Reverse Osmosis
The phenomenon of water molecules spontaneously migrating through a permeable membrane being used to separate a dilute solution from a concentrated solution until the concentration in both is uniform is called osmosis. After a while the water level on one side of the membrane will be higher, the difference in height is called the osmotic pressure.
When pressure is added to the higher-level side at a level greater than the current osmotic pressure, the flow is reversed. This reversal allows the contaminant solution to be further concentrated and produces purified water. Adding pressure to enact this reversal is called Reverse Osmosis or RO.
Reverse Osmosis can typically remove 85 to 99% of most mineral contaminants present in water.
Pre-filtering out larger particles
Reverse Osmosis uses membranes with very small passageways and can be quickly clogged by high-turbidity water. A pre-filter with a larger pore size captures larger solids before they enter the RO system. Bag filters are relatively inexpensive compared with RO and are an essential part of any RO design.
Desalination by Reverse Osmosis
Reverse Osmosis is often used for desalination of saline water. The main streams are:
- Saline feed water
- Low-salinity produced water
- Brine or concentrated saline reject water
Desalination process
The feed water is pretreated, pressurized, separated through RO membranes, and then post-treated for drinking water or industrial use.
Advantages of Reverse Osmosis for Desalination
- Removes organic and inorganic contaminants.
- Has minimal environmental impact aside from brine disposal.
- Can scale to almost any size.
- Typically uses minimal chemicals and maintenance.