United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
I /,
Research and Development
EPA-600/S2-84-195 Mar. 1985
Project Summary
Liquid-Liquid Extraction of
Trace Level Pesticides from
Process Streams
G.V. Hiler and S.D. Cameron
Previous research has demonstrated
that liquid-liquid extraction for the
treatment of pesticide manufacture
wastewater is competitive with existing
methods of treatment and is a po-
tentially less costly alternative. The ob-
jective of this research program was to
resolve further the feasibility of this
process.
Experiments were conducted using
the Solvent Extraction of Organic
Pesticides (SEXOP) process, modified
to optimize the system for treating
effluent samples from commercial 2,4-
D and bromacil manufacturing opera-
tions.
EPA standard analytical methods
were used to compare the treated
effluent from a series of SEXOP runs to
the untreated starting material. These
analytical data were used to calculate
pesticide extraction efficiency. Results
show that pesticide removal in excess
of 98 percent is attainable during initial
operation, and 70 percent on a steady-
state basis for a single-pass system for
both samples tested. Staging of extrac-
tion units and increased solvent/water
ratios would be expected to optimize
steady-state efficiencies above 90
percent.
An economic analysis, projecting
engineering cost estimates for both a
large and small commercial-scale
SEXOP process, is also presented. A
projected large SEXOP plant should be
able to process 301 million gal./yr* of
effluent at an estimated cost of about
$2/1,000 gal.
*)Readers more familiar with the metric system may
use the following conversion factors: 1 ft3 =
2.832x10"2m3, 1 gal. =0 3785x10~3m3,and1 HP =
0 7460 kW.
This Project Summary was developed
by EPA's Air and Energy Engineering
Research Laboratory, Research Triangle
Park, NC, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering
information at back).
Introduction
This report describes continued research
to explore the feasibility of extracting
pesticides from process streams, using
high-volatility solvents and a liquid-liquid
solvent extraction approach. During the
course of prior research conducted by S-
CUBED, a bench-scale SEXOP device
was constructed and used to demonstrate
that liquid-liquid extraction for the
treatment of pesticide manufacturing
wastewater is a viable technology and an
effective method of treatment. The
central feature of the SEXOP device is a
high-speed rotary-disc, counter current
liquid-liquid extraction column, designed
to use high-volatility solvents as the
extraction media. Other components of
the bench-scale system include a glass-
bead-packed stripper column and a
condenser for the stripping, condensation,
and subsequent recycle of extraction
solvent. The SEXOP process was modified
for use on relatively low partition
coefficient (Kp) pesticide/solvent systems
with the objective of exploring the
feasibility of treating effluent samples
acquired from commercial 2,4-D and
bromacil manufacturing. This objective
was carried out during bench-scale
studies using the SEXOP apparatus and
real-world effluent samples obtained
from pesticide manufacturers.
-------
Results and Conclusions
Eight experiments using actual 2,4-D
and bromacil manufacturing wastewaters
were conducted with the bench-scale
system to demonstrate further the
effectiveness of continuous liquid-liquid
extraction for extracting pesticides from
process waste streams.
A variable of significant importance
explored during the current investigation
was the extraction solvent. Hexane was
the solvent used for the previous DDT
extractions and also for initial experiments
in this program. It was clear from the
initial bromacil extraction efficiencies
obtained that a different solvent with a
higher partition coefficient would be
necessary to attain the desired high
extraction efficiency.
The partition coefficient of a solvent/
wastewater system constitutes a primary
consideration in whether a solvent
extraction process will be effective.
Partition coefficient, Kp, is defined as:
Kp= 'Se)o
(SB)w
(D
where SB is the solubility of the pollutant in
in the phase noted by the subscript 0 for
organic (solvent) and W for aqueous.
Theoretical Kp's of solvent/pesticide
systems of interest are listed in Table 1.
Conclusions based on a review of
solvent and solvent system literature,
along with data obtained from previous
screening extraction studies, resulted in
a change of solvent from hexane to butyl
chloride for extraction of wastewaters
containing 2,4-D and bromacil. The first
seven experiments are summarized in
Table 2. The greatly improved extraction
efficiencies (98.6 percent and 97.9
percent) show that the solvent has a very
Table 1. Partition Coefficient, Kp. of Pesticides
DDT
Toxaphene
Chlordane
Norflurazon
Diuron
2,4-D
Bromacil
Glyphosate
Hexane
320,000
74,000
11,000
17
3.5
0.24
1.32
0.111
Pentane
270.000
39,000
26,000
27
3.0
0.19
1.29
0
Isopropyl
Ether
230,000
140,000
84,000
61
53.3
83.9
10.7
0.048
Ether
960.000
180,000
130,000
190
182
65.8
18.1
0.109
Butyl
Chloride
370.000
160,000
240.00
200
95.1
5.7
28.7
0.030
significant impact on extraction efficiency.
They also show that the partition coefficient
continued to be an important variable but,
due to the increased mechanical efficiency
of the modified rotating disc contactor
(RDC), need not be nearly as high as the
previously studied DDT/hexane system
may have indicated. Moreover, it is clear
from subsequent experiments that clean-
up of pesticide manufacturing wastewaters
in the upper 90th percentile is possible,
using a solvent that provides a relatively
low Kp value. The Kp value for 2,4-D in
butyl chloride is 5.7 compared to 28.7 for
bromacil and 320,000 for DDT in hexane.
Even so, extraction efficiencies were all
maintained above 95 percent during the
first hour of operation.
With the present system configuration
and methods of operation used, extraction
efficiencies typically decline over time
from some point until equilibrium is
attained. This was demonstrated in an
extended experiment. During the 7-hour
run, an equilibrium point was reached in
the 70 to 80 percent range as shown in
Figure 1.
Theoretically, this equilibrium is con-
trolled by the partition coefficient achieved
by the solvent, the solvent and water-flow
rates, and the water/solvent volume
ratio. Therefore, the level of decline and
point of leveling off experienced can be
adjusted by changing these parameters.
While the water/solvent volume ratio
Table 2. Summary of Project Experiments*'**
Pesticide Extraction Efficiency (%)
Run
No.
1
2
3
4
5
6
7
To
80.7
58.8
98.6
97.9
99.1
98.9
r,
61.7
45.3
97.3
95.4
98.6
96.9
T2
50.6
25.8
95.3
93.2
97.3
93.4
73
40.7
16.2
92.9
89.5
95.5
92.4
T,
36.6
15.2
91.7
84.8
95.6
90.4
Ts Aqueous Feed
Deionized
Water
30.2 Synthetic
Bromacil
Solution
0.3 Bromacil
Plant
Wastewater
90.2 Bromacil
Plant
Wastewater
79.4 Bromacil
Plant
Wastewater
2,4-D Plant
Wastewater
88.8 2,4-D Plant
Wastewater
So/vent
Hexane
Hexane
Hexane
Butyl
Chloride
Butyl
Chloride
Butyl
Chloride
Butyl
Chloride
Water
Flow
Rate
ml/min
40
40
40
40
40
80
Water/Solvent
Flow Rate
2-1
2:1
2:1
2:1
2:1
4:1
Water/Solvent
Volume Ratio
1:4
1:4
1:4
1:4
1:4
1:4-4:1
Exchanges
Per Hour
0.76
0.76
0.76
0.76
0.76
1.27
aA typical run consists of the following: 1) Fill the RDC column with solvent. 2) Start the mixer motor and wastewater input, allowing the water to
displace about 20% of the so/vent volume. 3) When the water/solvent volume ratio reaches 1.5, start the solvent flow in and water flow out. 4)
Maintain this steady state condition until 3 hours have elapsed from the time the mixer motor and wastewater input were started. 5) Take aliguots of
treated water every 30 minutes.
hMot or speed = 1800 rpm.
^Solvent flow rate =20 ml/min.
-------
too
95
I 90
o.
ai
8
.o
85
80
75
70
i
012345678
Sample Number (Samples Taken Every 30 Minutes}
10 11 12 13
significantly impact the economic analyses
made in the prior project. Tables 3 and 4
show the capital and operating cost data
for both a small and large commercial-
scale SEXOP process. The results show
that the cost of SEXOP technology
compares favorably with alternative
wastewater treatment options.
Figure 1. Run 8 pesticide extraction efficiency vs. sample time.
was 4:1, a desirable ratio for running the
RDC with the water phase dispersed in
solvent, an increase in solvent/water
flow rate and/or change to a solvent that
yields an increased partition coefficient
would almost certainly improve the over-
all pesticide extraction efficiency and es-
tablish a higher level of equilibrium ef-
ficiency. Economically, increasing the
solvent flow rate over the water flow rate
will not result in a very significant in-
crease in operating expense, since the
solvent is recycled and loss would con-
tinue to be minimal. Larger equipment
might be required for increased solvent
flow rate.
In summary, over the course of conduct-
ing eight experiments, three process
variables and two engineering modifica-
tions were investigated: extraction
solvent, process wastewater, water flow
rate, rod agitators, and settling reservoir.
Results of the experiments show
several important advances in the
process:
High extraction efficiency is attain-
able for bromacil and 2,4-D effluent
streams.
The partition coefficient is very
important in achieving high efficien-
cy. Mechanically induced column
turbulence can offset low partition
coefficients to produce high efficien-
cies.
Extraction efficiency declines over
time, but levels off at a steady-state
level that depends on flow rates,
column turbulence, and solvent.
A preliminary economic assessment
was performed for the SEXOP process
using butyl chloride as the extraction
solvent and some engineering modifica-
tions. The findings of this study did not
-------
Table 3. Capital Equipment Requiring Initial Expenditure Outlay So/vent Extraction
Small Plant (91.000 gal./day) Large Plant (910,000 gal./day)
Component Description
Cost $*
Component Description
Cost $*
J) Wastewater feed pump (not
explosion proof; 10 HP
motor; 3,800 gal./hr; 60
gal. /min
2) Makeup solvent feed pump
(explosion proof) 1 HP
motor; 380 gal./hr; 6
gal./min
3) RDC shaft motor (explo-
sion proof) 1 HP
4) RDC extraction vessel
(with shaft & discs)
1,300 gal.; 170ft3
5) Extract stripper - 1,000
gal.; 140ft; includes
7,176
5,125
200
34,855
1) Wastewater feed pump (not
explosion proof); 100 HP
motor; 38,000gal./hr;
630 gal. /min 20.503
2) Makeup solvent feed pump
(explosion proof) 10 HP
motor; 3.800 gal./hr;
60 gal. /min 10.252
3) RDC shaft motor (explo-
sion proof) 10 HP 1.025
4) RDC extraction vessel
(with shaft & discs)
13.000 gal.; 1.700 ft3 210.158
5) Extract stripper - 11.000
gal.; 1.400 ft3; includes
stripper tower packing
6) Solvent vapor condenser
7) /V2 compressor - 300
ft3/min
8) Nz storage vessel 50 ft3
9) Raffinate stripper -
1.000 gal.; 140 ft3;
includes stripper tower
packing
TOTAL
23.579
16.403
23.579
15.377
23.579
149.873
stripper tower packing
6) Solvent vapor condenser
7) /V2 compressor - 3,3000
ft3/min
8) /V2 storage vessel 500ft3
9) Raffinate stripper -
1 1,000 gal.; 14,000 ft3:
includes stripper tower
packing
TOTAL
86,113
164.025
112.768
153.774
86.113
844.731
"All estimates represent installed costs corrected to 1984 dollars.
Table 4. Summary of First
Year O&M Cost For Solvent Extraction
Small Plant (91.000 gal./day)
O&M Category
1) Initial solvent charge +
makeup
2) Labor (administrative
and technical mix)
3) Maintenance
4) Electrical (6.3 x JO5
kWh)
5) Debt service and
amortization"
6) Real estate taxes
and insurance*1
TOTAL
Cost S
5,000
20,000
15.000
44.000
30. 195
2.997
117.192
Large Plant (910,000 gal./day)
O&M Category
1 ) Initial solvent charge +
makeup
2) Labor (administrative
and technical mix)
3) Maintenance
4) Electrical (4.4 x 106
kWhJ
5) Debt service and
amortization*
6) Real estate taxes
and insurance*
TOTAL
Cost $
56.000
40,000
30,000
308.000
169.254
16.895
620. 149
°At 10% interest over 7 years.
"At 2% of the total capital.
U. S, GOVERNMENT PRINTING OFFICE:!985/559 111/10800
-------
G. V. Hiler and S. D. Cameron are with S-Cubed, P. 0. Box 1620, La Jo/la. CA
92038-1620.
Robert V. Hendriks is the EPA Project Officer (see below).
The complete report, entitled "Liquid-Liquid Extraction of Trace Level Pesticides
from Process Streams," (Order No. PB 85-152 650/A S; Cost: $13.00, 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:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
OOOC329 PS
CHICAGO
RN STREET
IL
------- |