Ammoniacal nitrogen removal in biological aerated filters: The effect of media size

Recent legislation has led to stringent ammoniacal-nitrogen consents and th e need for first-time sewage treatment in coastal areas where land is limit ed. This has led to the need to improve 'small footprint' sewage-treatment processes (such as biological aerated filters) which can be used for carbon aceous treatment, nitrification, or for combined treatment. The removal of ammoniacal nitrogen in filters containing different sizes of Lytag medium a nd operated for combined carbonaceous treatment and nitrification, was comp ared at different hydraulic and volumetric loading rates. The results sugge st that filters containing the smallest media size (2-4 mm), gave optimum n itrification at ammoniacal-nitrogen loading rates up to 0.6 kg/m(3), d. At higher loading rates there was a rapid decrease in nitrification for this s ize of medium but, with 2.8-5.6 mm medium, nitrification continued at loadi ng rates up to 1 kg amm. N/m(3) d. The filters containing larger media size s (4-8 mm and 5.6-11.2 mm) exhibited low levels of nitrification above a lo ading rate of 0.2-0.4 kg amm. N/m(3). d.