Water desalinationWei-Ting SHIH Martin Degos

Introduction• Desalination is a process that removes minerals from saline water.

• Salt water is desalinated to produce fresh water suitable for human consumption or irrigation.

• “At the moment, around 1% of the world's population are dependent on desalinated water to meet their daily needs, but by 2025, the UN expects 14% of the world's population to be encountering water scarcity”

Christopher Gasson (Global Water Intelligence)

Where are they used ?• Australia

• Many countries in the Middle East: - The single largest desalination project

is Ras Al-Khair in Saudi Arabia (1,025,000 cubic meters per day)

- Israel produces 40% of its domestic water use from seawater desalination

Methods• Distillation

• Multi-stage flash distillation (MSF)• Multiple-effect distillation (MED|ME)• Vapor-compression (VC)

• Ion exchange• Membrane processes

• Electrodialysis reversal (EDR)• Reverse osmosis (RO)• Nanofiltration (NF)• Membrane distillation (MD)• Forward osmosis (FO)

• Freezing desalination

• Geothermal desalination• Solar desalination

• Solar humidification-Dehumidification (HDH)• Multiple-effect humidification (MEH)

• Methane hydrate crystallization• High grade water recycling• Seawater greenhouse

Multistage flash desalinator• Multi-stage flash distillation plants produce about 60% of all desalinated

water in the world

• An evaporator consists of several consecutive stages (evaporating chambers) maintained at decreasing pressures from the first stage (hot) to the last stage (cold).

Ion exchange

Ion exchange resin beads

Reverse osmosis

Energy consumptionDesalination

Method Multi-stage Flash Multi-Effect Distillation

Mechanical Vapor Compression

Reverse Osmosis(RO)

Electrical energy (kWh/m3) 4–6 1.5–2.5 7–12 3–5.5

Thermal energy (kWh/m3) 50–110 60–110 None None

Electrical equivalent of thermal energy (kWh/m3)

9.5–19.5 5–8.5 None None

Total equivalent electrical energy (kWh/m3)

13.5–25.5 6.5–11 7–12 3–5.5

Drawbacks• Thermohaline circulation