Water Treatment Systems Filtration (II)

 

Neutralizing filters are typically used for pH modification, or treating acidic water. A neutralizing filter is normally a pressure filter tank filled with limestone chips. As the water passes through the filter bed, calcium carbonate is dissolved into the water and the water pH is increased, reducing its acidity.

Reverse Osmosis or "R.O." filtration systems for home water treatment are relatively new, although the process has been used extensively for industrial processes. Reverse osmosis treatment decreases dissolved minerals in the water. It successfully treats water with high salt content, and dissolved minerals such as nitrate, sulfate, calcium, magnesium, potassium, manganese, aluminum, fluoride, silica, boron and bicarbonate. R.O. is also effective with some taste, color and odor-producing chemicals, certain organic contaminants, and specific pesticides.

Although the R.O. membrane is capable of rejecting virtually all microorganisms, it can develop pinholes or tears that allow bacteria or other microorganisms to pass into the treated water. So R.O. is recommended only for bacteriologically safe water.

Household R.O. systems typically treat 3 to 5 gallons of water per day. However, some can treat between 1 to 9 gallons. R.O. systems range in cost between $100 and $850. The wide range reflects differences in capacity and design. The simplest home R.O. system consists of a membrane filter connected to the faucet spout. Most popular is a membrane, a storage container for the treated water, and a flow regulator for the reject water. The pressure for R.O. is usually supplied by the line pressure of the water system in the home. A sediment prefilter and activated carbon prefilter or postfilter might be included. The prefilter removes sand, silt and sediments, while the activated carbon removes the organic materials and dissolved gases not treated by the R.O. membrane. Water softeners are used in advance of the R.O. system when household water is excessively hard.

Water Softening or Ion Exchange

Water softening to condition hard water is perhaps the most familiar water conditioning system known to consumers. Hard water is caused by calcium and magnesium that are dissolved in the water. This causes scale to form in hot water pipes and water heaters. It interferes with the cleaning action of soaps and detergents, and forms a film on skin, clothing and fixtures. Hardness is measured either as milligrams per liter or parts per million. However, it is normally expressed in grains of hardness per gallon of water.

Softeners also will remove small amounts of iron and manganese if they are in a soluble or ferrous form.

The most common way to soften water is the cation-exchange water softener. A synthetic resin with a strong attraction for calcium, magnesium and other positively charged metal atoms called "cations" is saturated with sodium from a salt solution. As water passes through the resin, the sodium exchanges with the calcium and magnesium. Eventually, so much hardness collects on the resin that the unit can no longer soften the water and recharging is necessary. Then, the softening material is backwashed with a brine solution to replace the sodium and enable the ion exchange process to continue.