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UV Oxidation and Disinfection Technical Information
 "The
Discovery and Subsequent Research of Cryptosporidium Inactivation"
The disinfection of pathogenic microbes in
drinking water has been largely successful over the last century due
to the use of chlorination. However, research conducted in the 1970's
revealed that by-products formed during the chlorination process are
potentially carcinogenic and that there is a direct correlation
between the concentration of chlorination by-products and the
probability of certain cancers and other health problems. Following
these discoveries, drinking water regulators have struggled to find a
balance between the benefits of chlorination and the harmful side
effects caused by chlorination, within the confines of technological
and economic limitations.
In the U.S.A., the Surface Water Treatment Rule (SWTR) of 1989
mandates inactivation levels for giardia cysts and enteric viruses,
and also sets treatment standards for Trihalomethanes (THMs). The SWTR
provides guidance to drinking water facilities through "CT" tables
that prescribe the inactivation efficacy of various processes under
varying water quality conditions. By following this guidance, most
water treatment plants were able to provide an adequate degree of
disinfection while not compromising their Disinfection By-Product
(DBP) limits and without requiring major changes to their
plants. However, continuing DBP health effect research indicated that
even the DBP standards required in the 1989 SWTR produced an
unacceptable level of risk and the SWTR was amended in 1996 to further
lower DBP standards. In addition, a major outbreak of
cryptosporidiosis in Milwaukee in 1993, and other minor
cryptosporidiosis outbreaks caused regulators to create a removal
requirement for cryptosporidium oocysts in the 1998 Interim Enhanced
Surface Water Treatment Rule (IESWTR) and most likely a disinfection
requirement in the final ESWTR (LT2ESWTR). The new DBP standards have
caused many plants to fall out of compliance, requiring either
extensive plant modifications or new disinfection strategies. The
LT2ESWTR will include a cryptosporidium disinfection requirement and
many surface water plants will fall out of compliance due to the very
poor efficacy of chlorination for cryptosporidium. Therefore, due to
these apparently conflicting conditions, a void was created for a
water treatment technology that is effective for protozoa and viruses,
does not create DBPs, and is economically feasible.
UV technologies have long been known to be effective for viruses and
bacteria in drinking water and guidelines for the disinfection of
viruses exist in the Alternative Disinfectants and Oxidants Guidance
Manual. However, UV was widely considered to be ineffective for
encysted protozoa as it was thought that the UV light would not
penetrate the cyst membrane, and since giardia is the controlling
microbe for chlorine dose determinations, no reductions in chlorine
usage could be gained by using UV. Therefore, UV Disinfection was not
used for surface waters in North America.
New breakthrough research conducted by Calgon Carbon Corporation in
1998 however proved that UV disinfection is, in fact, very effective
for inactivating cryptosporidium and giardia at low UV
doses. Subsequent to Calgon Carbon's research, the USEPA created a UV
subworkgroup to report to the Federal Advisory Committee (FACA) on
issues and costs related to UV disinfection. In advance of new
guidance manuals for UV disinfection, many utilities have begun to
consider UV disinfection in their plants either as an additional
barrier for protozoa disinfection or to get "CT" credits for UV for
giardia so that chlorine doses can be lowered to meet the 1998 DBP
standards.
Authors: Daniel Brooks, Gary Van Stone, and
Wayne Lem, Calgon Carbon Corporation, Pittsburgh, Pennsylvania,
USA.
If you would like to view the complete text of
this paper, please register with
us.
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.
If you would like to view the complete text of
this paper, please register with
us.
This project evaluated a medium pressure
ultra-violet (UV) reactor downstream from a conventional surface water
treatment plant to determine the UV dose delivered by the reactor. The
data was compared with computational fluid dynamics (CFD) results
under the same test conditions to determine if CFD could accurately
predict the dose.
The UV disinfection reactor was challenge tested with MS2 coliphage at
a flowrate of 200 gpm and 600 gpm. The CFD model gave excellent
agreement at the 600 gpm case as the predicted dose was within 3% of
the dose obtained by biodosimetry. The CFD dose for the 200 gpm case
was high by about 17% compared to that observed by biodosimetry. In
general, the CFD model was able to accurately predict the dose
obtained by biodosimetry within 3%-17%. This is well within the range
of error expected in biodosimetry experimentation. The model was
tested over a wide range of both flow rate (200 and 600 gpm) and
number of lamps operating (1 or 4 lamps) in a Calgon Carbon 4x1 kW
Sentinel UV Disinfection Reactor.
CFD plays an important role for efficient reactor design at Calgon
Carbon Corporation. CFD is currently being utilized to optimize the
existing reactor designs with results showing that disinfection
treatment efficiency gains of up to 25-35% can be realized. Future
challenge studies incorporating these reactor modifications will be
compared with CFD predictions.
Authors: Wayne Lem, P.Eng., Calgon Carbon
Corporation, Pittsburgh, Pennsylvania, USA.
If you would like to view the complete text of
this paper, please register with
us.
Recently there has been considerable concern in
California about the detection of N-nitrosodimethylamine (NDMA) in
drinking water at levels as high as 900 ppt. NDMA was found to be a
carcinogen in animals and assessed as a Class 1 carcinogen. 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.
NDMA is thermally stable in aqueous solutions. Conventional methods
such as biological treatment, air stripping and activated carbon are
not effective for NDMA treatment. NDMA is photochemically labile, so
advanced oxidation technologies that are 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 contaminated groundwater.
In this paper, the selection and scale-up considerations for UV
systems designed to destroy NDMA are reviewed. A fundamental part of
UV system selection involves an evaluation of medium pressure and low
pressure UV systems. The differences between medium pressure and low
pressure systems are discussed and system costs are compared.
The water evaluated for this discussion was an NDMA-contaminated
drinking water at LaPuente Valley Water District treated through an
ISEP® continuous ion exchange module for perchlorate removal. The
stream was tested for the use of ultraviolet treatment in October
1998. The UV irradiations were carried out in a semi-batch 1 kW UV
Rayox® reactor (Calgon Carbon Corporation). The treatment results from
the 1 kW Rayox® reactor were used in Calgon Carbon's proprietary model
to confirm the results expected in the full-scale system. The
full-scale equipment, installed in December 1999, to treat a flowrate
of 2,500 gpm consisted of two Calgon Carbon 12 lamp Rayox® UV Towers
utilizing medium pressure UV lamps and a skid mounted peroxide dosing
module. Ultimately, the full-scale system performed very closely to
predicted results from lab scale efforts.
For virtually all large scale treatment applications, medium pressure
UV systems are advantageous over low pressure systems when comparing
the overall capital, installation, and operating costs for the
project. While economics is a big determinant in system selection,
other factors such as footprint, number of existing installations,
reliability, and ease of maintenance must be included in the selection
criteria. Taking into account all these factors, the Rayox® Tower,
with its high efficiency medium pressure UV lamps, was able to achieve
optimal performance for NDMA destruction with the lowest overall
lifecycle costs.
Authors: Wayne Lem, P.Eng., Calgon Carbon
Corporation, Pittsburgh, Pennsylvania, USA.
If you would like to view the complete text of
this paper, please register with
us.
The inactivation of Cryptosporidium parvum in
finished drinking water by medium-pressure UV light (200-300 nm) has
been investigated at both the bench scale, using a collimated beam
apparatus, and at the demonstration scale, using a Calgon Carbon
Corporation Sentinel™ system at the Mannheim Water Treatment
Plant, Kitchener, ON, Canada. The viability of the oocysts was
assessed using both in vitro (fluorogenic vital dyes (DAPI/PI) and
maximized in vitro excystation) and in vivo (neonatal mouse
infectivity) assays. In the bench-scale studies, a high degree of
inactivation (>4 logs) was found at UV doses as low as 41 mJ cm-2, as
assayed by neonatal mouse infectivity; whereas the in vitro surrogate
assays showed little or no inactivation at this and higher doses. This
indicates that the in vitro assays are unreliable and grossly
overestimate the UV doses required to prevent infection by the oocysts
in susceptible hosts. The demonstration studies, which were carried
out under the NSF/EPA ETV Program, provided results that agreed very
well with the bench-scale results and furthermore showed that a UV
dose as low as 19 mJ cm-2 provided 3.9 logs inactivation of the
Cryptosporidium oocysts.
Authors: James R. Bolton and Bertrand Dussert,
Calgon Carbon Corporation, Markham, ON, Canada; Zia Bukhari, Thomas
Hargy and Jennifer L. Clancy Clancy Environmental Consultants, Inc.,
St. Albans, VT .
If you would like to view the complete text of
this paper, please register with
us.
Visit the Calgon Carbon
Engineered Solutions web site for technical papers and other
decision-critical information about our Rayox® and Sentinel™
advanced oxidation and distillation technologies.
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