were 0.15 and 0.19 kg NH₃-N/m³-day for 100 and 200% recirculation, respectively. The experimental results demonstrated that the BAF can be operated at an HRT of 3 h with 200–300% recirculation rates with more than 96% removal of sCOD and ammonia and at least 75% removal of total nitrogen.

Keywords: Biological aerated filter; denitrification; hydraulic loading rate; nitrification; NPDES; recirculation

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