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:
|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
|2 ||CO2 addition + Calcite Limestone (CaCO3, MgO) percolation + Na2CO3 ||80 mg/L CaCO3 |
|3 ||CO2 addition + Dolomite Limestone (CaCO3, MgCO3) percolation + Na2CO3 ||80 mg/L CaCO3 + MgCO3 |
|4 ||Addition of CaCl2 + NaHCO3 ||100 mg/L CaCO3 |
100 mg/L Na + 50 mg/L Cl
Water Quality for drinking and Irrigation water:
|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 |
|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) |