| 摘要 |
PROBLEM TO BE SOLVED: To increase the nitrogen removal ratio of the equipment using activated sludge to a specified percent or higher by providing the equipment with a path for returning activated sludge solution from a rear-end stage aerobic vessel to a forefront stage anaerobic vessel. SOLUTION: Relating to this equipment, a raw water (untreated liquid waste) supply path 11 is provided with a branched supply passage 12 for supplying liquid waste to not only a forefront stage anaerobic vessel A1, but also other stage anaerobic vessel A2,...An, and functions of the path 11 can sufficiently be utilized. A return path 42 for returning activated sludge (treated liquid waste containing activated sludge) from the aerobic vessel to the anaerobic vessel, is placed, to improve the nitrogen removal ratio. The rear-end stage aerobic vessel On is provided with an external pressure type hollow fiber membrane module 21 so that solid-liquid separation is applied and the resulting separated water is discharged to the outside of the equipment through a pump 22 and water discharge path 23. Further, a large recycle path 31 for returning activated sludge from the rear-end stage aerobic vessel On to the forefront stage anaerobic vessel A1 is placed. When the total supply amount of war water (untreated liquid waste) to the rear-end stage anaerobic vessel An is xQ and the total return amount [(the large recycle amount passing through the large recycle path 31) + (the return amount passing through the return path 42] is R", the nitrogen concentration in the discharged water (the ratio to the nitrogen concentration in the raw water) is represented by the equation x/(1+R"), wherein when x=0.2 and R"=1×Q, the nitrogen removal ratio is 90 wt.%.
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