Removing Nitrate by Ion Exchange
Removal is Essential for Excess Nitrate
Five Nitrate Removal Methods
Understanding the Different Nitrate Units
Nitrate is a common contaminant in water supplies, and
especially prevalent in surface water supplies and shallow wells.
However, it can be found in any water source.
Nitrate contamination of drinking water is generally a manmade problem. Fertilizer is the largest contributor to nitrate pollution. Some sources say that poorly managed crops may only utilize 10% of the nitrate that is actually spread on the field. The runoff from these fields ends up in surface water sources. Nitrate can also percolate down through the soil and end up in the drinking water aquifers. Other sources of nitrate pollution are sewage treatment plants, septic systems, feed lots and industrial waste, both gas and liquid.
Water Technology, Volume 23, Number 11, November 2000, "Removing Nitrate by Ion Exchange"
Mike Keller is marketing specialist, domestic water services, for Sybron Chemicals, Inc. in Birmingham, N.J.
1) Margaret McCasland, et al, “Nitrate: Health effects in Drinking Water,” Natural Resources Cornell cooperative Extension, Cornell University, pmep.cce.cornell.edu/facts-slides-self/facts/nit-heef-grw85.html
2) Stan Ziarkowski, “Nitrate Removal by Ion Exchange” Internal Paper at Sybron Chemicals, Inc.
Nitrate is a simple ion that can occur naturally in mineral deposits or as a major end-product of biological degradation. All living things contain nitrogen in their proteins and DNZ, and microbes in soild and water tend to convert nitrogen compounds into nitrate, which is the preferred nitrogen source for plants. All living things and their waste products will produce nitrate as they decompose. You can expect to find elevate nitrate levels in agrigultural regions, areas of high population (human or animal) where there is poorly treated or untreated sewage, and in industrial areas where metals, munitions, paper and other products are manufactured.
A very stable ion
Nitrate is extremely soluble in water. It is also very stable -- it tends to remain as nitrate, rarely combining with other compounds to become more benign. It does not bind to soil particles, as many water contaminants do. This means it will move around with groundwater, you may find a sudden nitrate problem miles away from a potential source, or years after a farm or factory is gone.
The term "nitrates" is often used when talking about nitrate. Nitrates refers to combined nitrate and nitrite. Nitrite (NO2) is a very reactive ion and rarely lasts long -- it will quickly react with other chemicals, or become nitrate or ammonia. Most nitrate detection methods actually measure combined nitrate and nitrite. Nitrate (NO3) is colorless, odorless, and tasteless. Because it is so unreactive, it is not removed from water by standard water treatment dquipments such as carbon filters or softeners.
Nitrate and health
When humans (and most animals) take up nitrate in food or water, most of it is quickly eliminated from the body through the urine. Nitrate does not accumulate in body fat, as most herbicieds and psticides can do. It is not irritating to the skin or to mucous membranes. However, if there is a constant intake of nitrate -- as might be the case if drinking water contains high nitrate levels -- there wil always be some nitrate present in the body, and this is when health problems may occur.
Consumption of excess nitrate can cause "blue baby syndrome," or methemoglobinemia, in infants by interering with the ability of the blood to carry oxygen. Infants never should be given water containing more than the US Environmental Protection Agency (EPA) maximuym contaminant limit of 10 parts per milion (ppm) nitrate-N (as nitrogen). Long-term consumption of excess nitrate may increase the risk for cancer of the stomach and bladder, and non-Hodgkin's lymphoma. High nitrate levels may increase the chance for miscarriage, childhood asthma, and even juvenile diabetes. The elderly and those with reduced stomach acidity (such as people taking antacids) may also have problems with reduced oxygen in the blood. Livestock and pets are also affected by high nitrate levels in water.
Because of the nitrate's adverse effects on human health, the EPA has set the MCL for nitrate at 10ppm nitrate-N (45 ppm nitrate, or 0.71 millimolar nitrate) under the Clean Water Act and the Safe Drinking Water Act. Nitrate is a primary contaminant, meaning that all potable water in public supplies must be tested at least yearly for nitrate. Nitrate is also monitored in groundwater by state and federal agencies. Background nitrate levels rarely exceed 2 ppm nitrate-N.
The problem of drought
Because nitrate is unreactive and water-soluble, it will remain in a well or aquifer unles it is flushed out by water containing lower nitrate levels. Crought -- where the same quantity of nitrate is present, but in less water -- can dramatically increase the nitrate concentration of a water source. Water that had been safe might, under drought conditions, exceed the EPA safe drinking water limit.
Conversely, sudden increases in groundwater following flooding or excessive rain can also cause nitrate levels to rise in wells by flushing nitrate into a new area from a contaminated site. Large areas of the US are under drought conditions in the summers. If your business is locate in an agricultrual region and drought conditions are present, new nitrate problems will start to show up.
Testing and removal
There are many methods for testing water for nitrate, from test strips to sending samples to a certified testing lab. Test methods vary widely in accuracy and reliability, so choose the most reliable method available to you. On-site testing is always helpful, allowing you to demonstrate directly that there is a problem. Test strips and test kits are manufactured by a number of companies. Enzyme-based nitrate analysis has been used in biomedical research for many years and is now available in simplified test kit formats for on-site water testing. Test kits based on this method can provide reliable data even when ther eare other contaminants in the water.
Because nitrate is so soulble and non-reactive, it can be very difficult to remove from water. Under some conditions, for example, ion exchange media can actually increase the danger for nitrate: the media will have a higher attraction for less soluble ions such as sulfate, and will release the cound nitrate ions to make room for the others, causing nitrate breakthrough. All nitrate treatments require careful monitoring and maintenance.
On the horizon
Various biological systems are also on the horizon in the technology of nitrate removal. Microbes that use nitrate as an energy source can be contained in a clomyun or tank system for water treatment. A more sophisticated approach pruifies the enzymes within these organisms that catalyze the nitrate reduction reactions, and uses the enzymes alone for nitrate removal. The advantage of biological systems is that the nitrate is converted to safe nitrogen gas, which does not contribute to the greenhouse effect. But it may be some years before these new methods hurdle the technological, regulatory, and customer-perception barriers to make their way into common practice.
Ellen R. Campbell is vice president of The Nitrate Elimination Co., In, Lake Linden, MI, an environmental biotechnology company that develops enzyme-based technologies for water testing and treatment. More information about the company is available at: http://www.nitrate.com. Campbell can be reached at: firstname.lastname@example.org. A.J. Kemppainen is a production/chemical engineer at the company.
Nitrate removal includes biodentrification, distillation, electrodialysis, ion exchange and reverse osmosis:
1. Scott Harmon, "Nitrate removal: Searching for the ideal in an imperfect world," Water Technology, November 2002.
2. David Elyanow and Janet Persechino, Advances in Nitrate Removal, GE WAter & Process Technologies, 2005
Nitrate is reported in different terms (units) depending on where you live and your field of use. For example, 2 parts per million (ppm) nitrate-N in New YOrk would be reported as 9 ppm nitrate in California.
|US EPA Units
2 ppm nitrate-N
9-10 ppm nitrate (NO3)
140 micromolar nitrate
|10 ppm nitrate-N||45 or 50 ppm nitrate||710 micromolar nitrate|
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