The Role of Reverse Osmosis in Our Daily Lives
While many people will probably be unfamiliar with the technology involved, the process known as reverse osmosis (RO) plays an important part in several aspects of our daily lives. The technology is based on a modification to the natural property of a cell wall that allows the movement of water in or out of the cell in response to a force known as osmotic pressure. That force is created as a result of a difference in the concentration of dissolved solids between the water inside the cells and that in the water surrounding them. Water is forced in whichever direction is necessary in order to equalise the concentration of solids on both sides of the cell wall. So just how has this natural phenomenon been modified to provide the applications in which it now plays a key role?
The clue is in the word “reverse”. While osmosis utilises the natural pressure gradient between solutions of differing concentration, the process stops once equilibrium is reached. When applying an external pressure to overcome the natural gradient, all the water or solvent can then be forced across a semi-permeable membrane, leaving the dissolved solids or solute behind. This amounts to filtration at a molecular level and may be applied either for the purification of solvents, the recovery of solutes, or both. One of the most significant applications of this technology is its use in the reclamation of wastewater. While most of the suspended solids can be removed by a combination of sedimentation, filtration, and organic digestion, when subjected to reverse osmosis, it eliminates the need for chemical additives to remove pathogens and dissolved organic contaminants. The latter includes pesticide residues, pharmaceutical products, and by-products of disinfectants that would otherwise tend to remain largely unaffected when relying solely on methods involving biological degradation.
With a suitable choice of semi-permeable membrane, the inclusion of a final RO stage in the process provides treatment plants with an effective means to render wastewater potable. Furthermore, the process is also cost-effective, as it requires less energy than alternative technologies and is capable of removing both the soluble organic and inorganic substances present in wastewater. The near-disastrous 2018 Cape Town drought made world headlines and serves as a timely reminder that, in common with most parts of the world, South Africa is facing a water crisis. Once again, reverse osmosis offers a solution; not just by the recycling of wastewater but by removing the dissolved salts from brackish water in river deltas and seawater from the oceans around us. The idea, however, is far from new.
For example, it is known that Aristotle and his contemporaries successfully performed experiments with this end in mind and that these were based on distillation and filtration through soil. Many centuries later, in 1791, Thomas Jefferson introduced a simple desalination process for use on ships in case of emergencies. However, the first large-scale desalination process, which employed a principle known as multi-stage flash distillation (MSF), was developed in the USA in 1955 followed by the more efficient option known as multi-effect distillation (MED) in 1959. However, both processes require huge amounts of energy and thus reverse osmosis has been steadily replacing techniques involving distillation for the treatment of seawater in modern desalination plants.
One of the other sectors in which RO technology has a direct impact on our lives is the food and beverage industry. Not only does exceptionally pure water improve the taste of beverages such as beer but, bearing in mind that it can also be used to isolate solids, the technology can be applied to the preparation of concentrates like fruit juices. The food and beverage industry, of course, is not alone in its need for pure water; pharmaceutical companies have a similar need, while aid workers and the military often employ portable reverse-osmosis devices to obtain drinking water from contaminated sources when operating in remote regions. In the home, similar RO devices can be attached to a tap or built into the plumbing to further purify tap water, removing traces of fluoride and chlorine that some people find spoils its taste.
These are just a few of the ways in which this technology is playing a role in our everyday lives and one can be certain there will be many more applications for reverse osmosis in the future. WaterIcon is a leader in RO and all forms of water treatment.