Dolomite for Supplementation of Desalinated Drinking Water in Saudi Arabia with Magnesium, Calcium, and Hydrogen Carbonate Ions—Part 2

Maintaining the concentration of magnesium in potable water above the minimum levels has been suggested to have public health benefits. A twelve-month trial was conducted, attempting this goal via the partial replacement of limestone with dolomite in eight out of twenty-six post-treatment contactors at the Ras al Khair seawater desalination plant, the largest such plant in Saudi Arabia, with a daily production of over 1,000,000 m3 of desalinated water. Over the course of the trial, increases in Mg concentration in the range of 1 to 2 mg/L were achieved without necessitating increases in carbon dioxide utilization or any reduction in production volume. Alkalinity, calcium, and total dissolved solids remained within acceptable parameters. Calculated supersaturation values strongly suggest that it will not be possible to significantly increase concentrations further under the pH and temperature conditions of the study. Thus, while the use of dolomite to this extent is a very low-cost strategy for magnesium supplementation, its scope of application without additional carbon dioxide consumption and capital investment is limited. The ratio of magnesium to chloride in SWRO product water was estimated in the course of the study and was found to be approximately half of the ratio in standard seawater, suggesting that under operational conditions, the rejection of magnesium was significantly greater than the rejection of sodium.