IMPROVING SETTLED WATER QUALITY TO MEET IESWTR

摘要

The largest surface water treatment plant for the City of Austin, Texas is the A.R. Davis Water Treatment Plant (WTP). The Davis WTP was originally constructed in 1954 and was subsequently expanded in 1961 and 1974 to its present capacity of 120 MGD. Due to the hardness of the raw water, partial lime softening is the treatment process for the plant, which includes a raw water intake, three rapid mix basins, nine separate flocculation and sedimentation trains followed by filtration. Historically, it has been difficult to consistently achieve settled water turbidity from the basins under 2 NTU. With the passage of the Interim Enhanced Surface Water Treatment Rule, the filtered water quality requirements will be reduced from 0.5 NTU to 0.3 NTU. While the plant can typically achieve that requirement, it was felt that improvements were needed to insure that the filtered water turbidity would exceed the requirement all the time. With that, improvements were needed to the settled water quality to meet a goal of less than 2 NTU to insure compliance with the new filtered water turbidity requirements. As part of an overall rehabilitation project to replace the old flocculator equipment, the City took the opportunity to determine the improvements needed in the basins to reduce the settled water turbidity.