Removing Nitrate by Ion Exchange
Removal is Essential for Excess
Five Nitrate Removal Methods
Understanding the Different
Removing Nitrate by Ion Exchange
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.
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
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
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
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.
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
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….
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.
Removal is Essential for
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
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.
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.
Distillation boils water, leaving the nitrate behind, and then condenses
and collects the steam/condensate. This process requires relatively
higher amounts of energy than other methods and is typically used when
virtually complete removal of nitrate is desired.
Electrodialysis uses an electrical current to move the nitrate threough
a series of anoin and cation selective membranes. The consecutive
membranes concentrate the ions in a waste stream and away from the water.
Electrodialysis may not be sot-effective for small-scale production.
Ion exchange uses a nitrate-selective resin to remove nitrate from water.
Care must be used: as the resin exchange sites fill with nitrate, nitrate
breakthrough can occur as the resin reaches full nitrate capacity. Ion
exchange is economical for large-scale nitrate removal.
Reverse osmosis (RO) traps the nitrate in a selctive membrane and allows
the water to pass through. RO is the most common method of nitrate
removal and is cost-effective when a small amount of water needs to be
purified (5 to 10 gallons daily).
Biodenitrification is a process that is typically associated with large-scale
wastewater treatment. In general, the nitrates are reduced to nitrogebn
using bacteria in an anaerobic environment.
1. Scott Harmon, "Nitrate removal: Searching
for the ideal in an imperfect world," Water Technology, November
2. David Elyanow and Janet Persechino, Advances
in Nitrate Removal, GE WAter & Process Technologies, 2005
Understanding the Different
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.
To convert from ppm nitrate-N to nitrate, multiply the nitrate-N value
by 4.4 (10ppm nitrate-Nx4.4=44 ppm nitrate).
To convert from ppm nitrate to ppm nitrate-N, multiply the nitrate value
by 0.23 (50 ppm nitratex0.23=11.5 ppm nitrate-N).
|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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