Have you ever wondered why the skin on your fingertips swells up with plump wrinkles after a long bath?
The answer will help you understand how Desalitech’s systems purify water.
The skin cells of your fingertips swell because they’ve absorbed water from the surrounding bath. All of your cells are wrapped in a semi-permeable membrane, meaning they allow water and some other molecules through while blocking the rest. Water naturally flows across semi-permeable membranes from areas of high concentration to lower concentration. The water in your cells is less concentrated than the water in your bath — it’s full of all the biological molecules that make up living things, while the water in your tub is mostly pure.
For the same reason, water will flow out of your cells if their surroundings are full of very salty water. A high concentration of dissolved salt means a correspondingly low concentration of water, so water flows out of your cells. (The same thing happens to snails and slugs if you sprinkle salt on them, to deadly effect.)
Natural osmosis only works to move water from areas of high concentration to low concentration — but sometimes, as when purifying water, we want to move water in the opposite direction. This is reverse osmosis, and can be achieved using pressure from a pump or other source. With enough pressure, water will flow across the membrane in the opposite direction, from low concentration to high.
Reverse Osmosis was not practically demonstrated until the early 1960s with the invention of asymmetric membranes at University of California at Los Angeles. The membranes are composed of a thin “skin” layer supported atop a highly porous and much thicker substrate. This basic structure remains the basis of reverse osmosis membranes today.