Understanding Reverse Osmosis

UNDERSTANDING REVERSE OSMOSIS

Definition:

Reverse Osmosis is a process by which a solvent passes through a porous membrane in the direction opposite to that for natural osmosis when subjected to a hydrostatic pressure greater than the osmotic pressure.

In Layman’s terms:

Osmosis is a natural process where the water of lower salinity is mixed with water of higher salinity. Water in its pure form has no salinity and or TDS (Total Dissolved Solids). As it encounters water that has higher salinity or TDS, it naturally mixes itself with the higher salinity water, which we name the process osmosis.

Water Flow

Reverse Osmosis is basically the same process in reverse. As water is pressured through a semi-permeable membrane, it is separated from the water of high salinity or TDS, hence bring water back to its pure form.

Water Flow

Why is reverse Osmosis technology so effective in removing contaminants

Reverse Osmosis filtration is a method where water is forced through a Semi-permeable membrane that has a pore size or roughly 0.0001 microns. In this state, the pore only allows some atoms or molecules to pass through while blocking other bigger particles from getting through the membrane.

In comparison, a typical Carbon filtration will have a micron size of 0.5 microns to 50 microns where most of the TDS will still be able to get through. Although Carbon filtration is great at removing odor, taste, colors and other chemicals found in the water due to their larger micron size and their absorbing ability, they are ineffective in removing contaminants such as arsenic, heavy metals, and sodium that are rated at much smaller micron sizes.

*Image is not to scale and is not an actual representation of the filter.

The Disadvantage of Reverse Osmosis Technology.

One of the biggest gripes about reverse osmosis filtration is the amount of water it needs to waste to purified the water. Like, almost all other water filtration, reverse osmosis is a technology that blocks contaminants from passing through its pores. However, unlike other filtration methods, it doesn’t have the luxury of letting those contaminants stay at the other side of the pore.

The below diagram shows three different types of water filtration with the same amount of contaminants filtering through them. As we can see, smaller contaminants pass through both sediment and carbon without issue as the pore size are much bigger than their physical size. However, the same types of contaminants are unable to pass through reverse osmosis and quickly clogged up the pores render the membrane useless.

Two of the most important factors for reverse osmosis is water temperature and water pressure.