|Ask The Expert: Industrial/Domestic Water Treatment
|Question: I would like to know ways of treating water -- both industrial and domestic -- for purposes of course research (school)!
Answer: There are many ways to treat water depending on the intended purpose, whether it's for potable (drinking) uses or commercial uses (cleaning produce in a grocery, a car wash, pool, restaurant or resort, hospital, clinic, nursing home, etc. -- and these last few could include potable) or industrial uses (for making electronics/semiconductors, power/nuclear plants, mining, recycling loops to reuse water or other factory uses). There are a myriad of uses that can fall under each of these categories. Even municipal water (which can include potable and wastewater) is treated to different levels depending upon whether you're going to drink it or use it to water golf courses and park lawns or send it back into a riverbed or lake.
For drinking water purposes, you want to make sure you have proper disinfection and filtration of water. In addition, coagulation (using a substance that collects particles in water and then drops to the bottom and/or is then filtered) and biological treatment (using natural or artificial organic growth in a water to consume contaminants) are two ways municipalities use to treat water. A disinfectant, chlorine, which first began to be used by cities in the United States in 1908, is credited as being the single most important health achievement of the 20th century, having virtually eliminated instances of typhoid and cholera in this country. The particular market segment of the overall water treatment industry that WC&P deals with is the point-of-use/point-of-entry (POU/POE) market, in other words primarily residential water. In the home, you use water for drinking, cooking, making ice cubes, washing dishes, doing laundry, taking baths or showers, cleaning the car, watering your plants, trees or lawn, for pets and maybe a few more purposes. Not all of these need to be as "pure" as the water you drink.
You may already be getting treated water if you live in a city. Or you may be using water drawn from a well on your property or in your neighborhood. If the first is the case, there are times that the city has problems in delivering treated water to you that could cause the quality to drop to varying degrees, sometimes dangerously. At such times, the city will issue a "boil water alert" to you, since boiling is the earliest form of water treatment. If you're on well water, you likely will need to treat the water to make sure any contaminants that are in the water or that get in the water as a result of it being drawn out of the ground, or aquifer far below the surface.
The first method of treatment is filtration, which can include cartridges or beds of sediment, spiral or other wound, bag or composite fibers, or carbon. More sophisticated filtration involves a process of ion exchange where certain basic components of things like calcium and magnesium which cause scale are removed and exchanged for sodium to remove them from water. Reverse osmosis is a form of filtration that uses pressure across a flow of water to pull contaminants from water using membranes as the "sieve," although the actual method is a much more complicated process.
Ozone oxidation/disinfection is a form of water treatment that uses an electric charge to create ozone (O3) from oxygen (O2) to disinfect water or make contaminants precipitate out from it. This is not the ozone you hear about related to pollution, but rather the same substance that you can smell after a lightning strike or when a copy machine has run for some time. It's beneficial because it's stronger than chlorine and the ozone quickly reverts back to oxygen after a few seconds and has few negative disinfection by-products (DBPs) that could be harmful. This however can be a drawback as well because there's little to prevent recontamination of the water as its being delivered via sometimes miles of pipes. That's why at least some chlorine or other chemical is required as a 'residual' disinfectant.
Ultraviolet light, or UV, uses certain wavelengths of light to disinfect water by inactivating contaminants through irradiation. This doesn't mean radiation but rather a reaction between certain contaminants and light that makes it inhospitable for the contaminants, to say the least. But UV suffers from the same problem as ozone in that it leaves no residual disinfectant to prevent recontamination. Both also require a reliable source of electrical power. Other treatment methods include distillation (a more sophisticated form of boiling) and aeration, which involves exposing water through a spraying or atomizing process to air to allow contaminants to react with oxygen in air to precipitate or oxidize them out into the air (this may require some form of air filtration as well to deal with problems such as radon, which is a naturally occurring radioactive substance).
All of these are different manners of treating water. Some are better for different intended purposes of the water or depending on the particular quality of the water to be treated. Generally, no single one is perfect in that it will completely "purify" your water and, oftentimes, using a combination of them is the best way to ensure you have the highest quality drinking water (or water for other uses) possible. There is much more that could be said, as there are volumes of books on the topic and whole courses of study in colleges, but I hope this helps with your report.
PS: For more information, you can contact the US Environmental Protection Agency at its Safe Drinking Water Hotline: (800) 426-4791; or at its website: www.epa.gov/safewater
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