The role of UV-irradiation pretreatment on the degradation of 2,4-dichlorophenoxyacetic acid in water

Article abstract of DOI:10.1002/bio.1198

The degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) in water by the combination process of UV-irradiation, humic acids and activated sludge treatment has been studied. The photoreaction rate of all irradiated samples was lowest for the sample irradiated at 308 nm (the XeCl excilamp) in the absence and in the presence of humic acids, and highest for the sample irradiated at 222 nm (the KrCl excilamp). Photolysis of 2,4-D has been shown to enhance the subsequent microbial degradation. Copyright

Full text of DOI:10.1002/bio.1198

Research article
Received: 8 September 2009,
Revised: 13 November 2009,
Accepted: 11 January 2010,
Published online in Wiley Online Library: 28 April 2010
(wileyonlinelibrary.com) DOI 10.1002/bio.1198
The role of UV-irradiation pretreatment on
the degradation of 2,4-dichlorophenoxyacetic
acid in water
O. Tchaikovskayaa*, I. Sokolovaa, G.V. Mayera, E. Karetnikovab,
E. Lipatnikovaa, S. Kuzminaa and D. Volostnovc
ABSTRACT: The degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) in water by the combination process of UV-irradiation,
humic acids and activated sludge treatment has been studied. The photoreaction rate of all irradiated samples was lowest for
the sample irradiated at 308 nm (the XeCl excilamp) in the absence and in the presence of humic acids, and highest for the
sample irradiated at 222 nm (the KrCl excilamp). Photolysis of 2,4-D has been shown to enhance the subsequent microbial
degradation. Copyright © 2010 John Wiley & Sons, Ltd.
Keywords: UV-irradiation; 2,4-dichlorophenoxyacetic acid; activated sludge; photobiodegradation; humic acids
electronic excitation, either directly or from the excited states (8).
HAs are able to degrade organic chemicals in water.
Introduction
The development and use of herbicides have played an impor-
tant role in the increase of agricultural productivity. On a world
level, herbicide production accounts for 46% of the total pesti-
cide production. Among the herbicides, acids are the most used
in the USA and Europe. Acidic herbicides are widely used for the
control of broad-leaved weeds and other vegetation. They are
relatively inexpensive and very potent even at low concentra-
tions. The majority of herbicides are directly applied to soil or
sprayed over crop fields, and as consequence of large production
and high stability, they are released directly to the environment
(1). The presence of the chlorine groups causes such compounds
to be more resistant to biodegradation than the unsubstituted
analogs. At present, a large number of studies concern a promis-
ing new technology for treatment of polluted water (2).
Wastewater treatment generally consists of a primary, second-
ary and sometimes an advanced treatment stage, with different
biological, physical and chemical processes for each stage of
treatment. Activated sludge treatment includes two major
steps: degradation of the pollution in the aeration basin followed
by the separation of sludge and treated water by setting in a
clarifier (3).
In this study the effect of UV-irradiation on 2,4-dichlorophen-
oxyacetic acid (2,4-D) utilization with the activated sludge in the
presence and absence of HAs is reported. Also, the toxicity of
2,4-D solutions was assessed using the bioluminescence assay,
which is based on lyophilized luminous bacteria Photobacterium
phosphoreum.
Experimental
The stock solution of 2,4-D was prepared by dissolving accurately
weighed amounts of analytical-grade 2,4-D (chemical purity
98%, purchased from Aldrich Chemical Co.) in distilled water
with an ultrasonic stirrer. Then the stock solution was diluted. For
the studies with the activated sludge, 100 mL of 2,4-D solution
(С = 1 × 10−4 to 1 × 10−3 M) was pre-irradiated.
Sample of the wastewater sludge was collected in the aeration
basin from a treatment plant about 5 km from Tomsk Town
(Siberia, Russia), containing wastewater and activated sludge in
the ratio 2:1. The sample sludge was collected in a dry autumn
period. Cultivation was conducted using 250 mL conical flasks
Humic acids (HAs) are omnipresent in the natural environment
and play a number of important roles, including controlling
the pH balance, governing the mobility of contaminants
through absorption, aggregation and sedimentation, and chelat-
ing metals. The photochemical reactivity of HAs in the environ-
ment has been investigated previously (4–8), and numerous
articles have suggested that HAs act as sensitizers or precursors
for the production of reactive intermediates, including 1O2,
superoxide anion and/or hydrogen peroxide in oxygenated
natural water. Humic acids encompass very diverse structures
containing chromophores that act as photosensitizers upon
* Correspondence to: O. Tchaikovskaya, Laboratory of Photophysics and Pho-
tochemistry of Molecules, Department of Physics, Tomsk State University,
36, Lenin Ave, 634050, Tomsk, Russia. E-mail: tchon@phys.tsu.ru
a
Tomsk State University, 36, Lenine Ave, Tomsk, 634050, Russia
b
Institute of Water and Ecological Problems of the Russian Academy of Sci-
ences, 65, Kim-Yu-Chen St., Khabarovsk, 680000, Russia
c
Nature Committee of State Department, 14, Kirov Ave, Tomsk, 634050,
Russia
Luminescence 2011; 26: 156–161
Copyright © 2010 John Wiley & Sons, Ltd.

Degradation of 2,4-dichlorophenoxyacetic acid in water
with 50 mL of the solution of 2,4-D and 50 mL of wastewater
sludge, at 24–26°C under stationary conditions. For absorbance
spectra recording, the particles of sludge were separated from
the culture liquid by filtration through membrane filters (0.2 μm
pore size; Vladipor, Russia). For non-irradiation or irradiation
batch experiments, 2,4-D solution was added to mineral salt
medium of the following composition (grams per liter of distilled
water): KNO3, 2; MgCO4, 0.4; NaCl, 2; K2HPO4, 2 (in the ratio 1:1).
The salt medium and distilled water for all microbiological exper-
iments was autoclaved at 121°C. 2,4-D solution with activated
sludge was incubated at 22 2°C for 20 h to 28 days.
intensity in the control (I0) was compared with the biolumines-
cence intensity recorded in the presence of 2,4-D (I). The toxicity
of 2,4-D solutions was expressed as I/I0. It is generally assumed
that I/I0 ≥ 1 is not toxicity, I/I0 > 0.7 is weak toxicity, I/I0 = 0.5 is
average toxicity, and I/I0 < 0.3 is acute toxicity. The degree of
detoxification of 2,4-D solutions with activated sludge treatment
was characterized using the detoxification coefficient K = Imax/I,
where Imax is the maximal bioluminescence intensity recorded in
the presence of 2,4-D after UV-irradiation. All results of the bio-
luminescence test were corrected for the ‘optic-filter effect’.
HA fractions were obtained from Fluka Chemical Co. The solu-
tions of HAs were prepared in according to the literature proce-
dure (7). The desired amount of HAs was dissolved in 0.1 M NaOH
aqueous solution. The solution was sonicated for 15 min at 40°C
in an ultrasonic bath. This procedure was repeated after 24 h. The
effective concentration of the dissolved HAs in 0.001 M NaOH
aqueous solution remained below 10−3 g l−1.
The UV-radiation sources used for photochemical investiga-
tions were: (1) a DRT-240 high-pressure mercury lamp (Hg) and
three barrier discharge excilamps [purchased from the Institute
of High Current Electronics of the Siberian Branch, Russian
Academy of Sciences (9)]. These were KrCl, XeBr and XeCl
excilamps emitting maximum UV-radiation at 222, 283 and
308 nm, respectively. The parameters and choice of the lamps are
discussed elsewhere (9). The exposure time was varied from 1 to
60 min at room temperature (23–25°C) under static conditions.
Pre- and post-irradiation electronic absorption and fluorescence
spectra were recorded by a conventional procedure using UV–Vis
Unicam spectrometry and a Cary Eclipse spectrofluorimetry, at
25 1°C in air equilibrated solutions. Fluorescence excitation
wavelengths were 330 and 360 nm; 330 nm is the fluorescence
excitation wavelength of emission of the assumed photolysis
product of 2,4-D transformation and 360 nm is the fluorescence
excitation wavelength of emission of HAs (10).
To determine the concentration of 2,4-D after UV-irradiation,
the samples were acidified with HCl to pH = 1 and extracted by
diethyl ether. The extracts were evaporated in the air flow to a
volume of 0.5 ml. The chromato-mass-spectrometric analysis of
the samples was performed on a Finnigan Model Trace DSQ facil-
ity (Thermo Electron Chromatography and Mass Spectrometry
Division, USA). Determination conditions were as follows: column,
Trace TR-5MS; temperature, 100°C (5 min); heating rate 10°C
min−1 to 180°C (5 min), then heating rate 100°C/min to 300°C
(1 min); carrier gas, helium.
Results and discussion
Photodegradation of 2,4-D in pure water
The maximum of absorption of molecular 2,4-D is located at
283 nm (see Fig. 1). The photodegradation of 2,4-D in oxygen-
saturated aqueous solution in the absence of HAs was carried out
by UV-irradiation from different sources. There were changes in
the shape of the spectrum with increasing UV-irradiation time.
The experimental details are presented inTable 1. It was observed
that irradiation resulted in a decrease in absorbance peaks of
2,4-D at 256 and 283 nm (see Table 1 for details, nos. 9–16). As
can be seen, the lowest photoreaction rate appeared with the
use of the XeCl excilamp (λrad = 308 nm). Long irradiation times
were necessary to observe a transformation because 2,4-D
weakly absorbs in this wavelength. The highest 2,4-D conver-
sions were achieved using the KrCl excilamp. When low initial
concentration (C = 1 × 10−4 M) of 2,4-D was used, the results
obtained with both the XeBr and KrCl excilamps were similar.
When high initial concentration (C = 1 × 10−3 M) of 2,4-D was used,
the results obtained with both the Hg lamp and KrCl excilamp
were similar. According to chromatography data, after irradiation
of the XeBr and KrCl excilamps, the 2,4-D conversion (99%) was
achieved. Based on the chromato-mass spectra data, we con-
cluded that 2,4-dichlorophenol was the main photoproduct of
2,4-D (see Fig. 2). It is in good agreement with reported data (1).
The total quinones concentration was also obtained by basic
photometric analytic procedure using benzosulfonic acid stan-
dard (see Table 2). However, the structures of these products
4
1,2
1,0
The concentration of carbon dioxide was determined on a
Chromatron GCHF 18.3 chromatograph with a thermal conduc-
tivity detector. Determination conditions were as follows: column,
9 mm in length and 3 mm in diameter packed with Spherochrom
impregnated with a dibutyrate triethylene glycol stationary
phase; carrier gas, helium (3 dm3/h); column temperature, 35°C;
detector temperature, 50°C; evaporator temperature, 50°C; and
sample volume, 1 mL.
The 2,4-D phototransformation rate in water and in the pre-
sence of HAs was determined by evolution of the initial bands of
2,4-D absorbance at 230, 256 and 285 nm vs irradiation time.
Bioluminescence measurements of toxicity of non-irradiated
2,4-D solution were performed with an Angstrem chemilumi-
nometer (design office Real, Novosibirsk, Russia) using the biolu-
minescence assay, which is based on lyophilized luminous
bacteria Photobacreium phosphoreum and produced at the Insti-
tute of Biophysics (Krasnoyarsk, Russia) (11).The bioluminescence
1
0,8
5
0,6
3
0,4
6
0,2
1
240
2
0,0
280
320
360
400
wavelength, nm
Figure 1. Absorbance spectra of 2,4-D solution in the absence (1) and in the pres-
ence of HAs (2) after UV-irradiation treatment for 32 min: 3 Œ by the Hg lamp; 4 Œ
by the XeBr excilamp; 5 Πby the KrCl excilamp; 6 Πby the XeCl excilamp.
Luminescence 2011; 26: 156–161
Copyright © 2010 John Wiley & Sons, Ltd.
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O. Tchaikovskaya et al.
Table 1. Spectral-fluorescent characteristics of 2,4-D solution (10−4 M) and HAs after UV irradiation
No.
Solution
The action of UV
irradiation
Absorbance, D/D0
Fluorescence
Time, min
At 230 nm
At 256 nm
At 285 nm
I
Lamp, λrad
λ
max (nm)
0
1
2
3
4
5
6
7
8
HAs in 0.001 M NaOH
aqueous solution
—
Hg
—
1
1
0.9
1
0.9
1
1
1
0.9
1
1
1
1
1.1
1
1.2
1.1
1.1
1.1
1
520
480
480
500
500
520
520
500
500
—
425
—
450
—
—
—
450
425
510
510
470
425
470
440
425
450
410
410
425
425
1.5
15
30
15
30
15
30
15
30
—
15
30
15
30
15
30
15
30
—
15
1.4
1.1
1.4
1.4
1.4
1.2
1.2
1.1
—
0.5
—
0.8
—
KrCl
XeCl
XeBr
1
1.1
1.1
1
1
1
11
11.2
15
2
2.5
6
10
11
1
1
0.8
0.8
1
0.5
0.7
0.5
0.8
0.8
1
9
2,4-D in water
—
Hg
10
11
12
13
14
15
16
17
18
19
1
2
2
1
KrCl
XeCl
XeBr
1
—
—
1.1
1.2
1
1
1.1
1
0.5
1
0.5
0.5
1.8
1.6
1.7
0.6
1.81
2
0.6
0.9
0.3
0.3
0.8
1.4
—
Hg
2,4-D in water + HAs
0.7
2.2
20
30
0.6
1.8
0.9
21
22
23
24
25
26
KrCl
XeCl
XeBr
15
30
15
30
15
30
0.8
0.6
1
1
1
2.3
2.3
1.6
1.8
1.2
1.4
1.3
1.2
1
1
1.1
1.2
0.9
The fluorescence excitation wavelength was 365 nm. D0 is the intensity of absorbance of unirradiated solution, D is the intensity
of absorbance irradiated solution and I is the intensity of fluorescent band (rel. un.).
ary photoproducts from the photolysis of 2,4-D were formed. Our
results indicate (see Figs 3 and 4), that photoproducts did not
differ in the pathway for photodegradation of 2,4-D upon irradia-
tion by the KrCl and XeBr excilamps.
COOH
H2C
O
OH
The experimental values of I/I0 are collected in Table 3. The
2,4-D present in the solution reduced the intensity of biolumines-
cence of the test bacteria I/I0 = 0.66 (see Table 3, no. 1); that is, the
solution was toxic. The bioluminescent analysis of the toxicity of
solutions containing 2,4-D showed that their toxicity was
decreased during UV-irradiation by both the Hg lamp and XeCl
excilamp (I/I0 ≈ 1), detoxification coefficient K > 1 (see Table 3, nos
4 and 11); that is, photodetoxication took place. The effect of
detoxication was maximum upon irradiation with the XeCl
excilamp for 15 min. The solutions of 2,4-D exposed to the KrCl
excilamp radiation were possessed the greatest toxicity (see
Table 3, no. 20).
Cl
Cl
hν
Cl
Cl
2,4-dichlorophenol
2,4-D
Figure 2. Scheme of phototransformation of 2,4-D in water.
were not identified. In order to estimate the efficiency of the
physical treatment for the removal of 2,4-D, the fluorescence data
after exposure to UV-irradiation were compared. According to
fluorescence spectra, after UV-irradiation of 2,4-D solution the
fluorescent photoproducts were formed (see Figs 3 and 4). 2,4-D
in water did not have fluorescence. This may be because second-
Irradiation of 2,4-D in the presence of humic acids
In this chapter we also describe the dependence of the fluores-
cence intensity of HAs upon 2,4-D quencher concentration. The
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Degradation of 2,4-dichlorophenoxyacetic acid in water
Stern–Volmer plot (12) is linear, which indicated that only one
type of quenching occurs. From the slope of the Stern–Volmer
plot, one can calculate that K = 70 M . This is the value expected
for the diffusion-controlled bimolecular rate constant between
2,4-D and HAs, which indicated efficient quenching by 2,4-D. Also
this is the value expected for the diffusion-controlled bimolecu-
lar rate constant between macromolecule and quencher (12).
We observed weak changes in the HAs absorption spectra
under UV-irradiation from mercury and exciplex lamps around
256 nm, while the absorption intensity around 285 nm was
affected by the XeCl excilamp irradiation (see Table 1, nos 0–8).
On exposure to UV-radiation the fluorescence bands were
observed to appear one after another around 520 → 500 →
480 nm. The fluorescence intensity decreased in the fundamen-
tal band around 520 nm, as the exposure time was increased.
It appears that some of the HA fragments were phototrans-
formed too.
−1
Table 2. The total quinones concentration in 2,4-D
solutions exposed to UV irradiation from exciplex lamps
The wavelength at 256 nm is the absorbance region of assump-
tive phototransformation products of 2,4-D (see Fig. 1). Accord-
ing to the absorbance data (see Fig. 5), in the presence of HAs
the phototransformation of 2,4-D was not effective in contrast to
irradiative solution in the absence of HAs. When 2,4-D was irradi-
ated with the Hg lamp in the presence of HAs, both direct pho-
tolysis and photoinduced reactions could occur and the
photoinduced transformation was the main route. That is why
No.
t
exc (min)
UV irradiation
KrCl excilamp XeBr excilamp
6.2 × 10−6
M
6 × 10−6
M
1
2
3
15
30
60
2 × 10−5
5 × 10−5
M
M
7.5 × 10−6
2.5 × 10−5
M
M
14
12
10
8
1
3
2
4
6
4
2
0
300
400
500
600
700
wavelength, nm
Figure 3. Fluorescence spectra of 2,4-D in water at a concentration 10−3 M after exposure to the XeBr excilamp radiation (E = 1.7 J cm−3) for 60 min. The fluorescence excita-
tion wavelengths are 280 nm (1), 260 nm (2), 330 nm (3) and 400 nm (4).
3
15
5
1
2
4
10
5
0
300
400
500
600
700
wavelength, nm
Figure 4. Fluorescence spectra of 2,4-D in water at a concentration of 10−3 M after exposure to the KrCl excilamp radiation (E = 1.9 J cm−3) for 60 min. The fluorescence
excitation wavelengths are 280 nm (1), 260 nm (2), 330 nm (3), 350 nm (4) and 400 nm (5).
Luminescence 2011; 26: 156–161
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O. Tchaikovskaya et al.
Table 3. Bioluminescence analysis of the toxicity of 2,4-D solutions at a concentration of 10−4 M after UV irradiation and
activated sludge treatment (AST)
No.
Sample
I/I0
0
1
2
3
4
5
6
7
8
Control
in water
1
0.66
0.81
1.18
0.95
1.22
1.25
1.05
1.08
1.23
1.07
1. 03
0.71
0.79
1.25
1.25
1.29
1.18
0.79
0.62
0.42
1.36
1.06
+ 15 min irradiation with the Hg lamp
+ 30 min irradiation with the Hg lamp
+ 60 min irradiation with the Hg lamp
+ 60 min irradiation with the Hg lamp + 68 h AST
+ 30 min irradiation with the Hg lamp + 20 h AST
+ 30 min irradiation with the Hg lamp + 116 h AST
+ 60 min irradiation with the Hg lamp + 116 h AST
+ 60 min irradiation with the Hg lamp + 20 h AST
+ 15 min irradiation with the Hg lamp + 14 days AST
+ 15 min irradiation with the XeCl excilamp
+ 30 min irradiation with the XeCl excilamp
+ 60 min irradiation with the XeCl excilamp
+ 15 min irradiation with the XeCl excilamp + 20 h AST
+ 30 min irradiation with the XeCl excilamp + 20 h AST
+ 30 min irradiation with the XeCl excilamp + 116 h AST
+ 60 min irradiation with the XeCl excilamp + 116 h AST
+ 15 min irradiation with the KrCl excilamp
+ 30 min irradiation with the KrCl excilamp
+ 60 min irradiation with the KrCl excilamp
+ 30 min irradiation with the KrCl excilamp + 20 h AST
+ 30 min irradiation with the KrCl excilamp + 116 h AST
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
1.23
1.06
+ 60 min irradiation with the KrCl excilamp + 68 h AST
+ 60 min irradiation with the KrCl excilamp + 116 h AST
fluorescent photoproducts of 2,4-D after UV-irradiation treat-
ment by excilamps.
D
0,5
0,4
0,3
0,2
0,1
0,0
Synergetic degradation of 2,4-D by integrated photo- and
activated sludge treatment
Biodegradation of 2,4-D was estimated according the respiration
activity of microbial complex of activated sludge by CO2
chromatograph analysis. In the presence of non-irradiated and
pre-irradiated solutions of 2,4-D (C = 10−4 M) respiration activity
of sludge increased in comparison to control (see Fig. 6). This
confirms that products of 2,4-D photolysis were not toxic for
microorganisms, i.e. destructors. From using two resources of
UV-radiation the respiration activity was higher with the sequen-
tial photo-biodegradation of 2,4-D using the XeBr excilamp.
Sequential photo-biodegradation allows reduction of the tox-
icity of pre-irradiated 2,4-D solutions, I/I0 > 1, detoxification coef-
ficient K = 1.6–3.4 (see Table 3, nos 6, 14 and 22). The mechanism
of detoxification with activated sludge is very complex. First of
all the biological treatment based on biochemical and partly on
biophysical processes occurs (13). Then the complexity of HAs
leads to a variety of physical–chemical behaviors and chemical
interactions (14). In addition, upon exposuree to light HAs can
promote pollutant degradation via the generation of many
chemical transients (15). The presence of HAs in 2,4-D solution
was not inhibited the respiration activity of microbial complexes
of activated sludge.
1
2
3
4
5
6
7
8
9
10
Figure 5. The comparison of the absorbance intensity at 256 nm of 2,4-D in water
(1) without (1–5) and in the presence (6–10) of HAs with no preliminary UV-irradia-
tion (1, 6) and pre-irradiation for 30 min: 2, 7 – by the KrCl lamp; 3, 8 – by the XeBr
lamp; 4, 9 – by the XeCl lamp; 5, 10 – by the Hg lamp.
the degradation of 2,4-D solution within HAs after action UV-
irradiation with the Hg lamp was accompanied by the formation
of the new product fluorescing at 440 nm (see Table 1, nos 10
and 20).
When 2,4-D was irradiated in the presence of HAs the sets
of fluorescent photoproducts were different (for example, see
Table 1, nos 10 and 19) than in distilled water. In the presence of
HAs the fluorescent products of 2,4-D at 410 and 440 nm were
defined. HAs apparently catalyzed the formation some different
According to chromatography data, the sequential action of
UV-irradiation with the XeBr excilamp for 1 h and after 7 days of
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Copyright © 2010 John Wiley & Sons, Ltd.
Luminescence 2011; 26: 156–161

Degradation of 2,4-dichlorophenoxyacetic acid in water
5
4,5
4
3,5
3
3 days
7 days
2,5
2
1,5
1
0,5
0
1
2
3
4
Figure 6. The comparison of the respiration activity of activated sludge microorganisms without (1) and in the presence of 2,4-D (2–4): 1, control; 2, 2,4-D; 3, 2,4-D
irradiated with XeBr excilamp for 30 min; 4, 2,4-D irradiated with KrCl excilamp for 30 min.
4. Aguer J-P, Richard C. Reactive species produced on irradiation at
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Conclusion
The results of our study imply that it is possible to optimize the
configuration of biological wastewater treatment plants to
improve the removal of some herbicides in wastewater before
they are discharged into the environment. The wavelength of
UV-irradiation influences the toxicity of 2,4-D solutions.
Acknowledgments
The authors wish to thank Professor N. Kudryasheva and Dr E.
Fedorova (Institute of Biophysics, Krasnoyarsk, Russia), for the
grant of lyophilized luminous bacteria Photobacreium phospho-
reum. The work was supported in part by the Russian Basic
Research Foundation (Project no. 09-08-90705-mob_st) and
Federal Target Program ‘Scientific and Teaching Staff of Innova-
tive Russia’ for 2009–2013 (no. P1128).
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