Increasing drinking water pH with limestone contactors

Raw water catchment basins are currently used by Hawaii Volcanoes National Park to provide water to thousands of visitors and staff per year. However, the volcanic gases nearby cause the raw water to have a significantly low pH, causing pipe corrosion and "red water". One of the design alternatives analyzed for raising the pH of the water was the limestone contactor, an open vessel, which allows water to contact limestone chips. The limestone contactor was selected as the best alternative based on its low cost, simple operation and maintenance, and its applicability to small water treatment systems. Although noted for its simplicity, the success of the limestone contactor requires an understanding of its basic elements. This article describes the design process and the specific design parameters of the limestone contactor alternative. Lastly, data for limestone contactors; currently in use is provided.