| 摘要 |
PROBLEM TO BE SOLVED: To prevent the clogging of a filter chamber certainly to sufficiently stably treat BOD and SS. SOLUTION: Biological treatment is executed by alternately performing aeration/ filtering operation and backwashing operation and, at a time of aeration/filtering operation, a treated soln. is circulated along with carriers 3 having specific gravity slightly larger than 1 to simultaneously perform the removal of SS and the decomposition of a soluble substance in the treated soln. and, during this period, the carriers 3 flowing in a filter chamber 7 from the entrance and exit part 8 of the upper end part thereof are put to practical use as a filter material to guide the treated soln. from which SS is removed by filtering to the outside of the reaction tank 1 from the filter chamber 7. In backwashing, the feed-in of sewage and aeration operation are stopped before filtering resistance is abnormally increased by an increase in the catching amt. of SS in the carriers 3 within the filter chamber 7 and backwashing air is ejected from the backwashing air diffusing port part 9 of the lower part in the filter chamber 7 not only to push out the carriers 3 to the reaction tank 1 outside the filter chamber 7 from the entrance and exit part 8 but also to send out caught SS and the sending of air to the backwashing air diffusing port part 9 is stopped.
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