PURPOSE:To discharge only a supernatant soln. of good quality by preventing the outflow loss of yeast fungi and floating activated sludge bacteria by arranging a ceramic/sirasu porous glass supernatant soln. extraction cylinder at the supernatant soln. discharge lower water level of a yeast acidic fermentation tank or a recovery aeration tank and extracting a supernatant soln. by the extraction pump installed outside the tank. CONSTITUTION:A hermetically closed yeast acidic fermentation tank 4 is provided with a ceramic/sirasu porous glass supernatant soln. extraction cylinder 1, an extraction pump 3, a supernatant soln. transfer pipe 8, a treated water transfer pump 9, a treated water transfer pipe 10 and a treated water tank 11 at the supernatant soln. discharge lower water level thereof. 90% or more of the total nitrogen component in the hermetically closed yeast acidic fermentation tank 4 is confined in the soln. within the tank to be prevented from flowing out of the tank and, when the total nitrogen component in the tank exceeds a tolerance amt., a proper amt. of yeast fungi-activated sludge containing the total nitrogen component is drawn out of the tank from the drain 17 attached to the bottom part of the tank to be subjected to dehydration/drying treatment. The total nitrogen component in the supernatant soln. discharged from the extraction cylinder 1 is always suppressed to 1-2% or less of the total nitrogen component in the tank 4.
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