| 摘要 |
PURPOSE:To reduce the time for the SS to increase and the leak-time of the flocculant by performing the filtration while adding the filtrate having SS larger than the specified concn. to the original water when the water to be treated added with flocculant is filtered after the backwashing of the sand filter bed. CONSTITUTION:The filtrate contg. 0.2ppm SS flowing out in the early stage of the filtration is accumulated in a backwashing tank 5, when the filtration of the original water 8 is started after the backwashing of a sand filter 4. Then, the filtrate is pushed out by a portion of the filtrate supplied from a line 12 in the progress of filtration, overflown into an intermediate tank 5', and added to the original water 8 through a line 14 as circulating filtrate. The filtrate filtered by the sand filter 4 is taken out from a line 11, and a portion thereof is stored in the backwashing tank 5 and the large portion in a filtrate tank 6.
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