This article, written by the American Ground Water Trust was originally published in THE AMERICAN WELL OWNER, 2002, Number 4]
SOLUTIONS TO NITRATE PROBLEMS
Nitrogen is important to all life. Nitrogen is most commonly found as a colorless, odorless and tasteless gas that makes up about 78 percent of the earth’s atmosphere. Nitrogen also exists in the environment in many other forms and changes forms as it moves through the nitrogen cycle. It can be combined into living and non-living material, and then eventually returns back to the soil or air in a continuing cycle. Although nitrogen is an essential component of protein in our bodies, excessive concentrations of nitrate- nitrogen in drinking water can be hazardous to health, for infants and pregnant women.
The main source of nitrogen in soils is from plant and animal residues. When changed into nitrate, a nitrogen/oxygen ion (NO3-) by bacteria in the soil it becomes an important plant food. Farmers also add nitrate to the soil as fertilizer. However, nitrate is highly leachable and if there is excessive rainfall, over- irrigation or over application of fertilizers (as manure or chemical) nitrate will be leached below the plant- root zone and may reach groundwater.
The principal health concern occurs when bacteria in the digestive system transforms nitrate to nitrite. The nitrite oxidizes iron in the hemoglobin of red blood cells to form methemoglobin, which lacks the oxygen-carrying ability of hemoglobin. The transformation of nitrate to nitrite is more likely to occur when the pH level in the digestive tract is high (low acidity), allowing bacteria levels to rise.
This condition is known as methemoglobinemia, sometimes referred to as "blue baby syndrome" because in infants under six months of age, the digestive system has an underdeveloped capability to secrete gastric acid, and the bacteria count in the digestive system may rise. The condition may also be of concern for anyone with a gastrointestinal condition producing high pH or an impaired enzyme system for metabolizing methemoglobin back to hemoglobin.
The United States Environmental Protection agency has determined that levels of nitrate in drinking water should not exceed 10 parts per million (ppm or milligrams per liter). Treatment methods commonly available to homeowners to reduce nitrate levels in drinking water, including distillation, anion exchange and reverse osmosis.
Distillation is one of the oldest methods of water treatment, though not commonly used today as a home treatment method. Distillation units or stills generally consist of a boiling chamber, where the water enters, is heated and vaporized; condensing coils or chamber, where the water is cooled and converted back to liquid water; and a storage tank for purified water.
Inorganic compounds such as nitrate, other large non-volatile organic molecules and compounds with boiling points greater than 100°C (212°F) do not evaporate with the water and are left behind. Compounds that have a boiling point temperature less than water will NOT be removed by a simple distillation treatment because they will vaporize before the water and then recondense in the collection tank along with the purified water.
The process is only capable of producing a small volume (5 to 15 gallons) of water per day from a typical residential installation. Because the units have low production volumes they are commonly installed as “point-of-use” (POU) treatments for drinking and cooking purposes only. This is frequently an acceptable and satisfactory remedy for solving a nitrate contamination problem because nitrate is not absorbed through the skin in a significant amount.
Unevaporated residual liquids and solids must be removed from the evaporation area to ensure that the heating elements operate at the lowest demand level for heating energy.
The process is similar to common “water softening” ion-exchange except anions (negatively charged ions) are removed from the raw water rather than cations (positively charged ions) such as calcium or magnesium carbonate. Anion exchange uses chloride anions to remove various anion species including sulfate, sulfite, phosphate, nitrate, nitrite, bicarbonate, fluoride, arsenic and others. The anion exchange
treatment process reduces the pH of the water. A water neutralizing system may be necessary following the exchange unit in order to correct the pH of the water.
Anion exchange systems can be regenerated with strong (brine) solutions of chloride anions. The chloride brines reattach to the resin beads and release the exchanged anions during a backwash process.
The reverse osmosis (RO) process involves filtering the raw water with semipermeable membranes that will allow water molecules to pass but not the molecules of dissolved solids such as nitrate. Pressure is applied to the raw water to accelerate its passage through the membrane. The residual raw water retaining the dissolved solids is released to drain and the RO filtered water is collected in a storage tank until needed for drinking or cooking. Household RO units usually have a pre-filter canister for sediment removal and an activated carbon post-filter for taste and odor removal. RO units are usually capable of producing between 10 to 20 gallons of good quality drinking water per day and are therefore best suited as point-of-use (POU) installations. The treated drinking water is quite corrosive because it is lacking dissolved solids. RO water will leach metals from metal pipes and should be stored in plastic tanks and plumbed with plastic piping (Be sure to upgrade the piping with plastic tubing on any ancillary water use devices in the kitchen such the ice maker).
Nitrate-nitrogen occurs naturally in groundwater, usually at concentrations far below a level of concern for drinking water safety. Nitrate in water is undetectable without testing because it is colorless, odorless, and tasteless. The American Ground Water Trust recommends that new drinking water supplies be tested for nitrate to determine the baseline concentration, especially for households with infants, pregnant women, nursing mothers, or elderly people who are the most susceptible to nitrate. In addition, if the water supply has never been tested for nitrate, it should be tested. Keep a record of the nitrate levels in your well water to monitor the levels from year to year to assess if the concentration is changing up or down. It may take months or years for nitrate from nearby failed septic systems or agricultural uses to reach your well.
[© American Ground Water Trust. This article may be reprinted for non-commercial educational purposes provided it is used in its entirety and that reference is made to its source as an article in THE AMERICAN WELL OWNER, 2002, Number 4]
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