Removal of Water Hardness: Comparative Study

Abstract

Water hardness, resulting from the presence of divalent calcium and magnesium ions, is an important parameter in water treatment due to its effects on household and industrial installations, as well as its broader environmental and health implications. This study presents a comparative evaluation of four hardness-removal techniques: thermal softening, lime–soda treatment, ion exchange using a commercial softening filter, and adsorption using coconut-based granular activated carbon (AC). Artificial hard water with a total hardness of 320 mg CaCO₃/L was prepared and analyzed following Polish and ISO standards.Thermal softening removed 39% of total hardness, confirming its selectivity for temporary hardness. The lime–soda process significantly improved hardness reduction, achieving 72% removal under cold conditions and 83% under hot conditions, with enhanced precipitation of CaCO₃ and Mg(OH)₂ at elevated temperatures. Ion exchange produced the most effective softening, reducing total hardness by 86%, including 83% calcium and 91% magnesium hardness removal. Adsorption studies showed that hardness removal increased with contact time and AC dose, reaching equilibrium after approximately 11 hours and achieving up to 75.5% removal at 12 hours. The comparative analysis demonstrates substantial performance differences between methods and confirms ion exchange as the most efficient and universal technique. However, adsorption and lime–soda softening provide viable alternatives in contexts where chemical availability, energy consumption, or waste generation are important considerations. These results support informed selection of softening technologies in drinking water treatment and industrial applications.