Remineralization of desalinated water: Duality roles of H2SO4 and CO2 injection during calco-carbonic equilibrium of osmosis water

Abstract

In a desalination station, the remineralization step of osmosis water (OW) is essential to return to produced water its calco-carbonic equilibrium. For this, the use of calcite CaCO3 or lime Ca(OH)2 for water equilibrium in post-treatment processes needs the utilization of both CO2 and/or H2SO4 in osmosis water. For this reason, we describe here in detail, the effect of H2SO4 and CO2 on the remineralization process in a post-treatment desalination plant, especially with using hydrated lime Ca(OH)2 and calcite contactor (CaCO3)·In this paper, the different cases were discussed and investigated, by monitoring several indicator parameters such as pH, Ca2+ content, alkalinity, Langelier Index, etc. After the remineralization stage, we have shown that the efficiency of the remineralization process by CaCO3 or Ca(OH)2 depends on CO2 or H2SO4 content. Remineralization by CaCO3 (limestone) coupled with CO2 acidification is easy and more operator-friendly compared to the process using Ca(OH)2 (lime); it provides a clean environment for people working in the plant. In addition, the H2SO4 injection in the pretreatment stage followed by CaCO3 contact could lead to great results and correct calco-carbonic equilibrium. In the end, a comparative study of the investment cost in each process shows that the acidification of raw water with sulfuric acid (pretreatment) is the cheapest one, according to many studies. But on the other hand, the direct injection of CO2 is the easiest one to use for water balancing.

Keywords

• Remineralization
• Calco-carbonic equilibrium
• CO2
• Lime
• H2SO4