We often say that reverse osmosis removes 99% of contaminants and call them a long list. Today let’s talk about the other side of the issue – what reverse osmosis can’t remove and why it happens.
What’s inside your home filter?
Most likely, if you are interested in the topic of this article, you already know what elements your filter consists of, nevertheless we will try to briefly repeat this information.
Structurally, the system is a multi-stage water purification station in a reduced form. First, the source water goes to a block of three prefilters (some manufacturers’ models have two). Inside the three flasks are cartridges that trap mechanical particles, chlorine and organic substances. The need for this step is primarily due to the danger of these substances to the sensitive web of the membrane element.
After pre-treatment, the water flows to the membrane, which is actually the main filtering element. Thanks to the reverse osmosis process, it only allows water molecules and partially some ions to pass through. It also removes heavy metal ions. After all, it is because of their high molecular weight that they are called “heavy” and hardness salts and most organic matter.
After the membrane the water goes back to the activated carbon filter, called post-filter. Here it removes residual gases and specific organic impurities, if they did manage to get through the membrane.
Mineralizer is an additional step; it does not purify the water, but merely adds magnesium and/or calcium, which are also removed in the purification process. For this reason, light scaling in the kettle often occurs after mineralization filters.
Now let’s try to understand in detail what contaminants are removed by the filter and how it does it.
Does reverse osmosis remove bacteria and viruses?
Microbiological safety of water is one of the primary factors of its evaluation and the main task of water utilities. For this purpose, at water treatment stations they dose chlorine compounds into the water, which are able to destroy microorganisms. Nevertheless, cases of the spread of infectious diseases through water occur even today, both in centralized and decentralized sources.
Reverse osmosis is able to remove 100% of bacteria, viruses and parasite eggs, which because of their size are simply unable to squeeze through the membrane. For this reason, reverse osmosis water can actually be drunk without boiling.
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Does reverse osmosis remove heavy metals and nitrates?
Toxicity of compounds of metallic chemical elements increases with increasing their serial number and molecular weight. Fortunately, the degree of removal of these compounds also increases with their mass, that is, the more toxic the element, the less chance it has of passing through the membrane.
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Quite an old study of Dow Filmtech TW30-1812-50 membranes confirms that they can effectively remove copper, zinc and nickel salts; reverse osmosis is also effective in removing arsenic, lead and other metals. As for nitrates, reverse osmosis is also effective.
Along with the exceptional advantages, there are also disadvantages of reverse osmosis. It does retain sodium, potassium, magnesium and calcium, which are good for humans. However, water is not the main source of these minerals and they are successfully assimilated from foodstuffs. In order to saturate it with calcium and magnesium there are special mineralizers, which release exactly those minerals necessary for our organism into water.
In general, if you summarize the relationship between osmosis and heavy metals, it is one of the most common methods of cleaning wastewater from heavy metals in industry, in the domestic environment alternatives to this technology today simply do not.
Chlorine and reverse osmosis
To put it simply, reverse osmosis membranes do not like chlorine, and chlorine does not like them. It can destroy the structure of a thin polyamide membrane fabric and significantly reduce the service life of the membrane element, but it can also successfully bypass the membrane. But it’s not that simple. Above we briefly reviewed the structure of the reverse osmosis system – precisely in order to remove chlorine and organic substances (which we will talk about above) in front of a membrane set one or two cartridges with activated carbon. And organic substances, which even with pre-treatment accumulate on the membrane surface after some time of operation and actively oxidize, do not give it any chance at all to pass through the membrane.
Does Reverse Osmosis Remove Organic Compounds?
There are natural organic substances in water from surface sources. Chlorine oxidizes them, and as a consequence, toxic organochlorine compounds are formed. In addition to natural organic compounds in the water may contain a variety of chemical pollutants, in particular phenolics: pesticides washed off from the fields, industrial effluents, etc. The danger of organochlorine in the first place is that it is a proven carcinogen when water is drunk for long periods of time, even in low concentrations.
Activated carbon together with the reverse osmosis membrane can effectively remove this group of contaminants as well. The positive effects of removing organic substances, pesticides, etc., have been repeatedly shown.
If you still have any questions about the effectiveness of reverse osmosis – ask them in the comments.