Leakage of Turbidity to Filtrate by Picophytoplankton and Investigation for Measures in Water Purification Plant

Abstract

Cell concentration of micro-phytoplankton and Flagellates were high in raw water of Kunijima purification plant of Osaka waterworks, from July to August, 1996.
Then, turbidity was leaked to filtrate of water purification system, and the majority of turbid were due to picophytoplankton. Leakage was remarkable in the raw water which was taken in from afternoon to evening. 14 thousands cells/mL of picophytoplankton in filtrates show 0.1 degree of turbidity.
The results of coagulation-sedimentation by jar test examination were follows:
(1) Dosage of combined chlorine was effective. (2) Optimum pH of coagulation and floc formation was<7.2 by aluminium sulfate, <7.4 by polyaluminium chloride. (3) Increase of coagulant dose was effective but cells could not be removed over 99% in spite of 120mg/l dose.
The turbidity<0.1 was achieved by measures of chlorination, increase of coagulant dose, and pH modification.