seawater desalination
Current status of seawater desalination:
The global daily output of seawater desalination is about 35 million cubic meters, of which 80% is used for drinking water, solving the water supply problem of more than 100 million people, that is, 1/50 of the world’s population relies on seawater desalination for drinking water. According to statistics from the International Desalination Association, there are about 18,000 seawater desalination plants in 150 countries and regions around the world, among which reverse osmosis (RO) is one of the main membrane technologies for removing dissolved salts and other impurities from ocean or groundwater sources.
Average water consumption and cost of supply by seawater desalination at US$1 per cubic metre (±50%)
| Area | Consumption Litre/person/day | Desalinated Water Cost US$/person/day |
| US | 378 | 0.38 |
| Europe | 189 | 0.19 |
| Africa | 57 | 0.06 |
| UN recommended minimum | 49 | 0.05 |
What is reverse osmosis?
Reverse osmosis is to apply a great pressure on the seawater to allow water molecules to pass through a special semi-permeable membrane, while salt and other impurities are blocked and cannot pass through, so that fresh water can be obtained. This semi-permeable membrane is like a super filter that only allows water molecules to pass through. Many small seawater desalination devices now use this method because it is relatively simple and low-cost.
Reverse Osmosis Process
Select a process
1.Seawater Intake
2.Seawater pretreatment
3.High-pressure pumping
4.Reverse Osmosis Separation
5.Freshwater post-treatment
Seawater Intake
Naturally occurring components in seawater are usually so numerous that additional measures need to be taken to remove them during the desalination process to meet quality requirements for human consumption. These components are carried into the reverse osmosis stage and may produce unwanted residues or by-products
Related parameters:
pH
Conductivity/TDS/Salinity
Suspended solids
Turbidity
Chlorine
Redox potential
Oil in water
Total organic carbon
Seawater pretreatment
Pretreatment is the key initial link in the desalination process. It is like a meticulous “gatekeeper” that removes suspended matter and large particle impurities, controls microorganisms, and removes special substances from seawater, laying a good foundation for subsequent desalination operations and ensuring efficient and stable operation of the entire desalination system.
Related parameters:
pH
Conductivity/TDS/Salinity
Turbidity
Total Organic Carbon
Hardness
Alkalinity
Chlorine
High-pressure pumping
The pre-treated seawater must rely on a high-pressure pump to increase the pressure to 5-7MPa. This pressure can overcome the osmotic pressure and allow water molecules to penetrate from the high-salinity seawater side through the reverse osmosis membrane to the low-salinity freshwater side.
Related parameters:
Rated pressure
Maximum working pressure
High-pressure pump speed
Rated power
Rated flow
Inlet and outlet pipe diameter
Reverse Osmosis Separation
Under high pressure, seawater enters the reverse osmosis membrane assembly. The pore size of the reverse osmosis membrane is about 0.1 nanometers, and only water molecules can pass through. Salt ions such as sodium ions and chloride ions and large molecular impurities cannot pass through. On the freshwater side of the membrane, the permeated water molecules gather into freshwater, and the salt concentration of the seawater on the seawater side increases and becomes concentrated brine.
Related parameters:
Acidity/Redox Potential
Ultra-low Chlorine Concentration
Conductivity High and Low Range
Turbidity Low Range
Total Organic Carbon
Boron
Alkalinity
Temperature
Freshwater post-treatment
Degassing: Use a degassing tower to remove dissolved carbon dioxide and other gases in the water to avoid affecting the water quality.
pH adjustment: Add alkaline agents such as sodium hydroxide to adjust the pH value of fresh water to 6.5 – 8.5.
Mineralization: Add minerals such as calcium and magnesium ions to fresh water according to the purpose to improve the taste and quality.
Sterilization: Use chlorine dioxide, ultraviolet rays, etc. to sterilize again to meet the microbial indicators.
Related parameters:
pH
Ionic compounds
Chloride
Conductivity
Turbidity
Hardness
Fluoride
Nitrate
Phosphate
Sulfate
Iron
Manganese
Potassium
Magnesium
Calcium
Sodium
Total alkalinity
Silica
