Method and device for removing biological nitrogen and support therefor

A biological nitrogen removal method making use of an anaerobic ammonia oxidation reaction, which comprises:

• causing to flow a support, under aerobic conditions, in water to be treated containing a soluble nitrogen which has been poured in a reaction tank, the support having, on the surface portion thereof, a two-layered microbial film which holds, in the outer layer, nitrite type nitrifying bacteria contributing to a nitrite type nitrification reaction or aerobic bacteria decomposing the soluble nitrogen other than ammonia into ammonia and nitrite type nitrifying bacteria contributing to a nitrite type nitrification reaction as a dominant species and, in the inner layer, 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 thereby carrying out denitrification of the water to be treated by making use of 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.

A biological nitrogen removal device making use of an anaerobic ammonia oxidation reaction, comprising:

• a reaction tank for receiving water to be treated containing a soluble nitrogen,
• a support placed in the reaction tank and having, on the surface portion thereof, a two-layered microbial film which holds, in the outer layer, nitrite type nitrifying bacteria contributing to a nitrite type nitrification reaction or aerobic bacteria decomposing the soluble nitrogen other than ammonia into ammonia and nitrite type nitrifying bacteria contributing to a nitrite type nitrification reaction as a dominant species and, in the inner layer, anaerobic ammonia oxidizing bacteria present as a dominant species while being surrounded with the nitrite type nitrifying bacteria;
• a flow means placed in the reaction tank for causing the support to flow in the water to be treated;
• and
• an air diffusion means placed in the reaction tank for supplying oxygen to the water to be treated,
• wherein the flow means is a stirrer having a stirring power able to adjust a moving speed, per unit surface area of the film, of ammonia ions to the microbial film through the adjustment of the flow rate of the water to be treated at the surface portion of the support.