| 摘要 |
<p>The reliability of backwashing valves constituted of first backwashing valves and second backwashing valves is ensured. A first backwashing valve (backwashing-gas rear valve) (7) that controls gas for backwashing and a second backwashing valve (backwashing-gas front valve) (6) that operates at slower speed than the first backwashing valve (7) are disposed, in a series including two or more thereof, at backwashing-gas introducing pipes individually provided for each of the filter blocks.</p> |
