AWWA MTC64534

Water District No. 1 of Johnson County, Kansas (WaterOne), is a large utility that supplies water to approximately 340,000 people in the Kansas City metropolitan area. WaterOne has two facilities (55 and 125 mgd) that treat water from the Missouri and Kansas Rivers by presedimentation, preoxidation and disinfection with chlorine dioxide, two-stage lime softening, dual media filtration, and disinfection with chlorine. Currently, WaterOne is planning a new 30 mgd treatment facility that will treat Missouri River water withdrawn through horizontal collector wells. One proposed treatment process would include lime softening and filtration by microfiltration (MF)/ultrafiltration (UF) membranes. WaterOne and Black & Veatch performed a 6 month pilot study to evaluate the potential effects of lime-softened water, specifically water with pH of 9.5 and calcium carbonate precipitation potential greater than 20 mg/L as CaCO₃, on the MF/UF membranes. The membrane system suppliers were allowed to specify the flux and other operating setpoints, but were required to meet water recovery, membrane cleaning, and specific flux recovery following CIP values outlined in the pilot testing protocol. The pilot testing extended over several seasons, so the impact of water temperature, TOC increases with spring runoff, and process changes upstream of the membrane systems were investigated. An on-line alkalinity, total hardness, and TOC analyzer were also used to determine the effects of calcium carbonate precipitation potential and TOC on the membrane fouling rate. The paper discusses the results of the pilot study and fouling rates as a function of TOC concentration, upstream treatment with polymer, and calcium carbonate precipitation potential. The paper also provides practical guidance for other softening plants that are considering MF/UF membranes. Includes tables, figures.