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.

Original at: http://www.survivalunlimited.com/waterfilters/treatment.htm