Document Type

Thesis - University Access Only

Award Date


Degree Name

Master of Science (MS)

Department / School

Civil and Environmental Engineering


Incrustation of filter media occurs in water softening plants at varying degrees. There may be chemical, physical, and operational reasons why this occurs and to what degree it occurs. This thesis explores these reasons and correlates them to incrustation that has occurred at water softening plants. Chemical features that were studied include polyphosphate addition, chlorine addition before and after the filtration process, calcium and magnesium concentration of water, and calcium content incrusted on the media. Physical aspects that were studied include media type, age of filters, density of media and particle distributions. Some of the operational aspects studied were backwashing practices, backwashing indicator, and overall operation of the softening plant. A survey was sent to every water softening treatment plant in the State of South Dakota to gain general knowledge on the factors listed above. The survey included questions about chemical additions throughout the plant and the filter influent and effluent pH, alkalinity, hardness, temperature, and turbidity. There were also questions regarding backwashing practices including method, frequency, backwash flowrate, and backwash indicator. Information was requested regarding the physical aspects of the filters themselves, such as size and number. The survey results indicated a number of items that may have contributed to either causing a high degree of incrustation or preventing significant incrustation to occur. Polyphosphate addition prior to the filtration process appeared to prevent excessive incrustation. A majority of the sites that exhibited low incrustation were employing a surface wash prior to either air or water backwash. This prevented calcium carbonate from building up on the surface of the filter media. Lastly, the calcium carbonate precipitation potential (CCPP) may be a useful tool in indicating whether the water is precipitating large quantities of calcium carbonate and whether the operation of the facility may be adjusted to remediate this problem.

Library of Congress Subject Headings

Water -- Softening Filters and filtration



Number of Pages



South Dakota State University