Som Piseth Proposal

APPLICATIONS OF FENTON AND FENTON-LIKE REACTIONS WITH

SUBSEQUENT HYDROXIDE PRECIPITATION FOR DERUSTING

WASTEWATER TREATMENT

PISETH SOM

A PROPOSAL SUBMITTED IN PARTIAL FULFILLMENT OF THE

REQUIREMENT FOR THE MASTER DEGREE OF ENGINEERING

IN CHEMICAL AND ENVIRONMENTAL ENGINEERING

BURAPHA UNIVERSITY

NOVERMBER 2013

COPYRIGHT OF BURAPHA UNIVERSITY

ii

TABLE OF CONTENT

TABLE OF CONTENT ................................................................................................. iiLIST OF TABLES ........................................................................................................ ivLIST OF FIGURES ....................................................................................................... vABBREVIATION......................................................................................................... viCHAPTER 1 INTRODUCTION ................................................................................... 1

Statements and Significant of Problems .................................................................. 1Objectives ................................................................................................................ 3Research Hypothesis ................................................................................................ 4Scope of the Study ................................................................................................... 4Significance of the Study ......................................................................................... 4

CHAPTER 2 LITERATURE REVIEW ....................................................................... 6Advanced Oxidation Processes (AOPs) ................................................................... 6Fentons Reagent and Reaction Mechanism ............................................................ 8

Basic Principle ................................................................................................ 8Fenton Reaction .............................................................................................. 9Fenton-like Reaction ..................................................................................... 10

Hydroxyl Radical Reaction with Organic Compounds ......................................... 11Iron Ligand, Chelators and Coordination .............................................................. 13Factors Affecting Fenton and Fenton-like Process ................................................ 14

Effect of pH ................................................................................................... 14Effect of Temperature ................................................................................... 15Effect of Iron Concentration ......................................................................... 16Effect of H2O2 concentration ........................................................................ 17Effect of Reaction Time ................................................................................ 18

Chelating Agents Degradation by Various Fenton Processes ................................ 19CHAPTER 3 RESEARCH METHODOLOGY .......................................................... 25

Derusting Wastewater Characteristics ................................................................... 25Materials and Chemical Reagents .......................................................................... 25Experimental Design and Procedure ...................................................................... 27

Determine wastewater characteristics ........................................................... 27Hydroxide Precipitation of Iron Before Fenton and Fenton-like Processes . 28Effects of Initial pH on Fenton-like Process ................................................. 28

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Effects of H2O2 Concentration on Fenton-like Process ................................ 29Effects of Reaction Time on Fenton-like Process ......................................... 30Hydroxide Precipitation of Iron After Fenton-like Process .......................... 31Effects of Initial pH on Fenton Process ........................................................ 32Effects of Fe2+ Concentration on Fenton Process ......................................... 33Effects of H2O2 Concentration on Fenton Process ....................................... 33Effects of Reaction Time on Fenton Process ................................................ 34Hydroxide Precipitation of Iron After Fenton Process ................................. 35

Optimum Conditions .............................................................................................. 36Analytical Method ................................................................................................. 36Kinetic Study ......................................................................................................... 37

REFERENCES ............................................................................................................ 39APPENDICES ............................................................................................................. 44

Appendix A: Activities plan .................................................................................. 44Appendix B: Chemical Analysis Procedures ......................................................... 45Appendix C: Fentons Reagent Preparation .......................................................... 50

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LIST OF TABLES

Table 2.1 Oxidizing potential for conventional oxidizing agents ................................. 6Table 2.2 Summary of Fenton process for various wastewater treatments ................ 23

v

LIST OF FIGURES

Figure 2.1 Classification of advanced oxidation processes (AOPs). ............................ 8

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ABBREVIATION

AOPs : Advanced Oxidation Processes

EDTA : ethylenediamine tetraacetic acid

COD : chemical oxygen demand

BOD5 : biological oxygen demand in 5 day

1

CHAPTER 1

INTRODUCTION

This chapter covers the fundamental background of research and problems in

consideration of Advanced Oxidation Processes (AOPs) based on Fenton and Fenton-

like processes for derusting wastewater; then, the research objectives and research

hypothesis are formulated accordingly. Finally, significance and scope of the study are

also provided.

Statements and Significant of Problems Chemical cleaning of pipes, tanks, boilers, and power plants has been operated

to remove the deposits and scales for reactivation and reuse of them. There are various

types of chemicals that have been used for cleaning depending on the equipment including inorganic acids, organic acids, chelating agents, alkali agents and aids agents.

The inorganic acids include hydrochloric acid, sulfuric acid and nitric acid. The

hydrochloric acid is the most widely used for chemical cleaning. The examples of

organic acids are citric acid, glycolic acid, and formic acid. The organic acids are used

extensively for cleaning of recent new boilers. The most widely used chelating agent is

ethylenediamine tetraacetic acid (EDTA). The ammonia, which is alkali agent, is used

to clean the scale containing large quantities of copper. The aids agents such as acid

inhibitors and reducing agents are used to reduce and to prevent the corrosion of the

materials, respectively. The sodium nitrite can be used as inhibitor for protection of

carbon steel in salt solution (Hayyan, et al., 2012). During the cleaning operation, two

methods for dissolving encrustation or rust are applied. First method is a two-step

process: first stage uses inhibited hydrochloric acid solution for iron oxide dissolution

followed by the second stage of dissolving the metallic copper by ammonia and

oxidizing agents. Another method involves a single cleaning stage. In this method, iron

oxide and metallic copper are dissolved simultaneously by using hydrochloric acid in

the presence of chelating agents and citric acid. Consequently, the cleaning wastewater

often contains large amounts of iron and copper including high concentration of

chelating agents (Huang et al., 2000; Bansal, 2012). Iron (Fe3+) is the most prevalent

cation, generally present at a concentration of 1000-10000 mg/L. Copper is the second

2

most abundant metal with minor level of nickel, chromium, and zinc, typically, present

at the concentration less than 100 mg/L (Huang et al., 2000; Kim et al., 2010).

The EDTA and citric acid are used at the concentrations of 2-5% and up to 10% by weight, respectively, in cleaning process (Huang et al., 2000; Kim et al., 2010).

Chelating heavy mental wastewater must be treated not only for the toxic heavy mental,

but also the chelating agents. Heavy metals are considered toxic to human being and

aquatic life. Furthermore, the EDTA causes the complexation and immobilization of

heavy metals. The EDTA complexation is biologically persistent and cannot be readily

degraded by conventional biological treatment processes (Ghiselli et al., 2004; Citra et

al., 2011). The presence of chelated complex causes constraints and ineffective

application of lime or caustic treatment, chemical precipitation, ion exchange as

reported in the literatures (Citra et al., 2011; Lan et al., 2012; Fu et al, 2009). Metal

chelated wastewater can be treated by electrochemical reduction (Huang et al., 2000)

and interior microelectrolysis (Lan et al., 2012). Both processes can successfully

remove metal; however, interior microelectrolysis cannot remove or degrade chelating

EDTA and electrochemical reduction can achieve EDTA recovery for reuse. To

remove metal and mineralize the metal-EDTA complexes, there is an urgent need to

search for a feasible, efficient, economical, and eco-friendly approach (Bautista et al.,

2008; Bianco et al., 2011).

For last few decades, advanced oxidation processes (AOPs) are known for

their capability to mineralize, decompose, and degrade non-biodegradable organic

compounds (Poyatos et al., 2010; Ameta et al., 2012). Particularly, Fenton and Fenton-

like processes are adopted for wastewaters treatment in terms of organic pollutant

destruction, toxicity reduction, biodegradability improvement, COD removal, odor and

color removal, and heavy metal removal due to the economic advantages, ease of

application, and effectiveness (Matthew Tarr, 2003; Bautista et al., 2008; Lucas &

Peres, 2009; Bianco et al., 2011). Fenton is one of the AOPs that has been commonly

applied for industrial wastewater including textile effluent (Kang et al., 2002;

Karthikeyan et al., 2011), olive oil effluent (Lucas & Peres, 2009; Kiril Mert et al.,

2010), pulp and paper mill effluent (Pirkanniemi et al., 2007), cosmetic wastewater

(Bautista et al., 2007), bleaching effluent (Wang et al., 2011), highly polluted industrial

wastewater (San Sebastin Martinez et al., 2003), complex industrial wastewater

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(Bianco et al., 2011). However, application of Fenton and Fenton-like reactions for

boilers chemical cleaning wastewater is not extensively documented. An integration of

Fenton oxidation with other conventional treatment methods have been conducted to

degrade EDTA complex and to removal metals from the waste stream. Synthetic

NiEDTA was successfully removed using Fenton and Fenton-like reactions followed

by precipitation (Fu et al., 2009, 2012). The degradation of Cu-EDTA complex can

also achieved (Lan, et al., 2012) with interior microelectrolysis and Fenton oxidation

coagulation. However, Fe-EDTA complex has not been conducted yet. To our

knowledge; Therefore, Fe-EDTA removal by Fenton and Fenton-like is important since

their applications are limited.

As mentioned above, chemical cleaning wastewater contains high iron species

including Fe2O3,/Fe3O4 (rust) and Fe2+ or Fe3+ depending on the pH, which can reach

up to hundreds of mg/L. It is assumed that Fenton or Fenton-like reactions should take

place to generate hydroxyl radicals (OH) when H2O2 is added to the iron-rich

wastewater because the rust (Fe2O3/Fe3O4) particles and iron (Fe2+/Fe3+), which have

already presented in wastewater, could be effective catalysts in the generation of strong

oxidant (Kitis & Kaplan, 2007; Kim et al., 2010; Lan et al., 2012).

Objectives The overall objective of this study is to evaluate the feasibility and efficiency

of Fenton and Fenton-like oxidations for removals of organic pollutants measured as

COD and inorganic pollutants including various iron species concentrations as the main

parameters and chemicals in derusting wastewater. Following specific objectives are

included:

1. To determine the optimum initial parameters of Fenton and Fenton-like reactions including pH, Fe2+ concentration, H2O2 concentration for the

treatment of derusting industrial wastewater.

2. To determine the optimum reaction time and reaction kinetics for the treatment

of derusting industrial wastewater

3. To determine the optimum precipitation pH for Fenton and Fenton-like

reactions for the treatment of derusting industrial wastewater.

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4. To investigate the effects of Fenton and Fenton-like reactions on the ammonia

and nitrite removals in the treatment of derusting industrial wastewater.

Research Hypothesis 1. The presence of chelating agent, EDTA, can inhibit the precipitation of iron in

the derusting wastewater.

2. Utilization of existing Fe (III)/Fe (II) and additional iron can be beneficial for

Fenton and Fenton-like oxidation for degradation of EDTA complex in term

of COD reduction and total Fe removal.

Scope of the Study This study is limited with following conditions.

1. Treatment performance evaluation is conducted using Jar test apparatus under

normal laboratory room temperature at Department of Chemical Engineering,

Faculty of Engineering, Burapha University.

2. Real wastewater taken from Kation Power Ltd (Thailand) is used throughout

the experiments

3. Organic degradation will measured in COD value.

4. Oxidation products are not investigated in this study

Significance of the Study The results of this study can provide the following contributions:

Firstly, this study demonstrates the fessibility of Fenton and Fenton-like

process applications as methods to solve the encountered derusting wastewater

treatment problem as practiced in accordance with standard effluent stipulated in

national regulation.

Secondly, even though Fenton oxidation have been applied extensively and

enormously in many differrent types of wastewater, its application for derusting

wastewater was not well documented in literatures. Thus, this study will contribute to

comprehensive and extensive knowlegde and discussion on real wastewater treatment

which is known to be contiminated with chelating organic compounds and high metal

concentration.

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Finally, it is probably advantageous for Fenton and Fenton-like process to

utilize iron metals (ferric and ferrous ions) that have already existed in cleaning

wastewater. If they do, there will be economical and cost-effective for reagents usages

for the treatment of this wastewater.

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CHAPTER 2

LITERATURE REVIEW

This chapter provides a comprehensive review on advanced oxidation

technologies (AOTs). Next, theoretical and empirical reviews on Fenton and Fenton-

like reaction mechanisms influencing factors and their applications are conducted.

Finally, the applications of Fenton oxidation for chelating agent, EDTA, are also

reviewed.

Advanced Oxidation Processes (AOPs) The development of cost-effective technical solutions is needed to deal with

the increasingly complex problems arising in the field of industrial wastewater.

Recently, advanced oxidation processes (AOPs) have been applied successfully for the

removal or degradation of recalcitrant pollutants based on the high oxidative power of

the hydroxyl radical (HO). It has electrochemical oxidation potential (EOP) o f2.8 V, which is comparatively be second to fluorine as shown in Table 2.1 (Poyatos et al.,

2010).

Table 2.1 Oxidizing potential for conventional oxidizing agents

Oxidizing agent Oxidation Potential (EOP), V EOP relative to

Chlorine (V)

Fluorine

Hydroxyl radical (HO)

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: Poyatos et al., 2010.

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A chemical wastewater treatment using AOPs can produce the complete

mineralization of pollutants to CO2, water, and inorganic compounds, or at least their

transformation into more harmless products. Furthermore, the partial decomposition of

non-biodegradable organic pollutants can lead to biodegradable intermediates;

therefore, AOPs are commonly applied as pre-treatments processes, followed by

biological or chemical processes (Poyatos et al., 2010). AOPs represent the newest

methods in H2O2 technology which include photochemical degradation processes

(UV/O3, UV/ H2O2), photocatalysis (TiO2/UV, photo-Fenton reaction), and chemical

oxidation processes (O3, O3/ H2O2, H2O2/Fe2+). Although advanced oxidation processes

(AOPs) have employed different reagent systems, they all produce hydroxyl radicals.

These radicals are very reactive and they can attack most organic compounds

nonselectively (Kalra et al., 2011; Lucas & Peres, 2009; Poyatos et al., 2010).

Advanced oxidation processes (AOPs) can be classified either as homogeneous or

heterogeneous. Homogeneous processes can be further subdivided into energy-

activated and non-energy activated processes as shown in Figure. 2.1. The following

sections describe a wide range of advanced oxidation systems that are currently being

studied for their possible use in wastewater treatment (Poyatos et al., 2010).

Among advanced oxidation technologies, Fenton oxidation has been

frequently involved in many different industrial wastewater treatment processes for

degrading and remediating of a wide range of contaminants, predominately toxic,

recalcitrant, and persistent organic pollutants (POPs). It is also due to economic

advantages, ease of application, and effectiveness in the contaminant reduction and

mineralization (Matthew Tarr, 2003). It was also considered that Fenton oxidation

presents one of the best methods for clean and safe processes for the degradation of

organics even at higher initial organic content (Bianco et al., 2011; Lucas & Peres,

2009).

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Figure 2.1 Classification of advanced oxidation processes (AOPs).

Fentons Reagent and Reaction Mechanism Basic Principle

The term Fentons reagent refers to the aqueous mixture of Fe (II) and

hydrogen peroxide. The Fentons reagent 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 with the solution containing dissolved Fe2+

ions. Forty years later, after a controversial history about the reaction mechanism of

Fentons reaction, its reaction mechanism was interpreted by Haber and Weiss in 1934

that Fentons 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 Fentons reaction for toxic organics degradation was not

Advanced Oxidation Processes

Homogeneuos process

Using Energy

Ultraviolet Radiation

- O3/UV- H2O2/UV- H2O2/O3/UV- Photo-Fenton(Fe2+/ H2O2/UV)

Ultrasound Energy

- O3/US- O3/US

Electrical Energy

- Anodic Oxidation - Electro-Fenton

Without Energy

- O3 in alkaline Medium- O3/ H2O2- Fenton ProcessFe2+/ H2O2

- Fentton-like Fe3+/H2O2Fe0/H2O2

Heterogeneuos process

- Catalytic Ozonization- Photocatalytic Ozonization-Heterogeneous Photo-catalysis

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applied until the late 1960s (Ciambelli et al., 2008; Matthew Tarr, 2003; Neyens &

Baeyens, 2003).

Fenton Reaction

The oxidation mechanism in the Fenton process involves using ferrous ions to

react with hydrogen peroxide, producing hydroxyl radicals with powerful oxidizing

ability to degrade organic pollutants. The oxidation mechanism of Fenton reaction is

very complex, but the widely accepted major chemical reactions are summarized as

shown below (Ameta et al., 2012; Bianco et al., 2011; Jiang et al., 2010; Lee & Shoda,

2008; Lucas & Peres, 2009; Matthew Tarr, 2003; Neyens & Baeyens, 2003; Munter,

2001).

Fe2+ + H2 O2 Fe3+ + OH + OH k1 = 70 M-1s-1 (2.1)RH + OH R + H2O k2 =107 -1010 M-1s-1 (2.2)R + Fe3+ R+ + Fe2+ N/A (2.3)Fe2+ + OH Fe3+ + OH k4 = 3.2 108 M-1s-1 (2.4)H2 O2 + OH HO2 + H2O k5 =3.3 107 M-1s-1 (2.5)

As shown in equation (2.1), the ferrous iron (Fe2+ ) initiates and catalyses the

decomposition of hydrogen peroxide (H2O2) to generate the hydroxyl radicals (OH).

The reaction (2.1) is commonly known as the main reaction of Fenton process (Neyens

& Baeyens, 2003). The generated hydroxyl radical reacts immediately with organic

substances (RH) resulting in a free organic radicals (R). These radicals are

subsequently oxidized by ferric ion to generate other oxidation products (Matthew Tarr,

2003). In addition to the main reaction, various additional competitives or scavenging

reactions are also possible involving ferrous ions (Fe2+) , hydroxyl radicals (OH), and

hydrogen peroxide (H2O2) as listed in reactions (2.4)-(2.5). During the reaction, the

newly formed ferric ions (Fe3+) may continuously catalyze hydrogen peroxide to

produce ferrous ions and superoxide (HO2). The reaction of hydrogen peroxide with

ferric ions is referred to Fenton-like reaction (Ameta et al., 2012; Bianco et al., 2011;

Matthew Tarr, 2003; Neyens & Baeyens, 2003). Fenton-like reactions are listed as

below:

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Fe3+ + H2O2 Fe2+ + H+ + HO2 k6 = 0.001-0.01 M-1s-1 (2.6) Fe3+ + HO2 Fe2+ + H+ + O2 k7 = 1.2 106 M-1s-1 (2.7) Fe2+ + H2O2 Fe3+ + OH + OH k8 = 70 M-1s-1 (2.8) RH + OH R + H2O K8 = 107 -1010 M-1s-1 (2.9)

In the presence of organic substrates (RH), highly reactive hydroxyl radical

which is species with a relatively short life-span (rate constants in the range 107 -1010

M-1s-1), undergoes oxidation generating a new radical (R) as shown in reaction (2.9).

The possible organic compounds present in reaction mixture can suffer an abstraction

of a hydrogen atom (proton abstraction) or addition of hydroxyl radical (OH) with the

production of organic radicals (R) which can subsequently be oxidized by ferric ions

(Fe3+) as indicated in reaction (2.3). Indeed, the reaction (2.3) regenerates ferrous ions

(Fe2+) which ensure the continuity of the chain reaction. As long as the concentration

of reactants are not limited or available in the system, the iron species continually cycle

between Fe2+ and Fe3+ unless additional reaction result in formation of insoluble iron

oxides and hydroxides. This can lead ultimately to the decomposition of organic

substrate in carbon dioxide (CO2) and water inorganic salts (Lucas & Peres, 2009;

Matthew Tarr, 2003; Neyens & Baeyens, 2003).

Fenton-like Reaction

The conventional Fenton has been modified to improve treatment efficiency

with the reduced inorganic sludge production and prevention of inhibition reaction of

some ions. Those modified Fenton technologies includes photo-Fenton, electro-Fenton,

electro-photo Fenton and Fenton-like reaction. Fenton-like process uses other

transition metal catalyst other than Fe2+ (Fu et al., 2009). The conventional Fenton has

been applied numerously while Fenton-like is not well elucidated. The introduction of

lower cost Fe3+ in Fenton-like process may overcome the drawback of conventional

Fenton (S. Wang, 2008).

Recent applications of other transition metals in addition to Fe2+ including Fe-

containing zeolites, soluble manganese (II) and amorphous and crystalline manganese

(IV) oxide, soluble iron (III), mixture of Fe2+/Cu2+ and Fe3+/Cu2+, suspended iron

powder, clay-based Fe nanocomposite and zero valent iron (ZVI) were investigated.

However, ZVI and Fe3+ have been commonly used as catalysts in Fenton-like reaction

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due to their comparable efficiency and capacity (Fu et al., 2009 & 2013; Hodaifa et al.,

2013; Jiang et al., 2010 & 2013). Since the Fenton-like reaction can be applied

interchangeably and comparatively with Fenton reaction, it was recently selected for

wastewater treatment application in term of cost-effectiveness, efficiency, and easy of

application (Fu et al., 2009; Hodaifa et al., 2013; Jiang et al., 2010, 2013; Kim et al.,

2010; Kiril Mert et al., 2010; Li et al., 2013). Other investigations of Fenton and

Fenton-like process by using iron originated in wastewater still remain questionable

even though iron waste existed in the wastewater was feasibly use as catalyst for Fenton

reaction (Lan et al., (2012).

Jaing et al. (2013) has indicated the interconversion of Fe(III)/Fe(II) in Fenton

and Fenton-like reaction that they are co-occurring or coexisting. A Fenton-like

reaction involves a classical Fenton reaction, and Fenton reaction may also involve a

Fenton-like reaction step. However, Jaing et al. (2010) and Neyens & Baeyens (2003)

demonstrated conventional Fenton reaction was referred to the Fe2+/H2O2 system,

whereas Fenton-like reaction was included in the Fe3+/H2O2 system. Therefore, the

reaction mechanisms are similar in both systems, but are different in terms of catalysts

that are utilized to initiate the reaction.

Hydroxyl Radical Reaction with Organic Compounds For the reaction of hydroxyl radical with organic species, there are three

common reaction pathways: (a) hydroxyl radical addition to an unsaturated compound

(aromatic or aliphatic) to form the free radical products, (b) hydrogen abstraction where

an organic free radical and water are formed (c) electron transfer, where ions of higher

valence state are formed reducing hydroxyl radical to hydroxide ions (Matthew Tarr,

2003; Munter, 2001; Neyens & Baeyens, 2003). Reaction pathways are shown below:

RH + OH (OH)RH C6H6 + OH (OH) C6H6

(Hydroxyl Radical

Addition)

(2.10)

RH + OH R + H2O CH3OH + OH CH2OH + H2O

(Hydrogen Abstraction)

(2.11)

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RH + OH (RH) + + OH [Fe(CH)6]4 + OH [Fe(CH)6]3 + OH

(Direct Electron Transfer) (2.12)

Additional reactants including Fe2+, Fe3+, H2O, O2, H+ , OH, other metals,

other organics, and other radicals present in the system are necessary to complete these

subsequent reactions. Further oxidation processes continuously occur and dimerizeation can also occur if the initially formed radical species reacts with another

identical radical. Other possible reactions including radical interaction where the hydroxyl radical reacts with other hydroxyl radical to combine or to disproportionate

to form the stable products (Munter, 2001; Neyens & Baeyens, 2003). They are shown as following:

OH + OH H2O2 (dimerization of OH) (2.13) R + H2O2 ROH + OH (2.14) R + O2 ROO (2.15) ROO + RH ROOH + R (2.16)

The organic free radical produced in the above reactions may then be oxidized

by Fe3+ reduced by Fe2+, or dimerized according to the following reactions.

R + Fe3+ -oxidation R+ + Fe2+ (2.17)R + Fe2+ -reduction R + Fe3+ (2.18)R + R -dimerization RR (2.19)

By applying Fentons Reagent for industrial waste treatment, the predominant

reaction are hydrogen abstraction and oxygen addition. Typical rates of reaction

between the hydroxyl radical and organic materials are 109 1010 k (M-1 s-1) (Matthew

Tarr, 2003).

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Iron Ligand, Chelators and Coordination Chelating agents still remained contradicted for Fenton reaction. Addition or

presence of resolubilizing chelators or chelating agents cause an increase in the

occurrence of reaction in the catalytic Fenton process. In contrast, chelating agents can

interfere the Fenton process by scavenging ability of the chelator. A good scavenger

may appear to have a lower production rate of hyrdoxyl radical due to rapid trapping of

the radical by the chelator. In addition, very strong iron chelators inhibit the formation

of hydroxyl radical. Iron ligands can also act as hydroxyl radical scavengers. Ligands

are more likely to react with hydroxyl radical than pollutants that are not in close

proximity to the iron because radical is always formed in close proximity to these

ligands. Such coordination will alter the kinetics of hydroxyl radical formation as well

as the dynamics of hydroxyl radical interaction with pollutants. Matthew Tarr (2003)

concluded that the inability of hydroxyl radical to reach sorbed or sequestered

pollutants is one of the major drawback to the application of Fenton degradation

method. However, it is suggested that aggressive conditions including high H2O2

concentration could make possibility for direct degradation of sorbed species.

Several studies have been investigated for the effect of chelators on Fenton

reaction. Addition of chelators to Fe(III)-H2O2 systems (Fenton-like reaction) allows

for effective degradation at near neutral pH values. The influence of the iron chelators

form increased solubility of iron species at higher pH value. Iron chelators improved

the Fenton oxidation of pollutant by increasing iron solubility and increases the rate

constant for hydroxyl radical formation from peroxide. The chelators also act as

hydroxyl radical scavengers from potential interaction with pollutants. Earlier studies

indicated that at pH 7.3, each EDTA-Fe complex was able to produce more than 50

hydroxyl radical before being degraded (Eckenfelder, 2000). The relative efficiencies

of the chelators for hydroxyl radical formation determine whether the added chelators

will have a positive or negative effect on radical formation. The complexation of EDTA

with iron minimized free ions for Fentons oxidation, resulting in a slow generation of

OH radical (Sillanp et al., 2011). However, the chelating agent may activate H2O2

oxidation at a neutral pH range. This pH ranges might affect the Fentons process due

to iron precipitation (Ghiselli et al., 2004). It reaches to a conclusion that the presence

14

of iron ligands and coordination could bring both positive and negative influences on

Fenton process depending on specific property of iron-coordinating complex.

Factors Affecting Fenton and Fenton-like Process The significant factors affecting both processes are both H2O2 and Iron

concentrations, pH, reaction time, temperature, and initial pollutant concentration.

Effect of pH

The optimal pH for Fenton process is also determined to be between pH 3 and

pH 6. The application of the Fenton process at high pH value will result into the

inhibition of Fenton reaction since the Fe2+ ions will form the colloidal Fe3+ ions.

Likewise, the application of Fenton at very low pH value would result into the

decomposition of hydrogen peroxide into water and oxygen by iron without forming

hydroxyl radical (Neyens & Baeyens, 2003). Furthermore, Fenton oxidation presented

the maximum catalytic activity at pH 2.8-3.0. At very low pH, H2O2 is stabilized as

H3O2+ (Wang et al., 2011). The reaction between OH and H+ also occurs. Fe2+

regeneration by the reaction of Fe3+ with H2O2 is inhibited at more acidic pH value. On

the other hand, at the pH higher than 3, Fe3+ can precipitate as Fe(OH)3 and decompose

of H2O2 into O2 and H2O without OH production (Bautista et al., 2007, 2008). A study

on EDTA degradation by Fenton process with pH ranged from 2 to 7 found that

degradation of EDTA decreased from 80.3% to 27.5% over the reaction time of 10 min

(Lou & Huang, 2009). This result indicated that the pH value significantly influenced

the removal of EDTA by directly affecting the generation of OH which found that the

optimum range for Fenton oxidation was 2-4 (San Sebastin Martinez et al., 2003;

Bautista et al., 2007; Z. Wang et al., 2011; Jiang et al., 2013). At high pH, oxidation

yield of the process decreases due to the precipitation of Fe3+ as Fe (OH)3 which

hindered the reaction between Fe3+ and H2O2 and thus influenced the regeneration of

Fe2+. Moreover, Fe(OH)3 functionally catalyzed the decomposition of H2O2 into O2 and

H2O which decrease the production of hydroxyl radical (OH). Therefore, pH of 2 was

the optimum condition for Fenton method in removal of EDTA. Similarly, Fu et al.

(2009 and 2012) and Lan et al. (2012) found the optimal pH of 3 and 2-5, accordingly,

for metal-EDTA complex wastewater treatment.

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A second aspect of pH deals with its shift as the reaction progresses. During

the Fenton reaction, an initial wastewater pH typically degreases. This pH decrease is

caused by the addition of FeSO4 catalyst, which typically contains residual H2SO4. A

second, more pronounced drop in pH occurs as the H2O2 is added, and continues

gradually at a rate which is largely dependent on catalyst concentration. This drop in

pH is attributed to the fragmenting of organic material into organic acids. This pH

change is often monitored to ensure that the reaction is progressing as planned. The

absence of such a pH decrease may mean that the reaction is inhibited and that a

potentially hazardous build-up of H2O2 is occurring within the reaction mixture. In

highly concentrated waste streams (COD >10 g/L), it may be necessary to perform the

oxidation in steps, readjusting the pH upwards to pH 4-5 after each step in order to

prevent low pH from inhibiting the reaction (www.usperoxide.com)

Effect of Temperature

The effect of temperature on the rate of reaction of the Fenton process

increases as the solution temperature increases. The application of temperature greater

than 40 C, the treatment efficiency declined due to the decomposition of H2O2 into

oxygen and water. Fenton process has been normally conducted at temperature of 20 to

40 C (Bautista et al., 2008). A comparative study of Fenton and Fenton-like reaction

kinetics in decolorization of wastewater. The result has been indicated that temperature

had little influence on overall dye degradation in the range 15-45 C (Wang, 2008).

Dye degradation rate decreased when the temperature greater than 30 C due to

decomposition of H2O2 at higher temperature. Similarly, San Sebastin Martinez et al.,

(2003) found that temperature showed only a mild positive effect on COD removal.

The significance of temperature influencing the Fenton and Fenton-like oxidation was

clear that the increase of temperature could increase the removal efficiency in the

system because higher temperature increases the reaction between hydrogen peroxide

and Fe2+/Fe3+, and improve the generation rate of hydroxyl radicals. The increase

temperature from 25 to 50 C, the removal efficiency of Ni increased from 72.1 to

97.2% for Fenton and from 74.3 to 96.7% for Fenton-like after 20 min (Fu et al. 2009).

Since Fenton reaction is exothermic (optimal temperature varied from 20 to 30 C), it

allow an industrial treatment of OMW without temperature control (Nieto, Hodaifa,

Rodrguez, Gimnez, & Ochando, 2011). Consequently, temperature was not

16

considered in the optimization of Fentons reaction in highly polluted industrial

wastewater. This leads to a conclusion that temperature is important but not necessary

for Fenton reactions because of exothermic effects of reaction leading to increase of

temperature in a suitable of range as found in the works of Bautista et al (2008); Wang

(2008); Fe et al. (2009, 2012);and Lan et al.(2012).

Effect of Iron Concentration

Iron concentration plays a vital role treatment efficiency of Fenton and Fenton-

like reactions because the production rate of OH is proportional to the concentration of

iron and hydrogen peroxide. However, iron content is the determining factors in sludge production as a challenge for Fenton reaction (Wang et al., 2011). In the absence of iron, there is no evidence that OH is produced in wastewater. Inadequate concentration of iron in the operating condition will lead to insufficient production of OH, whereas

overdosing of iron can favor the scavenging reaction which prevents the reaction of

OH with contaminants resulting in poor treatment efficiency (Matthew Tarr, 2003;

Neyens & Baeyens, 2003). The influence of ferrous concentration on EDTA degradation have been indicated that increase of ferrous concentration from 10-4 M to

10-2 M resulting in the degradation of EDTA from 29.8% to 98.5% at a reaction time of

10 min., respectively. However, increasing Fe2+ concentration from 10-2 M to 10-1 M decreased EDTA degradation from 98.5% to 44.9%, accordingly. A higher Fe2+ dose provided the scavenging reaction between Fe2+ and OH (Lou & Huang, 2009). Another study found that the increase of initial Fe2+ or Fe3+ from 0 to 1.0 mM resulting in the

increasing of removal efficiency remarkably. When Fe2+ or Fe3+ concentration was 1.0

mM, Fenton and Fenton-like systems achieved 92.8% and 94.7% of Ni removal

efficiencies after 60 min. of reaction time, accordingly. However, further increase of

Fe2+ and Fe3+ concentration did not achieve the improvement in Ni removal (Fu et al.,

2009). This indicated that the use of much Fe2+concentration could lead to the self-

scavenging of OH by Fe2+ as explained in the literatures (Matthew Tarr, 2003; Neyens

& Baeyens, 2003). A minimal threshold concentration of 3-15 mg/L Fe which allows

the reaction to proceed within a reasonable period regardless of the concentration of

organic materials. A constant ratio of Fe:substrate above the minimal threshold,

typically 1 part Fe per 10-50 parts substrate, which produces the desired end products.

The ratio of Fe:substrate may affect the distribution of reaction products. A

17

supplemental aliquot of Fe which saturates the chelating properties in the wastewater;

thereby, availing unsequestered iron to catalyze the formation of hydroxyl radicals.

Iron dose may also be expressed as a ratio to H2O2 dose. Typical ranges are 1 part Fe

per 5-25 parts H2O2 (wt/wt) (www. usperoxide.com).

Effect of H2O2 concentration

The amount of H2O2 is considered one of the most important factors in Fenton

and Fenton-like reaction owing to its economic cost, sources of OH generation,

improvement of treatment efficiency and side effects in overdosing. The H2O2 dose

has to be fixed according to the initial pollutant concentration (Matthew Tarr, 2003).

It is frequent to use an amount of H2O2 corresponding to the theoretical

stoichiometric H2O2 to chemical oxygen demand (COD) ratio, although it depends on

the response of the specific contaminants to oxidation and on the objective pursued in

term of reduction of the contaminant load (Neyens & Baeyens, 2003; Bautista et al.,

2007; Lan et al.,2012). Effect of H2O2 on the removal of COD was indicated that increase in [H2O2]/[COD] from 0.5 to 2.0, the COD removal increased remarkably from

73.6% to 89.4%. However, the further increase in [H2O2]/[COD] from 2.0 to 6.0, the removal of COD was negligible or unchanged (Lan et al., 2012; Wang et al., 2011).

The marginal improvement of COD removal may be explained by the scavenging effect

of excessive H2O2 to OH and recombination of OH which were supported in literatures (Neyens & Baeyens, 2003; Matthew Tarr, 2003; Bautista et al., 2007, 2008; Wang,

2008; Wang et al., 2011; Lucas & Peres, 2009). Therefore, stoichiometric relation

between COD and H2O2 are significant for Fenton reaction and acceptable

[H2O2]/[COD] weight ratio should in the range of 2-4.

For most applications, it is important to optimize the molar ratio of [Fe2+/3+]/

[H2O2] for estimation of reagent requirement and convenience of experiments

(Matthew Tarr, 2003; Neyens & Baeyens, 2003). The presence of Fe2+ or Fe3+ salts not

only functions as catalytic reagents to decompose H2O2 for OH generation, but also

reduces the scavenging effect of OH radical from H2O2. The role of Fe3+ plays an

important role in oxidizing the target organic compound and producing OH radical

through Fe2+ reaction (Kim et al., 2010). The [Fe2+/3+]/[H2O2] ratio is difficult to specify

and is varied according to the degradation of different pollutants covering the range

from 1:1 to 1:400 for a complete oxidation as reported in De Souza et al. (2006).

18

Effects of [Fe2+]/[H2O2] molar ratios of 1:50, 1:20, 1:10, 3:4 were conducted

for removal of initial COD of 300 mg/L by applying [H2O2]/[COD] of 4. Greater than

55% of COD removal was achieved in the first 10 min at higher [Fe2+]/[H2O2] molar

ratio. This results from higher generation of OH radical according to reaction (2.1) as

shown previously. However, COD removal tended to decline in molar ratio of

[Fe2+]/[H2O2] greater than 1:20 due to quenching or scavenging effects of OH radical

by excessive Fe2+ according to reaction (2.2). [Fe2+]/[H2O2] ratio of 1:20 attained

highest performance for greater than 85% of COD removal (Wang et al., 2011). To

achieve 90% removal of 362000 mg/L COD, it was required to maintain the optimal

[Fe2+]/[H2O2] molar ratio of 1:10, while [H2O2] was 3M (San Sebastin Martinez et al.,

2003). This molar ratio was comparatively found to be lower than that of [Fe2+]/ [H2O2]

molar ratio at 1:15 resulting in the study of Lucas and Peres (2009). It is clear that

[Fe2+]/[H2O2] molar ratio varies according to type and concentration of organic

pollutant existing in the wastewater. The typical range of Fe2+]/ [H2O2] ratios are 1:5-

25 as reported in Bautista et al. (2008) and www.usperoxide.com.

Effect of Reaction Time

The time needed to complete a Fenton reaction depends on many variables

discussed above, most notably catalyst dose and wastewater strength. Typical reaction

times are 30-60 minutes for low strength wastewater. For more complex or more

concentrated wastes, the reaction may take several hours. Determination of reaction

completion prove troublesome (Matthew Tarr, 2003). A study on Fenton and Fenton-

like reactions from 20120 min. was conducted. Reaction time of 60 min for both

processes was determined for reduction of Ni concentration from 50 mg/L to 1 mg/L

and COD decreased from 252 mg/L to 53.3 mg/L, indicating about 78.8% COD

removal. After 60 min of reaction, the removal efficiency was marginal or almost

unchanged (Fu et al. 2009, 2012). This reaction time for Fenton oxidation is consistent

with Lan et al. (2012), who found optimum reaction time at 60-80 min. However, with

heterogeneous and complicated characteristics of wastewater, it was required 120 min

for reduction of COD from 300 mg/L to 40 mg/L (Wang et al., 2011).

The reaction time for a completion of Fenton reaction also depends on the its

reagents (Fe2+ and H2O2 ) because the contaminant degradation rate is proportional to

the hydroxyl radical produced (Matthew Tarr, 2003). San Sebastin Martinez et al.

19

(2003) and Jiang et al. (2013) achieved optimum efficiencies in the first 10 min of

Fenton reaction due to the fast reaction in the first stage of Fenton oxidation, while

prolonging the reaction time remained efficiency insignificantly changed. However, it

was required longer than 1 hour reaction time for metal-complex wastewater treatment

due the persistency of organic compounds (Pirkanniemi et al., 2003). Therefore, the

application of Fenton oxidation to industrial wastewater treatment typically varies from

1 to 4 hours for optimal reaction time as reviewed in Bautista et al., (2008).

Chelating Agents Degradation by Various Fenton Processes There were a number of studies of advanced oxidation processes based on

Fenton oxidation to degrade or mineralize the chelating agents particularly EDTA. Due

to mineralizing ability of H2O2 for organic pollutants, H2O2 is considered as eco-

friendly and safe reagent (Bautista et al., 2008). Without Fe2+ activation, excessive

concentration H2O2 in alkaline environment (pH=10) was unable to degrade 0.04 mM

EDTA. It was recommended that the use of an effective catalyst might increase the

conversion rate into more biodegradable decomposition products (Rm & Sillanp,

2001). However, with the presence of transition metals (Fe2+), treatment of waste

containing EDTA by chemical oxidation obtained 90% of EDTA was degraded at the

initial concentration of 70 mM in 45 min (Tucker et al., 1999).

A study on Fentons oxidation to degrade EDTA from bleaching wastewater

reported that an almost complete removal of EDTA was achieved at the H2O2

concentrations of 74 mM, the pH of 4, and the H2O2:Fe2+:EDTA ratio of 70:2:1

(Pirkanniemi et al., 2007). This result was comparatively higher than whose previously

accomplished by Tucker et al. (1999), indicating 90% of EDTA at an initial

concentration of 70 mM as provided in Table 2.2. Further study is needed to check the

applicability of this method for the treatment of real wastewater and to develop

heterogeneous catalysts for this process. In addition, conventional Fenton process has

been modified to Fenton-like, electro-Fenton and photo-Fenton processes by using iron-

supported catalyst like Fe(III) and zero-valent iron (ZVI) to improve efficiency and

sludge associated problem caused by conventional Fenton process (Neyens & Baeyens,

2003; Bautista et al., 2008; Jiang et al., 2013; Zhou et al.,2009 & 2010). To degrade 1

mM EDTA, oxygen activation scheme applied in zero-valent iron system attained 95%

20

of EDTA degradation at an initial concentration of 1 mM at pH 6.5 within 2.5 h

(Noradoun & Cheang, 2005). In another study, Zhou et al. (2009) applied an oxidative

treatment by using heterogeneous ZVI and ultrasound to facilitate reduction of O2 to

H2O2. While being oxidized to Fe2+, ZVI induced series of Fenton-like oxidation and

degraded EDTA. In the system, EDTA acts as a complexing agent with the dissolved

Fe2+ and generates H2O2. The result indicated that a lower EDTA degradation (81%) at

its concentration of 0.32 mM at pH 7.5 due to excessive iron catalyst added in solution

that prevented the formation of O-2-FeII/III EDTA, slowing down EDTA degradation by

Fenton-like oxidation.

The application of heterogeneous metallophthalocyanine (FePcS) in Fenton-

like oxidation to degrade five different chelating agents including EDTA from

bleaching effluent was conducted. The rate of EDTA degradation was found to be

dependent on the concentration of Fe2+, H2O2, its molar ratio to the Fentons reagent,

pH, and temperature. Almost complete degradation of iron complexes of chelating

agents studied was remarkably obtained between 60% to 100% under pH 1.5 and initial

chelants concentration of 0.1M within a reaction time of 1 h. In addition, the most

relevant iron, manganese, sodium, copper and calcium EDTA complexes can be

successfully eliminated, the conversions being 93, 76, 68, 62 and 49%, respectively,

after 3h of reaction (Pirkanniemi et al., 2003). More description is detailed in Table 2.2.

Application Fenton and Fenton-like reactions under UV-A irradiation to

degrade the 5 mM EDTA achieved 80% of EDTA removal with EDTA:Fe2+ and

EDTA:Fe3+ ratio of 1:1 with the initial peroxide concentration of 100 mM in 4 hours.

However, in both cases the reaction rates were increased after 4 hours irradiation with

the total EDTA mineralization of 92 % (Fe2+, Fe3+, Fe3++Cu2+ system). The photolysis

of Fe(III)-EDTA complex in EDTA destruction can make use of high peroxide

concentration unnecessary. Photo-Fenton reaction was suitable for the treatment of

wastewater from cleaning and decontamination of nuclear power plant because this

wastewater contained small amount of Fe2+ and Fe3+ coming from corrosion process

(Ghiselli et al., 2004). For high iron content and organic citric acid (8 % synthetic citric

acid solution) in the derusting wastewater, UV photo-Fenton-like oxidation was used

because excessive amount of iron caused Fenton reaction occur automatically when

H2O2 was added. It was indicated that UV/H2O2/Fe3+ could decomposed citric acid

21

better than UV/H2O2 and Fe2+/H2O2. This is apparently due to the important role of UV

in allowing Fe3+ and H2O2 to function as strong oxidant in producing radical chain

reaction. In Fe2+/H2O2 system without UV, only 10% of complex removed due

chelating effects and precipitation. 93% COD reduction was achieved for

UV/H2O2/Fe3+ (Kim et al., 2010). Photo-Fenton oxidation with the application of

visible radiation, UV radiation, and sunlight achieved a complete degradation of 20000

mg/L EDTA. within 31, 6 and 3 hours, respectively. The kinetics of photodegradation

using solar-Fenton reaction follow the order of solar-Fenton > UV (254 nm)- Fenton >

Visible-Fenton. The pH changes from acidic to alkaline range during the photo-Fenton

process indicated loss of chelating ability of EDTA and formation of amide was

confirmed. Therefore, the design and treatment of large volume of decontamination

waste containing EDTA using a solar Fenton process is easy, cost effective, and safe to

operate (Chitra et al., 2011). Mechanism of UV induced destruction, OH radical

induced destruction, and ferric ion induced destruction were implied for EDTA (Kim

et al., 2010).

Metal chelating complexes are not be easily removed or degraded by a single

process. Therefore, a number of studies have incorporated Fenton reaction with other

treatment methods to improve its efficiency (Bautista et al., 2008). The application of

Fenton, Fenton-like, and advanced Fenton reactions followed by hydroxide

precipitation in removal of Ni from NiEDTA wastewater were conducted. The

complete disappearance of NiEDTA and 92% of Ni (II) removal were obtained. Fenton

and Fenton-like reactions were effective to degrade EDTA and the fragmentation of

NiEDTA freed up Ni(II) ion which was removed by precipitation. Fenton-like process

representing higher Ni(II) removal efficiency than Fenton process can be attributed to

the mechanism of ligand exchange. However, advanced Fenton process (Fe0 + H2O2)

shows higher removal efficiency of Ni (98.2%) and requires lower H2O2 amount than

Fenton or Fenton-like processes. COD decreased from 252 mg/L to 53.3 mg/L;

indicating about 78.8% COD reduction. Lower percentage of COD removal may be

attributed to the formation of intermediates of acetate and formate. Less than 0.03 mg/L

of residue iron concentration was identified after Fenton type processes, which required

no further treatment options. This leads to a conclusion that Fenton type processes

seems to be an economically and environmentally friendly process for remediation of

22

strong stability chalated heavy metal wastewater (Fu et al., 2009, 2012). The optimum

operating parameters are also provided in Table 2.2

23

Table 2.2 Summary of Fenton process for various wastewater treatments

Wastewater

Type

Pollutant

Concentration

Optimum Conditions Efficiency Reference

EDTA 70 mM pH=4, T= 20 C, [Fe2+]= 5 mM, [H2O2]= 100 mM, RT= 30 min, EDTA=90% Tucker et al. (1999)

Fe-EDTA 200 mM pH=1.5, T= 40 C, [Fe2+]= 0.03 mM, [H2O2]= 0.88 mM,

RT= 180 min

EDTA=90% Pirkanniemi et al. (2003)

EDTA 76 mM pH=3, T= 40 C, [Fe2+]= 0.5 mM, [H2O2]= 18.5 mM, RT= 3 min EDTA=98% Pirkanniemi et al.(2007)

EDTA 68.5 mM pH=3, T= 40 C, [Fe2+]= 0.04 mM, [H2O2]= 0.88 mM,

RT= 720 min

EDTA=99% Chitra et al. (2004)

EDTA 5 mM pH=3, [Fe2+]= 200 mM, [H2O2]= 0.55 mM, RT= 240 min EDTA=80% Ghiselli et al. (2004)

Ni-EDTA Ni=25 mg/L pH=3, T= 40-50C , [Fe2+/3+]= 1 mM, [H2O2]= 141 mM,

precipitation pH= 11, RT= 60 min

Ni=92%

EDTA=100%

Fu et al. (2009)

Ni-EDTA Ni=25 mg/L

COD= 252 mg/L

pH=3, T= 40-50C , [ZVI]= 2 g/L, [H2O2]= 35 mM, precipitation

pH= 11.5, RT= 60 min

Ni=98.2%

COD=79%

Fu et al. (2012)

Cu-EDTA Cu=225.3 mg/L;

COD=1096 mg/L

pH=2-5, T= 40-50C , [Fe2+]/[H2O2] molar ratio = 2 ,

[H2O2]:[COD]=0.2-0.3, RT= 60-80 min

Cu=100%

COD=87%

Lan et al.(2012)

Olive oil Phenol = 66.2 mg/L;

COD=4017 mg/L

pH=3, Fe3+ = 0.35-0.4 g/L, FeCl3/H2O2 = 0.026-0.058 w/w, COD=97%

Phenol=92%

Hodaifa et al. (2013)

Note: T : temperature, RT: reaction time

24

The treatment of metal chelating complex wastewater is not only for metals removal

but also for organic compound degradation. Another study combined interior

microelectrolysis (IM) and Fenton oxidation-coagulation (IM-FOC) to treat EDTA-

Cu(II) containing wastewater. COD was used indirectly to determine the concentration

of EDTA species in the wastewater. IM process provide nearly complete Cu(II)

removal and yielded 336.1 mg/L Fe(II) concentration at very low pH (pH=1.39) in

accordance with IM reaction mechanism as reported in reviews (Ju et al., 2011; Ju &

Hu, 2011). The poor treatment performance of COD by IM, indicating that EDTA

species cannot be effectively decomposed into small biodegradable organic molecules

by IM process. The Fe(II)-rich effluent of IM was suitable for direct treatment in a

subsequent Fenton oxidation without Fe(II) addition or pH adjustment. Under the

optimal operating condition, Cu(II) and COD decrease from 225.3 mg/L and 1096.6

mg/L to 0 mg/L and 142.6 mg/L with overall removal efficiency of 100% and 87%,

respectively by IM-FOC process. After treatment, the BOD5/COD ratio of wastewater

was enhanced from 0 to 0.42, indicating that EDTA was effectively oxidized in the

combined system (Lan et al., 2012).

25

CHAPTER 3

RESEARCH METHODOLOGY

This chapter provides methodology, materials, and reagents required for this

study. Experimental variables are also determined. Experimental procedures,

analytical methods, and kinetic modeling are described as follows:

Derusting Wastewater Characteristics The derusting wastewater used in this study was obtained from the Kation

Power company, a cleaning service company, located in Rayong Province, Thailand.

This cleaning service company produces varying amount of wastewater according to

the numbers and types of cleaning processes. According to Huang et al. (2000), the

average cleaning wastewater is about 2300 m3 during each boiler cleaning. However,

the approximate amount of wastewater ranges from 15 to 600 m3/week. The wastewater

is originally produced from cleaning processes of pipes or boilers. The wastewater

taken from the company is stored temporarily in a storage tank for further experiments.

During the cleaning processes, various chemicals and chelating agent (EDTA) are

applied to remove rusts and to protect pipe and boiler from corrosion. Furthermore, the

derusting wastewater is in the dark red color due to high iron content, which will form

a complex with the EDTA.

Materials and Chemical Reagents The reagents used in this study are the analytical grade reagents and will be

used without any further purification. Deionized or distilled water will be used in all

experiments. Chemical reagents for Fenton and Fenton-like processes and chemical

reagents for wastewater parameters analysis are included as described and listed below:

1. Chemicals for Fenton and Fenton-like Processes

1.1 Hydrogen Peroxide (H2O2 -35% w/w),

1.2 Sodium Hydroxide (NaOH, 10N)

1.3 Sulfuric Acid (H2SO4, 5N)

1.4 Ferrous Sulfate (FeSO47H2O) for Fenton reaction 1.5 Manganese Dioxide (MnO2)

26

2. Chemicals for Parameters Analysis

2.1 COD

2.1.1 Standard Potassium Dichromate Digestion Solution

2.1.2 Sulfuric Acid reagent

2.1.3 Ferroin Indicator

2.1.4 Standard Ferrous Ammonium Sulfate (FAS) Titrant

2.2 Total Iron/Soluble Iron/Ferric/Ferrous Iron

2.2.1 Hydrochloric Acid (HCl) conc,

2.2.2 Hydroxylamine solution, AR Grade

2.2.3 Ammonium Acetate buffer solution

2.2.4 Sodium Acetate solution, AR Grade

2.2.5 Phenanthroline solution, AR Grade

2.2.6 Potassium Permanganate (KMnO4)

2.2.7 Stock Iron solution

3. Equipment and Materials

3.1 Jar Test apparatus (six paddles and six beakers with volume of 1L)

3.2 pH meter (EUTECH)

3.3 Multiparameter Photometer (Hana Instruments HI 83205-2008)

3.4 Analytical balance (OHAUS)

3.5 UV-Vis Spectrophotometer (Varian)

3.6 Turbidity meter (EUTECH)

3.7 Drying oven

3.8 Evaporating dishes

3.9 Suction flask

3.10 Desiccator

3.11 0.45m filter paper (GF/C ) 3.12 Burette stand

3.13 Separatory funnel

3.14 Centrifugal machine (Harmonic Series)

3.15 Other glass wares (pipettes, burette, measuring cylinder, volumetric

flash, small beakers...)

27

Experimental Design and Procedure Treatment efficiency of Fenton and Fenton-like reactions are the function of

the operating parameters including dosage of [H2O2], [Fe2+] and [Fe3+], initial pH, and

reaction time. Therefore, the variables of the experiment are classified and described

as follows:

a. Independent Variables - Initial pH values: 2, 3, 4, 5, 6, 7 - [Fe2+] concentrations: 0.005, 0.01, 0.05, 0.08, 0.1 and 0.15 M - [H2O2] concentrations indicated as Fe2+:H2O2 molar ratios:1:10,

1:20, 1:30, 1:40, 1:50, 1:60

- Precipitation pH values: 6, 7, 8, 9, 10, 11. - Reaction time: 20, 40, 60, 80, 100, and 120 min.

b. Dependent Variables - Total COD (TCOD), Soluble COD (SCOD), Total Iron, Soluble Iron,

Fe2+, Fe3+, Ammonium Nitrogen, Nitrite Nitrogen, Nitrate Nitrogen,

TSS, conductivity, and TDS as objective parameters

c. Control Variables - Room temperature (28C) corresponding to the wastewater

temperature during Fenton and Fenton-like processes.

- Rapid mixing at 150 rpm for 2 min followed by slow mixing at 50 rpm.

- Homogenous wastewater characteristic in all experiments.

The proposed experimental design is divided into 2 sets of experiments. First

set of experiment is referred as the Fenton-like reaction (addition of H2O2 only) by

utilizing existing iron in the wastewater as catalyst. The second set of experiment is

referred as Fenton reaction (additions of both H2O2 and Fe2+). The detail experimental

design and procedures are provided in following steps and figure 3.1.

Determine wastewater characteristics

For each experiment, the wastewater stored in the storage tank is

poured in a large tank and is then mixed thoroughly so that the homogeneous

28

mixture will be achieved. The sample will be randomly collected for analyses

of wastewater characteristics. Various water quality parameters including

Total COD, Soluble COD, Total Iron, Soluble Iron, Fe2+, Fe3+, Ammonium

Nitrogen, Nitrite Nitrogen, Nitrate Nitrogen, conductivity, TSS and TDS.

Hydroxide Precipitation of Iron Before Fenton and Fenton-like

Processes

1. Prepare a Jar Test apparatus equipped with 6 beakers (size 1000-L

each). Fill every beaker with 500 mL of wastewater sample taken

from the large tank and then start mixing at 50 rpm for a few minutes

to have homogenous characteristic of wastewater

2. Adjust the pH of wastewater with H2SO4 or NaOH to pH values of 6,

7, 8, 9, 10, 11 in beaker No. 1, 2, 3, 4, 5, 6, respectively.

3. Keep mixing the solution in each beaker at the mixing speed of 50

rpm for 15 min.

4. At the end of mixing period, measure the parameters such as pH,

TDS, conductivity in the beaker and then collect the samples for

additional analyses including TCOD, SCOD, Total Iron, Soluble

Iron, Fe2+, Fe3+, Ammonium Nitrogen, Nitrite Nitrogen, and Nitrate

Nitrogen.

5. Stop mixing and allow the precipitates to settle for 30 minutes.

6. Collect the supernatant for sample analyses. The supernatant will be

centrifuged at 2000 rpm and filtrated by 0.45m filter paper for analyses of TCOD, SCOD, Total Iron, Soluble Iron, Fe2+, Fe3+,

Ammonium Nitrogen, Nitrite Nitrogen, and Nitrate Nitrogen.

Effects of Initial pH on Fenton-like Process





29


4, 6, 8, 10, 12 in beaker No. 1, 2, 3, 4, 5, 6, respectively. Keep mixing

the solution in each beaker at the mixing speed of 50 rpm for a few

minutes. Then, measure the parameters such as pH, TDS,

conductivity in the beaker and then collect the samples for additional

analyses including TCOD, SCOD, Total Iron, Soluble Iron, Fe2+,

Fe3+, Ammonium Nitrogen, Nitrite Nitrogen, and Nitrate Nitrogen.

7. Gradually add H2O2 at the concentration of 2.0 M into each beaker.

Keep mixing at the same speed for 60 minutes.





Nitrogen.

9. After collecting the samples, adjust the pH to 8 to stop the fenton-like

reaction. Continue mixing for another 15 minutes, and then stop

mixing and allow the precipitates to settle for 30 minutes.




11. Repeat steps 1-10 with various pH values around the optimum pH

determined previously to obtain the best pH value.

Effects of H2O2 Concentration on Fenton-like Process


each). Adjust the pH of wastewater in the large tank with H2SO4 or

NaOH to the optimum pH value determined from the previous study.

Fill every beaker with 500 mL of wastewater sample taken from the

large tank and then start mixing at 50 rpm for a few minutes to have

homogenous characteristic of wastewater

30

2. Gradually add H2O2 with six different concentrations of 1.0, 1.5, 2.0,

2.5, 3.0, and 3.5 M into each beaker. Keep mixing at the same speed

for 60 minutes.





Nitrogen.







Effects of Reaction Time on Fenton-like Process







2. Gradually add H2O2 at the optimum concentration determined from

previous study into each beaker. Keep mixing at the same speed for

20, 40, 60, 80, and 120 minutes of beaker No.1, 2, 3, 4, 5, and 6,

respectively.

3. After each mixing period of each beaker, measure the parameters

such as pH, TDS, conductivity in the beaker and then collect the

samples for additional analyses including TCOD, SCOD, Total Iron,

Soluble Iron, Fe2+, Fe3+, Ammonium Nitrogen, Nitrite Nitrogen, and

Nitrate Nitrogen.

31







Hydroxide Precipitation of Iron After Fenton-like Process


each). Adjust the pH of wastewater in the large tank to the optimum

pH value determined from the previous study and then Fill every

beaker with 500 mL of wastewater sample taken from the large tank

and then start mixing at 50 rpm for a few minutes to have


2. Gradually add H2O2 at the optimum concentration determined from

previous study into each beaker. Keep mixing at the same speed for a

period of the optimum reaction time.

3. After ending the mixing perioid, adjust the pH of wastewater with

H2SO4 or NaOH to pH values of 6, 7, 8, 9, 10, 11 in beaker No. 1, 2,

3, 4, 5, 6, respectively.


rpm for 15 min.





32

Effects of Initial pH on Fenton Process






3, 4, 5, 6, 7 in beaker No. 1, 2, 3, 4, 5, 6, respectively. Keep mixing

the solution in each beaker at the mixing speed of 50 rpm for a few

minutes. Then, measure the parameters such as pH, TDS,

conductivity in the beaker and then collect the samples for additional

analyses including TCOD, SCOD, Total Iron, Soluble Iron, Fe2+,

Fe3+, Ammonium Nitrogen, Nitrite Nitrogen, and Nitrate Nitrogen.

3. Adjust the mixing speed to 150 rpm, and then add Fe2+ with a

concentration of 0.05 M. Maintain the mixing speed for 10 minutes

to distribute the ferrous thoroughly in the beaker.

4. After 10 minutes, gradually add H2O2 at the concentration of 2.0 M

into each beaker. Keep mixing at the same speed for 60 minutes.





Nitrogen.







8. Repeat steps 1-10 with various pH values around the optimum pH

determined previously to obtain the best pH value.

33

Effects of Fe2+ Concentration on Fenton Process







2. Adjust the mixing speed to 150 rpm, and then add Fe2+ with six

different concentrations of 0.005, 0.01, 0.05, 0.08, 0.1 and 0.15 M

into beaker No.1, 2, 3, 4, 5, and 6, respectively. Maintain the mixing

speed for 10 minutes to distribute the ferrous thoroughly in the

beaker.

3. After 10 minutes, gradually add H2O2 at the concentration of 2.0 M

into each beaker. Keep mixing at the same speed for 60 minutes.





Nitrogen.







Effects of H2O2 Concentration on Fenton Process





34



2. Adjust the mixing speed to 150 rpm, and then add Fe2+ with the

optimum concentration determined from previous study. Maintain

the mixing speed for 10 minutes to distribute the ferrous thoroughly

in the beaker.

3. After 10 minutes, gradually add H2O2 with six different

concentrations of 1.0, 1.5, 2.0, 2.5, 3.0, and 3.5 M into each beaker.

Keep mixing at the same speed for 60 minutes.





Nitrogen.







Effects of Reaction Time on Fenton Process









35


in the beaker.

3. After 10 minutes, gradually add H2O2 at the optimum concentration

determined from previous study into each beaker. Keep mixing at the

same speed for 20, 40, 60, 80, and 120 minutes of beaker No.1, 2, 3,

4, 5, and 6, respectively.

4. After each mixing period of each beaker, measure the parameters

such as pH, TDS, conductivity in the beaker and then collect the

samples for additional analyses including TCOD, SCOD, Total Iron,

Soluble Iron, Fe2+, Fe3+, Ammonium Nitrogen, Nitrite Nitrogen, and

Nitrate Nitrogen.







Hydroxide Precipitation of Iron After Fenton Process


each). Adjust the pH of wastewater in the large tank to the optimum

pH value determined from the previous study and then Fill every

beaker with 500 mL of wastewater sample taken from the large tank

and then start mixing at 50 rpm for a few minutes to have

homogenous characteristic of wastewater.




in the beaker.

36

3. After 10 minutes, gradually add H2O2 at the optimum concentration

determined from previous study into each beaker. Keep mixing at the

same speed for a period of optimum reaction time.

4. After ending the mixing perioid, adjust the pH of wastewater with

H2SO4 or NaOH to pH values of 6, 7, 8, 9, 10, 11 in beaker No. 1, 2,

3, 4, 5, 6, respectively.


rpm for 15 min.





Optimum Conditions The optimum condition is determined for each ferrous and hydrogen peroxide

concentration by computing the removal efficiencies of pollutants at different varying

concentration of reagent used in Fenton and Fenton-like oxidations. The removal

efficiency (R) is calculated by the following equation:

Removal EfficiencyR = A- BA 100 where, A represents the initial characteristic of the objective parameters; B represents

the final characteristics of the objective parameters. The objective parameters include

the TCOD, SCOD, Total Iron, Soluble Iron, Fe2+, Fe3+, Ammonium Nitrogen, Nitrite

Nitrogen, and Nitrate Nitrogen..

Analytical Method The analytical methods for each parameters will be analyzed according to the

Standard Method for the Examination of Water and Wastewater (APHA, 2005). They

are briefly described as following:

1. The TCOD and SCOD of treated water is determined by the close reflux

titrimetric method (Method 5520).

37

2. The pH of solution will be measured with a EUTECH pH meter.

3. Total iron, soluble iron, ferric and ferrous concentrations will be analyzed by

Phenanthroline Method (Standard Method 3500).

4. Total suspended solid (TSS) determined by standard method (Method 2540).

Total solid and total dissolved solids (TDS) dried at 103-105C are

determined according to Standard Method (Method 2540)

5. Total dissolved solid (TDS) is determined by portable TDS meter (STARTER

300C)

The detail description of each parameter analytical method is referred to

Appendix B.

Kinetic Study Due to the complexity of the organic pollutant in the derusting wastewater and

intermediates formed in the Fenton and Fenton-like reactions, it is impossible to

conduct a detailed kinetic study with the different individual reactions that take place

during the reaction. However, it is possible to conduct an approximated kinetic study

for organic compound degradation measured in COD removal (Wang et al., 2011;

Lucas & Peres , 2007). The complete oxidation reaction of Fenton and Fenton-like

reactions in removal of COD can be represented as below:

Organic matter (COD) + OH Oxidized product (P) + CO2 + H2O (3.1)

The kinetic removal of COD removal by Fenton and Fenton-like reaction can

be represented by the following nth-order reaction kinetics as described in Skoog and

West (2004), Bautista et al. (2007) and Wang (2008).

dCODdt

=kCODn

where n is the order of the reaction, k is the reaction rate constant and t is the

time.

According to the equation (19), the kinetic removal of COD can be written in

second order reaction according to the study of Samet et al.,(2011) as provided below:

38

dCODdt

=k[OH]COD (second order reaction)

However, Lucas & Peres (2007) & Samet et al.,(2011) assume that the

hydrogen peroxide (H2O2) during the reaction is far excess and OH concentration is

constant during the reaction. Therefore, the kinetic removal of COD during Fenton and

Fenton-like reactions can be simplified to a pseudo-first order reaction as follow:

dCODdt

=COD ( pseudo-first order reaction)

which can be integrated between t=0 and t=t, yielding:

=C0 expkappt or ln COD0COD = kapp

where kapp is the pseudo-first order apparent rate constant (kapp = k[OH].

The kapp constants are obtained from the slope of the straight lines by plotting

ln (Ct /C0) as a function of time t. The data is fitted using the first order and second

order rate equation. The best fit is chosen when the coefficient of linearity is nearly

equal to the value of 1 (Skoog and West, 2004; Samet et al., 2011).

39

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