The Water Quality Assn. (WQA), a founding member of the European Drinking Water (EDW...
Brushing up on water treatment 101
How does everyone achieve effluent water that meets their needs and demands? Each situation is different, but a simplistic explanation of various technologies will be discussed in this article. Each of the following categories has had much written about them, but this article will be an overview of several methods in order to help you educate the general public so they can make an intelligent decision, purchase something of value and continually seek professional consultation.
Reiterating a point from the previous article and what should be an emphasis to consumers is that water treatment should be done by respectable and knowledgeable professionals who have experience in dealing with problem waters. Over-the-counter remedies or products at discount stores are not the answer in most cases, since understanding influent water and the technologies used to treat a certain problem or application may not be addressed. Understanding water chemistry and specific applications takes years of experience. There are water treatment companies that don’t get it correct even after many failures because they did not look closely enough at the raw water and, therefore, the desired result of the effluent water was not achieved. Also, often they simply did not understand the application or technologies used. With the amount of possible contaminants that may be present in our water, it can get rather ambiguous and difficult to find answers unless the pollutant can be identified and then the proper treatment can be understood and applied.
The U.S. Environmental Protection Agency has an available list of pollutants and their maximum contaminant levels (MCLs), but when compared to the amount of possible contaminants that could be found in water, this list is not exactly complete. Every year more contaminants are added and others come under scrutiny for tighter controls and lowered levels of acceptance (e.g., MTBE and arsenic). Water quality seems to be in the limelight more and more as we go into the future and governing agencies are taking notice of what has happened to our most precious and life-sustaining resource. With water being polluted, how do we change our lifestyles to keep it fresh and pure and reduce the environmental effects that have caused the problems? Businesses, industries and residences rely on this resource for survival for life, production, manufacturing and conveniences of modern-day living.
Whether the influent water is taken from a lake, river, stream, well or ocean, it must be treated in some form. Municipalities must make sure that water is bacterial free, colorless, odorless and noncorrosive, in addition to being plentiful and affordable. Homeowners, either must use city water or well water, and then are left to deal with the water that is available. This also is true for businesses and manufacturing firms. So, how does everyone achieve effluent water that meets their needs and demands? Each situation is different, but a simplistic explanation of various technologies will be discussed in this article. Each of the following categories has had much written about them, but this article will be an overview of several methods in order to help you educate the general public so they can make an intelligent decision, purchase something of value and continually seek professional consultation.
Water softeners have been an excellent, effective answer for water treatment for years. With the technologies and synthetic resin materials developed over the years, these systems have become less expensive and easier to understand. Hardness, which is caused by calcium and magnesium, has been a constant problem for most of the world and has been handled quite well by the use of cation exchange softener media and sodium regeneration. Even low levels of iron and manganese have been removed with these systems, in addition to low levels of hydrogen sulfide.
There are many resin media to select from, and each can be applied to specific water problems. There are cation and anion exchange media and many manufacturers that produce an array of products for water treatment. A dealer would need to consult his suppliers in order to obtain information for a specific need.
For the most part, softeners work very well in most applications, but certain industries require the water to be free from the sodium or potassium ion used in regeneration. This is when the understanding of other technologies comes into play.
Reverse osmosis (RO) water is quite popular and is used in a variety of commercial and industrial applications, research centers and residences. When applied properly after a high-quality pretreatment, RO systems last for years and give the end user very high quality water. The problem that arises with RO is the fact that if it is not installed with a pretreatment, the membranes become fouled so the filters need to be changed frequently, thus reducing the quality of the water and life of the filter. This can create a maintenance headache for the user.
There are two types of membranes available and each varies in the type and amount of contaminants it removes. There are thin film composite (TFC) and cellulose triacetate (CTA) membranes that are used in this process. The TFC membrane removes a higher percent of the contaminant than does the CTA membrane. However, the TFC reacts with chlorinated water and the membranes break down faster, so a pretreatment for chlorine is necessary. Removing iron, manganese and sulfur prior to RO systems also is recommended so the membranes do not become fouled and shorten the life and water quality the RO system was employed to achieve. Too many times water is treated without pretreatment and the RO system fails prematurely or does not work at all because the influent water and application were never considered.
RO water is very aggressive and can cause problems by leaching minerals from the pipes and faucets into which they are installed, thus requiring stainless steel or plastic pipe to be used. This must be considered when designing water treatment using RO. Another drawback of using RO is the wastewater, since approximately 75 percent of each gallon is lost and dumped down the drain. There are many brands and manufacturers of RO systems and they should be contacted for technical information before commissioning an RO system.
Ultraviolet (UV) light and RO are both proven and effective means of removing bacteria and viruses from water. RO does this by not allowing the viruses or bacteria from passing through the membrane, whereas UV light prevents microorganisms from reproducing. These methods of treatment do not put anything into the water, while providing a 99.99 percent inactivation rate of bacteria and viruses. An article written by Tom Schaefer of Aquionics in a previous issue of Water Quality Products entitled, “Ultraviolet for Disinfection1” (available in the online article archives at www.waterinfocenter.com), explains this alternative of disinfection very well. One of the disadvantages of using UV light is making sure the quartz sleeve stays clean and the water being disinfected is free from turbidity. If this sleeve gets scaled, the UV light cannot penetrate the water and effective treatment will not be achieved.
Causes of scale are hardness, turbidity or a variety of contaminants from the associated water source. In many cases, pretreatment of the water before a UV light application is recommended. Fruit and vegetable washes and ornamental fishponds tend to have trouble with effective treatment because of this issue.
Filtration is another way of dealing with problem waters. A dealer should know that a soluble cannot be filtered effectively and must be altered into an insoluble. Ferrous iron is an example of a soluble that when oxidized becomes ferric iron, which is insoluble and can be filtered. Ferrous iron is found in well water and is colorless until it oxidizes and then even at low levels (.3 ppm) will cause staining and other problems. Iron and manganese-related bacteria can cause a rotten egg smell and bio slimes. Although not harmful, they cause problems with plumbing fixtures and water heaters, in addition to being associated with an annoying smell.
There are numerous media or multimedia that can be used when removing iron, manganese and hydrogen sulfide. Greensand has long been a favorite and acceptable medium for removing iron and manganese. A method of oxidation is used with this type of filter to get the contaminant to flocculate and precipitate from a soluble into an insoluble to become filterable. Generally, these media, much like the softener media, need to be regenerated. The use of chemicals such as potassium permanganate or chlorine is involved during this process.
There are many types of media that can be used when designing a system for multimedia use, and each application is different. Consulting your supplier would be the best advice for choosing the correct media to achieve a particular result. Identifying the contaminant is the first thing that needs to be considered. A dealer must keep in mind that a certain smell such as rotten eggs does not always imply that the problem may be hydrogen sulfide or sulfur. Iron, manganese and tannins also can give this same symptom, but each would require a different treatment. This is just another reason why consumers should consult a professional who can test the water for such contaminants. Filtration gets rather involved because there are so many possibilities with applications, contaminants and types of filtration. This section merely brushes over a few basic concepts in order to help explain the most common problems in water treatment.
Next month the last of this series of articles will explain a little about ozonation, ionization, distillation and aeration. Many books have been written on water treatment and there has been much development of equipment to treat water. (Visit the SGC Bookstore at www.waterinfocenter.com for some available publications.) New technologies and applications constantly are being tested and studied to remedy problems associated with water quality. This series of articles just scratches the surface of what a seasoned professional should offer his clients for proper water treatment.
The final installment of this series will appear in the July issue.