Immediate Delivery
Treating The Water We Drink, When and Where We Drink It.
This article is an overview of common Point-of-Use and Point-of-Entry water treatments, including Activated Alumna; Activated Carbon; Anion and Cat ion Exchange; Disinfection Technologies including Chlorination, Microfiltration, Ozone, and Ultraviolet Light; Distillation, and Reverse Osmosis.
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 centers 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 potable water to have unpleasant tastes, colors, and odors.
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 sulfur. 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 vapor 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
be 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 Alumna
Activated alumna is a filter media made by treating aluminum ore so that it becomes porous and highly
adsorptive. Activated alumna will remove a variety of contaminants, including excessive fluoride, arsenic,
and selenium. The medium requires periodic cleaning with an appropriate regenerant 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 adsorb 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 Cat ion Exchange
Anion exchange and cat ion exchange use the chemical ion exchange process to exchange anions and
cat ions on a “resin” bed for cat ions and anions of the contaminant that needs to be removed from the
water. For example, in cat ion exchange, a cat ion of hardness mineral such as calcium is exchanged for
two cat ions of sodium, effectively removing most of the calcium, and softening the water.
The anions or cat ions on the resin are eventually exhausted, and replaced by the anions or cat ions of the
contaminant being removed. When this occurs, the bed must be backwashed using a concentrated
solution of the base cat ion 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. Cat ion 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
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.
Chlorination
Chlorination adds a concentration of the chemical chlorine or chloramines to the water supply, where the
oxidizing ability of this chemical “burns up” the organic contaminants in the water. Chlorine can
effectively treat biological pathogens like coliform bacteria and legionella, though it is ineffective against
hard-shelled cysts like those produced by Cryptosporidium. Chlorination also treats for
organically-related taste, color, and odor problems.
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 Cryptosoridium 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.
Microfiltration
Microfiltration uses a filter media with a pore size smaller than 0.2 microns to physically prevent
biological contamination from passing through. Ceramic and solid block carbon are commonly used to
provide microfiltration. Ceramic filters have and advantage in that they can often be cleaned and reused a
number of times before they lose effectiveness.
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 . Microfiltration is effective
for treating the full range of biological contaminants, including hard-shelled cysts like Cryptosporidium.
Ozone
Ozone treatment has typically been used in large-scale commercial and industrial applications; however,
there has been a recent growth in the number of ozone units designed for use in a single home or
business application.
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 a 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.
Ultraviolet Light (UV)
Ultraviolet light has treated water since the beginning of time through natural sunlight. Modern ultraviolet
treatment units use a UV bulb in a clear quartz or plexiglass housing, around which flows the untreated
water. The UV light destroys the genetic material of pathogens like colliform bacteria and legionella,
which effectively neutralizes them by preventing them from reproducing. UV is not effective for the
treatment of hard-shelled cysts like Cryptosporidium and Giardia lamblia.
Distillation
Distillation produces high quality, treated water by heating the raw water until it turns to steam. The steam
goes through 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 vapors 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
Reverse osmosis (RO) is a common treatment technology that produces high quality water. The process
works by forcing water under great pressure against a semipermiable 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 two or three years, and the
carbon filter cartridges six to twelve 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; directories of these personnel in your area are available at this
site.
With a knowledgeable application of these effective POU/POE technologies, you can take the quality of
your water into your own hands.