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Graduate School of Sciences
Electroanalytical Research Laboratory atChemistry Department
Institut Francilien des Sciences Appliques
Laboratoire Gomatriaux etEnvironnement
DOCTORAL THESIS
To obtain the degree of Doctorof the "University of Paris-Est"- France and "Anadolu University"- Turkey
Speciality: Environmental Science and Techniques
Ali OZCAN
March 19th, 2010
DEGRADATION OF HAZARDOUS ORGANIC COMPOUNDS BY
USING ELECTRO-FENTON TECHNOLOGY
DEGRADATION DES POLLUANTS ORGANIQUES PAR LATECHNOLOGIE ELECTRO-FENTON
Supervisors: Prof. Mehmet A. OTURAN (Universit Paris-Est)
Prof. Ycel SAHIN (Anadolu University)
Jury:
Reviewers: Prof. Figen KADIRGAN Istanbul Technical University
Prof. Otavio GIL Universit de Caen Basse Normandie
Examinators: Prof Kadir PEKMEZ Hacettepe University
Dr. Nihal OTURAN Universit Paris-Est
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Acknowledgement
This thesis has been carried out at the Electroanalytical Research Laboratory of
Chemistry Department and Laboratoire Gomatriaux et Environnement in the frame of
convention for the joint supervision of thesis between Anadolu University and University of
Paris-Est.
First of all, I wish to express my heartfelt thanks to the laboratory directors, Prof. Dr.
Mehmet A. OTURAN and Prof. Dr. Ycel AHN for giving me the chance to conduct the
experiments.
I would like to acknowledge my sincere gratitude to my supervisors, Prof. Dr. Mehmet
A. OTURAN and Prof. Dr Ycel AHN for their endless support, innovative guidance and
continuous encouragement throughout this work.
I want to express my gratitude to reviewers of this thesis, Prof. Dr. Figen KADIRGAN
(Istanbul Technical university) and Prof. Dr. Otavio GIL (Universit de Caen Basse
Normandie) for accepting to read and evaluate my work and for providing valuable
suggestions and comments.
I wish to thank my dissertation committee, Prof. Dr. Mehmet A. OTURAN, Prof. Dr.
Ycel AHN, Prof. Dr. Figen KADIRGAN, Prof. Dr. Otavio GIL, Prof. Dr. Kadir
PEKMEZ (Hacettepe university-Ankara) and Dr. Nihal OTURAN for their valuablecomments and suggestions on this work.
I gratefully acknowledge financial support of Anadolu University Research Found
(Project No: 061022).
A very special thanks to Prof. Dr. Mehmet A. OTURAN, Dr. Nihal OTURAN and
their family for their hosptality during my studies in France.
I would like to thank to Prof. Dr A. Sava KOPARAL (Anadolu University-Eskisehir)
for his support, suggestions and comments.I thank to Anadolu University Plant, Drug and Scientific Researches Center and Erol
ENER for performing the LC-MS analysis.
I also would like to thank to my colleaques of the Chemistry Department, especially to
Levent ZCAN for their assistance, their support and friendship.
I express my gratitude to The Scientific and Technical Research Council of Turkey
(TUBITAK) Scientific Human Resources Development (BAYG) for the fellowship.
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Finally, I would like to dedicate the thesis to my wife Aya Atlr ZCAN and my son
Hasan Berk ZCAN and all my family for their guidance, support, love and enthusiasm.
Without these things this thesis could not have been possible.
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ABSTRACT
In this thesis, a detailed investigation has been carried out on the use of electro-Fenton
technique for the oxidation of the some persistent organic pollutants for the sake of waterremediation. This technique produces OH radicals electrocatalytically and uses them to
oxidize the organic pollutants.
The overall study can be divided into three parts. In the first part, the removal of
selected synthetic dyes and pesticides from water was investigated by using carbon felt (CF)
cathode. The oxidation kinetics of the synthetic dyes (Acid Orange 7 and Basic Blue 3) and
pesticides (picloram, propham, azinphos-methyl and clopyralid) were determined.
Mineralization kinetics of the related organic pollutants in aqueous medium was followed by
total organic carbon and chemical oxygen demand analysis. The overall mineralization was
obtained in all cases. Identification and quantification of the oxidation by-products of the
given synthetic dyes and pesticides were performed by high performance liquid
chromatography, gas chromatography-mass spectrometry, liquid chromatography-mass
spectrometry and ion chromatography. These systematic analysis showed that the initial
organic pollutants were converted into three intermediate forms; organic intermediates, short-
chain aliphatic carboxylic acids and inorganic ions. Based on the intermediates identified, a
plausible mineralization pathway was proposed for each dye and pesticide.
In the second part of the study, the H2O2 production ability of carbon sponge (CS) as a
novel cathode material for the electro-Fenton technique was investigated for the first time in
the literature. The obtained results indicated that CS has a H2O2 production ability three times
higher than the classical cathode CF.
In the third and last part, the efficiency of boron doped diamond (BDD) as an anode in
the electro-Fenton technique was investigated. Firstly, the oxidation and mineralization ability
of BDD was tested for herbicide propham in anodic oxidation conditions. Then, the
combination of CS and BDD electrode in the electro-Fenton technique was examined. The
obtained results indicated that this combination allowed the most efficient results throughout
the thesis. Moreover, the use of BDD anode in the electro-Fenton technique had considerable
effect on the oxidation and mineralization of organics and especially carboxylic acids such as
oxalic and oxamic acids which were highly resistant to mineralization in the case of Pt anode.
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RESUME
Une tude dtaille a t effectue sur l'utilisation de la technique lectro-Fenton pour
l'oxydation de quelques polluants organiques persistants (POP) dans le but du traitement des
eaux uses. Cette technique gnre, in situ et de manire lectrocatalytique, les radicauxhydroxyles (OH) afin de les utiliser pour oxyder la polluants organiques.
Le travail de thse est constitu en trois parts. Dans la premire partie, l'limination de
l'eau des colorants synthtiques et pesticides choisis comme polluants modles a t effectue
en utilisant une cathode en feutre de carbone. Les cintiques d'oxydation des colorants
synthtiques (Acide Orange 7 et Bleu Basique 3) et des pesticides (picloram, prophame,
azinphos-mthyl et clopyralid) ont t dtermines. La cintique de minralisation des
solutions aqueuses des polluants organiques en question a t suivie par des analyses decarbone organique totale (COT) et demande chimique en oxygne (DCO). Une minralisation
quasi-totale a t obtenue dans tous les cas. L'identification et la quantification des sous-
produits d'oxydation des colorants synthtiques et pesticides ont t effectues par les
techniques d'analyse suivantes: Chromatographie liquide haute performance (CLHP),
chromatographie en phasegazeuse-spectromtrie de masse (GC/MS), chromatographie liquide
haute performances-pctromtrie de masse (HPLC/MS) et chromatographie ionique. Ces
analyses systmatique ont mis en vidence que les polluants organiques initiaux ont sont
convertis en trois formes d'intermdiaires ractionnels; intermdiaires organiques, acides
carboxyliques courte chane et ions inorganiques. Bas sur l'identification ces des
intermdiaires ractionnels, une schma de minralisation plausible a t propos pour chaque
colorant et pesticide tudi.
Dans la deuxime partie de l'tude, la capacit de production de peroxyde d'hydrogne
(H2O2) de la cathode en ponge de carbone comme matriau original de cathode pour la
technique lectro-Fenton a t tudie pour la premire fois. Les rsultats obtenus ont indiqu
que le l'ponge de carbone possde une capacit de la production d'H2O2 trois fois plus
leve par rapport la cathode classique (feutre de carbone).
La troisime et dernire partie de cette thse a t consacre l'tude de l'efficacit et
l'utilisation en lectro-Fenton d'une anode de nouvelle gnration, le diamant dop au bore
(BDD pour "Boron Doped Diamond"). Tout d'abord, l'efficacit d'oxydation et la capacit de
minralisation de l'anode BDD ont t examines sur l'herbicide propham dans les conditions
d'oxydation anodique. Ensuite, la combinaison de cathode en feutre de carbone et l'anode
BDD dans la technique lectro-Fenton a t examine. Les rsultats obtenus ont montr que
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cette combinaison conduit aux rsultats significativement meilleurs que le systme classique
feutre de carbone - Pt. L'utilisation de l'anode BDD dans l'lectro-Fenton amliore
considrablement la cintique d'oxydation et l'efficacit de minralisation des polluants
organiques et en particulier des acides carboxyliques tels que les acides oxalique et oxamique
qui rsistent la minralisation dans le cas de l'anode Pt.
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SUMMARY
1. INTRODUCTION 1
1.1. Principles of electrochemical advanced oxidation processes. 11.2. Criteria for selection of organic pollutants. 3
1.3. Objectives of study.5
2. EXPERIMENTAL SECTION 6
2.1. Electrochemical system.. 6
2.2. Analytical Measurements...6
3. RESULTS AND DISCUSSION 8
3.1. Removal of selected hazardous organic pollutants
by electro-Fenton technology using carbon felt (CF) cathode...8
3.1.1. Synthetic dyes..... 8
3.1.1.1. Acid orange 7.. 9
Paper 1.. 11
3.1.1.2. Basic Blue 3. 20Paper 2. 22
3.1.2. Pesticides32
3.1.2.1. Picloram... 33
Paper 3. 36
3.1.2.2. Propham... 47
Paper 4. 50
3.1.2.3. Clopyralid 59
Paper 5. 62
3.1.2.4. Azinphos-Methyl. 72
Paper 6. 74
3.2. Investigation of the H2O2 production ability of carbon sponge (CS)
as a novel cathode material for electro-Fenton process.......... 79
Paper 7. 82
3.3. Investigation of the efficiency of boron doped diamond (BDD)
anode in the electro-Fenton process... 91
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Paper 8. 95
Paper 9. 106
REFERENCES 114
CURRICULUM VITEA 120
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1. INTRODUCTION
1.1. Principles of Electrochemical Advanced Oxidation Processes
Water is of fundamental importance for life on the Earth. The whole mechanism
of metabolism, the synthesis and structure of colloidal cellular constituents, the
solution and transport of nutrients inside the cells and interactions with the
environment are closely related to the specific characteristics of water. On the other
hand, the part of the freshwater (grounwater, lakes and rivers, polar ice and glaciers in
height) that can be used by the human beings is only 2.66% of the global water
resource. Furthermore, these freswater resources, in particular surface water is
exposed to the pollution coming from various human activity. Therefore, in order to
protect natural water resources it is necessary to treat efficiently wastewater effluents
before their injection in the natural water system.
Common physico-chemical wastewater treatment methods such as activated
carbon adsorption and membrane filtration transform the pollutants from one phase to
another, so they separate but not eliminate the water pollutants. Ozone and
hypochlorite oxidations are efficient methods for water disinfection but remaininefficient in case of effluents of hard COD (effluents from industrial or agricultural
activities). On the other hand, they are not desirable because of the high cost of
equipment, operating costs and the secondary pollution arising from the residual
chlorine (Malik and Saha, 2003).
Recent progress in the treatment of persistent organic pollutants (POPs) in water
and/or wastewater has led to the development of advanced oxidation processes
(AOPs). These processes involve chemical, photochemical or electrochemicaltechniques to bring about chemical degradation of organic pollutants. The most
commonly used oxidation processes use H2O2, O3 or O2 as the bulk oxidant to form
principal active specie in such systems, i.e., the hydroxyl radical, OH, a highly
oxidizing agent of organic contaminants (Lin and Lo, 1997; Huston and Pignatello,
1999; Oturan, 2000; Dutta et al., 2001; Malik and Saha, 2003; Swaminathan et al.,
2003; Pignatello et al., 2006. Brillas et al., 2009). These radicals react with organic
pollutants and thus lead to their degradation by hydrogen abstraction reaction
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(dehydrogenation), by redox reaction or by electrophilic addition to systems
(hydroxylation) (Oturan, 2000).
The most commonly used AOPs for the removal of persistent organic pollutants
from water are based on the Fentons reaction. However, this reaction has somelimitations in application such as the use of large quantities of chemical reagents,
large production rates of ferric hydroxide sludge and slow catalysis of the ferrous ions
generation (Boye et al., 2002; Brillas et al., 2004). Electrochemical AOPs overcome
these drawbacks and offer many advantages such as low operational cost and high
mineralization degree of pollutants compared to other known chemical and
photochemical ones. In this sense, anodic oxidation and electro-Fenton processes are
very commonly used electrochemical AOPs.In anodic oxidation, pollutants are mineralized by direct electron transfer
reactions or action of radical species (i.e. hydroxyl radicals) formed on the electrode
surface. In this manner, a wide variety of electrode materials have been investigated
recently, but the boron doped diamond (BDD) has attracted great attention because of
its high O2 evolution overvoltage, high stability and efficiency (Chen and Chen, 2006;
Guinea et al., 2008). This electrode allows to produce large quantities of hydroxyl
radicals from water or hydroxide oxidation decomposition on the electrode surface
(Eqs. 1.1 and 1.2) (Comminellis, 1994; Marselli et al., 2003; Michaud et al., 2003;
Canizares et al., 2004; Panizza and Cerisola, 2005). The formation of H2O2 is also
possible depending on the cathode materials used during the anodic oxidation process.
The oxidation of formed H2O2 to HO2 (Eq. 1.3) or to O2 (Eq. 1.4) takes place at
anode surface (Boye et al., 2002). The formed reactive species may react with the
organics but their oxidation ability are poor compared to adsorbed OH radicals.
H2OOHads+H
+ +e (1.1)
OH OHads +e (pH10) (1.2)
H2O2 HO2 + H+ + e- (1.3)
HO2 O2 + H
+ + e- (1.4)
In the electro-Fenton process, pollutants are destroyed by the action of Fentons
reagent in the bulk together with anodic oxidation at the anode surface in the case of
the use of a high O2 evolution overvoltage anode such as BDD. Fentons reagent is
formed in the electrolysis medium by the simultaneous electrochemical reduction of
O2 to H2O2 (Eq. 1.5) and Fe (III) to Fe (II) ions (Eq. 1.6) on the cathode surface.
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(Gzmen et al., 2003; Guivarch et al., 2003). The reaction between these two species
in the homogeneous medium allows the formation ofOH radicals (Eq. 1.7) (Oturan,
2000; Oturan et al., 2001; Brillas et al., 2005). The Eqs. 1.3 and 1.4 can also take
place during the electro-Fenton process. Moreover, the oxidation of regenerated Fe2+to Fe3+ may occur at the same time (Eq. 1.8) on the anode surface. On the other hand,
the existence of these reactions (Eqs. 1.3, 1.4 and 1.8) are negligible compared to
reaction (1.7) which occurs in the bulk because of the limited surface area of anode.
Finally, iron species (Fe3+/Fe2+) can react with the formed reactive species from
anodic and cathodic reactions (Eq. 1.9-1.11) (Sirs et al., 2007). The overall effect of
these reactions influences the mineralization process of organics in the electro-Fenton
treatment.O2 + 2H
+ + 2e- H2O2 (1.5)
Fe(OH)2+ + e- Fe2+ + OH- (1.6)
Fe2+ + H2O2 + H+ Fe3+ + H2O +
OH (1.7)
Fe2+ Fe3+ + e- (1.8)
Fe3+ + H2O2 Fe2+ + H+ + HO2
(1.9)
Fe3+ + HO2 Fe2+ + H+ + O2 (1.10)
Fe2+
+ HO2
Fe3+
+ HO2-
(1.11)The hydroxyl radicals (OH) formed by the electrochemical (Eq. 1.1) or bulk (Eq. 1.7)
are very powerful oxidizing agents. They react unselectively with organics giving
dehydrogenated and/or hydroxylated reaction intermediates before their total
conversion into CO2, water and inorganic ions, whenOH are produced in continue.
Because OH production does not involve the use of harmful chemical reagents which
can be hazardous for the environment, electrochemical processes can be seen as
environmentally friendly techniques. In conclusion, these processes seem to be verypromising for the purification of water polluted by persistent and/or toxic organic
pollutants.
1.2. Criteria for selection of organic pollutants
In this study, organic pollutants were chosen from synthetic dyes and pesticides
which are the most prominent pollutants of water.
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Synthetic dyes are extensively used in textile, leather, paper, pharmaceutical and
food industries. They thus constitute the major components of wastewaters released
from these industries. The dyes are generally designed to resist biodegradation, so
they cause severe ecological and environmental problems (Allen et al., 1995). Thisenvironmental problem is highlighted by the estimation of a charge up to 50 000 tons
of dye wastes discharged annually from dyeing installations worldwide (Brown,
1987). In addition, some dyes or their metabolites are either toxic or mutagenic and
carcinogenic (Heiss et al., 1992; Chen et al., 2003). Thus, the treatment of the
effluents containing such compounds is important for the protection of natural waters
and environment.
Synthetic dyes divided into two categories as acidic and basic dyes according totheir acidic characters. We have chosen two synthetic dyes, Acid Orange 7 and Basic
Blue 3, which represent these two subgroups.
Natural or synthetic pesticides are used to kill various kinds of animal and plant
pests. Pesticides cover a wide range of products including weedkillers, insecticides,
fungicides, wood preservatives and rodenticides. Of the pesticides that are used far
less than 1% actually reaches a target organism; the rest ends up contaminating the air,
soil, water, plants and animals.
Pesticides have been used extensively to increase the agricultural productivity as
well as their household usage. Food and Agriculture Organization reported that more
than 1.2 million metric tons of pesticides were sold to the agricultural sectors during
the middle of the last decade (Shulze et al., 2002). These substances are in fact very
effective against the harmful microorganisms, weed and insects in order to increase
agricultural yields; however, because of their hazardous nature, the waste and rinsate
from spray and storage equipment have been considered as one of the major threats to
the environment. Thus, treatment of effluents containing pesticides is of
environmental importance. In this study, we investigated the ability of the electro-
Fenton process to eliminate three herbicides which belong to different chemical
family: Picloram (systemic herbicide), propham (carbamate herbicide) and
chlopyralid (systemic herbicide) and a organophosphorus non systemic insecticide:
Azinphos-methyl.
According to our knowlodge, the electro-Fenton removal of the selected organic
pollutants were not reported before.
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1.3. Objectives of Study
This study is aiming to achieve the following objectives:
a) To investigate various operational parameters affecting oxidation and
mineralization kinetics of the selected synthetic dyes and pesticides in the
electro-Fenton technique using carbon felt cathode.
b) To determine and quantify the oxidation intermediates such as aromatic
indermediates, short-chain aliphatic carboxylic acids and inorganic ions as
end-products formed during the electro-Fenton treatment.
c) To study the mineralization reaction pathways of the related pollutants.
d) To investigate the effectivenes of a novel cathode material, carbon sponge,
in the electrogeneration of hydrogen peroxide in acidic solutions.
e) To investigate the effectivenes of boron doped diamond (BDD) electrode as
anode in the electro-Fenton process.
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2. EXPERIMENTAL SECTION
2.1. Electrochemical System
Experiments were performed at room temperature in an undivided cylindrical
glass cell equipped with two electrodes. Carbon felt, carbon sponce and Pt gauze were
used as cathode. The anode was Pt gauze and boron doped diamond (BDD). Prior to
the electrolysis, compressed air was bubbled through the aqueous solution, which was
agitated continuously by a magnetic stirrer. In the case of electro-Fenton experiments,
a catalytic quantity of iron(III) sulphate pentahydrate was introduced into the
electrolysis solution and the pH of the solution was setted at 3 by addition of aqueous
H2SO4 (1 M). The current and the amount of charge passed through the solution was
measured and displayed continuously throughout electrolyses by aDC power supply.
The ionic strength was maintained constant by the addition of 0.05 M Na2SO4.
2.2. Analytical Measurements
The evaluation of the concentrations of the selected organic pollutants were
monitored by high performance liquid chromatography (HPLC) using an Agilent
1100 system equipped with a diode array detector and an autosampler. A reversed
phase Inertsil ODS-3 (5 m ID, 4.6 mm x 250 mm) column was used in the analyses.
The column was thermostated at 40 C. 20 L samples were injected. A suitable
eluent mixture was used during the analysis. Carboxylic acids were identified and
quantified by a Supelcogel H column ( = 7.8300 mm) which was thermostated at
40 C with a mobile phase of 4 mM H2SO4. The detection was performed at 210 nm.
The formed aromatic reaction intermediates during the electrolysis of the
selected hazardous organic compound were determined by HPLC, gas
chromatography coupled with mass spectroscopy (GC-MS) or liquid chromatography
coupled with mass spectroscopy (LC-MS).
The inorganic end-products formed during the mineralization of selected
hazardous organic compound were measured by ion chromatography. A cationic
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exchanger column was used to determine cationic species and an anionic exchanger
column was used to determine anionic species.
The total organic carbon (TOC) of the initial and treated samples was
determined by a Shimadzu TOC-V analyzer. A platinium catalyst was used in thecombustion reaction. The carrier gas was oxygen with a flow rate of 150 ml min1. A
non-dispersive infra-red detector, NDIR, was used in the TOC system. Calibration of
the analyzer was attained with potassium hydrogen phthalate (99.5%, Merck) and
sodium hydrogen carbonate (99.7%, Riedel-de Han) standards for total carbon (TC)
and inorganic carbon (IC), respectively. The difference between TC and IC values
gives TOC value of the sample.
The chemical oxygen demand (COD) analysis and hydrogen peroxidedetermination were performed according to certified analytical methods.
The mineralization current efficiency (MCE) values were determined by using the
following expression (Eq. 2.1) (Brillas et al., 2004; Sires et al., 2006; Diagne et al.,
2007):
100)TOC(
)TOC(MCE
theor
exp
= (2.1)
where (TOC)exp is the experimental TOC at a given time and (TOC)theor is thetheoretical TOC value considering the applied electrical charge (=current x time)
consumed for the complete mineralization of organic pollutant under study according
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3. RESULTS AND DISCUSSION
The obtained results throughout this thesis work are divided into three main
sections; (i) Removal of selected hazardous organic pollutants by electro-Fenton
technology using carbon felt (CF) cathode, (ii) H2O2 production ability of carbon
sponge (CS) as a novel cathode material for electro-Fenton process, and (iii) Use and
efficiency study of boron doped diamond (BDD) anode in the electro-Fenton process.
3.1. Removal of selected hazardous organic pollutants by electro-
Fenton technology using carbon felt (CF) cathode
3.1.1. Synthetic dyes
Synthetic dyes are extensively used in textile, leather, paper, pharmaceutical and
food industries. They thus constitute the major components of wastewaters released
from these industries. The dyes are generally designed to resist biodegradation, so
they cause severe ecological and environmental problems (Allen et al., 1995). This
environmental problem is highlighted by the estimation of a charge up to 50 000 tons
of dye wastes discharged annually from dyeing installations worldwide (Brown,
1987). In addition, some dyes or their metabolites are either toxic or mutagenic and
carcinogenic (Heiss et al., 1992; Chen et al., 2003). Thus, the treatment of the
effluents containing such compounds is important for the protection of natural waters
and environment.
Common physico-chemical treatment methods for the decolourization of dye
wastewaters such as activated carbon adsorption and extraction are able to separate
these pollutants to form a concentrated waste to be treated subsequently, and so they
are inefficient to eliminate the pollutants. Ozone and hypochlorite oxidations are
efficient decolorizing methods, but they are not desirable because of the high cost of
equipment, operating costs and the secondary pollution arising from the residual
chlorine (Malik and Saha, 2003) or because of remained oxidation reaction
intermediates. Other conventional processes based on biological treatment (aerobic
anaerobic) are relatively ineffective in effluent decolourisation, because high
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molecular weight compounds are not easily degraded by bacteria, and thus coloured
compounds pass through the treatment system largely undegraded (Banat et al.,
1996).
3.1.1.1. Acid orange 7
The azo dye Acid Orange 7 (AO7), also called Orange II (Fig. 3.1) is a widely
used synthetic dye. It does not decompose biologically, and resists to photochemical
degradation and chemical oxidation. It is generally used as a model substrat for the
azo dyes. Therefore, its removal has been studied by several research groups; Bandara
et al. (1996) used photo-Fenton reactions in the presence ofnatural sunlight, Kiwi etal. (2001) reported a catalytic photo-assisted system, Fe3+/nafion/glass fibers,
Daneshvar et al. (2003) employed electrocoagulation, Ray et al. (2004) performed
photocatalytic oxidation in the presence of TiO2, Ramirez et al. (2005) investigated
optimum conditions for Fenton's oxidation and Inoue et al. (2006) used ultrasound
waves. In addition, Daneshvar et al. (2008) were studied the electrochemical
degradation of AO7 in potentiostatic conditions and obtained a mineralization ratio of
75%.
N
OH
N SO3Na
Figure 3.1. The molecular structure of Acid Orange 7
In this part of the study, we report a detailed discussion on the oxidative
degradation of AO7 in acidic aqueous solution by the electro-Fenton process. Theexperiments were carried out under constant current electrolysis conditions in
undivided electrochemical cell by using a carbon-felt cathode and a Pt anode. The
kinetics of AO7 degradation by OH during electro-Fenton process has been
examined. The absolute rate constant of the reaction between AO7 and OH was
determined as (1.20 0.17) x 1010 M-1 s-1 by the competition kinetic methodusing
benzoic acid as a reference competitor (Gzmen et et al., 2003). The effect of the
applied current and catalyst concentration on the degradation of AO7 was studied.
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The optimal current value and Fe2+ concentration for the degradation of AO7 were
found as 300 mA and 0.1 mM, respectively. AO7 degradation rate was found to
decrease by increase in Fe3+ concentration beyond 0.1 mM. Mineralization of AO7
aqueous solutions was followed by total organic carbon (TOC) measurements and themineralization degree was found to be 92% after 8 h of treatment.
The reaction between organics and hydroxyl radicals has led to the formation of
aromatic intermediates, short-chain aliphatic carboylic acids and inorganic ions.
Several aromatic intermediates such as 1,2-naphthaquinone, 1,2-naphthalenediol, 4-
aminobenzenesulfonic acid, 4-aminophenol, 4-hydroxybenzenesulfonic acid, 2-
formyl-benzoic acid, 2-hydroxy-1,4-naphthalenedione, 2,3-dihydroxy-1,4-
naphthalenedione, salicylic acid, 1,4-benzoquinone, hydroquinone and 1,2,4-benzentriol were identified by high performance liquid chromatography (HPLC) and
gas chromatography-mass spectrometry (GC-MS) analysis. Maleic, acetic, malonic,
glyoxylic, formic and oxalic acids were identified as short-chain aliphatic carboxylic
acids by ion exclusion chromatography. The sulphate, nitrate and ammonium was
determined as final by-products by ion exchange chromatography. Based on TOC
evolution and identification of aromatic intermediates, short-chain carboxylic acids
and inorganic ions released during treatment, a plausible mineralization pathway was
proposed.
The thorough results of this section are included in the following paper (Paper 1).
Ali zcan, Mehmet A. Oturan, Nihal Oturan, Ycel ahin, (2009). Removal of
Acid Orange 7 from water by electrochemically generated Fentons reagent.
Journal of Hazardous Materials, 163(2-3), 1213-1220.
The following presentations in a congress are related to this work:
Ali zcan, Ycel ahin, Nihal Oturan, Mehmet A. Oturan, Removal of Acid
Orange 7 from water by electrochemically generated Fentons reagent, Journees
dElectrochimie 2007, Lyon, France, 2-6 July 2007 (Poster presentation).
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Paper 1
Ali zcan, Mehmet A. Oturan, Nihal Oturan, Ycel ahin (2009).
Removal of Acid Orange 7 from water by electrochemically generated Fentons
reagent.
Journal of Hazardous Materials, 163(2-3), 1213-1220.
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3.1.1.2. Basic Blue 3
Basic Blue 3 (BB3) is a cationic dye (Fig. 3.2). Cationic dyes, commonly known
as basic dyes, are widely used in acrylic, nylon, silk, and wool dyeing. Due to theircomplex chemical structure, they are recalcitrant to treatment by chemical, physical
and biological methods. Furthermore, any degradation by physical, chemical or
biological treatments may produce toxic and carcinogenic products (McKay et al.,
1985; Gregory et al., 1991).
O
N
N N
Cl-
Figure 3.2. Chemical structure of BB3 ((7-Diethylamino-phenoxazin-3-ylidene)-diethyl-
ammonium chloride).
The removal of BB3 from water was already investigated by different process.
Akbari et al. (2002) used a polyamide-based nanofiltration membrane for the removal
of BB3 from textile dye effluent. Moreover, Daneshvar et al. (2006) used
electrocoagulation for decoloration of BB3 containing solutions. Adsorption process
for the removal of BB3 from water was also performed by using peat ( Allen et al.,
2004) and rice straw (Abdel-Aal et al., 2006).
In this part of the study, we focused our effort on the identification of the
oxidation reaction intermediates and the elucidation of the degradation pathway
during electro-Fenton treatment of synthetic BB3 aqueous solutions.
The decay of BB3 and the evolution of its oxidation products during electrolysis
were monitored by high performance liquid chromatography (HPLC). The absoluterate constant of the BB3 hydroxylation reaction has been determined as (2.61 0.06)
x 109 M-1 s-1 by using the competition kinetic method. The effect of the applied
current on the BB3 removal rate was examined. The optimal current value for the
mineralization of BB3 aqueous solution was found as 300 mA. It was also observed
that the catalyst (Fe3+) concentration values more than 0.2 mM have a negative effect
on the mineralization rate of BB3. The mineralization of BB3 aqueous solution was
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followed by total organic carbon (TOC) measurements. The mineralization ratio was
found upper to 98%.
Decolorization of a solution can be observed when the chromophore responsible
of the color is chemically destroyed but this does not constitute an indication ofelimination of the organic compounds from the treated solution. In addition, the
oxidation treatment can lead to a more toxic solution when the formed chemical
intermediates are more toxic than the parent dye molecule. Thus, information relative
to chemical compounds produced during the decolorization process constitues an
important issue. In order to determine aromatic degradation products of BB3, several
experiments were performed by using chromatographic and mass analysis. Generation
of short chain carboxylic acids is expected from the oxidative breaking of the arylmoiety of aromatic products. The qualification and quantification of short chain
carboxylic acids was performed by ion-exclusion chromatography. The obtained
results indicate the formation of several carboxylic acids. We could only determine
oxalic and oxamic acids which are the dominant ones. The ion chromatography
analysis allowed qualitative and quantitative monitoring of inorganic ions resulting
from the mineralization of BB3. The formed inorganic ions were determined as
ammonium, nitrate, diethylammonium and methylammonium by retention time
comparison and standard addition method. Based on the identified intermediates, a
general mineralization mechanism was proposed.
The thorough results of this section are included in the following paper (Paper 2).
Ali zcan, Ycel ahin, A. Sava Koparal, Mehmet A. Oturan (2009).
Electro-Fenton removal of the cationic dye Basic Blue 3 by using carbon felt
cathode.
Journal of Environmental Engineering and Management, 19(5), 267-275.
The following presentations in a congress are related to this work:
Ali zcan, Ycel ahin, A. Sava Koparal, Mehmet A. Oturan
Removal of Basic Blue 3 from Water by Electrochemically Generated
Fentons Reagent
The 6th Spring Meeting of the International Society of Electrochemistry, Foz do
Iguau, Brasil, 16-19 March 2008. (Poster presentation).
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Paper 2
Ali zcan, Ycel ahin, A. Sava Koparal, Mehmet A. Oturan, 2009.
Electro-Fenton removal of the cationic dye Basic Blue 3 by using carbon
felt cathode.
Journal of Environmental Engineering and Management, 19(5), 267-275.
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3.1.2. Pesticides
Pesticides are natural or synthetic substances used to kill various kinds of animal
and plant pests. Pesticides cover a wide range of products including weedkillers,
insecticides, fungicides, wood preservatives and rodenticides. Of the pesticides that
are used far less than 1% actually reaches a target organism; the rest ends up
contaminating the air, soil, water, plants and animals. As a result, pesticides constitues
a potential threat to human health because of their solubility in lipid and accumulation
in our fatty tissues in a process called bioconcentration. Biomagnification is what
happens when organisms eating contaminated organisms concentrate the pesticides
and then in turn are eaten by other organisms. As a result those on the top of the foodchain (all meat-eating humans) are most at risk because the concentration is magnified
at each step of the food chain. Furthermore because pesticides are designed to kill
organisms due to their neurological or reproductive toxicity they also have many
similar deleterious effects in humans, and many show adverse effects on the immune
system at very low doses. Pesticides have many ecological effects of concern as well.
Ecological effects are often considered to be an early warning indicator of potential
human health impacts. In the environment pesticides can kill organisms, causecancers, tumors and lesions in fish and wildlife, suppress the immune system, cause
reproductive failure, damages on DNA, disrupt the endocrine (hormonal) system, and
cause physiological birth defects (teratogenic effects) (Sazova, 2004).
These substances have been used extensively to increase the agricultural
productivity as well as their household usage. Food and Agriculture Organization
reported that more than 1.2 million metric tons of pesticides were sold to the
agricultural sectors during the middle of the last decade (Shulze et al., 2002). These
substances are in fact very effective against the harmful microorganisms, weed and
insects in order to increase agricultural yields; however, because of their hazardous
nature, the waste and rinsate from spray and storage equipment have been considered
as one of the major threats to the environment. Thus, treatment of effluents containing
pesticides is of environmental importance. In this study we investigated the ability of
the electro-Fenton process to eliminate three herbicides belonging to different
chemical family: Picloram (systemic herbicide), propham (carbamate herbicide),
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chlopyralid (systemic herbicide) and a organophosphorus non systemic insecticide:
Azinphos-methyl.
3.1.2.1. Picloram
Picloram (4-amino-3,5,6-trichloro-2-pyridincarboxylic acid) is a herbicide used
for broadleaf weed control in pasture and rangeland, wheat, barley, oats, and for
woody plant species (Fig. 3.3) (Ahrens, 1994). Picloram is moderately to highly
persistent in the soil environment, with reported field half-lives from 20 to 300 days
and an estimated average of 90 days (Wauchope et al., 1992). Photodegradation is
significant only on the soil surface and volatilization is practically nil. Degradation bymicroorganisms is mainly aerobic. Increasing of soil organic matter enhances the
sorption of picloram and the soil residence time (Ahrens, 1994). Picloram is poorly
bounded to soils, although its adsorption became better by soils with higher
proportions of organic matter (Ahrens, 1994). It is soluble in water, and therefore may
be mobile (Kidd and James, 1991). These properties, combined with its persistence,
mean it may constitute a risk of groundwater contamination.
N
ClCl
Cl
2
O
OH
Figure 3.3. Chemical structure of picloram
The degradation and removal of picloram from water was investigated by
several authors in the literature. Ghauch (2001) used zero-valent iron for the
degradation of picloram. He observed that picloram is converted to 4-amino-2-
pridylcarbinol molecule in one hour reaction but it is not degraded completely to non-
hazardous species. Rahman and Munuer (2005) used heteregenous photocatalysis in
the presence of different kinds of titanium oxide catalysts. Adsorption process by
using the calcinated hydrotalcite (Pavlocia, 2005) and calcinated Mg-Al-CO3-LDH
(Cardoso and Valim, 2006) as sorbents for the removal of picloram from water was
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also performed. According to literature there was no study on the degradation and
mineralization of picloram by using electro-Fenton process.
In this part of the study, we investigated the removal of picloram from its
aqueous solution by electro-Fenton technique using carbon felt cathode. Firstly, thedegradation kinetics of picloram was investigated. Kinetic results evidence a pseudo-
first-order reaction, with an oxidation reaction rate constant of picloram by hydroxyl
radicals of (2.73 0.08) x 109 M-1 s-1. The effect of applied current and catalyst
concentration on the degradation and mineralization of picloram was also
investigated. The optimum applied current and catalyst concentration values for the
degradation of picloram was determined as 300 mA and 0.2 mM Fe3+, respectively.
Mineralization of picloram aqueous solutions was followed by the total organiccarbon (TOC) analysis. At the end of 8 h ofelectrolysis, 95% of the initial TOC was
removed.
The HPLC analysis of electro-Fenton treated aqueous solution of picloram (I)
showed the formation of several intermediate products. In order to determine these
products several analysis were performed by using some chromatographic techniques.
LC-MS analysis showed that picloram degradation has led to the formation of several
products but a dominant aromatic intermediate; 4-amino dichloro hydroxy picolinic
acid. 2,3,5-Trichloro-pyridin-4-ylamine, 3,5,6-Trichloro-pyridine-2-carboxylic acid, 4
amino-5,6-dichloro-3-hydroxy-pyridine-2-carboxylic acid and 5,6-Dichloro-3-
hydroxy-pyridine-2-carboxylic acid were identified by GC-MS analysis. The oxalic,
oxamic, glyoxylic, glycolic, and formic acids were detected by ion-exclusion
chromatography as short-chain carboxylic acids. The formation of chloride, nitrate
and ammonium was observed during the electro-Fenton treatment of picloram. The
identified by-products allowed to propose a mineralization pathway for the picloram
mineralization.
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The thorough results of this section are included in the following paper (Paper 3).
Ali zcan, Ycel ahin, A. Sava Koparal, Mehmet A. Oturan (2008)
Degradation of picloram by the electro-Fenton process.
Journal of Hazardous Materials, 153(1-2), 718-727.
The following presentations in a congress are related to this work:
1. Ali zcan, Mehmet A. Oturan, Ycel ahin, A. Sava Koparal
Degradation of picloram by the electro-Fenton process
Journees dElectrochimie 2007, Lyon, France, 2-6 July 2007 (Poster
presentation).
2. Ali zcan, Ycel ahin, Mehmet A. Oturan
Identification Of Oxidation By-Products Of Picloram
6th Aegean Analytical Chemistry Days, Denizli, Turkey, 9-12 October 2008
(Poster presentation).
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Paper 3
Ali zcan, Ycel ahin, A. Sava Koparal, Mehmet A. Oturan (2008)
Degradation of picloram by the electro-Fenton process,
Journal of Hazardous Materials, 153(1-2), 718-727
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3.1.2.2. Propham
Propham is a carbamate herbicide used for the control of weeds in alfalfa,
clover, flax, lettuces, afflow, spinach, sugar beets and pees. It prevents cell divisionand acts on meristematic tissues. Moreover, it could be degraded into aniline
metabolites which are more dangerous substances than the parent molecule (Orejuela
and Silva, 2004). The presence of this herbicide in surface water was reported by
Meister (2000). On the other hand, the maximum allowed amount of this substance in
water intented to human consumption is 0.1 g L-1 in water intended for human
consumption according to the EU Directive 98/83(EC, 1999). Therefore, the removal
of this substance from aqueous solutions has great importance.
N
H
O
O
Figure 3.3. Chemical structure of propham
In this part of the study, the removal of a carbamate herbicide, propham, from
aqueous solution has been carried out by the electro-Fenton technique. The
degradation kinetics of propham evidenced a pseudo-first-order degradation. The
absolute (or second-order) reaction rate constant of the reaction between propham and
hydroxyl radicals was determined as (2.20.10) x 109 M-1 s-1. The mineralization of
propham was followed by the total organic carbon (TOC) removal. The optimal Fe3+
concentration was found as 0.5 mM at 300 mA. 94% of initial TOC of 0.25 mM
propham aqueous solution was removed in 8 h.
HPLC, GC-MS and LC-MS analysis were used to determine the aromatic by-
products of propham oxidation and the results are given in Table 1. The HPLC
chromatograms showed that the degradation of propham has led to formation of
several intermediates. Two of them exhibits dominant peaks but they have not been
identified by HPLC. A single electrolysis was performed for 15 min and the formed
aromatic intermediates were extracted with dichloromethane, and then the obtained
extract was analyzed by GC-MS. Two dominant peaks in the GC chromatogram were
identified as o- and p-hydroxypropham based on their molecular ion and mass
fragmentation. Moreover, we prepared the trimethylsilyl (TMS) derivatives of the
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intermediates and identified a new product which was different from those obtained
by using HPLC and GC-MS analysis. In the LC-MS analysis, two dominant peaks in
the LC chromatogram were identified as p- and o-hydroxypropham according to
(M+1)+
values and mass fragmantations.The oxidative breaking of the aryl moiety of aromatic products forms the short
chain carboxylic acids during the electro-Fenton process. These substances were
identified and quantified by ion-exclusion chromatography with two well-defined
peaks related to oxalic (tr: 7.04 min) and oxamic (tr: 10.60 min) acids as ultimate
carboxylic acids. Oxamic acid can be produced from the degradation of nitrogen
containing by-products of propham. In the first 80 min of the electrolysis, the
formation of maleic, glyoxylic, lactic, formic, acetic and fumaric acids were alsoobserved.
The nitrogen atom found in the propham structure was converted to nitrate and
ammonium ions which were identified by ion chromatography analysis. The
formation rate of ammonium ions in the first 30 min of the electrolysis was very fast.
After that time, ammonium formation rate gradually decreased and reached a steady
state value. This behaviour can be explained via the slow degradation rate of oxamic
acid because it forms stable iron complexes and shows resistance to the
mineralization.
The identified by-products allowed proposing a pathway for the propham
mineralization.
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The thorough results of this section are included in the following paper (Paper 4).
Ali zcan, Ycel ahin, Mehmet A. Oturan (2008)
Removal of propham from water by using electro-Fenton technology: Kinetics
and mechanismChemosphere, 73(5), 737-744.
The following presentations in a congress are related to this work:
1. Ali zcan, Ycel ahin, Mehmet A. Oturan
Mineralization of Propham in Aqueous Medium by using an
Electrochemical Advanced Oxidation Process
The 58th Annual Meeting of the International Society ofElectrochemistry, Banff, Canada, 9-14 September 2007 (Oral
presentation).
2. Ali zcan, Ycel ahin, Mehmet A. Oturan
Determination Of Degradation Intermediates Of Propham With
Chromatographic And Mass Spectrometric Analysis
6th Aegean Analytical Chemistry Days, Denizli, Turkey, 9-12 October 2008.
(Poster presentation)
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Paper 4
Ali zcan, Ycel ahin, Mehmet A. Oturan (2008)
Removal of Propham from Water by Using Electro-Fenton Technology; Kinetics
and Mechanism
Chemosphere,, 73(5), 737-744
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3.1.2.3. Clopyralid
Clopyralid (CLPYD, 3,6-dichloro-2-pyridinecarboxylic acid) is a systemic
herbicide registered by US environmental protection agency (US EPA, 1998) forcontrol of weeds and woody plants on rangeland and permanent grass pastures, non-
cropland areas and rights-of-way. It affects plant cell respiration and growth. This
herbicide is generally active in the soil and may be persistent in soils under anaerobic
conditions and with low microorganism content. The half-life in soil can range from
15 to more than 280 days. Degradation products have not been identified in the soil up
to now (Corredor et al., 2006). Due to its high solubility in water, this herbicide is not
adsorbed onto soil particles. It may leach into ground-water by surface water infiltration and constitute a potential threat to the human health and environment.
Therefore, the removal of this herbicide from water resources is very important.
N
Cl
Cl
O
OH
Figure 3.4. Chemical structure of clopyralid
The removal of CLPYD from aqueous solutions was performed by the electro-
Fenton process using carbon felt cathode. The decay kinetics well fitted to pseudo-
first order reaction and absolute rate constant of the oxidation reaction of CLPYD was
determined as (4.4 0.2) x 108 M-1 s-1. Mineralization ability of the system was
followed by the chemical oxygen demand (COD) analysis. The total mineralization
was achieved at almost 120 and 240 min electrolysis for 1.5 and 3.0 mM CLPYD
solutions, respectively. The obtained results indicate that the electro-Fenton process is
very effective for the removal of this pollutant from water.
HPLC analysis of electro-Fenton treated solutions of CLPYD showed the
formation of several by-products but three of them were dominant. The CLPYD peak
was rapidly decreased and the peaks corresponding to the by-products were appeared
and increased in the first 5 min. After that time, they gradually decreased and
completely disappeared in 20 min. This situation indicates that the formed by-
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products were unstable at the given oxidizing conditions. Therefore, they did not
accumulate during the electrolysis. Moreover, the gas chromatography-mass
spectrometry (GC-MS) analysis of the samples gave no meaningful results.
Formic, oxalic, maleic, fumaric, oxamic and glyoxylic acids were determinedas short-chain carboxylic acids. While the formation rates of oxalic, maleic and
oxamic acids are very high in the first 90 min, after that time, their accumulation rates
gradually decreased.
The ion chromatography analysis indicated the formation of ammonium, nitrate
and chloride ions. The formation rate of chloride ions was very high in the first 30
min of electrolysis. The released quantity of chloride ions was almost reached to its
maximal value at 60 min. After that time, its concentration is nearly the same. Thestoichiometric ratio of initial chlorine was achieved at the end of the electrolysis.
Nitrogen atom found in the CLPYD structure was rapidly converted to ammonium
ions in the first 30 min of the electrolysis. After that time, ammonium formation rate
gradually decreased and reached a steady state value. This behaviour can be explained
via the slow degradation rate of oxamic acid because it forms stable iron complexes
and shows resistance to the mineralization. The formation of nitrate ions can be
attributed to the oxidation of ammonium ions on the Pt anode. The obtained
concentrations of NO3- and NH4
+ ions showed that 98% of the initial nitrogen was
converted to the NH4+ ions during the electro-Fenton process. We quantified almost
99% of initial nitrogen as NH4+ and NO3
- ions after 6 h electrolysis.
Based on these intermediates, a general oxidation mechanism was proposed in
acid medium.
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The thorough results of this section are included in the following paper (Paper 5).
Ali zcan, Nihal Oturan, Ycel ahin,Mehmet A. Oturan (2010)
Electro-Fenton treatment of aqueous Clopyralid solutions
International Journal of Environmental Analytical Chemistry(in press).
The following presentations in a congress are related to this work:
Ali zcan, Nihal Oturan, Ycel ahin, Mehmet A. Oturan
Electro-Fenton treatment of aqueous Clopyralid solutions
,5th European Conference on Pesticides and Related Organic Micropollutants
in the Environment and11th Symposium on Chemistry and Fate of Modern
Pesticides, October 22-25, 2008, Marseille, France. (Poster presentation)
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Paper 5
Ali zcan, Nihal Oturan, Ycel ahin,Mehmet A. Oturan (2010)Electro-Fenton Treatment of Aqueous Clopyralid Solutions
International Journal of Environmental Analytical Chemistry, in press.
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3.1.2.4. Azinphos-Methyl
Azinphos-methyl (AZPM) is an organophosphorus non-systemic pesticide
widely used to control a variety of insects in food and non-food crops, ornamentalsand forest trees (Fig. 3.5). It is mainly applied as a foliar spray during the growing
season. It has been reported that AZPM had the seventh highest use of all pesticides in
the United States in 1997 (US EPA, 1998). Although its high toxicity and widespread
usage, a limited number of studies was reported in literature for the removal of AZPM
from water resources. To the best of our knowledge, the degradation of AZPM by the
electro-Fenton process was not reported previously in the literature.
This part of the study deals with the degradation of AZPM and its commercialformulation, (GMWP25), by the electro-Fenton process using carbon felt cathode.
The degradation kinetics and mineralization efficiency was deeply investigated. The
identification and evolution of the degradation intermediates was also performed by
HPLC, GC-MS and IC analysis. Based on identified intermediates, a general reaction
sequence was proposed for the degradation of AZPM in acidic media by
electrochemically generated hydroxyl radicals.
OCH3
P
OCH3S
S
N
N
N
O
Figure 3.5. Chemical structure of azinphos-methyl
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The study related to the work on AZPM resulted to the following publication in 5th
European Conference on Pesticides and Related Organic Micropollutants in the
Environment which is published in the congress proceedings.
Ali zcan, Ycel ahin, Mehmet A. Oturan (2008)
Mineralization of a commercial formulation of Azinphos-methyl, Gusathion M WP
25, in aqueous medium by indirect electrochemical advanced oxidation method,
Proceedings of 5th European Conference on Pesticides and Related Organic
Micropollutants in the Environment and 11th Symposium on Chemistry and Fate
of Modern Pesticides, October 22-25, 2008, Marseille, France.
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Paper 6
Ali zcan, Ycel ahin, Mehmet A. Oturan (2008)
Mineralization of a commercial formulation of Azinphos-methyl, Gusathion M
WP 25, in aqueous medium by indirect electrochemical advanced oxidation
method.
Proceedings of 5th European Conference on Pesticides and Related Organic
Micropollutants in the Environment and 11th Symposium on Chemistry and
Fate of Modern Pesticides, October 22-25, 2008, Marseille, France.
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3.2. Investigation of the H2O2 production ability of carbon sponge
(CS) as a novel cathode material for electro-Fenton process
Considerable efforts have been made by many researchers to find appropriate
treatment systems in order to remove pollutants and impurities from wastewaters
emanated from the textile industries. Among the treatment Technologies developed,
the advanced oxidation processes (AOPs) are considered as the most attractive
methods for the treatment of water and wastewater containing toxic, persistent and
non-biodegradable pollutants. AOPs are based on the generation of very reactive non-
selective transient oxidizing species such as hydroxyl radicals (OH), which were
identified as the dominant oxidizing species. In this context, the electro-Fenton
process constitute an emergent and promising wastewater treatmrnt method.
Oxidation power of the electro-Fenton system was mainly related to H2O2
production ability of cathode material used in the electrolysis. Therefore, the cathode
materials which have high H2O2 production ability are very important for the effective
destruction of pollutants since the formation rate of hydroxyl radicals through
Fentons reaction is conditioned by H2O2 formation rate on the cathode employed. In
this manner, several electrode materials such as mercury pool (Oturan and Pinson,1995), graphite (Do and Chen, 1994), reticulated vitreous carbon (Alvarez-Gallegos
and Pletcher, 1999), carbon felt (Oturan, 2000; Oturan et al., 2000 and 2001), O2-fed
carbon polytetrafluoroethylene (Brillas et al., 1996; Boye et al., 2003; Sirs et al.,
2007), and activated carbon fiber (Wang et al., 2005) were investigated as the cathode
material in the electro-Fenton process. Consequently, we have investigated carbon
sponge (CS) as a novel cathode material for the first time in the literature. The
efficiency of the CS electrode was comparatively discussed with carbon felt (CF)electrode for degradation of the synthetic dye, Basic Blue 3 (BB3).
Fig. 3.6 shows the H2O2 concentration produced on the CS and CF electrodes as
a function of time. As can be seen, the electrogeneration of H2O2 on both electrodes
showed similar behaviours. In the first fifty minutes of electrolysis, there was a fast
electrogeneration of H2O2 but after that time the H2O2 accumulation rate was
decreased and reached to a steady state value when its generation rate at the cathode
(Eq. 2) and its decomposition rate at the anode become equal. The concentration of
H2O2 reached via CS and CF electrodes was 8.05 and 2.70 mM, respectively, at the
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end of the 180 min. electrolysis. The results obtained with the CS was nearly three
times higher than that of CF. According to these results, it can be concluded that CS
was a favorable cathode material for the electrogeneration of H2O2.
The effect of some operational parameters such as applied current value, type ofsupporting electrolyte, O2 flow rate, pH and temperature on the generation of H2O2 by
CS was investigated. The optimal current value for the H2O2 production was 100 mA
(5.6 mA cm-2). The temperature and O2 flow rate have also a significant effect on the
amount of electrogenerated H2O2, whereas supporting electrolyte and pH of the
solution have a slight affect. The degradation and mineralization of the BB3 were
followed by using HPLC and TOC analysis, respectively. The degradation and
mineralization of BB3 using CS cathode was found faster than that of CF cathode. Atthe end of eight hour electrolysis under the same conditions, 91.6% and 50.8% of the
initial TOC of the BB3 aqueous solution was removed by using CS and CF cathodes,
respectively. The mineralization current efficiency (MCE) of CS electrode was four
times higher than that of CF electrode. The results showed that the CS electrode
provides an alternative cathode material for future designing of water treatment
system in the electro-Fenton process.
0
3
6
9
0 50 100 150 200
Time / min
[H2O2]/mM
Figure 3.6. The amount of electrogenerated H2O2 on the CS () and CF () surfaceas a function of time at room temperature. [Na2SO4] : 0.05 M, I : 100 mA, pH : 3, V :0.125 L, O2 flow rate : 100 mL min
-1.
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The thorough results of this section are included in the following paper (Paper 7).
Ali zcan, Ycel ahin, A. Sava Koparal, Mehmet A. Oturan (2008)
Carbon sponge as a new cathode material for the electro-Fenton process.Comparison with carbon felt cathode and application to degradation of
synthetic dye basic blue 3 in aqueous medium.
Journal of Electroanalytical Chemistry, 616 (1-2), 71-78.
The following presentation in a congress is also related to this work:
Ali zcan, Ycel ahin, Nihal Oturan, Mehmet A. Oturan
H2O2 production ability of carbon sponge(CS) as a novel cathode material for
the electro-Fenton process.
Electrochimie et ses Applications Industrielles et Environnementales RNE
05 (Cinquime Rencontre Nationale d'Electrochimie), Agadir (Marocco), 27-29
March, 2008. (Poster presentation).
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Paper 7
Ali zcan, Ycel ahin, A. Sava Koparal, Mehmet A. Oturan (2008)
Carbon sponge as a new cathode material for the electro-Fenton process.
Comparison with carbon felt cathode and application to degradation of
synthetic dye basic blue 3 in aqueous medium
Journal of Electroanalytical Chemistry, 616 (1-2), 71-78.
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interesting to note that while the initial degradation rate of propham was almost the
same for all applied current values, the TOC removal values greatly increased at
higher applied current values. This situation can be explained in the following way.
The aromatic reaction intermediates formed by the oxidation of propham are morereactive towards hydroxyl radicals than propham. By increasing applied current
values, the formation rate of OH also increased and these radicals were consumed
simultaneously by the aromatic and aliphatic by-products. As a result the degradation
rate of propham did not change significantly. On the other hand, the TOC removal
values remained almost constant at 300 and 500 mA. The results show that the
optimal current value was about 300 mA for mineralization of propham.
The effect of temperature on the anodic oxidation behavior of propham wasinvestigated at different temperature values between 15 and 35 C at 100 mA constant
current. The degradation of propham showed similiar trend for all temperature values.
By increasing the temperature from 15 C to 35 C, a significant increase was
obtained in the degradation rate of propham.
The pH of electrolyses medium is the other important parameter for the
electrochemical oxidation procedures. The results indicated that the efficiency of the
process was increased in acidic media.
In order to verify the influence of the supporting electrolyte on the degradation
kinetics and mineralization efficiency of propham aqueous solutions, the experiments
were performed in acidic medium (pH 3) containing different supporting electrolytes
as 0.05 M Na2SO4, 0.1 M NaNO3, LiClO4 and NaCl. The degradation rate of propham
was slightly increased when the Na2SO4 was used as supporting electrolyte instead of
NaNO3. The complete degradation of propham almost took place in a 180 min
electrolyses period in the presence of Na2SO4, NaNO3 and LiClO4. However, it
finished in 15 min in the case of NaCl. The TOC removal values of propham
mineralization were increased in the following order: NaCl < NaNO3 < LiClO4