Chemical conditioning of drinking groundwater through Ca2+/Mg2+ ratio adjust as a treatment to reduce Ca precipitation: Batch assays and test bench experiments

Abstract

Drinking groundwater sources can vary in their calcium (Ca)/magnesium (Mg) ratios, alkalinity levels, and temperatures. High levels of calcium relative to magnesium in water encourage Ca precipitation, causing pipe obstruction problems during water distribution. Ca/Mg ratio was studied in batch experiments using synthetic and real groundwater at different alkalinity levels, and temperatures to obtain an optimal condition that reduces Ca precipitation. The addition of magnesium salts to real drinking water was also investigated as a means of adjusting the Ca/Mg ratio and reducing Ca precipitation. A test bench was used to examine the effect of water velocity during its conduction on Ca precipitation, simulating an intermittent water supply. The results were analyzed and compared in terms of initial precipitation, rate of precipitation, and maximum precipitation of Ca using a modified model of Gompertz, and the precipitate was analyzed through X-ray Diffraction. The results of the present work found an optimal Ca/Mg ratio (1.1) that avoided Ca precipitation at batch conditions and during water conduction at different velocities, as well as Ca/Mg ratios that retarded or increased both the induction time and the maximum rate of Ca precipitation. Chemical conditioning by adjusting the Ca/Mg ratio is a viable option to minimize Ca precipitation in pipes.