| 摘要 |
PROBLEM TO BE SOLVED: To scum, concentrate and store the sludge accumulated in a foreign matter removing tank, to reduce the volume of the sludge stored in the tank and to miniaturize a septic tank by providing a means for injecting a nitrate nitrogen soln. at the bottom of the removing tank, with respect to the septic tank provided with the foreign matter removing tank and an aeration tank. SOLUTION: Domestic waste water is charged into a foreign matter removing tank 1, solids are separated, org. matter is anaerobically decomposed, and then the water to be treated is transferred to an aeration tank 2. An air diffuser pipe 12 for blowing the air from a blower 8 is set in the aeration tank 2, and org. matter is aerobically decomposed. A contact filter medium 15 is provided in the tank 2, a sludge extracting pipe 9 is extended from the bottom of the tank 2, and excess sludge is returned to the tank 1 by the air from a blower 10. An injection pipe 3 is extended to the bottom of the tank 1, and a nitrate nitrogen soln. from a tank 13 is forcedly injected into the bottom of the tank 1 from the outlet 5 of the injection pipe 3 through a solenoid valve 14.
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