A Division of Arctic Refrigeration and Merchandise Inc.

312 S. Santa Fe Ave. Pueblo, Colorado. 81003 719-545-1800 Order line 1-800-360-2660

Email: water@arctic-1.com 

Various Drinking Water Treatment Methods


There are a number of other drinking water treatment methods used to improve the quality of
drinking water other than the Doulton ceramic filters. The following is a summary of some of the
more popular of those methods:

Activated Carbon 

Three forms activated carbon are used in the treatment of drinking water.

Granulated Activated Carbon
Activated carbon surfaces are both hydrophobic (water hating) and oleophilic (oil
loving); that is, they "hate" water but "love" oil. When flow conditions are suitable,
dissolved organics in water flowing over the carbon surface "stick" to the carbon in a
thin film while the water passes on. This process is call adsorption. All activated
carbon, including granulated activated carbon (GAC), has a tremendous surface area
resulting from its porous structure.

As a result of the adsorption process, GAC filters are an effective method of
removing volatile organic carbon compounds (insecticides and/or pesticides) from
drinking water. Uniform, appropriate, flow rate is critical to effective removal of
these organic compounds. If flow rate is excessive the residence time is not sufficient
for the GAC to remove organic compounds.

While some solid particulate may be removed by GAC filters, normally they are not
designed for this purpose. Since GAC filters are not cleanable, water supplies with
high solids and/or turbidity can significantly reduce the useful life of GAC filters.

GAC, under quite normal operating conditions, can and do become breeding
grounds for bacteria, including pathogenic bacteria. Therefore, steps should be taken
to remove any pathogenic bacteria ahead of GAC filtration.

Purchase and installation costs are normally relatively low. Filter element replacement
frequency is relatively high.

In most cases, prefiltration, including a ceramic filter element, will improve the
effectiveness of the GAC filter.

Carbon Block
Carbon block (CB) filters are an effective method of removing volatile organic
carbon compounds (insecticides and/or pesticides) from drinking water.

As with GAC, uniform, appropriate, flow rate is critical to effective removal of these
organic compounds. Though CB may impose a higher pressure drop than GAC, it
will not form "channels" under the flow pressures normally found in domestic water
systems ... which can happen with GAC. When channels form in GAC, supply water
can pass through without adequate contact with the carbon surfaces to act on the
dissolved organics. Since CB is solid, it cannot "channel."

Solid particulate is removed by CB filters, however, normally they are not designed
for this purpose. Since CB filters are not cleanable, water supplies with high solids
and/or turbidity can significantly reduce the useful life of CB filters.

CB, under quite normal operating conditions, can and do become breeding grounds
for bacteria, including pathogenic bacteria. Therefore, steps should be taken to
remove any pathogenic bacteria ahead of CB filtration. CB filters generally have a
significantly higher pressure drop than GAC filters. Purchase and installation costs
are relatively low. Filter element replacement frequency is relatively high.

In most cases, prefiltration, including a ceramic filter element, will improve the
effectiveness of the CB filter.

Powdered Activated Carbon
Powdered activated carbon (PAC) filters are an effective method of removing
volatile organic carbon compounds (insecticides and/or pesticides) from drinking
water. As with GAC and CB, uniform, appropriate flow rate is critical to effective
removal of these organic compounds.

While solid particulate are removed by PAC filters, normally they are not designed
for this purpose. Since PAC filters are not cleanable, water supplies with high so
turbidity can significantly reduce the useful life of PAC filters.

PAC, under quite normal operating conditions, can and does become breeding
grounds for bacteria, including pathogenic bacteria. Therefore, steps should be taken
to remove any pathogenic bacteria ahead of PAC filtration. Purchase and installation
costs are relatively low. Filter element replacement frequency is relatively high.

In most cases, prefiltration, including a ceramic filter element, will improve the
effectiveness of the PAC filter. 

Boiling 

Boiling water is an effective method of treating drinking water because no important
waterborne diseases are caused by heat resisting organisms. Boiling water for 1520
minutes in an open container will disinfect the water.' it also drives off any volatile
organic compounds.

The disadvantages of boiling are that it wastes water (driven off as steam) and
requires energy. 

Bromination 

Bromine is an oxidizing agent that has been used quite successfully to disinfect
swimming pool water. However, it is not normally used to treat drinking water. 

Chlorination 

Chlorination is used extensively by municipal water treatment plants to disinfect
water. However, the gaseous chlorine used by these plants is much too dangerous
for home use.

Household bleach (a 5.25% solution of sodium hypochlorite which is equivalent to
5% available chlorine) can be used for disinfecting drinking water. Calcium
hypochlorite granules (with about 70% available chlorine) are also available but are
not very convenient to use. When chlorine is fed into water, it first reacts with any
iron, manganese, or hydrogen sulfide that may be in the water. If any residual
(unreacted) chlorine remains, after reacting with these minerals, it will next react with
any organic material (including bacteria) present.

The rate of feed of the sodium hypochlorite solution is normally adjusted to make
sure that sufficient chlorine is available to fully react with the organics present. When
both the mineral and organic reactions have been completed, any residual chlorine
remains in the drinking water. Many people find the taste of water with residual
chlorine to be objectionable.

Chlorination kills many pathogenic bacteria (including those which cause typhoid,
cholera and dysentery). However, cyst forming protozoa which cause amoebic
dysentery, and giardiasis are resistant to chlorination.

Home chlorination systems are costly to purchase, operate, and maintain. When
properly adjusted to deal effectively with pathogenic bacteria, they leave a taste and
odor in the water that many people find objectionable. Contact time and temperature
are critical; high flow rates and/or low temperatures reduce the effectiveness of
chlorination. Supply water with high pH values may require excessive contact time or
solution concentrations. Chlorine can react with organic compounds to form
trihalomethane compounds which are known carcinogens. 

Distillation 

Distillation is usually an effective method of preparing safe drinking water. However,
carry overs of volatile organic compounds (herbicides and/or pesticides) may be an
issue since they may be evaporated and re-condensed with the water.

I Distillation is not normally 'water efficient' and waste water rejected by the system
may be significant. Distillation also requires external energy sources; energy costs
must be considered. Purchase and installation costs can be significant.

In most cases, pre-filtration, including a ceramic filter element, will improve the
effectiveness of a distillation system by improving the quality of supply water (which
reduces the waste water rejected from the system). 

Iodination 

Iodination may be used for emergency treatment of drinking water. Tests show that a
20 exposure to 8.0 ppm of iodine is usually adequate to render water potable ... free
from pathogenic bacteria and many viruses. Not enough is yet known about the
physiological effects of iodinated water on the human system; however, it is known
that high levels of iodine are toxic to humans. For this reason, the use of iodine for
drinking water treatment should be considered only for emergency situations. 

Ion Exchange 

Ion exchange (IEX) systems, such as water softening systems, are effective in the
removal of dissolved minerals from the supply water. Waste water rejected by the
system and energy costs for operation must be considered when selecting IEX
systems. Salt is necessary for regenerating the ion exchange beds. Salt and salt
handling costs must be considered. Purchase and installation costs can be significant.

The ion exchange resin in IEX systems may become fouled if the supply water
contains significant quantities of suspended particulate or volatile organic compounds.
In most cases, pre-filtration, including a ceramic filter element, will improve the
effectiveness of a ion exchange system by improving the quality of supply water,
which reduces the possibility of any fouling of the ion exchange resin. 

Ozone systems 

Ozone is a disinfecting agent that can be used in drinking water applications. Because
ozone is so active (chemically) it is not possible to maintain an ozone residual in
water. Therefore, the most widely used method to produce ozone is electrical
(corona) discharge in air or oxygen. Once the ozone is produced, it must be
distributed throughout the water to disinfect it. Ozone treatment is generally effective
in dealing with pathogenic bacteria and cysts. It does not remove heavy metals,
volatile organic chemicals, or chlorine. Ozone systems require external energy
sources; energy costs must be considered. Purchase and installation costs can be
significant. 

Reverse Osmosis 

Reverse osmosis (RO) is a membrane filtration process separating dissolved salts
from a water stream. In RO, not only are insoluble particles retained by the
membrane but also molecules and ions in solution. Concentration of ions near the
membrane sets up 'polarization' phenomena which results in an increase in the
osmotic pressure of the solution to be treated ... sometimes followed by
precipitation. The continuing flow of input water flushes the membrane which
removes the ion concentrations and/or precipitates. By subjecting the membrane to
pressures on the order of 30 800 p.s.i., 'pure' water is forced through the membrane.

RO is often used to produce fresh water from salt and/or brackish water. In some
cases, it is used to concentrate waste.

RO operation requires relatively high pressure on the inlet side to the membrane.
External energy, for the pressure pump, is required. Energy costs must be considered
when selecting RO as the treatment method. RO systems are not normally 'water
efficient' and waste water rejected by the system may be significant. Purchase and
installation costs can be significant.

In all cases, prefiltration, including a ceramic filter element, will extend the usefid life
of the RO membrane. 

Sediment filters 

Sediment filters are suitable for the removal of dense and/or large particulate matter
and, in some cases, reduction of turbidity. Pleated paper or spun plastic fiber are
typical examples of sediment filters. They are not satisfactory performers in the
removal of pathogenic bacteria or cysts, heavy metals, pesticides, or insecticides.
They cannot be cleaned. These units are usually quite low in cost but filter element
replacement frequency is quite high.

In some applications, sediment filters may be used as a prefilter, ahead of a ceramic
filter, to reduce cleaning frequency for the ceramic filter. 

Ultraviolet 

Ultraviolet systems (UV) expose supply water to intense ultraviolet light which kill
pathogenic bacteria (cholera, typhoid, salmonella dysenteriae, etc.) and may remove
some pathogenic cysts.

The power rating for a UV lamp may be as high as 200 watts. The wavelength of the
UV light is normally in the 200300 nm (2,000 3,000 Angstrom units) range. The
most efficient microbicidal action is about 250 rim. Water must flow very close to the
light source, in a thin layer, and at a uniform, appropriate, flow rate to assure that
bacteria are destroyed.

Since any suspended particles (or turbidity) in the water could "shade" bacteria from
the direct rays from the UV source, "live" bacteria could pass through the system.
For this reason, all UV systems have pre-filtration, often including a ceramic filter
element, to assure the effectiveness of the UV system.

UV, by itself, does not remove any particulate matter or turbidity. It does not remove
volatile organic compounds such as pesticides or insecticides. External energy is
required for operation; energy costs must be considered when selecting UV as the
treatment method. Purchase, installation, operating and maintenance costs should be
considered before selecting UV as a drinking water treatment system.