Reverse osmosis is a widely used technology for the desalination of water. Reverse osmosis is absolutely useful in technical applications under controlled conditions. However, the use in the home raises some questions we answer below.
Reverse osmosis was originally developed in California in collaboration with the State of Israel to turn saltwater into drinking water. In reverse osmosis, a membrane made of polyamide (PA, see Wikipedia entry here) is used. The plastic is polymerized on a porous support material in such a way to create the largest possible surface. The first rectangular support is then glued to make a bag and the bag is then attached to a perforated pipe. The PA layer is located outside on the bag.
Then the bag is rolled around the tube which is facing forward, poking out from behind the rolled-up bag. A curtain-like spacer is then wrapped to allow the water to flow between the layers of the rolled bag. A spacer is also built in on the clean water side to allow the water in the bag surrounding the perforated pipe to flow to the tap.
That’s an awful lot of plastic offering bacteria plenty of room to grow, even on the purified side of the pipe.
The transport of water and dissolved particles takes place through these three mechanisms:
While the reverse osmosis membrane is very good at catching ions, it is not so good at catching dissolved organic matter. Depending on the type of pesticide or other dissolved organic matter, the retention rate is only between 20% and 80%.
Cold water that comes out of our tap is usually in chemical equilibrium, which means that no dissolved substances are being released and no substances are being absorbed from its environment. In some regions (for example, the foothills of the Alps, the water has excess calcium in it making it hard, while in other regions the water tries to absorb minerals as it flows by (for example, in the Bavarian Forest).
If one removes the minerals dissolved in water, this changes the water’s pH level and it will try to absorb new minerals to restore its equilibrium. The same thing happens when you change the pressure or temperature of the water. In reverse osmosis, H2O is extracted from the water and that has consequences.
Reverse osmosis is a process developed for removed dissolved components from the water in industrial plants, not in the home. A big problem is the formation of biofilm on the reverse osmosis membrane.
Bacteria having a size from 0.5 microns are smaller than standard carbon filters, as they are often used as a precursor to small reverse osmosis systems in the household, so they can pass directly through the membrane. There they find a concentrated supply of nutrients, making it the ideal environment for a biofilm to develop on the membrane. The bacteria of the biofilm then produce EPS substances (slime), which then provide even more nutrients directly on the membrane, which in turn accelerates the transport of solutes through the membrane.
The reverse osmosis membranes also constantly show various production defects and are particularly tricky when a thick biofilm forms on the membrane. The bacteria migrate to the permeate side of the drinking water through any hole through which they can fit.
The following materials are held by the reverse osmosis well back:
The following substances are of the reverse osmosis not sufficiently retained:
In the treatment of drinking water for use in the private sector, Seccua filtration systems offer unique options. Typically, they are installed in the basements of private households, right at the point where the public water line enters the home.
Together with a Seccua biofilter, they then remove all pathogens and all dissolved elements in the water such as pesticides, drug residues, and plasticizers. By removing the bacteria and nutrients at the inlet, biofilms will still grow back within a few weeks. Compared to the reverse osmosis systems often employed in the private sector, Seccua’s filtration system offers many more benefits.
Advantages of Seccua filtration compared to reverse osmosis:
Point-of-Use RO under the sink
Aesthetic water characteristics
Clear, sometimes a taste of plastic
crystal clear, no bad taste
chemical water characteristics
water consumption per produced water
25 – 50 %
less than 1 %
In essence, reverse osmosis for home use can be summarized as follows:
If you want a good piece of equipment, you’ll need to pay a high price. But high prices do not necessarily guarantee high quality. Often the majority of the price consists of commission to the salesperson and does not go into product development. Often cheap membranes are installed. There are different manufacturing processes and levels of quality that will, of course, affect the quality of the reverse osmosis and the water’s taste.
It is impossible to tell if a membrane is damaged. When reverse osmosis is not used, the pressure equalizes on both sides of the membrane. This causes the membrane to lose its effectiveness and is unnoticed by the casual observer. Since low-quality membranes are often installed, their useful life and their collection rates can vary considerably.
Slow operation results in a relatively low flow rate and a storage tank is needed. These storage tanks are breeding grounds for bacteria. There is an increased risk, depending on the storage time and temperature of the stored water. In addition, the membrane is very susceptible to contamination because there concentrate suspended solids and bacteria and the filter modules are not flushed.
Reverse osmosis drops the pH drops and osmosis water can become very aggressive, only usable with high-quality stainless steel or plastic pipes. In addition, the osmosis water tastes like plastic. An active carbon filter is therefore often used to enhance the flavor of the reverse osmosis water.
Reverse osmosis was designed to remove dissolved substances in industrial water, not in private households. Generally pesticides and solvents are not removed effectively enough. Instead, reverse osmosis removes the naturally occurring, healthy minerals and trace elements in the water. Therefore osmosis water often has to be enriched with expensive mineral powders.
We’re experts in purifying drinking water. That’s why we’re able to give you detailed information about the safest and best technologies for water purification.
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