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:

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)

Desalination Key issues

Seawater Intake

Desalination Pretreatments

Desalination Post-treatments

• Boron Removal
• Remineralization
• Neutralization

Reverse Osmosis Desalination Process

Desalination and Energy Costs

Brine Disposal

Membranes cleaning

Storage and Distribution

Containerization / Tropicalization

Instrumentation and Control (SCADA)