Nitrates are very soluble and do not bind to soils, therefore, they have a high potential to migrate to groundwater sources. When these ground waters are purposed for potable drinking water sources, the presence of nitrates can pose serious health risks, especially for infants and pregnant women. Likewise, proper treatment of nitrate-containing wastewaters from industrial processes requires treatment prior to discharge to groundwater sources and/or for reuse.
Ion exchange provides effective nitrate removal
Nitrates have no detectable color, taste or smell at the concentrations involved in drinking water supplies, and can occur both naturally and from man-made sources. Because they do not evaporate, nitrates/nitrites are likely to remain in water until consumed by plants or other organisms. Nitrate contamination originates mainly from agricultural operations including farm runoff and fertilizer usage, septic system failure and improper discharge of industrial and food processing waste and wastewater. Since they are very soluble and do not bind to soils, nitrates have a high potential to migrate to ground water. The primary inorganic nitrates which may contaminate drinking water are potassium nitrate and ammonium nitrate both of which are widely used as fertilizers.
Nitrates can occur in water sources at a level that does not generally cause health problems. The concentration level and length of exposure, however, can cause illness and death. In infants, serious illness is due to the conversion of nitrates by bacteria in the stomach to toxic nitrites. This can interfere with the oxygen-carrying capacity of the child's blood and can cause an acute condition in which health deteriorates rapidly over a period of days. Symptoms include shortness of breath and methemoglobinemia, a condition known as "blue baby" syndrome.
The US Environmental Protection Agency (EPA) has set a Maximum Contaminant Level Goal (MGL) for nitrates at 10 parts per million (ppm), and for nitrites at 1 ppm, because EPA believes this level of protection would not cause any of the potential health problems described above.
The EPA approved treatment methods for removing nitrates/nitrites in waters destined for drinking purposes includes Ion Exchange and Reverse Osmosis.
Ion exchange is the most frequently used treatment technology for nitrate removal. This technology removes nitrate ions from the aqueous phase by replacing them with the anion present in the ion exchange resin. As contaminated water is passed through the resin, contaminant ions are exchanged for other ions, most often chlorides in the resin. The advantages of ion exchange are simple operation; the process is independent of temperature, can be automated, and is essentially unaffected by varying nitrate concentrations.
Reverse Osmosis provides effective nitrate removal
Nitrate removal by reverse osmosis uses a semi-permeable membrane to selectively remove various inorganics within the water. Pressure is applied to the water to force it through the membrane. As the water passes through the membrane and effectively leaves the impurities behind. Membranes do not exhibit high selectivity for any given contaminant, and therefore, the RO process results in the removal of many contaminants, including nitrates. Estimates predict that from 85 to 95 percent of the nitrate can be removed with reverse osmosis. Actual removal rates may vary, depending on the initial quality of the water, the system pressure, and water temperature.