A Reverse Osmosis component to your filtration system can provide cleaner, clearer water for your drinking pleasure and daily needs. But what is Reverse Osmosis and how exactly does it affect the water in your home?
What is Reverse Osmosis — The Short Answer
What is reverse osmosis? Basically, Reverse Osmosis (RO) is like a filtration process that can successfully remove the smallest minerals, salts and particles in water. This is accomplished by passing the water through a specially designed “semi-permeable” RO Membrane.
Water passed through the RO membrane is 99% demineralized, desalinated and deionized. This is far better suited to human usage and consumption than water copper, iron, calcium, sodium, sulfide and chloride.
What is Reverse Osmosis? — The Detailed Explanation
Before we can begin to understand how reverse osmosis is so beneficial to water treatment, we should first explore the natural phenomena called “osmosis”.
Osmosis is a natural occurrence observed when weaker saline solutions migrate through certain membranes into more saline solutions. This is observed when tree roots absorb water from the soil or when water is filtered from the blood in the kidneys.
To arrange a simple experiment, we would need two containers of water with different levels of salinity separated by a semipermeable membrane. As time goes by the water with lower levels of salinity will begin to migrate through the membrane to the side with greater salinity as per the action of osmosis.
Of course, this is not very helpful when trying to remove salinity from water, so the natural process had to be reversed. Whereas osmosis naturally passes the water with less salinity into the water with greater salinity, reverse osmosis applies pressure to the water with greater salinity, passing it through the RO membrane into the water with less salinity. When the pressure of the contaminated water is increased the water passes through the RO membrane, but no contaminants are allowed to pass. This effectively removes up to 99% of the salts, bacteria, pyrogens, and organics. For more water softener alternatives be sure to check out our blog.
How does Reverse Osmosis work?
The water that is processed through the RO membrane is called the permeate. The permeate has had all the contaminants removed and is ready to be used. The water that has not yet been processed and carries with it many contaminants is called the brine or reject stream.
Reverse osmosis is achieved by the use of a high-pressure pump on the side of the water with the contaminants and minerals. This high amount of pressure forces the water through the RO membrane with a tolerance of a small fraction of a micron. The pressure required to force the water through the RO membrane must be selected on the needs of the filtration system and water source in question. The higher the concentrations of minerals and chemicals the greater the pressure needed to push the water through the membrane.
As the pressurized water pushes against the RO membrane only pure water is forced through the tiny spaces between the semi-permeable membranes. All the salts and other contaminants are left behind in the brine stream, which will sometimes be fed back into the filtrations system and sometimes be sent down the drains. The water that successfully makes it through the RO membrane will then be passed along through the permeate route where it will be made available for consumption
It is important to understand that a RO membrane does not function like a regular filtration system. With a regular filtration system there is a single-entry point, water is passed through a filter and clean water is passed out the other side. With a RO membrane, the cross-filtration system is used. This means that the water is crossed from one stream of water to another, through a RO membrane. This means that there are essentially two outlets. One carries away the permeate and the other the brine. This allows the pressure and flow of the water on the reject or brine side to keep the membrane clean.
To protect the integrity of the RO membrane, most of the larger contaminants will be removed from the water with a classic activated carbon filtration system. After which, the RO is capable of removing over 99% of the particles, colloids, bacteria, pyrogens and dissolved salts. This is because of the molecular weight of these pollutants.
Pure water molecules have a molecular weight of 18 (MW18). Anything with a weight higher than a certain number will not be passed through the tolerance of the RO membrane. This depends greatly on the exact RO membranes used but most exclude anything with a molecular weight higher than 150.
In Conclusion
RO is the preferred method of water purification for water that is basically clean but still a bit brackish. While they are an important component of a complete water filtrations system, it is best if they are supplemented with an activated charcoal filtrations system as well.