BURAPHA UNIVERISTY
Faculty of Engineering
Term Assignment in Advanced Researh Method
Proposed Topic
REMOVAL OF COD AND COLOUR FROM
TEXTILE WASTEWATER BY ADVANCED OXIDATION
PROCESS USING FENTON PROCESS
Submitted to : Pro. Wirogana
Submitted by: Mr. Piseth Som
Academic Year: 2012
1
Abbreviation
AOPs
: Advanced Oxidation Processes
BOD
: Biological Oxygen Demand
COD
: Chemical Oxygen Demand
EOP
: Electrochemical Oxidation Potential
EPA
: Environment Protection Agency
F/M
: Food to Microorganism
mg/l
: milligram per liter
Pt-Co
: Platinum Cobalt
SS
: Suspended Solid
TDS
: Total Dissolved Solid
Vol
: Volt
WOP
: Wet Air Oxidation Process
2
Chapter I
Introduction
1.1.
Background
Textile industry is one of the most complicated industries among manufacturing
industry . The main sources of wastewater normally come from cleaning water,
pretreatment, dyeing and finishing process water non-contact cooling water and
others. The amount of wastewater varies widely depending on the type of process
operated at the mill, and various toxic chemicals such as complexing agents, sizing,
wetting, softening, anti-felting and finishing agents, wetting agents, biocides, carriers,
halogeneted benzene, surfactants, phenols, pesticides dyes and many other additive
are used in wet processing, which are mainly called washing scouring, bleaching,
mercerizing, dyeing, finishing (EPA, 2004; Adel et al, 2004).
It was also provided that composite textile wastewater is characterized mainly
by measurements of biochemical oxygen demand (BOD), chemical oxygen demand
(COD), suspended solids (SS) and dissolved solids (DS). Textile wastewater includes a
large variety of dyes and chemicals additions that make the environmental challenge
for textile industry not only as liquid waste but also in its chemical composition (Adel
et al, 2004 (Cited from Venceslau et al., 1994 ). Main pollution in textile wastewater
came from dyeing and finishing processes. These processes require the input of a
wide range of chemicals and dyestuffs, which generally are organic compounds of
complex structure. Because all of them are not contained in the final product, became
waste and caused disposal problems.
The combination of textile processes and products make the wastewater from
textile plant contains many type of pollutants. These pollutants contributes to high
suspended solids (SS), chemical oxygen demand (COD), biochemical oxygen demand
(BOD), heat, color, acidity, basicity and other soluble substances.
COD values of composite wastewater are extremely high compare to other
paremeter. In most cases, BOD/COD reatio of the composite textile wastewater is
primarily high which can represent the fact that wastewater contains large amount of
3
non-biodegradable organic matter. The removal of colour and COD from textile
industry and dyestuff manufacturing industry wastewaters represents a major
environmental concern as reported that out of 87 dyestuff only 47% are
biodegradable. (shanshask et al,. 2011; Adel et al, 2004).
1.2. Problem Statement
The application of conventional textile wastewater treatment processes become
challenged to environmental engineers with restrictive effluent quality by water
authorities and national standard for effluent. Conventional treatment such as
biological treatment discharges will no longer be tolerated as 53% of 87 colours are
identified as non-biodegradable. Therefore, the use of convitional textile wastewater
treatment processses become drastically challenged to fresh water bodies and
environment. The conventional treatment such as biological treatment discharges
will no longer to tolerated as 53% of 87 colours are indentified as non-biodegradable
and toxic to the microorganisms. These dyes can be treated if conventional treatment
methods are incorporated with the advanced oxidation process which have their
potential application for breaking the complex structure of the dye and make it more
amenable to bio-degradation (shanshask et al,. 2011; Adel et al, 2004).
Therefore, Advanced Oxidation Process (AOPs) have recieved considerable
atttention and hold great promise to provide alterative for better treatment and
protection of environment because it is possible to degrade organic compounds and
colours from textile wastewater. Also, it was supported by Giusy Lofrano(2012) that
AOPs are being employed to treat biologically inert, hazardous, toxic, and other
problematic pollutants found in air, water, and wastewater. Amoung the variety of
AOPs available, Fenton and Photo-fenton (Fe2+/H202/UV) treatment system have gain
its practical use than other due to their superior reation rate and effeciency, technical
feasibility and attractive process economic.
At present, several methods have been developed to treat textile wastewater
but they cannot be used individually because this wastewater has high salinity, color
and non biodegradable organics. In coagulation process, large amount of sludge is
4
created which may become a pollutant itself and increase the treatment cost.
Oxidation process such as ozonation effectively decolorizes almost all dyes except
disperse dyes but does not remove COD effectively (Ahn et al., 1999).
Adsorption is an effective method of lowering the concentration of dissolved
dyes in the effluent resulting in color removal. Other means of dye removal such as
chemical oxidation, coagulation and reverse osmosis are generally not feasible due to
economic considerations (Tsai et al., 2001). The adsorption process is one of the most
efficient methods to remove dyes from effluent. The process of adsorption has an
edge over the other methods due to it sludge free clean operation and complete
removal of dyes even from dilute solution (Malik, 2003).
Activated carbon is the most widely used adsorbent because of its extended
surface area, microporous structure, high adsorption capacity and high degree of
reactivity. However, commercially available activated carbons are very expensive
(Malik, 2003).
It was also documented taht conventional process used to treat wastewater
from textile industry includes chemical precipitation with alum or ferrous sulphate
which suffers from drawbacks such as generation of a large volume of sludge leading
to the disposal problem, the contamination of chemical substances in the treated
wastewater, etc. Moreover these processes are inefficient in completely oxidizing
dyestuffs and organic compounds of complex structure (Shanshask et al,. 2011).
Therefore, Advanced Oxidation Process (AOPs) have recieved considerable
atttention and hold great promise to provide alterative for better treatment and
protection of environment because it is possible to degrade organic compounds and
colours from textile wastewater. Also, it was supported by Giusy Lofrano(2012) that
AOPs are being employed to treat biologically inert, hazardous, toxic, and other
problematic pollutants found in air, water, and wastewater. Amoung the variety of
AOPs available, Fenton and Photo-fenton (Fe2+/H202/UV) treatment system have gain
its practical use than other due to their superior reation rate and effeciency, technical
feasibility and attractive process economic (Giusy Lofrano, 2012).
5
1.3. Objective of the Study
The overal objective of this study is to apply Fenton Method in Advance
Oxidation Process (AOPs) for COD and colour reduction in a selected textile industrial
wastewater, which will minimize the treatment cost. The specific objectives are :
-
To determine the treatment performance of Fenton in removing the Coulor
and COD
-
To find optimal conditions for removal of COD and color of dying textile
wastewater
-
To investigate the effect of the H202 dosage, Fe2+ dosage, H2O2/ Fe2+
molar ratio, initial pH, reaction time and dosage method on Fenton
Oxidation process
1.4. Scope of Study
This research study is limited to the following condition:

Focus only the removal effeciecy of COD and color parameters

Kenetic Study will not be conducted in this study

Due to the limitation of the equibment, only conventional Fenton
Oxidation will be applied in this studies.

Operational other parameters such as temperature and mixing time is
mentioned in this study
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1.5. Singneficant of Study
Price competition, demand in high quality products, new and innovative
products that are highly durable put further pressure to the industry as they have to
use more dosage of chemicals and continually change to new chemicals to suit the
market demand. However, the national regualation and law have put the restriction
on the effluent standard which industries have to be complied. This will finally result
in the complication in the wastewater that is being discharged. Thus there is a need
for continues study and research on the waste water treatment to find new methods
of treatment in order to sustain the industry. The overall motivation for the present
study is to explore the possibility of using Fenton processes in the treatment of
highly colored wastewater from a dying textile producing plant and, eventually, to
evaluate the best treatment technology for this specific industrial sector. Better
water and wastewater management is of great importance to textile industry. The
results of this study should contribute to the evaluation of the best method of
treatment of dying textile wastes and eventual water reuse.
7
Chapter II
Literature Review
2.1. Wastewater from textile industry
There are several different steps in the production of textiles and these
processes generate highly contaminated liquid streams. The quantity and
composition of these wastewaters depend on many different factors, including the
processed fabric and the type of process. Type of machinery, chemicals applied and
other characteristics of the processes also determine the amount and composition of
the generated wastewater. The main sources of wastewater normally come from
cleaning water, pretreatment, dyeing and finishing process water non-contact cooling
water and others. The amount of wastewater varies widely depending on the type of
process operated at the mill, and various toxic chemicals such as complexing agents,
sizing, wetting, softening, anti-felting and finishing agents, wetting agents, biocides,
carriers, halogeneted benzene, surfactants, phenols, pesticides dyes and many other
additive are used in wet processing, which are mainly called washing scouring,
bleaching, mercerizing, dyeing, finishing (Adel et al, 2004). It was also provided by
Shanshask et al,. (2011) that the textile wastewater is characterized by high content
of dyestuff, salts, high COD derived from additives, suspended solid(SS) and
fluctuating pH. The textile industry uses approximately 21-377 m3 of water per ton
of textile produced and thus generates large quantities of wastewater from different
steps of dyeing and finishing process. In the textile sector, although processes should
be considered separately, treatment of each process may not be considered
individually. Combined selected streams can lead to a better treatable wastewater. A
stream could be separated from the rest to facilitate the recovery of water or
chemicals, or to prevent dilution of a compound difficult to remove(Adel et al, 2004).
“Some processes in a textile mill hardly generate wastewater, such as yarn
manufacture, weaving (some machines use water), and singeing (just some lightly
polluted cooling water). The amount of wastewater produced in a process like sizing
is small, but very concentrated. On the other hand, processes like scouring, bleaching
8
and dyeing generate large amounts of wastewater, varying much in composition”
(Metcalf and Eddy, 1991). According to EPA, (2004), it was documented that Likely
sources of textile process wastewater include wet processes such as scouring, dyeing,
finishing, printing and coating of textile products. Dyeing processes are one of the
largest sources of wastewater. The primary source of wastewater from dyeing
operations is spent dyebath and washwater. Finishing processes generally produce
wastewater containing natural and synthetic polymers. Chemical handling and high
pH are the primary pollution concerns associated with the bleaching process.
Although effluent characteristics differ greatly even within the same process,
some general values for major processes in a textile mill. Mixed textile wastewater
generally contains high levels of COD and color, and usually has a high pH (Dos Santos
et al., 2007 ;Shanshask et al,. 2011).
2.2. Textile Wastewater Characteristics and Environmental Impact
Although effluent characteristics differ greatly even within the same process,
some general values for major processes in a textile mill. Mixed textile wastewater
generally contains high levels of COD and color, and usually has a high pH (Dos Santos
et al., 2007 ;Shanshask et al,. 2011).
Strong colour is another important component of the textile wastewater which
is very difficult to deal with and colour is noticed in the wastewater effluent and the
presence of small concentrations of dyes in water is highly visible, and may affect
their transparency and aesthetics (EPA, 2004). The non-biodegradability of textile
wastewater is due to the high content of dyestuffs, surfactants and other additives,
which are generally organic compounds of complex structure” (Gharbani et al., 2008).
Textile mill effluents are known to have extremes pollutants contributes to high
suspended solids (SS), chemical oxygen demand (COD), biochemical oxygen demand
(BOD), heat, color, acidity, basicity and other soluble substances(table 1). As
presented in Table 1 below, COD values of composite wastewater are extremely high
compare to other paremeter. In most cases, BOD/COD reatio of the composite textile
9
wastewater is around 0.26 that implies that wastewater contains large amount of
non-biodegradable organic matter. Main pollution in textile wastewater came from
dyeing and finishing processes. These processes require the input of a wide range of
chemicals and dyestuffs, which generally are organic compounds of complex
structure (shanshask et al,. 2011; Adel et al, 2004).
Table 1 : typical charateristics of textile wastewater
Parameters
Values
pH
6.0– 10.0
Temperature (0 C)
35-45
Biochemical Oxygen Demand (mg/L)
100 – 4,000
Chemical Oxygen Demand (mg/L)
150 – 10,000
Total Suspended Solids (mg/L)
100 – 5,000
Total Dissolved Solids (mg/L)
1,800 -6,000
Chloride (mg/L)
1,000 – 6,000
Total Alkalinity (mg/l)
500 – 800
Sodium (mg/l)
610 – 2,175
Total Kjeldahl Nitrogen (mg/L)
70 – 80
Colour (Pt-Co)
50-2500
Source: Sheng and Chi, 1993; Txitzi et al., 1994; Azbar et al., 2004 (cited
in nshask et al,. 2011; Adel et al, 2004).
Dye wastewater from textile mills is a serious pollution problem because it is
high in both colour and organic content. A dye is a colored substance that can be
applied in solution or dispersion to a substrate in textile manufacturing, thus giving a
color appearance to textile materials. Discharging of dyes into water resources even
in a small amount can affect the aquatic life and food web. One of the main problem
regarding textile waste-waters is the colored effluent. The colored effluent contains
visible pollutants. The primary concern about effluent color is not only its toxicity but
also its undesirable aesthetic impact on receiving waters. Non-biodegradable nature
of most of the dyes reducing aquatic diversity by blocking the passage of sunlight
through the water represents serious problems to the environment. In some cases,
dyes in lowconcentration are harmful to aquatic life. Since many dyes have adverse
effect on human beings, the removal of color from the effluent or process has
appeared of importance for ensuring healthy environment. Hence, it is imperative
10
that a suitable treatment method should be applied. The colour of the effluent
discharges into receiving waters affects the aquatic flora and fauna and causes many
water borne diseases. Some of dyes are carcinogen and others after transformation or
degradation yield compound such as aromatic amines, which may carcinogen or
otherwise toxic. In addition, dyes accumulate in sediments at many sites, especially at
location of wastewater discharge, which has an impact on the ecological balance in
the aquatic system. These pollutants because of leaching from soil also affect ground
water system (EPA, 2004).
EPA,(2004) also raised that the discharge of organic pollutant either BOD or
COD to the receiving stream can lead to the depletion of dissolved oxygen and thus
creates anaerobic condition. Under anaerobic condition foul smelling compound such
as hydrogen sulfides may be produced. This will consequently upset the biological
activity in the receiving stream.
2.3. Treatment of Textile Wastewater
Common treatment methods for textile wastewaters are: biological treatment,
physical treatment and chemical treatment. These treatment methods and their
efficiencies are reviewed in following sections.
2.3.1.
Bioligical Method
There are many types of biological treatment methods. Among them include
trickling filters, activated sludge process, anaerobic process, oxidation ponding etc.
To date the commonest treatment of textile wastewater has been based on mainly on
aerobic biological process, consisting mainly conventional and extended activated
sludge system. The trickling filters simulate stream flow by spraying wastewater over
a broken, medium such as stone or plastic. The medium serves as a base for biological
growth, which attacks the organic matter of wastewater, and uses it as food.
In activated sludge process, the wastewater flows into a tank after primary
settling. The microorganism in activated sludge is suspended in the wastewater as
11
aggregates. The sludge and wastewater is kept in suspension by compressed air,
which also supplies the oxygen, necessary for biological activities. The aerated waste
is continuously withdrawn and settled and a portion of the sludge is returned to the
influent (Metcalf and Eddy, 1991).
Biological treatment can be applied to textile wastewaters as aerobic, anaerobic
and combined aerobic-anaerobic. In most cases, activated sludge systems (aerobic
treatment) are applied. In all activated sludge systems, easily biodegradable
compounds are mineralized whereas heavily biodegradable compounds need certain
conditions, such as low food-to-mass-ratios (F/M) (<0.15 kg BOD5/kg MLSS.d),
adaptation (which is there if the concerned compounds are discharged very
regularly) and temperature higher than 15oC (normally the case for textile
wastewater) (Lacasse and Baumann, 2004).
Ineffectiveness of aerobic biological treatment in reducing color caused by
heavily biodegradable organics causes aesthetic problems in the receiving waters and
encourages researchers to investigate alternatives. Dyes themselves are generally
resistant to oxidative biodegradation, and a difficulty occurs in acclimation the
organisms to this substrate. Acclimation presents a problem with textile wastewater
due to constant product changes and batch dyeing operations (Reife and Freeman,
1996).
“Depending on the dyeing process; many chemicals like metals, salts,
surfactants, organic processing assistants, sulphide and formaldehyde may be added
to improve dye adsorption onto the fibers” (Dos Santos, 2007). These chemicals are
mainly in toxic nature and decrease the efficiency of biological treatment in color
removal regarding textile wastewater.
“The treatment and safe disposal of hazardous organic waste material in an
environmentally acceptable manner and at a reasonable cost is a topic of great
universal importance. There is little doubt that biological processes will continue to
be employed as a baseline treatment process for most organic wastewaters, since
they seem to fulfill the above two requirements. However, biological processes do not
12
always give satisfactory results, especially applied to the treatment of industrial
wastewaters, because many organic substances produced by the chemical and related
industries are inhibitory, toxic or resistant to biological treatment.
Due to insufficiency of biological treatment in the removal of the dyes from
textile and dyestuff manufacturing, this process requires the involvement of other
physical, chemical, and physicochemical operations” (Rai, 2005; Banat et al., 1997).
“Physical and chemical treatment techniques are effective for color removal but use
more energy and chemicals than biological processes. They also concentrate the
pollution into solid or liquid side streams requiring additional treatment or disposal”
(Shaw et al., 2001).
Therefore, the tendency in recent years is towards using alternative
technologies, especially advanced oxidation processes for the removal of color caused
by hardly biodegradable organics (Baban et al., 2003; Sevimli and Sarıkaya, 2002;
Birgül and Solmaz, 2007).
2.3.2.
Physical Method
The common physical treatment methods used for the treatment of colored
textile effluents include membrane filtration, ion exchange, adsorption with activated
carbon, irradiation and coagulation and flocculation (Doble and Kumar, 2005; Metcalf
and Eddy, 1991)
Membrane based separation processes have gradually become an alternative
method in the treatment of textile wastewaters. Application of membrane
processes allows reuse of water besides high removal efficiencies. “Ultrafiltration
has been successfully applied for recycling high molecular weight and insoluble
dyes (e.g. indigo, disperse), auxiliary chemicals (polyvinyl alcohol) and water.
However, ultrafiltration does not remove low molecular weight and soluble dyes
(acid, reactive, basic, etc.), but efficient color removal has been achieved by
nanofiltration and reverse osmosis” (Fersi et al., 2005).
13
Related to ion exchange, Mock and Hamodua (1998) reported that an ion
exchange system would decolorize a dilute mixture of a colored wastewater sample.
However, because the colorant was irreversibly adsorbed onto the resin and
regeneration was not possible this technology does not seem effective. They
claimed that, further testing with ion exchange-macroreticular polymer systems
might have been successful but initial cost estimates, requirement for off-site resin
regeneration, and secondary waste disposal requirements resulted in removal of this
technology from consideration for color destruction. Robinson et al. (2001) also
documented that ion exchange can not be used for the treatment of dye-containing
effluents mainly due to cost disadvantage and its ineffectiveness in disperse dyes.
“The coagulation and flocculation process is a versatile method used either
alone or combined with biological treatment, in order to remove suspended solids
and organic matter as well as providing high color removal in textile industry
wastewater” (Meriç et al, 2004). “ Many coagulants are widely used in the
conventional wastewater treatment processes such as aluminum, ferrous sulphate,
sulphate and ferric chloride” (Anouzla, 2009).
The adsorption is one of the effective methods and the main adsorbent used in
dye removal is activated carbon. Activated carbon has been generally used to remove
composite reactive dye from dyeing unit effluent. The main disadvantage of activated
carbon adsorption method is its high regeneration cost (Demirbaş, 2009).
Moreover, the color of wastewater from today’s new dyes is much more difficult
to treat by physical techniques such as adsorption and chemical coagulation to
achieve complete decolorization, especially for highly soluble dyes (Oğuz and
Keskinler, 2008). “On the other hand, methods such as coagulation/flocculation and
activated carbon adsorption can only transfer the contaminants from one phase to
another leaving the problem of color in dyehouse effluent essentially unsolved.
Therefore, much attention has been paid to the development of water treatment
techniques that lead to complete destruction of the dye molecules” (Solmaz et al.,
2006).
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2.3.3.
Chemical Method
Chemical method includes coagulation or flocculation and oxidation. The main
advantage of the conventional coagulation and flocculation is removal of the waste
stream due to the removal of dye molecules from the dyebath effluent and not due to
partial decomposition of dyes which can lead to an even more potentially harmful and
toxic aromatic compound (Metcalf and Eddy, 1991). It was also documented that in
treatment of textile wastewaters, chemical treatment methods are known to be much
more effective than others in breaking down the straight, unsaturated bonds in the
dye molecules (Ciardelli et al., 2001).
Chemical oxidation uses strong oxidizing agents such as hydrogen peroxides,
chlorine and others to force degradation of resistant organic pollutant. Chemical
oxidation is the most commonly used method of decolourization by chemical owing to
its simplicity and the main oxidizing agent is hydrogen peroxide (Metcalf and Eddy,
2003)
Chemical oxidation typically involves the use of an oxidizing agent such as
ozone(O3), hydrogen peroxide(H2O2), Fenton’s reagent, permanganate (MnO4) etc. to
change the chemical composition of a compound or a group of compounds, e.g. dyes
(Metcalf and Eddy, 2003). Fenton oxidation operates at acidic pH in the presence of
H2O2 and excess ferrous ions yielding hydroxyl radicals which oxidize organic
matter. Fenton’s reagent is effective in reducing COD, color and toxicity of textile
wastewaters, but has the disadvantage shifting problems from water into the solid
phase. Therefore a further removal mechanism is required for the Fenton sludge
(Meriç et al., 2004; Eckenfelder et al., 1994).
Recently, a growing interest is observed in combined methods of chemical
oxidation by means of H2O2 and O3 as well as O3 and UV radiation, and of the three
agents simultaneously (Perkowski et al., 1999). “Advanced technologies based on
chemical oxidation seem to be viable options for decontaminating a biologically
recalcitrant wastewater. Such oxidation technologies are broadly classified as follows:
15
(i) advanced oxidation processes (AOPs) including wastewater remediation
based on ozone, hydrogen peroxide, hydrogen peroxide/ferrous iron catalyst
(the so called Fenton’s reagent), UV irradiation, photocatalysis and
electrochemical oxidation;
(ii) wet air oxidation processes (WAO)” (Mantzavinos and Psillakis, 2004).
2.4. Advanced Oxidation Processes (AOPs)
Advanced Oxidation Processes( AOPs) represents the newest development in
H202 technology, and have been defined as a process that generate highly reactive
oxygen radicals. The goal of any AOPs design is to generate and use hydroxyl free
radical (HO-) as strong oxidant to destroy compound that can not be oxidized by
conventional oxidant. Table 2 shows the relative oxidation potentials of several
chemical oxidizers. Advanced oxidation processes are characterized by production of
OH- radicals and selectivity of attack which is a useful attribute for an oxidant.The
application of AOP is also enhanced by the fact that they offer different possible ways
for OH- radicals. A list of the different possibilities offered by AOP is given in Table
3. Generation of HO- is commonly accelerated by combining O3 , H2O2 , TiO2 , UV
radiation, electron-beam irradiation and ultrasound (shanshask et al,. 2011; Adel et
al, 2004).
Table 2: Oxidizing potential for conventional oxidizing agents
Oxidizing agent
Electrochemical oxidation
EOP relative to chorine
potential (EOP), V
Fluorine
Hydroxyl radical
Oxygen (atomic)
Ozone
Hydrogen peroxide
Hypochlorite
Chlorine
Chlorine dioxide
Oxygen (molecular)
3.06
2.80
2.42
2.08
1.78
1.49
1.36
1.27
1.23
2.25
2.05
1.78
1.52
1.30
1.10
1.00
0.93
0.90
Source: (Shanshask et al,. 2011; Adel et al, 2004; Metcalf and Eddy, 2003; and
www. H2O2 .com)
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Table 3: Advanced Oxidation Processes
H2O2/UV/ Fe2+ (photo assisted Fenton)
H2O2 /Fe2+ (Fenton)
H2O2/UV(also applicable in the gas phase)
Ozone/ H2O2
Ozone /UV/ H2O2
Ozone/TiO2/Electron–beam irradiation
Ozone/TiO2 / H2O2
Ozone + electron-beam irradiation
Ozone/ultrasonics
H2O2/UV
Source: Shanshask et al,. 2011; Adel et al, 2004; and www. H2O2 .com
2.5. Conventional Fenton Process
The Fenton process produces radical intermediate compounds by the reaction
of H2O2 and Fe2+. The Fenton process has been applied in wastewater treatment
processes and is known to be very effective in the removal of many hazardous organic
pollutants (Mathew A. Tarr, 2003). Radical intermediate compounds produced from
the Fenton process is composed mostly of hydroxyl radicals. Hydroxyl radicals exhibit
faster rates of oxidation reactions as compared to those using conventional oxidants
like hydrogen peroxide or permanganate (Gogate, 2002).
The conventional Fenton process was first discovered and used by H. J. H.
Fenton in 1894 when he observed that the rate of oxidation of tartaric acid increased
dramatically when dilute hydrogen peroxide was added with the solution containing
dissolved Fe2+ ions. Fenton’s chemistry is a reaction between hydrogen peroxide
(H2O2) and Fe2+ ions forming hydroxyl radicals, which is the main oxidizing agent.
However the hydroxyl radical mechanism of the Fenton’s reaction was only identified
40 years after its discovery (Mathew A. Tarr, 2003).
Hydroxyl radicals (OH·) are short-lived reactive oxygen species with a high
oxidation potential that can rapidly destroy many biorefractory contaminants (Watts,
2005). It is one of the most reactive chemical species; second only to elemental
fluorine in its relative oxidation power as listed in Table 2 above (Metcalf and Eddy,
17
2003; and www. H2O2 .com). It was raised by B. Bianco et al., (2011) that the
oxidation using Fenton’s reagents (Fenton’s process) causes the dissociation of the
oxidant and the formation of reactive hydroxyl radicals that destroy organic
pollutants to harmless com-pounds (CO2, water and inorganic salts). Fenton’s
reagents are H2O2 and ferrous ions. They generate hydroxyl radicals following the
chain reaction schematized as follow:
Fe2+ + H2 O2 → Fe3+ + OH• + OH−
OH• + Fe2+ → OH− + Fe3+
(chain initiation)
(chain termination)
(1)
(2)
As shown in Equation (1) and (2), the ferrous iron (Fe2+) starts the reaction and
catalyses the decomposition of H2 O2 in hydroxyl radicals (B. Bianco et al., 2011;
Mathew A. Tarr, 2003). However, the newly formed ferric ions (Fe3+) may decompose
hydrogen peroxide in water and oxygen (forming ferrous ions and radicals):
Fe3+ + H2 O2 ↔ Fe− OOH2+ + H+
(3)
Fe – OOH2+ → HO2 • + Fe2 +
(4)
The above reactions are referred as Fenton-like reaction. The organics (RH) are
oxidized by hydroxyl radicals proton-abstraction ending with the production of
organics radicals (R•). These last products are highly reactive and can be further
oxidized:
(5)
RH + OH• → H2 O + R• + further oxidation
It was also supported in AOPs applicationn that Fenton’s reagent treatment
system have gain its practical use than other due to their superior reation rate and
effeciency, technical feasibility and attractive process economic. The oxidation
mechanism in the Fenton process involves the reactive hydroxyl radical generated
under acidic conditions by the catalytic decomposition of hydrogen peroxide, which
reacts unselectively with organic substances (RH), which are based on carbon chains
or rings and also contain hydrogen, oxygen, nitrogen, or other elements (Giusy
Lofrano, 2012).
18
The reaction mechanism has been summarized as follow:
Fe2+ + H2O2 → Fe3+ + OH− + •OH
(6)
RH + •OH → R• + H2O
(7)
R• + Fe3+ → product + Fe2+
(8)
Fe2+ + •OH → Fe3+ + OH−
(9)
Fe3+ + H2O2 → Fe2+ + H+ + HO2•
(10)
Inhibitions to the Fenton process have also been investigated in recent studies.
Anions like H2PO4, Cl-, NO3 and ClO-4 was found to inhibit the Fenton reaction;
therefore, reducing its efficiency. Among the anions, H3PO4 was found to inhibit the
reaction the most since the phosphate ions will produce a complex reaction with
ferrous and ferric ions (Lu 1997). The inhibition of low concentration chloride ions
was found to be controlled by extending the reaction time. However inhibition is
significant if the ratio of chloride to ferrous ions is greater than 200. Likewise, inhibition by
chloride ions was controlled by increasing the initial pH near to 5 and increasing the
amount of ferrous ions (Lu 2005; Sajiki 2004). Presence of chloride ions in the Fenton
process also produces chloroorganic compounds as byproducts (Gaca 2005).
The effect of temperature on the rate of reaction of the Fenton process was also
studied and was found to increase as the solution temperature was increased.
However, the effect of temperature was only obvious at temperatures lower than
200C. In addition to this application of temperatures greater than 400C, the treatment
efficiency declines due to decomposition of H2O2 into oxygen and water. Application
of the Fenton process has been normally conducted at temperatures of 20 to 400C
(Watts, 2005).
The optimal pH range for the application of the Fenton process was also
determined to be at pH 3 and pH 6. Application of the Fenton process at high pH
values will result into inhibition of the Fenton reaction since the Fe2+ ions will form
colloidal Fe3+ ions. Likewise, application of the Fenton process at very low pH values
would result into the decomposition of H2O2 into oxygen and water by iron without
forming hydroxyl radicals (Neyens, 2003)
19
Chapter III
Research Methodology
3.1. Textile Wastewater
Textile wastewater used was supplied by textile industry in Rayong Province,
Thailand. Raw textile wastewater is containing high content of COD, pH, and Color
which resulting from Dying and Finishing processes. Table 4 shows characteristics of
the livestock wastewater. The main characteristics of this textile wastewater are that
the pH was in the range of 8.4–8.7, the chemical oxygen demand (COD) was 5,000–
5,700 mg/L. The maximum color absorbance at 287 nm was 2.1 and the color was
dark grey.
Table 4: Characteristics of textile wastewater from Rayong Textile Industry.
Parameters
Value
pH
COD (mg/L)
8.4 – 8.7
6,500 – 27, 000
8,500-10,000
2.1
BOD (mg/L)
Color (absorbance at 287
nm )
(*Based on Secondary data)
3.2.
Material and Fenton’s Reagent
H2O2 (34.5% v/v) and FeSO4 · 7H2O will be used during experiments. H2SO
and NaOH also used for pH adjustment.
3.3. Experimental Procedures
The Fenton method was applied in 200 mL flasks containing 100 mL samples of
textile wastewater. All procedures were carried out at room temperature (22–25 0C)
and at atmospheric pressure. First, the initial pH of the sample was adjusted to the
desired pH value at 4 using 0.2N and 2N H2SO4. Then, a H2O2 solution (34.5%, v/v)
and FeSO4·7H2O powder were added to the flask and the mixture was vigorously
stirred to dissolve the powder FeSO4·7H2O for 1min. The flask was then allowed to
stand without stirring for 30 min. After that, the pH was neutralized to 7–8 (average
7.5) using 1N and 10N NaOH, and the precipitation was allowed to occur for 1h in
20
standing flasks. Experimental conditions were varied as following. First, the initial pH,
reaction time, and Fe2+ dose were kept constant while the H2O2 dose was varied.
Second, the initial pH, reaction time, and H2O2 dose were kept constant while the Fe2+
dose was varied. Third, the reaction time, H2O2 dose, and Fe2+ dose were kept
constant while the initial pH was varied. Fourth, the initial pH, H2O2 dose and Fe2+
dose were kept constant while the reaction time was varied. Finally, all other
conditions were kept constant while either Fe2+ dose or H2O2 dose was given in
several aliquots. The experimental procedures are shown in Fig. 1, where the initial
pH was set at 4, the reaction time at 30 min, and the Fe2+ was given in either one or
five doses and H2O2 was given in either one or three doses (Adapted from Hyunhee
Lee Method (2008).
Sample
(Textile wastewater)
pH adjustment to 4
Total dosage of H2O2 and
division dosage of 1/5 Fe2+
Total dosage of Fe2+ and
division dosage of 1/3 H2O2
Total
dosage
of H2O2
Repeat
once
10 min
6 min
pH adjustment to 4
Division dosage
of 1/3 H2O2
pH adjustment to 4
Repeat 3
times
10 min
Total dosage
of Fe2+
30 min
Division dosage
of 1/5 Fe2+
6 min
Neutralization to 7-8
Precipitation
1h
Analysis of supernatant
Figure.1. Experimental procedures in this study including a single H2O2 dosage and
three division H2O2 dosages and a single Fe2+ dosage and five division Fe2+dosages
(initial pH 4, reaction time = 30 min)
21
3.4. Laboratory Analytical Method
COD was measured by a closed reflux titrimetric method according to standard
methods. The pH values will be measured with a pH meter. The H2O2 concentrations
are measured by using a H2O2 sensor. Color intensities of samples are measured in
Space Unit (SU) by a spectrophotometer in consistent with Standard Method. COD
and color removal efficiency are principally determined as following:
COD Removal Eff. (%) =
COD(in) − COD (out)
∗ 100
COD (in)
Color Removal Eff. (%) =
Abs(in) − Abs (out)
∗ 100
Abs (in)
Where
COD (in)
: Initial COD concentration (mg/l)
COD (out)
: COD concentration after treatment (mg/l)
Color (in)
: Initial Color value
Color (out)
: Color effluent after treatment
3.5. Statistical Analysis Method
Statistical analyses used for calculating significant differences are the PairedSamples T-test and Single Sample T-test using SPSS version 16.0 of SPSS. Significant
differences were concluded when the significance level value obtained was less than
0.05 using 95% level of confidence. Likewise the Single Sample T-test was used when
the significant difference between two parameters or indexes was determined at the
same experimental conditions. In addition, Microsoft Excel 2007 is also used for
simple calculation of COD and Color Removal Efficiency and Graphical representation
when a set of data obtained from SPSS data will have been revealed.
22
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25
Appendix 1: Research Action Plan
Activities
2013
Dec
Jan
Feb
Mar
May
Apr
Jun
2014
Jul
Aug
Topic Selection
Literature Review
Proposal Preparation
Proposal Defense
Proposal Revision
Sample collection
Laboratory Testing
Data Analysis
Thesis Reports
Thesis
submission
and Revision
Final Thesis Report
Final Thesis Defense
Publication
26
Sep
Oct
Nov
Dec
Jan
Feb
Mar
Apr
May