|Limestone Bed Contactors for Control of Corrosion at Small Water Utilities (EPA/600/2-86/099) February 1987
Project Summary (EPA/600/S2-86/099) February 1987
A study was conducted to investigate the use of limestone contactors for mitigating corrosion in small water supply systems that use dilute acidic (corrosive) water. As water is transported through a packed bed of crushed limestone, calcium carbonate dissolves and the pH, calcium ion concentration, and alkalinity increase. A mathematical model was derived for use in contactor design.
The model is based on the interfacial transport of calcium ion and relates the depth of limestone required in the contactor to the desired effluent water chemistry, influent water chemistry, limestone particle size and shape, limestone bed porosity, water temperature, and superficial velocity. The model was calibrated and tested using laboratory column experiments.
In a field contactor monitored for 2.5 years, the water quality following treatment (except for the initial few months) was essentially constant. No gradual, long-term degradation in performance was noted. After several months of operation, however, the rate of calcium carbonate dissolution was not as high as that observed in the laboratory using fresh limestone. The rate of dissolution was possibly reduced by an alumino-silicate residue that remained after the calcium carbonate was dissolved from the limestone matrix. A microbiological film may also have been a limiting factor. Field studies indicated that limestone contactors can effectively reduce the tendency of water to take up corrosion by-products (copper, lead, and zinc) from surfaces in piping systems.
This report covers August 1, 1982 to July 31, 1985. Work was completed July 31, 1985.
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