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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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