Nghiên cứu xử lý phenol trong nước thải quá trình luyện cốc bằng phương pháp ozon hóa kết hợp với xúc tác tt tiếng anh

MINISTRY OF EDUCATION
AND TRAINING

VIETNAM ACADEMY OF
SCIENCE AND TECHNOLOGY

GRADUATE UNIVERSITY OF SCIENCE AND TECHNOLOGY
----------------&---------------

NGUYEN THANH THAO

STUDY ON PHENOL TREATMENT IN COKING
WASTEWATER BY OZONATION PROCESS
COMBINED WITH CATALYST

Major: Environmental Engineering
Code: 9.52.03.20

SUMARY OF DOCTORAL THESIS OF
ENVIRONMENTAL ENGINEERING

Hanoi, 2019


The work was completed at Graduate University of Science and
Technology – Vietnam Academy of Science and Technology

Scientific Supervisor 1: PGS.TS. Trinh Van Tuyen
Scientific Supervisor 2: PGS.TS. Lê Truong Giang

1st Reviewer:…

2st Reviewer:…
3st Reviewer:…

The thesis will be defended at the Academic Review Board of the
Graduate University of Science and Technology - Vietnam Academy of
Science and Technology, 18 Hoang Quoc Viet Street, Cau Giay District,
Hanoi, Vietnam at…hour…date…month…in 2019

The thesis can be found at:
- Vietnam National library
- Library of the Graduate University of Science and Technology


PUBLISHED ARTICLES USED IN THIS THESIS
1. Nguyen Thanh Thao, Trinh Van Tuyen, Le Truong Giang.
Study on Pre-Treatment of Phenol, COD, Color in the coke
wastewater by ozonation Process. Journal of Science and
Technology, ISSN 2525-2518, 55, (4C) (2017), pages 271-276
2. Nguyen Thanh Thao, Le Trung Viet, Nguyen Quang Trung.
Development of method for analysing major phenol derivatives in
coke wastewater. Jounal of Analytical Sciences, ISSN 0868-3224
(22) (2017), pages 30-36
3. Nguyen Thanh Thao, Trinh Van Tuyen, Le Truong Giang.
Evaluating chemical compounds in coke wastewater of Thai
Nguyen iron and stell SJC, Thai Nguyen province. Jounal of
Analytical Sciences, ISSN 0868-3224, (23), number 1/2018, pages
22-29.
4. Thao T Nguyen, Tuyen V Trinh, Dung N Tran, Giang T Le,
Giang H Le, Tuan A Vu and Tuong M Nguyen. Novel FeMgO/CNT
nano composite as efficient catalyst for phenol removal in

ozonation process. Materials Research Express. Volume 5, Number
9, 095603, 2018.
5. Hoang Hai Linh, Nguyen Quang Trung, Nguyen Thanh Thao.
Removal phenol in coke wastewater by ozone combine with
modified laterit. Jounal of Analytical Sciences, ISSN 0868-3224,
(23), number 4/2018, pages 295-304.
6. Nguyen Thanh Thao, Trinh Van Tuyen, Nguyen Quang Trung.
Simultaneous determination of hydroquinone, catachol and
benzoquinone during phenol ozonation by high-perfomance liquid
chromatoghaphy. Jounal of Analytical Sciences, ISSN 0868-3224,
(21), number 3/2016, pages15-24.


7. Nguyen Thanh Thao, Trinh Van Tuyen, Le Truong Giang.
Study on the kinetics of phenol degradation in aqueous solution
by ozonation process at neutral media. Jounal of Analytical
Sciences, ISSN 0868-3224 (has been approved for publishment).
8. Thao Nguyen Thanh, Tuyen Trinh Van, Giang Le Truong,
Tuan Vu Anh. Study on Phenol treatment by Catalytic Ozonization
using Modified dolomite. Jounal of Analytical Sciences, ISSN
0868-3224 (has been approved for publishment).
9. Nguyen Thanh Thao, Trinh Van Tuyen, Le Truong Giang.
Study on degradation of phenol in aqueous solution by ozonation
combined with FeMgO/CNT. Jounal of Analytical Sciences, ISSN
0868-3224 (has been approved for publishment).


1
INTRODUCTION
Since the late 20th century, there have been many warnings

about the existence of phenol and phenol compounds in the
environment, especially the water environment. Phenol pollutes the
natural water environment due to its presence in many industrial waste
streams such as petrochemical, coke, steel ... [1-3]. Although widely
used in many industries, science has proved that phenols are toxic to
humans and organisms. Thus, phenol pollution in water is becoming a
serious problem for many countries, including Vietnam. Many methods
have been applied to treat phenol in water such as adsorption, biology,
catalytic wet oxidation ... However, it is often necessary to combine two
or more technologies to completely remove phenol from the waste
stream. Recently, catalytic Ozonation Process (COP) or catazon has
emerged as a new strategy for the treatment of persistent organic
substances and has proven very effective in treating wastewater.
contains phenol compounds. This method has many advantages such as
no problems related to chemicals, high efficiency of pollutant
decomposition, fast processing time, simple equipment, easy to install,
no waste sludge and In particular, ozone can be.
Some solid catalysts have been shown to increase the efficiency
of phenol removal in water by catalytic ozonation process such as metal
oxides Mn/Al2O3, MgO, ZnFe2O4, metals on carbon materials such as
AC/Fe2O4, CNT/Fe2O3, CNF/Fe2O3 or minerals such as perovskite,
honeycomb ceramic material ... [6-10]. Carbon nanotubes (CNTS)
materials with the advantages of large surface area, unique structure
have been becoming a new, promising and advanced class of materials
in this field of catalytic synthesis. However, the catalysts based on this
material are mainly applied to remove phenol in water by catalytic wet
oxidation and adsorption method, which is rarely studied to treat phenol
by heterogeneous catalytic ozonation process. FeMgO/carbon nanotube
composite (FeMgO/CNT) and dolomite modified by KOH (M-Dolomit)

2
are the first time to be evaluated for catalytic role for the removal
phenol in water by heterogeneous catalytic ozonation process.The thesis
with the title "Study on phenol treatment in coking wastewater by
ozonation process combined with catalyst” has been conducted to study
the treatment of coking wastewater containing toxic phenol compound
by ozonationprocess combined with heterogeneous catalysts, using
available catalyst materials produced in Vietnam with low cost and
environmentally friendly.
Objectives of thesis:
Study on phenol treatment in water by ozonation process
combined with catalysts. An empirical kinetic model and one quadratic
regression equations were built based on experimental data for
destroying phenol by heterogeneous catalytic ozonation process with
response variables (initial pH, ozone concentration, catalyst
concentration and reaction time). Application of phenol treatment in
coking wastewater.
Contents:
1. Overview of phenol pollution status in coking effluent, sources,
composition, toxicity and phenol treatment technologies in these kinds
of wastewater.
2. Study on phenol treatment in water by heterogeneous catalytic
ozonation process with two catalytic materials selected: FeMgO/CNT
and M-Dolomite. From studied results, select one best catalytic material
for further phenol treatment.
3. Develop the empirical kinetic model and quadratic regression
equations for decomposing phenol by O3/FeMgO/CNT process with
response variables (initial pH, ozone concentration, catalyst
concentration and reaction time).

4. Treatment of coking wastewater of Thai Nguyen Iron and Steel JSC
with pilot scale.


3
New contributions of the thesis:
- The first time, FeMgO/CNT composite and M-Dolomite materials
prepared from inexpensive clay minerals have been evaluated catalytic
characteristic to decompose phenol in the water by heterogeneous
catalytic ozonation process.
- Development of the empirical kinetic model and the quadratic
regression equations for decomposing phenol in water by
O3/FeMgO/CNT process with response variables.
CHAPTER 1. LITERATURE OVERVIEW
1.1.Technology for coke production and source of coking
wastewater
1.2. Phenol toxicity and treatment methods for the removal of
phenol from coking wastewater
1.3. Ozone-Based Oxidation processes
1.4. Experimental planning and Box-Hunter experimental planning
CHAPTER 2. SUBJECTS AND RESEARCH METHODS
2.1. Objects and scope of the thesis
Water samples containing phenol prepared from phenol crystals
and coke wastewater samples were taken from Thai Nguyen Iron and
Steel Joint Stock Company and Formosa Ha Tinh Steel Corporation.
2.2. Chemicals and equipments
2.3. Research methods
2.3.1. Experimental methods
2.3.1.1. Experimental description
2.3.1.2. Evaluation on the catalytic activity of materials

2.3.1.3. Study on phenol treatment in water by ozone and heterogeneous
catalytic ozonation processes
2.3.1.4. Development of an empirical kinetic model for treatment of
phenol by O3/FeMgO/CNT process
2.3.1.5. Development of a quadratic regression equations for treatment
of phenol by O3/FeMgO/CNT process


4
2.3.1.6. Treatment of coke wastewater of Thai Nguyen Iron and Steel
Joint Stock Company by O3/FeMgO/CNT process
2.3.2. Field survey and sampling methods
2.3.3. Analysis methods
2.3.4. Data processing methods
2.3.4.1. Efficiency of pollutants removal
2.3.4.2. Method of calculating pseudo first order reaction rate
constant
2.3.4.3. Method of developing an empirical kinetic model
2.3.4.4. Method of developing a quadratic regression equation
CHAPTER 3. RESULTS AND DISCUSSIONS
3.1. Characteristics of coking waste water
The analysis results of 16 samples of coking wastewater were
taken from Thai Nguyen Iron and Steel Joint Stock Company and
Fomosa Ha Tinh Steel Corporation show that this wastewater has a
pungent odor (smell of phenol) and many parameters with high
concentration such as color, COD, BOD5, CN-, phenols (phenol and
total derivatives), phenol, total nitrogen, NH4-N. Other parameters such
as heavy metals, total grease, total phosphorus, Cl-, S2-, residual chlorine
are quite low. The pH of the samples ranged from 6.7 to 9.5 (average at
7.9). For Fomosa samples, the pH ranged from 6.7 to 8.4 (average 7.6).

The wastewater is dark brown with average color 673 - 712 Pt/Co. TSS
parameter is from 132 - 357 mg/L. However, the total organic
compounds (COD) is high, ranging from 5.014 to 6.350 mg/L (5.794
mg/ L on average) for Thai Nguyen samples, higher than the average
3,871 mg/L in Fomosa samples. BOD5 in all samples has a ratio of 3033% compared to COD. Phenol and CN- are two parameters with a high
concentration in all samples. The content of phenols in Thai Nguyen
samples has a high content in the range of 850 - 1,052 mg/L (average
949.3 mg/L), higher than 738 mg/L as the average value of Fomosa
samples. Coking wastewater has a high COD parameter because it is


5
complex wastewater. Besides of high levels of phenol, there are many
derivatives of phenol as well as other organic substances. The average
concentration of phenol in Thai Nguyen samples is 665 mg/L, higher
than the average of 629 mg/L in Fomosa ones. The ratio of derivatives
and phenols of all samples varied greatly, accounting for 14.7 - 70%.
CN- concentration averaged 31.5 mg/L for Thai Nguyen samples and
26.5 mg/L for Fomosa ones.
06 samples of coking wastewater collected at Thai Nguyen Iron
and Steel Joint Stock Company were analyzed 09 derivatives of phenol
commonly found in this kind of water [19, 31, 54] and simultaneously
analyzed 943 organic substances by AIQS - DB software by GCMS.
The results reveal four highly concentrated derivatives, including: 2methylphenol (3.1 - 33.7 mg/L), 3 methylphenol (7.4 - 46.69 m/L), 4 methylphenol (3.1, -16.6 mg/L); 3,5 - dimethylphenol (8.9 - 35.4 mg/L)
and 2.5 - dimethylphenol (1.23 - 20.8 mg/L). Other derivatives such as
2,3-dimethylphenol; 3,4-dimethylphenol, 2,4-dimethylphenol; 2,6dimethylphenol are also detected but in small concentrations.
3.2. Evaluation of the catalytic activity of materials
3.2.1. Evaluation of adsorption capacity of dissolved O3 on material
surfaces

Fig 3.1: Dissolved O3
concentration in solution with
and without catalyst

Fig 3.2: The effects of tert-butanol on the efficiency of
phenol decomposition with and without catalyst

The results show that the concentration of dissolved O3 in the
solution with catalysts were always higher than without catalyst. When


6
there is no catalyst, the measured concentration are 2.8; 3.6; 3.2; 3 mg/L
at 5; 10; 15; 20 minutes, higher than 2.4; 3.2; 2.7; 2.5 mg/L in the
presence of M-Dolomite and 2; 2.8; 2.5; 2.2 mg/L with FeMgO/CNT
catalyst (Fig 3.1). That indirectly proves the selected materials have
catalytic activities. The dissolved O3 produced in the solution has been
adsorbed and decomposed on the surfaces of the material to form free
radicals OH. The analytical results of phenol adsorption capacity on
the surface of FeMgO/CNT and M-Dolomite catalyst in 60 minutes
show that phenol is not adsorbed on the surface of catalysts.
3.2.2. Evaluation of the role of free hydroxyl radicals contribute to
phenol treatment by heterogeneous catalytic ozonation process
The presence of tert-butanol in solution reduced the efficiency
of phenol decomposition in both cases with and without catalyst. Fig 3.2
shows the phenol decomposition efficiency are 60.7; 70.9; 76.5; 82.2;
86.2% in ozonation process corresponds to pH values: 3; 5; 7; 9; 11 but
reduced to only 50; 53; 54; 55; 52% in ozonation process with tertbutanol.
The efficiency of phenol decomposition without tert-butanol are
41-78.8%; 50.7-85.5% and 74.1-90.1% corresponding to processes O3;

O3/M-Dolomite; O3/FeMgO/CNT processes when pH values increase
from 3 to 11 but only reach 37.5 - 55%; 20.1 - 25.2%; 54.3 - 57.2% with
scavenger. In particular, the O3/M-Dolomite+tert-butanol process is
affected highly. In alkaline media, the phenol decomposition efficiency
decreases much more than the neutral and acidic media. Due to in
alkaline media, reaction mechanisms by •OH played a key role.
3.2.3. Evaluate concentration of metals being released into the
solution and contribute to the efficiency of phenol decompose by
homogeneous catalytic ozonation process
The results showed that the Fe, Mg metals in FeMgO/CNT and
Ca, K, Mg in M-Dolomite were dissolved into phenol solution increase
to the maximum concentration and then gradually decreased. The


7
concentration of Fe and Mg reaches maximum at concentrations of
0.044 and 0.067 mg/L after 20 minutes and then decreases to 0.018 and
0.03 mg/L after 60 minutes. However, the concentration of Mg and Fe is
quite small. For M-Dolomite catalysts, the concentrations of metals Ca,
K, Mg reach maximum after 10 minutes of reaction at the values of
0.35; 1.19 and 26.4 mg/L but decreased to 0.18; 0.7; 21.4 mg/L after 60
minutes. Among the 3 metals in the M-Dolomite catalyst, metal K is
released into the solution with the concentration up to 21.4 mg/L.
The Fe, Mg metals with the maximum concentration released
into the solution in the composition of FeMgO/CNT materials do not
show the catalytic activity of decomposing phenol by homogeneous
catalytic ozonation process. In contrast, mixtures of Ca, K, Mg metals in
M-Dolomite material composition at concentrations of 0.35; 1.19 and
26.4 mg/L represent catalytic activity. After 60 minutes of reaction,
phenol decomposition efficiency reached 64.8%, an increase of 8.8%

compared to the efficiency achieved by O3 process.
3.2.4. Evaluate the ability of adsorption of phenol on the surface of
the catalysts
Results of the investigation of phenol adsorption capacity on the
surface of FeMgO/CNT and M-Dolomite materials in 60 minutes
showed that phenol is almost unabsorbed on the surface of materials.
This proves that the adsorption process does not contribute to the phenol
decomposition efficiency for O3/FeMgO/CNT and O3/M-Dolomite
processes.
3.3. Study on phenol treatment in water by ozone and
heterogeneous catalytic ozonation processes
The removal efficiency of phenol, COD, TOC and apparent
reaction rate constant with (kcata) and without catalyst (k) tend to
increase with increasing pH solution. When there is no catalyst, k
increases 2.8 times when the pH of the solution increases from 3 to 11.
kcata increase gradually from 0.0122 - 0.0312 (1/min) in O3/M-Dolomite


8
process when increasing pH from 3-11 but increase from 0.022 to
0.0392 (1/min) with O3/FeMgO/CNT process.
The presence of FeMgO/CNT catalyst has accelerated the
decomposition rate of phenol with kcata fold 1.4 - 2.5 times higher than k
without catalyst when increasing pH from 3-11 but only fold 1.1- 1.4
times with M-Dolomite catalyst (Fig 3.8). The increasing k value when
the pH increase of the thesis is also different from the results of the
research by Yousef Dadban Shahamat and colleagues (2014) [9]. The
study of Yousef Dadban Shahamat showed that k decreased when
increasing the pH of phenol solution from 4 to 6 and then increased
when pH increased from 6-10 when phenol was treated with O3 process.

3.3.1.Effect of pH on phenol treatment efficiency

Fig 3.7: Effect of pH on the ability to
decompose phenol with and without
catalyst

Fig 3.8: Effect of pH on the apparent
reaction
rate
constant
of
phenol
decomposition with and without catalyst

The removal efficiency of COD by O3 process reached 13.4 29.3%, corresponding to pH from 3-11 but increased to 21.2 - 33.2%
with O3/M-Dolomite process and 34,3 - 43 , 2% with O3/FeMgO/CNT
process. Similar to COD, TOC mineralization efficiency reaches 11.122% with O3/M-Dolomite, 6.1 to 18.5% higher than the efficiency of O3
process. O3/FeMgO/CNT process gives the highest mineralization
efficiency, reaching 21 - 29.2% when increasing pH from 3 - 11. pH = 7
was chosen as phenol solution for further studies of the phenol treatment
in water by ozone and heterogeneous catalytic ozonation processes.


9
3.3.2. Effect of catalyst concentration on phenol treatment efficiency
The removal efficiency of phenol, COD, TOC, and apparent
reaction rate constants of phenol decomposition tend to increase with
increasing catalysts concentration. Figure 3.12 shows the removal
efficiency of phenol after 60 minutes with O3/FeMgO/CNT process with
increasing catalyst concentrations: 0; 0.5; 1; 2; 3; 3.5 g/L corresponds to

56; 72.1; 78.1; 79.2; 86.3; 87.3%. The cause of increased removal
efficiency of phenol when increasing FeMgO/CNT catalyst
concentration is due to: 1) The surface area of catalysts increases with
higher amount of catalyst, increasing the amount of O3 molecules
adsorbed on the surface. The hydroxyl radicals •OH produced by the O3
self-decomposition reaction increased [110, 112]. 2) The amount of
CNT material participating in the reaction is higher, leading to an
increase in the amount of •OH producing the reduction reaction (e) of O3
on the CNT surface, increasing the solution pH. Increased pH increases
•
OH produced by the O3 self-decomposition reaction increased. 3). The
number of ions Fe2+, Fe3+ and MgO in FeMgO/CNT material also
increase when the amount of catalyst increased. The chain of reactions
produced •OH is more due to the reaction of O3 with the active
components of the catalyst. The amount of •OH in the solution
increases, increasing the efficiency of phenol decomposition. Phenol
decomposition efficiency reaches 56; 59.4; 63.7; 70.1; 80.3; 81% in the
O3/M-Dolomite process corresponds to a catalyst concentration of 0; 1;
2; 3; 4; 5 g/L. kcata fold 1.8 and 2.2 times corresponding to O3/MDolomite process (4 g/L) and O3/FeMgO/CNT process (3.5 g/L)
compared with k obtained by ozone process.
COD removal efficiency after 60 minutes increased from 18 to
41.5%, corresponding to increasing the catalyst concentration from 0 to
3.5 g / L for O3/FeMgO/CNT process but only increased from 18 to
35% with O3/M-Dolomite process when increasing the catalyst
concentration from 0 - 5 g/L. Similar to COD, the efficiency of TOC


10
mineralization increased from 11 - 26.8% and 11 - 23.5% corresponding
to the O3/FeMgO/CNT and O3/M-Dolomite processes. The value of

COD, TOC at the concentration of 3.5 g/L FeMgO/CNT respectively
decreased from 0.96 g/L and 0.3 g/L before treatment decreased to 0.66
g/L and 0.24 g/L after 60 minutes after treatment.

Fig

3.12: Effect of
concentration
on
efficiency of phenol

catalyst
removal

Fig 3.13: Effect of catalyst concentration on
apparent constant rate of phenol
decomposition

The concentration of 3 g/L of FeMgO/CNT and 4 g/L MDolomite catalyst was selected as the optimal concentration for further
studies in the phenol treatment by heterogeneous catalytic ozonation
processes.
3.3.3. Influence of stirring speed on phenol treatment efficiency
The results show the removal efficiency of phenol, COD, TOC
and apparent rate constants of phenol decomposition tend to increase as
the speed of stirring increases.
Phenol decomposition efficiency increased from 42.3% to
56.3% when increasing the stirring speed from 150-300 rpm when
treating phenol by ozone process but the influence is not significantly
increased when the stirring speed increased from 200 to 300 rpm.

Fig 3.15: Influence of speed
stirring to removal efficiency of
phenol with and without catalyst

Fig 3.16: Influence of speed stirring to
apparent reaction rate constants of phenol
removal with and without catalyst


11
In the presence of FeMgO/CNT and M-Dolomite catalysts, the
efficiency of phenol decomposition increased from 64.2 to 86.3% and
60 - 80.3% respectively when increasing the stirring speed from 150 to
300 rpm.
Increased phenol decomposition efficiency when accelerating
the stirring process is due to the increased ability to diffuse O3 from the
gas phase to the liquid phase increases and increases the collision
between the substances in the solution to increase the reaction rate.
Phenol decomposition effects [92, 94, 96]. However, the efficiency of
decomposing phenol only increases to a maximum value and does not
increase further because at this stirring speed the ability to diffuse O 3
from the gas phase to the maximum liquid phase, the concentration of
O3 dissolves in the solution saturated.
k increase from 0.01 to 0.015 (1/min) when increasing the
stirring speed from 150 - 300 rpm with O3 process but increases from
0.016 to 0.026 (1/min) with O3/FeMgO/CNT process and 0,018 - 0,032
(1/min) with O3/M-Dolomite process. COD removal efficiency
increased from 14.6 to 18.1% when the stirring speed increased from
150 - 300 rpm with O3 process but increased to 21.2 - 34.6% with O3/MDolomite process and 27 , 2 - 40% with O3/FeMgO/CNT process.
Similar to COD, TOC mineralization efficiency increased from 8 11.2% in O3 process but increased to 15 - 23.2% and 19.1 - 26.4%

respectively in O3/M-Dolomite and O3/FeMgO/CNT processes. The
research results clearly show that the speed of 200 rpm is the optimal
stirring speed for O3 and O3/FeMgO/CNT processes and 250 rpm for
O3/M-Dolomite process.
3.3.4. Influence of temperature on phenol treatment efficiency
Figure 3.18 shows that the removal efficiency of phenol after 60
minutes by O3 process is merely 48% and 56% corresponding to the
temperature of 10oC and 25oC. The removal efficiency increases
because at this temperature range, the process of decomposing O3 into


12
•

OH and the ability to diffuse the reaction substances prevail. But if the
temperature continues to increase, the removal efficiency of phenol is
reduced to 32.2% at 35oC and 28.6% at 45oC due to the reduction of the
concentration of O3 dissolved in the solution. The results also show that
M/Dolomite catalyst depends on temperature. 86% of phenol is
decomposed after 60 minutes at 10°C but decreased to only 80.3; 64.2;
60% corresponds to temperature 25; 35; 45oC.

Fig 3.18: Effect of solution
temperature on the removal
efficiency of phenol with and without
catalyst

Fig 3.20: Effect of solution
temperature on the apparent
reaction rate constant of phenol

removal with and without catalyst

Figure 3.20 shows the effect of temperature on k with and
without the catalyst. In O3 process, the value of k increased from 0.011
to 0.015 (1/min) corresponding to the temperature increase of 10 - 25oC
but decreases to only 0.006 (1/min) at 35oC and 0.005 (1/min) at 45 °C
after 60 minutes of reaction. The kcata value of O3/FeMgO/CNT process
is quite stable at all investigated temperature. In contrast, the O3/MDolomite process depends on temperature. The kcata values decrease
from 0.03 (1/min) to 0.025 (1/min), correspondingly increasing the
solution temperature from 10°C to 45°C. The thesis selected phenol
solution at 25oC for further studies of phenol decomposition with O3 and
catalytic ozonation processes because this temperature is favorable for
temperature regulation during the study.
3.3.5. Effect of ozone concentration on phenol treatment efficiency


13
The O3 concentration is selected from 0,152 to 1,216 g/L. The
study results show the removal efficience of phenol, COD, TOC, and
apparent reaction rate constants tend to increase when increasing the
ozone concentration.

Fig 3.23: Effect of O3 concentration on
the removal efficiency of phenol after 60
minutes with and without catalyst

Fig 3.24:The effect of O3 concentration
on the apparent reaction rate constants of
phenol removal with and without catalyst

The results show that 44.6% of phenol is decomposed in 60
minutes at 0.152 g/L O3 concentration without catalyst but only 40
minutes in O3/FeMgO/CNT process or 50 minutes in O3/M- Dolomite
process to achieve the same efficiency. At O3 concentrations 0.152;
0.304; 0.608; 0.912 g/L efficiency of phenol decomposition after 60
minutes reaches 44.6; 56; 70.8; 85.1% with O3 process but increases
52.7; 80.3; 91.7; 98.1% and 63.2; 86.3; 94.8; 99.6% corresponds to
O3/M-Dolomite and O3/FeMgO/CNT processes.
The removal efficiency of phenol increases when increasing the
O3 concentration in all the experiments due to the increase in the
concentration of O3 in the gas, increasing the concentration of dissolved
O3 in the solution. The reaction of O3 with the active components in
catalysts such as MgO, Fe2+, Fe+3, CNT occurs faster. The more •OH
produced increase the rate of reaction while the phenol concentration in
the solution is constant. In all experiments, no residual O3 is observed
even when 100% of phenol is completely decomposed because many
intermediate products are generated in reaction and also react with O3 in
solution.


14
k of phenol decomposition without catalyst increase from
0.0103 (1/min) to 0.05 (1/min) when increasing O3 concentration from
0.152 g/L to 1,216 g/L. The presence of catalysts increase these reaction
rate constants. With the same O3 concentration studied, the kcata values
increase from 0.0129 (1/min) to 0.072 (1/min) for O3/M-Dolomite
process and increase sharply from 0.0162 (1/min) to 0,1064 (1/min)
with O3/FeMgO/CNT process (Fig 24). kcata increased by 1.6 - 2.6 times
compared to k achieved in the presence of FeMgO/CNT catalyst but
only increase by 1.3 -1.9 times with M-Dolomite catalyst.

The removal efficiency of COD and TOC tends to increase
when O3 concentration increases. After 60 minutes, COD removal
efficiency by O3 process increased from 14.9 to 32.6% when increasing
O3 concentration from 0.152 g/L to 1.216 g/L. Efficiency of phenol
removal increased from 28.3 to 64.8% with O3/FeMgO/CNT process
and 23 - 55.4% for O3/M-Dolomite process. The ability of TOC
mineralization is only from 7.8 to 15% in O3 process when increasing
O3 concentration from 0.152 to 1,216 g/L but increased to 13.5 - 32.5%
and 18.4 - 39.5% corresponds to O3/M-Dolomite, O3/FeMgO/CNT
processes. The thesis selected 0.304 g/L O3 as the concentration of O3
applied for further studies in this thesis because at this concentration,
phenol decomposition rate occurs at a moderate speed, convenient for
sampling, calculating of kinetic constants with and without catalysts.
3.3.4. Effect of phenol concentration on phenol treatment efficiency
The study results show the removal efficiency of phenol,
COD, TOC and apparent reaction rate constants of phenol
decomposition tend to decrease when increasing the initial phenol
concentration. After 60 minutes of reaction at 0.1 g/L phenol
concentration, only 86.4% of phenol was decomposed by O3 process but
increased to 100% after 25 minutes of reaction by O3/FeMgO/CNT
process or 35 minutes by O3/M-Dolomite process. The presence of
catalysts increases the removal efficiency of phenol at the same initial


15
phenol concentration. After 55 minutes, phenol is completely
decomposed at an initial concentration of 0.2 g/L in O3/FeMgO/CNT
process but only reached 76.5% and 92.7% corresponding to O3, O3/Mdolomite processes. At the investigated phenol concentrations 0.3; 0.4;
0.5; 0.6 g/L, the efficiency of phenol removal after 60 minutes reached
62.7; 56; 46.4; 35.1% with O3 process but increase to 53.6; 60.4; 80.3;

86.8% with O3/M-Dolomite process and 67; 76.4; 86.3; 98.5% with
O3/FeMgO/CNT process. When increasing the phenol concentration
leads to increase the competition O3 between phenol and intermediate
products generated during the reaction. The concentration of O3 is fed
into a fixed reactor, so the amount of •OH are generated by the selfdecomposition process and the reaction with the active components of
the catalyst does not increase. Therefore, if the phenol concentration in
solution continues to increase, the treatment efficiency decreases.

Fig 3.26: Effect of initial phenol
concentration on the efficiency of phenol
decomposition by O3/FeMgO/CNT
process

Fig 3.28: Effect of initial phenol
concentration on apparant reaction rate
constants of phenol removal with and
without catalysis

Efficiency of of COD, TOC removal gradually decreases when
increasing the phenol concentration in the solution. After 60 minutes,
100% COD was removed at the initial phenol concentration of 0.1 g/L
and 0.2 g/L in the O3/FeMgO/CNT process. Phenol decomposition
efficiency decreased from 66.8% to 9% when increasing phenol
concentration from 0.2 g/L to 0.6 g/L in O3 process but decreased from
100% to 21.5% with O3/FeMgO/CNT process and from 90% to 17%
with O3/M-Dolomite process.


16
3.3.5. Influence of NH4+, CN-, HCO3- on phenol treatment efficiency

NH4+, CN-, HCO3- are influencing factors selected because they
have a high concentration in coking wastewater and reacting with O3 in
solution. NH4+ 0.5 g/L concentration; CN- 0.03 g/L; HCO3- 1 g/L are
chosen because these are the average values detected in 16 wastewater
samples in this thesis.
The results show that the presence of NH4+ in solution does not
affect the efficiency of phenol decomposition in both cases with and
without catalyst at pH=7. This proves that O3 competition between
phenol, NH4+ and intermediate products is produced in the reaction
process. However, it is possible that the concentration of O3 in the
reactor is not high enough so that NH4+ has not been decomposed.
Studies have shown that NH4+ decomposition efficiency increases when
the solution pH increases and this process consumes high amounts of O3
concentration.
The results of the influence investigation of 1 g/L HCO3- in the
solution containing 0.4 g/L phenol show the presence of HCO3- ions
without affecting the removal efficiency of phenol. The results reveal
that the competition for oxidation agents between phenol, HCO3- as well
as byproducts in solution. Phenol concentration at the time of sampling
is similar to the initial phenol concentration.
Variation of CN- concentration after 60 minutes of reaction in
phenol solution with and without catalyst under conditions pH=7; O3
0.304 g/L with the optimal concentration of catalyst determined. The
results show that O3 competition between phenol and CN- that reduced
the removal efficiency of phenol in solution (Table 3.3).
The efficiency of CN- decomposition after 60 minutes only
reached 8.2% in O3 process but increased to 15.4% and 97.2%
corresponding to O3/M-Dolomite and O3/FeMgO/CNT processes. The
FeMgO/CNT catalyst exhibits the best catalytic activity of degradation
of CN-. When CN- ion in solution, the efficiency of phenol removal

17
decreases by 43.9% compared to the efficiency achieved without CNwith O3/FeMgO/CNT process.
3.3.6. Evaluate the regeneration ability of catalysts
The efficiency of phenol removal decreased only 9.7% (from
86.3% to 76.6%) after 4 times using FeMgO/CNT catalyst but decreased
by 11.6% after 2 times using M-Dolomite catalyst. After 3 times using
M-Dolomite catalyst, the catalyst is almost inactivated. The efficiency
of phenol decomposition increased only 2.3% compared to the
efficiency achieved by the O3 process and the loss of activity after 4
times of use. M-Dolomite catalyst significantly reduced its activity
because of the concentration of K content in the phenol solution with
quite high concentration, the alkalinity of the catalytic centers
decreased. EDX spectra results of 2 catalytic materials after using 4
times also demonstrate the relevance to the research results. The EDX
spectrum of M-Dolomite material after 4 times of use no longer shows
the presence of element K as the EDX image captures M-Dolomite
material before processing But the ratio of the main elements in
FeMgO/CNT catalyst is not much different from the first time. The ratio
of 4 major elements in the catalyst is C; O; Mg; Fe corresponding 86; 8;
2.4; 2.7% in the catalytic component after 4 times of use, quite close to
the initial ratio of 84.8; 9.79; 2.5; 2.85% when not in use. The results of
the thesis also open a new research direction using catalysts of natural
origin to treat persistent organic substances by heterogeneous catalytic
ozonation process.
3.4. Establishment of the empirical kinetic mode for phenol
treatment in water by O3/FeMgO/CNT process
3.4.1. Effect of catalytic concentration on apparent reaction rate
constants of phenol decomposition at pH 7

kcata reaches the values: 0,0109; 0.0175; 0.0210; 0.0490; 0.027;
0.0313 (1/min) corresponds to FeMgO/CNT concentrations: 0; 0.5; 1; 2;


18
3; 3.5 g/L. The relationship between the kcata reaction rate constant and
the FeMgO/CNT catalytic amount is shown in Figure 3.33 b.
The line y = 0.0158x + 0.0578 with tagα = 0.0158 and R2 =
0.93. We have: α3 = k2k5 = 0,0158 (L2/g2.min); α2_pH7 = 0,0578 (L/g.min).

Fig 3.33: Effect of catalytic concentration on kcata (a); The relationship between α1
and the catalytic concentration (b) at pH=7

3.4.2. Effect of catalytic concentration on apparent reaction rate
constants of phenol decomposition at pH 5; 9; 11
Similar to pH = 7, the apparent rate constant for phenol
degradation when changing the catalyst concentration at pH = 5 tends to
increase when the FeMgO/CNT catalyst concentration increases. kcata
reaches 0.0109 values; 0.0175; 0.0210; 0.0490; 0.027; 0.0313 (1/min)
corresponds to FeMgO/CNT concentration: 0; 0,5; 1; 2; 3; 3.5 g/L
(Figure 3.34 b). The line: y = 0.0164 [cata] +0,0453 with R2 = 0.93.
We have: α2_pH5 = 0.0453 (L/min).

Fig 3.34: The relationship between α1
and catalytic concentration (b) at pH=5

Fig 3.35: The relationship between α1
and catalytic concentration (b) at pH=9

19
Similarly, at pH = 9, the line y = 0.0144 [cata] +0.0732 with R2
= 0.96. We have: α2_pH9 = 0,0732 (L/g.min)
At pH=11, the line: y=0,0129 [cata]+0,0891 with R2=0,99. We
have: α2_pH11=0,0891 (L/g.min)

Fig 3.36: The relationship between α1 and
catalytic concentration (b) at pH=11

Fig 3.37: The relationship between α2
when changing the initial pH of the
phenol solution

The line equation shows the relationship between α2 and the
initial pH of the phenol solution with linear form: y = 0.0073 [pH]
+0.0081. The higher the pH of the solution, the higher the α2 coefficient.
We have: k1 = 0,0081 (L/g.min); k2k4 = 0,0073 (L2/g2. min); k2k5 =
0,0158 (L2/g2. min)

kcata  0,0081[O3 ]  0,0073[O3 ]  pH  0,0158[cata ][O3 ]
d [ P]
 (0,0081[O3 ]  0,0073[O3 ]  pH  0,0158[cata ][O3 ])[ P]
dt
[ P]
 exp{(0,0081[O3 ]  0,0073[O3 ]  pH  0,0158[cata ][O3 ])} t
[ Po ]
The empirical kinetic mode shows that the process of
decomposing phenol in water with O3/FeMgO/CNT process depends on
pH, O3 concentration and catalyst concentration. Relative error between
experimental and predicted phenol concentration by empirical mode at

5.7%.



20
3.5. Establishment of the quadratic regression equation for phenol
treatment in water by O3/FeMgO/CNT process
The results of phenol concentration treated after conducting 31
experiments in the correct order and experimental conditions given by
Modde 12.1 software. The regression coefficient values for coded
variables of the polynomial function is shown in Table 3.11.
Table 3.1. Regresstion coefficients values (coded variables) of the
polynomial model of responses for phenol treatment
Coded
variables

.

Y

Regression
coefficients

Variations

Student standard (t)

bo

153,143

54,907

b1

-21,792

14,458

b2

-19,042

12,634

b3

-74,542

49,457

b4

-43,542

28,889

b11

1,329

0,962*

b22

-2,296

1,663*

b33

16,204

11,735

b44

8,204

5,941

b12

0,813

0,441*

b13

-0,937

0,508*

b14

-1,937

1,051*

b23

0,812

0,441*

b24

-0,937

0,508*

b34

-6,937

3,763

*

Note: < t (0,95, 6)=2,447

After eliminating the non-significant regresstion coefficients
values (<2,447), we have a quadratic regression equation of the response
functions for phenol treatment (Y) as follows:
Y  153,14  21,79 x1  19,04 x2  74,54 x3  43,54 x4  16,2 x3  8,2 x 4 6,94 x3 x4
2

2


21
Replacing the variables x1, x2, x3, x4 by real values (pH,
FeMgO/CNT, O3 concentration and reaction time), we have a regression
equation of phenol concentration after treatment.
[ P]  663,1  10,9[ pH ]  19[ FeMgO / CNT ]  390,1[O3 ]  15,79[t ]  0,33[t ]2 
4,5[O3 ][t ]  175,29[O3 ]2

The regression equation for right value in the ranges of real
variables is as follows: 3≤pH≤11; 0≤O3≤1,216; 1≤FeMgO/CNT≤5;
5≤t≤25.
The result of calculating the F value for Ct-phenol is 3 (eliminating the lack of fit for the model. The statistical significance of
the model is confirmed by the determination coefficient (R2), the
adjusted determination coefficient (R2adj), and Fisher distribution (Ftest). The R2 value and R2adj are 0,985; 0.981. These values are very
close to 1. Demonstrate that the model fit well with experimental data.
Average relative error of phenol concentration after treatment between
experiment and the regression equation of 31 experiments at 5.5%. This
error level is within the acceptable range, demonstrating that the
regression equation is properly described.

Fig 3.39. The effect of variables on the value of the regression equation

3.6. Experimental results of coking wastewater treatment Thai
Nguyen Iron and Steel Joint Stock Company with O3/FeMgO/CNT
process
The coke wastewater collected at Thai Nguyen Iron and Steel
Joint Stock Company in August, 2018 was pre-treated with sand filter