TRƯỜNG ĐẠI HỌC BÁCH KHOA HÀ NỘI

LUẬN VĂN THẠC SĨ

Research on the degradation of CIP
residues in RO treated wastewater by AOP
processes using different oxidation agents
Phan Thi Huong Quynh
Ngành Kỹ thuật hóa học

Giảng viên hướng dẫn:

GVC.PGS.TS. Nguyễn Minh Tân

Viện:

Kỹ thuật Hóa học

Hà Nội, 2022


ACKNOWLEDGMENT
It is the most challenging part of my thesis; I have many things that I desire
to say, and I also have many people to whom I want to express my gratitude.
According to this, I am lost in words and do not know where to start.
To begin with, when I began doing this study two years ago, I did not think
that it had lasted so long. After a long battle, this thesis is the report of my
challenging process; although it can not illustrate all the time that I snuggled with
experiments in the laboratory, my disappointment when failing in doing research,
and my joy when seeing the results.
Firstly, I would like to thank Assoc. Prof. Nguyen Minh Tan from Hanoi

University of Science and Technology guided me throughout the working process,
provided all the equipment, and created conditions for me to develop and complete
this thesis. Secondly, I thank the School of Chemical Engineering for
understanding and giving me more time to complete this project.
I would like to give my sincere thanks and deep gratitude to my parents
because they have always supported me on my scientific path and have always
cheered me on when I thought I would give up.
To Dr. Nguyen Thi Thu Trang, Institute of Environmental Technology –
Vietnam Academy of Science and Technology, who has always been patient with
me, I do not know what words I can use to show my happiness because I receive a
lot of help from her. Big thanks to MSc. Pham Duc Chinh from INAPRO for all
the scientific inputs and lab support; he had a vital role in my scientific path; I was
greatly influenced by his scientific style and worked much harder words of
encouragement.
Finally, to the students at INAPRO, I want to send a special thanks from
my heart; if I do not have your help, I cannot complete all the experiments in this
research.
Phan Thi Huong Quynh
Hanoi, 2021

i


DECLARATION OF AUTHORSHIP
I now declare that I have written the presented research thesis myself and
have not used tools other than those specified. The use of references in the project
has been clearly stated in the references section. The research team and I make the
data and results presented in this project, and it is completely honest.
Furthermore, I certify that this research thesis or any part thereof has not
been submitted for a degree or any other degree at any educational institution in

Vietnam or abroad.
Hanoi, June 2022

Phan Thi Huong Quynh

ii


ABSTRACT
The treatment of traces of pharmaceuticals residual, especially antibiotics
residual, is a challenge for existing water treatment technologies. A recently
selected solution to overcome this obstacle is the application of advanced oxidation
processes. In this study, experiments were performed to evaluate the efficiency of
CIP degradation by direct photolysis, UV/ TiO2, UV/ H2O2, and UV/ TiO2/ H2O2.
The survey showed that a CIP concentration of 5mg/L is the most suitable for
research. The AOPs all handle CIP best when Re = 6546 and UV density at 225
W/m2. UV/ H2O2 system best cures CIP after 60 minutes; efficiency is about
99,16% at optimum working conditions. Meanwhile, direct photolysis is less
efficient when treating CIP; the best efficiency is only 11,64 % after one hour of
decomposition. The UV/ TiO2 system achieved an efficiency of 74,4%. However,
if TiO2 and H2O2 are combined at low concentrations, the process efficiency can
be 93,21%. CIP decomposes best in neutral media. For the water matrix, the
treatment of CIP in tap water is less effective than in RO and distilled water.
Keywords: Ciprofloxacin (CIP), advanced oxidation processes (AOPs), treatment,
titanium dioxide, hydrogen peroxide

iii


TÓM TẮT

Việc xử dư lượng dược phẩm trong nước thải, đặc biệt là thuốc kháng sinh,
là một thách thức đối với các cơng nghệ xử lý nước hiện có. Một giải pháp được
lựa chọn gần đây để khắc phục trở ngại này là áp dụng các q trình oxy hóa tiên
tiến. Trong nghiên cứu này, các thí nghiệm đã được thực hiện để đánh giá hiệu quả
của quá trình phân hủy CIP bằng phương pháp quang phân trực tiếp, UV / TiO2,
UV / H2O2 và UV / TiO2 / H2O2. Cuộc khảo sát cho thấy nồng độ CIP 5,0 mg/ L
là thích hợp nhất để nghiên cứu. Các q trình AOPs ứng dụng đều xử lý CIP tốt
nhất khi Re = 6546 và mật độ UV ở 225 W/ m2. Hệ thống UV / H2O2 xử lý CIP tốt
nhất sau 60 phút; hiệu suất đạt khoảng 99,16% ở điều kiện làm việc tối ưu. Trong
khi đó, quang phân trực tiếp kém hiệu quả hơn khi xử lý CIP; hiệu suất tốt nhất chỉ
sau một giờ phân hủy là 11,64%. Quá trình UV / TiO2 đạt hiệu suất 74,4%. Tuy
nhiên, nếu kết hợp TiO2 và H2O2 ở nồng độ thấp thì hiệu suất của q trình có thể
đạt 93,21%. Bên cạnh đó, CIP phân hủy tốt nhất trong mơi trường pH trung tính.
Đối với nền nước, việc xử lý CIP trong nước máy kém hiệu quả hơn trong RO và
nước cất. Q trình UV / H2O2 tiêu thụ năng lượng ít nhất, trong khi quá trình UV/
TiO2/ H2O2 tiêu thụ năng lượng khơng đáng kể. UV/ TiO2 là q trình có giá trị
EE/ O cao nhất.
Keywords: Ciprofloxacin (CIP), advanced oxidation processes (AOPs), treatment,
titanium dioxide, hydrogen peroxide

iv


Table of Contents
ACKNOWLEDGMENT ......................................................................................... i
DECLARATION OF AUTHORSHIP ................................................................... ii
ABSTRACT .......................................................................................................... iii
TÓM TẮT ............................................................................................................. iv
TABLE OF FIGURES ........................................................................................ viii
TABLE OF TABLES............................................................................................. x

ABBREVIATION AND SYMBOLS ................................................................... xi
INTRODUCTION.................................................................................................. 1
CHAPTER 1: OVERVIEW ................................................................................... 3
1.1. Pharmaceuticals in the environment ........................................................... 3
1.2. Ciprofloxacin............................................................................................... 5
1.3. Ciprofloxacin in Environment .................................................................... 6
1.3.1. Occurrence ........................................................................................... 6
1.3.2. Risks to the Environment and Humans ................................................ 7
1.4. Potential treatment techniques .................................................................... 8
1.5. Advanced Oxidation Processes (AOPs): Overview .................................. 10
1.5.1. The superiority of Advanced oxidation processes ............................. 11
1.5.2. Classification of advanced oxidation processes (AOPs) ................... 12
1.5.3. Characterization of typical advanced oxidation processes (AOPs) ... 13
1.6. Advanced Oxidation Processes (AOPs): Typical processes ..................... 16
1.6.1. UV direct photolysis .......................................................................... 16
1.6.2. The H2O2/UV process ........................................................................ 16
1.6.3. Heterogeneous photocatalysis ............................................................ 19
1.6.4. The UV/TiO2/H2O2 process ............................................................... 24
1.7. Current uses and challenging of AOPs ..................................................... 25
1.8. Research objective and research approach ............................................... 26
1.8.1. Research objective ............................................................................. 26
1.8.2. Research approach ............................................................................. 27
CHAPTER 2: MATERIALS AND METHODS ................................................. 28
2.1. Materials .................................................................................................... 28
v


2.1.1. Ciprofloxacin (CIP) ............................................................................28
2.1.2. Titanium dioxide (TiO2) .....................................................................29
2.1.3. Hydrogen peroxide (H2O2) .................................................................30

2.1.4. The reaction system ............................................................................31
2.2. UV-Vis Spectroscopy ................................................................................32
2.2.1. Measuring Sample Absorbance ..........................................................35
2.2.2. CIP Concentration Standard Line .......................................................35
2.3. Calculation Formulas .................................................................................35
2.3.1. CIP decomposition efficiency .............................................................35
2.3.2. Reynolds number ................................................................................35
2.3.3. Energy consumption ...........................................................................36
2.3.4. Determination of kinetic constants of CIP degradation reaction ........36
2.4. Data processing methods ...........................................................................37
CHAPTER 3: EXPERIMENTAL PROCEDURE................................................38
3.1. Experimental location ................................................................................38
3.2. Experimental setup ....................................................................................38
3.2.1. Chemicals............................................................................................38
3.2.2. Experimental instruments and equipment ..........................................39
3.3. CIP's calibration curve process ..................................................................40
3.3.1. Sample preparation .............................................................................40
3.3.2. Wavelength Selection .........................................................................40
3.3.3. Procedure ............................................................................................41
3.4. Determine the effect of initial CIP concentration ......................................41
3.4.1. Sample preparation .............................................................................41
3.4.2. Procedure ............................................................................................41
3.5. Investigate factors affecting CIP degradation in water..............................41
3.5.1. Effect of UV photolysis on the degradation of CIP............................41
3.5.2. Effect of UV intensity on the degradation of ciprofloxacin ...............42
3.5.3. Effect of TiO2 concentration on CIP degradation...............................42
3.5.4. Effect of H2O2 concentration on CIP degradation ..............................43
3.5.5. Effect of TiO2 combined with H2O2 on CIP degradation. ..................43
vi



3.5.6. Effect of pH on the degradation of CIP ............................................. 44
3.6. Water matrix effects on CIP degradation .................................................. 44
CHAPTER 4: RESULTS AND DISCUSSION ................................................... 45
4.1. Influence of technological parameters on CIP treatment by AOPs .......... 45
4.1.1. Effect of initial CIP concentration ..................................................... 45
4.1.2. Effect of UV intensity ........................................................................ 46
4.1.3. Effect of UV process and TiO2 concentration on CIP degradation ... 47
4.1.4. Effect of H2O2 concentration on CIP degradation ............................. 51
4.1.5. Effect of hydrodynamic conditions on CIP treatment efficiency ...... 54
4.1.6. Effect of TiO2 combined with H2O2 on CIP degradation .................. 57
4.1.7. Effect of pH on the degradation of CIP ............................................. 59
4.2. Water matrix effects on CIP degradation .................................................. 61
4.3. Kinetics of advanced oxidation processes of CIP treatment and Energy
consumption ..................................................................................................... 64
4.3.1. Kinetics of advanced oxidation processes of CIP treatment .............. 64
4.3.2. Energy consumption .......................................................................... 67
CHAPTER 5: CONCLUSIONS AND OUTLOOK ............................................ 70
5.1. Conclusions ............................................................................................... 70
5.2. Outlook ...................................................................................................... 70
REFERENCES ..................................................................................................... 72
APPENDIX A - CIP's calibration curve ............................................................. 80
APPENDIX B - List of published works ............................................................ 81

vii


TABLE OF FIGURES
Figure 1.1. Pharmaceuticals' main pathways for entering the environment [12]. 3
Figure 1.2. Wastewater treatment. ........................................................................ 4

Figure 1.3. Chemical structure of ciprofloxacin. .................................................. 5
Figure 1.4. The structural formula of ciprofloxacin.............................................. 5
Figure 1.5. Four levels of degradation of Advanced oxidation processes [52]. . 11
Figure 1.6. Classification of Advanced Oxidation Processes ............................. 13
Figure 1.7. Molecular structure of hydrogen peroxide. ...................................... 17
Figure 1.8. Hydrogen peroxide decomposition. .................................................. 17
Figure 1.9. Molecular structure of Titanium dioxide. ......................................... 20
Figure 1.10. Crystal structure of TiO2. ................................................................ 20
Figure 1.11. Five Steps in Heterogeneous Photocatalysis Process. ................... 21
Figure 1.12. Photocatalytic mechanism. ............................................................. 22
Figure 1.13. Band positions of selected semiconductor photocatalysts and redox
potentials [68]. ..................................................................................................... 22
Figure 1.14. The UV/TiO2/H2O2 mechanism. ...................................................... 24
Figure 1.15. The water purification system of Panasonic. .................................. 26
Figure 2.1. Ciprofloxacin used in this research; a: Ciprofloxacin Kabi
200mg/100ml; b: Ciprofloxacin ≥ 98%. .............................................................. 29
Figure 2.2.Titanium dioxide (Merck, Germany).................................................. 30
Figure 2.3. Hydrogen peroxide 30% (GHTech, China) ...................................... 31
Figure 2.4. (a) Low-pressure mercury UV lamp inside a quartz tube; (b) Reactor.
.............................................................................................................................. 31
Figure 2.5. Experimental system; (a) diagram, (b) set-up system....................... 32
Figure 2.6. A diagram showing the major components of a UV-Vis
spectrophotometer [81]. ...................................................................................... 33
Figure 2.7. Diagram of a cuvette-based UV-Vis spectroscopy system [81]. ...... 34
Figure 2.8. Perkin Eimer Lambda35 UV/Vis Spectrometer. ............................... 35
Figure 3.1. Chemicals used in this study ............................................................. 38
Figure 3.2. Experimental equipment. (a) Analytical balance OHAUS; (b) Filter
45 μm; (c) Centrifuge machine UNIVERSAL 320; (d) Umex UVA Messsystem;
(e) pH meter; (f) Ultrasonic bath. ........................................................................ 39
Figure 3.3. Experiment setup ............................................................................... 40

Figure 3.4. UV Spectrum of CIP; (a) standard solution; (b) CIP Kabi .............. 41
Figure 3.5. Direct photolysis experimental procedure ........................................ 42
Figure 4.1. Effect of initial CIP concentration, direct photolysis process, no pH
adjustment, Re = 6546. ........................................................................................ 45
Figure 4.2. The CIP degradation efficiency after 45 min with [CIP]0 varied from
1 to 20 mg/L; UV-only process. ........................................................................... 46
viii


Figure 4.3. Effect of UV intensity on CIP treatment efficiency. .......................... 47
Figure 4.4. The influence of TiO2 concentration on CIP degradation; (A) Re =
2000; (B) Re = 6546; (C) Re = 8560. .................................................................. 49
Figure 4.5. Effect of H2O2 concentration on CIP degradation; (A) Re =2000;
(B) Re =6546; (C) Re = 8650. ............................................................................. 53
Figure 4.6. Effect of hydrodynamic conditions on CIP treatment efficiency....... 55
Figure 4.7. Major steps in solid-liquid heterogeneous photocatalysis [84]........ 56
Figure 4.8. CIP degradation when treated with UV/ TiO2/ H2O2........................ 58
Figure 4.9. The efficiency of CIP treatment by UV/ TiO2/ H2O2 process at
different pH values ............................................................................................... 59
Figure 4.10. Ciprofloxacin ionized species [91]. ................................................ 60
Figure 4.11. The degradation rate constants of CIP at various pH values ......... 61
Figure 4.12. CIP degradation by different AOPs and aqueous media. (A)
Decomposition of CIP in 3 aqueous media by UV/ TiO2 process.; (B)
Decomposition of CIP in 3 aqueous media by UV/ TiO2/ H2O2 process; (C)
Decomposition of CIP in 3 aqueous media by UV/ H2O2 process; (D) The
efficiency of AOPs when treating CIP in the water matrix. ................................. 64
Figure 4.13. Compare different AOPs when treating CIP .................................. 65
Figure 4.14. The rate constants (kapp) and efficiency coefficients (R2) of CIPdegrading AOPs in the study................................................................................ 66

ix



TABLE OF TABLES
Table 1.1. Potential Treatment Methods ............................................................... 9
Table 1.2. Oxidation Potential of Common Chemical Oxidants ......................... 12
Table 1.3. Features of typical advanced oxidation processes (AOPs) ................ 14
Table 1.4. General characteristics of advanced oxidation processes AOPs ....... 16
Table 2.1. Ciprofloxacin Kabi 200mg/100ml. ..................................................... 28
Table 2.2. Ciprofloxacin ≥ 98%, Sigma-Aldrich Specification ........................... 28
Table 2.3. Characteristic data of TiO2 Merck ..................................................... 29
Table 2.4. The physical properties of H2O2 30% ................................................. 30
Table 2.5. Strengths and limitations of UV-Vis spectroscopy ............................. 34
Table 3.1. List of chemicals used ......................................................................... 38
Table 3.2. List of devices...................................................................................... 40
Table 3.3. UV density ........................................................................................... 42
Table 3.4. TiO2 and H2O2 concentrations............................................................ 43
Table 4.1. Kinetic parameters for the degradation of CIP with different initial
CIP concentration ................................................................................................ 45
Table 4.2. CIP degradation reaction efficiency at different TiO2 concentrations
and flow rates ....................................................................................................... 50
Table 4.3. CIP degradation efficiency by UV/H2O2 processes ............................ 54
Table 4.4. The efficiency of CIP degradation reaction by UV/TiO2/H2O2
processes .............................................................................................................. 59
Table 4.5. Reaction efficiency of various advanced oxidation processes under
CIP treatment ....................................................................................................... 65
Table 4.6. Kinetic parameters for the degradation of CIP .................................. 67
Table 4.7. Summary of energy consumption of various AOPs for CIP degradation
.............................................................................................................................. 68

x



ABBREVIATION AND SYMBOLS
CIP

Ciprofloxacin

AOPs

Advanced oxidation processes

ABs

Antibiotics

WWTP

Wastewater Treatment Plant

EU

European Union

RO

Reverse Osmosis

UV

Ultraviolet


xi



INTRODUCTION
Currently, many studies have shown that plenty of chemicals has caused
immediate or long-term negative impacts on ecosystems, especially human health,
that have not been classified as contamination substances in the past, for example,
antibiotics, organometallic complexes,... Hence, the term "emerging pollutants"
was coined to describe pollutants that are not "new" chemically or biologically yet
present in the environment. However, no attention has been paid to, surveyed, or
researched eradication methods.
Among all types of pollutants, a gaggle of recalcitrant compounds is formed
by antibiotics (ABs), discharged into the wastewater in large quantities from
industrial activities, or excreted by humans or animals. The accumulation of ABs
within the environment risks aquatic flora and fauna and causes resistance in some
bacterial strains. Due to their complicated structure, these compounds are tough to
decompose, rendering them relatively durable and poorly biodegradable [1, 2].
Hence, the removal of antibiotics from sewage constitutes one of the most
significant challenges in water treatment. Preventing the degradation of the water
environment caused by these pollutants is the trend of many studies [3]. However,
it is complicated to control in practice because of the extensive dispersion of their
emission sources, such as home wastewater, hospital wastewater, industrial waste,
or landfills. Furthermore, they are relatively non-biodegradable compounds. As a
result, standard activated sludge treatment, commonly employed in municipal
wastewater treatment plants, is insufficient to remove these chemicals [4].
According to those problems, using other technologies is necessary to
remove the ABs. Advanced oxidation processes (AOPs) are a method that has high
application potential in today's modern technologies, mainly due to the high

reactivity and low selectivity of hydroxyl radicals. Since the identification of AOPs
in 1987, the subject has experienced fast advancements in both theory and
application. TiO2/UV systems, H2O2/UV systems, Fenton, photo-Fenton, and
Electro-Fenton systems have all been developed and successfully employed on a
pilot scale in the treatment of general pollution. Recently, a promising research
direction has been the application of AOPs to drug residue treatment.
Fluoroquinolones are a class of broad-spectrum synthetic antibiotics that
have been widely utilized in aquaculture, farming, human, and veterinary medicine
since their introduction in the 1980s [5]. As a second-generation fluoroquinolone
agent, ciprofloxacin (CIP) inhibits both gram-positive and gram-negative bacteria.
It is one of the most regularly prescribed fluoroquinolones globally, and it is
commonly used to treat serious infections that conventional antibiotics do not
work, such as skin infections, pneumonia, bronchitis, bone and joint infections,
1


gonorrhea...[6]. Unfortunately, more than 95 % of fluoroquinolones are excreted
unmetabolized or as active metabolites and end up in municipal wastewater [7].
Even at low concentrations, the presence of CIP in aquatic settings may pose major
hazards to the ecology, human health, and the biological treatment process of
wastewater treatment [8]. Because CIP removal in conventional WWTP is
insufficient, and unnecessary antibiotic exposure of aquatic environmental biota
should be kept to a minimum, alternative effective physiochemical technologies
are being considered, including advanced oxidation processes, effective for
removing pharmaceuticals herbicides, and other micropollutants.
In the advanced oxidation process of CIP degradation, the influence of the
concentration of active hydroxyl radicals and the problem of combining agents and
processes plays a vital role in increasing compound removal efficiency and costeffectiveness, as well as the basis for selecting the technology and working modes
of the process of removing pharmaceutical residues in general in wastewater. Few
researchers have investigated CIP degradation by AOPs; thus, additional studies

covering a wide variety of AOP parameters are required.
This work aims to study the AOP process of using H2O2, TiO2, and agent
combination to decompose CIP in RO water, which is reagent-grade bacteria-free
water, and consider the influence of other factors such as concentration or Re on
these processes. The topic of this master's thesis is: "Research on the degradation
of CIP residues in RO treated wastewater by AOP processes using different
oxidation agents."
This thesis is divided into four sections:
Chapter 1 examines existing knowledge about the presence and impact of
pharmaceuticals in the environment, emphasizing the need to remove these
substances from water. It is then followed by a section on AOPs, focusing mainly
on the UV/H2O2, UV/TiO2, and UV/H2O2 combined with TiO2.
Chapter 2 begins with a list of the materials and then moves on to a
description of the research methodologies. In addition, the methodology used to
assess the CIP deterioration process is given here.
Chapter 3 describe and summarize experimental procedures
Chapter 4 examines the results obtained from the experiment and then
makes assessments, comparisons, and discussions.
Chapter 5 illustrates the major conclusions of this work as well as future
research directions.

2


CHAPTER 1: OVERVIEW
1.1. Pharmaceuticals in the environment
Scientists recently have discovered pharmaceuticals and personal care
products (PPCPs), including EDCs, in ground and surface water sources [9, 10].
Sub-nanogram quantities of ABs, E.D.C.s, PPCPs, metals, and nitrosamines in the
environment have been studied that they have interfered with human and animal

hormone systems [11]. Pharmaceuticals reach the environment through a variety
of routes, including WWTP effluent, landfill leakage, agricultural activities, or
directly excreted from the human body into water sources. Fig.1.1 depicts the main
entrances for Pharmaceuticals into the environment.
Antibiotics

Human(House
hold, Hospital,
Industry)

Agriculture/
Food
Processing

Unused

Excretion

Landfill

WWTPs

Slaugter/
excretion

Surface
water

Soil


Veterinary
(Aqua, Pets,
Livestock...)

leakages
Groundwater

Drinking
water

Sediment

Food chain

Figure 1.1. Pharmaceuticals' main pathways for entering the environment [12].
As of lately, two gatherings of drugs have emerged to the consideration of
specialists given their perceivable impact even at low concentrations, including the
EDCs and the ABs [13]. EDs such as xenoestrogens influence the reproductive
capacities of people, weakening fruitfulness in a variety of natural life species [14].
EDCs are currently being studied to treat by green algae technology combined with
ultrafiltration and have an efficiency of 60% [15]. On the other hand, ABs ushered
in a new age of medical advancement in treating bacterial infections. According to
an American Academy of Sciences research, antibiotic consumption skyrockets in
low- and middle-income countries[16]. Antibiotic consumption in India has more
than doubled in the last 16 years, while it has climbed by about 80% in China[16].
Besides, in 2009, the level of antibiotic use in 15 major Vietnamese hospitals was
3


recorded, with mean daily data per 100 bed days (D.D.D./100 bed days). The

findings revealed that the average antibiotic consumption was 274.7 DDD per 100
bed days, much higher than the data from 139 hospitals in 30 European nations in
2001 (49.6 DDD per 100 bed days)[17]. As a result, the detection of antibiotics in
surface water, groundwater, and drinking water [18] is an understandable
phenomenon. Antibiotic resistance can emerge when substantial doses of
antibiotics accumulate in water and are not effectively handled. As a logical
consequence, antibiotics become ineffective, resulting in protracted infections
requiring previously unavailable alternative therapy due to cost or adverse side
effects such as increasing pharmacological toxicity [19]. Furthermore, antibiotics
prevalent in ecosystems can harm microflora and -fauna as well as accumulate in
food chains and organisms.
In order to remove toxins from wastewater, two primary procedures are
currently used, as shown in Fig.1.2. Physical procedures such as screening and
filtering are used in primary treatment to remove sludge, debris, and other solid
materials from sewage. Bacteria are used in secondary treatment to remove
dissolved organics and finer organic particles from sewage via biological
processes. Furthermore, secondary treatment technologies include sludge
processing and tricking filters. In some WWTPs, a tertiary stage employs advanced
treatment technologies to eliminate elements not addressed by primary or
secondary treatment [9]. Although chlorine is used as a disinfectant in the last
phase of most wastewater treatment plants, not all authorities agree on this [20].

Raw effiluent

Primary
treatment

Secondary
treatment


Tertiary step

Figure 1.2. Wastewater treatment.
Despite medicines entering the sewage network and arriving at the
WWTPs, these traditional WWTPs are not designed to eliminate pharmaceuticals,
particularly antibiotics, existing at low levels owing to low biodegradability, and
hence the applied treatments are inefficient in their removal [13], [21], [22]. So as
to resolve this concern, several techniques such as membrane filtration, activated
carbon adsorption, Membrane Bioreactor (MBR), and advanced oxidation
processes (AOPs) have been used [13], [21].

4


1.2. Ciprofloxacin
Ciprofloxacin (CIP), ID-CAS 85721-33-1, a second-generation
Fluoroquinolone, was invented by Bayer A. Grass in 1983 and recognized by the
Us in 1987. Ciprofloxacin appears in the form of a white powder with a harsh
flavor. To avoid photolytic deterioration, it should be kept at 4°C in the dark. At
278.5°C, it melts. CIP dissolves completely in acetic acid and is mildly soluble in
water (approximately 350mg/L in water), methanol, ethanol, or acetone.
Ciprofloxacin's octanol/water partition coefficient was found to be lower than 163.
The molecular weight of CIP is 173.168 g/mol.
CIP’s full chemical name is 1-cyclopropyl-6-fluoro-1, 4-dihydro-4-oxo-7(1-piperazinyl)-3-quinoline carboxylic acid [23]. CIP's molecular structure is
divided into a quinolone structure with a benzene ring and a piperazine ring
structure with a six-membered N ring. Fig 1.3 illustrates the chemical structure of
ciprofloxacin [24].

Figure 1.3. Chemical structure of ciprofloxacin.
Fig 1.4a shows that a cyclopropyl group is attached to a nitrogen atom at

position 1. At position 7, the piperazine radical is attached to a second nitrogen
atom - the radical directly responsible for the antimicrobial activity of the
Flourroquinolone molecule. The two six-membered benzene rings are the
quinolone molecule and, together with the piperazine substituent, are the attack
sites required for oxidation. In Fig 1.4b, the blue box is the quinolone structure of
ciprofloxacin, and the red circle is the piperazine ring.

Figure 1.4. The structural formula of ciprofloxacin
5


1.3. Ciprofloxacin in Environment
1.3.1. Occurrence
1.3.1.1. The situation in the world
Scientists from the University of York (UK) conducted antibiotic-resistant
bacteria studies at 711 locations on rivers in 72 nations across six continents. The
Chao Phraya, Danube, Mekong, Seine, Thames, Tiber, and Tigris rivers have all
been sampled. The results published at the United Nations in 2019 revealed that
65 percent of the survey sites were contaminated by antibiotics, with rivers in
Africa and Asia being the most contaminated globally. Ciprofloxacin, a drug used
to treat certain bacterial infections, was found to have frequently surpassed the
acceptable level, crossing the threshold at 51 test sites.
Plosz et al. (2010) undertook research to compare CIP incidence in
Brazilian hospital effluents and WWTP effluents to previously reported
occurrences of CIP in Europe and the United States [25]. According to the study,
there was a significant CIP level in Brazil's surface water since hospitals and
WWTPs frequently lacked suitable removal procedures or bypassed treatment
entirely.
Karthikeyan and Meyer (2006) did an investigation in the United States,
analyzing seven wastewater treatment facility effluents [26]. The investigation

discovered six distinct antibiotics in the effluent, at varying quantities in various
plants: trimethoprim (0,12–0,55 µg/L), macrolides (approx. 0,3 µg/L),
tetracycline (0,07–0,37 µg/L), sulfamethoxazole (0,05–0,37 µg/L), and
ciprofloxacin (0,04–0,14 µg/L). It was also discovered that concentrations differed
according to the season.
Fick et al. (2009) conducted research in a region of India known for its
pharmaceutical industry [27]. The plants employed various treatment methods,
including biological treatment and adsorption. Approximately 12,000 ng/L CIP
was found in the waterways upstream of the facility. After treatment, roughly
2,500 g/L of CIP was recorded 150 meters downstream, and 10,000 ng/L of CIP
was measured 30 kilometers downstream from the treatment plant. According to
the research, WWTPs do not consistently or efficiently remove CIP from influents,
so CIP is leaked into the water.
These and other investigations demonstrate the frequency with which CIP
is prevalent in the environment. Wastewater treatment plants' ability to remove
CIP varies, resulting in considerable volumes of CIP being discharged into the
environment. Failure to effectively remove CIP from wastewater, along with tiny

6


quantities of CIP that seep into the soil via septic systems or incorrect disposal, is
contaminating ground and surface water in many parts of the world.
1.3.1.2. The situation in Vietnam
Nguyen Dinh Tuan and Hoang Thi Thanh Thuy surveyed the presence of
antibiotics in wastewater and surface water downstream of the Saigon - Dong Nai
basin (2013). The results showed that CIP ranked second among substances found
in water and mud. In particular, the frequency of occurrence of CIP in rivers where
there is direct discharge is particularly high, 25% in water and 100% in sludge
[28].

In 2019, Nguyen Thi Thu Trang et al. conducted a survey of domestic
wastewater in some areas in Hanoi. In addition to pollutants typical for domestic
wastewater such as COD, ammonium, phosphorus, ..., the wastewater also
contains residues of pharmaceuticals with a very high concentration of certain
substances, such as antibiotics Ciprofloxacin, Norfloxacin, in addition to
tetracycline, and pain relievers Ibuprofen, Acetaminophen. Notably, conventional
treatment systems cannot remove these substances from the system [29].
For several common antibiotics, including ampicillin, amoxicillin, and
ciprofloxacin, as retention times increased from 0,5 to 3 days, their percentage
reductions were 75, 17, and 0%, respectively [30]. It is easy to see that antibiotics,
especially CIP, are stable chemical compounds and are difficult to decompose
under normal conditions.
In general, in Vietnam, there are relatively few reports related to the
problem of antibiotics in wastewater as well as measures to deal with them.
Meanwhile, the use of antibiotics without a prescription, especially CIP - a
common antibiotic that can be bought everywhere, is taking place every day. This
pollution occurrence is essential to investigate since related environmental and
health consequences are discussed in the next section.
1.3.2. Risks to the Environment and Humans
Antibiotic-polluted livestock products may have negative consequences in
humans, such as allergic responses or anaphylaxis, and disrupt the microbiota in
the gastrointestinal system. This is yet another route via which resistance might
emerge [31]. Kümmerer (2008) has thoroughly examined antibiotics in wastewater
and discovered that the quantity of antibiotics that finally reach the environment is
in the range of ng/L to g/L, which is regarded to be minimal. However, nothing is
known about the destiny of metabolites and how it impacts humans. The low
dosages and long-term effects of medications or antibiotics in wastewater reused
in agriculture on consumers and the repercussions for newborns, fetuses, and the
7



elderly are also unclear [32]. Sub-therapeutic antibiotic dosages on bacteria over a
long period result in resistance, which is a hazard to the environment [33].
Ahmad et al. was carried out on the resistance of common bacteria to CIP,
such as fecal coliforms such as E. coli and enterococci. Water samples from
wastewater treatment plants were collected and examined for CIP and other
antibiotic resistance. Several methods were used to determine if fecal coliforms
had intermediate resistance to CIP. Reduced susceptibility to CIP was also
discovered in 3.5% of total fecal coliforms and 52%t of enterococci in the influent
[34].
Along with this study, Coelho (2010) conducted another to investigate the
influence of residential wastewater treatment facilities on bacterial resistance to
CIP. According to the findings, nutrient-rich environments such as sewage and
wastewater create excellent conditions for horizontal gene transfer, allowing
bacterial resistance to spread among organisms. As a result, wastewater treatment
plants provide perfect breeding habitat for bacterial-resistant species [35].
For 35 days, Richards et al. (2004) exposed outdoor microcosms to a
combination of CIP, fluoxetine, and ibuprofen in three concentrations: low,
medium, and high. As a response, fish died in fewer than 35 days under medium
dosage and less than 4 days under high level. Phytoplankton and Zooplankton
abundance rose while variety declined in the high treatment, whereas medium and
low levels showed constant trends [36].
Furthermore, EU research indicates that sulfanomides and fluoroquinolones
are incredibly harmful to aquatic species, including cyanobacteria, freshwater
algae, and duckweeds [37]. Because these organisms play an important part in
aquatic habitats, antibiotics can disrupt entire ecosystems. Due to the widespread
distribution of these antibiotics, ciprofloxacin was added to the second EU watch
list of compounds for union-wide management in the field of water policy (EU
Decision, 2018) [38].
1.4. Potential treatment techniques

It was evident from the preceding section that traditional wastewater
treatment plants were not intended to remove pharmaceuticals from wastewater,
and hence they are incapable of providing efficient treatment of antibioticcontaminated water. As a result, modern water treatment technologies are essential
to enable successful pharmaceutical removal in aqueous systems. Table 1.1
compiles brief summaries, benefits, and downsides.

8


Table 1.1. Potential Treatment Methods
Technologies
Adsorption

Advantages
-

Activated
muds

Membrane
filtration

-

-

Bio-membrane technology
(MBR)
-


-

Advanced
oxidation
processes
(AOPs)

-

-

High efficiency of
elimination
Treatment time is
short, and the process
is straightforward.
Low
operating
expenses
Simple maintenance
Elimination
of
dissolved pollutants
in a relatively safe
manner
Basic utilize
High efficiency of
elimination
Without the use of
chemicals

Quick and simple
process
Do not use chemical
disinfectants
Treatment tank size
is
smaller
than
traditional
technology.
Short HRT (HRT:
Hydraulic Residence
Times)
Long SRT (SRT:
Sludge
Residence
Times)
Controlling
the
automatic
monitoring process is
simple
High efficiency of
pollutants
degradation and the
possibility
of
complete
mineralization in a
short period

Include
environmentally

Disadvantages
-

-

-

Ref

Material expenses [39]–[44]
are high.
Non-destructive
method, secondary
hazardous waste

Require
the [45]
removal of leftover
mud.
Toxin or antibiotic
susceptibility
High operating and [40]–[43],
maintenance costs [46], [47]
Membrane
clogging
Unsuitable for vast
amounts of sewage

Costly
operation [48], [49]
and maintenance
Membrane
clogging Expensive
initial investment
Applying with a
massive volume of
effluent is limited.

High operating and [42], [44]
investment
expenses.
Post-treatment is
necessary
to
eliminate toxicity
in the case of
partial
mineralization.
9


friendly, safe, and
sustainable processes
- Disinfection
properties
According to Table 1.1, physical procedures such as adsorption and
membrane filtering have one major limitation: the generation of secondary waste.
Pollutants are transported from the liquid phase of wastewater to the solid phase

of adsorbents in the case of adsorption, or collected on the membrane surface in
the case of membrane filtration, with no breakdown. This means that ABs do not
alter their chemical structure and keep their dangerous potential [40]. Furthermore,
the produced waste must be appropriately disposed of, increasing the cost of
treatment technology. As a result, the primary benefit of AOPs is the noticeable,
efficient reduction of pollutants, with the possibility of total mineralization.
AOPs are now being explored extensively by several research groups
because they produce highly promising findings and have a high potential for
widespread application. According to studies, the best performance is connected
with antibiotic removal procedures that integrate many stages. A mixture of AOPs
or a combination of AOPs and membrane filtration are examples. However, more
advancements are required to make these procedures cost-effective while
maintaining great efficiency.
1.5. Advanced Oxidation Processes (AOPs): Overview
According to Staehelin & Hoigne (1985), the advanced oxidation process
or AOP is characterized by the production of strong oxidants to oxidize organic
compounds. Most advanced oxidation processes produce a reactive and nonselective hydroxyl radical, which is the strongest oxidizing agent in aqueous
media. The hydroxyl radicals can oxidize nearly all organic compounds to water,
carbon dioxide, and mineral salts through a process called mineralization [50]. The
reaction mechanism is as follows:
R+HO• → ROH ….

(Re.1)

R+HO• → R + H2O …..

(Re.2)

Rn + HO• → Rn-1 + OH─….


(Re.3)

Advanced oxidation processes are suitable for dealing with persistent
organic substances such as detergents, antibiotics, pesticides, dyes,..., and
inorganic substances, toxic substances such as cyanide, sulfide, and nitrite.
Besides, they are also prevalent in the sterilization process because the ●OH radical
does not produce toxic or dangerous by-products. AOPs can also destroy bacteria
and viruses such as Coliform, Terina, Escherichia Coli,...[51].
10


1.5.1. The superiority of Advanced oxidation processes
It is not always necessary to completely oxidize a compound or a group of
compounds. In most cases where the desired end product quality should be
considered, partial oxidation is usually sufficient to reduce the toxicity of specific
compounds or make them more easily handled in the following process. The
degree of recession is divided into four groups as follows:

Primary degration

Acceptable
degradation

• Cause a structural change in the
compound, allowing it to be more simply
eliminated by other procedures (biological
treatment, adsorption, ...)

• Toxicity is reduced by structural changes
in the original compound.


Mineralization
process

• Organic carbon compounds convert to
inorganic carbon dioxide (CO2).

Unacceptable
Recession

• Structural changes in the parent compound
lead to increased toxicity.

Figure 1.5. Four levels of degradation of Advanced oxidation processes [52].
As a result, it is not essential to accomplish a mineralization effect to have
a beneficial process while conducting advanced oxidation. This characteristic of
this method can be advantageous in terms of both energy and economics.
In most advanced oxidation processes, hydroxyl radicals (HO•) are
generated to oxidize pollutants in water and air, but some processes are also carried
out based on other oxidizing radicals such as sulfate or chlorine. Oxidation is the
loss of electrons by an atom, molecule, or ion. Therefore, each oxidizing agent has
an oxidation potential (V) to characterize its oxidizing strength. The oxidation
potential of certain well-known chemical oxidants is shown in Table 1.2, compared
to oxygen's oxidizing capacity.

11


Table 1.2. Oxidation Potential of Common Chemical Oxidants
Oxidation radical


Symbol

Oxidation
potential (V)

Compared with the
oxidation potential of
oxygen gas (%)

Fluor

F2

3,03

246,3

Hydroxyl

•

2,80

227,6

Ozone

O3


2,07

168,3

Hydroperoxide

H2 O2

1,78

144,7

Pemanganat

MnO4-

1,68

136,6

Chlorine dioxide

ClO2

1,57

127,6

Hypobromua acid


HBrO

1,59

129,3

Hypoclorua acid

HClO

1,49

121,1

Chlorine

Cl2

1,36

110,6

Oxygen

O2

1,23

100,0


Bromine

Br2

1,09

88,6

Iod

I2

0,54

43,9

OH

Table 1.2 shows that the hydroxyl radical has a relatively high oxidation
potential (2,80 eV), only inferior to fluorine. However, it is about 2,3 times higher
than the oxidation potential of common oxygen, so it can non-selectively strongly
oxidize pollutants in the environment [53].
1.5.2. Classification of advanced oxidation processes (AOPs)
Indeed, there are many ways to classify advanced oxidation methods.
However, this thesis presents the classification based on the state of the reaction
solution. The different AOPs are classified into 2 main categories: heterogeneous
or homogenous [52], [54]. The latter is usually further subdivided on the basis of
energy used.

12