Reverse osmosis
There are several ways and techniques for individuals to clean their water. The most popular is from the 1950th, and it’s called “reverse osmosis” (RO).
Reverse osmosis is a technology used to make drinking water from saltwater. It uses a semipermeable membrane, which is an imitation of membranes, found in nature. The technology can be used to remove unwanted molecules, particles, and ions from drinking water.
Reverse osmosis uses the principle of osmosis, just in the other direction. In normal osmosis, the solvent (water) moves from an area of low solute concentration, through a membrane, to an area of high solute concentration.
Since the dissolved molecules, particles and ions cannot move through a semipermeable membrane, the water moves through the membrane to equalize the concentration of solutes.
The water pressure created by the movement of water is called osmotic pressure and is always in the direction of the highest concentration of dissolved substances.
We could say that water strives to achieve even solute concentration on both sides of the membrane and travels from side A (where there are fewer particles) to side B (where there are more particles) in order to establish such a state.
In reverse osmosis, it is just the other way around. Applied pressure is used to overcome osmotic pressure - the water must move from a high concentration to a low concentration. In this way, you get clean drinking water on one side of the membrane while concentrating the amount of salt, chemicals, bacteria and other molecules on the other (inorganic minerals, pollutants, including viruses, bacteria, pesticides, arsenic, fluorine, drugs, mercury, nitrate, microbes, heavy metals, all radioactive materials, and many more). Compared to all other filtration systems, RO removes everything from the water, both good and bad.
The principle of reverse osmosis is that the saline raw water is passed over a membrane. Through the microscopic pores in the surface of the membrane, only H2O - the pure water molecules - will pass, because the water molecule is one of the smallest molecules in liquid form. The microscopic pores in the osmosis membrane are adapted to the water molecule and therefore do not release contaminants such as (e.g. heavy metals, chemicals, viruses, bacteria), because all these substances are larger than a water molecule.
All contaminants are rejected, but oxygen - O2 and CO2 - which is a gas, and smaller than the water molecule, will escape through the osmosis membrane so that the natural oxygen in the water is preserved.
When understanding osmosis principles, it is also easy to understand why such a process is still considered the best for water filtration, even after so many years of use. But as it also removes all the good minerals from the water, these should be added after the cleaning process when using the RO systems.
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The pressure in the process must be higher than the osmotic pressure, otherwise, the process will stop because the water will seep back through the membrane. In fact, the pressure must be a lot higher for the process to be efficient, so large pumps are used to create the right pressure. Almost all major ships have a plant for making freshwater from saltwater.
Normally seawater must have a pressure of about 28 bar in order for the desalination plant using reverse osmosis to work. As the process runs, the seawater concentration of salt will rise, so it will have to pressure in the saltwater too. Therefore, a pressure of 40-70 bar is used on ships, depending on the size of the plant and the need for freshwater.
Sailers have used reverse osmosis to make drinking water from seawater since 1950 when the technique was invented in California. The smart thing about the technique is that it utilizes physical laws. Many breweries and other industries that need clean water also use the method.
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Reverse osmosis is also used in countries where there is no groundwater. Huge plants are constantly running to make clean drinking water from saltwater. Worldwide, a very big share of drinking water actually comes from desalination with reverse osmosis.
About 300 million people lived on freshwater from desalination in 2015, and approx. 86.6 million cubic meters of water are processed this way every day. -
It takes energy to run the process with reverse osmosis: 5 kWh / m3 of water in the inlet. One kWh costs DKK 2.37 and you waste 3 liters of water for every liter you produce.
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Not all ions can be held 100%, but the efficiency of most RO systems is 96-98%. A certain portion (1-2%) will pass through the membrane - this depends on both the molecular size and the membrane itself. If a low residual concentration of ions is desired, it may, therefore, be necessary to use several RO plants in series or combine with ion exchange.
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Membranes for use in industrial plants are usually made of polyamide or polysulfone, which can work in the pH range of 2-12. The filtered liquid is called “the permeate”, while the retained concentrated liquid is called the concentrate.
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RO Membrane
A reverse osmosis membrane consists of many layers of very thin films wrapped around a tube in the middle. These films have very small holes in a tens of thousands µ (0.0001µ). The unit of measurement is micron, my or just µ. 1 µ is a millionth of a meter or a thousandth of a millimeter (0.001 millimeters).
The membrane is placed on gaskets in a container called a membrane housing, which thus has two exit channels: The furthest emits pure osmosis water. Clean water and filtered water cannot be mixed, so the membrane housing has two outputs: one for the clean water and one for the wastewater.
The capacity of purification is indicated in Gallons / Liter per day. 1 gallon = 3.78 liters.
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Filtration percent
The filtration rate indicates how many percents of what is NOT water is being filtered out. It is an average of all water-containing substances measured with a TDS / EC / MicroSiemens gauge.
Actually, the electrical conductivity of the water is measured and there is an estimate. In the shown example of photos, my tap water is 343ppm and the filtered osmosis water is 10ppm. It gives a filtration rate of 100 - (10 / 3.43) % = 97%.
The tap water in Copenhagen is measured at 350ppm (700µS), and boiled water comes down to 230ppm (460µS).
With an osmosis plant, 10-20ppm (20-40µS) is obtained. You don't have to be a professor of microbiology to understand what it means: much cleaner water.
Why Wetality RO system is superior?
Reverse osmosis plants remove 90-99% of all solids in the water.
Reverse osmosis also removes inorganic minerals, pollutants, including viruses, bacteria, pesticides, arsenic, fluorine, drugs, mercury, nitrate, microbes, heavy metals, all radioactive materials and many more.
So it truly is a powerful system!
Why did we even bother to make it better?
A reverse osmosis plant typically consists of 2-3 filters followed by an osmosis membrane.
It works like this:
- Sediment filter
- Carbon filter
- RO membrane
The membrane is the most expensive, so a common goal is to remove as much as possible before the water reaches the membrane. In this way, it lasts longer.
It is also a good idea to soften the raw water in a softening filter to prevent lime build-up and thereby clogging of the membranes, which also helps prolong the life span of the membrane.
We could say that RO systems work so good for water purification, that general concern of most producers is how to make them last longer. If you continue reading you will understand why we have chosen a Reverse Osmosis system as foundation for
the Wetality water solution.
Standard osmosis treatment systems
Reverse osmosis (RO) is a separation and water treatment process that uses pressure to force water through a membrane that retains the solute on one side and allows the purified water to pass to the other side. More formally, it is the process of forcing a solvent from a region of high solute concentration through a membrane to a region of low solute concentration by applying a pressure in excess of the osmotic pressure.
The membranes used for reverse osmosis have a dense barrier layer in the polymer matrix where most separation occurs. In most cases, the membrane is designed to allow only water to pass through this dense layer while preventing the passage of solutes (such as salt ions). As the membranes get clogged with the matter filtered from the water, the system must go through a rinse cycle to clean the filter.
Water used in the rinse cycles can equal 25% to 75% of the amount of filtered water the system produces. It is important to use the RO water judiciously to minimize water waste, as every gallon of water RO water produced can require the input of 1.75 gallons of potable water.
This means that a standard RO system can be very slow and inefficient because it produces too much excess waste water.
This is neither convenient nor ecological.
Apart from solving this problem, we went one more step ahead and, after detailed market research, decided to build an all-in-1 water filtration system which also offers benefits that are usually found in alternative water treatment systems, but not together with RO.
Wetality water cleaning system offers:
3 filters even before RO membrane - to make sure that membrane can focus only on the job it really needs to do and that it can do it as efficiently as possible.
3 powerful stages and a final UV filter:
Hydrogen Boost - Adding hydrogen ions to your water also increases antioxidants and helps revitalize the whole body.
PH + Boost - Alkaline water filters have already entered main-stream with their popularity, believed to neutralize acid and help overall well-being.
Mineral Boost - Adds an ideal amount of minerals back to your water, because RO has removed also all the good things which our body needs.
UV Light - Disinfecting the water from any possible leftovers of microbiological contaminants and colloidal particles without changing the good properties of the filtered water.
Additionally, the Wetality water cleaning system has a powerful 400 GPD water flux - even 5x faster than standard RO systems.
Wetality water cleaning system does not have an additional external water pressure tank, which takes up space and makes the whole system harder to install. Instead, it comes with built-in pressure - no additional tank.