vvEPA
United States
Environmental Protection
Agency
Municipal Environmental Research C*
Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-82-028 Sept. 1982
Project Summary
Collection and Treatment of
Wastewater Generated by
Pesticide Applicators
Kenneth F. Whittaker, John C. Nye, Ronald F. Wukash, Robert G. Squires,
Alan C. York, and Henry A. Kazimier
A research project was conducted
to develop a system for the control of
pesticide-contaminated wastewaters
generated by pesticide applicators.
The problem was approached in three
phases. First, the practices that are
currently used to handle pesticide-
contaminated wastewaters were eval-
uated, followed by the development of
a system for collecting them. Finally, a
treatment plant was developed to
remove pesticides from the contami-
nated wastewaters and to produce
high-quality effluents.
The treatment plant is well suited for
treatment of pesticide formulations of
varying concentrations. Much of the
toxic material can be removed during
the first coagulation stage, which is
followed by activated carbon absorp-
tion to remove most of the remaining
pesticides. This low-cost, low-tech-
nology system seems particularly
appropriate for small-scale field op-
erations.
This Project Summary was devel-
oped by EPA's Municipal Environ-
mental Research Laboratory, Cincin-
nati, 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 disposal of pesticide-contami-
nated wastewaters has attracted na-
tional attention during the past two
decades. Considerable environmental
degradation has been caused by the im-
proper disposal of pesticide-contami-
nated wastes. Current Federal regula-
tions on the control and disposal of toxic
wastes, along with existing pesticide
certification programs, will have far-
reaching impacts on how pesticide ap-
plicators dispose of wash water used to
clean application equipment. In an
effort to provide applicators with an
alternative method for handling the
wastewater, a low-cost collection and
treatment system was developed.
The objectives of the research were:
1. To evaluate the practices used by
pesticide applicators to control
wastewater generated during the
cleanup of application equipment
2. To construct a system to collect
the wastewater generated by
pesticide applicators.
3. To design, construct, and evaluate
a wastewater treatment plant
capable of removing pesticides
from the wastewaters generated
by pesticide applicators.
Wastewater Control Practices
Pesticide applicators have used
numerous techniques to dispose of the
wastewaters that are generated during
cleanup of equipment. The triple rinse
procedure for cleaning pesticide con-
tainers, which is recommended by the
U.S. Environmental Protection Agency
(EPA), is generally followed when
cleaning a spray system. The 100 to 400
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L of wastewater used each time a plane
is cleaned is usually dumped in the
cleanup area. A few applicators haul the
dilute rinsewater back and spray it on
the target area. As fuel costs increase,
this practice is seldom followed. More
common disposal practices involve
dumping of wash water into a holding
pond or gravel trench. Research is
underway at Texas A&M and at Iowa
State to provide applicators with evap-
orative disposal practices. The residue
left after evaporation of the water
usually accumulates in the evaporative
disposal systems. The ultimate fate of
the pesticide is unknown.
The cleanup practices used by aerial
applicators vary, but several consistent
practices were observed. The application
equipment is thoroughly cleaned about
once a week by most applicators. The
spray system and hoppers are usually
washed daily. Most applicators try to
organize their daily operations to that
insecticides and fungicides are applied
first, and herbicide applications are
made during the latter part of the day.
After herbicides are applied, the equip-
ment must be thoroughly cleaned to
avoid any carryover to the next spray
job. This management practice allows
the applicator to minimize the amount of
wastewater that is generated each day.
Wastewater Characteristics
Wastewater from an aerial applicator
at Delray Beach, Florida, was obtained
and analyzed for total suspended solids
(TSS), suspended volatile solids (SVS),
chemical oxygen demand (COD), and
pH. Nineteen-liter buckets were used to
collect the wastewater. Samples in-
cluded the pesticide dumped out of the
hopper, the wash water used to clean
the spray boom, the wastewater used to
clean the aircraft hopper, the wash
water from the surface of the plane, and
a composite sample of all the wash
water and wasted pesticides that would
be generated during the cleanup of the
equipment. Results are presented in
Table 1.
The highly variable concentration of
pollutants represented a severe prob-
lem in developing a treatment system to
handle the wastewater. The different
types of pesticides (i.e., wettable
powders, emulsifiable concentrates,
granules, soluble salts, etc.) also
challenged most treatment options.
Wastewater Collection
A simple wastewater collection
system was installed at Monon, Indiana.
Table 1. Volume and Characteristics of Wastewater Generated by Aerial Pesticidt
Applicators
Characteristics
COD
Source
Volume
(L)
Total Soluble pH TSS SVS
(mg/Li (mg/L) (mg/Lj (mg/L)
Pesticide formulation
in hopper
Rinse water used to
clean spray boom
Wash water used to
clean hoppe'r
Wash water used to
clean aircraft
Composite wastewater
samples
5-20 60,000
40-WO 13,000 9,600 6.5 11.600 8.90C
20-40 88,500 5,000 7.0 18,000 14.00C
75-200 1,200 500 7.5 600 35C
150-360
1.200
900 6.9 1,100
95C
The existing concrete pad was modified
to divert all wastewater to one corner of
the pad, where a sump was installed
(Figure 1). Wastewater was pumped
from the sump to a steel storage tank.
At 1980 prices, a collection system
would cost an applicator about $1,600
for a 15- x 15-m concrete slab with a
sump, $150 for a chemically resistant
sump purnp, and $500 for a 2,000-L
above-ground storage tank. All waste-
water is stored in one composite tank
with this type of collection system. Rain
water is also collected unless provision
can be made to divert the runoff. With
this simple collection system, a treat-
ment system is required that can handle
the wide variety of pesticides used by
aerial applicators.
Treatment System
Based on the results for several
treatment options analyzed in the
laboratory, a pi lot treatment system was
developed consisting of coagulation/
flocculation/sedimentation, filtration,
oil coalescence, and activated carbon
absorption (Figure 2). After initial tests,
the filters and oil coalescers were
removed, and the pilot plant was
mounted on a small trailer. Thef iltration
step was discontinued because the
fabric filter and diatomaceous earth
filters did not significantly improve
effluent quality, and the oil coalescer
plugged too quickly to be practical.
Coagulation Studies
Thecoagulation/flocculation/sedi-
mentation process was expected to
reduce the pesticide concentration to its
water solubility level or below. Two-liter
Figure 1. Sump installed in one
corner of a concrete pad
to collect all wastewater.
Figure 2. Pilot plant treatment system
for wastewater from pesti-
cide application equipment.
jar tests were conducted on synthetic
wastewater solutions containing (1
carbaryl (Sevin),* a widely used N-alky
carbamate insecticide, (2) malathior
(cythion), a commonly used phosphoro-
dithioate insecticide, and (3) metribuzir
(Sencor), a triazine herbicide.
"Mention of trade names or commercial products
does not constitute endorsement or recommenda-
tion for use
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Even though alum was chosen as the
coagulant for this study, it should be
noted that in preliminary studies,
equivalent doses of ferric chloride were
equally effective. When aluminum or
iron salt coagulants are used, sufficient
alkalinity must be present in the
solution to allow a complete reaction.
Approximately 0.85 mg/L of alkalinity
as CaCo3 must be present for each mg/L
of alum reacted. Sufficient alkalinity
was maintained by adding NaOH to the
solution. Effective alum coagulation is
limited to the pH range of 6.5 to 8.0.
Only one of the collected samples was
outside this pH range, and this was
easily adjusted to the proper level by
adding NaOH.
After a series of 2-L jar tests was
conducted, pilot-scale studies were
begun. The pilot plant (Figure 3)
consisted of a 380-L tank, 0.7 m in
diameter and 1.1 m high. Three taps
were located on the tank: two on the
side (approximately 0.5 and 0.7 m below
the top of the tank) and one at the bottom
of the tank. The side taps were used to
draw off supernatant after settling. A
variable-speed mixer was mounted
above the tank with a 10- x 30-mm
paddle blade mixer inserted into the
tank to a depth of approximately 0.7 m.
Flocculation of the suspended solids
(SS) was achieved by adding alum,
alkalinity, and an anionic polymer to
350-L batches of wastewater and
mixing at full speed (about 250 rpm) for
2 min. The variable-speed mixer was
slowed to 30 rpm for 30 min to build the
large floes that would settle rapidly (in
less than 1 hr) when the mixer was
stopped (see Table 2). After 1 hr, the
solids settled 0.5 m, and a transparent
supernatant was obtained. Little addi-
tional settling was observed after 1 hr.
Since the coagulation/flocculation/
sedimentation treatment system pro-
duced a sludge after each treatment,
studies were conducted to determine
the effect of this buildup of sludge solids
on the treatment of subsequent batches.
To conduct this test, wastewater was
added to the settled sludge. The solids
concentration of the mixture ranged
from an initial 2,000 to 20,000 mg/L
TSS after 10 batches of wastewater
were treated. At the higher solids
concentration, settling took longer (up
to 90 min), but the solids concentrations
of the supernatant was less than 40
mg/L TSS. Above 15,000 mg/L TSS,
alum addition was unnecessary. Large
floe formed and settled with only the
addition of 1 mg/L anionic polymer. The
HT\ Holding Tank
C J Pump
fCV Flow Control Valve
[WM] Water Meter
3 Way Selector Valve Activated Carbon
Absorption Columns
[pt~i] pH Adjustment
•x
Sludge Discharge
S Sampling Point
Mixer
[22 Liquid Level Control
Figure 3. Schematic diagram of the pesticide treatment plant.
samples tested in this experiment
contained the wettable powder formu-
lation of carbaryl.
After the successful removal of
wettable powder formulations such as
carbaryl, the next phase was to analyze
emulsion removal. Initial jar tests were
performed on tap water solutions of
malathion at a concentration of 200
mg/L (water solubility, 145ppm). Alum
doses of 100 mg/L or greater (with
anionic polymer) gave excellent super-
natant quality. The effects of varying the
malathion dose at a constant alum dose
(100 mg/L) and 1 mg/L anionic polymer
are illustrated as follows:
Table 2. Settling Rate of Waste-
Treated with Alum
Settling Time
(min)
30
45
60
Sample
Tap*
Top
Bottom
Top
Bottom
Top
Bottom
SS
(mg/L)
205
225
25
52
16
42
Initial
Malathion
Concentration
(mg/L)
10
30
75
150
300
Final
Malathion
Concentration
(mg/L)
9-14
9-11
11-13
15-18
20-25
Based on these results, full-scale
tests were conducted using field samples
of wastewater mixed with previously
settled alum sludge and sufficient
malathion formulation to give 180 to
200 mg/L of the pesticide. With an SS
concentration of 24,000 mg/L, it took 60
to 90 min for the solids layer to settle 0.7
m. The supernatant malathion concen-
tration was 35 mg/L. Studies of tap
*The sample taps were located 0.5 and
0.7 m below the surface of the tanks,
which were 1.1m deep.
water with malathion added were less
successful, yielding a supernatant
concentration of 55 mg/L. Later tests
on a solution with lower SS concentra-
tions showed a malathion reduction
from 400 to 41 mg/L after 1 hr of
settling. Increasing alum dosages up to
500 mg/L did not improve performance.
As the SS increased to near 50,000
mg/L in the sample, so did the mala-
thion concentration of the supernatant,
reaching as high as 81 mg/L in one
case. This solution of wastewater was
diluted to 12,000 to 15,000 mg/L SS;
200 mg/L of malathion was then added
along with alum and anionic polymer.
Settling after coagulation reduced
malathion concentration to 27 mg/L.
No change in malathion concentration
was observed after 18 hr of settling.
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Subsequent coagulation studies on
solutions of widely differing SS concen-
trations showed that the 12,000 to
15,000 mg/L concentration range was
the maximum that could be effectively
treated with our system. Higher concen-
trations did not settle below the bottom
tap after 45 to 60 min of settling.
Later attempts to use the standard
alum coagulation procedure on a
mixture of wettable powders and
emulsions collected at the Purdue
University farm were completely un-
successful, even at greatly increased
coagulant doses, with and without
polymers. Several alternative tech-
niques, including acid cracking of the
emulsion, were likewise unsuccessful.
The difficulties seemed to arise from the
presence of a wetting agent added to the
mixture. Addition of calcium salts
(approximate calcium to wetting agent
molar ratio of 2:1) destabilized the
emulsion and made it amenable to alum
coagulation. Another field sample
collected sometime later also required
the addition of calcium salts. In this
case, 0.5 to 1 mg/L of Ca (introduced as
CaCI2) successfully destabilized the
emulsion.
In the next series of tests, metribuzm,
a soluble herbicide, was added to
wastewater and mixed with resuspen-
ded alum sludge. Some dissolved metri-
buzin was removed by coagulation. This
removal is especially apparent in the
three lowest concentrations shown in
TableS. One possible explanation is that
previously settled emulsified material,
when resuspended, may have con-
tributed to a partial extraction and
hence removed some of the dissolved
organic compounds from solution. This
explanation is consistent with the low
malathion concentrations observed
after coagulation. Since the sludge con-
tains some emulsifying chemicals, re-
suspending the sludge allows them to
extract some of the dissolved pesticides.
This conclusion was corroborated with
full-scale testing in which metribuzin
concentrations of 200 and 264 mg/L re-
duced solids levels of 12,000 to 15,000
mg/L to 115 and 140 mg/L, respect-
ively — well below the water solubility
concentration of 1,200 mg/L.
Based on our observations, jar testing
of solutions should be used to deter-
mine proper coagulant dose and sub-
sequent settleability. This method
should provide enough information to
indicate when solids wasting is neces-
sary or when additions of calcium salts
are required.
Table3.
Alum
Dosage
(mg/L)
Effect of 200- and 500-mg/L Alum Doses on Metribuzin Removal b)
Flocculation/Sedimentation
Initial
Concentration
of Metribuzin
(mg/L)
Final
Concentration
of Metribuzin
(mg/L)
200
500
200
500
200
500
200
500
200
500
200
500
100
WO
500
500
750
750
1,250
1,250
2,000
2,000
3,000
3,000
81
90
330
315
585
585
1,050
1,125
996
982
920
1,000
Carbon Absorption Studies
The original field-collected carbaryl
solution had a concentration of 450 to
480 mg/L after coagulation and sedi-
mentation, and the main hydrolysis
product (naphthol) had a concentration
of 225 mg/L The high carbaryl concen-
tration indicated that a good deal of
suspended material was left in the
supernatant, but these tests were
conducted early in the study before the
coagulation procedure had been opti-
mized. By passing the solution through
the carbon columns at 3.8 L/min (90
L/mm per m2) with a contact time of 8
mm, the concentrations of both carbaryl
and naphthol were reduced to less than
1 mg/L.
The capacity of activated carbon to
absorb pesticides varies with the
pesticide Exhaustion tests were con-
ducted on malathion and metribuzin to
determine this capacity. Small glass
columns that held 25 g carbon were
used for this test. Figure 4 shows the
breakthrough curve for malathion. The
carbon had absorbed 0.17 g malathion/
g carbon by the time the effluent
malathion concentration reached 3
mg/L. The carbon was exhausted (that
is, the effluent malathion concentration
reached the influent concentration)
after 0.28 g malathion/g carbon had
been absorbed. The activated carbon
can absorb more metribuzin. In similar
studies, the exhaustion point for metri-
buzin was found to be 0.43 g metribu-
zin/g carbon.
By using 2 carbon columns in series,
it is possible to saturate the first column
with pesticide before the pesticide
concentration leaving the second column
reaches the detection limit.
Initial Malathion Concentration
Activated Carbon Column -
25 50 75 100 125 15i
Liters of Malathion Applied
Figure 4. Breakthrough curve for
malathion applied to
activated carbon.
The ability of activated carbon to
absorb a variety of pesticides was tested
in additional samples in which mala-
thion, carbaryl, and metribuzin were
added to wastewater samples that had
been collected in the field. Although
these initial tests demonstrated that the
pilot plant carbon columns would
absorb the pesticide to below the
detection limits, no attempt was made
to determine the exhaustion point of
pilot plant columns. Additional studies
determined the exhaustion points for
mixed groups of pesticides and herbi-
cides.
The carbon columns on the pilot plant
were not exhausted in the field test
because each column held about 20 kg
of carbon. To exhaust them, about
40,000 L of typical wastewater would
have to be treated. During our test, only
20,000 L of wastewater could be
collected.
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Conclusions
The pesticide treatment plant described
here appears to be well suited for
treatment of pesticide formulations of
varying concentrations. A large per-
centage of these toxic materials can be
successfully removed during the first
coagulation stage. The phase separa-
tion process is followed by activated car-
bon, an adsorbent well known for re-
moving many types of organic com-
pounds from aqueous solution. This
low-cost, low-technology system seems
particularly appropriate for small-scale
field operation, an area in which accept-
able treatment alternatives are notably
lacking. One possible advantage of the
system (over and above the obvious
benefits of protecting wildlife, crops,
and water supplies) might be the reuse
of the treated water for mixing new
formulations or for washing theapplica-
tion equipment. Such an option would
achieve the goal of zero discharge.
The following conclusions are based
on the test conducted to evaluate the
two-step process to remove pesticides
from contaminated wastewater:
1. All pesticide-contaminated waste-
water that is generated during the
cleanup of application equipment
can be combined in one collection
and storage system. The widely
varying concentrations, types of
formulations, and variety of pesti-
cides can be treated by the two-
stage process.
2. Alum can be used as a flocculant
to reduce the concentration of
pesticide in the contaminated
wastewater to below the water
solubility of the compound. An
amonic polymer enhances the
sedimentation.
3. Activated carbon can remove most
other pesticides in the supernatant
of the first stage sedimentation
process. The capacity of the
carbon to absorb the contaminant
depends on the chemical structure
and characteristics of the pesticide.
4. Particle size filtration and oil coa-
lescence are not effective in
removing pesticides from waste-
water,
Recommendations
The disposal of the sludge and spent
activated carbon must be considered.
These problems appear to be manage-
able, though more study is needed.
Approximately 20,000 L of wastewater
was treated in this study, with an
accumulation of less than 200 L of
sludge. Several techniques to encap-
sulate or fix the sludge in a concrete
mixture were also evaluated with some
success. The carbon can be thermally
destroyed or regenerated by commercial
firms. Other techniques for disposal of
the waste sludge and carbon must also
be found. Currently the sludge and
carbon would be considered a hazardous
waste and would require disposal in an
approved landfill.
The detection of pesticide break-
through during carbon absorption must
also be further evaluated to ensure that
the effluent is free of trace quantities of
pesticides.
The full report was submitted in
fulfillment of Grant No. R805466010by
Purdue University under the sponsorship
of the U.S. Environmental Protection
Agency.
Kenneth F. Whittaker, John C. Nye, Ronald F. Wukash. Robert G. Squires, and
Alan C. York are with Purdue University, West Lafayette, IN 47906; Henry A.
Kazimier is with Aeronautic Commission of Indiana, Indianapolis, IN 46206.
Frank Freestone is the EPA Project Officer (see below).
The complete report, entitled "Collection and Treatment of Wastewater Gener-
ated by Pesticide Applicators," (Order No. PB 82-255 365; Cost: $12.00,
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:
Oil and Hazardous Materials Spills Branch
Municipal Environmental Research Laboratory—Cincinnati
U.S. Environmental Protection Agency
Edison, NJ 08837
. S. GOVERNMENT PRINTING OFFICE: 1982/559-092/0521
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Environmental Protection
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