| Understanding
Water Treatment Systems
It's not hard to understand water
treatment systems, they generally fall into one or a combination
of these five basic categories:
Disinfection
Disinfection methods
kill most of the harmful bacteria, viruses, cysts and worms
found in water that can cause acute illness. Disinfection
methods include chlorination, pasteurization, ultraviolet
light and boiling
Chlorination
The most common, oldest
and relatively inexpensive method used to disinfect water
is chlorination. A chemical feed pump continuously dispenses
chlorine chemicals into the water supply. Chlorine, an oxidizing
agent, kills most bacteria and some viruses. In the proper
concentrations and under adequate exposure time, chlorine
is an excellent disinfectant.
However, care must be
taken to ensure that only clean, clear water is used. Chlorine
reacts with certain metals and organic matter in the water.
The major problem with chlorination is the potential formation
of hazardous, chlorinated, organic chemicals (trihalomethanes)
when the chlorine reacts with organic molecules in the
water supply. Using an activated carbon filter after
chlorination will remove excess chlorine and limited amounts
of chlorinated chemicals formed. Chlorination may also oxidize
and remove some color and odor-causing substances including
some iron and hydrogen sulfide.
Contaminants Removed:
Bacteria, Iron, Hydrogen Sulfide, Some Viruses
Pasteurization
With pasteurization,
water is heated to kill bacteria, viruses, cysts and worms.
The limited efficiency of the heat exchange makes pasteurization
expensive. Pasteurization does not leave behind a residual
product which continues to disinfect beyond the immediate
treatment period.
Contaminants Removed:
Bacteria, Viruses, Cysts, Worms.
Ultraviolet
radiation (UV)
Low-pressure mercury
arc lamps produce ultraviolet light, which has germicidal
properties. The radiation kills or deactivates pathogens.
Bacteria are killed with relatively low amounts of radiation,
viruses are more resistant, and cysts and worms are unaffected.
Ultraviolet (UV) Water
Filters UV Filters are able to kill the majority of bacteria
and viruses in the water which passes through them. However,
they won't remove chemical pollutants from the water. Also
you should note that the treatment is ineffective outside
of the treatment area, so water should be used immediately
after it is treated.
The lamp's efficiency
decreases with age and must be replaced annually. Colour,
turbidity and organic impurities in the water also interfere
with transmission of ultraviolet energy and may reduce efficiency
to unsafe levels. Also, radiation leaves no residual product
that continues to disinfect beyond the treatment period.
Contaminants Removed:
Bacteria, Viruses.
Boiling
Boiling water for three
minutes kills bacteria, including disease-causing organisms
and giardia cysts. However, boiling concentrates inorganic
impurities such as nitrate and sulfates. Boiled water also
tastes flat because the carbon dioxide is removed.
Filtration
Filter systems are a
relatively simple and effective way to control a variety of
contaminants. These include mechanical filters, activated
carbon filters, oxidizing filters and neutralizing filters.
Filtration systems are designed for use only on potable (not
portable) water. This means that your water supply
should be clean, uncontaminated and suitable for drinking.
Mechanical filters (microfiltration)
Mechanical filters remove
suspended material from water, including sand, silt, clay
and organic matter. They do not remove dissolved or very fine
particles and are often used in combination with other treatment
equipment. Filters are commonly of fabric, fibre, ceramic
or other screening material. Mechanical filters can be cartridge
units, mounted in a single waterline or on a tap, or tank
units, which treat an entire household water supply. The filters
must be serviced periodically. Remember, these filters do
not purify or soften water--they only remove some suspended
particles and dissolved organic compounds that cause disagreeable
odors and tastes.
Contaminants Removed:
Sediment
Activated carbon filters
Activated carbon filters
absorb impurities as they pass through a carbon cartridge.
Generally, they are used to eliminate undesirable odours and
tastes, organic compounds and to remove residual chlorine.
Most inorganic chemicals, metals, micro organisms and nitrates
are not removed by the filters.
Carbon filters also
remove some potentially hazardous contaminants such as radon
gas, many dissolved organic chemicals and trihalomethanes.
If low levels of these contaminants exist, a whole-house unit
can be used. However, these filters are not designed to remove
persistently high levels of these contaminants. When contamination
cannot be eliminated, an alternative water supply may be the
safest solution.
The carbon filter loses
its effectiveness as it becomes saturated with contaminants
and must be replaced on a regular basis. Using the filter
longer than its rated lifetime may cause contaminants to be
flushed into the drinking water.
The material in an activated
carbon filter provides a growth surface for certain bacteria.
If the filter has not been used for five or more days, simply
run chlorinated water through the filter for at least 30 seconds
before use.
Activated Carbon Filtration
is an established technology that works through absorption
of the problematic compounds, primarily to remove taste and
odour but systems will also remove some harmful contamanents.
AC is a highly porous material with a very large surface area.
Chemical pollutants are attracted to and held by the AC's
surface. These water filters are best suited for the removal
of organic compounds.
Contaminants Removed:
Hydrogen Sulfide, Radon, Chlorine, Volatile Organic Compounds,
Pesticides, Benzene, Colors, Odors.
Oxidizing filters
Oxidizing filters remove
iron, manganese and hydrogen sulfide (rotten egg odour). A
manganese zeolite-coated filter causes dissolved iron and
manganese to form particles the filter then traps. These filters
are useful in removing iron if a water softener is not wanted.
The filter usually treats the entire household water supply.
Periodically, the filter must be rinsed with a chemical solution
to remove the accumulated iron and manganese.
Contaminants Removed:
Hydrogen Sulfide, Iron, Manganese.
Neutralizing filters
Neutralizing filters
treat acidic water. The filter treats all of the home water
supply by passing it through limestone chips or other neutralizing
agent. Where acidic water does occur, it can leach lead, copper
or other toxic metals from household pipes into the water
supply.
Two potential problems
occur with the filter. First, it may increase water hardness.
Secondly, acidic water may intensify any iron problems already
present in the water supply. The filter requires little maintenance
except the need to occasionally replace the limestone chips.
Contaminants Removed:
Acidity
Reverse
osmosis
Reverse osmosis pressurises
and passes impure water through a semi-permeable membrane
and removes many of the impurities including fluoride
and approximately 90 percent free of mineral and biological
contaminants. The quality of the membrane and the pressure
of the water help determine how effectively the water separates
the contaminants.
Reverse osmosis (RO)
units remove substantial amounts of most inorganic chemicals
(such as salts, metals and minerals), most micro organisms
and many organic chemicals. They do not effectively remove
some organic compounds such as nitrate; they will reduce levels
somewhat.
Mechanical filters and
activated carbon filters are most always used with an RO unit.
First, the mechanical filter removes dirt, sediment and other
impurities that clog the reverse osmosis membrane. The RO
unit is installed next. An activated carbon filter then removes
some organic compounds which pass through the RO unit. Nitrates,
however, will pass through carbon filters.
Contaminants Removed:
Lead, Sulfate, Calcium, Magnesium, Sodium, Potassium, Manganese,
Aluminum, Chloride, Nitrate, Fluoride, Boron, Most
Microorganisms, Organic Chemicals.
Distillation
Distillation heats water
until it vaporizes as steam. Minerals, bacteria and other
substances are left behind when the steam recondenses into
relatively pure water. Distillers remove bacteria, minerals,
trace amounts of metals, many organic chemicals and nitrate.
Some stills allow contaminants with boiling points lower than
water (some pesticides and volatile solvents) to vaporize
with the water and recondense with the distilled water. A
vented distiller avoids this problem. Distillers also remove
beneficial minerals and make water taste flat or bland.
The distillation process
is very slow. Approximately five litres of tap water
are required to produce one litre of distilled water. Stills
are relatively expensive. They require frequent cleaning and
may be difficult to keep clean. The maintenance requirements
and electricity consumption should be major considerations
when purchasing a distiller.The major drawback to this method
is that it requires a large amount of energy.
Contaminants Removed:
Bacteria, Lead, Nitrate, Sodium Chloride, Organic Chemicals,
Many Pesticides
Ion exchange
(water softeners)
A common problem of
water supplies is hardness, mainly caused by excess calcium
and magnesium. Ion exchange systems soften hard water by removing
the minerals causing hardness. These hardness minerals may
interfere with the cleaning action of soaps and detergents
and cause scale build up in hot water pipes, water heaters
and fixtures. The system also effectively removes some iron,
manganese and many heavy metals.
The hard water is pumped
through a tank containing an exchange resin. Sodium on the
exchange resin replaces the hardness minerals. The sodium
remains in soluble form in the softened water. Persons with
heart problems should discuss this issue with a physician
who will need to know the sodium level in the existing household
supply of softened water.
To function properly,
the resin tank must be periodically flushed (or recharged)
with a solution of sodium chloride (salt). Some softeners
automatically recharge the tank either on a regular schedule
or when an electronic sensor detects that the resin needs
to be recharged. With automatic recharge you only need to
keep the sodium storage container filled. Other softeners
must be recharged manually and are usually serviced by water
treatment companies.
Contaminants Removed:
Iron, Magnesium, Calcium, Manganese.
See our Terms
& Germs for explanations on contaminants.
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