AWWA JAW17911

This article discusses a study which was conducted to derive an accurate theoretical expression for exactly evaluating the pH of saturation and to develop a simplified method of accurately predicting the pH of saturation. Two new expressions for the pH of saturation were derived. One is a simplified equation developed from an aqueous carbonate equilibrium system in which correction for ionic strength was considered. The other is a more accurate quadratic formula that involves computerized calculation of the pH of saturation and takes into account ionic speciation and an activity correction factor. Different methods of determining the pH of saturation of 155 Florida water samples were compared using the Langelier equation, the Larson-Buswell formula, the two pH of saturation equations derived in this study, two mathematical models obtained from multivariate analysis, the WATSPEC2 computer program, and Caldwell-Lawrence diagrams. Values from the new pH of saturation equations, the WATSPEC2 computer program, and the four- and five-variable mathematical models derived in this study are close to one another, whereas those from the Langelier and Larson-Buswell equations are generally lower. The graphical values approximated from the Caldwell-Lawrence diagrams are consistently higher. Includes 41 references, tables, figures.