Effectiveness of reducing Ca–Mg hardness using NaOH precipitation, in Ghardaïa groundwater

Articles in Press

Document Type : Special Issue: New Approaches to Water and Soil Management and Modeling

Authors

1 Laboratory of Materials, Energy Systems Technology and Environment, Université de Ghardaia, Ghardaia, Algeria

2 Department of Process Engineering, Faculty of Science and Technology, Mathematics and Applied Science, Ghardaïa University, Ghardaïa, Algeria

Abstract

In Saharan regions, ensuring fresh water to consumers is very difficult, as the predominant source is groundwater loaded with mineral salts from reservoir rocks. The study is based on the choice of caustic soda (NaOH) as a treatment element by chemical precipitation. The protocol followed includes treatment with different doses of NaOH: (500 mg/L of NaOH), (250 mg/L of NaOH and 250 mg/L of Na2CO3 adjusting once with acetic acid CH3COOH and another time with hydrochloric acid HCl), then optimized doses of NaOH alone. The results are then examined, on the one hand, on the reduction of hardness (TH) and, on the other hand, on its impact on pH, electrical conductivity (EC) and salinity. The results indicate that the first dose significantly reduces permanent calcium and magnesium hardness (TH) from 558 mg/L exceeding (Algerian standard limited 500 mg/L) to 328 mg/L, with increases in pH exceeding the potability threshold, while treatment with sodium hydroxide and sodium carbonate are effective in reducing or even eliminating Ca2+ and Mg2+ ions, but there is still a strong increase in alkalinity. The solution is adjusted by an acid still presents additional effects such as solubility of salts and therefore the need to adjust the electrical conductivity (EC). Finally, the treatment is optimized at a low dose of NaOH (20 mg/L) without the addition of sodium carbonate. This dose has proven to be the most adequate, thus allowing a substantial reduction in TH (615 reaching 400 mg/L) while balancing the pH and electrical conductivity (EC) parameters. These results demonstrate the effectiveness of NaOH in the treatment of hard water, while keeping control of its influence on other parameters such as sodium (225.77 mg/L of Na+) where it presents an increase of up to 10%, although it is a significant increase, it is found that the waters of the region exceed this dose in their natural state. Overall, the experience still offers promising and practical solutions for domestic, agricultural and industrial applications and guaranteeing compliance with water quality standards.

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Main Subjects

Water and Soil Management and Modelling

Articles in Press, Accepted Manuscript
Available Online from 26 October 2025

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History

  • Receive Date: 14 September 2025
  • Revise Date: 26 October 2025
  • Accept Date: 26 October 2025

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