 |
 |
|
|
|
1-800-743-6621 / In Savannah, GA 912-356-9001 |
 |
|
 |
 |
 |
 |
|
 |
Every year over 500 billion pounds of hazardous chemical wastes are improperly disposed of, 85 percent of the time directly above aquifers. 100 billion gallons of these hazardous wastes are then absorbed into groundwater supplies. Of the 700 chemicals already found in drinking water, most water companies test for less than 30. Not to mention natural and organic hazards and toxins, that clear, odorless, tasteless glass of water on your table may not be as safe as you presume. Glossary of Terms and Contaminants Aesthetics: Otherwise harmless contaminants like chlorine, sulfur, iron, and manganese that cause taste, color, and odor problems. Water Hardness: Hard water contains excessive levels of the minerals calcium and magnesium, a condition found in 85 percent of the United States. Hard water shortens the life of household plumbing and water-using appliances, makes cleaning and laundering tasks more difficult and gradually decreases the efficiency of water heaters. Lead: Used extensively in plumbing materials (pipes and lead-based solder) until the late 1980's, lead can leach into water supplies. Low levels of lead have been linked to learning disabilities in young children, and high levels can cause hypertension in adults. Biological Pathogens: Waterborne organisms that can cause disease in humans. They include cysts like Cryptosporidium and Giardia; bacteria like typhus, fecal coliform and cholera; and viruses like influenza. These organisms typically cause unpleasant intestinal disorders and can pose a significant threat to the immune-impaired. Nitrates: Nitrogen compounds are sometimes found in ground and surface water in rural areas, often as a result of nitrogen-based fertilizer runoff. Excess nitrate levels can interfere with the oxygen-carrying capacity of blood, especially in babies, and have been linked to high incidences of miscarriages. Heavy Metals: Metals like mercury, zinc, copper, and cadmium usually enter the water supply as industrial waste and, in excessive concentrations, can cause physiological damage to humans, including damage to the central nervous system. Radium/Radon: Naturally occurring radioactive elements linked to cancer in humans. Radon is found in gaseous form, and is absorbed through drinking, as well as through inhalation during washing or showering. VOCs: Volatile organic compounds, such as the petroleum distillate benzene and the industrial degreasing compound trichloroethylene. High concentrations of VOCs are linked to organ damage and cancer in humans. THMs: Trihalomethanes are by-products produced when chlorine reacts with organic compounds in water. THM's are primarily absorbed through inhalation, and have been linked to bladder and rectal cancer. Asbestos: A fibrous mineral that contaminates water naturally or through its past use in concrete water pipes. Asbestos has been linked to lung and other forms of cancer. Arsenic: Both a natural and manufacturing-induced ground water contaminant, arsenic is linked to various cancers and may damage the circulatory and central nervous systems. Sediments: Solid particulates in water that can settle out over time. The presence of sediments in water is typically an aesthetic concern. Low/High pH: pH refers to "potential hydrogen," and is a measure of acidity or alkalinity on a 14-point scale (zero through six is acidic; seven is neutral; and eight through 14 are alkaline). Extreme measures of acidity in water can be corrosive, whereas high alkalinity can be the source of aesthetic problems.
The most common water quality problem reported by consumers throughout the U.S. is hard water. A U.S. Geological Survey indicates that hard water is found in more than 85 percent of the country. So then, what makes water hard, and what can consumers do to treat this problem? Hard Water For example, if a water test indicates a range of 1.0 to 3.5 gpg, the water is considered slightly hard. If the measurement is greater than 10.5 gpg, the water is rated as being very hard. Hard water can be detected easily, even as one performs personal hygiene such as hair washing, or through the appearance of fixtures and appliances or changes in heating costs.
In areas where the water is hard or very hard, the local water utility may soften the water to about 5 or 6 gpg. This figure is still considered moderately hard, and consumers may still wish to soften the water further. The most common option for consumers is ion exchange water softening in the home. Domestic softening makes economic sense because it only softens the water to be used for laundering, cleaning, and other home uses. Softening at the central treatment facility is costly because it softens all water, including that which is used for fighting fires and cleaning streets. Water Softening Three main parts make up most water softeners:
Many installed water softeners are fully automatic. An automatic unit regenerates according to a preset clock. For example, it might be set to regenerate every third night at 3am. Other systems may use an electronic sensor that regenerates the system according to water usage. Size and Type Considerations There are several factors that a person must take into consideration before purchasing a softener, including the number of people in the home, how much water is used, and the hardness of the water. Determining the size of the softener, knowing these factors, is rather simple. Multiply 75 (average gallons per day used per person) by the number of people in your household. For example, four people in a household will likely use 300 gallons of water per day. Multiply the 300 gallons per day by the number of grains per gallon of hardness present in your water. Continuing the example, 300 gallons per day times 20 gpg gives a figure of 6000 grains of hardness per day that would require removal. Given a typical regeneration capacity of 18.000 to 30,000 grains per regeneration, a softening system in this case would optimally be regenerated every three to five days. The Sodium Issue Further, according to Dr. Andrew Zeifer, Director of the Hypertension Clinic at the University of Michigan, "Drinking water represents a very small part of sodium intake in most persons. Even water softening systems using salt don't introduce enough salt to be of concern." Similar view were expressed in the New England Journal of Medicine, and by the U.S. Environmental Protection Agency. If consumers do not want to add any additional sodium to their diet, or if they are on a medically prescribed diet, they may choose to connect their water softener to the hot water line only, thus leaving consumers able to drink and cook with unsoftened cold water. Another option would be to install a reverse osmosis or distillation system, and have the full benefits of both technologies in their home. Benefits of Softened Water
A final tip: Look for the WQA Gold Seal on home water treatment systems. This recognizable symbol gives the consumer the assurance that the equipment has been tested against industry standards, and successfully passed these tests, and has been validated for performance capabilities. This article first appeared in the Water Review Technical Brief, (1990) Volume 5, No. 1; a publication of the Water Quality Research Council. Copyright 1990, 1995 by the WQA. All rights reserved.
Anyone who has been through a high school science class will likely be familiar with the term osmosis. The process was first described by a French Scientist in 1748, who noted that water spontaneously diffused through a pig bladder membrane into alcohol. Over 200 years later, a modification of this process known as reverse osmosis allows people throughout the world to affordably convert undesirable water into water that is virtually free of health or aesthetic contaminants. Reverse osmosis systems can be found providing treated water from the kitchen counter in a private residence to installations used in manned spacecraft. Reverse Osmosis is a technology that is found virtually anywhere pure water is needed; common uses include:
How Reverse Osmosis Works A semi permeable membrane, like the membrane of a cell wall or a bladder, is selective about what it allows to pass through, and what it prevents from passing. These membranes in general pass water very easily because of its small molecular size; but also prevent many other contaminants from passing by trapping them. Water will typically be present on both sides of the membrane, with each side having a different concentration of dissolved minerals. Since the water I the less concentrated solution seeks to dilute the more concentrated solution, water will pass through the membrane from the lower concentration side to the greater concentration side. Eventually, osmotic pressure (seen in the diagram below as the pressure created by the difference in water levels) will counter the diffusion process exactly, and an equilibrium will form. The process of reverse osmosis forces water with a greater concentration of contaminants (the source water) into a tank containing water with an extremely low concentration of contaminants (the processed water). High water pressure on the source side is used to "reverse" the natural osmotic process, with the semi-permeable membrane still permitting the passage of water while rejecting most of the other contaminants. The specific process through which this occurs is called ion exclusion, in which a concentration of ions at the membrane surface from a barrier that allows other water molecules to pass through while excluding other substances. Semi permeable membranes have come a long way from the natural pig bladders used in the earlier osmosis experiments. Before the 1960's, these membranes were too inefficient, expensive, and unreliable for practical applications outside the laboratory. Modern advances in synthetic materials have generally solved these problems, allowing membranes to become highly efficient at rejecting contaminants, and making them tough enough to withstand the greater pressures necessary for efficient operation. Even with these advances, the "reject" water on the source side of a Reverse Osmosis (RO) system must be periodically flushed in order to keep it from becoming so concentrated that it forms a scale on the membrane itself. RO systems also typically require a carbon prefilter for the reduction of chlorine, which can damage an RO membrane; and a sediment prefilter is always required to ensure that fine suspended materials in the source water do not permanently clog the membrane. Hardness reduction, either through the use of water softening for residential units or chemical softening for industrial use, may also be desirable in hard water areas. Low Pressure (Residential) Systems Low pressure RO systems generally refer to those systems with a water feed pressure of less than 100 psig. These are the typical countertop or under sink residential systems that rely primarily on the natural water pressure to make the reverse osmosis process function; a typical system is shown schematically below. Countertop units typically have an unpressurized storage tank; Under sink units typically have a pressurized accumulator storage tank where the water pressure tends to increase as the tank fills. This pressurized system provides sufficient pressure to move the water from the under sink storage tank to the faucet. Unfortunately, this also creates a back pressure against the membrane, which can decrease its efficiency. Some units overcome this by using unpressurized tanks with a pump to get the treated water where it is needed. Low pressure units typically provide between 2 and 15 gallons per day of water, with an efficiency of 2-4 gallons of reject water per gallon of treated water. Water purity can be as high as 95 percent. These systems can be highly affordable, with countertop units starting at about US $150, and under sink units starting at about US $500. These units produce water for a cost as low as ten cents per gallon once maintenance and water costs are factored in. Maintenance usually requires replacing any pre- or postfilters (typically one to four times per year); and the reverse osmosis cartridge once every two to three years, depending on usage. Look for the WQA Gold Seal (S-300) to find products that have been successfully tested to industry performance standards; and to Certified Water Specialists (CWS I-VI), Certified Sales Representatives (CSR), and Certified Installers (CI) for advice on your water needs, and equipment installation. High Pressure (Commercial/Industrial) Systems High pressure systems typically operate at pressures between 100 and 1000 psig, depending on the membranes chosen and the water being treated. These systems are usually used in industrial or commercial applications where large volumes of treated water are required at a high level of purity. Most commercial and industrial systems use multiple membranes arranged in parallel to provide the required quantity of water. The processed water from the first stage of treatment can then be passed through additional membrane modules to achieve greater levels of treatment for the finished water. The reject water can also be directed into successive membrane modules for greater efficiency (see diagram below), though flushing will still be required when concentrations reach a level where fouling is likely to occur. High pressure industrial units typically provide from 10 gallons to thousands of gallons per day of water with an efficiency of 1-9 gallons of reject water per gallon of treated water. Water purity can be as high as 95 percent. These systems tend to be larger and more complicated than low pressure systems, and this is reflected in their costs, which range from US $1000 through tens of thousands of dollars for a large, multi-module unit capable of providing desalinated drinking water for a resort facility or water bottling plant. What Reverse Osmosis Treats Reverse osmosis can treat for a wide variety of health and aesthetic contaminants. Effectively designed, RO equipment can treat for a wide variety of aesthetic contaminants that cause unpleasant taste, color, and odor problems like a salty or soda taste caused by chlorides or sulfates. RO can also be effective for treating health contaminants like arsenic, asbestos, atrazine (herbicides/pesticides). fluoride, lead, mercury, nitrate, and radium. When using appropriate carbon prefiltering (commonly included with most RO systems), additional treatment can also be provided for such "volatile" contaminants as benzene, trichloroethylene, trihalomethanes, and radon. Some RO equipment is also capable of treating for biological contaminants like Cryptosporidium. The Water Quality Association (WQA) cautions, however, that while RO membranes typically remove virtually all known microorganisms and most other health contaminants, design considerations may prevent a unit from offering foolproof protection when incorporated into a consumer drinking water system. When looking for a product to treat for a given health contaminant, care should be used to find products that have been tested successfully for such purposes at a quality testing laboratory. Conclusion Reverse osmosis is a relatively new, but very effective, application of an established scientific process. Whether it is used to meet the needs of a typical family of four, or the needs of an industrial operation requiring thousands of gallons per day, it can be a cost effective to provide the required quantity of highly treated water. With continual advances in system and membrane design that boost efficiency and reliability, RO can be expected to play a major role in water treatment for years to come. This article first appeared in the Water Review Technical Brief, (1995) Volume 10, No. 3; a publication of the Water Quality Research Council; Copyright 1995 by the WQA. All rights reserved.
|
 |
|
 |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 |
 |
|
