Proof Of Concept For Reverse Osmosis Technology

The invention and large-scale application of Reverse Osmosis (RO) is a landmark achievement in the development of modern water treatment technology. As an advanced membrane separation technology developed after the 1950s, RO has been widely used in desalination, brackish water desalination, domestic water purification and wastewater reuse, etc. In 2018, more than 11 billion tonnes of desalinated water were produced worldwide using RO technology, which could be used by 320 million people.

Over the past 70 years, many important scientists, entrepreneurs and a large number of technology companies have joined forces to perform a fascinating history of the development of reverse osmosis technology.

Proof of concept for reverse osmosis technology

As the name suggests, reverse osmosis is the term used in relation to osmosis (Osmosis) and refers to the reverse process of the osmosis phenomenon. At the heart of both osmotic and reverse osmosis processes is a semi-permeable membrane.

Semi-permeability simply means that water can pass through, while the salts or other solutes dissolved in the water cannot. If the solute concentration in the solution on both sides of a semi-permeable membrane is not the same, water molecules will spontaneously pass through the membrane from the low concentration side to the high concentration side until the concentration of the solution on both sides of the membrane is the same, or a certain net pressure difference is established on the low concentration side of the membrane due to a rise in the water level. This is the phenomenon of osmosis, and the net pressure difference is the osmotic pressure.

We know that doctors often use saline, which is an aqueous solution of sodium chloride at a concentration of 0.9%, when giving fluids to patients. This concentration is comparable to the concentration of human body fluids and therefore the infusion does not cause harm to the body due to the significant osmotic phenomena that occur on both sides of the cell membrane. Although osmosis occurs in our bodies on a daily basis, it was not until 1748 that it was first discovered scientifically by the French physicist Jean-Antoine Nollet.

Nollet was a great man with a passion for science and is said to have demonstrated the Leyden bottle discharge experiment to Louis XV. He experimentally observed the phenomenon of osmosis by using a pig bladder as a semi-permeable membrane to separate two aqueous solutions of ethanol of different concentrations. in 1886, a Dutch scientist summarised the experimental data and came up with the company for calculating the osmotic pressure of dilute solutions. If you have studied physical chemistry, you may remember that this man was called Van't Hoff.

In the 1950s, the Kennedy administration began to look to desalination in order to address water shortages in some arid regions of the US and the national problem of overuse of groundwater. 1952 saw the passage of the Saline Water Conversion Act by the US Congress. 1953 saw the start of funding for research into desalination technology, although the funding for that year was only $175,000. In 1955, the US Department of the Interior established the Office of Saline Water (OSW) to co-ordinate research into various desalination technologies.

Membrane desalination research was first initiated by Gerald Hassler and others at UCLA in 1949. 1950 saw Hassler describe the concept of a 'Salt Repelling Osmotic Membrane' in an internal UCLA report, but his subsequent research went a bit off the rails. In August 1956, Hasler first coined the term 'Reverse Osmosis' in another internal UCLA report.

Around 1954, Professor Charles Reid's team at the University of Florida, with funding from OSW, also began researching desalination osmosis membranes. They evaluated a number of commercially available membranes and found that cellulose acetate membranes had good semi-permeability, a salt retention rate of >99% and a water permeability coefficient of 0.00012m3/m2-d-atm. Although the membranes were more than two orders of magnitude less permeable than modern commercial membranes and were not commercially viable, they were the first to experimentally validate the concept of pressure-driven reverse osmosis membrane desalination using synthetic membranes. The term "RO" was used by Riddell and his colleague E. J. Breton in a report to OSW in April 1957.

Interestingly, at a time when there was no internet or circle of friends, although both universities were working on desalination membranes, they were unaware of each other until they met at a workshop organised by OSW in November 1957.