Temperature-dependency of nitrification and required anoxic volume for denitrification in the biological treatment of veal calf manure

Abstract

Since 1976 veal calf manure has been treated aerobically in central treatment plants in the Netherlands. Reduction of BOD and removal of nitrogen by nitrification and denitrification are the main objectives of this treatment. Until 1991 the manure was treated discontinuously in 24-h aeration cycles. One of the conditions for denitrification is the availability of an electron donor (degrable organic matter). Because of the low BOD₅/N ratio in the manure, denitrification is sometimes incomplete in the existing plants, resulting in accumulation of nitrite and nitrate. Introduction of a continuous treatment with an anoxic zone might lead to a more efficient use of the available organic matter for denitrification. The nitrogen removal rates at 5, 10, 15 and 20°C as well as the optimum ratio between anoxic and aerated volumes at 10°C using manure with different BOD₅/N ratios were investigated in a laboratory-scale, contiuous-treatment plant with separate anoxic and aerated reactors.