The removal efficiency of nitrogen and organic matter in an anoxic/aerobic upflow fixed bed filter was studied. Tests were carried out on the effects of aeration, hydraulic loading rate, and COD/N ratio on nitrogen removal and carbon oxidation. A synthetic high nitrogen concentration wastewater was used as substrate feed in the study. At an influent concentration of 250 mg N/L, and for volumetric loadings of up to 1 kg N/m3.day, between 41% and 86% of the nitrogen was removed. This was achieved without the recycling of effluent for denitrification. Nitrogen removal was possible when simultaneous denitrification took place inside the support media where oxygen was lacking. COD removal efficiency was consistently above 95% even at a high volumetric loading of 5 kg COD/m3.day and a bulk liquid dissolved oxygen level as low as 1.1 mg/L.

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