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Disinfection workshop summary
Weighing the risks and benefits of wet-weather disinfection
Presented at The Rosamond Gifford Zoo, Syracuse, NY
October 15, 2002
2. History of wet-weather disinfection
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Average annual volume of combined sewage
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Mr. Moffa presented background information on CSO
disinfection and the County's CSO abatement approach.
Onondaga County's engineering consultants have
been researching chlorine and alternatives for
disinfection of wet-weather flows since 1979. The
conclusion is that chlorination with dechlorination is
the best alternative.
System wide, 74% of average annual combined
sewage volume is transmitted in the interceptor sewer
to the Metropolitan Syracuse Wastewater Treatment Plant (Metro), an additional 16% of the volume
would be captured by proposed RTFs and transmitted in
the sewer interceptor to Metro, and the remaining 10%
of the volume would be treated and discharged at the
proposed RTFs.
By-products are formed when chlorine is added
to CSO for the purpose of disinfection, and often
there is residual chlorine. Dechlorination eliminates
the residual and prevents additional by-products from
forming. By-products produced during the disinfection
process before dechlorination are discharged with the
treated CSO. The Water Environment Research Foundation
Project, presented in this workshop, is examining and
evaluating the potential human health effects and
potential for aquatic organism toxicity associated
with various disinfectants including
chlorination-dechlorination.
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Number of CSO facilities in the U.S. (Feb 1999)
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Ms. Stinson presented a current status of CSO
disinfection throughout the nation and summarized
research on chlorine and alternative disinfectants
used for CSO.
and have been used for CSO.
chlorination, are still experimental for CSO.
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Results of an in-house survey
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Mr. LaGorga introduced an ongoing project funded by
USEPA to identify and communicate the benefits and risks
of disinfecting wet-weather flows. Aquatic whole
effluent toxicity (WET) results were presented.
chlorine dioxide, ozone and ultraviolet light
technologies during nine rain events at Metro on
combined sewage. The combined sewage received
screening and degritting at the Metro headworks before
disinfection. This level of treatment was most
representative of the County's proposed treatment at
the CSO locations.
of bacteria reduction during demonstration.
water fleas (representative species).
residual chlorine produced no mortality in
representative species.
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Pilot study results (results assume no dilution of effluent)
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Four steps of risk assessment—USEPA methodology from 1983
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Dr. Goodrum described the USEPA chemical risk assessment
approach for protecting aquatic organisms and human
health. Information gathered on the toxicity of
disinfection by-products associated with the WERF
Project was presented.
exposure and toxicity.
understanding of the concentrations in water and
activities of the exposed population. For human health
risk assessment, an example was given for a
recreational exposure scenario (swimming).
| Bioconcentration potential |
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BCF
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Category
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> 1000
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Very high
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100-1000
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High
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30-100
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Moderate
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< 30
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Low
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All but one chemical estimated o have lowest potential (BCF < 30), 2,4,6-trichloropehnol (BCF=55)
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studies. For aquatic toxicity, estimates can be made
either directly or from the literature. John LaGorga
presented results of direct testing using aquatic
whole effluent toxicity (WET) studies (see above).
Literature information from USEPA's database called
AQUIRE was also presented. For human health, USEPA
summarizes toxicity values to assess non-cancer and
cancer risk in a database called IRIS.
Chlorination-dechlorination by-products for which IRIS
numbers are available were presented.
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AQUIRE—percent of available data by chemical class and species category
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the subset of chlorination-dechlorination by-products
for which toxicity data are available. To be
protective, the highest measured concentrations from
the nine sampling events were paired with the lowest
available toxicity values.
very low tendency to bioconcentrate in aquatic
organisms.
exposure, it is not likely that the
chlorination-dechlorination by-product concentrations
in receiving waters will be high enough to result in
adverse impacts to the aquatic ecosystem or to human
health.
| History of wet-weather disinfection research |
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Year
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Completed
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1979
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USEPA research on vortex/high-rate disinfection including chlorine
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1979
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Syracuse CSO facility plan, storage, vortex, high-rate disinfection
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1984
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Syracuse CSO best management practices
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1987
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Initiated update of CSO long-term control plan (LTCP)
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1996
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NYC demo of chlorination-dechlorination (toxicity), chlorine dioxide, ultraviolet light, ozone
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1997
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Signed consent order, separation, storage, vortex, high-rate disinfection
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1998
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NYC demo of chlorination-dechlorination (toxicity), chlorine dioxide, ultraviolet light
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2001
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Environmental technology verification of high-rate mixers
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Ongoing
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USEPA-funded disinfection demonstration by Water Environment Research Foundation
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Completed testing
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Chlorination-dechlorination (toxicity), chlorine dioxide, ultraviolet light, ozone
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Q: Do European countries use chlorine?
Q: USEPA identified 886 permitted CSO treatment facilities in 1999. What type of facilities are they?
A: The 886 permitted CSO treatment facilities in
1999 included many types of facilities including
netting facilities, storage facilities with overflow,
vortex facilities with and without chlorination. Of
the 886 facilities 174 facilities chlorinated and 18
dechlorinated.
Q: Does high-rate disinfection require a higher disinfectant dose?
A: In addition to the intense mixing that results, use
of high-rate mixers allows lower dosing because of the
induction of a molecular form of chlorine, which is
the most-effective form of chlorine for disinfection.
Q: The acute WET test tests for mortality: are there any other effects that have been studied other than mortality?
A: The amount of aquatic toxicity information
available will vary by chemical. But yes, the
information on aquatic toxicity that is available on
USEPA's database called AQUIRE does include endpoints
other than mortality. For example, the concentration
that affects growth in 50% of test organisms is
referred to as an
EC50.
Other endpoints may include effects on development or
reproduction. For the WERF Project, we used a
screening level approach, which means that for each
chemical, we identified the lowest available toxicity
value that was associated with any endpoint of
concern, thus it does reflect organism health if it is
the lowest value.
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Chemical classes of disinfection by-products — Summary of lowest LC / EC50 values for aquatic species
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Results of screening level calculations
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Q: The acute WET test only looks at an organism for 48 hr. What happens to the life cycle of an organism that is exposed for a longer time?
A: An organism that does not show acute toxicity
over 48-hours may exhibit a sub-lethal health effect
(for example, impaired growth or reproduction) over
longer periods of exposure to the same dose. To
confirm this, a chronic toxicity test would need to be
conducted. These tests were not performed for the WERF
project; however, sub-chronic and chronic endpoints
for some chlorination-dechlorination by-products were
identified through a literature review. Based on the
literature review values, concentrations measured in
the WERF project would not be high enough in the
receiving water to result in adverse impacts to the
aquatic ecosystem or to human health.
Q: In the WERF project fathead minnows and water fleas were studied. Were plants considered?
A: The potential presence of aquatic toxicity was
assessed by performing tests on animal species with
actual chlorinated-dechlorinated effluent and by
performing a literature review to identify potential
toxic concentrations of chlorination by-products. The
actual tests were performed on fathead minnows and
water fleas while effects on plants and other
organisms were included as part of the literature
review.
Q: Was the WERF data collected locally? Is it available?
A: Data regarding bacteria reductions and
by-product formation were collected locally during a
demonstration project for the Water Environment
Research Foundation (WERF).
Chlorination-dechlorination, chlorine dioxide, ozone,
and ultraviolet light technologies were operated
during nine wet-weather events on combined sewage.
This is an ongoing project that is scheduled to
conclude in July 2003. Preliminary summary results
from this project were presented in the workshop. Data
will eventually be published WERF and available
through the WERF web site.
Clarification: The demonstration was conducted at
O'Brien and Gere Laboratories in Syracuse NY using
screened and degritted combined sewage collected at
Metro during wet-weather events.
Q: A partial quote from the County's Newell Street Disinfection Study web site was presented. "Since the 1970s, growing awareness of the adverse environmental impacts associated with the byproducts and residuals
of chlorination has led to increasingly more restrictive residual chlorine requirements."
A: The Newell Street study was focused on potential
use of chlorine dioxide and ultraviolet light in lieu
of chlorination with dechlorination. The purpose of
this study was to determine if chlorine dioxide or
ultraviolet light could provide greater bacteria
reductions and lower toxicity at a cost competitive
rate as compared to chlorination-dechlorination. The
conclusion of this study and a related study in New
York City shows chlorination-dechlorination to be the
preferred alternative.
Clarification: The Newell Street Disinfection Pilot
Demonstration project was unable to be completed as
planned because of generally dry weather conditions
over the demonstration period. However, wet-weather
events were simulated and related data from New York
City piloting was included in the draft Newell Street
Report.
Q: Is current TRC control equipment reliable?
A: Yes, TRC control equipment is reliable. Other
controls such as ORP are also available. Most every
wastewater treatment plant and CSO facility that
disinfects with chlorination uses this type of
equipment. Data presented during this workshop for
Augusta, Maine and Rockland, Maine, show how this
equipment can be used to achieve TRC concentrations
below permit requirements.
Q: A workshop attendee thought the presentation on toxicity of by-products from chlorination-dechlorination was biased because it did not take into account the scientific evidence of health effects of organochlorine
compounds. (Hoyer, A. P., Grandjean, P., Jorgensen, T., Brock, J. and Hartvig, H.B. 1998. Organochlorine exposure of breast cancer.
Lancet.
352:1816-1920. Steingraber, S. 1997.
Living Downstream.
Addisen-Wesley Publishing Company. The attendee also suggested that in the absence of information, it is advisable to adopt the precautionary principle.
A: The workshop presentation focused on only the
subset of chlorine compounds that are associated with
disinfection treatment processes. The toxicity data
available for these chemicals, when combined with
conservative estimates of exposure, suggests that the
human health risks are extremely low. In addition,
epidemiological studies suggest that there is weak
evidence of an association between exposure to
disinfection by-products and adverse health effects in
humans.
Clarification: As identified in the cited literature,
it is true that exposure to some chlorinated
compounds, such as organochlorines like PCBs, increase
the risk of negative human health impacts. However, it
is important to note that complex organochlorines like
PCBs are not a by-product of CSO
chlorination-dechlorination.
Q: What are the fates of these by-products in the environment?
A: The environmental fate data for the by-products
was not explored for the WERF project.
Clarification: Subsequent to the workshop, a
preliminary review of chemical properties and
degradation half-lives was performed. Many of the
by-products, such as the trihalomethanes, are expected
to volatilize rapidly, thereby being unavailable for
exposure to aquatic organisms and humans. Most other
classes of by-products for which measurements are
available suggest that biodegradation half-lives are
on the order of a day or less.
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Susan Miller, Project Deputy Director
Onondaga County Dept of Water Environment Protection