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Comparison of Fenton and Photo-Fenton
Processes for Livestock Wastewater
Treatment
JAE-HONG PARK a , IL-HYOUNG CHO b & SOON-WOONG CHANG c
a Research Institute for Environmental Technology and Sustainable
Development, Korea University , Seoul, Korea
b New Town Development Division , Gyeonggi Innovation
Corporation , Suwon, Korea
c Department of Environmental Engineering , Kyonggi University ,
Suwon, Korea
Published online: 18 Aug 2006.
To cite this article: JAE-HONG PARK , IL-HYOUNG CHO & SOON-WOONG CHANG (2006) Comparison of
Fenton and Photo-Fenton Processes for Livestock Wastewater Treatment, Journal of Environmental
Science and Health, Part B: Pesticides, Food Contaminants, and Agricultural Wastes, 41:2, 109-120
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Journal of Environmental Science and Health Part B, 41:109–120, 2006
Copyright C© Taylor & Francis Inc.
ISSN: 0360-1234 (Print); 1532-4109 (Online)
DOI: 10.1080/03601230500364740
Comparison of Fenton
and Photo-Fenton Processes
for Livestock Wastewater
Treatment
Jae-Hong Park,1 Il-Hyoung Cho,2 and Soon-Woong Chang3
1Research Institute for Environmental Technology and Sustainable Development, Korea
University, Seoul, Korea
2New Town Development Division, Gyeonggi Innovation Corporation, Suwon, Korea
3Department of Environmental Engineering, Kyonggi University, Suwon, Korea
In this study, the photochemical degradation of livestock wastewater was carried out
by the Fenton and Photo-Fenton processes. The effects of pH, reaction time, the mo-
lar ratio of Fe2+/H2O2, and the Fe2+ dose were studied. The optimal conditions for the
Fenton and Photo-Fenton processes were found to be at a pH of 4 and 5, an Fe2+ dose
of 0.066 M and 0.01 M, a concentration of hydrogen peroxide of 0.2 M and 0.1 M, and
a molar ratio (Fe2+/H2O2) of 0.33 and 0.1, respectively. The optimal reaction times in
the Fenton and Photo-Fenton processes were 60 min and 80 min, respectively. Under
the optimal conditions of the Fenton and Photo-Fenton processes, the chemical oxygen
demand (COD), color, and fecal coliform removal efficiencies were approximately 70–79,
70–85 and 96.0–99.4%, respectively.
Key Words: Livestock wastewater; Fenton process; Photo-Fenton process.
INTRODUCTION
In general, wastewaters derived from livestock farms, including cattle, swine,
and poultry farms, are highly concentrated in organic matter and nutrients
(i.e., nitrogen and phosphorus). Therefore, although the quantity of livestock
wastewater is small compared with that of municipal and industrial wastewa-
ter, its concentration of pollutants is 50–150 times higher than that of municipal
wastewater in Korea.[1]
In Korea, livestock wastewater is either treated separately or combined
with municipal wastewater and night soil. However, the treatment capacities
Received August 17, 2004.
Address correspondence to Jae-Hong Park, Research Institute for Environmental
Technology and Sustainable Development, Korea University, Seoul, Korea; E-mail:
jhong@korea.ac.kr
109
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110 Park, Cho, and Chang
of these methods are insufficient to deal with all of the livestock wastewater that
is generated. Therefore, it is believed that the excess is discharged untreated
into soil, farmland, and watersheds. However, the inappropriate disposal of
livestock wastewater may pose environmental problems such as the accumula-
tion of pollutants in soil and the pollution of ground and surface water due to
the leaching and runoff of pollutants. For this reason, livestock wastewater is
considered to be one of the main sources of water pollution in Korea.
The problem posed by the inappropriate disposal of livestock wastewater is
not limited to Korea but is also a problem faced by countries all over the world.
For example, in a pollutant source survey conducted in 1998 in the USA,[2] it
was shown that about 60% of river water pollution and about 45% of lake wa-
ter pollution were caused by agriculture sources. Concentrated animal feeding
operations (CAFOs) were considered to be the main source of such pollution.
The high concentration and industrial typology of livestock farms, which
are often not connected with land cultivation, lead to the excessive generation
of animal wastes, at a level which is frequently higher than their recycling
potential on land as a fertilizer. Livestock farms located in both sewered
and nonsewered areas generate an intermittent type of wastewater discharge
with a high organic content that should be removed in such a way as to en-
sure compliance with effluent limitations. From a technological standpoint,
biological treatment processes appear to constitute the only viable alterna-
tive for the handling of these wastewaters. However, many studies have re-
vealed that biologically treated effluents may contain nonbiodegradable or-
ganic fractions, consisting of chemicals that either were initially present in the
wastewater or were microbially generated during the biological processes.[3−5]
These residual or inert fractions are of great import in meeting the discharge
standards.
Therefore, advanced methods of wastewater treatment based on chemical
oxidation, which generate powerful oxidants (hydroxyl radicals), are gain-
ing importance. They allow these nonbiodegradable and/or inert organic
compounds to be oxidized by free radicals and bring about their complete
mineralization to water and carbon dioxide. The classical Fenton oxidation
reaction and photoassisted Fenton oxidation reaction, usually referred to as
Photo-Fenton oxidation, are two such methods which offer the possibility of
producing hydroxyl radicals.
Recently, several studies on the degradation of nonbiodegradable, toxic,
and hazardous substances were carried out using the Fenton and Photo-Fenton
reactions.[6−10] However, few studieshave been carried out on the treatment of
real livestock wastewater using these methods. The purpose of this study was
to evaluate the use of the Fenton and Photo-Fenton reactions for the treatment
of livestock wastewater using a lab-scale reactor. The effect of adding hydrogen
peroxide and a ferrous salt, and the influence of the pH value on the degradation
of organic pollutants, color, and fecal coliform were investigated. The feasibility
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Comparison of Fenton and Photo-Fenton Processes 111
of the real-scale application of the Fenton and Photo-Fenton processes at the
farm level was also evaluated.
MATERIALS AND METHODS
Chemical Reagents
The pH was controlled with an accuracy of ±0.02 by adding either sodium
hydroxide (reagent grade, Duksan) or sulfuric acid (reagent grade, Duksan).
Ferrous sulfate heptahydrate (FeSO4·7H2O, 99.5%) obtained from Duksan,
hydrogen peroxide (H2O2, 30%, wt) from Merck, and ferric chloride (FeCl3,
97%) from Samchon were used.
Preparation of the Livestock Wastewater
The livestock wastewater, which was pretreated by coagulation with 3000
mgL−1 FeCl3,was obtained from a livestock wastewater treatment plant lo-
cated in Kyonggi province in Korea. The characteristics of the settled livestock
wastewater used in this experiment were as follows: COD 5320 mgL−1, fecal
coliform 3.5 × 1010 number/100 mL, and color 0.3215 abs.
Experimental Procedures
A 2 L beaker equipped with a glass bar with a diameter of 10 mm acting as
a baffle was used as the Fenton reactor. The reactor was first filled with 1 L of
livestock wastewater and the pH was adjusted with concentrated H2SO4 and/or
NaOH. The second step was the addition of ferrous sulfate (analytical grade,
heptahydrate). The third step was the addition of hydrogen peroxide (reagent
grade, 30%) and the reaction was started.
The concentration of hydrogen peroxide was measured using the iodometric
method.[11] After the reaction was finished, the pH was adjusted to 8.5, and then
the liquid was transferred to a graduated cylinder and allowed to precipitate for
3 h. After the precipitation was completed, the upper 30% portion of the liquid
was separated from the precipitate, and the COD, color, and fecal coliform were
measured.
A schematic diagram of the Photo-Fenton experimental setup used in this
study is shown in Figure 1. It consists of an irradiation source and a photoreac-
tor. All of the experiments were carried out in a continuous flow through eight
cylindrical quartz columns (each having a diameter of 10 mm and a length of
700 mm) with recirculation of the solution. The light source was provided by
40 W UV lamps (Sankyo Denki Co., Ltd., 1200 mm in length, 32 mm in diam-
eter), mounted on standard fluorescent tube holders. The column was exposed
to a luminous source composed of eight UV lamps with a maximum emission at
254 nm. The total UV intensity was controlled by turning on different numbers
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112 Park, Cho, and Chang
Figure 1: Schematic diagram of the Photo-Fenton reactor.
of UV lights, and the maximum intensity was 4.325 mWcm−2 (with all eight
UV lights on). The effective volume of the photoreactor (550 mm (width) × 640
mm (length) × 110 mm (height)) was 1.88 L. The bottom of the photoreactor
was wrapped in aluminum to reflect any illumination toward the column.
For the Photo-Fenton experiment, the livestock wastewater (5 L) was con-
tained in a 10 L Pyrex glass vessel and was stirred. The livestock wastewater
circulated through the eight modules of the Photo-Fenton reactor (Fig. 1) at a
flow rate of 1 L min−1. The eight modules were connected in series, and the
livestock wastewater flowed directly from one to the other and finally to the
reservoir tank. The temperature of the livestock wastewater was maintained
at 25 – 27◦C during the reaction. The H2O2 dosage was determined based on the
stoichiometric ratio with respect to the COD, and ferrous salt was also added
at a molar ratio of H2O2 to Fe(II). For the analysis, a 50 mL aliquot was taken
at various intervals. After the reaction was finished, the pH was adjusted to
8.5, and then the liquid was transferred to a graduated cylinder and allowed
to precipitate for 3 h. After the precipitation was completed, the upper 50%
portion of the liquid was separated from the precipitate, and then the COD,
color, and fecal coliform were measured.
Analytical Methods
The UV intensity was measured with a radiometer (VLX-3W Radiometer
9811-50, Cole Parmer lnstrument Co.) at 254 nm. The pH was measured by
means of an Orion pH meter, model 525A. The concentration of hydrogen per-
oxide was measured using the iodometric method.[11] The decolorization of the
livestock wastewater was monitored using a UV-Vis spectrometer (Shimadzu
UV-1201, absorption at λmax, 355 nm). The potassium dichromate closed reflux
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Comparison of Fenton and Photo-Fenton Processes 113
colorimetric method was used to measure the COD.[12] The fecal coliform was
measured using the standard method.[12]
RESULTS AND DISCUSSION
The Effect of pH
The pH value has a decisive effect on the oxidation potential of OH radicals
because of the reciprocal relation between the oxidation potential and the pH
value (Eo = 2.8 V and E14 = 1.95 V).[6] Furthermore, the concentration of inor-
ganic carbon and the hydrolytic speciation of the Fe(III) species were strongly
affected by the pH value.[6] Therefore, the pH is an important parameter in the
Fenton and Photo-Fenton processes.
Figure 2 illustrates the effect of the pH on the COD removal efficiency in
the Fenton and Photo-Fenton processes. The experiments have been carried out
at pH range from 2 to 9, and detailed experimental conditions in the Fenton
and Photo-Fenton processes were: [Fe2+] of 0.1 M and 0.01 M, [H2O2] of 0.1 M,
reaction time of 1 h and 4 h, and UV254 intensity of 4.325 mWcm−2, respectively.
The pH values of 4 and 5 were found to be the optimum pH values for the
Fenton and Photo-Fenton processes, respectively. However, the COD removal
efficiency was hardly influenced by the pH below pH 3, due to the hydroxyl
radical scavenging effects of H+ at low pH. Also, the COD removal efficiency
rapidly decreased with increasing pH in the range of 5–9. Our results are in
good agreement with those of previous reports.[13−15]
Hydrogen peroxide was most stable in the range of pH 3–4, but the decom-
position rate rapidly increased with increasing pH above pH 5.[13] When the pH
of the reaction was higher than 5, the COD removal efficiency rapidly decreased
with increasing pH, not only due to the decomposition of hydrogen peroxide,[14]
but also because of the deactivation of the ferrous catalyst due to the formation
of ferric hydroxy complexes.[15]
Figure 2: Effect of pH on COD removal.
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114 Park, Cho, and Chang
The Effect of Fe2+ and H2O2
Addition of an excess of H2O2 did not improve the maximum degradation
in either the Fenton or Photo-Fenton process. This may be due to the autode-
composition of H2O2 to oxygen and water and the recombination of OH radicals
(OH·) as follows:
2 H2O2 −→ 2 H2O + O2 (1)
OH· + H2O2 −→ H2O + HO2· (2)
Since the OH radicals react with H2O2, the H2O2 itself contributes to the
OH· scavenging capacity.[16] Therefore, H2O2 should be added at the optimal
concentration to achieve the best degradation.
Also, the higher addition of Fe(II) results in a brown turbidity that hinders
the absorption of the UV light required for photolysis and causes the recombi-
nation of OH radicals. In the case, Fe(II) reacts with OH radicals, acting as a
scavenger.[17]
OH· +Fe2+ −→ OH− + Fe3+ (3)
It is desirable that the ratio of H2O2 to Fe(II) should be as small as possible,
so that the above recombination reaction can be avoided and the production of
sludge resulting from the iron complex is also reduced.
To determine the optimal ratio of Fe2+/H2O2 in the Fenton process, experi-
ments were carried out at 10 different molar ratios from 0.1 to 5. The detailed
experimental conditions were: a pH of 4, a reaction time of 1 h, and [Fe2+] of
0.05 M.
Figure 3 shows that the COD removal efficiency was distinctly increased
by decreasing the dosage of hydrogen peroxide. However, the COD removal
efficiency decreased with decreasing dosage of hydrogen peroxide when the
Fe2+:H2O2 ratio was less than 0.33. From these results, it was determined that
the optimal ratio of Fe2+/H2O2 for COD removal was 0.33.
Figure 4 illustrates the COD degradation process as a function of H2O2 at
the optimal Fe2+/H2O2 molar ratio. The investigation was conducted at a dosage
Figure 3: Variation of COD removal with molar ratio in Fenton oxidation.
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Comparison of Fenton and Photo-Fenton Processes 115
Figure 4: Variation of COD removal with H2O2 dosage in Fenton oxidation.
of H2O2 ranging from 0.01 to 0.45 M, and detailed experimental conditions were:
a pH of 4, a reaction time of 1 h, and Fe2+/H2O2 ratio of 0.33. The COD removal
efficiency was increased by increasing the dosage of H2O2 in the range of 0–
0.2 M. However, it hardly changed above an H2O2 dosage of 0.2 M. Therefore,
the optimal dosage of H2O2 for COD removal was considered to be 0.2 M.
In the Photo-Fenton process, the presence of hydrogen peroxide can increase
the efficiency of COD removal. Being an electron acceptor, hydrogen peroxide
reacts with conduction band electrons [Eq. (4)] to generate hydroxyl radicals,
which are required for the photomineralization of organic pollutants. When
hydrogen peroxide absorbs UV light with a wavelength <300 nm, one H2O2
molecule is converted to two OH radicals, as shown in Eq. (5).[18]
H2O2 + e− −→ OH· + OH− (4)
H2O2 + hv −→ 2OH· (5)
However, if the H2O2 concentration is too high, the COD removal efficiency
does not improve the maximum degradation because of the autodecomposition
of H2O2 and the recombination of OH radicals (OH·), as indicated in Eq. (2).
To determine the optimal Fe(II) dosage in the Photo-Fenton process, ex-
periments were conducted at five different dosages from 0.025 to 0.05 M. The
detailed experimental conditions were: a pH of 5, UV254 intensity of 4.325 mW-
cm−2, and [H2O2] of 0.1 M.
Figure 5 shows the effect of Fe(II) dosage on the COD removal efficiency. The
optimal Fe(II), dosage for COD removal was found to be 0.01 M. COD removal
efficiencies of 70 to 74% were achieved at higher concentrations of Fe(II), and
only about 30 to 36% of the COD was eliminated at lower concentrations of
Fe(II), whereas 83% of the COD was eliminated at the optimal Fe(II) dosage at
the reaction time of 2 h.
Figure 6 shows the effects of the dosage of H2O2 on the COD removal effi-
ciency in the case of the Photo-Fenton process. The investigation was carried
out at H2O2 dosages ranging from 0.01 to 0.2 M, and detailed experimental
conditions were: a pH of 5, UV254 intensity of 4.325 mWcm−2, and [Fe2+] of
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116 Park, Cho, and Chang
Figure 5: Effect of Fe2+ dosage on COD removal in Photo-Fenton oxidation.
0.01 M. As expected, the COD removal efficiency was increased by increasing
the concentration of H2O2. The optimum H2O2 dosage was found to be 0.1 M.
The Effect of Fe(II) on the Color Removal Efficiency
In order to determine the effects of Fe(II) on the color removal efficiency, ex-
periments were conducted at various Fe(II) dosages under the optimal operating
conditions of the Fenton and Photo-Fenton processes. As shown in Figure 7, the
Figure 6: Effect of H2O2 dosage on COD removal in Photo-Fenton oxidation.
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Comparison of Fenton and Photo-Fenton Processes 117
Figure 7: Variation of color removal with Fe2+ dosage.
color removal efficiency rapidly increased with increasing Fe(II) dosage in the
range of 0 – 0.07 M and 0 – 0.006 M in the case of the Fenton and Photo-Fenton
processes, respectively. However, in the Fenton process, the color removal effi-
ciency was not influenced by the Fe(II) dosage at dosages above 0.07 M. This
could be explained by the fact that the addition of a large amount of Fe(II)
resulted in a brown turbidity that hindered the absorption of the UV light.
Even with no addition of Fe(II) in the Photo-Fenton process, the color re-
moval was 25%. This reduction may be due to the photolysis of H2O2 when
hydrogen peroxide absorbs the UV light at a wavelength <300 nm (Eq. 5) and
the direct photolysis of the organic pollutants. Because the lamp used in this
study emits in the UV-C range, the photolysis of H2O2 takes place simultane-
ously during the reaction. Due to their direct photolysis, the organic pollutant
molecules may enter an excited state in which they can be partly oxidized by
the oxygen present in the solution.
The Sludge Production
Figure 8 shows the sludge production as a function of the Fe2+ dosage
under the optimal conditions of the Fenton and Photo-Fenton processes, re-
spectively. The sludge production increased rapidly with increasing Fe(II)
dosage. As shown in Figure 8, the sludge productions were 36 mL/100 mL and
7.5 mL/100 mL, respectively.
Figure 8: Production of sludge with Fe2+ dosage.
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118 Park, Cho, and Chang
Figure 9: Variation of fecal coliform removal with reaction time at the optimal conditions.
The Fecal Coliform Removal Efficiency
Figure 9 shows the fecal coliform removal efficiency under the optimal
conditions in the Fenton and Photo-Fenton processes, respectively. The fecal
coliform removal efficiency increased rapidly with increasing reaction time.
However, in comparing the results of the Photo-Fenton and Fenton oxidation
reactions (Fig. 9) it is evident that the Photo-Fenton reaction results in greater
and faster reduction of fecal coliform than the Fenton reaction.
CONCLUSION
Based on the present study of the treatment of livestock wastewater by the
Fenton and Photo-Fenton processes, the following conclusions can be drawn.
The Fenton oxidation rate is influenced by many factors, such as the pH
value, molar ratio of Fe2+/H2O2, and the amounts of hydrogen peroxide and
ferrous salt. The optimum conditions for degradation were found to be: a pH
of 4, a reaction time of 60 min, a molar ratio of Fe2+/H2O2 of 0.33, a hydrogen
peroxide concentration of 0.2 M, and a ferrous salt concentration of 0.066 M.
Under the optimal conditions of the Fenton process, the COD, color, and fecal
coliform removal efficiencies were about 70, 85, and 96.0%, respectively, and
the sludge production was 36 mL from 100 mL of solution.
The optimum conditions for degradation in the case of the Photo-Fenton ox-
idation were: a pH of 5, a reaction time of 80 min, a ferrous salt concentration
of 0.01 M, and a hydrogen peroxide concentration of 0.1 M. Under the optimal
conditions of the Photo-Fenton process, the COD, color, and fecal coliform re-
moval efficiencies were about 79, 70, and 99.4%, respectively, and the sludge
production was 7.5 mL from 100 mL of solution.
Based on the results presented in this study, the Photo-Fenton process
shows a lower color removal efficiency compared with the Fenton process, but
it has a higher COD and fecal coliform removal efficiency under the optimum
conditions. Also, the Photo-Fenton process was associated with lower sludge
productioncompared with the Fenton process.
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Comparison of Fenton and Photo-Fenton Processes 119
The study of the Fenton and Photo-Fenton processes for livestock wastew-
ater treatment is important for developing a new approach to the treatment of
highly concentrated livestock wastewater. Based on the results of our study,
it can be concluded that the Fenton and Photo-Fenton processes represent
good alternative treatment methods for livestock wastewater, provided that
the amount of suspended solids is not too high. When the solid concentration
is very high, the penetration of light into the Photo-Fenton reactor is impeded.
In general, livestock wastewater is treated using conventional biological
treatment methods, which do not allow for the effective removal of the COD
and color. Based on our results, we suggest that the combined use of the
Fenton/Photo-Fenton process with biological treatment would provide a promis-
ing alternative to the existing methods because it would take advantage of the
best aspects of both methods.
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