Treatment facility employees are often asked, “What does reverse osmosis do?” particularly by groups of students on their annual field trip. I remember asking, “What is reverse osmosis, anyway?” But, the answer was somewhat confusing.
Conservation was one of my favorite classes. The professor, Mr. Elston was one of my favorite teachers and usually he could handle any question that we threw out. But, when asked, what does reverse osmosis do, he faltered, just a little.
It really all depends on the application for which it is being used or it’s intended purpose. It is one step used in drinking water purification and wastewater treatment. It is used in kidney dialysis machines. It is used by the food industry, car washes, maple syrup and hydrogen production, by reef aquariums and for desalination.
So, I asked, “what is reverse osmosis”, because that answer applies to all of the system’s uses. Simply put, there is something unwanted in the liquid that needs to be removed and the system is used to take it out.
Osmosis is the natural process that allows roots and sponges to absorb water, as well as other naturally occurring processes in animals and plants. So attempting a joke, my teacher answered, “what is reverse osmosis”, with, “it’s the opposite of osmosis.” No one laughed.
So, in order to clarify the question, you might ask, “What does reverse osmosis do for water?” That’s a little easier to answer. Depending on the size of the pores in the membrane, it may be used to remove rocks, dirt, minerals and many other contaminants.
If you are concerned about contaminants that are not removed by your treatment facility, the answer to “what does reverse osmosis do for water” is different. Those traces are in the parts per million or parts per billion. While RO membranes may be able to remove many things, the pores cannot be small enough to neutralize those trace contaminants.
Treatment facilities use RO to try to make the public as safe as possible, but they also have to disinfect and they typically use chemicals, such as chlorine or chloramines to accomplish that task. RO will not remove bacteria, parasites, protozoa and other microscopic life. In fact those things build up on the membranes, along with algae growth, so chemical disinfectants must be used to control them.
Like many of you, my tap water contains too much chlorine. Up to 3.8 parts at times, which is just under the EPA standards and .8 higher than what you can safely swim in. What is reverse osmosis supposed to do about the chlorine? The answer is nothing.