I. SUMMARY ................................................................................................................. 1

I.1. Soils Characterization.................................................................................................... 1

I.2. Adsorption of Selected Organic Compounds on Soils.................................................... 1

I.3. Electro-Osmosis Studies............................................................................................... 2

I.4. Electro-Fenton Studies.................................................................................................. 3

II. SOIL CHARACTERIZATION.................................................................................. 5

II.1. Composition Analysis.................................................................................................. 5

II.2. Soil pH........................................................................................................................ 5

II.3. Soil Organic Matter..................................................................................................... 5

II.4. Soil Effective Cation Exchange Capacity...................................................................... 5

II.5. Moisture Content......................................................................................................... 5

II.6. Specific Surface Area.................................................................................................. 6

II.7. pHZPC......................................................................................................................... 6

II.8. Hydraulic Conductivity and Hydraulic Permeability....................................................... 6

II.9. Analysis of Organic Compounds in Soils...................................................................... 7

II.10. Analysis of Heavy Metals in Soils............................................................................... 7

III. ADSORPTION OF SELECTED ORGANIC COMPOUNDS ON SOILS.......... 18

III.1. Methods .................................................................................................................. 18

III.1.1. Chlorophenols....................................................................................................... 18

III.1.2. PCE and TCE....................................................................................................... 18

III.1.3. Naphthalene.......................................................................................................... 19

III.2. Results and Discussion.............................................................................................. 19

III.2.1. Chlorophenols....................................................................................................... 19

III.2.2. PCE and TCE....................................................................................................... 20

III.2.3. Naphthalene.......................................................................................................... 21

IV. ELECTRO-OSMOSIS STUDIES.......................................................................... 45

IV.1. Methods.................................................................................................................. 45
...
IV.2. Results and Discussion............................................................................................. 47

IV.2.1. Electro-Osmosis Water Flow................................................................................ 47

IV.2.2. Coefficient of Electro-Osmosis Permeability (ke)................................................... 48

IV.2.3. Influent-Effluent pH Changes................................................................................. 48

IV.2.4. Contaminant Removal........................................................................................... 49

IV.2.5. The pH Profile, Water Content and Contaminant Distribution................................. 49

IV.2.6. Mass Balance....................................................................................................... 50

V. ELECTRO-FENTON STUDIES.............................................................................. 65

V.1. Electro-generation of Hydrogen Peroxide................................................................... 65

V.1.1. Methods................................................................................................................. 65

V.1.1.1. Reactor Configuration......................................................................................... 65

V.1.1.2. Power Supply and Equipment Configuration........................................................ 66
....
V.1.1.3. Methods............................................................................................................. 67

V.1.2. Results and Discussion.......................................................................................... 68
.
V.1.2.1. Effect of Current Intendity................................................................................... 68
.
V.1.2.2. Effect of Solution pH.......................................................................................... 69
.
V.1.2.3. Effect of Oxygen Bubbling System...................................................................... 69

V.1.2.4. Effect of Solution Temperature............................................................................ 70

V.1.2.5. Effect of Cathode Geometry............................................................................... 70

V.1.2.6. Current Efficiency for Hydrogen Peroxide............................................................ 71

V.1.2.7. Hydrogen Peroxide Stability................................................................................ 72

V.2. Fenton's Reagent Oxidation....................................................................................... 91

V.2.1. Introduction........................................................................................................... 91

V.2.1.1. Mechanism of Fenton's Reagent Oxidation........................................................... 91

V.2.1.2. Applications of Fenton's Reagent Oxidation......................................................... 93

V.2.1.3. Advantages of Fenton's Reagent Oxidation.......................................................... 95

V.2.1.4. Current Objective............................................................................................... 95

V.2.2. Methods................................................................................................................ 96

V.2.2.1. Properties of Selected Organic Compounds......................................................... 96

V.2.2.2. Batch and Pulse Fenton Oxidation....................................................................... 96

V.2.3. Results and Discussion........................................................................................... 98

V.2.3.1. Naphthalene........................................................................................................ 98

V.2.3.2. Tetrachloroethylene(PCE)................................................................................... 99

V.2.3.3. Trichloroethylene(TCE)..................................................................................... 100

VI. REFERENCES...................................................................................................... 116
..
VII. APPENDIX........................................................................................................... 119

A. Soils Characterization................................................................................................. 119

B. Electro-Osmosis Experiments..................................................................................... 125

C. Electro-Fenton Experiments....................................................................................... 126

LIST OF TABLES

Table 2.1 Physical-chemical characteristics of soil samples................................................... 8

Table 2.2 Organic compounds in soil samples...................................................................... 9

Table 2.3 Heavy metal fractionation in the soil samples....................................................... 10

Table 3.1 Langmuir constants for chlorophenol binding to kaolin ( Constants are
calculated by non-linear least squares)............................................................................... 25

Table 4.1 Some experimental conditions of the electro-osmosis tests with phenolic
compounds....................................................................................................................... 45

Table 4.2 Mass balance for phenol and chlorophenol experiments...................................... 51

Table 5.1 Reactor dimensions........................................................................................... 65

Table 5.2 Current efficiency for the hydrogen peroxide generation...................................... 72

Table 5.3 Standard reduction potentails of some oxidants................................................... 92

Table 5.4 Properties of the selected organic compounds.................................................... 97

Table 5.5 Comparison of removal efficiencies of naphthalene by batch and pulse
Fenton oxidation............................................................................................................... 99

Table 5.6 Comparison of removal efficiencies of PCE by batch and pulse

Fenton oxidation............................................................................................................. 100

LIST OF FIGURES

Figure 2.1 Specific Surface Area of Soil-A by Dye Adsorption.......................................... 11

Figure 2.2 Specific Surface Area of Soil-B by Dye Adsorption.......................................... 11

Figure 2.3 Specific Surface Area of Soil-C by Dye Adsorption.......................................... 12

Figure 2.4 Specific Surface Area of Soil-D by Dye Adsorption.......................................... 12

Figure 2.5 Specific Surface Area of Soil-E by Dye Adsorption.......................................... 13

Figure 2.6 Specific Surface Area of Soil-F by Dye Adsorption.......................................... 13

Figure 2.7 The fractionation of Pb in soil samples............................................................... 14

Figure 2.8 The fractionation of Cd in soil samples.............................................................. 15

Figure 2.9 The fractionation of Cu in soil samples.............................................................. 16

Figure 2.10 The fractionation of Zn in soil samples............................................................. 17

Figure 3.1 Binding of representative chlorophenols to kaolinite........................................... 23

Figure 3.2 The pH dependence of chlorophenol binding to kaolinite................................... 24

Figure 3.3 The isotherms of PCE at various soil to solution ratios....................................... 26

Figure 3.4 The isotherms of TCE at various soil to solution ratios....................................... 27

Figure 3.5 The adsorption capacity of PCE vs. various soil concentrations......................... 28

Figure 3.6 The adsorption capacity of TCE vs. various soil concentrations.......................... 29

Figure 3.7 The distribution ratio of PCE............................................................................. 30

Figure 3.8 The distribution ratio of TCE............................................................................. 31

Figure 3.9 The solubility of PAHs vs. volume fraction of methanol...................................... 32

Figure 3.10 The isotherms of naphthalene with 27% methanol at various soil
to solution ratios................................................................................................................ 33

Figure 3.11 The isotherms of naphthalene with 47% methanol at various soil
to solution ratios................................................................................................................ 34

Figure 3.12 The isotherms of naphthalene with 67% methanol at various soil
to solution ratios................................................................................................................ 35

Figure 3.13 The isotherms of naphthalene with 87% methanol at various soil
to solution ratios............................................................................................................... 36

Figure 3.14 The adsorption capacity of naphthalene with 27% methanol vs.
various soil concentrations................................................................................................. 37

Figure 3.15 The adsorption capacity of naphthalene with 47% methanol vs.
various soil concentrations................................................................................................. 38

Figure 3.16 The adsorption capacity of naphthalene with 67% methanol vs.
various soil concentrations................................................................................................. 39

Figure 3.17 The adsorption capacity of naphthalene with 87% methanol vs.
various soil concentrations................................................................................................. 40

Figure 3.18 The distribution ratio of naphthalene with 27% methanol.................................. 42

Figure 3.19 The distribution ratio of naphthalene with 47% methanol.................................. 42

Figure 3.20 The distribution ratio of naphthalene with 67% methanol.................................. 43

Figure 3.21 The distribution ratio of naphthalene with 87% methanol.................................. 44

Figure 4.1 Schematic diagram of the electro-osmosis laboratory apparatus......................... 46

Figure 4.2 Electro-osmotic water daily flow for phenol and chlorophenol
experiments....................................................................................................................... 52

Figure 4.3 Current density as a function of time for phenol and chlorophenols
experiments....................................................................................................................... 53

Figure 4.4 Correlation between electro-osmotic water flow and current
density for phenol and chlorophenol experiments................................................................ 54

Figure 4.5 Accumulative electro-osmotic water flow as a function of time for
phenol and chlorophenol experiments................................................................................ 55

Figure 4.6 Average electro-osmotic water flow as a function of pore volume
for phenol and chlorophenols experiments.......................................................................... 56

Figure 4.7 Coefficient of electro-osmotic permeability as a function of time for
phenol and chlorophenols experiments............................................................................... 57

Figure 4.8 Influent pH as a function of time for phenol and chlorophenols
experiments....................................................................................................................... 58

Figure 4.9 Effluent pH as a function of time for phenol and chlorophenols
experiments....................................................................................................................... 59

Figure 4.10 Accumulative removal (%) of phenol and chlorophenols
as a function of time........................................................................................................... 60
.
Figure 4.11 Percentage contaminant removal as a function of pore volumes
of flow.............................................................................................................................. 61

Figure 4.12 The pH profile as a function of normalized distance from anode
for phenol and chlorophenol experiments........................................................................... 62

Figure 4.13 Water content distribution as a function of normalized distance
from anode for phenol and chlorophenols experiments....................................................... 63

Figure 4.14 Contaminant distribution through the soil as a function of
normalized distance from anode for phenol and chlorophenol experiments.......................... 64

Figure 5.1 Schematic of the reactor configuration............................................................... 73

Figure 5.2 Schematic of the electrolysis cell for the production of hydrogen
peroxide........................................................................................................................... 74

Figure 5.3 Shematic of three cathodes geometry................................................................ 75

Figure 5.4 Schematic of the laboratory setup configuration................................................. 76

Figure 5.5 Flow diagram for the research approach........................................................... 77

Figure 5.6 The relationship between the applied voltage and the current
intensity in a 7.75 M NaClO4 ionic strength solution.......................................................... 78

Figure 5.7 The effect of current intensity on hydrogen peroxide concentration..................... 79

Figure 5.8 The generation of hydrogen peroxide over time for a
constant current intensity of 1 Amp.................................................................................... 80

Figure 5.9 The generation of hydrogen peroxide over time for different pH
values............................................................................................................................... 81

Figure 5.10 The effect of pH on hydrogen peroxide concentration...................................... 82

Figure 5.11 The effect of oxygen bubbles' size on hydrogen peroxide
generation......................................................................................................................... 83

Figure 5.12 The effect of oxygen quality on hydrogen peroxide concentration..................... 84

Figure 5.13 The effect of solution temperature on hydrogen peroxide
concentration.................................................................................................................... 85

Figure 5.14 The generation of hydrogen peroxide concentration over
time as a function of solution temperature........................................................................... 86

Figure 5.15 The generation of hydrogen peroxide over time as a function
of the cathode's surface area.............................................................................................. 87

Figure 5.16 The effect of cathode's surface area on hydrogen peroxide
concentration.................................................................................................................... 88

Figure 5.17 Current efficiency for the hydrogen peroxide generation................................... 89

Figure 5.18 Hydrogen peroxide stability over time as a function
of solution pH................................................................................................................... 90

Figure 5.19 Voaltile speed of naphthalene........................................................................ 101

Figure 5.20 Calibration curve of naphthalene.................................................................... 102

Figure 5.21 Batch Fenton oxidation of naphthalene. (The dosage
of hydrogen peroxide is 5x10-4M.)................................................................................. 103

Figure 5.22 Batch Fenton oxidation of naphthalene. (The dosage
of hydrogen peroxide is 1x10-3M.)................................................................................. 104

Figure 5.23 Batch Fenton oxidation of naphthalene. ( The dosage
of hydrogen peroxide is 2x10-3M.)................................................................................. 105

Figure 5.24 Pulse Fenton oxidation of naphthalene. (Hydrogen
peroxide was added at the time of 0, 11, 21 minutes.)...................................................... 106

Figure 5.25 Calibration curve of tetrachloroethylene (PCE).............................................. 107

Figure 5.26 Batch Fenton oxidation of PCE. (The dosage of
hydrogen peroxide is 1x10-3M.)..................................................................................... 108

Figure 5.27 Batch Fenton oxidation of PCE. (The dosage of
hydrogen peroxide is 5x10-3M.)..................................................................................... 109

Figure 5.28 Pulse Fenton oxidation of PCE. (Hydrogen peroxide was
added at the time of 0, 11, 21 minutes.)........................................................................... 110

Figure 5.29 Calibration curve of trichloroethylene (TCE).................................................. 111

Figure 5.30 Batch Fenton oxidation of TCE. (The dosage of
hydrogen peroxide is 2x10-3M.)..................................................................................... 112

Figure 5.31 Batch Fenton oxidation of TCE. (The dosage of
hydrogen peroxide is 5x10-3M.)..................................................................................... 113

Figure 5.32 Batch Fenton oxidation of TCE. (The dosage of
hydrogen peroxide is 1x10-2M.)..................................................................................... 114

Figure 5.33 Batch Fenton oxidation of TCE. (The dosage of
hydrogen peroxide is 2x10-2M.)..................................................................................... 115

 
I. SUMMARY

I.1. Soil Characterization

Soil samples from three industrial sites at two depth ranges (2'~4' feet and 8'~14' feet ) were received and pertinent physico-chemical properties, such as pH, specific surface area, moisture content, organic matter content, hydraulic conductivity, cation exchange capacity (CEC), pH at zero point of charge (pHzpc), particle size distribution, organic contaminants and heavy metals fractionation were analyzed.

Results show that clay and silt are the major components in the soil samples, which exhibits a relatively low hydraulic conductivity of about 10-7~10-8 cm/sec. The pH value of soil samples is in the neutral range (from pH 6.1 to 7.6) and its variation with depth is insignificant. Organic matter content is another important factor which affects soil properties such as specific surface area, chemical adsorption capacity and cation exchange capacity. Results indicate that the organic matter content ranges between 0.79% and 1.81%. The effective cation exchange capacity is from 13.8 to 21.2 meq/100g. The values of moisture content, specific surface area and pHzpc range from 10.2~16.9 (%), 0.4~0.9 (m2/g) and 2.18~2.60, respectively.

I.2. Adsorption of Selected Organic Compounds on Soils

Knowledge of the interaction of organic compounds with soil materials is important in the assessment of the mobility and fate of these compounds in the environment. The study of organic compounds adsorption on soils will provide valuable information on their potential of migration into the groundwater. In this study we investigated the adsorption of chrolophenols on kaolinite and in order to obtain a general information about organics adsorption. In addition, we studied the adsorption behaviors of PCE, TCE, and naphthalene on soil from the industrial site as well.

Chlorinated phenols, PCE, TCE, and naphthalene are the priority pollutants recognized as hazards to health and the environment. The kaolinite is a 1:1 dioctahedral clay mineral with high electroosmotic water transport efficiency, on the contrary, the soil from industrial site is with low. The information obtained from these adsorption experiments are useful for the understanding of organic matter adsorption on soils as well as for the electro-osmosis experiments.

Batch adsorption experiments for chlorophenols were conducted at various soil to solution (weight) ratios from 1:3 to 1:20 and initial concentrations of chlorophenols. Adsorption isotherms can be fitted by the Languir equation. Constants for the series of chlorophenols obtained from non-linear least square are obtained (Table 3.1). The maximum adsorption density values are approxiamtely the same for different chlorophenols indicating a common mode of binding. In order to test whether the binding of chlorophenols is occuring through equilibration of the surface and the protonated form, the pH dependence of binding was determined for 3 representative chlorophenols with different amounts of chlorine substitution. Results indicate that the data are consistent with binding of the protonated species.

Batch adsorption isotherms for PCE and TCE were also conducted at various soil to solution (weight) ratios from 1:5 to 1:100 and initial concentrations from 0.1 Cs to 0.8 Cs with Cs being saturation solubility. The PCE isotherms could be closely fitted by the Langmuir equation, whereas the TCE isotherms could be closely fitted by the linear adsorption equation. The different adsorption mechanisms can be attributed to the different polarity of PCE and TCE and to the surface characteristics of the soil. As a result, the adsorption capacity of PCE is low at 200 µg/g to 3500 µg/g while the adsorption capacity of TCE is high at 500 µg/g to 15000 µg/g.

Batch adsorption experiments on naphthalene adsorption were conducted at various soil to solution ratios (by weight) from 1:5 to 1:20, and various volume fractions of a cosolvent (methanol) from 0.2 to 0.8 in various initial concentrations of the organic compound (0.1Cs to 0.8Cs,Cs being the saturation solubility). At low equilibrium concentrations of naphthalene, the isotherm could be nearly fitted by a linear adsorption equation. As the cosolvent and naphthalene concentration increases, the adsorption isotherm could be closely fitted by the Langmuir equation. The major mechanism for the interaction between naphthalene and the soil surface is van der waals force. At low naphthalene concentrationin in the soil-soution mixture, the adsorption capacity is proportional to the equilibrium concentration. At high solute concentration, a constant adsorption capacity is observed since the limited surface sites have been filled by the naphthalene molecules. Furthermore, it is also noted that the adsorption capacity increases from hundreds of µg/g to thousands of µg/g with the cosolvent concentration increasing from 20% to 80%, V/V.

The soil to solution ratio can have significant effect on the adsorption behavior. This is known as "soil to solution ratio effect" which would change the adsorption density with various soil to solution ratios. Our results show that high soil to solution ratio (low soil concentration) increases the adsorption density of PCE, TCE, and naphthalene.

I.3. Electro-Osmosis Studies

Electrochemistry plays an important role during an electro-osmosis process. The generation of pH gradients and possible effects, such as ion exchange and the change in the soil composition caused by the acid front which is originated at the anode, ensure a diminishing of the water flow compromising the efficiency of the process. The build up of acidic condition at the anode during the application of electro-osmosis process is due to the oxidation of water. The products of the oxidation are oxygen gas (O2) and hydrogen ions (H+). Inversely, the basic condition at the cathode is attributed to the reduction of water. This electrochemical reaction decomposes the water producing hydrogen gas (H2) and hydroxyl ions (OH-).

As an inovative contaminant removal method, the technique demonstrates to be effective depending upon conditions related to the physico-chemical properties of the packed soil core. Among these conditions, the pore volume was proved to be important and closely related to the removal efficiency.

In this study, the phenol distribution obtained in the soil core indicates that the contaminant movement is not uniform throughout the medium and accumulates near the cathode. This could be used as a tool to concentrate the pollutants in a specific area between the electrodes for further remediation treatment.

A 93% removal was achieved for the 2-chlorophenol showing that electroosmosis can be an effective way to remediate phenol-contaminated soils.

This work illustrates some of the practical difficulties and advantages of electro-osmosis as a clean up technique. Major considerations to the successful application of electro-osmosis include detailed physico-chemical characteristics of the contaminated soil and the electrochemistry which accompanies the electrokinetic process.

I.4. Electro-Fenton Studies

Advanced chemical oxidation processes can be effective means for water and groundwater remediation. While most of the aqueous effluents have been treated by biological processes in the past, chemical oxidative degradation is being used for those wastes which can not be easily decomposed by biological activities. Electro-Fenton oxidation is an electochemical process effectively used to remove organic contaminants from the water. The main difference from conventional Fenton oxidation process is that in the electro-Fenton oxidation the electrolysis generates the hydrogen peroxide, which in the presence of ferrous ion (Fe2+) produces hydroxyl radicals (·OH). Hydroxyl radical, with the second highest oxidation potential which leads to the unselective oxidation property, have gained attention over the past decade (Matsue et al, 1981; Sudoh et al, 1985).

The major advantages of Fenton's reagent as a hazardous waste treatment technology are: i) no chlorinated organic compounds formed during the oxidation processes, ii) both H2O2 and ferrous ion are cheap and nontoxic, iii) no mass transfer limitation due to its homogeneous catalytic nature, iv) no light involved as catalyst (Huang et al, 1993). Due to these advantages, Fenton's reagent has been widely applied in the treatment of hazadous organics. Phenolic compounds were effectively degraded to organic acids and carbon dioxide by Fenton's reagent oxidation (Sudoh et al, 1986). The oxidations of chlorinated aromatic hydrocarbons (CAHs), alkylbezenes and cresol isomers with Fenton's reagent have also been investigated (Sedlak et al, 1991; Matsue et al, 1991; Zheng et al, 1993). In addition, Fenton's reagent has been effectively applied to decolorize the dye wastewater (Kuo et al, 1992).

One major objective of this study is to clarify the effect of various parameters on the electrochemical production of hydrogen peroxide. Influential parameters, such as cell voltage and current intensity, solution pH, oxygen bubble size and oxygen quality, solution temperature, and cathode geometry were tested to determine the best working conditions which enhance the production of hydrogen peroxide. Results show that the optimum conditions are 1 Amp of current intensity, solution pH 3.0, stone diffusion system, pure oxygen, ambient solution temperature (25 oC), long finger cathode. In addition, we also investigated the stability of hydrogen peroxide in solutions. Results indicate that hydrogen peroxide is stable in acidic solutions but unstable in basic solutions. In the alkaline pH range hydrogen peroxide may decompose to give oxygen and water, losing its oxidation ability.

The other objective is to determine the optimal experimental conditions required to oxidize the selected organic compounds, such as polycyclic aromatic hydrocarbons (PAHs), trichloroethylene (TCE), tetrachloroethylene (PCE), chloroform, carbon tetrachloride, and trichloroacetic acid (TCA) by Fenton's reagent, and to establish the oxidation pathways of these organics. During the first year of this research project, hydrogen peroxide was added to the reaction system instead of being generated in the process. Experiments were first conducted to determine the degradable characteristics of naphthalene, PCE, TCE by conventional Fenton oxidation. Results indicate that all the three organic compounds can be readily degraded by the Fenton's reagent oxidation. The degradation curve is characterized by a rapid oxidation reaction which is followed by a much slower reaction step. A total removal of these compounds is possible. The weight ratio of hydrogen peroxide to naphthalene for a nearly total removal is about 1.20 ~ 1.40 : 1, and the ratios are 1.40 :1, 0.405 :1 for PCE and TCE, respectively. The dosage of Fenton's reagent is very cost-effective.

II. SOIL CHARACTERIZATION

The soil samples from three industry sites in two depth ranges (2'~4' feet and 8'~14' feet) were received and pertinent physical-chemical properties, such as pH, specific surface area, moisture content, organic matter content, hydraulic conductivity, cation exchange capacity (CEC), pH at zero point of charge (pHzpc), particle size distribution and organic contaminants and heavy metals fractionation were analyzed.

II.1. Composition Analysis

Table 2.1 shows the results of composition analysis obtained by using the sedimentation method (Appendix A.1.) for the soil samples received. Clay and silt are the major components in all soil samples which indicates that the application of electro-osmosis technology will be feasible for these soils.

II.2. Soil pH

The soil pH values were measured by using 0.01 M CaCl2 as electrolyte. The results shown in Table 2.1 indicate that most of the soil samples are in the neutral region (pH from 6.1 to 7.6) and the pH variation with depth is insignificant. The method is described in Appendix A.2.

II.3. Soil Organic Matter

Organic matter is an important component of the soil system. It can affect other soil physical properties such as specific surface area, chemical adsorption capacities, and CEC. Table 2.1 shows the results of organic matter content . The analytical method is described in Appendix A.3.

II.4. Soil Effective Cation Exchange Capacity

Table 2.1 shows the results of effective cation exchange capacity (ECEC) of soil samples, the measured ECEC range is from 13.8 to 21.2 meq/100g. The experimental procedures for determination of ECEC are presented in Appendix A.4.

II.5. Moisture Content

The moisture content results are shown in Table 2.1 . The moisture content range is from 10.2 % to 16.9 %. The analytical method is described in Appendix A.5.

II.6. Specific Surface Area

Figures 2.1 to 2.6 show the results of dye adsorption of all soil samples analyzed. Table 2.1 summarizes the specific surface area of samples tested. The specific surface area data will be useful for future work on organic compounds adsorption and electro-osmosis experiments.The method is described in Appendix A.6.

II.7. pHZPC

It has been reported in the literature that the electro-osmotic water flow is direct proportional to the zeta potential (Sims and Heckendorn , 1991):

(2.1)

where e, f, z, h, and L are the dielectric constant, electrical field strength, zeta potential, viscosity of the fluid, and distance between electrodes. This equation shows that the electrical property of the soil will directly affect the electro-osmotic process.

Since the application of electro-osmosis will be investigated in this project, it is crucial to know the microscopic electrical properties of the soil samples. Table 2.1 shows the zeta potential for all soil samples tested. The method is described in Appendix A.7.

II.8. Hydraulic Conductivity and Hydraulic Permeability

Hydraulic conductivity is an important soil properity, because the electro-osmosis technique can be applicable to the contaminated soils with low hydraulic conductivity (lower than 10-5 cm/sec). Hydraulic permeability can be caculated from the following equation:

(2.2)

where K= hydraulic conductivity

µ= dynamic viscosity

= the fluid density

The results of hydraulic conductivity and hydraulic permeability are shown in Table 2.1. Experimental procedures are presented in Appendix A.8.

II.9. Analysis of Organic Compounds in Soils

Table 2.2 shows the results of qualitative analysis of several organic compounds in the soil samples. Solvent extraction followed by gas chromatograhy, analysis with mass spectrometry detector was employed. The detailed procedures are described in Appendix A.9.

II.10. Analysis of Heavy metals in Soils

Table 2.3 and Figures 2.7 to 2.10 show the results of fractionation analysis of lead, cadmium, copper, and zinc in soil samples. The fractions represent the exchangeable, sorbed, organic, carbonate and sulfide forms of metals present in the soils respectively. No significant differences in the heavy metals content were observed among all the soil samples.

Table 2.1 Physical-chemical characteristics of soil samples
 

Soil Sample a	A	B	C	D	E	F
Sand (%)	9	23	22	18	14	22
Silt (%)	46	36	37	36	38	47
Clay (%)	45	41	41	46	48	31
pH	6.10	7.46	7.58	7.60	7.60	7.52
ECEC (meq/100g)	14.7	21.2	21.2	21.2	20.5	13.8
Organic Matter(%)	1.81	0.97	0.82	1.07	0.79	1.17
Moisture (%)	16.9	12.4	11.1	12.7	13.6	10.2
Hydraulic Conductivity (10-8cm/s)	9.52	38.8	1.72	48.4	2.49	11.7
C2Cl4 in Soil (µg/kg) b	ND	ND	137,116	172,972	ND	9,877
Zeta potential (mV)	-14.7	-17.6	-26.3	-32.8	-35.1	-22.8
pHzpc	2.60	2.46	2.48	2.20	2.34	2.18
Hydraulic Permeability(10-7cm2)	9.71	39.6	1.76	49.4	2.54	12.0
Specific Surface Area (m2/g)	0.9	0.7	0.4	0.6	0.4	0.5

a: A ( SB009, depth 2'~4' )

B ( SB009, depth 9'~11' )

C ( SB010, depth 4'~6' )

D ( SB010, depth 8'~10' )

E ( SB011, depth 4'~6' )

F ( SB011, depth 12'~14' )

b: Extraction Method: 2g soil + 8mL hexane + 2mL H2SO4(1N)

ND: not detectable

Table 2.2 organic compounds in soil samples.
 

Soil Sample	A	B	C	D	E	F
Aniline		+
Hexachloroethane		+++
Pentachlorobutadiene		+++
Hexachlorobutadiene		+++
Tetrachloroethylene			+++	+++		++
Decane					+++
Tetracosane				++
Undecane		+			+++

+++: relatively high concentration

++: intermediate concentration

+: relatively low concentration

 Table 2.3 Heavy metal fractionation in the soil samples.
 

Soil Sample	A	B	C	D	E	F
Lead
exchangeable	51.8	45.2	45.2	45.2	45.2	45.2
sorbed	43.1	43.1	43.1	43.1	43.1	43.1
organic	75.4	86.2	75.4	86.2	75.4	75.4
carbonate	43.1	32.3	32.3	43.1	43.1	43.1
sulfide	25.9	25.9	25.9	32.3	25.9	32.3
Copper
exchangeable	13.5	12.4	12.4	12.4	12.4	11.2
sorbed	10.9	10.9	9.0	10.9	10.9	10.9
organic	22.6	24.5	12.9	3.2	ND	ND
carbonate	ND	ND	1.3	1.3	1.3	1.3
sulfide	10.0	11.2	8.9	10.0	11.2	10.0
Cadmium
exchangeable	5.1	5.4	3.8	3.0	2.7	1.9
sorbed	2.6	1.9	1.9	1.3	2.6	1.3
organic	8.4	7.8	5.8	1.3	ND	ND
carbonate	ND	ND	ND	ND	ND	ND
sulfide	ND	ND	ND	ND	ND	ND
Zinc
exchangeable	3.3	3.3	3.3	3.0	3.0	2.7
sorbed	2.3	2.3	1.7	1.7	1.7	1.7
organic	5.1	6.2	4.5	4.5	4.5	4.5
carbonate	1.1	2.3	1.1	0.6	1.1	1.7
sulfide	2.0	2.7	1.7	2.0	2.4	2.4

Note: concentrations in mg/Kg

ND: not detectable

Figure 2.1 Specific Surface Area of Soil-A by Dye Adsorption.

Figure 2.2 Specific Surface Area of Soil-B by Dye Adsorption.

Figure 2.3 Specific Surface Area of Soil-C by Dye Adsorption.
 
 
 
 

Figure 2.4 Specific Surface Area of Soil-D by Dye Adsorption.

Figure 2.5 Specific Surface Area of Soil-E by Dye Adsorption.
 
 

Figure 2.6 Specific Surface Area of Soil-F by Dye Adsorption.

Figure 2.7 The fractionation of Pb in soil samples.

Figure 2.8 The fractionation of Cd in soil samples.

Figure 2.9 The fractionation of Cu in soil samples.

Figure 2.10 The fractionation of Zn in soil samples.
 
 
 
 

III.1. Methods

III.1.1. Chlorophenols

Batch adsorption experiments were conducted at various soil to solution ratios (by weight) from 1:3 to 1:20 and an initial concentration of organic compound (4-chlorophenol, 2,4-chlorophenol and 2,4,5-chlorophenol ). The procedures were as follows.

To a series of glass bottles, the desired amount of kaolinite and organic compounds solution in 0.05M (NaNO3) ionic strength electrolyte were added. The bottles were placed in a shaker. After shaking for 24 hours, the mixtures were centrifuged to removed the solids material and analyzed for the residual concentration of organic compound in queation.

Concentrations of phenols were measured with a spectrophotometer at their corresponding optical wavelength. Samples were diluted in acidic ethanol to give absorbances less than 1.2 except for some measurements of 2-chlorophenol which were done in basic methanol.

III.1.2. PCE and TCE

Batch adsorption experiments of PCE (tetrachloroethylene ) and TCE (trichloroethylene) were conducted at various soil to solution ratios (by weight) from 1:5 to 1:100 and initial concentrations of organic compounds from 0.1Cs to 0.8Cs with Cs being the saturation solubility. The solubility of PCE and TCE is 150 mg/l and 1,100 mg/l, indivially. The procedures were as follows.

To a series of glass bottles, a desired amount of soil, and organic compound in solution of constant ionic strength electrolyte (0.05M NaNO3) were added. The bottles were placed in a shaker and shaken constantly for 48 hours. The mixtures were then centrifuged at 2,500 rpm using a Prescion Scientiftic Co. model K-9 centrifuge to seperate the solid material from the solution. The residual concentration of the organic compound in the centrate was analyzed.

For PCE and TCE analysis, the samples were extracted one time in hexane then determined with a GC/MASS, Hewlett-Packard, model 5972.

III.1.3. Naphthalene

Batch adsorption experiments on naphthalene adsorption were conducted at various soil to solution ratios (by weight) from 1:5 to 1:20, and various volume fractions of a cosolvent (methanol) from 0.2 to 0.8 in various initial concentrations of the organic compound (0.1Cs to 0.8Cs,Cs being the saturation solubility). The procedures were as follows.

To a series of glass bottles, a desired amount of soil and organic compound in solution of constant ionic strength electrolyte (0.05M NaNO3) were added. The bottles were placed in a shaker and shaken constantly for 48 hours. The mixtures were then centrifuged at 2,500 rpm using a Prescion Scientiftic Co., model K-9 centrifuge to remove the solid material from the solution. The residual concentration of the organic compound was determined.

Naphthalene concentration was measured spectrophotometrically with a spectrophotometer, at its corresponding optical wavelength ( = 266nm). Samples were extracted one time in hexane to minimize the interference from organic matter in soils during spectrophotometrical measurements.

III.2. Results and Discussion

III.2.1. Chlorophenols

Adsorption isotherms for phenols with varying chlorine substitution are shown in Figure 3.1. The isotherms show saturating binding as the concentration of phenol is increased and they can be fitted by the Langmuir equation:

(3.1)

Constants for the series of phenols obtained from non-linear least square fits of data such as the data shown Figure 3.1 are presented in Table 3.1. For phenol the binding is weak and only 0.6 µmol/g is adsorbed at 8 mM phenol. Thus only the product Q0b can be determined. The values of Q0 are approximately the same for the series of chlorophenols indicating a common mode of binding. If the molecules are assumed to bind in an orientation in which the plane of the phenol ring is parallel to the adsorbing surface the area covered is 1.2-1.85 m2/g assuming a surface area of 0.532 nm2/molecule (Lu, et al., 1988). Since the surface area of the kaolinite is 6.9 m2/g only a portion of the surface is covered with phenol.

Kaolinite, a two layer clay, has been proposed to have three classes of surfaces (Pefferkorn, et al., 1987): an aluminum oxide surface like gibbsite, a silica surface and 'edge' surface. The silica surfaces are charged at pH above 2 while the alumina surfaces have a pKZPC about 9. Binding of monophenols to alumina surfaces is weak (Holmes-Farley, 1988). Binding occurs only upon proton dissociation to form the phenolate. Adsorption is enhanced for catechol and a bidentate complex with the phenolate is suggested (McBride and Wesselink, 1988). The properties of the kaolinite surfaces suggest that binding of phenols is predominantly at the edge surfaces which have been measured to comprise about 15 to 35% of the total surface area (Lee, et al., 1991; Denoyel and Rouquerol, 1991). Our results are consistent with those reported by other researchers. It should be noted that the 'edge' surfaces depend upon sample environmental history and may arise from depodition of colloidal silica and alumina on basal faces (Ferris and Jepson, 1975; Diz and Rand, 1989). The edge binding surfaces may be isolated from each other, consistent with the Langmuir nature of the binding which presupposes interaction of bound molecules with the surface alone and not with each other.

In order to test whether the binding of phenols is occurring through equilibration of the surface and the protonated form, the pH dependence of binding was determined for 3 representative chlorophenols with different amounts of chlorine substitution (Figure 3.2). The data are consistent with binding of the protonated species; the experimental values can be fit by assuming that the free concentration of unionized phenol [ClPh]0 is given by:

(3.2)

This value is then inserted in the Langmuir equation using the same constants as in Table 3.1 to generate the curves given in Figure 3.2. The agreement with the experimental binding data demonstrates that binding is predominantly from the protonated species. The data for 2,4-dichlorophenol and 2,4,5-trichlorophenol indicate that the binding does not change when the "edge" surface is titrated (pKa = 5.9).

III.2.2. PCE and TCE

Adsorption isotherms for PCE and TCE are shown in Figure 3.3, Figure 3.4. The PCE isotherms could be closely fitted by the Langmuir equation, whereas the TCE isotherms could be closely fitted by the linear adsorption equation. For PCE, the major adsorption force on soils is speculated to be van der waals since it is nonpolar organic compound. As for TCE which is a polar organic compound, the forces responsible for its adsorption can be dipole and van der waals. The different adsorption mechanisms can be attributed to the different polarity of PCE and TCE and to the surface characteristics of the soil. Most organic matter in natural soils is polar with a combination of hydroxy- and oxy-moieties exposed to their exterior (Schwarzenbach,et al., 1993). As a result, the adsorption capacity of PCE is low at 200 µg/g to 3500 µg/g while the adsorption capacity of TCE is high at 500 µg/g to 15000 µg/g.

Figures 3.5 (PCE) and 3.6 (TCE) show the effect of soil to solution ratio on the adsorption behavior. This is known as "soil to solution ratio effect". This effect has been observed on phophate adsorption and has received a great deal of attention (Barrow and Shaw, 1979). It has been reported that phosphate adsorption increases as soil to solution ratio increases (Fordham 1963; Barrow et al., 1965; and White, 1966). Hope and Syers (1976), however, reported that high ratio results in a lower phosphate adsorption. Our results show that high soil to solution ratio (low soil concentration) increases the PCE and TCE adsorption density.

Figures 3.7 and 3.8 present the solid-water distribution ratio (Kd) of PCE and TCE. Results show that the Kd value range from 20 to 240 l/kg for PCE and from 5 to 40 l/kg for TCE, respectively. It is noted that the Kd values increase with increasing soil to solution ratio. This means that PCE would be transported from the water phase into soils easily compared to TCE. As a result, the solubility of PCE around 150 mg/l (250C) and of TCE around 1,100 mg/l (250C) can be achived under most circumstance prefers to stay in the bulk water more than PCE. However, Results in figures 3.3 and 3.4 show that the adsorption capacity of TCE is higher than that of PCE. This could be attributed to the difference in total adsorption sites for PCE and TCE on the soil surface.

III.2.3. Naphthalene

Figure 3.9 shows that the solubility of three PAHs compounds increase with increasing the methanol content (cosolvent) in the solution. The solubility of naphthalene, phenanthrene and pyrene at ambient temperature is around 30, 1.0, and 0.15 mg/l, respectively. Basicly the trend of cosolvency obeys a log-linear expression with respect to the volumetric concentration of cosolvent in a solvent mixture (Yalkowsky et al., 1981).

The adsorption isotherms for naphthalene at various cosolvent concentrations are shown in Figures 3.10, 3.11, 3.12, and 3.13. At low equilibrium concentrations of naphthalent, the isotherm could be nearly fitted by a linear adsorption equation (Figure 3.10). As the cosolvent and naphthalene concentration increases, the adsorption isotherm could be closely fitted by the Langmuir equation (Figures 3.11, 3.12, and 3.13). As mentioned above the major mechanism for the interaction between naphthalene and the soil surface is van der waals force as naphthalene is a nonpolar organic compound. It is further assumed that there are different limited surface sites in all mixtures for the attachment of naphthalene. Thus at low naphthalene concentrationin in the soil-soution mixture, the adsorption capacity is proportional to the equilibrium concentration since the limited sites have not been filled by the naphthalent molecules. However, at high solute concentration, a constant adsorption capacity is observed since the limited sites have filled by the naphthalent molecules. Furthermore, it is also noted that the adsorption capacity increases from hundreds of µg/g to thousands of µg/g with the cosolvent concentration increasing from 20% to 80%, V/V. This is obvious as methanol is a polar organic which would be uptaken by the polar organic matter in soil. Because naphthalene is dissolved in methanol, it would result in an increasing density for naphthalene.

It is noticed that the soil to solution ratio also influences the adsorption behavior of naphthalene singnificantly (Figures 3.14, 3.15, 3.16, and 3.17). Generally, the higher soil to solution ratio ( the lower soil concentration) increases the uptake of naphthalene in soil.

Figures 3.18 to Figure 3.21 show that the cosolvency and soil to solution ratio influence the distribution ratio of naphthalene in the soil-cosolvent-water system. It is noticed that the Kd values at various solute concentrations decrease with increasing soil to solution ratio (1:5 to 1:20) when the cosolvent (20% methanol, V/V) content is low in the mixtures (Figure 3.18). However, the trend changes at high cosolvent concentration. That is, the higher the soil to solution ratio, the higher the Kd value (Figures 3.19 - 3.21). In addition, the change of volume fraction of methanol (20% to 80%) seems to cause no affect on the value of Kd (1 to 10 l/kg) even the solubility of naphthalene changes greatly from 100 to 12,000 mg/l. Consequenctly, the cosolvent increases the total adsorption capacity (Qe) of the hydrophobic organic compound on the soil surface; it merely influences the distribution ratio of solute between solid and liquid phases.

Figure 3.1 Binding of representative chlorophenols to kaolinite. The amount of chlorophenol bound was obtained from
the difference between total chlorophenol added and the free concentration at equilibrium for kaolinite suspended
in NaNO3(pH~4). The lines are fits of the data to the Langmuir isotherm with constants given in Table 3.1.
 
 

Figure 3.2 The pH dependence of chlorophenol binding to kaolinite.

 Table 3.1 Langmuir constants for chlorophenol binding to kaolin ( Constants are calculated by non-linear least squares)
 

Compound	Q0 (µmole/g)	b (mM-1)
Phenol		0.075 (Q0B)
2-chlorophenol	2.46 ± 0.12	0.42 ± 0.04
3-chlorophenol	2.31 ± 0.10	0.49 ± 0.06
4-chlorophenol	2.61 ± 0.10	0.42 ± 0.10
2,3-dichlorophenol	3.42 ± 0.25	0.72 ± 0.14
2,4-dichlorophenol	2.28 ± 0.05	1.69 ± 0.14
2,5-dichlorophenol	3.49 ± 0.05	0.60 ± 0.02
2,6-dichlorophenol	2.8 ± 0.3	0.85 ± 0.24
3,4-dichlorophenol	2.75 ± 0.13	1.82 ± 0.32
3,5-dichlorophenol	2.25 ± 0.10	1.49 ± 0.19
2,4,5-trichlorophenol	3.0 ± 0.2	2.3 ± 0.3
2,4,6-trichlorophenol	2.76 ± 0.13	2.07 ± 0.26

 

Figure 3.3 The isotherms of PCE at various soil to solution ratios
The curves are fits of the data to the Langmuir equation Cs = 150 mg/l.

Figure 3.4 The isotherms of TCE at various soil to solution ratios
The lines are fits of the data to the linear equation Cs = 1,100 mg/l.

Figure 3.5 The adsorption capacity of PCE vs. various soil concentrations.

  Figure 3.6 The adsorption capacity of TCE vs. various soil concentrations.

  Figure 3.7 The distribution ratio of PCE.

Figure 3.8 The distribution ratio of TCE.

  Figure 3.9 The solubility of PAHs vs. volume fraction of methanol.

  Figure 3.10 The isotherms of naphthalene with 20% methanol at various soil to solution ratios,
The lines are fits of the data to the linear equation, Cs = 100 mg/l.

Figure 3.11 The isotherms of naphthalene with 40% methanol at various soil to solution ratios, Cs = 497 mg/l.

Figure 3.12 The isotherms of naphthalene with 60% methanol at various soil to solution ratios, The lines are fits of the
data to the Langmuir equation, Cs = 2,450 mg/l.

Figure 3.13 The isotherms of naphthalene with 80% methanol at various soil to solution ratios, The lines are fits of the
data to the Langmuir equation, Cs = 12,000 mg/l.

Figure 3.14 The adsorption capacity of naphthalene with 20% methanol vs. various soil concentrations.

Figure 3.15 The adsorption capacity of naphthalene with 40% methanol vs. various soil concentrations.

Figure 3.16 The adsorption capacity of naphthalene with 60% methanol vs. various soil concentrations.

Figure 3.17 The adsorption capacity of naphthalene with 80% methanol vs. various soil concentrations.

Figure 3.18 The distribution ratio of naphthalene with 20% methanol.

Figure 3.19 The distribution ratio of naphthalene with 40% methanol.

Figure 3.20 The distribution ratio of naphthalene with 60% methanol.

Figure 3.21 The distribution ratio of naphthalene with 80% methanol.

IV. ELECTRO-OSMOSIS STUDIES

IV.1. Methods

Four electro-osmosis experiments were conducted using various phenolic compounds. Soils contaminated with phenol, 2-chlorophenol, 3-chlorophenol and 4-chlorophenol were utilized and the same experimental procedures were applied to all of the tests. Table 4.1 below shows some of the experimental conditions of the electro-osmosis tests performed with phenolic compounds.

The soil was a combination of Ottawa sand (U.S. Silica Company) and Georgia kaolinite (Georgia Kaolin Company) at ratio 1:1 (w:w). A solution of the phenolic compound (in NaCl 10-3 M) was mixed well with the dry soil and let stand for about 24 hours to reach an equilibrium and consequently provide an uniform distribution of the contaminant in the soil system. The mixture was then carefully packed in the acrylic cylinder to avoid formation of large air spaces.
 

To begin the tests, the electrodes were connected to a 12 volts DC power supply (Power/Mate Corporation; model E-12/158). The anode container was kept filled with NaCl 10-3 M electrolyte solution and the cathode compartment was initially empty. Daily water samples were taken at the cathode side and during the experiments parameters such as amount of water flow, current, effluent contaminant concentration, pH of catholyte and anolyte were monitored as a function of time.

At the conclusion of test, the soil samples were removed from the cell and sliced into 10 sections. Each one was then analyzed for water content, pH and contaminant concentration.

IV.2. Results and Discussion

IV.2.1 Electro-Osmosis Water Flow

Figure 4.2 shows the amount of electro-osmotic flow produced as a function of time. In general, the flow reached a maximum value and then decreased gradually possibly due to changes in the electrical properties of the packed soil cores originated from the electrochemistry associated with the electro-osmosis process. By applying a potential to the system, water decomposed to H+ and O2 at the anode and these hydrogen ions flushed across the cell modifying the original conditions of the pore fluid. Simultaneously, vigorous production of OH- took place at the cathode because of the electrochemical reduction of water. Accounting for these occurrences, the hydraulic properties of the soil could be altered by dissolution of salts and clay minerals, adsorption/desorption interactions, precipitation of metal hydroxides and cation exchange (Hamed et al., 1991). The complexity of the soil system turned very difficult to interpret the specific causes of the changes of the electrical properties soil core. Pamukcu and Khan (1989) suggested that reversing the current of the electrical system and replacing the electrolyte solutions by fresh solutions would indicate any structural changes in the packed soil. If there are any variations in water flow after these changes, the hydraulic properties of the soil system is believed to be altered with respect of the initial condition. Based on this, the authors demonstrated that no changes in the soil structure was observed during the electro-osmosis process at least for kaolinite and the electrical properties of the pore fluid significantly affected the electro-osmotic water flow. To better illustrate these changes, a plot of current density (current per cross sectional area of flow) versus time is presented in Figure 4.3. It was observed that the current also reached a maximum value at the first days of experiments and then decreased gradually.

A linear correlation was found between the average water flow and the average current density (Figure 4.4). The higher the current density, the greater was the water flow. The current passing through the soil core was mainly credited to the ions in the liquid phase. Some of these ions (cations) were responsible for the water flow and a high current should evidently yield high electro-osmotic water flow. Therefore, current density could be used as a measurement of the efficiency of electro-osmotic process.

Noticeable differences among the experiments were related to the water flow. Figure 4.5 presents the diagram of accumulative flow versus time. The test with 2-chlorophenol produced the highest flow while the blank test showed the lowest water flow. It was noticed that the water flow was also related to the pore volume of the soil core. The larger the pore volume, the larger was the electro-osmotic water flow since more water was available to be transported. Obviously there is a limitation in this occurrence; if the pore volume is too large (see blank test), the system behaves as a free electrolyte solution and less electro-osmotic flow is recorded (Kezdi, 1980). Figure 4.6 exhibits the average flow in toatl of each experiment versus pore volume. The average flow increases with increasing pore volume until a point then decreases abruptly.

IV.2.2 Coefficient of Electro-Osmotic Permeability (ke)

Figure 4.7 shows the changes of the coefficient of electro-osmotic permeability (ke) as a function of time. As expected, the pattern is similar as for the electro-osmotic water flow since the latter and electro-osmosis permeability are closely related as demonstrated in equation (4.1):

(4.1)

This equation can be used to estimate the ke values of a soil system (Casagrande, 1949). In the present case the potential gradient ie and the cross section area A were constant. The ke values were found to be consistent with those reported in the literature (Casagrande, 1949) of about 10-5 cm2/V.s.

IV.2.3. Influent-Effluent pH Changes

The influent and effluent pH variation during the electro-osmosis experiments are presented in Figures 4.8 and 4.9, respectively. As mentioned previously, hydrogen ions (H+) were produced from the oxidation of water causing the drop in pH at the anode and hydroxyl ions (OH-) from the reduction of H2O were responsible for the pH increase at the effluent. For all experiments the pH at the anode (influent) decreased from values around 5 to approximately 2.5 to 3.0 while the effluent pH (cathode) rose to values between 12 to 13 and then decreased gradually due to the acid front generated at the anode. It is well known that hydrogen ions have higher mobility than hydroxyl ions (Acar and Alsahwabkeh, 1993). Thus, hydrogen ions move towards the cathode faster (due to its higher electrochemical mobility and convection) than the hydroxyl ions to the anode and a decrease in pH would be expected at the cathode solution.

IV.2.4. Contaminant Removal

Figures 4.10 and 4.11 present the percent contaminant removal as a function of time and the percent removal related to the total water volume flushed through the soil cores (in units of pore volumes of flow), respectively. The results demonstrated that good contaminant removal was achieved from the cathode side. For these experiments, no samples of the anode were analized for contaminant concentration. The 2-chlorophenol was almost completely removed from the soil (94 %) while only 58 % of the phenol was carried out by the electro-osmosis process. The removal of 3-chlorophenol and 4-chlorophenol were 85 % and 79 %, respectively. In Figure 4.11, one can observe that the removal efficiency was proportional to the amount of water passed through the soil samples. The greater the amount of liquid flushed through the soil, the greater was the contaminant removal. Acar and Alsahwabkeh (1993) demonstrated that high removal of phenols from kaolinite were achieved by passing at least 2 pore water volumes through the soil. High removal were observed in the tests with 3-chlorophenol and 2 chlorophenol and Figure 4.11 shows that more than 2 pore water volumes were flushed through the simulated contaminated soil. All the tests were run for 13 to 17 days and the differences in contaminant removal were greatly affected by the fluid velocity through the soil. The test with 2-chlorophenol presented the highest removal and average fluid velocity. It is crucial to understand factors influencing the fluid velocity (or water flow rate) of the electro-osmotic process. Results from this study indicate that physical properties of the soil core are very important.

IV.2.5. The pH Profile, Water Content and Contaminant Distribution

After the completion of the tests, the samples were sliced into 10 sections and analyzed for pH, water content and contaminant concentration. The resulted pH profiles for the 5 tests performed shown in the Figure 4.12 were originated exclusively from the redox reactions of water at the electrodes and demonstrated to have the same pattern as the profiles determined by Hamed et al. (1991). The acidic electrolyte solution generated at the anode reservoir flowed across the soil sample lowering the pH to values around 3 to 4 until near to the cathode the pH rose to values about 8 to 9 because of the basic conditions produced by the reduction of water.

Water content was measured in order to determine the concentrations of the phenolic contaminants per gram of dry soil and it was found to have almost an uniform distribution across the cell with an average value of 14 to 15 % as presented in the Figure 4.13. The section closest to the anode presented higher water content than the other sections. This result was expected since the liquid flow was directed towards the cathode and water was supplied continually at the anode side.

Figure 4.14 shows the distribution in relative concentration of the phenolic compounds remained in the soil. Small amounts of 4-chlorophenol and high concentration of phenol were retained while no 2-chlorophenol and 3 chlorophenol were found in the soil. An accumulation of phenol above the initial concentration (represented by the solid straight line at C/Co value of 1) was detected near the cathode, indicating that the contaminant does not move uniformly across the soil core. At high pH conditions (such as in the vicinity of the cathode), the phenol molecules (pKa = 9.9) were in the unprotonated form, or as anions, and therefore suitable to electromigration towards the anode. Because the water flow rate of the experiment with phenol was low, the electromigration overcame the convective velocity in the region close to the cathode. As a result, high concentration of phenol was detected at that zone. For the other tests, similar accumulation was not observed because the convective velocity was large enough to "push" the contaminants out of the soil. The remaining contaminant concentration of the phenolic compounds tested do not appear to be affected by the compound type since all the mono-chlorophenols possess similar physical properties. As discussed above, the fluid velocity plays an important role on the removal of pollutants from soil by electro-osmosis and the test for phenol presented the lowest average water velocity through the soil.

IV.2.6. Mass Balance

The mass balance for the phenol and mono-chlorophenols are summarized in the Table 4.2. The differences can be attributed to the transport (diffusion and/or migration) of the compounds to the anode reservoir and to the efficiency of the extraction method used to determine the contaminant concentrations in the soil.

Table 4.2. Mass balance for phenol and chlorophenol experiments
 

Test	ph	2Clph	3Clph	4Clph
Mass
removed from the soil (mg)	120.6	165.5	157.1	144.2
remained in the soil (mg)	81.3	N.D.a	N.D.a	10.4
total (mg)	201.9	165.5	157.1	154.6
initial mass (mg)	207.0	179.2	183.9	185.0
difference (mg)	5.1	13.7	26.8	30.4

a : Not detectable

Analysis of the contaminants at the anode reservoir were not performed in these experiments. Moreover, loss of chlorophenols by volatilization was not monitored. Nevertheless, the results of mass balance were satisfactory.

Figure 4.2 Electro-osmotic water daily flow for phenol and chlorophenol experiments.

Figure 4.3 Current density as a function of time for phenol and chlorophenols experiments.

Figure 4.4 Correlation between electro-osmotic water flow and current density for phenol and chlorophenol experiments.

Figure 4.5 Accumulative electro-osmotic water flow as a function of time for phenol and chlorophenol experiments.

Figure 4.6 Average electro-osmotic water flow as a function of pore volume for phenol and chlorophenols experiments.

Figure 4.7 Coefficient of electro-osmotic permeability as a function of time for phenol and chlorophenols experiments.

Figure 4.8 Influent pH as a function of time for phenol and chlorophenols experiments.

Figure 4.9 Effluent pH as a function of time for phenol and chlorophenols experiments.

Figure 4.10 Accumulative removal (%) of phenol and chlorophenols as a function of time.

Figure 4.11 Percentage contaminant removal as a function of pore volumes of flow.

Figure 4.12 The pH profile as a function of normalized distance from anode for phenol and chlorophenol experiments.

Figure 4.13 Water content distribution as a function of normalized distance from anode for phenol and chlorophenols experiments.

Figure 4.14 Contaminant distribution through the soil as a function of normalized distance from anode
for phenol and chlorophenol experiments.

 
V. ELECTRO-FENTON STUDIES

V.1. Electro-generation of Hydrogen Peroxide

V.1.1. Methods

V.1.1.1. Reactor Configuration

Table 5.1 shows the dimensions of the reactor utilized for the present research. The anodic chamber is approximately 40% of the total reactor volume, while the cathodic chamber is 60% of the total volume. This means that more than 4.5 liters of waste water or any contaminated water can be treated.

Table 5.1. Reactor dimensions.
 

Item	Value
Cathodic Chamber	10 x 5 x 5.5 in5 (254 x 127 x 139.7 mm3) Vc = 4.51 L
Anodic Chamber	10 x 3.5 x 5.5 in3 (254 x 88.9 x 139.7 mm3) Va= 3.15 L
Total Reactor Volume	Vt = 7.66 L

 

V.1.1.1. Electrolysis Cell

Figure 5.1 shows a schematic diagram of the reactor used in this research. The reactor is made of acrylic and it is mainly formed by two chambers: the anodic and the cathodic, in which the anode and the cathode are respectively placed. These two chambers are separated by a cation exchange membrane (Model CMX Neosepta Cation Selective Membrane, Electrosynthesis, E. Amherst, NY). The cation exchange membrane avoids the decomposition of hydrogen peroxide once it is formed in the cathode surface.

In the anodic chamber the oxidation of the water takes place, discharging electrons, oxygen gas, and hydrogen ions into the solution. In the chatodic chamber, oxygen is bubbled into the anolyte solution and it is electrochemically reduced to hydrogen peroxide. These two reactions are schematically represented in Figure 5.2.

V.1.1.2. Electrodes

Two working electrodes, the anode and the cathode, are made of graphite (grade 2020, Carbone of America, Ultra Carbon Division, Bay City, MI).

The anode has a rectangular geometry of 4.0'' x 6.0'' x 0.1'' dimensions with a total available surface area of 48.0 square inches.

Three different cathode geometries as shown in Figure 5.3 are tested to determine the influence of the cathode surface area:

a) The first cathode geometry is called ''plate''. It has the following dimensions :

8.0'' x 6.0'' x 0.1'', which means a total surface area of 96.0 square inches for the hydrogen peroxide generation.

b) The second cathode geometry is called "short finger". Its structure is made of a

base plate (with the same dimensions as the plate); four rectangular plates called ''fingers'' are connected on the base plate. The fingers have a length of 0.4 ".

c) The last cathode geometry is called "long finger". It has the same structure as the short finger but the finger length is longer: 0.6". The difference in length

between these two fingers can contribute to a large difference in the hydrogen

peroxide generation.

V.1.1.3. Oxygen Bubbling System

Oxygen is bubbled directly on to the cathode surface. Two different mechanisms are utilized: a six stone diffusers system and a pipe in which several holes were made. The diffuser system is able to produce smaller bubble sizes while the bubbles generated in the pipe are larger.

The oxygen source is obtained by a compressed oxygen bottle. Air (23% oxygen content) and a 50% oxygen-nitrogen mixture are also tested in order to determine the quantitative amount of oxygen needed for the hydrogen peroxide production.

V.1.1.2. Power Supply and Equipment Configuration

Figure 5.4 shows a schematic diagram of the laboratory setup for this experiment. The following apparatus are utilized:

a) A DC power supply to generate the current intensity that flows through the electrodes.

b) A pH meter and a pH controller to control and maintain constant any selected pH value.

c) A temperature control system to keep constant the temperature during the experiment.

d) Three flow meters to accurately maintain a constant gas flow rate for the oxygen, nitrogen, and compressed air.

e) Piping system to transport the gases to the reactor.

V.1.1.3. Methods

V.1.3.1. Theoretical Parameters Affecting Hydrogen Peroxide Production

Two main chemical reactions are involved in the production of hydrogen peroxide:

anodic oxidation of water:

(5.1)

cathodic reduction of oxygen:

(5.2)

From these two reactions it is obvious that current intensity, hydrogen ion concentration or pH, and oxygen concentration are determinant parameters. The solution temperature also affects the dissolved oxygen in the solution and the kinetic constant of the reaction. Since the reactions occur on the surface of the electrodes, the total available surface area of the cathode influences the hydrogen peroxide production.

a) Current Intensity. Current intensity affects the production of hydrogen peroxide in terms of current density, which is defined as the amount of amperes that flows through the anode surface area. At a certain current density value, the hydrogen peroxide production efficiency is maximum. Higher current density values will not give a better efficiency but will produce a faster consumption of the anode. Different intensity values are tested in order to determine this theoretical minimum value that gives the best efficiency with the most durability of the anode material.

b) Solution pH. Production of hydrogen peroxide is a function of the solution pH. Equation (V.2) shows that hydrogen peroxide concentration increases with decreasing the solution pH, since the hydrogen ion concentration increases as the pH decreases. The experimental results will determine the actual pH influence.

c) Oxygen Supply. Oxygen is both quantitatively and qualitatively a limiting factor for equation (V.2). Depletion of oxygen will decrease the potential hydrogen peroxide production. So, an external source of oxygen has to be supplied. Two parameters are decisive to enhance the reaction efficiency: oxygen concentration and oxygen bubble sizes.

d) Solution Temperature. Solution temperature affects the production of hydrogen peroxide in two different ways: temperature modifies the solubility of oxygen in the solution, and it also affects the reaction kinetic constant. Oxygen solubility increases when the solution temperature decreases. The overall influence of the temperature in the oxygen solubility in the aqueous phase is tested in this experiment.

e) Cathode Surface Area. Since the hydrogen peroxide is produced on the cathode surface, larger surface areas are expected to give higher concentrations.

V.1.3.2. Procedures

In order to test and demonstrate the theoretical parameters affecting the production of hydrogen peroxide, all of the described factors are tested. Figure 5.5 showes the research approach followed for this purpose. Current intensity is first tested and the most efficient value is recorded and utilized for the rest of the parameters, including pH, oxygen bubbling system, temperature and the surface area of the cathode. The following are experimental conditions:

a) Current intensity: 0.2, 0.4, 0.6, 0.8, 1.0, 1.2 Amp.

b) pH: 1.0, 2.0, 3.0, 4.0

c) Oxygen rate: 2,000 cc/min

d) Oxygen diffusion system: cylindrical pipe with 10 holes stone diffusers

e) Oxygen quality: compressed air (23% )

nitrogen-oxygen mixture (50% )

pure oxygen (100% )

f) Temperature: 12?C, 25?C (ambient), 45?C

g) Cathode surface area: 309.67 (48 sq.in),

743.22 (115.2 sq.in)

753.54 (116.8 sq.in)
 

V.1.2. Results and Discussion

V.1.2.1. Effect of Current Intensity

The relationship between the voltage applied to the electrodes and the current intensity is represented in Figure 5.6. This relation shows a linear behavior within the electrolyte and, consequently, an approximately constant conductivity in the tested aqueous solution.

Figure 5.7 shows the effect of current intensity on the production of hydrogen peroxide. Starting with 0.2 Amp, hydrogen peroxide concentrations are larger when increasing the current intensity. It follows an increasing behavior until it reaches a maximum value which corresponds to a current intensity of 1 Amp. This is the limiting value for the generation of hydrogen peroxide in this experiment. Higher values will accumulate approximately the same concentrations of hydrogen peroxide or even less. However, degradation of the anode may occur, reducing its life and, therefore, increasing the overall cost of the process. When anodic decomposition occurs, small graphite particles may release into the anolyte, coloring the solution.

The generation of hydrogen peroxide over time when working with the limiting current intensity value is represented in Figure 5.8. Up to 47.83 ppm can be generated for a three hour running experiment. The effect of current intensity is actually given by the current density value which is obtained by dividing the current intensity by the surface area of the anode. For this experiment a current density value of 6.45x10-3 Amp/cm2 is obtained.

V.1.2.2. Effect of Solution pH

Solution pH has a significant influence in the production of hydrogen peroxide since the hydrogen ion concentration in the solution is a contributing factor for the hydrogen peroxide formation reaction. Figure 5.9 shows the generation of hydrogen peroxide over time for different pH values. It can be seen that pH 3.0 is the most favorable value for the generation of hydrogen peroxide, as it was reported in different studies (Sudoh et al, 1986; Chu, 1995). Almost 160 ppm hydrogen peroxide can be accumulated in a solution pH 3.0 after three hours. In a pH 1.0 solution more than a hundred ppm hydrogen peroxide can be generated over the same period of time. At pH 2.0, just 50 ppm are obtained. Finally, at higher pH values (pH 4.0), less than 40 ppm can be accumulated.

Figure 5.10 shows this pH effect on hydrogen peroxide generation. These experimental results relating the influence of solution pH on the hydrogen peroxide generation agree with Sudoh's research (Sudoh et al, 1986). Sudoh has reported that the most favorable pH for hydrogen peroxide generation is 3.0, followed by 1.0, 2.0, and 4.0 as the least beneficial value.

V.1.2.3. Effect of Oxygen Bubbling System

Oxygen is continuously bubbled into the catholyte through a diffusion system. The oxygen inlet is placed right under the cathode in order to maximize the efficiency of the process. Figure 5.11 shows the effect of oxygen bubbles size on the production of hydrogen peroxide. Oxygen bubbles size are controlled by the use of gas diffusers. Two types of diffusers are used in this experiment: pipe diffusers and stone diffusers. Pipe diffusers are obtained by drilling ten small holes in a cylindrical pipe which is located right under the electrode in the cathodic chamber. Stone diffusers are made of a highly porous material and the compressed gas flows through these pores into the catholyte towards the cathode surface. It can be seen from Figure 5.11 that stone diffusers are more effective than pipe diffusers, since the former are able to produce smaller oxygen bubbles, which are more suitable to react on the cathode's surface to form hydrogen peroxide.

The effect of oxygen quality on hydrogen peroxide generation is shown is Figure 5.12. Three different sources of oxygen are tested. Compress air, with approximately 23% oxygen content, is bubbled into the solution. The graph shows a very small hydrogen peroxide accumulation, even after long running times. In the case of bubbling a mixture of nitrogen-oxygen (50% each), the results clearly indicate that more oxygen is transferred to the water. Pure oxygen (100%) is also bubbled into the solution and it is the most favorable situation for the hydrogen peroxide accumulation.

In conclusion, the formation rate of hydrogen peroxide is limited by the mass transport of oxygen to the cathode, the oxygen bubble size, and the oxygen content in the gas phase. Pure oxygen and the stone bubbling diffusion system are found to be the most efficient parameters for the hydrogen peroxide generation.

V.1.2.4. Effect of Solution Temperature

Solution temperature plays an important factor on the generation of hydrogen peroxide. Figure 5.13 represents the effect of temperature on the production of hydrogen peroxide for different times. From this graph it can be observed that at ambient temperature, 25?C, the generation of hydrogen peroxide is the more efficient than at 12? or 45?C.

Figure 5.14 represents the generation of hydrogen peroxide over time as a function of the solution temperature. Almost 200 ppm hydrogen peroxide can be accumulated after two hours at 25?C. Under the same experimental conditions, and at cooler temperatures, no more than 50 ppm hydrogen peroxide is obtained. Higher temperatures ( 45?C) are even worse and not even 10 ppm hydrogen peroxide is generated. Apparently, lower temperature inhibits the oxygen reduction reaction due to slower mass transfer process. High temperature, however, inhibits the solubility of oxygen into water. As a result an optimal temperature is necessary for the hydrogen peroxide formation reaction.

V.1.2.5. Effect of Cathode Geometry

Figure 5.15 represents the accumulation of hydrogen peroxide over time as a function of the cathode surface area. The plate electrode has the smallest surface area and, consequently, the lowest accumulation rate. The curve shows an increasing growth until it reaches a certain time in which the hydrogen production rate decreases to zero. The short finger cathode, with larger surface area produces higher yields, and follows the same trend, although the time to reach the steady state is larger. The long finger cathode produces the largest amount of hydrogen peroxide. Up to 273 ppm can be accumulated after 3 hours. Within this range, the production rate is linear with a value of 1.52 ppm accumulated per minute. This cathode geometry is supposed to follow the same trend as the plate and short finger. Consequently, for longer running times it will reach a certain point in which the generation rate will start to decrease.

Figure 5.16 shows the effect of the surface area of the cathode on hydrogen peroxide generation. The hydrogen peroxide production for the single plate is really low compared with the finger geometry cathodes. The largest difference is produced when looking at the hydrogen peroxide production in the short finger and comparing it with the long one.

V.1.2.6. Current Efficiency for Hydrogen Peroxide

Table 5.2 shows the calculated values for the current efficiency. The experimental conditions are as follows: 1 Amp; solution pH 3.0; stone diffusers; 100% oxygen; 2,000 cc/min oxygen flow rate; temperature 25?C; long finger cathode with a total available surface area of 753.54 sq. cm.

Figure 5.17 shows that the current efficiency for the formation of hydrogen peroxide is 81% after the first 5 minutes, but decreases rapidly as hydrogen peroxide accumulates in the acidic solution. Sudoh (Sudoh et al, 1986) obtained a maximum current efficiency for the hydrogen peroxide formation of 85% in a solution pH 3.0.

Table 5.2. Current efficiency for the hydrogen peroxide generation.
 

Time  (min)	Hydrogen peroxide (ppm)	Current efficiency  (%)
5	9.54	81.25
10	18.94	80.62
15	28.00	79.47
30	53.53	75.96
60	103.46	73.41
90	149.03	70.49
120	195.05	69.19
150	233.46	66.26
180	273.46	64.68

 

V.1.2.7. Hydrogen Peroxide Stability

From a theoretical point of view, the tendency of absolutely pure hydrogen peroxide to decompose into water and oxygen is negligible. This appears to be true even if the pure material is in aqueous solution, provided that the water of the solution is absolutely pure. However, in practice, numerous agents or conditions tend to initiate or accelerate decomposition. Thus, a very slight trace of dissolved impurity such as ferric ions or other metallic ions exert a marked catalytic decomposition effect.

Figure 5.18 shows the degradation rate of commercial hydrogen peroxide under different acidic pH values. Within the acidic pH range, the degradation of hydrogen peroxide is almost negligible. However, in the alkaline pH region, the hydrogen peroxide disappears after 10 hours.

 Figure 5.1 Schematic diagram of the reactor configuration

 Figure 5.3 Schematic diagram of three cathodes' geometry

 Figure 5.4 Schematic diagram of the laboratory setup configuration

 Figure 5.5 Flow diagram for the research approach

Figure 5.6 The relationship between the applied voltage and the current intensity in a 0.05 M NaClO• ionic strength solution.

Figure 5.7 The effect of current intensity on hydrogen peroxide concentration. Working conditions: solution ionic strength: 0.05 M NaClO•;
solution pH 2.0; pipe diffusion system; oxygen flow rate: 2,000 cc/min; 100% oxygen quality; 25ºC solution temperature; 753.54
sq.cm cathode's surface area.

Figure 5.8 The generation of hydrogen peroxide over time for a constant current intensity of 1 Amp. Working conditions: solution ionic
strength: 0.05 M NaClO•; solution pH 2.0; pipe diffusion system; oxygen flow rate: 2,000 cc/min; 100% oxygen quality; 25?C
solution temperature; 753.54 sq.cm cathode's surface area.

Figure 5.9 The generation of hydrogen peroxide over time for different pH values. Working conditions: solution ionic strength: 0.05M
NaClO•; current intensity 1 Amp; pipe diffusion system; oxygen flow rate: 2,000 cc/min; 100% oxygen quality;
25ºC solution temperature; 753.54 sq.cm cathode's surface area.

Figure 5.10 The effect of pH on hydrogen peroxide concentration. Working conditions: solution ionic strength: 0.05 M
NaClO•; current intensity 1 Amp; pipe diffusion system; oxygen flow rate: 2,000 cc/min; 100% oxygen quality;
25ºC solution temperature; 753.54 sq.cm cathode's surface area.

Figure 5.11 The effect of oxygen bubbles' size on hydrogen peroxide generation. Working conditions: solution ionic
strength: 0.05 M NaClO•; current intensity 1 Amp; solution pH 3.0; oxygen flow rate: 2,000 cc/min; 100%
oxygen quality; 25ºC solution temperature; 753.54 sq.cm cathode's surface area.
 
 

Figure 5.12 The effect of oxygen quality on hydrogen peroxide concentration. Working conditions: solution ionic
strength: 0.05 M NaClO•; current intensity 1 Amp; solution pH 3.0; oxygen flow rate: 2,000 cc/min; stone
diffusion system; 25ºC solution temperature; 753.54 sq.cm cathode's surface area.
 
 

Figure 5.13 The effect of solution temperature on hydrogen peroxide concentration. Working conditions: solution ionic
strength: 0.05 M NaClO•; current intensity 1 Amp; solution pH 3.0; oxygen flow rate: 2,000 cc/min; pipe
diffusion system; 100% oxygen quality; 753.54 sq.cm cathode's surface area.

Figure 5.14 The generation of hydrogen peroxide concentration over time as a function of solution temperature. Working conditions: solution ionic strength: 0.05 M NaClO•; current intensity 1 Amp; solution pH 3.0; oxygen flow rate: 2,000 cc/min; pipe diffusion system; 100% oxygen quality;
753.54 sq.cm cathode's surface area.

Figure 5.15 The generation of hydrogen peroxide over time as a function of the cathode's surface area. Working
conditions: solution ionic strength: 0.05 M NaClO•; current intensity 1 Amp; solution pH 3.0; oxygen flow
rate: 2,000 cc/min; pipe diffusion system; 100% oxygen quality; 25ºC solution temperature.

Figure 5.16 The effect of cathode's surface area on hydrogen peroxide concentration. Working conditions: solution
ionic strength: 0.05 M NaClO•; current intensity 1 Amp; solution pH 3.0; oxygen flow rate: 2,000 cc/min; pipe
diffusion system; 100% oxygen quality; 25ºC solution temperature.

Figure 5.17 Current Efficiency for the hydrogen peroxide generation. Working conditions: solution ionic strength: 0.05 M NaClO•;
current intensity 1 Amp; solution pH 3.0; oxygen flow rate: 2,000 cc/min; stone diffusion system; 100% oxygen quality;
25ºC solution temperature; 753.54 sq.cm cathode's surface area.
 
 

Figure 5.18 Hydrogen peroxide stability over time as a function of solution pH.
 
 

V.2. Fenton’s Reagent Oxidation

V.2.1. Introduction

V.2.1.1. Mechanism of Fenton’s Reagent Oxidation

Electro-Fenton oxidation is an electrochemical process widely used to remove organic contaminants from the water. The main difference from conventional Fenton oxidation process is that in the electro-Fenton oxidation the electrolysis generates the hydrogen peroxide, which in the presence of ferrous ion () produces the hydroxyl radicals (). These active radicals are known to have a very strong oxidation capacity.

The oxidation capacity of a substance is related to its oxidation potential. Even though a higher potential means a stronger oxidation capacity, kinetic effects can modify this ability. Table 5.3 shows a comparative relation among the standard reduction potentials of some oxidants.

Fluorine gas is the strongest element but it is not commonly used because it is very expensive and it can produce halogenated organic compounds during oxidation.

Hydroxyl radicals have the second highest oxidation potential. They can easily oxidize many different organic compounds such as aromatics, aliphatics, and also some inorganics under acidic conditions. These hydroxyl radicals can be generated from many different sources such as irradiation of water molecules with high energy electrons, a catalyzed hydrogen peroxide reaction with a UV source, a combination system of UV and ultrasound, decomposition of ozone in specific pH solutions, ozone decomposition catalyzed by hydrogen peroxide, or by the Fenton's reagent system.

Ozone has also been widely used as an oxidizing agent. It can react in two different ways: direct and indirect oxidations. The direct oxidation uses the ozone molecule as the oxidazing agent. This molecule is highly selective and the reaction is relatively slow. In the indirect oxidation process ozone is decomposed into hydroxyl radicals which are less selective and can degrade much faster.

Table 5.3 Standard reduction potentials of some oxidants (CRC, 1989).
 

Compound	Reaction	Eo, V
Florine		2.866
Hydroxyl radical		2.330
Ozone		2.076
Hydrogen peroxide		1.776
Permanganate ion		1.679
Hypobromous acid		1.596
Chlorous acid		1.570
Hypochloric acid		1.482
Hypoiodous acid		1.439
Chlorine		1.358
Bromine		1.087
Iodine		0.535
Chloro dioxide		0.954
Chlorite		0.760

Fenton's reagent is the result of a chain mechanism and free radical reaction resulting in highly reactive intermediates. In the presence of ferrous ion, hydrogen peroxide oxidizes ferrous iron to ferric ion, and it is decomposed to hydroxyl radical and hydroxyl ion, as it is shown in equation 5.3:

(5.3)

If no other substances are present, equation 5.4 takes place in which the hydroxyl radical oxidizes ferrous ion to ferric ion:

(5.4)

The overall reaction is reported in equations 5.5 and 5.6. These equations indicate the dependence of this process on the solution pH.

(5.5)

(5.6)

In the presence of organic compounds, the hydroxyl radical oxidizes the degradable compounds to a free radical and water (Equations 5.7 and 5.8):

(5.7)

(5.8)

These free organic radicals can be transformed into organic ionic species, as it is shown in equations 5.9 and 5.10:

(5.9)

(5.10)

V.2.1.2. Applications of Fenton’s Reagent Oxidation

Fenton's reagent has been widely used for the treatment of a large variety of organic pollutants and other contaminants.

Phenolic compounds were efficiently degraded to organic acids and carbon dioxide. Phenol was oxidatively degraded to oxalic acid and carbon dioxide (Sudoh et al, 1986).

Chlorinated aromatic hydrocarbons (CAHs) present in the environment from a variety of sources are difficult to degrade by conventional methods and they are very harmful for humans. Chlorophenols, chlorobenzene, and dichlorobiphenyls can be effectively degraded by the Fenton's process (Sedlack et al, 1991). The most direct mechanism for CAHs degradation proceeds through hydroxylation followed by ring cleavage and mineralization.

Oxidation of several alkylbenzenes such as toluene, ethylbenzene, and cumene by electrogenerated hydroxyl radical has also been carried out (Matsue et al, 1981). The reaction products in the oxidation of alkylbenzenes were generally classified into hydroxylated products of aromatic rings and oxygenated ones of side chains.

Oxidative destruction of cresol isomers (o-cresol, m-cresol, and p-cresol) in water was studied (Zheng et al, 1993). Cresols are slowly oxidized by hydrogen peroxide. Nevertheless, the oxidation rates can be enhanced by the Fenton's process or by the presence of other catalyst, such as UV irradiation.

Catalyzed hydrogen peroxide has been used as a pretreatment process for wastewater that contains refractory organics or compounds that are toxic to microorganisms (Spencer et al, 1994). The research indicates that stoichiometric ratios of contaminant degradation to the hydrogen peroxide consumption were sensitive to both the concentration of iron added and to the organic carbon content of the soil.

Fenton's reagent has also been applied for the decolorization of dye wastewater (Kuo, 1992). Experimental results showed that at pH below 3.5 the transparency of the wastewater was deeper, with an average percent removal of chemical oxygen demand (COD) of approximately 88%. Kuo found out that the effective dosage of hydrogen peroxide and ferrous sulfate is affected by different types of dyes and this must be related to differences in the molecular structures of dyes. Temperature greatly affects decolorization, and the time required for decolorization can be reduced by raising the temperature.

The effect of an oxidative treatment using hydrogen peroxide on dewatering of different activated sludge from pulp and paper mills was investigated (Mustransta et al, 1993). The effects of hydrogen peroxide and ferrous sulfate concentration, pH, reaction time, and temperature on the filterability of the sludge were tested, showing that the filterability was strongly dependent on the concentration of hydrogen peroxide and the reaction temperature.

Chlorinated compounds were degraded by Fenton reaction (Koyama et al, 1994). For the degradation of 10 mM 2-chlorobenzoate, 0.3% hydrogen peroxide and 0.02% ferrous chloride solutions were required to deplete it within one hour incubation at 60?C although a significant amount of unknown substances (40 - 50%) were generated through the Fenton's reagent.

Hayek et al (1990) studied the oxidation by hydrogen peroxide of phenolic compounds in an aqueous medium in the presence of various heterogeneous catalysts and in particular alumina supported iron. The catalytic oxidation of phenol is very weak and it depends on many different parameters, such as the preparation of the catalyst and the nature of the supported metals, the mode of thermal treatment of the catalyst and the reaction temperature, and the presence of polyhydroxybenzenes at the beginning of the reaction.

V.2.1.3. Advantages of Fenton’s Reagent Oxidation

Electrochemical processes can then be used for contaminated soil and groundwater remediation. Many waters contain naturally occurring compounds which are refractory, toxic, and inhibitory to standard treatment processes. Some chemicals, although biodegradable, require retention times that are not economically feasible yet. In conclusion, electro-Fenton oxidation incorporates several advantages such as:

a) In-situ remediation of toxic organic compounds.

b) Lower capital cost.

c) Less hydraulic retention time.

d) Decomposition of toxic organic compounds. Some of them can be completely

degraded to carbon dioxide and water. Others can be partially oxidizedto reduce

their toxicity and refractivity.

1. No chlorinated organic compounds such as trihalomethanes formed during

the degradation process since chlorine is not used.

2. The sludge produced in this process is chemically inert.
3. This process can be integrated into a biological treatment process to improve

V.2.1.4. Current Objective

In the current work, hydrogen peroxide was added to the system instead of being generated in the process. The research was focused on the estimation of the quantities of hydrogen peroxide and experimental conditions required to oxidize naphthalene, PCE, TCE. In next step, information obtained from conventional Fenton oxidation will be applied to electro-Fenton oxidation of the selected organic compounds.

 V.2.2. Methods

V.2.2.1. Properties of Selected Organic Compounds

It is expected that the following organic compounds will be present in the soils at specific DOE sites: poly aromatic hydrocarbons (PAHs) such as naphthalene, phenantrene, pyrene, trichloroethylene (TCE), tetrachloroethylene (PCE), chlorofom, carbon tetrachloride and trichloroacetic acid (TCA). Experiments were first conducted to determine the degradable characteristics of naphthaalene, PCE, TCE by conventional Fenton oxidation. The properties of these selected organic compounds are list in Table 5.4.

From Table 5.4 we know that naphthalene is semi-volatile and tetrachloroethylene (PCE) and trichloroethylene (TCE) are highly volatile. Though naphthalene evaporates from the solution to the air slowly, the reaction conditions may accelerate its evaporation. Therefore, the evaporation speed of naphthalene was tested using a stirring, open and 250 mL volume beaker. The initial concentration of naphthalene solution was 26.66 mg/L. Results shown in Figure 5.19 indicate that there is almost no naphthalene remaining in the solution after 30 minutes stirring. So, a closed and no head-space reactor was needed for the oxidation of naphthalene by Fenton’s reagent. Also, the same reactor was used to oxidize PCE and TCE since they are highly volatile.

V.2.2.2. Batch and Pulse Fenton Oxidation Experiments

Reagents. Reagent grade naphthalene, PCE and spectrophotometric grade TCE were obtained from the Aldrich Chemical Company. The purities of these organic compounds were 98%, 99% and 99.5+%, respectively. The oxidant hydrogen peroxide and the catalyst ferrous sulfate were obtained from the Fisher Scientific Company, both reagent grade , and with a purity of 31.5% and 98%, respectively.

Stock Solution. Stock solutions of the selected organic compounds were prepared in a stirred glass flask by dissolving them into distilled water. Naphthalene was crystal and both PCE and TCE were liquid. No cosolvents were used. Concentrations of stock solutions prepared were close to their solubilities except TCE, which has a large solubility of 1,100 mg/L.

 Table 5.4 Properties of the selected organic compounds (Karel Verschueren,1983)
 

Properties	Naphthalene	Tetrachloroethylene (PCE)	Trichloroethylene (TCE)
Molecular formula	C10H8	Cl2C = CCl2	CCl2 = CHCl
Melting point	80.2 oC	- 22.7 oC	- 87 oC
Boiling point	217.9 oC	121.4 oC	86.7 oC
Vapor pressure	1 mm at 53 oC	14 mm at 20 oC 24 mm at 30 oC 45 mm at 40 oC	20 mm at 0 oC 60 mm at 20 oC 95 mm at 30 oC
Solubility  (in distilled water)	31 ~ 34 mg/l at 25 oC	150 mg/l  at 25 oC	1,100 mg/l at 25 oC
Evaporation (25oC, 1ppm solution)	__	50% after 24 ~ 28 min 90% after 72 ~ 90 min	50% after 19 ~ 24 min 90% after 63 ~ 80 min

Analyses. Naphthalene, PCE and TCE were assayed by GC/MS (GC, 5890 series II; MS, 5972 seiries; Hewlett Parkard Company). The retention times for naphthalene, PCE, and TCE were around 6.96, 4.08 and 3.27 minutes, respectively.

Batch Fenton Oxidation. A 500 mL, narrow-mouth erlenmeyer flask was used as the reactor, which was stirred by a magnetic bar. The flask mouth was closed with a rubber stopper so that there was no head-space left. Experiments were conducted under room temperature. The reaction temperature would not increase much because the concentration of organic compounds was low. Besides, pH was not controlled during experiment. The solution pH (from pH2.50 ~ pH3.65) depended mostly on the dosage of ferrous sulfate. Experimental procedures were as follows:

a) Add 500 mL of stock solution of the selected compound and a certain amount

of ferrous sulfate into the reactor.

b) After adding hydrogen peroxide solution while stirring, close the reactor

immediately.

c) Take 4 mL sample at the time of 1, 3, 5, 10, 20, 30 minutes after the reaction

starts.

d) Immediately adjust the sample pH value above 8.0 using 1.0M NaOH solution

in order to stop the generation of hydroxyl radicals by the chain reaction, i.e.,

to stop the further degradation of organic compounds.

e) Use the same volume of hexane (4 mL) to extract the residual organic

compound from the aqueous phase, and then determine its concentration by

GC/MS.

Pulse Fenton Oxidation. All procedures were as same as those of batch Fenton oxidation experiments except that the dosage of hydrogen peroxide solution was fractionalized into 3 aliquots, and they were added at the time of 0, 11, 21 minutes after the reaction started. The total amount of ferrous sulfate was added into the reactor just along with the stock solution. It was expected that the pulse addition of hydrogen peroxide would delay the exhaustion of ferrous ions.

V.2.3. Results and Discussion

V.2.3.1. Naphthalene

Naphthalene calibration curve is shown in Figure 5.20. Actually, for each set of samples, the calibration curve needs to be modified at the same time because the working conditions of GC/MS often vary a little at different sets of runs.

Experiments were conducted in a completedly mixed system, batch or pulse Fenton oxidation. The dosages of hydrogen peroxide were 5x10^-4, 1x10^-3 and 2x10^-3 M and the molar ratios of hydrogen peroxide to ferrous ion were 1:1, 3:1, 5:1, and 7:1.

Results shown in Figure 5.21, 5.22, 5.23 clearly indicate that the degradation of naphthalene is very fast. Under the experimental conditions, a total removal of naphthalene was possible in less than 20 minutes when the dosages of both hydrogen peroxide and ferrous ion were more than 1x10^-3M. The degradation rate and removal efficiency of naphthalene increase with the increasing dosage of hydrogen peroxide, and at the same dosage of hydrogen peroxide, they increase with the increasing dosage of ferrous ion. Most naphthalene (about 60 ~ 70%) was degraded in the first 5 minutes, the rest could be totally degraded in the following 15 minutes. So, the degradation curve is characterized by a rapid oxidation reaction which is then followed by a much slower reaction.

For the purpose of comparison, the pulse Fenton oxidation of naphthalene was conducted. It was expected that the pulse oxidation would delay the exhaustion of ferrous ions, thus enhance the removal efficiency at the same dosage of hydrogen peroxide. The degradation curves are shown in Figure 5.24. The comparison on removal efficiencies of batch and pulse Fenton oxidation at the reaction time of 30 minutes is shown in Table 5.5.

Table 5.5 Comparison of removal efficiencies of naphthalene by batch and pulse Fenton

oxidation
 

Molar Ratio (H2O2 / Fe2+)	H2O2  (10-4M)	Fe2+  (10-4M)	Removal Efficiency of Batch Oxidation (%)	Removal Efficiency of  Pulse Oxidation (%)
3:1	5	1.67	59.7	56.9
5:1	5	1	43.3	40.9
3:1	10	3.3	98.4	94.6
5:1	10	2	79.2	77.1

From the above table, we learn that there is no much difference between batch and pulse oxidation. The removal efficiencies of pulse oxidation are even a little bit lower than those of batch oxidation.

To get a total removal of naphthalene, the dosage of hydrogen peroxide is only 1x10^-4M in stock solution. This means that the weight ratio of hydrogen peroxide to naphthalene is only about 1.20 ~1.40 : 1. It is very cost-effective.
 
 

V.2.3.2. Tetrachloroethylene (PCE)

PCE calibration curve is shown in Figure 5.25. Experimental conditions for PCE were the same as those for naphthalene. Since the concentration of the stock solution of PCE was much higher than that of naphthalene, higher dosages of hydrogen peroxide and ferrous ion were needed. The dosages of hydrogen peroxide were 1x10^-3, 5x10^-3M and the molar ratios of hydrogen peroxide to ferrous ion were 1:1, 3:1 and 5:1.

Results shown in Figure 5.26, 5.27 indicate that PCE can be degraded by Fenton’s reagent in a very short time. When the dosages of both hydrogen peroxide and ferrous ion were 5x10^-3 mole per liter stock solution, a total removal could be obtained. This exhibits that the weight ratio of hydrogen peroxide to PCE is only 1.40 : 1. The oxidation reaction was very fast, it was finished in less than one minute.

Figure 5.28 shows degradation curves of pulse oxidation. The comparison on removal efficiencies of batch and pulse Fenton oxidation at the reaction time of 30 minutes is shown in table 5.6. From this table, it is learned that PCE is degraded more thoroughly in pulse oxidation than in batch oxidation.

Table 5.6 Comparison of removal efficiencies of PCE by batch and pulse Fenton oxidation
 

Molar Ratio (H2O2 / Fe2+)	H2O2  (13-3M)	Fe2+  (13-4M)	Removal Efficiency of Batch Oxidation (%)	Removal Efficiency of  Pulse Oxidation (%)
3:1	1	3.3	81.3	86.5
5:1	1	2	77.9	80.5
3:1	5	16.7	95.8	99.8
5:1	5	10	84.6	95.6

 

V.2.3.3. Trichloroethylene (TCE)

TCE calibration curve is shown in Figure 5.29. At 25^oC, TCE has a solubility of 1,100 mg/L. In this research, the stock solution with a concentration of 433mg/L was perpared. The dosages of hydrogen peroxide were 2x10^-3, 5x10^-3, 1x10^-2, 2x10^-2 M and the molar ratios of hydrogen peroxide to ferrous ion were 1:1, 3:1, 5:1, 7:1, and 9:1.

Figure 2.30, 2.31, 2.32 and 2.33 show the degradation curves of TCE. When the dosages of both hydrogen peroxide and ferrous ion were 5x10^-3 mole per liter stock solution, 99.3% of TCE was degraded in one minute. The weight ratio of hydrogen peroxide to TCE is 0.405 : 1. Like naphthalene and PCE, the oxidation of TCE was very fast, only in one minute or even less.

Figure 5.19 Volatile speed of naphthalene. Working conditions: a stirring, open beaker containing 250mL naphthalene
solution with the initial concentration of 26.66mg/L.

Figure 5.20 Calibration curve of naphthalene.

Figure 5.21 Batch Fenton oxidation of naphthalene. (The dosage of hydrogen peroxide is 5x10^-4M.)

Figure 5.22 Batch Fenton oxidation of naphthalene. (The dosage of hydrogen peroxide is 1x10^-3M.)

 Figure 5.23 Batch Fenton oxidation of naphthalene. ( The dosage of hydrogen peroxide is 2x10^-3M.)

Figure 5.24 Pulse Fenton oxidation of naphthalene. (Hydrogen peroxide was added at the time of 0, 11, 21 minutes.)

Figure 5.25 Calibration curve of tetrachloroethylene (PCE).

Figure 5.26 Batch Fenton oxidation of PCE. (The dosage of hydrogen peroxide is 1x10^-3M.)

Figure 5.27 Batch Fenton oxidation of PCE. (The dosage of hydrogen peroxide is 5x10^-3M.)

Figure 5.28 Pulse Fenton oxidation of PCE. (Hydrogen peroxide was added at the time of 0, 11, 21 minutes.)

Figure 5.29 Calibration curve of trichloroethylene.

  Figure 5.30 Batch Fenton oxidation of TCE. (The dosage of hydrogen peroxide is 2x10^-3M.)

  Figure 5.31 Batch Fenton oxidation of TCE. (The dosage of hydrogen peroxide is 5x10^-3M.)

Figure 5.32 Batch Fenton oxidation of TCE. (The dosage of hydrogen peroxide is 1x10^-2M.)

Figure 5.33 Batch Fenton oxidation of TCE. (The dosage of hydrogen peroxide is 2x10^-2M.)

 
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VII. APPENDIX

ANALYTICAL METHODS

A. Soil Characterization

A.1. Composition Analysis

The composition of site clay material was analyzed by the sedimentation (hydrometer) method. The procedures were as follows:

a) Grind soil samples with mortar and pestle and sieve to make sure that all the diameters of the soil particles are less than 2 mm.

b) Take 50 gram of the ground soil sample and add 100 mL of 5% sodium hexametaphosphate.

c) Transfer the suspension to a sedimentation cylinder, insert a plunger and mix the contents thoroughly.

d) About 15 seconds after mixing the suspension, lower the hydrometer into suspension, and after 40 seconds, read the scale at the top of the meniscus.

e) Record the hydrometer value.

f) Record temperature of the sample and blank at the 40 seconds time mark. From these values, the percentage of sand can be calculated.

g) After 2 hours of standing lower the hydrometer into the sedimentation cylinder and record the hydrometer value, then record the temperature of sample and
blank. From these values, the percentage of clay can be calculated.

The equations for the calculation of the soil composition are as follows:

where: Corrected Weight of Soil = 

A.2. Soil pH

The pH measurement was made in 0.01 M CaCl2 solution. The samples were air dried and sieved through 2 mm sieve to remove the coarse soil fraction. Weigh 10 gram of the pretreated soil sample and mix with 10 mL of 0.01 M CaCl2. Mix thoroughly and let the sample stand for at least 1 hour. Record the pH value by using a pH meter.

A.3. Soil Organic Matter

The soil organic matter was determined by the loss of weight on ignition (L. O. I.) method.

Take 1 cm3 of air dried and sieved through 2mm sieve soil sample and place it into a 30 mL beaker. Dry the soil sample at 105 oC for two hours. Record the weight of soil sample plus beaker with an accuracy of +0.001 g. Heat the sample in oven at 360o C for two hours. Cool the sample to 105 oC and maintain at this temperature until weighing. Weigh the beaker with the ash in a draft-free environment to ±0.001 g.

where: Wb = weight of beaker,

Wbs = weight of beaker plus soil before ashing,

Wba = weight of beaker plus ashed soil.

A.4. Soil Effective Cation Exchange Capacity

a) Determination of the exchangeable cations

Weigh 10 g of soil sample into a 100 mL polyethylene cup and add 50 mL of 1 N ammonium acetate ( NH4OAc) to the cup as a buffer solution to maintain the solution pH at 7.0. Shake the cup for 30 minutes. Filtrate the suspension with No. 40 filter paper (Whatman) and add 25 ml of 1 N NH4OAc again to wash the filter paper. Collect the filtrate and determine the K, Ca and Mg concentrations by atomic absorption spectrophotometer.

b) Determination of exchangeable acidity

Weigh 10 g of soil sample into a 125 mL Erlenmeyer flask, add 25 ml of 1 N KCl solution and mix well. Filtrate the suspension into a 300 mL Erlenmeyer flask. Add 4 drops of phenolphthalein indicator to the KCl solution. Titrate the KCl solution with the standard 0.01 N NaOH. At the end point of titration, record the volume of NaOH used. Get the exchangeable acidity in (meq/100g).

c) Effective cation exchangeable capacity (ECEC)

The sum of the concentrations of exchangeable K, Ca, Mg and the exchangeable acidity is the effective cation exchangeable capacity (ECEC).

A.5. Moisture Content

Measure the empty aluminum plate and record the weight first. Weight 1 g of soil on the aluminum plate. Measure and record the weight of plate with soil and record it. Put the soil sample in oven at 105 oC for 24 hours to get rid of soil moisture. Take these samples from the oven to the desiccator and for cool. Measure the weight of the dried soil.

The moisture content is for calculated as the following:

where: M(%) = moisture content, percentage by weight

Wwet soil = weight of original soil sample + aluminum plate

Wdry soil = weight of the ashed soil + aluminum plate

Wplate = weight of the aluminum plate

A.6. Specific Surface Area

The dye adsorption method (Smith and Coachley, 1983) was selected to determine the specific surface area of siols in this study. A commercially available dye, coccine acid red #18 (Aldrich Chemical Company, Inc.), was utilized as an adsorbate. This dye has a molecular weight of 604.48 and a flat molecular area of 196 . Its structure is shown in the following figure.

A monolayer coverage is assumed for this dye adsorption onto soil surface. The experimental procedures for specific surface area measurement were as follows:

strength if necessary.

c) Measure the suspended solids (SS) concentration .

d) Distribute 100 (or 50) mL soil sample to a series of 125 mL plastic bottles.

e) Add different amounts of stock dye solution into these bottles. The following initial dye concentration are suggested:
1x10-6, 2.5x10-6, 5x10-6, 7.5x10-6, 1x10-5, 1.25x10-5 M.

f) Shake the bottles in a shaker for 30 minutes to achieve equilibrium.

g) Centrifugate each mixture at 15,000 rpm (550g) for 10 minutes to separate the soil from supernatant.

h) Prepare a series of standard stock solution with known concentrations of coccine dye for the purpose of calibration.

1. i) Read and record the absorbance of the standard solutions and the sample supernatant
2. by colorimetric method using a visible spectrophotometer (Hach model DR/2000, Hach
3. Co., Loveland CO) at a wavelength of 505 nm.

k) Calculate the maximum dye adsorption density, using a multilayer adsorption equation.

l) Compute the surface area by the following equation:

where: S is the specific surface area of the soil (m2/g);

is the maximum monolayer dye adsorption density (mole/g);

N is the Avogadro's number (6.023x1023 molecules/mole);

A is the area occupied by a single dye molecule (m2/molecule).

The multilayer adsorption model developed by Wang and Huang (1997) can be expressed as:

where: = overall dye uptake density (mole/g-SS)

= monolayer uptake density (mole/g-SS)

K1 = constant related to the adsorption energy for binding to the particle surface (M-1)

K2 = constant related to the adsorption energy for multilayer adsorption (M-1)

From the experimental data of the - C relationship, the constants K1, K2, as well as can be obtained by a nonlinear regression method.

A.7. pHZPC

Take the soil samples from the containers, dry at 105 oC, grind and then sieve through a mesh No.100 (150 µm).

For each sample, prepare a solution of 0.1 g/L of the pretreated soil in ionic strength of 0.05 M NaClO4. The zeta potential was measured with a zetameter (Laser Zee model 500) as a function of pH values ranging from 2 to 9. Plot the z values vs. pH and then the pHZPC is obtained at the pH of zero zeta potential

A.8. Hydraulic Conductivity and Hydraulic Permeability

A constant-head permeameter was used to measure hydraulic conductiveties as shown in the below figure. Water entered the medium cylinder from the bottom and was collected as overflow after passing upward through the soils.

From Darcy's law it follows that the hydraulic conductivity can be obtained from:

A.8.1

where V = flow volume in time t

A, L and h are shown in figure.

Hydraulic Permeablity k can be caculated by the below equation

A.8.2

where K = hydraulic conductivity

µ = dynamic viscosity

= the fluid density

g = acceleration of gravity

The qualifitative analysis of organic compounds in soils was conducted by mixing 2 g soil sample with 2 mL 1N H2SO4 and 8 mL hexane in a glass tube. The mixture was shaked for 2 hours. After shaking, centrifuge the mixture at 10,000 rpm for 20 minutes and get the supernatant analyzied by GC/MASS.

A.10. Heavy Metals in Soils

The experimental procedures for the fractionation of heavy metals in the soil samples were the same as described by Oake et al. (1984) and Rudd et al. (1988). The method consists of using sequential extraction with a series of reagents and dividing the metals present into fractions extracted by potassium nitrate (KNO3), potassium fluoride (KF), sodium pyrophosphate (Na4P2O7), sodium ethylenediaminetetracetic acid (Na2EDTA), and nitric acid (HNO3). These fractions broadly represent the exchangeable, sorbed, organic, carbonate and sulfide forms of heavy metals associated with the soil solid, respectively. The procedures are presented below:

a) Weigh 0.3 g dry soil, add 15 ml of 1 M KNO3 and shake for 16 hours in a mechanical shaker.

b) After shaking, centrifuge the mixture at 10,000 rpm for 20 minutes.

c) Remove the supernatant, filter through 0.45 µm membrane and retain the solution for heavy metal analysis.

d) Repeat steps a) to c) using the following extractants: 25 mL of 0.5 M KF, 0.1 M
Na4P2O7, 0.1 M N a2EDTA, and 15 mL of 6 M HNO3

e) Analyze the samples for heavy metals content using atomic absorption spectrophotometry method.

B. Electro-Osmosis Experiments

B.1. Contaminant Analysis in the Soil System

a) Phenol

Around 1 to 2 g (± 0.001 g) of soil samples containing phenol were extracted with 5 mL of HNO3 (1 M). The suspension was filtered through 0.45 µm membrane filter (Supor-450, Millipore Co., Bedford, MA) and the filtrate was analyzed using a UV-visible spectrophotometer (Hitachi Perkin-Elmer model 139, Tokyo, Japan) at wavelength of 271 nm.

b) Mono-Chlorophenols

The mono-chlorophenol compounds in the soil system were extracted by adding 2 mL of HNO3 (1M) and 3 mL of hexane to approximately 1 g to 2 g (± 0.001 g) of soil sample. The mixtures were then shaken at room temperature for 48 hours. After this process, the hexane phase was separated and subjected to gas chromatography analysis. A gas chromatograph equipped with electron capture detector (GC-ECD; Hewlett-Packard model 5890 series II) was employed for the determination of the phenolic compounds in the organic phase. The GC conditions were as follows:

- Column: DB-210 (50% trifluoropropyl, 50% methyl) 30 m x 0.25 mm internal diameter, 0.5 mm film thickness (J & W Scientific).

- Temperatures: Injection port 200 ^oC , Detector 225 ^oC, Oven initial 100 ^oC, rate 0 ^oC /min, final 100 ^oC

- Carrier gas: 90% argon/10% methane

-Column head pressure 12 psi

- Injection volume: 1 µL

- Run time: 10 min

All the determinations of the contaminant concentration in the soil were executed in duplicates. Previous studies demonstrated that the extraction method provided recovery efficiencies of more than 90 %. Simultaneously, a calibration curve with known concentrations of the correspondent phenolic compound was prepared and the statistical method of linear regression was used to fit the G.C. signals as a function of concentration and determine the contaminant concentrations in samples.

B.2. Contaminant Analysis in Water Solution

a). Phenol

Water samples containing phenol were filtered through 0.45 µm membrane filter (Supor-450, Millipore Co., Bedford, MA) and direct analysed using an UV-visible spectrophotometer at wavelength of 271 nm similarly as described previously. Dilutions were performed when necessary.

b). Mono-Chlorophenols

Liquid extraction and GC-ECD were employed to the analysis of the phenolic compounds in water solution. To 1 mL of the solution containing the target compound, 5 mL of hexane was added. The mixture was shaken for 5 minutes and the organic phase was then ready for the GC-ECD analysis. The GC conditions were the same as described in the previous section. The analysis of the phenolic compounds in water were also done in duplicates using a pre-prepared calibration curve.

C. Electro-Fenton Experiments

C.1. Hydrogen Peroxide

The hydrogen peroxide concentration was measured by a colorimetric method using a Hach DR/2000 direct reading spectrophotometer. The experimental procedures for the hydrogen peroxide measurement were as follows:

a). Mix 0.504 g titanium sulfate [ Ti(SO4)2 ] and 1.6 g ammonium sulfate [ (NH4)2SO4 ] in 50 mL concentrated sulfuric acid.

b). Heat the solution on a hot plate at 100 ^oC until the titanium salt is completely dissolved.

c). Dilute the heated solution to 1000 mL with distilled water.

d). Mix 9 mL titanium reagent with 1 mL aliquot of the sample containing hydrogen peroxide in a test tube.

e). Heat the test tube in a water bath at a constant temperature (57~63 ^oC) for 10 minutes.

f). Cool the sample down back to room temperature before it is analyzed in the spectrophotometer.