N-nitrosodimethylamine (NDMA) was first detected
in 1990 as a problem pollutant in drinking water wells at levels as
high as 3,000 ppt in Elmira, Ontario, Canada. The waste from a large
chemical plant over many years had led to the contamination of the
drinking water wells for the community. After extensive evaluation and
testing, it was determined that UV photolysis was the most effective
treatment method which led to the installation of a Calgon 270 kW
Rayox® UV system in 1991. The system has been continuously
treating water to this day. At about the same time, NDMA was found in
the drinking water on an Indian reserve in Ontario, and a similar UV
system was installed to remove NDMA from that water. Since then NDMA
has been detected as a pollutant in ground waters, surface waters,
industrial effluents and wastewaters in many jurisdictions. Many
sources have been identified, including chemical plants that
manufacture pesticides and herbicides, rubber manufacturing plants,
rocket fuel manufacturing plants and wastewater treatment
plants.
Recently there has been considerable concern in California about the
detection of NDMA in drinking water feed wells at levels as high as
900 ppt. NDMA was found to be a carcinogen in animals and assessed as
a Class 1 carcinogen by the USEPA. It is currently listed as a
priority pollutant on the US EPA National Priorities List. California
has set an "action level" of 20 ppt for NDMA and treatment systems are
required to treat to the detection limit of 2 ppt.
NDMA is often produced as a byproduct in the industrial use of
dimethylamine (DMA). DMA is a semi-volatile organic chemical that is
soluble in water and has been commercially used for several
decades. For example, from the mid 1950's till April, 1976, it was
manufactured and used as an intermediate in the production of
1,1-dimethylhydrazine, a storable liquid rocket fuel that contained
approximately 0.1% NDMA as an impurity. In addition
1,1-dimethylhydrazine oxidizes to produce NDMA. DMA is also used for
the inhibition of nitrification in soil, as a plasticizer for rubber
and polymers, as a solvent in the fiber and plastics industry, an
antioxidant, a softener of copolymers, and as an additive to
lubricants. DMA is used in rubber processing where it reacts with
nitrite to produce NDMA which can be present as a contaminant in the
final rubber product.
N-nitrosodimethylamine is also present in many other products such as
tobacco smoke and a variety of foods such as cheeses, soybean oil,
canned fruit, various meat products, bacon, various cured meat, cooked
ham, milk, fish and fish products, apple brandy, and other alcoholic
beverages including beer.
NDMA is thermally stable in aqueous solutions, and conventional
methods such as biological treatment, air stripping, and activated
carbon are not effective for NDMA treatment. Since NDMA is
photochemically labile, advanced oxidation technologies, based on
irradiation with ultraviolet (UV) light, have been promoted for the
removal of NDMA in contaminated waters. Direct UV photolysis readily
destroys the compound and has been used commercially for over 10 years
for the treatment of NDMA in contaminated groundwater.
In direct UV photolysis, a high powered lamp emits UV radiation
through a quartz sleeve into the contaminated water. The photons of
light are absorbed by NDMA resulting in breaking of the N-N bond in
the molecule. The destruction of NDMA is therefore dependent upon the
amount of UV light which is applied to the contaminated water and the
UV wavelengths emitted by the lamp.
Authors: Wayne Lem, P.Eng., Calgon Carbon
Corporation, Pittsburgh, Pennsylvania, USA.
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