Understanding Reverse Osmosis

Drinking water can be purified through reverse osmosis.

Drinking salt water can kill you. When it enters your stomach, water is pulled from other parts of your body to compensate for the increased levels of salt. Your body will become dehydrated if fresh water is not restored. Scientific discovery has made this scenario avoidable. The process is called reverse osmosis and it is used to purify water resources like salt water around the world.

Osmosis

To understand reverse osmosis it is necessary to first understand osmosis. According to the Merriam Webster Collegiate Dictionary osmosis is the "movement of a solvent through a semipermeable membrane into a solution of higher solute concentration that tends to equalize the concentrations of solute on the two sides of the membrane." This means when two solutions of water, one with a low concentration of solute like salt particles, and one with a high concentration of solute, are separated by a semipermeable membrane like that of a cell, the water will move through the membrane from the lower concentration to the higher concentration until the two solutions have equal solute concentrations.

Osmosis occurs when pores in the membrane are large enough to allow water molecules to pass, but not so large as to allow solute particles through. The pressure that pulls the water from one side to the other is called the osmotic potential. The greater the difference between concentrations of water solutions, the greater the osmotic potential will be.

Reverse Osmosis

Reversing osmosis involves moving water, not from the lower concentration to the higher concentration, but instead forcing water from the solution with the higher concentration of solutes to the one with the lower concentration. Thus, reversing the effects of natural osmosis.

The Process

Reversing the osmotic process requires overcoming the force of osmotic potential. To accomplish this task, outside pressure must be applied to the solution with the highest concentration of solute. Typically, the pressure required to overcome the osmotic pressure of freshwater is between 100 and 150 psi. More pressure is required for salt water, as its osmotic potential is much higher than that of fresh water.

Common Uses

Reverse osmosis is used for a variety of purposes including drinking water purification, dialysis, food industry needs, car wash rinses, hydrogen production and waste water purification. Drinking water purification can be carried out on a mass scale, like purifying the drinking water for a metropolitan population, or it can be practiced on a household level, using portable water filtration systems.

History

Jean Antoine Nollet first discovered the process of osmosis through a semipermeable membrane in 1748. The process was only put to use in laboratories unit 1948 when researchers at the University of California in Los Angeles (UCLA) began studying the use of semipermeable membranes to remove the salt from saltwater. By the 1950's the researchers along with others from the University of Florida succeed in separating seawater into fresh water and solute. The process was not efficient enough for commercial use until the 21st century when water-processing plants had become widespread throughout the world.

References

• "Handbook of water and wastewater treatment plant operations"; Frank R. Spellman; 2008
• "The early history of reverse osmosis membrane development"; J. Glater; 1998
• The Negev Academic College of Engineering: SIDNEY LOEB Co-Inventor of Practical Reverse Osmosis
• "The Economy of Nature"; Robert E. Ricklefs; 2007
• "Merriam-Webster's collegiate dictionary"; Merriam-Webster, Inc; 2003