It's ironic that many areas of the world face critical shortages of drinking water on a planet whose surface is 3/4 covered with water. Most of the water, of course, is seawater, which is far too saline for human consumption. And of the little 'fresh' water that remains, most is trapped in polar ice caps where it is difficult to harness for use by the world's population.
Much of the natural supply of potable water that is accessible faces stress from a growing world population, which increases the basic demand for this natural resource, while reducing the supply further through biological and industrial contamination.
Major population centres in developing nations without established waste treatment or water treatment infrastructures often suffer from epidemics of waterborne disease. In these areas, raw sewage often directly contaminates the rivers and streams used for drinking, washing, and cooking. In other cases, unchecked industrialization leads to water contamination through improperly disposed-of chemical and nuclear wastes.
Some good news about this problem is that individuals can take control of their own water quality, and treat their water for nearly all biological and chemical contaminants that may be encountered. These technologies also treat for 'aesthetic' contaminants that cause portable water to have unpleasant tastes, colours, and odours.
Point of Use (POU) and Point of Entry (POE) water treatment equipment can effectively treat the water used by a small community, home, or business.
POU equipment treats the water that is used at a single tap, while the rest of the water in the building remains untreated. POU equipment is primarily used to treat health contaminants like lead, and aesthetic contaminants like sulphur. These contaminants are a concern in water used for drinking and cooking.
POE equipment treats most or all of the water before it is distributed, either throughout a small community or at a single building. POE equipment treats for health contaminants like volatile organic compounds (VOC's) that can be absorbed through the skin, or contaminants like radon which exist as a harmful vapour suspended in the water that can be inhaled during showering. POE is also used to describe water softening, which inhibits scale formation in plumbing while increasing the efficiency and longevity of water-related appliances like water heaters.
There are many effective technologies used to provide POU/POE treatment solutions and no single technology is effective for treating all of the possible contaminants. A specific technology or combination of technologies is usually applied to treat the specific problem at hand.
It should be noted that different levels of performance can be found between products using each technology. If a product is to be used to treat a health contaminant, it is important that the specific product is tested successfully for the reduction of that contaminant. Offered below is a brief description of the main technologies, and what they are typically used to treat.
Activated alumina is a filter media made by treating aluminium more so that it becomes porous and highly adsorptive. Activated alumina will remove a variety of contaminants, including excessive fluoride, arsenic and selenium. The medium requires periodic cleaning with an appropriate regenerate such as alum or acid in order to remain effective.
Activated Carbon (Granular and Solid Block)
Granular activated carbon is a well-established technology for the reduction of a wide range of aesthetic contaminants and is quite effective in the reduction of some health contaminants such as volatile organic compounds (benzene, trichloroethylene, and other 'petroleum'-based contaminants).
Because of its molecular makeup, activated carbon can absorb well, meaning that it can take in or collect many organic molecules on its surface. Granular activated carbon filters are typically inexpensive and maintenance involves replacing six to twelve cartridges a year, depending on the quality of the raw water and the filter media.
Specially designed solid block and precoat activated carbon filters are also available, which are effective at reducing heavy metals such as lead and mercury. Solid block filters with a pore size smaller than 0.2 microns are often effective against biological contaminants as well.
Anion and Cation Exchange
Anion exchange and cation exchange use the chemical ion exchange process to exchange anions and cations on a 'resin' bed for cations and anions of the contaminant that needs to be removed from the water. For example, in cation exchange, a cation of hardness mineral such as calcium is exchanged for two cations of sodium, effectively removing most of the calcium, and softening the water.
The anions or cations on the resin are eventually exhausted, and replaced by the anions or cations of the contaminant being removed. When this occurs, the bed must be backwashed using a concentrated solution of the base cation or anion, which recharges the bed and flushes the built-up contaminant.
Anion exchange typically uses chloride or hydroxide anions, and can be used to treat for mercury, nitrates, arsenic, and various staining agents. Cation exchange typically uses sodium or potassium chloride and can also treat for some forms of lead and radium. It is also commonly used to soften water.
Disinfection technologies kill or screen-out biological contaminants present in a water supply. Chlorination, microfiltration, ozone and ultraviolet light are the four major technologies used to disinfect water.
Chlorine is typically fed directly into a well, or into a retention tank where concentration and contact time can be controlled. Chlorination is effective for treating pathogens like coliform bacteria and legionella, though it is ineffective against hard-shelled cysts like Cryptosporidium and Giardia lamblia. Other chemicals like bromine and iodine can also be used to disinfect water through much the same process as chlorination, though they are not as frequently used.
Carbon block media usually has to be disposed of after each use. This media, however, provides additional treatment for a variety of other health and aesthetic contaminants (see activated carbon section above). Microfiltration is effective for treating the full range of biological contaminants, including hard-shelled cysts like Cryptosporidium.
Ozone treatment oxidizes organic contaminants in much the same way that chlorine does. An ozone generator converts the oxygen found in air to O3, or ozone. As with chlorination, proper concentrations and contact time is essential for disinfection. Ozone usually requires the use of retention tank to accomplish this, and can be used to provide partial treatment in pools. Ozone is effective for treating pathogens like coliform bacteria and legionella, but it is not effective against hard-shelled cysts like Cryptosporidium or Giardia lamblia without using high contact times and concentrations.
Distillation produces high quality, treated water by heating the raw water until it turns to steam. The steam travels tough a condensation coil, where it is cooled and condensed back into liquid form in a separate section. Typically, the contaminants present when the water is converted to steam remain in the boiler section, with the condensed water in the second section being substantially free of contaminants. Maintenance of a distillation unit usually involves cleaning out the built-up contaminants on the boiler side of the unit.
Distillation typically provides a high degree of effectiveness against a broad range of health contaminants. Distillation is typically not effective for treating contaminants such as benzene and radon, which give off harmful vapours that can move through the system with the steam. The energy requirement of distillation and a relatively long production time typically limits its use to POU drinking water applications in home and commercial markets. Some distillation units are also tested and approved for the reduction of biological pathogens.
Reverse osmosis (RO) is a common treatment technology that produces high quality water. The process works by forcing water under great pressure against a semi permeable membrane, where ion exclusion occurs. With ion exclusion, water molecules form a barrier that allows other water molecules to pass through while excluding most contaminants.
Typical contaminant rejection rates range from 85% to 95%, and a gallon of highly treated water can usually be produced from two to four gallons of raw water, depending on the initial quality of the water. Maintenance involves the replacement of the RO membrane cartridge every one to two years, and the carbon filter cartridges two to three times per year.
RO is effective for the reduction of a broad range of health and aesthetic contaminants, though it is typically not used for the reduction of biological pathogens. RO also incorporates an activated carbon filter, which can provide added treatment for the volatile organic compounds (VOC's) not treated by the membrane itself.
It should be remembered that this brief description of water treatment technologies is only intended to provide an overview of how each technology can be applied to solve a water contamination problem. The advice of a WQA Certified Water Professional of Certified Sales Representative should be sought when looking for a specific treatment solution.
With a knowledgeable application of these effective POU/POE technologies, you can take the quality of your water into your own hands.
This article first appeared in the WaterReview Technical Brief.