| 摘要 |
PROBLEM TO BE SOLVED: To provide a septic tank constituted so that wastewater is necessarily passed through first and second cleaning treatment chambers from a discharge port, even if a large quantity of wastewater flows in the septic tank suddenly, to be discharged as cleaned water. SOLUTION: The septic tank 1 is demarcated into a receiving chamber 10, a first cleaning treatment chamber 11, a second cleaning treatment chamber 12 and a treated water chamber 13 by partition walls 2, 3, 4. Wastewater is treated in a filter bed 23 and a biological membrane filter bed 26 to be discharged through the treated water chamber 13. When a large quantity of wastewater flows in the receiving chamber 10 suddenly and the water levels of the first and second cleaning treatment chambers 11, 12 are raised suddenly, the water in the second cleaning treatment chamber 12 flows out to the treated water chamber through a backwashing water supply pipe 31. Since the level of the upper end of the partition wall 3b separating the first cleaning treatment chamber 11 and the treated water chamber 13 is higher than the level of the upper end of the backwashing water supply pipe 31, the water in the first cleaning treatment chamber 11 is prevented from overflowing the partition wall 3b to flow in the treated water chamber 13 in a short-circuited manner.
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