United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S2-85/015 May 1985
SER& Project Summary
Treatment Technology for
Pesticide Manufacturing
Effluents: Bentazon
Robert W. Handy, Doris J. Smith, and David A. Green
Laboratory studies were conducted
on the treatability of wastewater gen-
erated from the manufacture of ben-
tazon. The wastewater was character-
ized for pesticide content by high per-
formance liquid chromatography
(HPLC). Toxicity determinations on
bentazon and its major treatment pro-
duct (dichlorobentazon) were con-
ducted with Daphnia magna. Ben-
tazon was not toxic to the daphnids
at concentration of up to 50 ppm. The
major known by-product of chlorina-
tion of bentazon is dichlorobentazon,
which is toxic to daphnids at 50 ppm.
Emphasis was placed on the remov-
al of bentazon from wastewater by
treatment with sodium hypochlorite.
The effects of variations in the pH,
amount of hypochlorite, temperature,
and mode of hypochlorite addition
were studied. The temperature and
mode of addition had little effect on
the removal of bentazon. It was found
that bentazon is most efficiently re-
moved by hypochlorite when the pH
is 2 or below and when a 245- to
370-fold excess of hypochlorite is
used.
Based on assumed rates of process
wastewater production, the total cost
of the treatment was estimated.
This Project Summary was devel-
oped by EPA's Air and Energy Engi-
neering Research Laboratory, Re-
search Triangle Park, NC, to an-
nounce 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
This report describes a study of the
treatability of wastewater resulting from
the manufacture of bentazon, a postemer-
gence herbicide. The objective of this
project was to conduct a bench-scale
treatability study of bentazon pesticide
manufacturing wastewater using treat-
ment with sodium hypochlorite. Pesticide
removal was the principal criterion for
evaluating the usefulness of each control
treatment. Wastewater treatment oper-
ating conditions were chosen to simulate
actual commercial units in such param-
eters as contact time and temperature, so
that meaningful treatment cost estimates
for manufacturing processes could be
generated.
Under EPA's proposed Effluent Guide-
lines for Pesticides, bentazon may be reg-
ulated as part of Category 2 pesticides.
Based on production, the allowable dis-
charge per day is 4 Ib*, or a concentration
of 2.5 ppm based on a wastewater flow
of 135 gpm* at the specific manufacturing
plant tested. Preliminary studies con-
ducted by the manufacturer have shown
that oxidation with sodium hypochlorite is
effective in destroying bentazon in the
wastewater. Hypochlorite reacts with ben-
tazon as shown below.
'CH(CH3>2
SO, HOO*
NCH(CH3)2
(*)lb x 0.454 = kg; gal. x 3.785 = L.
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Excess hypochlorite is destroyed with
sodium bisulfite before the wastestream
reaches the biotreatment facility.
The large excess of hypochlorite in-
creases the salt content of the waste-
water, and free chlorine and bisulfite can
also be pollutants. Other organic materials
may react with hypochlorite to form prod-
ucts which may be harmful.
While the goal of the treatment is to
reduce bentazon to the 4 Ib/day level,
consideration must be given to the prob-
lems of the generation of additional
pollutants and requirements for com-
patibility with a downstream biotreatment
plant.
Treatability Studies
Samples of bentazon manufacturing
wastewater were obtained from the
manufacturer. Figure 1 is a diagram of the
plant treatment system, showing the
sampling points. Evaluation was carried
out on the sample collected after the car-
bon unit (Sampling Point 2 in Figure 1).
Preliminary treatability studies by the
manufacturer have shown that a 40:1
molar excess of hypochlorite over ben-
tazon was necessary at 24°C and pH 6.0
to achieve a 95% reduction in bentazon
level. This large HOCI excess was required
at both acid and alkaline pH. Since hypo-
chlorite is not selective in its action,
wastewater containing other amine bod-
ies, by consuming additional reagent, will
require an even larger hypochlorite excess
(90:1). Note that the desired conversion
was achieved at the expense of increasing
the salt content of the wastewater.
Excess hypochlorite must be destroyed
before the wastestream reaches the water
biotreatment facility. Sodium bisulfite has
been used successfully in eliminating free
chlorine, although it has been shown that
this reagent also regenerates bentazon
from its N-chloro analog.
NCH(CH3)2
A technique must be developed for
destroying free chlorine which will not
regenerate bentazon because it interferes
with the operation of the biosystem.
Free chlorine and excess bisulfite can
be pollutants. Other organic materials
react with hypochlorite to form products
which may also be harmful. This is par-
ticularly true for amines which can form
Plant
Sources
(*) One of three samp/ing points.
Figure 1. Wastewater treatment system.
potentially toxic and explosive N-chloro
compounds.
The bentazon waste stream entering
the activated carbon unit is expected to
have the following characteristics: pH,
1.0-2.0; temperature, ambient; and ben-
tazon content, 50-300 ppm.
The carbon columns step in the current
treatment process removes 50-75% of the
bentazon and about 95% of the mono-
chlorobenzene from the wastewater.
Therefore, the bentazon content of the
wastewater used in this study should be
between 38 and 150 ppm, based on the
manufacturer's information.
Treatment of Standard
Bentazon Solutions with
Aqueous Sodium Hypochlorite
A standard solution containing 55.2
ppm (within the 38-150 ppm range ex-
pected) bentazon was made up in 1 L of
water. This solution, in 100 ml portions,
was used for preliminary experiments. In-
itially, a 200-fold excess of hypochlorite (2
moles hypochlorite to 1 mole bentazon)
was utilized, timed aliquots of 10 ml were
"quenched" in sodium bisulfite (bisulfite)
to neutralize excess hypochlorite, and the
bentazon was determined by HPLC. Five
separate experiments were performed:
(1) Reagent blank (100 ml water).
Treated directly with hypochlorite.
(2) Dilution blank. Bentazon solution
with water in place of hypochlorite
and bisulfite.
(3) Neutral pH. Bentazon solution
treated directly with hypochlorite.
(4) Acidic pH. Bentazon solution ad-
justed to pH 4 with HCI before addi-
tion of hypochlorite.
(5) Basic pH. Bentazon solution ad-
justed to pH 10 with NaOH before
addition of hypochlorite.
In all cases, the bentazon disappeared
within 10 min, but was "regenerated"
after a period of time, slowly disappearing
again from solution. This suggests that a
rapid reversible reaction occurs which
slowly equilibrates, followed by the less
rapid formation of the final treatment
product. The disappearance of bentazon
was more rapid from neutral and acid
solutions.
In a subsequent experiment, a 100 ml
portion of standard bentazon solution was
treated with a 333-fold excess of hypo-
chlorite, aliquots were removed over time
and analyzed. No bentazon was found in
any of the aliquots (from just after
hypochlorite addition up to 1 hr later).
Treatment of Bentazon-
Containing Wastewater
Aliquots of wastewater taken after the
carbon unit were treated as described
below.
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A. Hypochlorite: 333-fold excess
Exp. No.
BG-10
BG-19
BG-16
BG-17
BG-3
pH
1
2
3
4
6
700
B. pH =1.5
Excess
Hypo-
chlorite/
Exp. No. Benta-
Temp. 20-28°C 3-7°C zon
BG-2,10 BG-20 333:1
BG-11 167:1
BG-12 BG-21 83:1
BG-13 17:1
333-Fold Excess Hypochlorite
at pH 1 and 6
Timed aliquots were taken after the ad-
dition of hypochlorite to 100 ml portions
of the wastewater and quenched in a
slight excess of bisulfite. A second aliquot
was taken immediately and quenched in 3
fold amount of bisulfite to test the effect
of excess bisulfite on bentazon concentra-
tion.
With the use of a 333-fold excess of
hypochlorite at pH 1, the bentazon disap-
peared almost completely within 10 min.
The amount of bisulfite excess made little
difference in the amount of bentazon
detected. At pH 6, the bentazon disap-
peared more slowly: even after 60 min,
more than 55% remained. Some of the
samples were not analyzed on the day the
experiment was run but at a later date.
The values obtained by HPLC were higher
by about 25% for these samples. How-
ever, in a later re-analysis of the pH 1.5
samples, all remained at zero or low
values. It is possible that the large amount
of flocculent material in the quenched ali-
quots may interfere in the analysis, or that
some bentazon is regenerated upon
standing under certain conditions.
333-Fold Hypochlorite Excess
at pH 2, 3, and 4
Timed aliquots were taken from each of
three 100-mL portions of wastewater ad-
justed to pH 2, 3, and 4 with 10N NaOH
and then reacted with a 333-fold excess
of hypochlorite. All aliquots were analyzed
by HPLC after quenching with bisulfite.
The results are shown in Figure 2. The
reaction at pH 2 was nearly identical to
that at pH 1.5; i.e., bentazon disappeared
immediately and was only observed in
very small amounts or not at all up to 3
50
Q)
DC
O
8
20
333-Fold Excess Hypochlorite
—^— Beginning pH = 3
Beginning pH - 4
Beginning pH = 2
5 10 20 30
60
120
180
Time, min
Figure 2. Bentazon-containing wastewater treated with hypochlorite at pH 2, pH 3, and pH 4.
hr. The reaction at pH 4 was more similar
to the previous reaction carried out at pH
6: some bentazon disappeared early in the
reaction (10 min), but about 70% re-
mained even after 3 hr. The pH 3 reaction
showed the bentazon concentration drop-
ping off rapidly at first and then decreas-
ing at a much slower rate to a concentra-
tion of about 20% after 3 hr. Another ali-
quot was taken at 5 hr: the bentazon con-
centration was still about 19%.
There was a distinct change in the reac-
tion between pH 2 and pH 3. The mech-
anisms involved in this treatment are not
known. The reaction mixture has been
titrated at the end of 3 hr and still con-
tained excess hypochlorite. The physical
appearance and amount of insoluble
material varied with time and conditions.
Variations of Temperature and
Hypochlorite Added to
Wastewater
The effects of variations in temperature
and hypochlorite addition were evaluated
in two experiments: in the first, 100 ml
aliquots were treated with a 333-fold ex-
cess of hypochlorite at room temperature
and near 0°C; and in the other, 100 mL
aliquots were treated with a 83-fold ex-
cess of hypochlorite at room temperature
and near 0°C. When a 333-fold excess of
hypochlorite was added, the bentazon dis-
appeared rapidly and was essentially gone
in 5 to 10 min. When this reaction was
carried out at near zero (3-7°C), the reac-
tion proceeded at a slower rate but
resulted in the nearly complete removal of
bentazon. This indicates that bentazon
can be removed at temperatures as low as
freezing.
The low temperature reaction using an
83-fold excess of hypochlorite proceeded
much more slowly than the ambient reac-
tion. In fact, at all points studied, more
bentazon was detected than was originally
present. In trials using a 167-, 83-, and
17-fold hypochlorite excess at room tem-
perature, bentazon levels remaining in the
reaction mixture were measured at levels
5 to 10 times greater than was originally
present. The early appearance of what ap-
pears to be additional bentazon in ex-
periments using less than 333:1 addition
of hypochlorite is striking. There is no ex-
planation for this phenomenon.
Stepwfse Addition of
Hypochlorite to Bentazon-
Containing Wastewater
Several additional experiments were
performed to determine more about the
nature of the hypochlorite/bentazon reac-
tion. First, half the amount necessary for
complete reaction was added (167-fold ex-
cess), and the reaction followed for 30
min. Another 167-fold hypochlorite excess
was added, and the reaction followed for
another 30 min. The same behavior was
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observed as before—the 167-fold excess
of hypochlorite resulted in an apparent
300% increase in bentazon by HPLC.
However, the second 167-fold addition
caused the reaction to behave as if a
333-fold excess had been added originally;
that is, the bentazon disappeared almost
completely within a few minutes.
In another experiment, hypochlorite
was added to the bentazon-containing
wastewater in increments every 5
minutes. Aliquots were taken before each
new hypochlorite addition. The bentazon
increased as expected with each addition
until a critical point was reached, then
rapidly fell off. This point was between
245 and 370 equivalents of hypochlorite.
Interestingly, the characteristic purple col-
or of this experiment did not disappear
until after the bentazon was gone.
100
80
60
I 40
I
S 20
03
—-— 200-fold excess hypochlorite
266-fold excess hypochlorite
— 500-fold excess hypochlorite
\ -,
10 20 30
60
720
780
Time, min
Fine-Tuning of Hypochlorite
Addition to Bentazon-
Containing Wastewater
To determine more precisely the
amount of hypochlorite needed to remove
bentazon from the wastewater in a rea-
sonable amount of time (10-30 min),
several concentrations were investigated
between 167- and 333-fold excess hypo-
chlorite: 200-fold excess hypochlorite to
correspond to 200-fold excess studied on
standard bentazon and 266-fold excess
(20% less than 333-fold excess). An ex-
periment was also carried out using a
500-fold excess (50% greater than
333-fold excess). The experiments were
carried out just as previous experiments:
timed aliquots were taken, quenched with
bisulfite, and analyzed by HPLC. The
results of these experiments are shown in
Figure 3.
It can be seen that neither the 200- nor
266-fold excess hypochlorite was as effec-
tive as the 333-fold excess in removing
bentazon from wastewater. The 500-fold
excess was, however, quite effective in
removing 98% of the bentazon in a 5 min
reaction time.
The timed aliquots were analyzed by
HPLC and also qualitatively by Thin Layer
Chromatography (TLC). At the end of the
experiment, a portion of the reaction mix-
ture was extracted with methylene chlo-
ride and the extract analyzed by TLC.
Dichlorobentazon was seen in all three
reaction mixtures, the largest amount in
the experiment using 266-fold excess
hypochlorite. This reaction also contained
the largest variety of compounds seen by
TLC.
Figure 3. Addition of different hypochlorite excesses to bentazon-containing wastewater.
Scaled-Up Treatment of
Bentazon-Containing
Wastewater with Hypochlorite
Using the most favorable conditions
from previous experiments (low pH with
addition of 333-fold excess hypochlorite),
the reaction was scaled up to 1 L of
wastewater. An aliquot was taken before
addition of hypochlorite, immediately after
hypochlorite addition, and again after 10
and 30 min. The entire reaction mixture
was then quenched with bisulfite. A final
aliquot was taken 10 min after bisulfite
addition. The results are in Table 1. The
removal of bentazon from solution was
essentially the same as the corresponding
100 mL reaction.
Identification of
Dichlorobentazon as Reaction
Product of Hypochlorite
with Bentazon
The major product of hypochlorite with
bentazon was initially assumed to be
dichlorobentazon based on TLC studies of
the reaction. To positively identify it as
the reaction product, authentic bentazon
was treated with hypochlorite, and the
product isolated and characterized.
Preliminary experiments with authentic
bentazon showed that under acidic condi-
tions dichlorobentazon was seen 10 to 162
min after hypochlorite addition. Bentazon
was extractable with methylene chloride
from neutral and acidic, but not basic.
Table 1. Larger Scale Treatment of Bentazon-Containing Wastewater with Excess Hypochlorite
Bentazon
Add hypochlorite
Add bisulfite
Time
min
0
1
10
30
30
40
Bentazon
Remaining, %
100
23
1.3
—
_
-
Temp
°C
25
27 to 29. 5
30
30
31
32
Reaction
Color changes
Orange, flocculant
material
Reddish material
separates out
Oil globules
adhere to flask
walls
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solutions. After testing on a small-size
reaction, dichlorobentazon was isolated,
using an extractive procedure.
Infrared spectra were generated for
bentazon, dichlorobentazon, and isolated
product using the Nicholet FT-IR. The
lack of resolution in the spectrum of the
product, and the complexity and similarity
of bentazon and dichlorobentazon spectra
made identification impossible.
The same materials were subjected to
low and high resolution mass spec-
trometry. The major treatment product
was shown to be the aromatic substituted
dichloro analog of bentazon. The spec-
trum so generated was compared to the
spectrum of dichlorobentazone standard
(supplied by the manufacturer). A com-
mon fragmentation pattern was observed:
m/e 308 (molecular ion), 264, 229, and
187. Peak-matching the 308 signal from
the treated bentazon spectrum gave
a mass of 307.9787, best match
doHuNjOaSCU—empirical formula of
dichlorobentazon. Thin layer chromatog-
raphy and infrared spectrometric analysis
of the HOCI-treated extract confirmed this
structure assignment.
The presence of a second treatment
product was indicated. This material gave
rise to a mass signal at 282 (281.9303 -
C12H4SO2CI2). The absence of a nitrogen
atom suggested the possibility that this
specie may be a fragment ion.
Characterization of other compounds
was not undertaken.
Daphnia B/oassay
Solutions of bentazon and dichloroben-
tazon were subjected to toxicity testing
with Daphnia magna. The test procedure
used is an EPA-approved acute static
bioassays procedure. The bentazon was
not toxic at the levels studied: 50, 5, and
0.5 ppm. The dichlorobentazon showed
toxicity at all levels, and was quite toxic
at 50 ppm.
Cost Estimate
A cost estimate, prepared for the HOCI
treatment of bentazon wastewater for the
specific site sampled, showed the esti-
mated capital cost to be $1.3 million and
yearly operating costs to be $3.6 million.
The following assumptions were used
in preparing the estimate:
(1) 333-fold excess of HOCI (2 HOCI/I
bentazon)
(2) 100 ppm .bentazon in wastewater
(3) 30 min residence time
(4) Use of NaHS03 to neutralize half of
added HOCI
(5) Operate 270 days/yr
This estimate does not take into con-
sideration the manufacturer's comment
that heat exchangers would be needed
that would add $1 million to the capital
costs. Installation of a storage tank for
hypochlorite would require heat ex-
changers to cool the hypochlorite to pre-
vent decomposition. Because of the cor-
rosivity of the hypochlorite, these ex-
changers must be made of carbon steel
shell with titanium tubes.
Results and Conclusions
The following results were obtained
from this hypochlorite treatment study of
bentazon-containing wastewater.
(1) The analytical HPLC method was
used successfully to monitor ben-
tazon levels in wastewater samples.
(2) Assuming a stoichiometry of 2
equivalents hypochlorite to 1 equi-
valent bentazon, the excess hypo-
chlorite (5% aqueous sodium hypo-
chlorite) required for complete ben-
tazon removal was between 245 and
370-fold.
(3) Bentazon disappeared rapidly as
long as the wastewater pH was 2 or
below with the use of a 333-fold ex-
cess of hypochlorite. A higher initial
pH resulted in incomplete bentazon
removal.
(4) The effect of temperature on the
reaction was of secondary impor-
tance over the temperature range
which the wastewater would en-
counter. Water temperatures
(3°-7°C) may slow the reaction a lit-
tle (the smaller the excess of hypo-
chlorite, the greater the slowing ef-
fect), but with a 333-fold excess the
effect was very small.
(5) The mode of addition of hypo-
chlorite had no effect on the treat-
ment process. As long as the cor-
rect excess was added, whether all
at once or in portions, the final
result was the same.
(6) Dichlorobentazon was the major
product of the reaction of bentazon
with excess hypochlorite in acidic
solutions. Other products have not
been identified.
(7) Bentazon was essentially nontoxic
to Daphnia magna up to at least 50
ppm. The major treatment product
of bentazon, dichlorobentazon, was
toxic to Daphnia magna at 50 ppm,
with some toxicity also at 5 and 0.5
ppm.
(8) The estimated unit cost of
hypochlorite treatment was
$0.0714/gal. Annualized costs were
estimated at about $3.6 million/yr.
Recommendations
The experimental findings have led to
the following possibilities for future work.
(1) Other treatment approaches could
lead to a system with a product less
toxic than bentazon or upgrade cur-
rent treatment to produce less ben-
tazon in wastewater.
(2) Other treatment conditions could
reduce the hypochlorite excess re-
quired for complete bentazon re-
moval (e.g., catalysis, nature of the
acidic agent).
U. S. GOVERNMENT PRINTING OFFICE: 1985/559 111/10831
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R. I/I/. Handy, D. J. Smith, and D. A. Green are with Research Triangle Institute,
Research Triangle Park, NC 27709.
Robert V. Hendriks is the EPA Project Officer (see below).
The complete report, entitled "Treatment Technology for Pesticide Manufacturing
Effluents: Bentazon," (Order No. PB 85-176 816/AS; Cost: $10.00, 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, NC27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
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