Lenntech Water treatment & purification Lenntech Water treatment & purification

Desalination Post-treatment: Neutralization / Remineralization for Drinking water

Why should desalinated water be remineralized?

Reverse Omosis is not a selective ion removal process. After the common 2-pass RO process for Boron Removal, delisalinated water is poor in minerals.

Low mineralized water have few adverse effects:

- High corrosion potential
- Dietary deficiency causing risks of ischaemic heart and cerebrovascular disease (WHO, 2005a; WHO, 2006; Cotruvo, 2006)

The WHO recommends 10 mg/L of Magnesium and 30 mg/L of Calcium for drinking water.

Double-pass SWRO system designed for enhanced Boron removal for dinrking water have a very low mineralization, about 5 to 10 mg/L of Na and 10 to 20 mg/L of Cl. Other ions are below 0.5 mg/L.

Four solutions are widely used to remineralize desalinated water:

Remin.
Process
Description Minerals
1 Blend with 1% clarified seawater + pH neutralization 15 mg/L Mg + 5 mg/L Ca
+ 125 mg/L Na + 220 mg/L Cl + 25mg/L SO4
pH 7-7.5
2 CO2 addition + Calcite Limestone (CaCO3, MgO) percolation + Na2CO3 80 mg/L CaCO3
pH 7-7.5
3 CO2 addition + Dolomite Limestone (CaCO3, MgCO3) percolation + Na2CO3 80 mg/L CaCO3 + MgCO3
pH 7-7.5
4 Addition of CaCl2 + NaHCO3 100 mg/L CaCO3
100 mg/L Na + 50 mg/L Cl
pH 7-7.5

Water Quality for drinking and Irrigation water:

Remin.
Process
TDS after 2-pass SWRO (Boron Removal Process for Drinking Water) EC after SWRO +IX (Boron Removal Process for Irrigation water) SAR after SWRO +IX
(Boron removal Process for Irrigation water)
1 350-400 mg/L 0.8-0.9 8
2 50-100 mg/L 0.3-0.4 2.5
3 50-100 mg/L 0.3-0.4 2.5
4 250-300 mg/L 0.6-0.8 6.5

Processes Comparison:

Process Investment Operation Water quality Ease of operation
1 Very Low Low Medium water quality - high sodium chloride content Easy
2 High High
Good water quality (very small sodium increase) Easy
3 High High
Very Good water quality (very small sodium increase, more magnesium) Easy
4 Very Low Low Medium water quality - high sodium chloride content Time consuming (chemical dissolution)

 

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