Seawater Desalination – The Best Choice for Solving Freshwater Shortage

Solution

Generally, there are two processes for seawater desalination. One is thermal desalination, also known as distillation, as it desalinates seawater and turn it into drinking water through distillation. As it costs too much, it is rarely used. The other one is the most popular and economical membrane technology.

Desalination membrane process:

Desalination membrane process

1. Flocculation and sedimentation pond. Seawater is pumped into the flocculation and sedimentation pond with a seawater pump. Coagulants are added into the pond for chlorine treatment and acid treatment.

2. Clean-water pond. The water in the flocculation and sedimentation pond flows into the V-type filter tank and clear-water pond after removing debris with gratings.

   Flocculation sedimentation pond

3. Self-cleaning filter. It consists of multimedia filter, activated carbon filter, water softener and ultrafilter (cartridge filter).

   1. Multimedia filter. It takes advantages of one or multiple filter media to guide high turbidity water passing through a granular or non-granular material with a certain thickness under pressure, thereby effectively removing suspended impurities and clarifying the water. The filter materials include quartz sand, anthracite, and manganese sand. They are mainly used for water treatment turbidity removal and softened water and pure water early stage pretreatment, so that the effluent turbidity can be less than 3 degrees.
   2. Activated carbon filter. It is a tank filter. It generally employs stainless steel or glass fiber reinforced plastic housings and filled with activated carbon inside for filtration. As a pretreatment of the water treatment desalination system, it absorbs residual chlorine that cannot be removed in the previous stage of filtration, and filters out free substances, microorganisms and some heavy metal ions in the water, and effectively reduces the chromaticity of water.
   3. Water softener. Under a certain pressure and flow, raw water flows through the water softener containing ion exchange resin. The exchangeable ion Na+ contained in the resin exchanges ions with cations in the water (Ca+, Mg₂+, Fe₃+, etc.), so that the Ca+/Mg₂+ contents of the effluent can meet relevant requirements.
   4. Cartridge filter. It is commonly known as ultrafilter. It generally adopts stainless steel housings and PP melt-blown filter cartridge, titanium filter cartridge, activated carbon filter cartridge or other tubular filter cartridges as internal filter elements.

   Self-cleaning filter

   Ultrafilter and its internal filter element

4. Ultrafiltration membrane system. Hollow fiber membranes are the main elements of the system.

   Hollow fiber membranes

   Hollow fiber membranes and its internal structure

5. RO reverse osmosis system. It consist of spiral-wound membranes and a FRP membrane housing.

   Reverse osmosis membrane is a kind of artificial semi-permeable membrane with certain characteristics made of simulated biological semi-permeable membrane. It is the core component of reverse osmosis technology. The principle of reverse osmosis technology is that under the action of the applied pressure higher than the solution osmotic pressure, only water can pass through the semi-permeable membrane, thereby removing other substances from water. The pore size of the reverse osmosis membrane is very small, so that it can effectively remove dissolved salts, colloids, microorganisms and organic matter from water.

   Spiral-wound membrane structure

   FRP membrane housing

6. Reverse osmosis water tank. Generally, reverse osmosis water tanks are stainless steel water tanks or FRP water tanks.

   Stainless steel reverse osmosis water tank

   FRP reverse osmosis water tanks