WRRCTR No.14 Removal of Color from South Kohala Water: Island of Hawaii

Abstract

The waters of the streams in the South Kohala district of the island of Hawaii have long been noted for their extremely 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 with unusually large and uneconomic chemical treatment. At the end of one year of research into the problem of removal of the color from water as typified by the water from Waikoloa stream, it has been found that the color bodies are predominantly organic and characteristic of humic and tannic acids of vegetable origin. The color of the water has varied from a maximum value of 320 units to a minimum value of 22 units, the average value, based on present data, is 80 units. The zeta potential of the color colloid complex has varied from 36 mv to 18.5 mv. Coagulation and removal of the color from the water can be a achieved using either alum or ferric sulfate. Alum with an average dosage of 25 mg/l can reduce the color level from 140 to as low as 10 mg/l while ferric sulfate at an average dosage of 20 mg/l can reduce the color level of the water to as low as 5 color units over a wide range of pH values (6.0 to 8.5). Such color reduction permits the water to meet the U.S. Public Health Service standards for interstate carriers. The use of coagulant aids holds great promise for successful color removals at lower coagulant dosage.