Nitrates

Removing Nitrate by Ion Exchange
Removal is Essential for Excess Nitrate
Five Nitrate Removal Methods
Understanding the Different Nitrate Units
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Removing Nitrate by Ion Exchange
 

DESCRIPTION

    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.
ANALYSIS
    It is very important to know how nitrate is expressed in a water analysis so a water treatment system can be sized properly.  The IUS Environmental Protection Agency (EPA) has set a primary drinking water standard for nitrate.  The maximum contaminant level (MCL) is 10 parts per million (ppm) nitrate as nitrogen (NO3 as N).  A laboratory may also choose to express nitrate as nitrate (NO3as NO3) in the water analysis, and in this case, the EPA MCL would be 44.2   pm (10ppm as N is equivalent to 44.2 ppm as NO3).
    A good accurate water analysis is especially critical in this application, since a health issue is being addressed.  The water analysis must include nitrate and sulfate.  Nitrate and sulfate levels are needed to calculate the operating capacity of the nitrate removal unit.
    These parameters will have to be converted to their calcium carbonate equivalent.  The conversion factor when nitrate is expressed as N is 3.57, and 0.81 when it is expressed as NO3.  Typically sulfate is expressed as SO4 in a water analysis.  Sulfate must also be converted to its calcium carbonate equivalent by multiplying by 1.04.  By converting to the calcium carbonate equivalent, the nitrate and the sulfate can be compared as equals. It is also important to know the hardness, iron, total alkalinity, total dissolved solids (TDS) and pH.
ANION vs. CATION RESINS
    Nitrate has a negative charge in water.  It can be removed from the water with a strong-base anion resin.  The resin can be regenerated with salt (NaCI) and works similarly to a water softener.  Anion resin is less dense than cation softening resin, so the backwash flow rate must be reduced as compared to a softening resin.  Check manufactures product data sheets for details.
    Typical type 1 and type 2 strong-base anions will remove nitrate from water.  Standard anion resins have an affinity for sulfate over nitrate.  The order of affinity is as follows:    Sulfate-2>Nitrate-1>Chloride-1>Bicarbonate-1.  These are the exhaustion bands in order of preference as a unit exhausts.  Sulfate has two negative charges (the valence) that give it a greater affinity to standard strong-base anion resin than nitrate with one negative charge.
    This is important since nitrate can be “dumped” from these types of resin.  Dumping is defined as the elevation of nitrates in the treated water over the level of nitrates in the raw (influent) water.  As the nitrate system reaches exhaustion, sulfates will displace nitrates, causing a significant increase in nitrate leakage corresponding to the nitrate and sulfate levels in the raw water.
    When the raw water sulfates are high, nitrates in the treated water can be significantly higher that the raw water.  This can be compensated for when sizing the system.  It is also best to use a standard anion resin when the system is monitored and/or the sulfate concentration is low.
    There are selective nitrate resins on the market.  These resins have a different exchange group that makes it possible for nitrates to be removed from water without the potential for dumping.  Typical nitrate-selective functional groups include triethylamine, tripropylamine and tributylamine.
    With these types of resins the nitrate is held preferentially over sulfate.  It should be noted that even though these resins are selective to nitrates they still remove other negatively charged ions, like bicarbonate alkalinity and sulfate, from the water.
Whether a standard anion resin or a selective nitrate resin is used, sodium chloride or potassium chloride is typically used to regenerate the system.  A high concentration of brine is used to strip nitrate from the anion resin. Care must be taken, as with any anion resin, to set an appropriate backwash flow rate to prevent resin loss.
The backwash flow rate of an anion resin is considerably lower than a cation softening resin’s, so check with the manufacturers’ specifications.  The use of a screen or upper basket in the valve will help to prevent resin loss during the backwash.
BE AWARE OF Ph CHANGES
    All nitrate removal resins will remove alkalinity, including nitrate-selective resins.  When alkalinity is removed from water, the pH will decrease.  The degree to which the pH will drop is dependent on the amount of alkalinity and carbon dioxide (CO2) in the water.     The decrease in pH occurs until the resin’s capacity for alkalinity is reached; at that point the pH will start to return to the influent level. Generally, on low total dissolved solids (TDS) water the pH drop will be more significant than on higher TDS water. Nitrates will be exchanged onto the resin, and chlorides will be released into the water.  This reaction will cause the chloride content of the treated water to increase.  If the TDS of the water is high, a salty taste may be detected.
SYSTEM COMBINATIONS
    Caution must be taken when a single unit utilizes both cation and anion for softening and nitrate removal.  During the regeneration, high levels of hardness and high alkalinity may exist, causing calcium carbonate precipitation.  This precipitation can foul the resin bed and/or plug the drain line.  Separate softening and nitrate removal units will prevent the precipitation from occurring.
    Demand-initiated valves should be used as the brains of the system.  These valves will monitor the amount of water treated and regenerate the resin before the capacity is exhausted.
    Nitrate-selective resins should be used in point-of-use cartridges where the tendency to overrun the system exists. The selective resins should be used on water with high sulfate concentrations. They should also be used when the system is not monitored. If the brine tank is not filled or the valve fails, nitrate dumping will not occur when using a selective resin.
Standard anion resins should be used on systems that are monitored. Standard nitrate removal resins will generally have a higher operating capacity than the nitrate-selective resins.  They should be used on fee-lot applications where sulfate and nitrate removal is important.
    It is beneficial to soften the water prior to nitrate removal. Softening will help to protect the nitrate removal system from fouling with metals like iron. Nitrate removal by ion exchange is set up similar to softening, with some modifications. This type of water treatment is not difficult and is within the expertise of most water treatment professionals….

SOURCE
Water Technology, Volume 23, Number 11, November 2000, "Removing Nitrate by Ion Exchange"

AUTHOR
Mike Keller is marketing specialist, domestic water services, for Sybron Chemicals, Inc. in Birmingham,  N.J.
 

REFERENCES
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.

Removal is Essential for Excess Nitrate
Too much of this is common, natural ion poses health risks.
by Ellen R. Campbell
Water Technology, September 2006, p.32



    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: ellenr@nitrate.com.  A.J. Kemppainen is a production/chemical engineer at the company.

Five Nitrate Removal Methods
by A.J. Kamppainen

Nitrate removal includes biodentrification, distillation, electrodialysis, ion exchange and reverse osmosis:

Distillation, electrodialysis and reverse osmosis are very effective at removing nitrate from water.  However, the high nitrate waste must still be sidposed of properly or contamination of groundwater can occur.

Sources:
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


Understanding the Different Nitrate Units
by Ellen Campbell

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
(NO3N, nitrate-nitrogen)		 California, Europe
9-10 ppm nitrate (NO3)		 Chemical Units
140 micromolar nitrate
 
10 ppm nitrate-N 45 or 50 ppm nitrate 710 micromolar nitrate

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