Patent ID: 8246830
Filing Date: 2012-08-21
Classification: C02F,Y02W

Abstract:
1. A biological nitrogen removal method including an anaerobic ammonia oxidation reaction, the method comprising: causing a support to flow, under aerobic conditions, in water to be treated containing a soluble nitrogen which has been poured in a reaction tank, the support having, on a surface portion thereof, a two-layered microbial film which holds, in an outer layer, a nitrite type nitrifying bacteria contributing to a nitrite type nitrification reaction or aerobic bacteria decomposing the soluble nitrogen other than ammonia into ammonia and a nitrite type nitrifying bacteria contributing to a nitrite type nitrification reaction as a dominant species and, in an inner layer, an anaerobic ammonia oxidizing bacteria contributing to an anaerobic ammonia oxidation reaction as a dominant species while being surrounded with the nitrite type nitrifying bacteria; and carrying out denitrification of the water to be treated using the anaerobic ammonia oxidation reaction; wherein a feed rate of the support (total surface area of the support per unit capacity of the reaction tank) and/or a flow rate of the water to be treated at the surface of the support is/are adjusted so that an amount of nitrous acid produced by the nitrite type nitrification reaction through the action of the nitrite type nitrifying bacteria reaches a level to inhibit a nitrate type nitrification reaction; wherein the denitrification of the water to be treated using the anaerobic ammonia oxidation reaction is performed without causing an active sludge to flow in the reaction tank; wherein the feed rate of the support is decreased so that the amount of nitrous acid produced by the nitrite type nitrification reaction through the action of the nitrite type nitrifying bacteria reaches the level to inhibit the nitrate type nitrification reaction; and wherein the water to be treated containing the soluble nitrogen is wastewater having a normal temperature and having a soluble nitrogen concentration of 50 mg/L or less.