Abstract
Through mid-May from 2009 late April, Synedra acus of diatoms is overgrowth in the dam of Chikugo River upstream. Filter clogging has occurred in Araki water purification plant. In Araki water purification plant, the head loss of filter rose sharply. On the other hand, We have to strengthen the coagulation treatment by the increase in the amount of water treatment chemicals and reduced the filter run time. However, since Synedra acus in the raw water grew day by day, we could not achieve a sufficient effect. As a result, the function of water treatment was significantly reduced.For these situations, we have emergency introduced change prechlorine injection point and the multi layer filtration. In the former, we could be improved by about 20％ a coagulating sedimentation removal effect in sedimentation pond. In the latter, we were able to suppress an increase in head loss by laying 50mm thickness anthracite about to half of the filter. These results, the function of water treatment has been restored.
