Evaluation of limestone water softening using calcium hydroxide and carbonation

Abstract

Water is a fundamental resource for life on earth and its quality defines its various uses. Water quality is known as the result from human actions and from its interaction with the physical environment. Thus water has physical, chemical and biological characteristics because of its solvent properties and its ability to carry particles. Among the chemical characteristics is the carbonate hardness that represents the ion concentration such as calcium and magnesium in solution. These ions are present in groundwater through of chemical weathering processes that depended on the contact time between water and rock, temperature, available CO2 and presence of organic and inorganic. At high levels of carbonate hardness the water has a different flavor that may be unpleasant to people. The aim of this paper is to verify the decreased concentration of calcium and magnesium carbonates by the dissolution of carbon dioxide and calcium hydroxide, changing the balance of the carbonate system. Carbonated water, carbonated and aerated water, and natural water were tested with five concentrations of calcium hydroxide (0, 25, 50, 75 e 150 mg L-1). The evaluated parameter was the carbonate hardness. The experiments were set up in factorial with two factors; the Tukey test was applied at a 1% significance level. The results showed that the water factor and the hydroxide concentration factor were significant at 1% of significance, but not the interaction of both factors. However the best result in the hardness removal was the concentration of 150 mg L-1 of calcium hydroxide in carbonated and aerated water.