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Turbidity, Color, Odour & Taste
Mechanical filters are specifically designed for the removal of solid particles from the water, and are available in several different types and sizes. These filters simply act as fine screens, which trap solid particles but allow the water to pass through.
One type of filter uses specially graded sand or other granular synthetic material as the filter media, in tanks with the same range of sizes as household water softeners. These filters are capable of filtering substantial flow rates, and usually are used to filter the entire household water supply. They will work very well when the suspended particles are relatively large or gelatinous in nature, but are not effective in some cases where the turbidity is due to extremely fine particles. These must be backwashed periodically to clean the beds and to flush the accumulated matter down a drain.
A second type of mechanical filter is the so-called "cartridge" filter. These units are usually smaller than the tank type filters, and are often installed to treat the water in a single line. Instead of the loose media in the tank type filters, these filters use media which is formed or shaped into more or less rigid cartridges. Although some of the cartridges are designed for mechanical cleaning and reuse, most are designed for replacement when they become clogged with accumulated solids.
These filter cartridges are available in several ratings based on the sizes of particles to be removed, and are capable of removing particles down to extremely tiny sizes. However, the cartridges with extremely small filtering pores have higher resistance to water flow, and can become clogged quite rapidly if high concentrations of large particles are present in the water.
Activated carbon is a unique material known for its ability to absorb soluble organic compounds and certain gases, such as chlorine and hydrogen sulfide, all of which may contribute tastes and odors to a water supply. Thus activated carbon filters are widely used in water treatment, both in the form of granular tank-type filters, and as finely divided powders incorporated into cartridges. The granular filters must be backwashed periodically, and the cartridges cleaned or replaced from time to time.
If the water to be treated with granular activated carbon contains a high concentration of organic matter or hydrogen sulfide, the carbon ultimately becomes saturated and can adsorb no more of these impurities. Some success has been reported in treating the beds with high dosages of household hypochlorite bleach to "burn off" the absorbed impurities, and extend the life of the bed. However, in time it usually becomes necessary to replace the activated carbon bed.
If the activated carbon is used for the removal of chlorine, some of the carbon is actually consumed in the process. In such cases, small amounts of carbon must be added to the bed to replace that which is lost.
Chemical feed pumps may also be used in some and odor cases in the treatment of color, taste and problems. A feed of an excess of chlorine, usually in the form of household hypochlorite bleach solution, is capable of oxidizing many of the impurities.
A relatively new process, called "reverse osmosis," has been developed in recent years. In this process, the water to be treated is forced against a semi-permeable membrane. This membrane allows some of the water but few of the impurities, including dissolved materials, to pass through. A small amount of the water containing the rejected impurities flows to waste. Thus one flow of water enters the unit, and two streams come out; one a stream of water with most of the impurities removed, and a second containing the concentrated impurities.
Unfortunately, large equipment of this type is relatively expensive, and thus it is not generally feasible to use it to treat all of the water in a home. However, small units which treat only the water to be used for cooking and drinking are available for household use. These units operate continuously, and contain a reservoir for the treated water. To avoid clogging of the membrane in the reverse osmosis unit, filtration of the water to the unit is often recommended. However, no regeneration or backwashing is required, and the membranes do have extended lives.