United States
Environmental Protection
Agency
Risk Reduction
Engineering Laboratory
Cincinnati, OH 45268
Research and Development
EPA/600/S2-91/047 Jan. 1992
4JrEPA Project Summary
Removal of DBCP from
Groundwater
Volume 2
Field Pilot Plant Operation
Karl E. Longley, George P. Hanna, and Barry H. Gump
Freundlich adsorption isotherm de-
terminations were performed on
groundwaters containing different pes-
ticide contaminants:1,2-dibromo-3-
" chloropropane (DBCP), ethylenedibro-
mide (EDB), and 1,2-dichloropropane
(DCP). The bottle-point Freundlich ad-
sorption isotherm constants for the
groundwater were considerably lower
than the constants for the same pesti-
cide in deionized reagent water indicat-
ing the natural matrix in the groundwa-
ter occupied or otherwise made un-
available to the pesticide a large num-
ber of the adsorption sites.
When performing the static Freund-
lich adsorption isotherm test, the GAC
was not exposed to the water for any
appreciable time before being exposed
to the pesticide thereby minimizing the
occurrence of preadsorption. Likewise,
when performing the dynamic isotherm
test, the pesticide broke through the
GAC bed immediately due to its rela-
tively high concentration and the small
amount of GAC in the micro-columns.
In this manner the Freundlich adsorp-
tion isotherm tests departed from prac-
tice where a significant part of a GAC
bed may not be in contact with the
natural organic matrix in the water be-
ing applied for days and even weeks
before being in contact with the pesti-
cide, thereby promoting preadsorption
and significantly decreasing the adsorp-
tion capacity of the GAC bed.
No decrease in the DBCP concentra-
tion or change in carbon use could be
attributed to bacterial organisms as de-
termined by the heterotrophic plate
count test. It should be noted that the
extracellular metabolic products of
these organisms could be a source of
material adsorbing onto the GAC.
This Project Summary was developed
by EPA's Risk Reduction Engineering
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
Two basic solutions exist for the prob-
lem of providing safe drinking water from
wells that obtain groundwater from aqui-
fers contaminated with synthetic organic
chemicals. One solution is to drill deeper
wells to tap aquifers containing water which
meets water quality standards. The sec-
ond solution is to continue to use existing
wells while removing the contaminants by
use of a treatment process. Granular
activated carbon (GAC) has long been
recognized as a substance capable of
adsorbing organic contaminants from wa-
ter. Competitive adsorption of target syn-
thetic organic contaminants and naturally
occuring dissolved organic substances is
a major factor responsible for GAC unit
performance variability. The primary em-
phasis in this report is the evaluation of
the field use of GAC for the removal of
DBCP and other pesticides from ground-
water containing natural dissolved organic
substances and experiencing natural vari-
abilities in water quality.
Printed on Recycled Paper
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Background
Large areas of California's irrigated farm-
lands were treated with the soil fumigant,
1,2-dibromo-3-chloropropane (DBCP), for
the control of nematodes. The DBCP has
migrated through the soil, contaminated
aquifers, and has been the cause for the
closure of thousands of wells used for
drinking water. California's San Joaquin
Valley now contains the nation's heaviest
and most widespread DBCP pollution. The
use of DBCP was suspended in California
in 1977 after it was identified as a testicu-
lar toxin and potential carcinogen to hu-
mans. Other pesticides used in the past
as soil fumigants and now found in ground-
water, though not as extensively as DBCP,
are ethylenedibromide (EDB) and 1,2-
dfchtoropropane (1,2-DCP).
The natural organic matrix in a ground-
water is poorly adsorbed by the GAG bed
of an adsorption unit, and when the unit is
put into operation, the natural organic ma-
trix is almost immediately in intimate con-
tact with the total contents of the carbon
bed. On the contrary, the organic com-
pound for which the water is being treated
may require days, weeks,' or even months
before it permeates the total GAC bed.
Throughout this time period, often lengthy,
the natural organic matrix has been
adsorbing to the carbon. This adsorption
by the natural organic material is poorly
reversible.
Extensive research during the 1960s on
the use of GAC in treating waters with a
very high organic content revealed sev-
eral attributes of GAC which remain appli-
cable today: pilot columns can model the
performance of full-scale beds; specific
synthetic organic contaminants can be re-
moved by GAC adsorption; and the re-
moval of compounds producing taste and
odor is more effective than the removal of
certain specific compounds. Technical dif-
ficulties with the use of GAC for water
treatment include the potential growth of
microorganisms on GAC surfaces and the
possible subsequent creation of harmful
substances such as endotoxins and nitro-
samines. Adverse chemical effects in-
clude the leaching of metals and other
inorganic metal elements from GAC. The
major disadvantages of GAC adsorption
can be minimized by proper operation and
monitoring.
Results and Discussion
A mini-pilot plant was constructed with
three columns having a 1.3 cm ID and
having 60x80 mesh GAC beds with depths
of 3, 6, and 9 cm. A fourth column with a
5.1 cm ID had a 16x40 mesh GAC bed
with a depth of 9 cm. The hydraulic
loading rate generally varied within the
range of 10 to 14 m/hr.
The organic matrix in the groundwater
was characterized by its concentration of
total organic carbon (TOG) which was
present at concentrations generally about
three orders of magnitude greater than
the pesticide. The mini-pilot plant was
operated under ambient conditions in the
field treating groundwaters containing dis-
solved organic substances and experienc-
ing natural variabilities in water quality in-
cluding a large variance in temperature
during its lengthy period of operation
(DBCP field site data collection began dur-
ing July 1987 and concluded during Feb-
ruary 1988). This temperature variation is
a real world phenomenon particularly im-
pacting Point-of-Entry/Point-of-Use sys-
tems treating groundwater since these sys-
tems treat small flows. The dynamic iso-
therm and carbon use data collected from
such a real world system can differ from
data obtained from temperature-controlled
bench studies conducted in the labora-
tory.
Conventional bottle-point and dynamic
adsorption isotherm determinations were
conducted in the laboratory. A micro-pilot
plant having 3 mm ID columns packed
with 80x100 mesh GAC to a bed depth of
1 cm was used for the dynamic isotherm
determinations. The higher pesticide con-
centrations used for these determinations
were within an order of magnitude of the
concentration of the TOG. Lower pesti-
cide concentrations approaching concen-
trations found in the environment were
also used when conducting the bottle-point
Freundlich adsorption isotherm test. When
performing this test, the GAC was not
exposed to the water for any appreciable
time before being exposed to the pesti-
cide, thereby minimizing the time for pre-
adsorption. Likewise, when performing
the dynamic isotherm test, the pesticide
broke through the GAC bed immediately
due to the relatively high pesticide con-
centration (106 to 298 n.g/L) and the small
amount of GAC in the micro-columns. In
this manner, the adsorption isotherm tests
departed from practice where a significant
part of a GAC bed may be in contact with
the natural organic matrix in the water
being applied for days and even weeks
before being in contact with the pesticide.
This might promote significant
preadsorption and possibly decrease the
adsorption capacity of the GAC bed for
the pesticide.
Figure 1 shows bottle-point, mini-plant,
and micro-plant Freundlich isotherm data
determined using DBCP field site water.
The regression line and the 95% confi-
dence limit lines were derived using only
bottle-point isotherm data. With the ex-
ception of one datum, all the values fall
within the 95% confidence limits.
Heterotrophic bacteria plate counts were
determined for a 51/2 month field run, start-
ing in July 1987 and ending in February
1988 on a groundwater containing DBCP.
The bacterial counts in the product water
were significantly greater than those in
the feed water during the warmer months.
These bacterial levels decreased to ap-
proximately feed water levels during the
colder months.
Conclusions
GAC contactors operating in the field
including point-of-entry/ppint-of-use units
can experience large variabilities in water
quality including water temperature. These
large variabilities in water quality can af-
fect the operational efficiency of the GAC
contactors.
The determination of adsorption iso-
therm data in the laboratory may use pes-
ticide concentrations up to several orders
of magnitude greater than the concentra-
tions of the pesticide normally found in
drinking water. The data collected under
these conditions do not represent "real-
world" conditions.
It appears that any of the three systems
(i.e., bottle-point, mini-plant, micro-plant)
are capable of determining carbon use
data for GAC at exhaustion. This is par-
ticularly interesting considering the tem-
perature variability experienced by the
mini-plant and the lack of preadsorption in
both the bottle-point and micro-plant tests.
These findings indicate that preadsorption
was not a significant factor. This finding
is significant since static isotherm data
are easier and less costly to develop.
No decrease in the DBCP concentra-
tion could be attributed to bacteria as de-
termined by the heterotrophic plate count
test. The extracellular metabolic products
of these organisms could be one source
of material adsorbing onto the GAC.
Recommendations
The significance of TOC preadsorbing
onto the active adsorption sites in a GAG
bed should be established for a range of
"typical" surface waters and groundwaters.
The effect on adsorption of microorgan-
isms colonizing the GAC bed of an
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1
adsorber should be determined including
the effect of extracellular metabolic prod-
ucts of the microorganisms.
Additional pilot-plant field work should
be carried out to determine the effect of
natural variations in temperature on the
adsorption dynamics of GAG.
The full report was submitted in partial
fulfillment of Cooperative Agreement CR-
812227-01-3 by the California State Uni-
versity, Fresno under the sponsorship of
the U.S. Environmental Protection Agency.
1000 p
100
, 10
Regression Line for Predicted Values
Upper 95% C.L
No te:
Lower 95% C.L.
Order of mini-plant data points
from high to low are columns 2,
1, 3, and 4, respectively.
D Bottle Point Isotherm Date
» Mini-Plant Isotherm Data
A Micro-Plant Isotherm Data
.001
.01 .1 1
DBCP Residual Cone. (Ce), mg/L
10
Figure 1. Bottle-point, mini-pilot plant and micro-pilot plant isotherm data with DBCP field site water.
•&V.S. GOVERNMENT PRINTING OFFICE: 1992 - £48-080/40128
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K.E. Longley, G.P. Hanna, and B.H. Gump are with California State University,
Fresno; Fresno, CA 93740-0094.
Walter Felga is the EPA Project Officer (see below).
The complete report, entitled Removal of DBCP from Groundwater; Volume2, Field
Pilot Plant Operation,'(Order No. PB91-234 609/AS; Cost: $26.00; 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:
Risk Reduction Engineering Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
Unitod States
Environmental Protection
Agency
Center for Environmental
Research Information
Cincinnati, OH 45268
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
Official Business
Penalty for Private Use $300
EPA/600/S2-91/047
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