United States
Environmental Protection
Agency
Water Engineering
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-88/034 Sept. 1988
SEPA Project Summary
Toxicity Reduction
Evaluation at the Patapsco
Wastewater Treatment Plant
John A. Botts, Jonathan W. Braswell, William L Goodfellow, and Dolloff F. Bishop
A water quality-based toxics control
process in wastewater treatment is
being established by the U.S. EPA to sup-
port the development of discharge per-
mits, including effluent toxicity
measurements. Upon confirmation of a
toxics water quality problem, a toxics
management program, referred to as a
Toxicity Reduction Evaluation (TRE), can
be implemented to Identify and control
the sources of the effluent toxicity. The
goal of a TRE is to determine the steps
that are required to reduce effluent tox-
icity to acceptable levels.
A municipal TRE research study was
recently completed at the Patapsco
Wastewater Treatment Plant in Baltimore,
MD. The purpose of the study was to
develop and evaluate procedures to
assess toxicity problems at a municipal
treatment plant receiving wastewater
from a wide range of industrial sources
and to develop practical approaches to
control the toxicity. The Patapsco study
revealed high levels of toxicity entering
the plant as measured by Ceriodaphnia
dub/a (acute and chronic), Mysidopsis
bah/a (acute), and Microtox (acute)
tests. The C. dub/a test was the most
sensitive indicator of influent and ef-
fluent wastewater toxicity. While the
Patapsco Plant met its permit re-
quirements for conventional pollutants
and achieved major reductions in waste-
water toxicity, substantial acute and
chronic toxicity as measured by C. dub/a
and M. ban/a, was continuously present
in the unchlorinated secondary effluent.
Substantial Microtox™ toxicity also was
'Mention of trade names or commercial products does
not constitute endorsement or recommendation for use.
intermittently present in the un-
chlorinated secondary effluent.
Characterization of the influent and ef-
fluent toxicity revealed that most of the
toxicity was associated with nonpolar
organic compounds that adsorbed
strongly to the solids in the wastewater.
Intermittent and modest amounts of tox-
icity were also associated with volatile
organics, ammonia, and polar organic
compounds. Identification of the
specific organic compounds causing the
toxicity was not achieved using standard
gas chromatography/mass spectroscopy
(GC/MS).
Batch treatability tests on selected in-
dustrial discharges using acute toxicity
assays as performance indicators provid-
ed a method for identifying and ranking
the industrial discharges as potential
contributors to the Patapsco plant's
wastewater toxicity. Efficient solids
separation treatment of the batch test ef-
fluent removed most of the acute
toxicity.
This Project Summary was developed
by EPA's Water Engineering Research
Laboratory, Cincinnati, OH, to announce
key findings of the research project that
is fully documented in a separate report
of the same title (see Project Report
ordering information at back).
Introduction
The Patapsco Wastewater Treatment
Plant in Baltimore, MD, is a municipal ox-
ygen activated sludge plant treating both
domestic-commercial wastewaters and
discharges from approximately 100 in-
dustries. The plant is well-operated and
meets its permit requirements for conven-
tional pollutants. Long-term historical data
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from Microtox™ tests and limited data
from C. dubia bioassays, however, revealed
high levels of toxicity in the wastewaters
entering the plant and substantial toxicity
pass-through in the plant's effluent. Thus,
in January 1986, the U.S. EPA and the City
of Baltimore entered into a cooperative
agreement to perform a research TRE
study at the Patapsco Plant. The TRE was
initiated in April 1986, and completed in
September 1987, and represents one of the
first case histories of a toxicity management
program at a municipal wastewater treat-
ment plant. During the study, the plant,
which is designed for 70 mgd, was
operated at approximately 45 mgd with its
oxygen bioreactors employing an average
14-day mean cell residence time in the
warm water season and approximately a
17-day mean cell residence time in the cool
water season
Research Objectives
The objectives of this TRE were:
• to evaluate the fate and impact of acute
and chronic toxicity during treatment and
the pass-through of toxicity in the plant
effluent;
• to characterize the toxicity as to broad
classes or types of toxics and, if possi-
ble, to identify the specific compounds
causing the toxicity; and
• to develop procedures to trace the tox-
icity to its sources and evaluate its
treatability both at the central treatment
plant and through pre-treatment.
Research Approach
The first element of the TRE involved the
characterization of plant operations and
performance using conventional pollutant
monitoring, monitoring for specific priority
(toxic) pollutants, and evaluation of acute
and chronic influent and effluent
wastewater toxicity. The collection of the
composite wastewater samples used in
monitoring were scheduled to account for
the average process hydraulic detention
time of the plant (i.e., secondary effluent
composites were collected 8 hr after
primary effluent composites). The toxicity
assays were C. dubia (acute and chronic),
M. bahia (acute), and Microtox™ (acute)
tests. The toxicity testing end points used
in the study included the LCSo defined as
the wastewater effluent concentration in
percent effluent in the test causing lethali-
ty to 50% of the test population in the
established test time, the EC50 defined as
the effluent concentration in percent ef-
fluent in the test causing a 50% reduction
in the "observed test effect (light
phosphorescence) in the established test
time, and the chronic value (ChV) express-
ed as percent effluent and defined as the
geometric mean between the no obser-
vable effects (NOEC) and the lowest obser-
vable effects concentration (LOEC) in the
life cycle test.
The characterization of plant operations
included biomass oxygen and substrate
(COD) uptake rates and adenosine
triphosphate (ATP) measurements in
laboratory studies to indicate potential in-
hibition impacts on the plant's biomass.
Because the domestic-commercial and in-
dustrial wastewater sources are largely
separated between two sewers, the
characterization study was able to evaluate
the relative importance of the two
wastewater sources to the wastewater tox-
icity in the treatment plant. Using the tox-
icity data for the influent and effluent
wastewaters, possible relationships (Pear-
son's Product-Moment Correlation) among
the three toxicity bioassays and relation-
ships between the Microtox™ toxicity and
other conventional performance indicators
were also evaluated. The objective was to
evaluate less expensive monitoring alter-
natives (Microtox™ and conventional per-
formance indicators such as oxygen and
COD uptake rates) as possible surrogates
for the classical bioassays in the prediction
of toxic events.
A second element of the TRE approach
involved characterization of the toxicity in
the Patapsco influent and effluent
wastewaters. Wastewater fractiona-
tion/identification procedures were used to
indicate the general classes of toxics caus-
ing the toxicity and to attempt to identify by
standard analytical techniques the specific
toxics causing the toxicity. The fractionation
procedures evaluated the amounts of tox-
icity removed by aeration, filtration, am-
monia stripping, Ci8 solid phase extraction
with methanol elution of non-polar organics,
and ion exchange separation for cations
and anions. The toxicity of the residual
compounds (i.e., polar organic compounds
not removed by C18 fractionation) was also
estimated. Because the fractionation
procedure is conducted as a series of
bench-scale treatment tests, the results of
the procedure provided insight into the
treatability of the toxicity.
The third element of the TRE approach
involved an evaluation of industrial
wastewater sources to determine their
relative contribution to the toxicity in the
plant effluent and the treatability of the in-
dustrial wastewater toxicity by the plant's
biomass. A toxicity treatability screening
procedure, developed during the TRE, was
applied to five of the largest industrial
dischargers to the Patapsco Plant. The t(
icity treatability screening procedure usi
batch treatability tests that simulated t
operation of the central treatment pla
The tests evaluated the contributions of t
industrial wastewaters with respect to
hibition of the plant's biological process
and to toxicity pass-through in the plan
effluent. The individual industrial was
waters were mixed in 2-L batch reactc
with central plant biomass and eitr
primary effluent or nontoxic synthe
wastewater and then biologically treated
a batch test food-to-mass ratio equivaU
to the nominal operating food-to-mass ra
in the Patapsco plant. After aeration, t
batch test mixed liquor was filtered throu
a coarse filter to simulate seconds
sedimentation.
Parameters used to evaluate t
treatability of the industrial wastewaters
eluded biomass activity as measured
changes in oxygen uptake and soluk
COD substrate uptake rates and effluc
toxicity as measured by Microtox™ and
dubia. Because the plant sludges were
cinerated, toxicity assays and speci
chemical analyses were not applied to t
batch test sludges. The wastewater frj
tionation/identification procedures we
also used to characterize the toxicity of t
batch test effluents.
Results
Plant Performance
A review of the operation and perfi
mance data revealed that the Pataps
Plant performed well in terms of conve
tional pollutant treatment during the TF
period of May 1986 to January 1987. T
effluent suspended solids typically vari
from 20 to 27 mg/L, while the BOD5 in t
effluent averaged 9 and 16 mg/L for t
warm and cool water seasons, respecti\
ly. The plant's effluent quality met t
plant's existing permit requirements a
the pass-through of toxicity was not cat
ed by plant operation or performan
deficiencies.
The influent to the Patapsco plant <
hibited high levels of acute and chronic t(
icity as measured by the 7-day static
dubia (acute-chronic), 96-hr static M. bal
(acute), and Microtox™ (acute) tes
Primary sedimentation did not redu
wastewater toxicity. Major reductions in ti
icity (Table 1) were achieved by the ;
tivated sludge process; however, subst;
tial acute and chronic toxicity as measur
by the C. dubia, M. bahia, and Microto
tests passed through in the Patapsco
fluent. The C. dubia test was the most s<
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TaWe 1. Toxicity Reduction at the Patapsco WWTP
Microtox™ M. bahia
C. dubia
Expressed as
Effluent Toxicity
(as % effluent)
Mean =F SD*
N Samples
% Toxicity
Reduction!
Mean =F SD
N Samples*
5-min EC50 96-hr LCSO 48-hr CL50 Chronic
7-day ChV
79.3 T 23.4 47.6 =F= 23.1 6,3 * 4.6 2.5 =F 2.1
40 44 45 45
87.7 =F 72.2 55.5 =F 76.8 60.7 =F 30.4 62.5 =F 37.7
37 72 73 72
*SD is the standard deviation.
t % Toxicity Reduction (TR) =
TU Primary Effluent - TU Secondary Effluent
X 100
TU Primary Effluent
and TU (toxic units) - 100/either the LCso, FCso, or ChV.
* % TR calculated only from individual pairs of influent and effluent samples (not the pooled data base)
sitive indicator of acute toxicity for the
Patapsco wastewaters. The C. dubia mean
48-hr LC50 was 6.3% and the mean 7-day
ChV was 2.5% effluent.
Except for most metals and eight
organics, the Patapsco plant reduced in-
fluent priority pollutant concentrations to
below the detection limit. The average ef-
fluent concentrations of 12 metals and 1
organic (alpha-hexachloro-cyclohexane)
were found to exceed EPA water quality
criteria for marine and freshwaters. In con-
trast to the chemical-specific data, results
of the wastewater fractionation/identifica-
tion tests indicated metals were not con-
tributors to the plant's effluent toxicity
The evaluation of the two main influent
sewers revealed that the wastewater enter-
ing the plant from the industrial service
area was highly and consistently toxic as
measured by the Microtox™ (EC50 about
3.5%). The influent wastewater from prin-
cipally domestic-commercial contributors
was highly toxic to Microtox™ (EC50
averaging about 7.6%) in the warm water
seasons and moderately toxic (EC50
averaging about 21.6%) in the cool water
season. The temperature dependence of
the toxicity in the domestic-commercial
wastewater suggested a warm weather sep-
ticity problem in the long sewers of the
domestic-commercial collection area.
No significant correlations were found
among Microtox™ EC50 values and the
LC50 values of C. dubia and M. bahia.
Microtox™ values exhibited strong correla-
tions with wastewater characteristics and
plant performance paramelers including
suspended solids, BOD5, and COD con-
centrations in the influent wastewater, and
with increasing BOD5 and COD concentra-
tions in the secondary effluent. An overall
analysis of the data, however, indicated that
Microtox™ and the operations and perfor-
mance parameters, including oxygen and
COD uptake rates and ATP measurements,
were not effective surrogates for the predic-
tion of acute and chronic responses of C.
dubia and M. bahia. Oxygen and COD up-
take rates and ATP measurements were
useful, however, in revealing inhibition ef-
fects on the Patapsco plant's biomass.
Characterization of Toxicity
Application of wastewater fractiona-
tion/identification procedures to primary ef-
fluent and secondary effluent Patapsco
wastewaters provided perspective on the
general characteristics of the toxic com-
ponents producing toxicity at the Patapsco
plant. The wastewater fractionation/iden-
tification procedures were able to
characterize the broad classes of toxics
responsible for the measured toxicity and
to provide information on potential toxicity
treatment options. GC/MS analysis of the
toxic wastewater fractions, however, was not
able to definitively identify the specific
organic compounds causing the toxicity.
The wastewater fractionation procedure
used a rapid screening test, C. dubia time
lethality test, as the toxicity indicator to
reveal (Figures 1 and 2) that non-polar (N-
P) organic compounds were the principal
toxicants in the influent and effluent
wastewaters. Toxicity results for fractions of
C18 methanol elution indicated that the N-
P organic compounds causing toxicity have
high log octanol to water partition coeffi-
cients and hence should adsorb onto
solids. This observation was supported by
a study that revealed the C. dubia toxicity
in the Patapsco Plant effluent was largely
associated with particles greater than 0.2
nm in size.
Lesser and intermittent amounts of
wastewater toxicity were attributed to com-
pounds removed by aeration and ammonia
stripping. The presence of toxicity in the
residual fraction of a secondary effluent
sample (December 10,1986) indicated that
other compounds may contribute to effluent
toxicity on an intermittent basis. This inter-
mittent residual toxicity was most likely
polar organic compounds not retained by
the Cis column or non-polar organic com-
pounds with molecular weights greater than
2000. The ion exchange separation pro-
cedures indicated that cations (metals) and
anions were not principal causes of the ef-
fluent toxicity
Toxicity Source Evaluation
Using Microtox™ as the toxicity in-
dicator, the batch treatability test revealed
that only one of the five selected industrial
wastewaters contained substantial toxicity
that was refractory to treatment by the
plant's biomass. The C. dubia test, however,
indicated substantial levels of toxicity in the
batch-treated effluents of all five industrial
wastewaters. C. dubia tests on samples of
plant biomass used for the batch tests
revealed substantial toxicity in the filtrate
(coarse filtration) of biomass. The biomass
toxicity was associated with the solids pass-
ing the coarse filter, which was used to
simulate plant clarification in the batch
tests, and masked C. dubia measurements
of refractory toxicity in the effluents from the
batch treatability tests. Further studies
revealed that most of the toxicity could be
removed from the coarse filtrate by efficient
filtration using a 0.2 ^m pore size filter or
by high speed centrifugation.
The combination of batch treatability and
batch effluent fractionation procedures
characterized the toxicity contribution by
the individual industrial wastewater enter-
ing the central treatment plant (Table 2,
Figures 3 and 4). The tests confirmed the
importance of the N-P organics to the tox-
icity problem at the Patapsco plant. The
batch treatability tests on the industrial
wastewaters used ranges of concentrations
of industrial wastewater greater than their
influent concentration entering the central
plant. The tests at the high concentrations
of industrial wastewater revealed toxicity
contributions from cations and anions in the
batch test effluents that were not found in
the effluent of the central treatment plant
because of dilution by the overall plant
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effluent samples from the Patapsco Plant, warm weather 1986.
Table 2.
Industry
Principal Toxic Fractions of the Industrial Wastewater Discharges Refractory
to Batch Treatment
Sample Data
Principal Toxic Fraction*
C
D
December 12, 1986
March 12, 1987
April 8, 1987
March 19, 1987
April 15, 1987
March 26, 1987
Residual
Non-Polar Organics
Non-Polar Organics
Non-Polar Organics
Non-Polar Organics
Anions
"Based on the acute toxicity (C. dubia 48-hr LCso) remaining after each fractionation step.
wastewater. Oxygen and COD uptake rate
tests also characterized the industrial
wastewater's potential for inhibition of the
central plant's biomass
Conclusions
The conclusions of the TRE study at the
Patapsco plant are as follows:
The influent to the Patapsco plant e:
hibited substantial acute and chronic to:
icity as measured by C dubia, M. bahk
and Microtox™ tests.
1 Although a major reduction in toxicity wa
achieved by the Patapsco plant, substai
tial acute and chronic toxicity a
measured by the C. dubia, M. bahk
and Microtox™ tests was present in th
plant effluent. The C. dubia test was th
most sensitive indicator of acute toxicil
for the Patapsco plant's wastewaters an
results of this test reveal a continuoi
discharge of effluent toxicity. The watt
quality impacts of the Patapsco plant's e
fluent toxicity on the Patapsco Riv<
estuary were not investigated and ai
thus unknown.
The Patapsco plant performed well du
ing the TRE period of May 1986, 1
January 1987, and the pass-through <
toxicity was not caused by poor plai
operation or performance. Based o
historical Microtox™ data, the in
plementation of secondary treatment an
the gradual development of an a<
climated biomass in the secondary pn
cess (1-yr) produced increases in toxic
ty removal, and hence substantial redu
tion in toxicity pass-through at th
Patapsco plant.
1 In-plant toxicity monitors (i.e., oxyge
utilization, substrate utilization, and AT
tests) were appropriate indicators of ii
hibitory effects on the Patapsco plant
biomass. A comparison of results of i
plant monitors and standard bioassa]
(i.e., 7-day C. dubia, 96-hr M. bahia, at
Microtox™ tests), however, found th
these in-plant tests were not suitable si
rogates for measurement of toxic effec
on aquatic biota. Furthermore, the i
dubia and M. bahia tests were more se
sitive indicators of effluent toxicity the
Microtox™.
• Historical Microtox™ data indicated th
there was a significant increase in toxici
following chlorination of the Patapsi
secondary effluent. Because dechlorin
tion will be implemented at the Patapsi
plant in the near future, this toxici
source was not evaluated durinq tl
TRE.
• Wastewater fractionation/identificatii
procedures were able to identify the bra
classes of compounds responsible for tl
measured toxicity and to provide infc
mation on potential toxicity treatme
options. The wastewater fractionatii
procedure revealed that non-polar orgar
compounds were the principal toxicar
in both the influent and effluent wasl
waters. GC/MS analysis of the non-pol
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industrial dischargers that interfere with
biological treatment at the Patapsco
plant; however, further research is need-
ed to confirm that the data on in-
terference effects are not false positive
results.
• The combination of the toxicity treatability
screening procedure and the fractiona-
tion procedure was an effective tool for
tracking and for characterizing toxic in-
fluent wastewaters, which were refractory
to treatment by the Patapsco plant's
biomass.
The full report was submitted in fulfill-
ment of Cooperative Agreement No.
812790-01-1 by the City of Baltimore under
the sponsorship of the U.S. Environmental
Protection Agency.
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Figure 4. Toxicity reduction and acute toxicity of various fractions of industrial wastewaters
(D and E) from the toxicity treatability test.
John A. Botts and Jonathan W. Braswell are with Engineering-Science, Fairfax,
VA 22030; William L Goodfellow is with EA Engineering, Science and
Technology, Sparks. MD 21152; and the EPA author Dolloff F. Bishop (also
the EPA Project Officer, see below) is with the Water Engineering Research
Laboratory, Cincinnati, OH 45268.
The complete report, entitled "Toxicity Reduction Evaluation at the Patapsco
Wastewater Treatment Plant," (Order No. PB 88-220 488/AS; Cost: $32.95.
subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Water Engineering Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
-------
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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