Color removal in groundwater through the enhanced softening process

The source of water for Miami-Dade County, Florida is groundwater derived from the Biscayne aquifer. The raw water is rich in natural organic material producing correspondingly high color levels. Currently, breakpoint chlorination is used at the water treatment plant to control the color problem. However, this results in the formation of disinfection by-products. Proposed alternatives to reduce color and avoid by-product formation include the addition of coagulants such as ferric chloride and organic polymers, and the operation of the existing lime softening process at a higher pH. This study uses jar tests to evaluate the relative effectiveness of the proposed alternatives. Results indicate that significant color reduction is achieved using the existing lime softening process with activated silica coagulant by increasing the softening pH to 11 or more. Elevated pH also produced a > 30% reduction in total organic carbon. In the presence of higher raw water color (> or = 80 units), the addition of ferric chloride as coagulant at dosages of 80 mg/L is recommended.