PH Neutralization FAQ
Low pH: Acid Water Conditions
The most common regions for acid water conditions in the United States are New England and in the Northwest in the states of Oregon, Washington, and along the Eastern Seaboard in the Carolinas, Georgia, Virginia, Delaware, southern New Jersey, Maryland and Tennessee. In Canada, the Maritime Provinces and the western part of British Columbia are noted for acid water conditions.
Acid surface water and acid well waters may be found in many areas in the United States and Canada and are usually very low in hardness as well as total dissolved solids. The chief influence on low pH values in water is the presence of carbon dioxide (CO2) and the lack of sufficient offsetting bicarbonate alkalinity. Surface water, lakes, reservoirs, and streams pick up C02 from the atmosphere. Well water can absorb C02 created by decaying vegetation. Carbon dioxide will combine with water to form carbonic acid (C03) which is classified as a weak acid.
The relative amount of carbon dioxide present in the water supply as carbonic acid the water more neutral. By taking a sample and accurately testing the pH value of the water, you can determine whether the water is acid and aggressive in nature, tending to corrode brass, copper, steel piping, and fixtures in the home, on the farm, or in the place of business. Acid water also can attack and dissolve several heavy metals – cadmium, zinc, and lead. The EPA action level for lead of 15 ppb (0.015 mg/L) in drinking water, has focused much more attention on undesirable low-pH municipal and private well water sources.
How does the pH scale work?
While highly alkaline waters can corrode the "white metals," the most common reason for water treatment is to prevent or eliminate corrosion of metal surfaces caused by low ph water. The aggressive tendency in many low-solids surface waters is partially caused by low pH values of these waters. The acidity of water is measured by the relative concentration of positive hydrogen ions and the negative hydroxyl ions. pH value contains equal concentrations of hydrogen ions and hydroxyl ions; when the pH is below 7.0, there are fewer hydroxyl than hydrogen ions. A water with 5.0 pH value is 10 times more acidic than one of a pH of 6.0, and a solution of pH 4.0 is 100 times as acidic as one of 6.0 pH value. This vast increment difference occurs because the pH scale is logarithmic rather than arithmetical. Again, a 5.0 pH value is 100 times more acid than the neutral 7.0 pH.
Calcite and Corosex Media for pH Modification
Calcite (the technical mineral reference for natural crystal-like calcium carbonate and the essential major ingredient in limestone, chalk, and marble. For water treatment, various high-grade limestone and marble products are crushed and screened to create a loose filter-type medium. The use of calcite in correcting low-pH water is akin to the gardening practice of spreading pulverized limestone on acid soil. The hard composition and irregular granular shape of the calcite carbonate particles expose a lot of surface area as well as forming various void pockets for suspended solids for and turbidity entrapment in the bed. The calcite product in neutralization application adds some calcium hardness to the water being processed. Therefore, calcite neutralization treatment should be applied ahead of water softening.
Calcium hardness is added to the treated water through pH modification. A typical hardness increase of almost 100 percent can be expected. As a rule of thumb, an increase of three to five grains of hardness can be expected to raise the pH by one point on the scale-for example, from 6.0 pH to 7.0 pH value.
Granular calcite (either southern marble or northern limestone) medium may be used both as a filter media for silt, turbidity and ferric iron and as a sacrificial calcium carbonate pH correction bed. Generally, a calcite medium filter will remove approximately one-third of the total ferric and ferrous iron content of a water supply.
Two sources of pH neutralization medias that are widely used and available in common U.S. mesh size for neutralizing filter medium beds are Calcite and Corosex. Calcite is actually consumed in this pH modification method and, thus, the bed must be inspected periodically and calcite added to bring the bed back up to its original depth. Also, as the granules of calcite are slowly dissolved, they become finer, and the backwashing of the bed will eliminate the finest of these particles, thus preventing considerable pressure loss.
The rate of solubility of calcite is dependent on several factors. In relatively mineral-free water, the average rate is 0.001 percent (approximately one-tenth of an ounce of calcite per gallon of water) at 77°F (25°C), but solubility increases in the presence of C02. Calcite solubility is also increased by falling temperatures and rising total pressure. At the same time, an advantage of calcite is that it will not "overcorrect" for pH. This calcite technique will raise the pH evenly under proper operating conditions.
The backwash rate is very important with this highly dense mineral and should done at a minimum of 8.0 U.S. gpm per square foot of bed area for good performance. If iron is present, a minimum of 10 U.S. gpm should be used. Backwashing should be carried out for no less than 10 minutes to remove dirt, iron precipitates, and calcite fines. For iron-bearing water with low pH, a backwash time of 15 to 20 minute flow rates that are inadequate to sufficiently expand, cleanse, and regrade the calcite regular schedule. Perhaps the most common cause of neutralizer failures is improper or lack of backwash.
Corosex is mineral-based product used to raise low· pH water is magnesia (magnesium oxide, or MgO). Magnesia, which has been used for years as an antacid therapy for indigestion (Milk of Magnesia), can likewise be an effective acid-water neutralizer. Under the trade name of Corosex , the bead form is available in standard 10-40 U.S. mesh and granular in 8-16 U.S. mesh. Like Calcite, hardness will be added to the treated water. Magnesium oxide dissolves at a faster rate than natural calcite, which makes the product valuable when used with calcite. It has become very effective to use a mixture of calcite and corosex with a calcite/corosex ratio of 3: 1. This will extend the life of the neutralizing media bed to its maximum potential and reduce frequency of replacement.