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LIBRARY
Michigan State ‘
Unlverslty

 

 

 

 

This is to certify that the

thesis entitled

AN EVALUATION OF ADVANCED OXIDATION PROCESSES
FOR THE TREATMENT OF
CHLORINATED BENZENE IN AQUEOUS SYSTEMS

presented by

Minmin Shu

has been accepted towards fulﬁllment
of the requirements for

M. S. degree in Environmental
Engineering

 

 

,f ‘.4

Iéjor professor

/

Date Apr“ 6, 1995

0-7639 MS U is an Afﬁrmative Action/Equal Opportunity Institution

PLACE ll RETURN BOX to removothb checkout from your record.
TO AVOID FINES Mom on or before date duo.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

MSU I. An Afﬁrmative ActIoNEqual Opportunity lnotltutlon
Wain-9.1

AN EVALUATION OF ADVANCED OXIDATION PROCESSES
FOR THE TREATMENT OF
CHLORINATED BENZENE IN AQUEOUS SYSTEMS

By
Minmin Shu

A THESIS

Submitted to
Michigan State University
in partial ﬁilﬁllment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Civil and Environmental Engineering

1995

ABSTRACT

An Evaluation of Advanced Oxidation Processes
for the Treatment of
Chlorinated Benzene in Aqueous Systems

By

Minmin Shu

The purpose of this study is to improve the understanding of the potential of
using advanced oxidation processes (AOPs) for the oxidation of chlorinated benzenes in
aqueous systems.

The efficiency of oxidation of 11,2-dichlorobenzene using ozone, ozone/UV,
ozone/peroxide, and ozone/UV/peroxide treatment was evaluated. The effect of pH,
humic acid and bicarbonate was investigated. Pentanoic acid was used as an OH radical
probe to estimate the steady state hydroxyl radical concentration and thus, compare the
processes studied in terms of their efﬁciency to generate hydroxyl radicals.

The results indicate that the highest removal rate of 1,2 -dichlorobenzene can be
obtained using the ozone/peroxide process in the optimum pH region (pH 6.8-8.5). There
is no signiﬁcant effect on treatment efﬁciency by humic acid and bicarbonate at
concentrations of 2 mg/l and 2 mM, respectively. The results of experiments
investigating the oxidation of pentanoic acid, the OH radical probe, supported the
hypothesis that the highest treatment eﬁicicncy of AOPs is obtained with the system that

generates the greatest concentration of OH radicals.

Dedicated to my family members and my friends for their support,
encouragement and understanding

iii

ACKNOWLEDGMENTS

I would like to thank my advisors Dr. Susan Masten and Dr. Simon Davies for
their encouragement, support and professional guidance throughout my graduate study.
Also I thank Dr. Craig Criddle for serving on my committee and for his concern with this
research.

I wish to extend my appreciation to all people who provided me with guidance
and assistance. In particular, I like to thank M. K. Chiang for the many hours of
assistance in the laboratory.

Funding for this research was provided by the Ofﬁce of Research and
Development, US. Environmental Protection Agency under Grant R-816922-01-O and by
the Great Lakes and Mid-Atlantic Hazardous Substance Research Center under grant R-
8157 5-01-0. This work was also ﬁnancially supported by Dow Chemical Company
through the Environmental Enhancement Grant. The content of this publication does not

necessarily represent the views of those agencies.

iv

TABLE OF CONTENTS

Page
LIST OF TABLES ............................................................................................ vii
LIST OF FIGURES ........................................................................................... viii
LIST OF SYMBOLS AND ABBREVIATORS ................................................. ix
1. INTRODUCTION ........................................................................................ 1
[-1 General ....................................................................................... I
I-2 Objectives of this Study ................................................................. 2
LB The Formation of OH Radicals in AOPs ........................................ 2
11. MATERIALS AND METHODS ................................................................. 8
11-1 Materials ........................................................................................ 8
General ....................................................................................... 8
Photochemical Reactor ............................................................... 8
UV Light .................................................................................... 8
Ozone Generation and Ozone Solution Preparation .................... 9
1, 2 -Dichlorobenzene Solution Preparation ............................... 9
Pentanoic Acid Solution Preparation .......................................... 9
Humic Acid Solution preparation ............................................... 9
HzOz Solution Preparation .......................................................... 12
Bicarbonate Solution preparation ................................................ 12
l, 3, 5 -Trichlorobenzene Stock Solution .................................... 12
11-2 Analytical Methods ....................................................................... 12
Ozone Analysis ........................................................................... 12
Analysis of 1, 2-Dichlorobenzene ............................................... 13
Analysis of Pentanoic Acid: Esteriﬁcation of Acid ..................... 13
using BF: in Methanol ..................................................... 13
Effluent I-IzOz Analysis: Flow Injection Analysis ......................... 13
11-3 Experimental Approach ................................................................. 16
Experimental Condition Control .................................................. 16
Sampling ..................................................................................... 17
Experimental Procedure .............................................................. 17

III. RESULTS ................................................................................................
III-1 OH Radical Probe Selection ........................................................
III-2 The Effect of pH on Dichlorobenzene Degradation ......................
III-3 The Effect of Humic Acid and Bicarbonate
on Ozone/UV Treatment ................................................

III-4 OH Radical Probe— The Degradation of
Pentanoic Acid ..............................................................
III-5 Overall Reaction Rate Constant ..................................................

IV. DISCUSSION .........................................................................................
IV-l Optimum Condition ....................................................................
IV-2 OH Radical Scavenger and Reaction Competition ......................
V. CONCLUSIONS .....................................................................................
VI. FURTHER WORKS ................................................................................
LIST OF REFERENCE ...................................................................................

APPENDIXES ................................................................................................

vi

19
19
22

22

27
33

37
37
39
41
42
43

45

LIST OF TABLES

Table 2-1. Headspace GC and Sampler Operation Conditions for DCB and

TCB Analysis ......................................................................................... 14
Table 2-2. Headspace GC and Sampler Operation Conditions for Pentanoic

Acid Analysis ......................................................................................... 15
Table 3-1 Effect of pH on TCB, DCB and Pentanoic A Degradation .................... 34
Table 3-2 Effect of Humic Acid and Bicarbonate on TCB, DCB and

Pentanoic Acid Degradation ................................................................... 35
Table 4-1 Estimated Steady State OH Radical Concentration ............................... 38

vii

Figure 1-1.
Figure 1-2.
Figure 2-1.
Figure 2-2.
Figure 3-1.

Figure 3-2.

Figure 3-3

Figure 3-4.

Figure 3-5.

Figure 3-6.

Figure 3-7.

Figure 3-8.

Figure 3-9.

Figure 3-10.

Figure 3-11.

LIST OF FIGURES

The Decomposition of Ozone in Pure Water ......................................... 3

The Decomposition of Ozone in Waters Containing Reactant Species. 4

System Conﬁguration ........................................................................... 10
The Photochemical Reactor Used in this Research ............................... 11
UVN is Spectrum for Pentanoic Acid (pH=2.5) ................................... 20
Variation of the Effluent Pentanoic Acid Concentration

with RetentionTime .............................................................................. 21
Effect of pH on various Treatment Processes ....................................... 23
Comparison of Treatment Efﬁciency at Optimum Region ..................... 24

Efﬁciency of O 3/UV for the Oxidation of DCB and TCB in the
Presence of Humic Acid at Optimum pH Region (pH=7.0-8.5) ........... 25

Efﬁciency of O 3/UV for the Oxidation of DCB and TCB in
the Presence of Bicarbonate ................................................................. 26

Comparison of DCB and OH Radical Probe Degradation Using Ozone
Treatment ............................................................................................. 27

Comparison of DCB and OH Radical Probe Degradation

Using Ozone/UV Treatment ................................................................. 28
Effect of pH on the Oxidation of DCB and OH Radical
Probe Using Ozone/Hydrogen Peroxide Treatment .............................. 30
Effect of Humic Acid and bicarbonate on DCB and OH
Radical Probe Using Ozone/UV Treatment .......................................... 31
Ozone Treatment of DCB and Pentanoic Acid at pH=6.9O ................... 32

viii

AOPs
DCB
TCB
PA
[DCB]0
[DCB]
['OH]

kl

LIST OF SYMBOLS AND ABBREVIATORS

Advanced oxidation processes

1, 2-dichlorobenzence

1, 3, 5-tn'chlorobenzene

Pentanoic Acid

Initial steady DCB concentration

DCB concentration in the reactor

Hydroxyl radical concentration

The reaction rate constant for the particular oxidant i
The conditional rate constant for the degradation of DCB
The light intensity

The quantum efficiency

The hydraulic retention time

ix

I. INTRODUCTION

[-1 General

The chlorobenzenes which are widely used in chemical industries, have been
associated with groundwater and surface water contamination. They are potentially
toxic and can impart a foul taste and odor to drinking water (Anselme, et al. , 1987).
The concern for maintaining the quality of water supplies has led to the development of
numerous remediation techniques. Advanced oxidation process is one of the several
environmentally sound remediation techniques that will destroy the pollutant instead of
merely transferring it from one phase to another.

Advanced oxidation processes (AOPs) are deﬁned as those techniques that
involve the generation of highly reactive radical intermediates particularly the hydroxyl
radical (OH) at ambient temperature (Glaze and Kang, 1990). Ozone is combined with
hydrogen peroxide and /or ultraviolet radiation in AOPs. The efﬁciency of advanced
oxidation processes depends on the oxidant dose, pH, retention time, UV light
intensity, the nature of the organic compound, and the concentration of scavenging,
promoting, or initiating solutes involved (Masten and Davies, 1993).

Previous research with chlorinated compounds by Masten and Davies (1992),
and Galbraith (1993) has shown that the high removal rate of chlorinated compounds
occurs at those conditions where ozone degrades to form secondary oxidants, because
peroxide and ozone are themselves relatively unreactive with the target compounds
and are selective oxidants for only a few classes of organic compounds that contain

electron donating groups.

In the previous studies certain compounds were used as kinetic probe to
measure the relative reactivity of AOPs. The work conducted by Yao points out that
the hydroxyl radical (H0) is the dominant oxidant in all AOPs (Y ao, et a1. , 1992).

[-2. Objectives of this Study

The purpose of this research is to assess the potential of AOPs for the oxidation
of dichlorobenzene and to improve our understanding of the mechanism by which
AOPs decompose target organic chemicals in aqueous systems. 1, 2- Dichlorobenzene
was chosen as the target compound because (1) it is reactive with both ozone and OH
radicals, (2) it is semi- volatile, (3) it is on the EPA list of priority pollutants and
(4) it is resistant to biological treatment (Kirk et a1. , 1989). Pentanoic acid anion was
chosen as OH radical probe because it is analytically detectable at low concentrations,
it produces no chloride ions upon oxidation, it does not absorb light at wavelengths
above 240 run, it reacts with OH radical, and it does not react appreciably with ozone
or such secondary radicals as H02- and ROz-(Yao et al., 1992).

Experiments were conducted to:

0 Select and evaluate compounds to be OH radical probe;

0 Determine the effect of pH on the efﬁciency of the advanced oxidation treatment

processes studied;
0 Compare the efﬁciencies of advanced oxidation treatment processes in the

presence and absence of humic acid or bicarbonate.

L3. The Formation of OH Radicals in AOPs
In water ozone decomposes rapidly to form more reactive secondary oxidants,
such as ~OH, 0'2, and H02' . The mechanism by which ozone decomposes in

water has been extensively studied. Figure 1-1 illustrates the reactions of ozone in

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The oxidants that can oxidize organic chemicals are indicated in the boxes.
(Adpapted from Staehelin and Hoigné, 1985)

Figure 1-1
The Decomposition of Ozone in Pure Water

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

:1:
.53.

 

 

C S'oxid. D

M : a micropollutant which reacts directly with ozone;

I : an initiator which reacts with ozone to initiate the chain reaction mechanism;

8 : a scavenger which reacts with OH radicals to terminate the chain reaction;

P : a promoter which reacts with OH radicals to form a radical species which result in chain propagation.

Oxidant species are indicated in boxes. ( Adapted from Staehelin and Hoigne’, 1985)

I Figure 1-2
The Decomposition of Ozone in Waters Containing Reactant Species

pure water (Staehelin and Hoigné, 1985). Hydroxide ions initiate ozone
decomposition to form superoxide anions which react via a cyclic mechanism to form a
hydroxyl radical. Figure 1-2 shows the complex mechanisms by which ozone
decomposes in waters containing species such as humic acid, carbonate/ bicarbonate,
iron, carboxylic acid and primary alcohols (Staehelin and Hoigné, 1985). These
species can act either as initiators, promoters or inhibitors of free radical reactions.
Initiation reactions involve superoxide ion (0,“) formation from ozone while
promoters are capable of regenerating this ion. Inhibitors decrease the amount of
superoxide formed resulting in a decrease in the rate of hydroxyl radical formation.
Scavengers directly consume hydroxyl radicals.
Previous studies indicate that there are three ways to initiate ozone
decomposition to produce OH radicals in the AOP system (Hoigné and Bader, 1987).
1) By increasing the hydroxide ion concentration ( i.e. , increasing the pH
value), more hydroxide ions will be available to react with 03, thus
increasing the rate of OH radical formation. Although there has been much
dispute as to the order of the reaction of ozone with CH ions, it is widely
accepted that the rate of ozone decomposition is proportional to the
concentration of OH' ion.
M = -k[031"[0H1b (1-1)
dt
where a, b >0
In an open system, where bicarbonate and/or carbonate is present, as the pH
above 6 there are fewer -OH radicals to attack the target compound due to

bicarbonate and/or carbonate scavenging.

2)

3)

HCOs’ HCOa'
N + OH = N + no (1-2)

COa' COa' ‘

Hydrogen peroxide dissociates to form hydroperoxide ions, which initiate
ozone decomposition to produce superoxide anions, which ultimately
produce OH radicals through a chain reaction. Unfortunately, the
ozone/peroxide reaction products consume OH radicals via a competition

reaction if the hydrogen peroxide concentration is too high.

[-1202 + m0» HOz' + H30“ (13)
Oa+HOz‘—) -OH +02' +02 (14)
HOz' + -OH—> HOz' (1-5)
03 + -OH -> H02 (15)
HOz' + Hoz' —> HzOz + 02 (1-7)
H02'+ on —> H2 0 + 02 (1-8)
2(-OH) -)HzOz (1-9)
-OH + 02' —> OH' + 02 (1-10)

Ultraviolet light initiates ozone decomposition to produce hydrogen peroxide
03+ hv + H20 —-> H202 (1-11)
The hydrogen peroxide formed then either react with ozone to produce OH
radicals (Eq.1-3 , 1-4) or undergo photolysis to generate the hydroxyl
radical
HzOz + hv —) 2 (OH) (1-12)

Hoigné (1987) indicated that ozone decomposition initiated by either OH' or
HzOz/ H02" results in similar yield of OH radical production. UV light (255 nm)
converts aqueous ozone primarily into OH radicals only at higher pH values (above 7
or 8, depending on the system), where the rate of reaction between H202/ H02‘ and
03 proceeds faster than the rate in low pH range, or at lower light intensities, where
ozone photolyzes more slowly, allowing the H202/ H02” initiated decomposition of

ozone to occur.

II. MATERIALS AND METHODS

II-l Materials
General

Figure 2-1 shows the system conﬁguration used in this study. The system
contains three major parts: 1) the aqueous ozone generation and contacting system;
2) the central reactor; 3) the monitoring system. Experimental conditions were
controlled by up to nine pumps.
PhatochemicaLReactur

A Supermix photochemical reactor (Model 7868, Ace Glass Inc. , NJ) was used
in this study (Figure 2—1). This reactor has two chambers with a total working
volume of 250 mL . In the smaller chamber an impeller is rotated using a stirrer motor
operated (Model 13583, Ace Glass, Inc. , NJ) at 425 rpm to provide efﬁcient mixing
by recirculating the liquid in the reactor between the two chambers. A quartz
immersion well is located in the main chamber of the reactor to house a low pressure
mercury lamp.
Lilliaht

A low pressure immersion lamp having a principal wavelength output 254 nm
was housed in a quartz immersion well in the reactor. Using a potassium ferrioxalate
actinometer developed by Murov (197 3), Galbraith (1993) determined the light
intensity of the lamp emitted to the aqueous solution to be 1.21 watts. It is 1.94
watts below its list output power value. This indicates UV absorption efﬁciency in the

reactor aqueous phase is 38 %.

C] Li . l O S l . P .
A Polymetrics ozone generator (Model T-408, San Jose, CA) was fed with pure

dried oxygen to produce gaseous ozone (approximately 3 % v/v ozone in oxygen).
The dielectric in the ozone generator was cooled by using of a circulating refrigerated
water bath system maintained at 10 °C. Aqueous ozone solutions were prepared by
continuously bubbling gaseous ozone into a three liter round -bottom ﬂask which was
continuously replenished with deionized water that had been acidiﬁed to pH 2 with
phosphoric acid. The solution was continuously mixed using a magnetic stirrer.

25 pl 99 % spectrophotometric grade 1, 2—dichlorobenzene (99 %
spectrophotometric grade, Aldrich, Chem. Co. , WI) was mixed with 6 L deionized
water for three days in a sealed glass ﬂask. This solution was stored in the dark and at
room temperature for a maximum of 10 days.

P . E . 1 CE I] S l . E .

A solution of sodium pentanate (0.1 M) was prepared by dissolving 0.1 M
pentanoic acid (99%, Sagam, MO.) and 0.1M NaOH in l L of deionized water. The
stock solution was stored in the dark, and at room temperature. It was diluted to the
appropriate concentration level before it was fed into the reactor.

H 'E’IIHEISI' P .

Humic acid (Sodium salt, Aldrich, Chem. Co. , WI) was dissolved in deionized
water which had been acidiﬁed to pH 2 with phosphoric acid. The suspension was
passed through glass ﬁber ﬁlters. Stock solutions were stored in the dark and at 4 °C

for up to 3 weeks.

10

Ozone
Generator

 

 

Pump

 

 

 

 

I'_—_—"——"———

t

PA Solution Bottle

5 a -
"-1— -‘www ‘I-' urn-w. -| -I at ,r ' ‘ |

C8 Solution
Bottle

L

 

 

 

 

 

 

 

 

 

 

 

 

 

   
 

 

 

 

 

 

 

 

 

   

 

F 1
Cooling Photo-
System —" chemical ‘—
Reactor
_ J
pH=2
~-....- Other
Oxygen Tank Chemical
Feeding
Flow Pumps
Injection
Analysis
_ __ .. Gas Line
__ Cooling Water Sampling
Pump Waste

Main Stream

Figure 2-1 System Conﬁguration

ll

FLEXIBLE SHAFT
CABLE

      

SAMPLE LINE ro
spscmomoromrzraa

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

\ i stoma
INPUT LINE
COOLING WATER
Poms
WATER coon-:0
cuss BEARING
corrrmuous FLOW
OUTLET roar
WELLER BLADE
SHAH
FLOW aacmcurmon
omecnon L00?
WELLER BLADES
QUAKI'Z
measron war.

 

 

 

. (Adapted from Masten and Davies, 1992)
Figure 2-2 The Photochemical Reactor Used in this Research

12

H O S l . P .

Hydrogen peroxide (30% solution, Sigma, MO. ) was diluted to 0.01 M and
standardized by direct UV absorption (6 =40.0 M"cm'l at k=240 nm). This standard
solution was diluted to an appropriate concentration level based on the experimental
requirement.
13' l S l . P .

Sodium bicarbonate (Analytical reagent, J .T. Baker Inc. , NJ) was dissolved in
deiomzed' water at the appropriate concentration level.
135$.“ l 5151'

1, 3, 5—Trichlorobenzene (99%, Aldrich, Chem. Co., WI) was used as internal
standard for headspace GC analysis, A stock standard solution (lOOOmg/L) was
prepared by dissolving trichlorobenzene in methanol.

II-2 Analytical Methods
W

The aqueous ozone concentration in the inlet stream to the reactor was
determined using a UV/vis spectrophotometer ( Shimadzu Scientiﬁc Instruments, Inc. ,
Model UV-1201, Columbia, MD) The solution was pumped through a ﬂow cell to
continuously monitor the absorbance at wavelength of 258 nm. An extinction
coefﬁcient of 3000 M'1 cm'1 (Galbraith, et a1. , 1992) was used to convert absorbance
units to concentration. A small portion of the inlet stream to the reactor was
continuously drawn through the ﬂow cell by a pump.

The concentration of ozone in the reactor was determined by the indigo blue
method (Bader et a1. , 1982) to avoid the possibility of interfering compounds

absorbing light at 258 nm. The samples were collected from the reactor outlet into

l3

volumetric ﬂasks containing known amounts of indigo blue solution. Calibration
curves for the determination of ozone concentration were made daily.

1, 2 -Dichlorobenzene and 1, 3, 5 -trichlorobenzene were determined by head-
space gas chromatography (Perkin Elmer, GC Model, Autosystem, Sampler Model :
HS-40, Norwalk, CT) equipped with a ﬂame ionization detector (FID) and a 30
meter, 0.53 mm ID silica glass capillary column (Perkin Elmer, Model 624,
Norwalk, CT). An internal standard was used in all samples and in calibration and
check standards. GC and sampler operating parameters are provided in Table 2-1.
H. ‘. '-. .u .3 '.- .3. .. or 0 a '. ,u: '11-....

Pentanoic acid concentrations were determined in water by a method that
involves the esteriﬁcation of the acid using BF: in methanol. The ester is then
quantiﬁed using head-space gas chromatography with an autosampler (Perkin Elmer,
GC Model : Autosystem, Sampler Model : HS-40, Norwalk, CT) equipped with a
ﬂame ionization detector (FID) and a 50 meter, 0.53 mm ID silica glass capillary
column (Perkin Elmer, Model 624, Norwalk, CT). This method gives good
linearity from 90 ppb to 5.5 ppm. The GC and sampler operating parameters are
provided in Table 2-2. The details of this method are presented in Appendix 1.

BED “051.131 1"!l'

Flow injection analysis is based on the colorimetric titration of a liquid sample,
that has been injected into a non-segmented, continuously moving carrier stream of a
suitable liquid. The injected sample mixes with the carrier liquid to form a zone of
colored liquid, which is then transported through a ﬂow cell that is positioned in the
spectrophotometer . The absorbance of the stream is continuously monitored.

The efﬂuent hydrogen peroxide concentration was determined by ﬂow injection
analysis (FIA) (Galbraith, 1993) with a UV/vis spectrophotometer at a wavelength of

14

Table 2-1
Headspace GC and Sampler Operation Conditions
for DCB and TCB Analysis
E] I . . D m:
Temperature 250 °C
I . .
Temperature 250 °C
Pressure 20 psi
Column DB-624, 30m x 0.53mm ID
5 C C l' .
Oven
Equilibration. Time 1.0 min
Temperature 110 °C
Program Time 12 min
Carrier Gass Helium (high purity)
Pressure 20 psi
5 l C I .
Equilibration Time 45 min
Equili. Temperature 90 °C
Transfer line and 100 °C
NeedleTemp.
Carrier Gas Helium (high purity)
Pressure Time 2.0 min

Injection Time 0.5 min

15

Table 2-2
Headspace GC Operation Conditions
for Pentanoic Acid Analysis
ElamalcnizaticnﬂemmLLEIDl
Temperature 250 °C
I . .
Temperature 250 °C
Pressure 20 psi
Column DB—624, 50m x 0.53mm ID
W
Oven
Equilibration Time 1.0 min
Initial Temperature 70 °C
Holding Time 18 min
Program Rate 40 °C/ min
Final Temperature 230 °C
Hold Time 17 min
Carrier Gass Helium (high purity)
Pressure 20 psi
5 l C l' .
Equilibration Time 20 min
Equilibration Temperature 70 °C
Transfer Line and Needle 100 °C
Temp.
Carrier Gas Helium (high purity)
Pressure Time 2.0 min
Injection Time 0.5 min

16

551 nm (Shimadzu Scientiﬁc Instrument, Inc., Columbia, MD) using a modiﬁcation
of the peroxidase N,N-diethyl-p-phenylenediamine (DPD) method (Bader et a1. , 1988).
This method is based upon the hydrogen peroxide in the sample oxidizing the
peroxidase in the carrier stream. The oxidized peroxidase then oxidizes the DPD to
the radical cation DPD + which has a relatively stable red color that can been
monitored by a UV/vis spectrophotometer. The FIA system conﬁguration is shown in
Appendix 2.

11-3 Experimental Approach
E . l C l' . C l

The hydraulic retention times in the reactor were controlled by the inﬂuent
ﬂow rates of ozone solution and target compound solution which were pumped by two
piston pumps (Fluid Metering Inc. , Model RHSY,Oyster Bay, NY) at an equal ﬂow
rates of 12.5 ml/min.

The pH value in the reactor were controlled by a syringe pump ( RAZEL
Scientiﬁc Instruments, Model A-99.ER Conn.) which pumped a NaOH solution
(0.5 or 1.0 N) into reactor at the speed required to achieve the desired pH values.

The aqueous ozone solution was maintained at a constant level in the contactor
by a peristaltic pump (Cole Parmer, Model 7520-35, Niles, IL) which was used to
continuously replenish the phosphoric acid solution in the contactor while the aqueous
ozone solution was pumped out at a same ﬂow rate.

Inﬂuent humic acid, bicarbonate and hydrogen peroxide solutions were pumped
into the reactor by syringe pumps (RAZEL Scientiﬁc Instruments, Model A.Z
Conn.) at the appropriate speeds.

17

Sampling

The DCB, PA samples were collected at the reactor effluent exit. The aliquots
were added to 150 uL sodium nitrite solution ( 0.9 M ) contained in 20 mL head space
GC vials. Efﬂuent hydrogen peroxide samples were collected into a test tube at the
reactor efﬂuent exit, then immediately bubbled with nitrogen gas to purge all ozone
before the sample was injected into the FIA system.

ExperimentaLPmcedurc

Nitrobenzene, l-chlorobutane, propionic acid (salt), butyric acid (salt) and
pentanoic acid (salt) were examined as OH radical probes. The choice of an
appropriate probe were made upon evaluating (1) the solubility, volatility and
reactivity of these compounds with ozone; (2) the results of GC analysis to determine
if these compounds interfered with the analysis of DCB; (3) the results of experiments
to determine a suitable analytical method for the probe compounds. PA was chosen as
the probe (see Section III-1).

Experiments were conducted to investigate the effects of pH, humic acid and
bicarbonate on the efﬁciency of AOPs to oxidize DCB and PA. A 10 min retention
time was used. Before turning on the ozone generator, the solutions containing the
target compound and an acidiﬁed solution (from ozone contactor ) were pumped into
reactor. Based upon the results of tracer mixing study, after six retention times the
system reached steady state (Appendix 3). As such, after one hour, the initial
samples were obtained. The efﬂuent concentrations determined during various
treatments were compared to this initial concentration to determine the treatment
efﬁciency of each process. All of the DCB and PA degradation results were compared
with 1,3, 5-trichlorobenzene (TCB) degradation results obtained by Galbraith (1993).

PA and DCB were not oxidized in the same solution. However, as we wished

to compare the results obtained with DCB with that of PA, it was mcessary to control

18

the experimental system so that the same experimental conditions could be used for
DCB and PA. As such, either PA or DCB could be pumped into the experimental
system by simply turning a swtching valve.

The Ozone/UV process was used as a cleaning process for the system after
each experiment, detergent/water washing, followed by organic solvent cleaning

were used when necessary.

III. RESULTS

III-1 OOH Radical Probe Selection

Based on the examination of the physical and chemical characteristics of the
probe chemicals, the results of our analytical method development, pentatonic acid
(salt) was found to be the most appropriate OH radical probe among the ﬁve examined
compounds (pentanoic acid (salt), propionic acid (salt), butyric acid (salt),
nitrobenzene and l-chlorobutane) examined.

Pentanoic acid (salt) has a high water solubility and dissolves in water instantly,
it is nonvolatile and does not have UV/vis spectum above 240 nm (Fig 3-1). It
produces no chloride ions upon oxidation, it reacts with OH radical and does not react
appreciably with ozone (See Fig 3-2) or the secondary radicals such as HOz'or R02'

(Y a0, et al. 1992), and it is analytically detectable at low concentrations.

Propionic acid (salt) and butyric acid (salt) have similarly physical and chemical
characteristics as those of pentanoic acid (salt). Methanol was used in esteriﬁcation of
the acid in the headspace GC/FID analysis and coeluding peaks were the major
problem in propionic acid (salt) analysis. Coelution also resulted in a slight reduction
in the reproducibility of butyric acid (salt) measurement.

Nitrobenzene was analyzed using same GC program as DCB, and
reproducibility was excellent. This GC program was modiﬁed by decreasing the start
temperature to 49 °C for l-chlorobutane analysis, but both of these compounds were
ruled out as :

(1) N itrobenzene has a no negligible reactivity with ozone and functions as a
promoter of radical chain reactions by increasing the rate of formation of OH radical

(Akata et al., 1992).
19

20

.3 u we 22 5.2.555 .5. 5.58% 32>: 3 8am...—

 

Ihuzmqmaqs

 

 

332.5232 :3 c. Em newssm 2.»:2933

s. 21$:

1 33.-.... . D

W

 

3311113305315

 

 

Pentanoic Acid Cocentration (ppb)

3100

2200

1900

1600

1300

1000

 

l

 

21

 

 

T I I I I

5 IO 15 20 25

Retention Time (min)

Figure 3-2
Variation of the Effluent Pentanoic
Acid Concentration with
Retention Time

22

(2) 1- Chlorobutane may produce chloride ions upon oxidation.
(3) Three days are required to prepare solutions of nitrobenzene and

1- Chlorobutane.

111-2. The Effect of pH on Dichlorobenzene Degradation

Figure 3-3 shows the effect of pH on the efﬁciency of oxidation of DCB in
ozone, ozone /UV and ozone /H202 treatment processes. The percentage of DCB
remaining in the reactor efﬂuent is plotted against reactor pH for each treatment
process. For all of three processes, the decomposition of DCB occurred fastest at a
pH between 7.0 to 8.5 . The efﬁciencies of ozone and ozone/H202 treatment for the
oxidation of DCB increased with pH in the pH region below 7, whereas, the
efﬁciencies decreased slightly with increasing pH in the pH region above 9.
Ozone/UV treatment was relatively insensitive to changes in pH. Figure 3-4
illustrates the comparison of each treatment process efﬁciency at optimum pH region
(pH about 7.0 to 8.5). The results indicate that ozone/H202 is most efﬁciency
treatment process. This can also be observed from the overall reaction rate constants
(see Table 3-2). Similar results were observed with both DCB and TCB.

III-3 The Effect of Humic Acid and Bicarbonate on Ozone/UV Treatment

Figure 3-5 and Figure 3—6 illustrate the effect of humic acid and bicarbonate on
DCB degradation in the ozone/UV system. For all experimental conditions, greater
than 84 % degradation of DCB was obtained. The addition of humic acid (2 and 10
mg/l) and bicarbonate (2 and 10 mM) resulted in decreases in the extent of degradation
of DCB and TCB. However, the decrease in the efﬁciency of DCB oxidation is small

compared to that observed for TCB degradation with a bicarbonate concentration

% DCB Remaining ClCo

100

80

60

40

20

23

 

 

 

 

 

 

 

l
‘
\
\
\
. \
\\ - + " OZONE ONLY
\\ - . * - - oa/Uv
. \\ —*-— 03/1-1202
0 2 4 6 8 10 12 14
Reactor pI-I Value
Figure 3-3

Effect of pH on Various Treatment Processes

96 DCB and TCB Remaining C/Co

12

H
O

I

oo

24

 

 

 

E] DCB
I TCB

 

 

 

 

 

   

 

 

 

 

. .

.J ,7

." ;.,

.‘,,
.7.“ '.l '

. .7:-‘, .

r q“

. 4”"-
L L ‘I k”
W _ .34

.1. am
., V.
-‘ . of.

03 Only O3/UV O3/HZOZ O3/H202/UV

 

Treatment Type

Figure 34
Comparison of Treatment Efﬁciency at
Optimum pH Region (pH-7.0-8.5)

25

96 DCB
and TCB
Remaining
C/Co

 

Humic Acid Concentration

Figure 3-5
Efﬁciciency of Os/UV for the Oxidation
of DCB and TCB in the Presence of Humic Acid at
Optimum pH Region (pH-7.0-8.5)

 

El DCB D TCB

 

 

 

96 DCB
and TCB
Remaining
C/Co

 

 

 

  
 

‘ I

l

H
I TCB

[HCO3]=0
[HC03]=2mg/l
[HCO31—10mg/l

Bicarbonate Concentration

Figure 3-6
Efﬁciency of Ozone/UV for the Oxidation
of DCB and TCB in the Presence
of Bicarbonate

27

of 10 mM. At the lower scavenger concentrations (2 mg/l humic acid and 2 mM
bicarbonate), which are similar to that observed in natural waters, the extent of
degradation of DCB exceeded 94%. Similar results were observed for TCB
degradation, where at these concentrations the extent of TCB degradation excwded
92 %.

III-4 OH Radical Probe — The Degradation of Pentanoic Acid

As stated previously, pentanoic acid was used as the OH radical probe. The
extent of DCB degradation was compared to the extent of PA degraded (Fig. 3-7 to
Fig. 3-10). Experimental results showed that the extent of DCB degradation was
always greater than the extent of PA reaction over the pH region studied for all
treatment processes. In the low pH region (pH < 2.5), DCB may degrade by the
direct reaction of DCB with ozone. However, at pH value above 6.8, the OH
radical reaction is expected to be important (kOH=4.0 x 109 M‘s" for DCB, koﬂ=2.9 x
109 M‘s" for PA), (Haag and Yao, 1992). As the rate constant kon for DCB is only
0.33 times higher than that for PA, the relative concentrations become one
considerable factor for the removal rate of DCB or PA if they both present in the
system at the same time. Figure 3-10 shows that the percentage of DCB remaining
(100% XC/Co) increased from 36.04% to 69.19%, when the concentration ratio of
PA over DCB was increaseed from 0.125 to 1.0. The presence of humic acid or
bicarbonate had similar effects on degradation of PA and DCB.

% Probe Remaining C/Co

100

cc
O

ON
C

.5
O

N
O

 

28

 

 

 

 

 

 

 

 

 

 

 

 

 

[:3 OH Radical Probe
- (PA) - 100
—t—— DCB
‘l—'—‘
- \ ,- 80
O
Q
U
- ~ 60 E”
.5.
E
40 m
9
.\°
.. - 20
0
2.28 5.71 7.02 8.04 11.7
pH Value
Figure 3-7
Comparison of DCB and OH

Radical Probe Degradation Using
Ozone Treatment

% Probe Remaining C/Co

29

 

 

 

 

 

3o - - 30
_OHRadical
~ Probe(PA)
25 - - 25
——I— DCB
5
20 - - 20 a
an
15 - - 15 a
0
—‘ a:
m
10 1 - 10 8
.\°

5_ '\-\._.../ _.

2.32 5.65 6.69 8.48 l 1.3
pH Value

 

 

 

 

 

 

 

 

 

Figure 3-8
Comparison of DCB and PA Degradation Using
Ozone/UV Treatment

30

 

E3 OHRadicalProbe(PA) [JDCB I

 

 

Figure 3-9
Effect of Ph on the Oxidation of
DCB and OH Radical Probe Using
Ozone/Hydrogen Peroxide Treatment

96 Pentanoic Acid and DCB Remaining C/Co

70-

60-

50-

40-1

30-

20-

10-

 

31

 

 

 

 

 

 

 

 

/ I- [:1 OH Radical Probe (PA) I DCB

 

 

 

 

 

 

 

 

 

 

I

 

 

 

 

 

 

[HA]=10mg/l [HA]=2mg/l [HC03]=10mM [HCO3]=2mM
Concentration

Figure 3-10
Effect of Humic Acid and Bicarbonate
on the Oxidation of DCB and Pentanoic Acid
Using Ozone/UV Treatment

 

96 DCB Remaning (C/Co)

8

A
C

N
O

 

32

pH=6.9O

 

I I I I

0.2 0.4 0.6 0.8
Molar Concentration Ratio
(Pentanoic Acid / DCB)

Figure 3-1 1
Ozone Treatment of DCB and
Pentanoic Acid at pH-6.9O

33

111-5. Overall Reaction Rate Constant

The reactor used in this study was a continuously ﬂowing stirred-tank reactor
(CFSTR). Based on the studies of other aromatic compounds (Langlais et al., 1991) the
rate of degradation of DCB is assumed to be ﬁrst order in the concentration of
DCB. In a CFSTR at steady-state, the rate of degradation of DCB is given by the

equation :

ﬂay—tail = %([DCB]0 — [DCB])—k[DCB]= o (3-1)

Where k[DCB]= k03[03][DCB]+k0H[0H][DCBl+kplroro[I¢][DCB] (3-2)
It: is the reaction rate constant for the particular oxidant; [03], [OH] and [DCB], are the
reactor ozone , OH radical and DCB concentrations, respectively; [DCB]0 is the initial
steady state concentration of DCB in the reactor; I is the light intensity and (D is the
quantum efﬁciency; 1 is the hydraulic retention time and k' is a conditional rate constant

for the degradation of DCB. From equation (3-1) k' can be expressed as :

 

k _ 1([DCB]o—[DCB]
' 1: [DCB]

) (3-3)

The conditional rate constant is useful in engineering design to evaluate the conditions
that control the rate of oxidation of the target chemical and to size the reactor. The
conditional rate constants calculated from the experiment results are classiﬁed and are
provided in Tables 3-1 and 3-2.

34

Table 3-1 Effect of pH on TCB, DCB and Pentanoic Acid Degradation

 

 

 

 

 

Treatment pH k'(min-1) pH k' (min-1) pH k' (min-1)
process TCB DCB PA
Ozone 2.24 0.08 i 0.009 2.28 0.015 :t 0.009 2.21 0.011 :1: 0.017
Ozone 2.92 0.07 :1: 0.009
Ozone 5.25 0.04 i 0.035 5.71 0.161 i 0.018
Ozone 6.21 0.79 :t 0.100
Ozone 7.17 1.03 n 0.07 7.02 0.765 2 0.056 7.02 0.533 1 0.113
Ozone 7.90 1.25 z 0.16 8.04 0.405 i 0.032
Ozone 9.48 1.09 3: 0.11
Ozone 10.55 0.74 1 0.07
Ozone 11.53 0.69 i 0.085 11.71 0.336 :t 0.052 11.5 0.215 1 0.035

Ozone/H202 2.35 0.20 :t 0.03 2.26 0.037 :t 0.008 2.28 0.024 :t 0.035
Ozone/H202 4.94 1.70 :1: 0.28

Ozone/11202 6.96 3.8 i 0.45 6.97 1.104 3. 0.334
Ozone/H202 8.53 3.8 i 0.55 8.27 6.580 t 0.807

Ozone/H202 10.10 1.2 3: 0.44

Ozone/11202 11.05 0.63 :1: 0.06

Ozone/H202 11.50 0.35 :t 0.44 12.19 1.879 :1: 1.828 12.1 0.343 :1: 0.156

Ozone/UV 2.32 2.3 :1: 0.22 2.28 1.638 :1: 0.181 2.31 0.271 1 0.106

Ozone/UV 4.75 3.0 :1: 0.25 5.65 2.505 3: 0.094

Ozone/UV 7.22 2.5 i 0.29 6.69 3.218 :1: 0.429 6.77 0.635 3: 0.240

Ozone/UV 8.95 2.0 :1: 0.22 8.48 3.693 3: 0.244

Ozone/UV 12.01 0.55 a: 0.22 11.34 1.059 :1: 0.055 11.00 0.503 :t 0.133

Ozone/UV/HzOz 8.34 5.125 i0.618 8.19 0.658 :1: 0.213

 

 

 

 

 

 

 

35

 

 

Table 3-2
Effect of Humic Acid and Bicarbonate on TCB, DCB
and Pentanoic Acid Degradation
Treatment Humic Acid Bicarbonate k' (min-1) k' (min‘l) k' (min-1)
Process (mg/l) (mM) TCB DCB PA

Ozone/UV 0 0 4.8 :1.- 0.87 3.22 :I: 0.429 0.64 i 0.24
Ozone/UV 1.6 0 1.9 i 0.18

Ozone/UV 2 0 2.13 :1: 0.17 0.89 :t 0.30
Ozone/UV 10 0 0.49 d: 0.07 0.67 :1: 0.10 0.06 :1: 0.04
Ozone/UV 0 0 4.8 :t 0.87 3.22 :t 0.43 0.64 :t 0.24
Ozone/UV 0 2 0.86 :1: 0.20 4.32 i 0.64 1.44 :t 0.59
Ozone/UV 0 10 0.37 i 0.03 3.23 i 0.35 1.02 :t 0.14

 

 

 

 

 

 

Equation 3-2 represent three pathway of DCB degradation: direct ozone
oxidation; sensitized photolysis and direct photolysis. Results show that about 13 %
and 28% of [DCB]o were degraded by direct ozone oxidation and direct photolysis,
respectively.

PA degradation can be expressed by similar forms of equations 3-1, 3-2 and 3-
3. Yao indicates that koa for PA is about 3.6 x1041 and direct photolysis is
unimportant (Yao et al.,1992).

HO- + HCOs' = 'COa' +HzO (3-3)
HO- + C032” = 'CO3‘+HO' (3-4)
03 + °C03‘ = dd (3-5)

36

The results indicated that the highest conditional rate constant occurred with
ozone/HzOz treatment at pH = 8.27 (Table 3-1). Under this condition turning on UV
light did not have any beneﬁcial for the removal of the target compound. An
interesting phenomenon is that the conditional rate constants did not decrease for both
DCB and PA, when 2 or 10 mM bicarbonate presented in the system. This is
contrary to what was Observed by Galbraith (1993) with TCB. A possible explanation
for the results with DCB and PA is that “C03" , produced from the reaction of
HC03/C032'with-OH may be capable of oxidizing DCB and PA. Another explanation
could be that ~COa" promotes the degradation of ozone and the product of this
reaction (dd) is a secondary oxidant capable of oxidizing DCB and PA. Further work
needs to be conducted to determine if these results are an experimental artifact or if

they are "real" , then research needs to be conducted to determine the reactive oxidant

species.

IV. DISCUSSION

IV-l. Optimum Condition

The overall reaction rate constant is highest for the most efﬁcienct treatment
conditions. For ozone treatment, the optimum condition for DCB degradation occurs
at approximately pH 7. The overall reaction rate constant decreased quickly when the
pH was either increased or decreased. At pH < 7, less hydroxide ion is available to
promote ozone decomposition; at pH > 7, bicarbonate/carbonate ions scavenge the
OH radical. The highest overall reaction rate constant of PA was also observed at pH
7, suggesting that the reaction with OH radical predominates under this condition (See
Figure 3-2, Table 3-2).

Similar results were observed for the ozone/ UV and ozone/11202 processes.
The optimum pH for contaminant oxidation occurred between 7.0 to 8.5 . Specially,
for ozone/UV process, it should be emphasized that in a very broad pH region, the
overall reaction rate constant of DCB did not change signiﬁcantly as the rate of OH
radical formation is independent of pH, but dependent on light intensity which was
constant over the experiment. This hypothesis is supported by the estimated OH
radical concentration which are calculated from PA degradation results. (see Table 4—1)

The estimated steady state OH radical concentration in the reactor can be
calculated by following equation: (Masten et al. , 1993).

d [PA] 1

_ = —([PA]o — [PAD -— koul-OHllPAl = 0 (4'1)
dt 1

37

38

 

1 [PA]o - [PA]
or! = - 4-2
[ l 1([PAlk0H) ( )

where kon is the rate constant for the reaction of OH radical with PA , and equals to
0.29 x1010 (M‘sl or s") (Buxton, C. V. et al 1988). The OH radical concentrations

are essentially constant over the pH region 2.3 to 11.4 under steady state conditions,

 

 

 

 

 

Table 4-1
Estimated Steady State OH Radical Concentration
pH DCB Remaining DCB Overall Reaction Estimated [-OH]
(C/Co) % Constant k'( min") (M)
03 2.28 86.91 0.015 :t 0.009 (0.62 z 1.01) x1013
7.02 11.56 0.765 2 0.056 (3.06 3: 0.65) x10-12
11.5 22.94 0.336 x 0.052 (1.24 :1: 0.20 )x10’12
mm 2.28 5.75 1.638 3: 0.181 (1.56 :1: 0.61) x10'12
8.48 2.64 3.693 1: 0.244 (3.65 i 1.38)x10'12
11.39 8.63 1.059 d: 0.244 (2.89 :1: 0.76) x10'12
OBIUV/HzOz 8.34 1.91 5.125 :1: 0.618 (3.79 :1: 0.95) x10'12
03/11202 2.26 76.52 0.037 :1: 0.008 (1.36 :1: 1.60) x1013
8.27 1.50 6.580 :t 0.807 (6.35 :1: 1.49) x10'12
12.19 5.05 1.879 i 1.828 (1.97:1: 0.70) x10"12

 

 

 

 

 

The ozone /HzOz treatment (pH of 8.27) was most efﬁcient process in terms of
both OH radical generation and DCB degradation. Table 4-1 shows a good agreement

39

for the percentages of DCB remaining, the DCB overall rate constant and the steady

state OH radical concentration.

IV-2. OH Radical Scavenger and Reaction Competition

In AOPs, humic acid and bicarbonate/carbonate act as OH radical scavengers
since they consume OH radicals and form products that do not enter the cyclic reaction
involved in the decomposition of ozone (see Fig 1-2). (Peyton & Gee, 1989; Yao,
1992). From the following reactions and rate constants, one can see ~OH scavenging
reactions involving such scavengers as humic acid and carbonate and the rate constants
for the oxidation of PA and DCB occur at rates that are on the same order of
magnitude. Thus, one would expect that C032; HA, PA and DCB would compete for
the available OH radicals.

Reaction Rate Constant
k (M'ls‘)
HO- + CO;2 = HO + CO; 0.39 x109 (4-3)
HO- + HCO,‘ = C0; + H20 0.85 x107 (44)
HO- + HA = A- + H20 0.30 x1010 (4-5)
HO- + PA = P- + H20 0.29 x1010 (4-6)
HO- + 1, 2 - dichlorobenzene 0.40 x1010 (4-7)
HCOs' = Ht + C032' 0.22 x10 (4-8)
03 + CO; = dd 0.10 x106 (49)

As such, the scavenging effect of humic acid is likely to depend on the relative
concentrations of humic acid , PA and any other reactants in the system. Figure 3-9

shows that when the concentration of humic acid was increased from 2 to 10 mg/l,

40

the degradation rate of PA decreased signiﬁcantly when using ozone/ UV treatment
(pH 5 7.3). It is very interesting that the addition of bicarbonate /carbonate did not
result in a decrease in the degradation rates of DCB and PA, in fact the rates of
degradations of both DCB and PA increased somewhat. Three possible explanations
for this result are: (1) as the rate constant of OH radical with DCB is approximately
two orders of magnitude higher than the rate constant of OH radical with bicarbonate,
10 mM bicarbonate did not show a scavenging effect on both DCB (2.590 mg/L) and
PA (4.560 mg/L). Although carbonate has a higher -OH rate constant than bicarbonate
(Eq. 4-3), at pH 7.3, carbonate would not play an important role (Eq 4-8 ), as its
concentration would be approximately three orders of magnitude lower than the
concentration of bicarbonate. (2) C03" , the product of reactions show in Eq 4-10
and Eq 4-11 initiates ozone decomposition, and the unknown product (dd) of the
reaction shown in Eq 4-12 (Y ao et al., 1992) may be an OH radical promoter. The
function of bicarbonate, as a scavenger or promotor, may depend on the experimental
condition in the system. (3) ~C032' or the product formed from the reaction of ozone
with CO'3‘ may be an oxidant capable of reacting with PA and DCB.

Because the km, of DCB is only 0.33 times higher than that of PA (k0H=4.0 x
109 M"S'1 for DCB, k0H=2.9 x 109M"S'1 for PA, Haag and Yao, 1992), their
relative concentrations may contribute to the phenomena discussed above (if they both
present in the system at the same time). Figure 3-1 lshows that concentration of DCB
remaining (C/Co) increased from 36.04% to 69.19% , when the concentration ratio of
PA to DCB increased from 0.125 to 1.0. This result suggests that concentrations of
OH radical probe must be as low as possible to avoid interference with target
compound degradation.

V. CONCLUSIONS

Of the ﬁve compounds evaluated, pentanoic acid (PA) was found to be most
appropriate OH radical probe due to its low volatility, low reactivity with ozone, high
solubility and low detection limit.

Variations in the pH had the greatest effect on ozone treatment. The efﬁciency
of ozone/ UV treatment was essentially independent of pH.

While in the AOPs system the addition of humic acid reduced the efﬁciency of
oxidation of DCB, removal efﬁciencies of > 80% were observed. Contrary to
expectation, 2 or10 mM bicarbonate did not affect the efﬁciency of DCB oxidation.

Results indicate that the competition reactions between OH radicals with PA and
OH radicals with humic acid are strong. The scavenging effect of humic acid depends
on the relative concentrations of PA and humic acid. The degradation rates of PA
increased slightly when 2 or 10 mM bicarbonate was added.

The results of DCB, TCB and PA are qualitatively similar, suggesting a
similar mechanism for the degradation of all three compounds.

As a result of this research, the optimum condition and Optimum process for
the treatment of 1, 2-dichlorobenzene using AOPs were found. The conditional rate
constant of each process was obtained. And useful information for engineering design

rt-

was provided.

41

VI. FURTHER WORKS

Although our results show that the OH radical is the principal oxidant in AOPs,
to fully understand the mechanism involved in these complex systems, it is necessary
to develop detailed kinetic models that accurately describe the rates of production
and/or losses of oxidants and the other reactions involved.

An economic evaluation should be done for the application of AOPs for the
treatment of hazardous wastes.

Practice is the way to make the public recognize and accept a novel technology,
so that, it is imperative to move AOPs out of the laboratory and to apply this technique

into the ﬁeld for the remediation of a site contaminated with hazardous chemical(s).

42

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Peyton, G.; Gee, C.; Bandy J. and Maloney, S. (1989). Catalytic Competition
Effects of Humic Substances on Photolytic Ozonation of Organic Compounds.
American Chemical Society, Advance in Chemistry Series, 219, 639-661.

Roth, A. J .; Moench L. W. and Debalak, A. K. (1983). Kinetic Modeling of the
Ozonation of Phenol in Water. Journal of WPCF., 54 (2), 135-139.

Staehelin, J. and Hoigné, J. (1985). Decomposition of Ozone in Water in Presence of
Organic Solutes Acting as Promotors and Inhibitors of Radical Chain Reactions.
Environ. Sci. Technol., 19, 1206-1213.

Yao, J. J. (1991). Ozoneation of Soils Contaminated with Polycyclic Aromatic
Hydrcarbons (PAHs). Master Thesis, Michigan State University.

Yao, C. C. D.;Haag, R. W. and Mill, T. (1992). KineticFeatures of Advanced
Oxidation Processes for Treating Aqueous Chemical Mixtures. Proc. of Second
International Symposium Chemical Oxidation Technology for The Nineties.
Nashlille, Tennessee. pp 124-152.

I"

P

.V'

APPENDIXES

Pentanoic Acid Estertiﬁcation Followed By Head-space GC/FID Method
Flow Injection Analysis System Conﬁguration

Reactor Tracer Mixing Experimental Result

Data Summary Of DCB And PA Degradation

Data Summary Of TCB Degradation

46

47

Appendix 1

Pentanoic Acid Estertiﬁcation Followed By Head-space GC/FID Method

 

48

Reference

Atsushi Akane, Shoju Fukushima, Kazuo Matsubara, Setsunori Takahashi
and Hiroshi Shiono, (1990) "Analysis of blood acetate by head-space gas
chromatography: comparative of reagents for the methyl esteriﬁcation" , Journal of
Chromatography, 529, 155-160.

Basic Reaction

BF3

C4H9-COOH + HO-CHs =5 C4H9-C02-CH3 + H20

C4H9-COz-CHa. the product of the esteriﬁcation reaction of PA and CHaOH can be
measured by using a head-space gas chromatography with ﬂame ionization detection.
A calibration curve (C4H9-COOH concentrations against C4H9—CO2-CH: response areas)
was prepared daily.

Reagents and Procedure
In a 20 m1 head-space GC vial
(1) Add 3.5 ml water sample which contain C4H9-COO‘ anions;
(2) Add 0.1 ml 2 N HCl solution, to maintain the sample pH <4;
(3) Add 0.4 ml boron triﬂuoride 10% in methanol solution (GC Analysis,
Fluka Chemical Corp. , Ronkonkoma, NY);
(4) Seal the vials and store them at 37 °C for 60 hours:
(5) GC analyze by GC.

Discussion

This method can directly measure C4H9-COO' anion in water solution at a low
concentration level (Figure A-l-l , A-1-2 ). However, this method is time consumpting
and sensitive to pH, storage temperature and storge time. Where pH > 4, other
reactions may occur and result in the formation of other compounds which showed up,
in our studies, as a double peak in GC analysis (Figure A-1-3). When storge
temperature was higher than 37°C, a good base line could not be acheved (storge 60

hours). When temperature lower than 37°C, the esteriﬁcation reaction was not
completed in 60 hours.

49

Result

1) The product rate of C4H9—CO-2-CH3 is 0.44 i 0.03

2) The results of headspace GC analysis

 

Pentanoic Acid Concentration (mg/ L)
(Mean i 95 % confident limit)

 

 

 

 

 

 

 

 

Ozone Treatment Oa/UV Treatment O3/H202 Treatment Oa/UV/ H202
3.549 i 0.109 4.404 $0.702 3.252: 0.691 3.252i 0.691
3.202 i 0.420 1.188 :1: 0.233 2.630: 0.239 0.429i 0.022
0.561 t 0.089 0.135 i 0.135 0.270: 0.009
1.125 i 0.121 0.730 i 0.051 0.7351- 0.157

3) Pentanoic Acid Calibration Curve
3500000 7
2500000 ..
3 2000000 >
3 1500000 .. '
IOOOOOO — .
500000 - '
I.
o i +4 — 1 ——-1
O I 2 3 4

PA Concentration (mg/LI

Figure A-1-1
Pentanoic Acid Calibration Curve

 

50

aw”.

 

 

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30.3
. .a
as. on.
noniuw
n.3,... w
in“?! .
cofﬁn}
on I.
u .
Iain ..
amemmoMHS
. Snowmflzz
can
hOn.u_lI_"IIIIIIII\.
4.an
.37: 13.4... v9.2
u
«3.24%.
nnh.u. .

 

 

v...~

 

 

 

 

I a . . 3 . . . . . Ted
0 a a o o u o o o o. =.
. . a o o o I a
u n u u u s e s e s
5 4 4 3 3 I 3 I I
at 2.3.3.1430:
— nlh— PM Ll! ﬁnnrﬂun— _ Inubﬂ H ‘9:..‘ thd a, SIC Ununﬂuuﬂ u tau-ul—hww
<<.

eeslsa . ea).—
In

‘.G.—‘Id"30 " O_.h

ulnu'ol

Figure A-l-2 GC Analysis Result

51

 

 

 

 

 

 

 

34...". To so
u...“
10.0N
\.
a.
. ..
nun.2|ﬁ“lll\ ..
III)»
.
rang
anode ..
10.0u
\
H'O.”M\
IIIII :O.n
Pho.a
03.9w .
. q a _ a 4 «I < o a
J I O O a O I O I I
o o o a e o e. o.
s u 5 o s 9 s m 3
4 4 3 3 z z 1 t
:8 aqOb.nnanNOuv
. no: no no... b.4332 . xuuha . $0.38. as: as as... rouse": . c0300....
O-IIIH " 0575. Ha . .

«Oa.ﬂnlﬂ.ﬂﬂw "

minutes

Figure A-1-3 GC Analysis Result

52

Appendix 2

Flowing Injection Analysis System Conﬁguration

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

\_ POD
SYRINGE .4 ’R
I \ f
\
\
\
PERIS’I‘AL’I’IC CARRIER - b >h mono»:
STREAM - U
PUMP ; A MIXING ZONE
3 TEES
‘ EXCESS I i
SAMPLE
e SAMPLE
mg?“ : I p. LOOP SPECTROPHO‘I‘O-
’ METER
FIA INJECTION

VALVE

(Adapted from Galbraith, 1993)

Figure A-Z-l FIA System Conﬁguration

53

Appendix 3

Reactor Tracer Mixing Experimental

(Motor Speed 425 rpm)

 

0.6 ..__-._.. _-.___.____

 

 

00.5 -I-——- » -~ g . l~————I——I———I—I

 

0.4 4e—-~-_———————__ ./ .. --.. -_ _
/.

 

 

 

 

up / -._-. .. _ .._.,_
0.3 /

Absorbance

 

I
2 I
0 q p-_.. - o.._._-___..__._.- ..
o ..

 

0.1 d-—--- .—-—.---_..__-_-._-

 

O 20 4O

Timelmini

---.. . -n- -—

60

 

 

Figure A-3-1 Reactor Tracer Mixing Experimental Result

54

Appendix 4

Data Summary Of DCB And PA Degradation

55

Experimental A. Ozone Treatment at Varying pH

Table A-1.

Target Compound: DCB

 

Hydraulic
Retention
Time (min)

10

10

10

10

10

 

UV Light

no

no

no

 

ReactorlpH

2.28

5.71

7.02

8.04

11.71

 

Inlet Ozone
Concentration

(mg/1)

12.16

12.16

12.08

12.08

12.08

 

Flow mOf
Inlet Ozone
Solution
(ml/hr)

750

750

750

750

750

 

Reactor Ozone
Concentration

(mg/l)

3.394

1.478

1.163

0.320

0.036

 

Humic Acid
Concentration

(mg/1)

 

Bicarbonate
Concentration
(mM)

 

Hydrogen
Peroxide
Concentration

(mM)

 

Target
Compound
Initial
Concentration
(gs/1)

2.720 1 0.147

2.720 :t 0.147

2.720 :1: 0.147

2.7203: 0.147

2.72021: 0.147

 

Reactor
Efﬂuent
Target
Compomd
Concentration

(mg/1)

2.364 :1: 0.147

1.043 :1: 0.062

0.315 :1: 0.012

0.539 1 0.021

0.624 i 0.083

 

% Remaining
of Target
Compound

 

86.91

 

38.34

 

11.56

 

19.80

 

22.94

 

Table A-2. Target Compound: Pentanoic Acid

 

 

 

 

 

 

 

 

 

 

 

 

Hydraulic Retention 10 10 10
Time (min)
UV Light no no no
Reactor pH 2..21 7.02 11.53
Inlet Ozone 12.00 12.08 12.08
Concentration (mg/l)
Flow Rate of Inlet 750 750 750
Ozone Solution (ml/hr)
Reactor Ozone 3.197 2.066 0.658
Concentration (mg/1)
Humic Acid 0 0 0
Concentration (mg/l)
Bicarbonate 0 0 0
Concentration (mM)
Hydrogen Peroxide 0 0 0
Concentration (mM)
Target Compound 3.549 1: 0.109 3.5491 0.109 3.549 :1: 0.109
Initial Concentration
(mg/1)
Reactor Efﬂuent Target 3.202 d: 0.420 0.561 t 0.089 1.125 :1: 0.121
Compound
Concentration (mg/l)
% Remaining of Target 92.22 15.81 31.70

Compound

 

 

 

 

 

Table B-1.

57

Experimental B. Ozone/UV Treatment at Varying pH
Target Compound: DCB

 

Hydraulic
Retention
Time (min)

10

10

10

10

10

 

UV Light

on

011

 

ReactoﬁiH

2.32

5.65

6.69

8.48

11.34

 

Inlet Ozone
Concentration

(mg/l)

12.64

12.32

12.80

12.00

12.48

 

Flow Rate of
Inlet Ozone
Solution
(ml/hr)

750

750

750

750

750

 

Reactor Ozone
Concentration

(mg/1)

0.188

0.167

0.226

0.029

0.017

 

Humic Acid
Concentration

(mg/1)

 

Bicarbonate
Concentration

(mM)

 

Hydrogen
Peroxide
Concentration
(mM)

 

Target
Compound
Initial
Concentration

(mg!)

2.284 i 0.078

2.284 :1: 0.078

2.284 :1: 0.078

2.2843: 0.078

2.2842: 0.078

 

Reactor
Efﬂuent
Target
Compound

Concentration

(mg)

0.162 :1: 0.017

0. 108:1: 0.003

0.0853: 0.011

0.074:1: 0.004

0.244 :1: 0.010

 

% Remaining
of Target

Compormd

 

5.75

 

3.84

 

3.01

 

2.64

 

8.63

 

Table B-2. Target Compound: Pentanoic Acid

 

 

 

 

 

 

 

 

 

 

 

 

Hydraulic Retention 10 10 10
Time (min)
UV Light on on on
Reactor pH 2.31 6.77 11.00
Inlet Ozone 12.48 12.48 12.72
Concentration (mg/l)
Flow Rate of Inlet 750 750 750
Ozone Solution (ml/hr)
Reactor Ozone 0.310 0.028 0.143
Concentration (mg/1)
Humic Acid 0 0 0
Concentration (mg/l)
Bicarbonate 0 0 0
Concentration (mM)
Hydrogen Peroxide 0 0 0
Concentration (mM)
Target Compound 4.404 :1: 0.702 4.404:t 0.702 4.404 :1: 0.702
Initial Concentration
(ms/l)
Reactor Efﬂuent Target 1.188i 0.233 0.1353: 0.135 0.7303: 0.051
Compound
Concentration (mg/1)
% Remaining of Target 26.97 13.60 16.58

Compound

 

 

 

 

59

Experimental C. Ozone/H202 Treatment at Varying pH

Table C-l. Target Compound: DCB

 

Hydraulic
Retention Time
(min)

10

10

10

10

 

UV Light

No

No

011

No

 

Reactor pH

2.26

8.27

8.34

12.19

 

Inlet Ozone
Concentration

(mg/1)

12.24

12.24

12.24

12.24

 

Flow Rate of Inlet
Ozone Solution
(ml/hr)

750

750

750

750

 

Reactor Ozone
Concentration

(ms/1)

2.682

0.068

0.243

0.112

 

Humit': Acid
Concentration
(ms/1)

 

Bicarbonate
Concentration
(mM)

 

Input Hydrogen
Peroxide Rate
()1 mol./hr)

90

9O

90

90

 

Reactor Efﬂuent
Hydrogen
Peroxide

Concentration

(11M)

41.480 1: 1.867

19.604 i 1.867

22.729 :1: 1.867

10.039 :1: 0.880

 

Target Compound
Initial
Concentration
(mg/1)

2.879 :1: 0.160

2.87921: 0.160

2.879 :1: 0.160

2.879 :1: 0.160

 

Reactor Efﬂuent
Target Compound
Concentration

(mg/1)

2.20321: 0.072

0.043:l: 0.004

0.055:l: 0.006

0.141:t0.141

 

% Remaining of
Target Compound

 

76.52

 

1.50

 

1.91

 

5.05

 

‘—

Table C-2 Target Compound: Pentanoic Acid

 

Hydraulic Retention
Time (min)
UV Light

10

10

10

10

 

Reactor pH

N0

2.28

No

on

No

 

Inlet Ozone

12.24

6.79

12.24

8.19

12.19

 

Concentration (mg/l)

Flow Rate of Inlet Ozone

12.24

12.24

 

Solution (ml/hr)

Reactor Ozone

750

2.740

750

750

750

 

Concentration (mg/l)

Humic Acid

0.227

0.327

0.183

 

Concentration (mg/l)

Bicarbonate

 

Concentration (mM)

Input Hydrogen Peroxide

 

Rate (1.1 mol./hr)

Reactor Efﬂuent

90

 

Hydrogen Peroxide
Concentration (11M)

Target Compound Initial

3.252 :1: 0.0.691

44.037 :1: 1.412

21.403 :1: 1.078

3.252 :1: 0.691

22.350 :1: 0.815

13.732 :t 1.051

 

Concentration (mg/l)

Reactor Efﬂuent Target

3.252 i 0.691

3.252 :1: 0.691

 

Compound
Concentration (mg/l)

% Remaining of Target

2.630 :1: 0.239

0.270 i 0.009

0.429 :1: 0.022

0.735 :l:0.157

 

Compound

 

8.30

 

13.18

 

22.59

 

 

61

Experimental D. Ozone/UV Treatment in The Presence of Humic

Acid and Bicarbonate

Table D-l. Target Compound: DCB

 

Hydraulic Retention

 

 

 

 

 

 

 

 

 

 

 

10 10 10 10
Time (min)
UV Light on on on on
Reactor pH 7.33 7.32 7.43 7.46
Inlet Ozone 12.18 12.00 12.08 12.00
Concentration (mg/l)
Flow Rate of Inlet Ozone 750 750 750 750
Solution (ml/hr)
Reactor Ozone 0.005 0.013 0.141 0.248
Concentration (mg/l)
Humic Acid 10 2 0 0
Concentration (mg/l)
Bicarbonate 0 0 10 2
Concentration (mM)
Input Hydrogen Peroxide 0 0 0 0
Rate (11 mol./hr)
Reactor Efﬂuent 0 O 0 0
Hydrogen Peroxide
Concentration (1.1M)
Target Compound Initial 2.592 1 0.113 2.5921: 0.113 2.592: 0.113 2.592 :1: 0.113
Concentration (mg/1)
Reactor Efﬂuent Target 0.338 1: 0.045 0.1173: 0.007 0.0795: 0.008 0.059 10.008
Compound
Concentration (mg/1)
% Remaining of Target 13.04 4.49 3.00 2.26

 

Compound

 

 

 

 

 

Table D-2. Target Compound: Pentanoic Acid

62

 

 

 

 

 

 

 

 

 

 

 

 

 

Hydraulic Retention 10 10 10 10
Time (min)
UV Light No No No No
Reactor pH 7.34 7.37 7.50 7.49
Inlet Ozone 12.08 12.16 12.08 12.00
Concentration (mg/1)
Flow Rate of Inlet Ozone 750 750 750 750
Solution (ml/hr)
Reactor Ozone 0.0633 0.439 0.195 0.078
Concentration (mg/l)
Humic Acid 10 2 0 0
Concentration (mg/1)
Bicarbonate 0 0 10 2
Concentration (mM)
Input Hydrogen Peroxide 0 0 0 0
Rate (11 mol./hr)
Reactor Efﬂuent 0 0 0 0
Hydrogen Peroxide
Concentration (uM)
Target Compound Initial 4.560 1 0.344 4.560 :1: 0.344 4.560 :1: 0.344 4.560 :t 0.344
Concentration (mg/l)
Reactor Efﬂuent Target 2.924 :1: 0.795 0.4612t 0.114 0.409 0.029 0.296 10.092
Compound
Concentration (mg/l)
% Remaining of Target 64.12 10.11 8.97 6.49

Compound

 

 

 

 

 

63

Experimental E. Ozone Treatment of DCB and Pentanoic Acid of Humic

at pH=6.90

Table E. Target Compound: DCB

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Hydraulic Retention 10 10 10 10
Time (min)
UV Light No No No No
Reactor pH 6.89 6.91 6.90 6.82
Inlet Ozone 12.24 12.40 12.24 12.32
Concentration (mg/l)
Flow Rate of Inlet Ozone 750 750 750 750
Solution (ml/hr)
Reactor Ozone 2.205 2.185 2.844 1.803
Concentration (mg/l)
Humic Acid 0 0 0 0
Concentration (mg/l)
Bicarbonate 0 0 0 0
Concentration (mM)
Input Hydrogen Peroxide 0 0 0 0
Rate (it mol./hr)
Reactor Efﬂuent O 0 0 0
Hydrogen Peroxide
Concentration (uM)
DCB Initial 2.195 t 0.072 2.431 :I: 0.203 2.398 1 0.082 2.418 :1: 0.161
Concentration (mg/1)
WAGE] 0.125 0.250 0.500 1.000
I DCB]
Reactor Efﬂuent DCB 0.778 t 0.044 1.164 :t 0.072 1.429 :t 0.048 1.673 10.059
Concentration (mg/l)
% Remaining of Target 36.04 47.88 59.59 69.19

Compound

 

 

 

 

 

Appendix 5

Data Summary Of TCB Degradation

65

Effect of pH on TCB Degradation using Ozone, Ozone/H202 and Ozone/UV
Treatment.

 

 

Treatment Process pH k', min
Ozone 2.24 0.08 .4: .0091
Ozone 2.92 0.07 i .009
Ozone 5.25 0.40 _+_ .035
Ozone 6.21 0.79 i .10
Ozone 7.17 1.03 i .07
Ozone 7.90 1.25 i 16
Ozone 9.48 1.09 i .11
Ozone 10.55 0.74 :1; .07
Ozone 11.53 0.69 i 085
Ozone/H202 2.35 0.20 i .03
Ozone/H202 4.94 1.7 i .28
Ozone/H202 6.96 3.8 i .45
Ozone/H202 8.53 3.8 i .55
Ozone/H202 10.10 1.2 i .44
Ozone/H202 11.05 0.63 :1; .06
Ozone/H202 11.50 0.35 i .04
Ozone/UV 2.32 2.3 i .22
OzonerV 4.75 3.0 i .25
Ozone/UV 7.22 2.5 :1: .29
Ozone/UV 8.95 2.0 i .22
Ozone/UV 12.01 0.55 i- .06

 

‘ mean _+_ 95% conﬁdence limits
(Adapted from Masten et al., 1993)

Effect of Humic Acid and Bicarbonate on TCB Degradation using Ozone,

66

Ozone/H202 and Ozone/UV Treatment.

 

 

Treatment Humic acid HCO,‘ k’ k’n,
Process mg/L mM min'l

Ozone 0 0 1.4 i .31' 1.00
Ozone 1.6 0 2.9 i 2.3 2.11
Ozone 10 0 085+ _ .13 0.61
Ozone/UV 0 0 4.8 -_1-_ .87 1.00
Ozone/UV 1.6 0 1.9 i .18 0.39
Ozone/UV 10 0 0. 49 1.07 0.10
Ozone/H202 0 0 3.8 i .45 1.00
Ozone/H202 1.6 0 4.2 i .53 1.10
Ozone/H202 10 0 0. 74 1.10 0.18
Ozone/HZOZ/UV 0 0 6.2 i 3.0 1.00
Ozone/HZOZIUV 1.6 0 2.2 i .89 0.36
Ozone/HZOZ/UV 10 0 0.65 i .07 0.10
Ozone 0 0 1.4 i .31 1.00
Ozone 0 2 0.10 i .012 0.07
Ozone 0 10 0.02 :1; .009 0.01
Ozone/UV 0 0 4.8 i .87 1.00
Ozone/UV 0 2 0 86 :1: .20 0.18
Ozone/UV 0 10 0 37 i .03 0.08
Ozone/H202 0 0 3 8 i .45 1.00
Ozone/H202 0 2 l 3 _-1_- .11 0.34
Ozone/H202 0 10 0 51 i .06 0.13
Ozone/HZOZIUV 0 0 6 2 :1: 3 0 1.00
Ozone/HZOZIUV 0 2 1 4 i .28 0.23
Ozone/HZOZ/UV 0 10 0 55 :1; .07 0.09 .

 

‘ mean :1: 95% conﬁdence limits

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