Date of Award

Summer 1992

Degree Type

Thesis - Restricted

Degree Name

Master of Science (MS)


Civil and Environmental Engineering

First Advisor

Crandall, Clifford J.

Second Advisor

Bergs, M. A.

Third Advisor

Zanoni, A. E.


Bench scale studies of precipitative softening were conducted over a temperature range of approximately 20 to 60°C. Three different water samples were utilized in the study. Well water had high Ca2+, Mg2+ and alkalinity. Tap water had moderate degree of Ca2+, Mg2+ and alkalinity. Synthetic water had a high Mg2+ content. Five different precipitants (lime, soda ash, caustic soda, phosphate and aluminum sulfate) were investigated for optimum hardness removal. The results show caustic soda removed hardness effectively and sodium phosphate improved hardness removal and alkalinity reduction. All precipitants achieved better performances when operated at higher temperature. Lime-soda ash and caustic soda were selected for a reaction time study. After a 1 minute reaction time, both treatment methods achieved a significant hardness reduction as determined by the atomic adsorption method. A high magnesium water concentration of 146.5 mg/L (as CaC03 ) was prepared for the synthetic water study. The concentration of magnesium was successfully reduced to less than 40 mg/L. Temperature was shown to be a significant factor for the precipitative softening process. Improved results were obtained at warm temperature compared to operation at ambient temperature.



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