Technical Report No. 14
Nathan C. Burbank, Jr., Po Lau Chan, Reginald H. F. Young
The waters of the streams in the South Kohala district on the island of Hawaii have long been noted for their extreme high color and at times a distinct peaty taste. Early attempts to treat this water have led to the conclusion that the color bodies occurring in the water were refractive in nature and very difficult to remove except by an uneconomic chemical treatment. Investigation, over a one-year period, has found the colored bodies in the water of the Waikoloa Stream to be predominantly organic in origin with the color colloid having a negative charge. The color of the water varies from a maximum value of 320 units to a minimum value of 22 units. The average value is about 80 units. The zeta potential of the color colloid has varied from negative 36 mv to negative 18.5 mv. It was possible to remove color to the U. S. Public Health Service standards for interstate carriers by coagulating the color bodies with either alum or ferric sulfate. Coagulant aids can significantly reduce the quantity of the coagulant required to effect color removal. Coagulant aids decrease the required retention time in the flocculation basin and effects a faster rate of sedimentation. Further, color removal is generally improved. The most satisfactory coagulant aid is a cationic polymer, which not only acts as an aid but also as a true coagulant in color removal. Reductions by as much as 20 percent in the amount of primary coagulant required is possible while obtaining the same resists. The optimum pH range is 6 to 7 and the optimum dosage of cationic polymer is from 1 to 3 mg/l in conjunction with 15 to 20 mg/l of coagulant.