Alkalinity is comprised primarily of carbon dioxide, bicarbonate, carbonate and hydroxides. Naturally occurring alkalinity is the earth s natural buffering system in that small doses of strong acids (e.g. acid rain) react with alkalinity and result in relatively small changes in pH. Carbon dioxide and bicarbonate are in a balance between the pH range of 4.4 and 8.2. At a pH of 4.4 or lower, all alkalinity is in the form of carbon dioxide. At a pH of 8.2, there is no carbon dioxide and all alkalinity is bicarbonate. Bicarbonate and carbonate are in a balance between the pH range of 8.2 and 9.6. At a pH of 9.6, there is no carbon dioxide or bicarbonate and all alkalinity is carbonate. As the pH increases above 9.6, hydroxyl alkalinity due to the presence of the hydroxide ion starts to occur. Most naturally occurring water sources have a pH between 6 and 8.4, so the presence of hydroxides is the result of man-made activity. This paper highlights the analysis of RO Water chemistry done in advance to designing RO systems.

Authors: Ted Prato and Chris Gallagher (formerly Ionics) Reprinted from International Water Conference