Application of sorbents derived and converted from agricultural wastes in removal of cationic dye, antibiotic, and heavy metal pollutants from aqueous solution

This study thus explores the potential of low-cost adsorbents derived from agricultural wastes in removal of typical ionic contaminants such as cationic dyes using methylene blue, MB, as

pollutants from aqueous solution

研 究 生 ：Nguyen Duy Hai (阮瑞海)

指導教授：Chu-Ching Lin (林居慶)

中 華 民 國 一 百 一 十 年 一 月

摘要

近年來由於工業化及人口增長等因素，許多開發中國家開始面臨日益嚴重的環境污染問題，包括有害物質對水源所造成的污染。而在水和廢水處理工法中，吸附一向被認為是成本相對較低且有效的方法，因此受到發展中國家的青睞，常用於去除受污染水源中有害、不可生物降解的污染物。在越南，由於農業仍在經濟上扮演著至關重要的角色，因此可將農業活動所衍生的大量農廢視為寶貴的原料，以合成碳吸附劑並應用在污染整治。儘管農廢合成的吸附劑常以活性炭（AC）為優先選擇，但傳統的 AC 在合成時常涉及高溫（600 - 1200

°C）的碳化和活化程序，反讓 AC 被視為是昂貴且較不環保的材料，故需開發更簡單、更綠色、更完善的方法合成碳基吸附劑，且能有效地應用於污染處理。水熱合成炭（HC）即是近期極受關注的碳屬吸附材，因為這種碳質材料是通過低溫（180 - 350 °C）的水熱碳化製備而來，因此可保有表面氧化官能基的豐富度。本研究即試著利用農業廢棄物以水熱法合成低成本的吸附劑，並在適當的改質下探討這些吸附劑用於去除水中典型的離子污染物，如陽離子染料（以亞甲基藍(MB)作為模擬化合物）、抗生素（以四環素(TC)作為目標藥物）以及金屬物種（以 Cu2+，Cd2+ 作為測試離子）的可行性及背後的吸附機制。

FTIR、XPS 技術和 Boehm 滴定(用以確定酸性官能基團)進行表徵。首先，經由廢棄的橙皮合成出水熱合成炭（原始水熱合成炭），然後再用硝酸對其進行改質

（氧化水熱合成炭）用以吸附 MB。結果表明，由 Langmuir 模型估算出 30 oC 時

Abstract

Due to the industrialization and population growth in recent years, Vietnam and other developing countries have begun to face problems of increasing environmental pollution, including water contamination with hazardous substances Of water and wastewater treatment methods, adsorption is considered a relatively low-cost and effective means favored by developing countries for the removal of harmful, non-biodegradable pollutants from contaminated water Because agriculture still plays a vital role in the economy of Vietnam, it becomes clear that the abundance of agricultural wastes can be valuable feedstocks of carbonaceous sorbents used for pollution handling in Vietnam While activated carbon (AC) derived from agricultural residues has been used as a preferential sorbent in this regard, the traditional way of AC synthesis involving processes of carbonization and activation under high-temperature (600–1200 °C) conditions makes AC an expensive, eco-unfriendly material Hence, there is a need for the development of carbon-based adsorbents via a simpler, greener, and robust way for effective use in dealing with pollution Recent attention has been drawn to hydrochar (HC), as this carbonaceous material is prepared through hydrothermal carbonization

at low temperature (180–350 °C) and thus the richness of surface oxygenated functionality can

be maintained This study thus explores the potential of low-cost adsorbents derived from agricultural wastes in removal of typical ionic contaminants such as cationic dyes (using methylene blue, MB, as the model compound), antibiotics (tetracycline, TC, as the targeted drug), and metal species (Cu2+, Cd2+ as the tested ions) from aqueous solution

Prior to adsorption tests, all synthetic sorbents were characterized through the SEM, SBET analyzer, FTIR, XPS techniques, and Boehm titration to determine the acidic functional groups First, hydrochars were derived from wasted orange peels (raw-hydrochars) and further modified with nitric acid (oxidized-hydrochars) to adsorb MB Results show that the maximum MB adsorption capacity at 30 oC estimated by the Langmuir model followed by

the order of mGH (246 mg/g) > mOPH (107 mg/g) > OPH (59.6 mg/g) > GH (54.8 mg/g) Second, teak sawdust was used to synthesize ACs through hydrothermal carbonization followed

by chemical activation with varying concentrations of ZnCl2 or K2CO3 For ACs, their MB-, Cd(II)-, and Cu(II)-adsorption capacity increased with the concentration of the activating agent: the maximum adsorption capacities were achieved when the weight ratio of the carbonaceous material to ZnCl2 reached 1.75 The maximum adsorption capacities obtained for MB, Cd(II), and Cu(II) were 516 mg/g, 166 mg/g, and 159 mg/g, respectively Finally, because TC is a pH-tunable compound, it was used to validate the adsorption pathways concluded from prior tests with those higher adsorption capacity-HC and AC materials The maximum adsorption capacities of TC estimated by the Langmuir model were found to follow the order: ACZ1175 (257.28 mg/g) > mGH (207.11 mg/g) > WAC (197.52 mg/g) > mOPH (168.50 mg/g) > OPH (85.79 mg/g) > GH (75.47 mg/g) at 25 oC and pH 5.5 In addition, potential adsorption mechanisms were deeply discussed in this study The electrostatic force was identified as the primary pathway that led to the adsorption of the tested contaminants onto the sample Further, while the π-π and n-π interaction became minor pathways for MB and TC adsorption onto oxidized-hydrochars, the complexation reaction was an important mechanism responsible for the adsorptive interaction between ACs and metal species (Cu2+, Cd2+) Moreover, the result illustrated that the amount of oxygen-containing functional groups is regarded as an important factor in determining the adsorptive amounts

It is expected that the knowledge obtained through extensive exploration in this study would help further development of the low-cost materials for the practical applications

Keywords: Agricultural wastes; Hydrochars; Activated carbons; Dyes and Tetracycline; Heavy

metals; Adsorption

Acknowledgments

I would like to express my appreciation to the people who have given me support and encouragement throughout my Ph.D journey

Firstly, I would like to sincerely express my great gratitude and special appreciation to

my supervisor Prof Chu-Ching Lin for his valuable advice, guidance, wonderful encouragement, and patience throughout the research and thesis preparation

Secondly, I wish to extend my warm thanks to Prof Huan-Ping Chao and Prof

Ching-Ju Monica Chin for their advice and helps, in particular for letting me use chemicals and

equipment in their laboratories I would also like to thank Prof Chiung-Fen Chang, Prof Jung Lin and Prof Jr-Lin Lin for their comments and suggestions, which greatly improved the quality of this thesis

Chin-Thirdly, I wish to express my gratitude to Dr Tran Nguyen Hai, all of my lab-mates and the staff in the Institute of Environmental Engineering at NCU as well as my co-workers at Faculty of Environment, TUAF for their help and collaboration during my study

I especially wish to express my sincere thankfulness to my beloved parents for your tremendous love and many prayers that have always been very valuable and for teaching me how to be a strong person unconsciously by making me get back up whenever I stumble

Special thanks go to all family members, including my parents-in-law, and my dear young sisters-in-law for their love, care and support along the way

Lastly, I am the most grateful to my wife Nguyen Ha Anh who overflows me with love and inspiration day by day I share this accomplishment with you Thank you for your encouragement, for believing in my capabilities, moral supports in all the good and hard times, and patience during these years

List of Contents

Pages

摘要 i

Abstract iii

Acknowledgments v

List of Contents vi

List of Figures x

List of Tables xii

Explanation of Symbols xiv

Abbreviations xv

CHAPTER 1 1

Introduction 1

References 7

CHAPTER 2 14

Background 14

2.1 Water and Sources of Water Pollution 14

2.2 Water Pollutants and Effect of Water Pollution on Human Health 16

2.2.1 Heavy Metals 16

2.2.2 Textile Dyes and Methylene Blue (MB) 18

2.2.3 Antibiotic Products 20

2.2.4 Effect of Water Pollution on Human Health 20

2.3 Wastewater Treatment Technologies 23

2.4 Adsorption 24

2.4.1 Basic Technical Terms Used in The Study of Adsorption 24

2.4.2 Physical and Chemical Adsorption 25

2.4.3 Mathematical Model 26

2.5 Adsorbents and Water Purification 29

2.5.1 Agricultural Wastes 29

2.5.2 Hydrochar Products 31

2.5.3 Activated Carbon Products 37

2.6 Adsorbent Characterization 40

2.7 Comparison of The Estimation of Adsorbent Production Cost 41

References 43

CHAPTER 3 61

Effect of Nitric Acid Oxidation on the Surface of Hydrochars to Sorb Methylene Blue: An Adsorption Mechanism Comparison 61

Abstract 61

3.1 Introduction 62

3.2 Materials and Methods 64

3.2.1 Feedstock and Chemical 64

3.2.3 Adsorbent Characterization 66

3.2.4 Adsorption Study 67

3.3 Results and Discussion 68

3.3.1 Morphological and Textural Properties of Hydrochars 68

3.3.2 Chemical Properties of Hydrochars and Oxidized Hydrochars 70

3.3.3 Methylene Blue Adsorption 74

3.3.4 Adsorption Mechanisms of MB on The Oxidized-Hydrochar 81

3.4 Conclusions 83

References 84

CHAPTER 4 91

Activated Carbons Derived from Teak Sawdust-Hydrochars for Efficient Removal of

Methylene Blue, Copper, and Cadmium from Aqueous Solution 91

Abstract 91

4.1 Introduction 92

4.2 Materials and Methods 94

4.2.1 Chemicals and Activated Carbon Preparation 94

4.2.2 Sorbent Characterization 96

4.2.3 Sorption Experiment and Data Analysis 97

4.3 Results and Discussion 97

4.3.1 Characteristics of Sorbents 97

4.3.2 Adsorption Capacity of MB, Cd(II), and Cu(II) by ACs 103

4.3.3 Comparison of Adsorption Mechanisms 107

4.4 Conclusions 113

References 114

CHAPTER 5 120

Using Tetracycline to Validate Adsorption Mechanisms Underlying the Ionic Organic Compound-Synthetic Sorbent Interaction 120

Abstract 120

5.1 Introduction 121

5.2 Materials and Methods 123

5.2.1 Tetracycline Characterization 123

5.2.2 Hydrochar and Activated Carbon Samples 123

5.2.3 Adsorption Kinetics 124

5.2.4 Adsorption Isotherms 125

5.2.5 Influence of pH Solution on TC Adsorption 125

5.2.6 Sorption Data Analysis 126

5.3 Results and Discussion 126

5.3.1 Adsorption Kinetic 126

5.3.2 Adsorption Isotherms 128

5.3.3 Influence of Solution pH and Adsorption Mechanisms 132

5.4 Estimation of Adsorbent Production Cost 134

5.5 Conclusions 136

References 137

CHAPTER 6 142

Summary and Suggestions 142

6.1 Conclusions 142

6.2 Suggestions 144

Appendix: VITA 145

List of Figures

Figure 2 1 Basic technical terms used in the study of adsorption [From (Tran et al 2017c) With permission] 25Figure 2 2 Classification of hydrothermal processing of biomass [adopted from (Kambo and Dutta 2015)] 32Figure 2 3 Propose modification techniques of HC adsorbents (Anastopoulos et al 2019; Wang and Wang 2019) 36Figure 2 4 Basis properties of HC & AC adsorbent determined by various techniques (Tran et

al 2017d; Wang and Wang 2019) 41

Figure 3 1 Schematic illustration of the preparation procedure for hydrochar (GH, OPH) and oxidized hydrochar (mGH, mOPH) 66Figure 3 2 Effect of pH of the MB solution on λmax values (without adsorbent) 67

Figure 3 3 SEM images of (a) D-glucose derived hydrochars (GH), (b) HNO3-modified GH (mGH), (c) Orange peel derived hydrochars (OPH) and (d) HNO3-modified OPH (mOPH) 69Figure 3 4 FTIR spectra of the synthesized hydrochar samples before and after adsorption (a)

GH and mGH, (b) OPH and mOPH 72Figure 3 5 Adsorption isotherms of GH, mGH, OPH and mOPH for MB at 30 oC (Experimental conditions: initial MB concentrations ranging from 100 to 1000 mg/L, initial solution pH: 7.0 and contact time: 24 h) 74Figure 3 6 (a) The pH dependence on adsorption capacity, (b) Point zero charge of the hydrochar samples (Experimental conditions: initial [MB]: 620 mg/L, contact time: 24 h, temperature: 30 oC and solution pH: 7.0) 79Figure 3 7 Proposed adsorption mechanisms for MB removal onto oxidized hydrochars 82

Figure 4 1 Schematic illustration of the preparation procedure for the activated carbon (AC)

samples 95

Figure 4 2 SEM images of (a) WAC, (b) ACZ1175, and (c) ACK1075 98

Figure 4 3 Pore size distribution of WAC, ACZ1175, and ACK1075 100

Figure 4 4 FTIR spectra of (a) WAC, (b) ACZ1175, and (c) ACK1075 101

Figure 4 5 Isotherms for adsorption of (a) MB, (b) Cd(II), and (c) Cu(II) onto WAC, ACZ1175, and ACK1075 at 30 oC, solution pH: 5.0 and contact time: 24 h) 105

Figure 5 1 Effect of pH of the TC solution on λmax values (without adsorbent) 123

Figure 5 2 Schematic demonstration of the preparation procedure for hydrochar (GH, OPH) and their modified-hydrochar (mGH, mOPH) and activated carbon (WAC and ACZ1175) 124 Figure 5 3 Adsorption kinetics of TC with the concentration of 500 mg L-1 on the hydrochar and ACs samples at 25 oC 127

Figure 5 4 Adsorption isotherm of TC on the hydrochar and ACs samples 129

Figure 5 5 Effect of pH on the adsorption of TC on hydrochar and AC samples Conditions: temperature 25 oC; [TC]= 50 mg/L; adsorbent dosage 0.05 g; different pH values (3.0, 5.5, 7.0, and 9.5) 133

List of Tables

Table 2 1 Properties of point and nonpoint sources of water pollution 15

Table 2 2 Chemical and physical properties of Cu(II) and Cd (II) 17

Table 2 3 Examples of the chemical formula and characteristic of MB and TC 19

Table 2 4 Toxic elements in drinking water and their impact on human health 21

Table 2 5 Kinetic model of the adsorption process 27

Table 2 6 Langmuir and Freundlich isotherm models 28

Table 2 7 Adsorbents resulting after thermochemical processes expressed as weight percentage 33

Table 2 8 The adsorption behavior of hydorchar/AC with recalcitrant pollutants 34

Table 2 9 Comparative analysis with other biomass-based chars reported on literature 42

Table 3 1 Textural properties of the hydrochar samples 69

Table 3 2 Surface elemental compositions of the hydrochar samples 71

Table 3 3 The FTIR spectral characteristic of modified and un-modifed hydrochar before and after adsorption of MB 73

Table 3 4 The acidic and basic groups of the hydrochar samples determined 73

Table 3 5 Corresponding isotherm parameters for MB adsorption onto the hydrochar samples 75

Table 3 6 Thermodynamic parameters for MB adsorption process on to the un-treated 77

Table 3 7 Comparison of adsorption capacities of various adsorbents for MB removal 80

Table 4 1 Name of the different AC products resulting from activated and non-activated teak sawdust-hydrochar 95

Table 4 2 Pore characteristics of the synthesized AC samples 99

Table 4 3 The FTIR spectral characteristic of AC before adsorption of heavy metals 101Table 4 4 Elemental compositions of the selected AC samples 102Table 4 5 Oxygen-containing functional groups (OFGs) of the AC samples 103Table 4 6 Methylene blue (MB) adsorption capacities of the AC samples synthesized through various processes of activation 104Table 4 7 Cd2+ adsorption capacities of the AC samples synthesized through various

processes of activation 106Table 4 8 Cu2+ adsorption capacities of the AC samples synthesized through various

processes of activation 107Table 4 9 Comparisons of the adsorption capacity of various adsorbents for methylene blue and heavy metals 110

Table 5 1 Adsorption kinetics parameters of TC on the hydrochar and AC samples 127Table 5 2 Corresponding isotherm parameters for TC adsorption onto the hydrochar and ACs samples 130Table 5 3 Cost estimation of Oxidized hydrochar and ACs production 134

Ce equilibrium concentration mmol/l or mg/l

Co Initial concentration mmol/l or mg/l

k1 Pseudo-first-order rate constant

k2 Pseudo-second-order rate constant

KL Langmuir affinity constant

KF Freundlich affinity constant

nF Freundlich heterogeneity factor

qe Equilibrium adsorption capacity mmol/g or mg/g

Qo

max Theoretical maximum adsorption capacity mmol/g or mg/g

qt Adsorption capacity at time t mmol/g or mg/g

Abbreviations

BET Brunauer-Emmet-Teller FTIR Fourier transform infrared spectroscopy

SEM Scanning Electron Microscopy XPS X-ray Photoelectron spectroscopy ACs Activated carbon samples

CHAPTER 1 Introduction

Aquatic environments contaminated with hazardous chemicals resulting from the concurrent expansion of industrialization and population growth has become one of the tough challenges that face developing countries like Vietnam in recent years Contamination may originate from point- or nonpoint-sources that discharge untreated or inadequately treated effluents to receiving water bodies, which not only results in deterioration of the aquatic environment but may also cause significant hazards to public health Pollutants have been gained great attention in Vietnam include those that are recalcitrant to biodegradation (e.g., dyes with complex structures) and those that are hardly removed from conventional wastewater treatment processes (e.g., heavy metals and contaminants of emerging concern like antibiotics) How to effectively remove these pollutants from wastewater has become an increasingly critical issue in many countries (Mohanty et al 2006)

To date, several methods have been developed to deal with hazardous substances in effluents (Cengiz et al 2012; Hequet et al 2001; Mohammadi et al 2011; Sud et al 2008; Wang 2017) Precipitation or ion exchange is commonly used to remove heavy metal ions from wastewater or water Photocatalysis and advanced oxidation processes can be adapted to decompose dyes (Chen et al 2017b; Kumar et al 2013; Liang et al 2015; Liu et al 2019) Although the aforementioned methods are effective, many investigators have sought simpler, lower-cost, and more eco-friendly processes (De Gisi et al 2016) Compared to these methods, adsorption is a relatively often used process and materials with high adsorption capacities thus can lower the costs of water and wastewater treatments (Murugan 2019; Padmapriya et al 2019; Yagub et al 2014)

In the past, activated carbon (AC) was used as the preferential sorbent in this regard, in

particular for the adsorption of non-ionic organic pollutants This is because AC possesses a higher specific surface area and pore volume Non-ionic organic compounds adsorb onto the surface of AC owing to the influence of van der Waals force or through other mechanisms (Tran

et al 2017b; Tran et al 2017c) However, the traditional way of synthesizing AC via high pyrolysis and (physical) activation temperatures has made AC, in general, a high-cost material (Zhang et al 2015) Moreover, the high carbonization temperature in the pyrolysis step of AC synthesis might reduce the amount of surface functional groups, such as OH and COOH (Tran

et al 2018), which can lead to the conditions for the adsorption of cationic contaminants onto

AC become unfavorable (Huang et al 2014) Hence, there is a need for the development of carbonaceous adsorbents via a relatively simple, green, and robust means for effective use in dealing with recalcitrant dyes, heavy metals, and emerging contaminants in aqueous solutions

Recent attention has been drawn to hydrochar, an emerging environmentally-friendly adsorbent that can be derived from hydrothermal carbonization (HTC) of organic wastes like agricultural wastes, forest residues, and animal husbandry manures (Fang et al 2015; Fang et

al 2017; Wang et al 2018b) HTC is considered a new process of carbonization In this process, agricultural wastes are carbonized through a hydrothermal process, where the feedstock is heated at relatively low temperatures (180 oC – 350 oC) and decomposed in a closed reactor under autogenous pressure (Fang et al 2017; Jain et al 2015; Libra et al 2011) The formation

of the products, i.e., hydrochars, is thus a result of the hydrolysis, condensation, decarboxylation, and dehydration (Berge et al 2011; Sevilla and Fuertes 2009; Xiao et al 2012) Although the specific surface area of hydrochar prepared in this way is typically lower than that of biochar - another less-expensive carbonaceous sorbent that is also considered an environmentally sustainable alternative to activated carbon, hydrochar may exhibit higher adsorption capacity toward the given contaminants as compared with biochar and even AC that is prepared using the traditional method because of its relatively abundant oxygenated functional groups (e.g.,

carboxylic, phenolic, hydroxyl) on the surface (Elaigwu and Greenway 2016; Jain et al 2016)

In fact, hydrochar can be subsequently applied to synthesize AC by chemical activation (Huang

et al 2014) Given that (i) the richness of surface functional groups on the carbonaceous materials is maintained and that (ii) the amount of surface functional groups is a critical factor

in determining the adsorption capacity of carbonaceous materials for heavy metal ions, the AC samples synthesized via HTC and chemical activation can be expected to possess high adsorption capacities for cationic contaminants

A considerable amount of investigations on the potential use of hydrochar in removing various contaminants from the aqueous phase have been undertaken lately (Islam et al 2017; Sun et al 2015; Xue et al 2012) For example, Sun et al demonstrated that for the given polar and nonpolar organic contaminants (e.g., bisphenol A, 17-ethinylestradiol (EE2), and phenanthrene), hydrochar possessed higher uptake capacity than biochar under otherwise identical conditions (Sun et al 2011); also, the study of Tran et al pointed out that increases in oxygenated groups on the surface of hydrochar resulted in electrostatic attraction, rather than π-π interaction, as the primary mechanism underlying the adsorptive interaction between hydrochar and methylene green, a cationic dye (Tran et al 2017a) Notably, hydrochar synthesized using different feedstocks may possess different kinds and varying abundances of surface functional groups (Libra et al 2011) In addition, several chemical agents have been applied to “activate” hydochar surface structure, including nitric acid (Güzel et al 2017; Jin et

al 2018; Shim et al 2001), sulphuric acid (Jiang et al 2003), hydrogen peroxide (Huang et al 2018; Wang et al 2018a; Xue et al 2012), potassium hydroxide (Sun et al 2015), ozone (Valdés

et al 2002), and phosphoric acid (Chen et al 2017a), which indeed results in the enhancement

in its adsorption performance (Xue et al 2012), even though such a chemical modification process may also affect the surface area and pore size distribution of the adsorbent (Güzel et al 2017) However, the underlying adsorption mechanisms have not been investigated and

discussed in depth

Given that a large fraction of solid wastes in developing country results from agricultural activities, it would make sense to study all the possible agro-based wastes as potentially inexpensive materials that would be useful in wastewater treatment Indeed, a variety of agricultural wastes including orange peels (Fernandez et al 2015; Tran et al 2016;

Xu et al 2014), rice straw (Chen et al 2018; Jiang et al 2012), rice husk (Mohanty et al 2006), and sugar cane bagasse, avocado, hami melon and dragon fruits (Mallampati et al 2015; Yahya

et al 2015) have been used to prepare adsorbents

This study focused on the removal of organic contaminant (methylene blue-MB), antibiotics (tetracycline), and heavy metals (cadmium (Cd) and copper (Cu)) from aqueous solution using various agricultural wastes-derived adsorbents Chapter 2 (background) contributes to the existing state of knowledge related to this study The shaping of wastewater treatment technologies and the recent progress in this area are introduced in detail Moreover, this chapter covers hydrochar/hydrochar-derived activated carbon production, its chemical composition, and its uses so far in relation to organic and inorganic contamination removal capacities The theories about the adsorption process, isotherms, kinetics, mechanisms, and the important parameters affecting the adsorption process are also reviewed The benefits of hydrochar/hydrochar-derived activated carbon use is mentioned since the prospects of this work imply the removal of both anions and cations by the same material A comparison of the estimation of adsorbent production cost is presented at the end of this chapter

Chapter 3 presents a novel, simple, and environmentally friendly technique for the preparation of hydrochar/oxidized-hydrochar through orange peel/D-glucose with and without HNO3 reflux This chapter is divided into three parts: (i) concern the preparation of hydrochar/oxidized-hydrochar from agricultural wastes (Orange peel/D-glucose) and its characterization The structures and physicochemical characteristics of hydrochar and oxidized-

hydrochar are described in detail in this part; (ii) the important parameters affecting the adsorption process are also reviewed (solution pH, pHPZC, temperature, contact time, etc.); (iii) the last is describing the interaction between hydrochar and MB adsorbates This chapter specifically investigated the methylene blue adsorption onto hydrochar/modified-hydrochar and the underlying mechanism Results of this chapter have been published as a journal article: Nguyen, D H., Tran, H N., Chao, H P., & Lin, C C (2019) Effect of nitric acid oxidation on the surface of hydrochars to sorb methylene blue: An adsorption mechanism comparison Adsorption Science & Technology, 37(7-8), 607-622

Chapter 4 describes two environmentally friendly processes employed for the removal

of some water contaminants such as metallic species (Cu (II), Cd (II), and cation dye (MB) The first process is one of adsorption on activated carbon prepared from teak sawdust-hydrochar (only high-temperature) and the second consists of chemical activation using ZnCl2/K2CO3 The results explore the characteristics and adsorption behavior of hydrochar-derived activated carbons It is revealed that hydrothermal carbonization/ZnCl2 activation plays

an important role in increasing the adsorption capacity of ACZ1175 The adsorption isotherms

as well as adsorption mechanisms are also presented, analyzed, and discussed This chapter has been published as "Activated Carbons Derived from Teak Sawdust-Hydrochars for Efficient Removal of Methylene Blue, Copper, and Cadmium from Aqueous Solution" in the journal

“Water” (Duy Nguyen, H., Nguyen Tran, H., Chao, H P., & Lin, C C (2019) Water, 11(12), 2581)

Chapter 5 demonstrates the experimental work regarding the process of tetracycline absorption onto hydrochar/hydrochar-derived activated carbon with a purpose to validate adsorption mechanisms underlying the ionic organic compound-synthetic sorbent interaction Due to the charge of tetracycline can be tuned by solution pH, the influence of solution pH is discussed in detail In addition, the cost analysis is performed to determine whether the whole production process of the HC/AC samples is feasible or not Hence, the adsorbent production

cost is estimated The outcomes of this study provide helpful information for future applications

of MGH and ACZ1175 for water treatment

Finally, chapter 6 summarizes the general conclusions drawn from this thesis and presents some suggestions for future studies

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CHAPTER 2 Background

2.1 Water and Sources of Water Pollution

Water is the most important compound for life on earth and it is a major global challenge for the 21st century to have drinkable water Pure and uncontaminated water is the basic requirement for all living organisms More than 71% of the earth's surface is covered with water, but only less than 1% of water is drinkable as per international standards because of different contaminations (Briggs 2003)

Water pollution is an undesirable change in the physical, chemical, or biological characteristics of water that can harmfully affect the health, survival, or activities of humans or other living organisms Two types of water pollutants exist: point source and non-point source (Agarwal 2009) Point sources of pollution occur when harmful substances are emitted directly into a body of water They include factories, wastewater treatment facilities, septic systems, and other sources that are discharging pollutants into water sources A non-point source delivers pollutants indirectly through environmental changes An example of this type of water pollution

is when fertilizer from a field is carried into a stream by rain, in the form of run-off which in turn affects aquatic life Non-point sources are much more difficult to control Pollution arising from nonpoint sources accounts for a majority of the contaminants in streams and lakes (Katan

2009) Sources that contribute to water pollution can be illustrated in Table 2.1

Table 2 1 Properties of point and nonpoint sources of water pollution

Different types of effluent

- Wastewater effluent (municipal

- Runoff from mines, oil fields,

unsewered industrial sites

- Storm sewer outfalls from cities with a

population >100,000

- Overflows of combined storm and

sanitary sewers

- Runoff from construction sites >2 ha

- Runoff from agriculture (including return flow from irrigated agriculture)

- Runoff from pasture and range

- Urban runoff unsewered and sewered areas with a population <100,000

- Septic tank leachate and runoff from failed septic systems

- Runoff from construction sites

- Runoff from abandoned mines

- Atmospheric deposition over a water surface

- Activities on land that generate contaminants, such as logging, wetland conversion, construction, and development

of land or waterways [Sources: adapted from (Carpenter et al 1998)]

The major sources of water pollution can be classified as municipal, industrial, and agricultural wastes Municipal wastewater results from homes and commercial establishments The characteristics of industrial wastewaters depend on the type of industry and the manufacturing process in question (Haas 1995; Wang et al 2009) The impact of industrial discharges depends not only on their collective characteristics, such as biochemical oxygen demand and the number

of suspended solids but also on their content of specific inorganic compounds The most common water pollutants are nutrients, organic matter, heavy metals, microbial contaminants,

toxic organic compounds (oil, pesticides, some plastics, and other industrial chemicals), salts, acids, sediments and suspended solids, and high temperature (Corcoran 2010; Revenga and Mock 2000) Water pollution has been widely studied by the government and scientists Therefore, protecting river water quality is extremely urgent because of serious water pollution and the global scarcity of water resources

2.2 Water Pollutants and Effect of Water Pollution on Human Health

Water pollution is a global issue and the world community is facing the worst results of polluted water Water pollutants are killing seaweeds, mollusks, marine birds, fishes, crustaceans, and other sea organisms that serve as food for humans

2.2.1 Heavy Metals

Due to the rapid development of industrial activities in recent years, the levels of heavy metals in the water system have substantially increased over time (Nouri et al 2006) Heavy metals are considered to be one of the most hazardous water contaminants They are major pollutants in marine, ground, industrial, and even treated wastewaters (Burton and Tchobanoglous 2018; Metcalf et al 1979) Unlike organic pollutants, metals are non-biodegradable and to accumulate in living organisms and many heavy metal ions are known to

be toxic or carcinogenic (Drinan and Spellman 2012) The presence of heavy metals in drinking water can be hazardous to consumers; these metals can damage nerves, liver, and bones and block functional groups of vital enzymes (Ewan and Pamphlett 1996) Metal ions in water can occur naturally from leaching of ore deposits and from anthropogenic sources, which mainly include industrial effluents and solid waste disposal The contamination of heavy metals in the aquatic environment has elicited significant attention due to its vas sources, inherent toxicity, and non-degradability (Xue et al 2012) Elements compound such as cadmium (Cd), copper (Cu), lead (Pb), arsenic (As), mercury (Hg), nickel (Ni), silver (Ag), and zinc (Zn) are classified

as heavy metals (Edwards 2019; Tillman 1996) They exist in the wastewaters from mining

activities, steel and battery industries as well as thermal plants The chemical and physical

properties of Cu (II) and Cd (II) are shown in Table 2.2 They impose serious environmental

problems and threats on human health and ecosystem at high concentrations (Hequet et al 2001; Ngah and Hanafiah 2008a)

Table 2 2 Chemical and physical properties of Cu(II) and Cd (II)

In particular, Cadmium (Cd) exposes human health to severe risks, due to its high toxicity, and can exert its toxic effect even at low concentrations Cadmium reaches the human body through food crops from soil irrigated by affected effluents (Friberg 2018) It can cause cancer, kidney damage, mucous membrane destruction, vomiting, diarrhea, bone damage, and

“Itai-Itai disease”, as well as affect the production of progesterone and testosterone (Menke et

al 2009) The increasing presence of cadmium in the environment derives mainly from industrial activities, such as electroplating, paint pigments, plastics, alloy preparation, and silver- cadmium batteries (Pinot et al 2000) Therefore, it is necessary to remove cadmium from industrial effluents Especially, Copper (Cu) is a very common metal, which is widely used in electroplate, light industry, mechanical manufacturing industry, and architecture Copper is an indispensable micronutrient to humans and other life forms (0.9 mg daily uptake)

Property

name

Chemical formula

Molecular Weight

Molecular structure

0.97 (+2)

For example, deficiency of copper in humans causes anemia, a low number of leucocytes, defects in animal tissue, and osteoporosis in infants However, the copper within the body beyond its permissible limit causes hematemesis, jaundice, melena, damage to the central nervous system, liver, and kidney problems Wilson’s disease a genetic disease is additionally caused by copper Consequently, exposure to high levels of copper can cause a toxic effect on humans and microorganisms (Tillman 1996; Trevors and Cotter 1990)

Faced with more and more stringent regulations, nowadays heavy metals are the environmental priority pollutants and are becoming one of the most serious problems So these toxic heavy metals should be removed from wastewater due to their toxicity in the aqueous or terrestrial environment and their persistence (Elaigwu et al 2014) to protect the people and the environment (Fu and Wang 2011; Ngah and Hanafiah 2008b)

2.2.2 Textile Dyes and Methylene Blue (MB)

In industrial wastewater, dye from wastewater from the textile, tannery, and dyestuff industries is one of the contaminants of difficult treatment This is because dyes usually have a synthetic origin and complex aromatic molecular structures which make them stable and more difficult to be biodegraded (Lazar 2005; Zollinger 2003) The presence of very low concentrations of dyes in the effluent can be highly visible and undesirable on aesthetic grounds Their presence disturbs aquatic communities present in the ecosystem by obstructing light penetration and oxygen transfer into water bodies It is reported that there are over 100 000 commercially available dyes with a production of over 7 x105 metric tons per year (Chequer et

al 2013; Christie 2007) It has been estimated that about 9 % (or 40,000 tons) of the total amount (450, 000 tons) of dyestuffs produced in the world are discharged in textiles wastewaters (O’neill et al 2000) Dye molecules comprise of two key components: the chromophores, responsible for producing the colour, and the auxochromes, which can not only supplement the chromophore but also render the molecule soluble in water and give enhanced

affinity towards the fiber type (Christie 2014) Dyes exhibit considerable structural diversity and are classified in several ways These can be classified both by their chemical structure and their application over the substrate Dyes may also be classified based on their solubility: soluble dye which includes acid, mordant, metal complex, direct, basic, and reactive dyes; and insoluble dyes including azoic, sulfur, vat, and disperses dyes (Allen 2013; Christie 2014) According to Fu and Viraraghavan (2001), dyes are classified as follows anionic dyes which include direct, acid, and reactive dyes, cationic dyes which include the basic dyes, and nonionic dyes which include the disperse dyes (Fu and Viraraghavan 2001) The chemical formula and

properties of MB and TC demonstrates in Table 2.3

Table 2 3 Examples of the chemical formula and characteristic of MB and TC

Examples of the structure of methylene blue is given in Table 2.3 Methylene blue

(cationic dye) is a common organic pollutant from textile industry, with a relatively large molecule size MB is also used as probe molecule for an adsorbent to test the capacity of removing organic compounds from water solution The basic dye, MB (Type: cationic; C.A.S: 7220-79-3; chemical formula: C16H18ClN3S.xH2O (x=2-3); Mw: 319.86 g/mol (anhydrous basic); λmax: 665 nm; Color index: basic blue 9) was chosen as the adsorbate MB was purchased from Fisher Scientific and the solution was prepared by dissolving MB in DI-water (Pelekani and Snoeyink 2000) The basic dyes work very well on acrylics due to the strong ionic

Property

name

Chemical formula

Molecular Weight

Molecular structure

pKa 1 pKa 2 pKa 3

interaction between dye functional groups such as -NR3+ or =NR2+ and the negative charges in the copolymer The most common structures are azo, diarylmethane, triarylmethane and anthraquinone (Alkan et al 2005; Vinod and Gowda 2008; Wan et al 2017)

2.2.3 Antibiotic Products

Antibiotic products are used extensively in human therapy and livestock husbandry Approximately 70% of annual antibiotic consumption is associated with agriculture, animal husbandry, and aquaculture Residual antibiotics enter surface water and groundwater through surface runoff, leaching, and other pathways (Zhang et al 2011)

Examples of the properties of the antibiotic tetracycline (TC, C22H24N2O8) is also given

in Table 2.3 above The TC exhibits broad-spectrum antibacterial activities by blocking DNA

replication enzymes and inhibiting bacterial growth TC has recently become a serious environmental concern (Gao et al 2012; Zhou et al 2017), as incompletely metabolized TC has been detected in both wastewater sludge-treated agricultural soils and surface waters affected

by effluents from wastewater treatment plants (Beausse 2004; Golet et al 2002) Hence, the removal of TC is of great interest The adsorption of TC by different sorbents, such as graphene oxide (Gao et al 2012), aluminum oxide (Chen and Huang 2010), Fe-Mn binary oxide (Liu et

al 2012), and montmorillonite (Parolo et al 2012), is considered the easiest and most economical available treatment

2.2.4 Effect of Water Pollution on Human Health

Health risk associated with polluted water includes different diseases such as respiratory disease, cancer, diarrheal disease, neurological disorder, and cardiovascular disease (Ullah et al 2014) Nitrogenous chemicals are responsible for cancer and blue baby syndrome (Krishnan and Indu 2006) Contaminated water has large negative effects on those women who are exposed to chemicals during pregnancy; it leads to the increased rate of low birth weight as a result fetal health is affected (Currie et al 2013) Poor quality water destroys the crop