For piping systems fed by water from a private well, one of the most common causes of corrosion is low pH. A low pH is water with a pH of less than 7.0 pH. Signs of acid water are corrosion of fixtures, pinhole leaks, blue staining (from copper pipes) or rust staining (from iron pipes).
Common causes for acidic water are acid rainfall due to atmospheric carbon dioxide and other airborne pollutants, runoff from mining spoils, and decomposition of plant materials. Acidic waters can be high quality and are typically low in buffering calcium minerals, but are high in dissolved carbon-dioxide gas, which can cause the low pH or acidity.
Treatment is accomplished by neutralizing the water with the use of an automatic calcite neutralizer. These water filter tanks are filled with a blend of calcium and magnesium carbonates made from naturally occurring minerals, which dissolve into the water, making it less corrosive. Calcite is a white granular mineral that adds calcium to the water raising the pH and increasing the alkalinity. Periodically, (once or twice a year for a typical residential application) more mineral is added to the filter tank.
In some cases, instead of dissolved carbon dioxide causing the low pH or acidity, the acidity is caused by mineral acids, either natural or from mining or other industrial wastes. Often the pH is very low, less than 5.0. Treating this type of water requires injection of soda ash or sodium hydroxide with a metering pump, and generally, the neutralizing type mineral filters described above will not work well on this type of water.
o Calcite neutralizers raise pH, hardness and alkalinity by adding calcium and magnesium to the water.
o Soda ash feeders raise pH and increase alkalinity but not hardness. Soda ash is sodium carbonate so soda ash feeders do increase the sodium content of the water.
One of the most convenient methods to raise pH, hardness and alkalinity is to use a calcite neutralizer filter. These filters will typically raise the pH of the water to 7.0 to 8.0 and add 30 to 100 ppm of hardness depending on the alkalinity and water hardness.
In neutralizer filters, acidic waters slowly dissolve the calcium and magnesium media on contact as the water flows through the filter, raising the pH of the water and increasing the alkalinity. This eliminates the effects of corrosive water chemistries and can help to prevent corrosion of piping and fixtures.
The size of the system is directly proportional to the flow rate of the water, in gallons per minute. The higher the flow rate, the larger the system required.
Soda Ash Feeders
Metering pumps are used to inject a small amount of soda ash (sodium carbonate) into the water, usually in conjunction with a contact tank. For best results, allow 10 minutes contact with the water for pH adjustment to occur.
For home wells, when the metering pumps are wired to turn on and start pumping soda ash solution, when the well pump is energized or running.
Soda ash is bought dry, usually in 25 or 50 lb bags and mixed with soft or pure water in the solution tank. When a saturated solution is achieved (approximately 1 pound per 5 gallons of water), a solution of between 50 and 500 ppm are injected, depending on the pH, alkalinity and flow rate of the water.
Follow-up Testing for Quality Assurance
The pH should be checked on-site and the metering pump adjusted after the system is installed and running. Routine weekly or monthly testing of the pH is recommended to make sure the treated water has the desired pH level.
If the piping in the home is copper it is also important to test for copper residuals to verify that the corrosion is slowing down or has stopped. A simple copper test, done on the water that is first drawn out of the tap will show if there is a copper residual still in the water, indicating corrosion. Over a period of six to twelve months the copper residual levels will slowly decrease in most cases, after the water has been treated.
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