METHOD FOR PURIFYING WATER AND DEVICE THEREFOR

PURPOSE:To suppress the generation of suspensoid, to prolong the filtering time of an active-carbon treating tower, to eiliminate the excessive injection of flocculant and to reduce the running cost of the flocculant by automatically controlling the amt. of flocculant to be injected into raw water with the turbidity of treated water as the index. CONSTITUTION:The turbidity of the flocculated and settled water 40 is measured by a turbidimeter 22, the measured result is calculated according to the relational expression between the treated water turbidity and the appropriate amt. of flocculant to be injected previously stored in a computing element 24, and the appropriate amt. of flocculant is injected into raw water through a controller 26 based on the calculated result. Consequently, the turbidity of the treated water 40 is reduced, and the filtering time of an active-carbon treating tower 16 is prolonged as compared with the conventional process.