In a sludge dewatering process using polymer, controlling the polymer dosage is an important factor for upgrading performance and achieving a saving on costs. A new automatic polymer dosage control method has been developed by the authors, which features the use of a streaming current detector or a colloid titrator. These detectors detect the colloidal charge of the filtrate from sludge. The said method was used with actual dehydrators and the following advantages were confirmed.
(1) The said method is applicable for various types of dehydrators.
(2) The said method is effective even when there are changes in sludge characteristics.
(3) The said method is more economical than a conventional solids proportional control method in that less polymer is used.