Assessment of Polyethylene Terephthalate Waste Carbon and Periwinkle Shells-based Chitosan as Adsorbent for Trichloroacetic Acid Removal from Water BY BABASANMI OLUWOLE ABIOYE (SCP18/19/R/0020) B.Sc. (Biochemistry), Ife A THESIS WRITTEN IN THE INSTITUTE OF ECOLOGY AND ENIRONMENTAL STUDIES, FACULTY OF SCIENCE, AND SUBMITTED TO THE POSTGRADUATE COLLEGE, OBAFEMI AWOLOWO UNIVERSITY, ILE-IFE, OSUN STATE, NIGERIA, IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE AWARD OF THE DEGREE OF MASTERS OF SCIENCE (M.Sc.) IN ENVIRONMENTAL CONTROL AND MANAGEMENT 2022 ii AUTHOURIZATION TO COPY OBAFEMI AWOLOWO UNIVERSITY, ILE-IFE HEZEKIAH OLUWASEYI LIBRARY POST GRADUATE THESIS AUTHOR: BABASANMI OLUWOLE ABIOYE TITLE: ASSESSMENT OF POLYETHYLENE TEREPHTHALATE WASTE CARBON · AND PERIWINKLE SHELLS-BASED CHITOSAN AS ADSORBENT FOR TRICHLOROACETIC ACID REMOVAL FROM WATER DEGREE: M.Sc. (Environmental Management and Control) YEAR: 2022 I, BABASANMI OLUWOLE ABIOYE hereby authorize the Hezekiah Oluwasanmi Library to copy my thesis, in whole or part, in response to request from individual rc:searcher and organizations for the purpose of private study or research. Student Signature Date iii � CERTIFICATION This is to certify that this research work was carried out by Babasanmi Oluwole Abioye (SCP18/19/R/0020) as part of the requirements for the award of Masters of Science degree in the Institute of Ecology and Environmental Studies, Faculty of Science, Obafemi Awolowo University, Ile-lfe, igeria._. Dr. (Mrs.) A. A. Okoya (Supervisor) Date Dr. M. B. Adewole Date Director, Institute of Ecology And Environmental Studies Date rovost, Postgraduate College iii iv ACKNOWLEDGEMENTS My heartfelt thanks to Almighty God, the Author and Finisher of my faith, for guiding me through my courses and research projects, as well as for His divine grace and assistance throughout this program. I would want to convey my heartfelt gratitude to Dr. (Mrs.) A. A. Okoya, my supervisor, for her intellectual and moral support during this program. Working under her capable direction and supervision is tremendously advantageous to me. May Almighty God abundantly reward and bless the Director, Dr. M. B. Adewole, and the entire staff of the Institute of Ecology and Environmental Studies, Obafemi Awolowo University, Ile–Ife, for their professional and unwavering support. Dr. Bankole Abimbola Akinyele's sacrifices and support for me during this research work are greatly appreciated. I would want to take this opportunity to thank the Solid Waste, Water and Environmental Chemistry (SwWECh) laboratory for their assistance in both training and research. It was a pleasure working with you, Mr. Babarinde Ayomide, Mr. Sule James, Mr. Olalekan Olaiya, Mr. Adegbaju Oyeyemi, Mrs. Olaoye Adeola, Miss Oguntunbi Esther, and other colleagues. Best of luck with your endeavors. Mr. Joseph Sunday Abioye and Mrs. Felicia Aduke Abioye, my parents, deserve my heartfelt thanks for their unwavering moral, financial, and spiritual support throughout my life. Thank you for making the unimaginable sacrifice of selflessly dedicating and committing to all of your children's education. I hope you live long enough to enjoy the results of your labor. I also appreciate my wonderful siblings, Mr. and Mrs. Familusi, Dr. and Dr. (Mrs.) Omoboye, Mr. and Mrs. Bamidele, v Abioye Olusola, Omoboye Adekunle, Tmilehin, David, Inioluwa, Varick, Grace, Isreal, and Vadick, thank you for your continuous encouragement and support. I hope that the bond that brought us all together as one large family will grow even stronger. vi TABLE OF CONTENTS Contents Page Authorization to Copy ii Certification iii Dedication iv Acknowledgements v Table of Contents vii List of Tables xv List of Figures xii Abstract xx CHAPTER ONE: INTRODUCTION 1.1 Background of the Study 1 1.2 Statement of the Research Problem 4 1.3 Specific Objectives of Research 4 CHAPTER TWO: LITERATURE REVIEW 2.1 Water Resources 6 2.2 Water Chemistry 6 2.3 Water Quality 8 2.3.1 Water quality parameters 8 2.3.1.1 Physical characteristics of water 9 2.3.1.1.1 Odour and taste 9 2.3.1.1.2 Turbidity 9 2.3.1.1.3 Temperature 9 2.3.1.2 Chemical characteristics of water 10 vii 2.3.1.2.1 Hydrogen ion concentration (pH) 10 2.3.1.2.2 Alkalinity 10 2.3.1.2.3 Acidity 10 2.3.1.2.4 Electrolytic conductivity 10 2.3.1.2.5 Sulphate (SO4 2- ) 11 2.3.1.2.6 Chloride (Cl-) 11 2.3.1.2.7 Nitrate (NO3 -) 11 2.3.1.2.8 Dissolved Oxygen (DO) 12 2.3.1.2.9 Biochemical Oxygen Demand (BOD) 12 2.3.1.2.10 Chemical Oxygen Demand (COD) 13 2.4 Pollution of Water 13 2.4.1 Water pollution causes 14 2.4.1.1 Natural pollution 14 2.4.1.2 Chemical pollution 14 2.5 Treatment Processes for Drinking Water 15 2.5.1 Physical treatment 15 2.5.1.1 Coagulation and flocculation 15 2.5.1.2 Sedimentation 16 2.5.1.3 Filtration 16 2.5.1.4 Aeration 16 viii 2.5.2 Chemical treatment 16 2.5.2.1 Control of pH 16 2.6 Water Disinfection 18 2.6.1 Chlorination 19 2.6.2 Chloramination 19 2.7 Disinfection By-products 20 2.8 General Information on Haloacetic Acids 20 2.8.1 Occurrence surveys of haloacetic acids 22 2.8.2 Physical and chemical properties of haloacetic acids 22 2.9 Trichloroacetic Acid (TCA) 23 2.9.1 Sources of trichloroacetic acid 26 2.9.2 Application of trichloroacetic acid 26 2.9.3 Trichloroacetic acid metabolism in animals and humans 27 2.9.4 Trichloroacetic acid’s health effect 27 2.10 Adsorption Techniques 29 2.10.1 Physical adsorption 29 2.10.2 Chemical adsorption 29 2.11 Adsorbent Physical Characteristics 29 2.11.1 Adsorbent pores 29 2.11.2 Specific surface area of adsorbent 30 ix 2.12 Activated Carbon 30 2.12.1 Activated carbon preparation 30 2.12.1.1 Physical activation 33 2.12.1.2 Chemical activation 33 2.13 Activated Carbon Chemical Structure 34 2.13.1 The textural properties 34 2.13.2 Surface functional groups 34 2.14 Polyethylene Terephthalate 35 2.14.1 Preparation of activated carbon from polyethylene terephthalate waste 38 2.15 Chitosan 40 2.16 Adsorption 40 2.16.1 Factors affecting the adsorbent/adsorbate interactions 40 2.16.2 Nature of the adsorbate's influence 42 2.17 Isotherm of Adsorption 43 2.18 Modelling Techniques 44 2.18.1 Single component adsorption isotherms models 44 2.18.1.1 Langmuir model (Type 1) 44 2.18.1.2 Freundlich model (Type II) 45 2.19 Instrumentation 45 2.19.1 Fourier transform-infrared spectroscopy (FT-IR) 45 x 2.19.1.1 Principles of FT-IR 46 2.19.2 Energy dispersive X-ray scanning electron microscope (SEM/EDX) 47 2.19.3 Ultraviolent-visible spectrometer 47 CHAPTER THREE: MATERIALS AND METHODS 3.1 Samples Collection and Preparation 52 3.2 Preparation of Cocoa Husk Ash 52 3.2.1 Determination of ash yield from cocoa husk 52 3.2.2 Preparation of caustic alkali from cocoa husk ash 52 3.3 Preparation of the Adsorbents 53 3.3.1 Activation of PET with caustic alkali 53 3.3.1.1 Carbonization of the activated PET 53 3.3.1.2 Determination of pH of the activated (PET) carbon 53 3.3.1.3 Determination of ash content activated (PET) carbon 54 3.4 Preparation of Chitosan from Periwinkle Shells 54 3.4.1 Deproteinization of periwinkle shells 54 3.4.2 Deproteinized periwinkle shell demineralization 54 3.4.3 Decolourization of demineralized-deproteinized periwinkle shells 54 3.4.4 Deacetylation of chitin 54 3.4.5 Preparation of chitosan gel 55 3.5 Chitosan Yield from Periwinkle Shell Determination 55 3.6 Determination of Moisture Content of Chitosan 55 3.7 Determination of ash content of chitosan 55 3.8 Modification of Adsorbent with Chitosan 56 xi 3.9 Characterization of Activated PET and Chitosan Modified Activated PET 56 3.10 Water Sample Collection 56 3.10.1 Determination of the physicochemical parameters of water samples 57 3.10.1.1 Water sample physicochemical parameters 57 3.10.1.2 Determination of temperature of water samples 57 3.10.1.3 Determination of electrical conductivity of water samples 59 3.10.1.4 Determination of pH of water samples 59 3.10.1.5 Determination of total dissolved solids of water samples 59 3.10.1.6 Determination of nitrate content of water samples 59 3.10.1.7 Determination of total suspended solids in water samples 59 3.10.1.8 Determination of turbidity of water samples 60 3.10.1.9 Determination of Chloride Content in Water 60 3.10.1.10 Water sample biological oxygen demand determination 60 3.10.1.11 Chemical oxygen demand of water samples determination 61 3.10.1.12 Determination of dissolved oxygen of water samples 61 3.10.1.13 Determination of acidity of water samples 61 3.10.1.14 Determination of alkalinity of water samples 62 3.11 Preparation of Working Standard 62 3.12 Analytical Determination of TCA 64 3.13 Batch Adsorption Experiment 64 3.13.1 Effect of pH on adsorption efficiency of adsorbent (PETAC and PETMAC) xii on simulated polluted water 65 3.13.2 Effect of adsorbent dosage on adsorption efficiency of the adsorbent on simulated polluted water 65 3.13.3 Adsorption efficiency as a function of contact time of APETC and PETMAC on TCA in simulated polluted water 65 3.13.4 Effect of initial concentration on adsorption efficiency of the adsorbent on simulated polluted water 66 3.14 Calculation of Adsorption Efficiency of the Adsorbent for TCA Adsorption 66 3.15 Adsorption Isotherms 66 3.15.1 Langmuir model 67 3.15.2 Freundlich model 67 3.15.3 Temkin isotherm 67 3.15.4 Dubinin-Radushkevich (D-R) 68 3.16 Recovery Experiment for Photometry Determination of TCA Standard 69 3.17 Reusability Experiment for the Adsorption of TCA 69 3.18 Statistical Analysis of Data 70 CHAPTER FOUR: RESULTS 4.1 Cocoa Husks, Periwinkle Shells and PET Samples |Collection 71 4.2 Cocoa Husk Ash 71 xiii 4.3 Caustic Alkali from Cocoa Husk Ash 71 4.4 Physicochemical Properties of PETAC 71 4.5 Physicochemical Properties of Chitosan from Periwinkle Shell 71 4.6 Characterization of PET Activated Carbon and Chitosan Modified Activated Carbon with SEM-EDX before Adsorption 75 4.7 Functional Groups of PETAC and PETMAC before Adsorption 75 4.8 Recovery Experiment for TCA Photometric Determination 79 4.9 Results of Physicochemical Parameters for Raw Water and Conventionally Treated Water before Adsorption 79 4.10 Parametric Studies on the TCA Removal from Aqueous Solution 79 4.10.1 Effects of contact time on TCA adsorption in its simulated solution 79 4.10.2 Effect of adsorbent dosage on the adsorption of TCA in its simulated solution 83 4.10 .3 Effect of pH on TCA adsorption in its simulated solution 83 4.10.4 The influence of the initial concentration on TCA adsorption in a simulated solution 83 4.11 Influence Raw Water and Conventionally Treated Water Adsorption Experiment 87 4.12 Characterization of PETAC and PETMAC with SEM-EDX after Adsorption 87 xiv 4.13 Functional Groups of PETAC and PETMAC after Adsorption 87 4.14 Physical Parameters of Water Quality before and after Adsorption 94 4.15 Adsorption Equilibrium Isotherm 94 4.16 Kinetics Studies 94 4.17 Reusability Potential of the Adsorbent 105 CHAPTER FIVE: DISCUSSION 107 CHAPTER SIX: CONCLUSION, RECOMMENDATION AND CONTRIBUTION TO KNOWLEDGE 6.1 Conclusion 117 6.2 Recommendation 117 6.3 Contribution to Knowledge 117 REFERENCES APPENDICES xv LIST OF TABLES Table Page 2.1 Disinfection By-products of various disinfectants 21 2.2 Physicochemical properties of haloacetic acid 24 3.1 Methods used in the chemical analysis of water quality parameters 58 3.2 Preparation of calibration standard for TCA 63 4.1 The Cocoa pod ash yield 72 4.2 Physicochemical properties of PETAC 73 4.3 Physicochemical properties of chitosan from periwinkle shell 74 4.4 Mean percentage (%) recoveries of TCA spiked raw and spiked treated water samples with spiked distilled water 80 4.5 Comparison of mean raw water and conventionally treated water with W.H.O (2017) drinking water quality standard 81 4.6 Adsorption Efficiency of PETAC, PETMAC, CAC on Raw and conventionally treated water samples 88 4.7 Comparison of mean raw water sample after adsorption on PETAC, PETMAC and CAC with W.H.O (2017) drinking water quality standard 95 4.8 Comparison mean of conventionally treated water sample after adsorption on PETAC, PETMAC and CAC with W.H.O (2011) drinking water quality standard 96 4.9 Isotherm characteristics parameters of langmuir and freundlich isotherm constants for TCA onto PETAC and PETMAC 101 4.10 Kinetic parameters for the first order and second order models 104 xvi LIST OF FIGURES Figure Page 2.1 Tetrahedral structure of water 7 2.2 Flow chart of water treatment processes 17 2.3 Trichloroacetic acid (TCA) 25 2.4 Metabolim of trichloroacetic acid 28 2.5 Schematic representation of external and internal adsorbent surface 31 2.6 Schema of the process of activated carbon manufacturing 32 2.7a Arrangement of carbon atoms in graphite crystal 35 2.7b microstructure of the activated carbon 35 2.8 Chemical structure of activated carbon 36 2.9 Surface functional groups of the activated carbon 37 2.10 Chemical structure of polyethylene terephthalate (PET) 39 2.11 Chemical structure of chitosan 41 2.12 Fourier transform-infrared spectroscopy (FT-IR) 47 2.13 Scheme showing the optical systems for optical-light microscopy and SEM 50 2.14 Schematic view of a spectrophotometer 51 4.1 Cross sectional SEM of PET activated carbon (PETAC) and chitosan modified Activated carbon PETMAC) before adsorption 76 4.2 EDX diagrams of PETAC and PETMAC before adsorption 77 xvii 4.3 FT-IR spectrum of PETAC and PETMAC after adsorption 78 4.4 Effect of time on the percentage removal of TCA into PETAC and PETMAC 82 4.5 Effect of adsorbent dosage on the percentage removal of TCA onto PETAC and PETMAC 84 4.6 Effect of pH on the percentage removal of TCA onto PETAC and PETMAC 85 4.7 Effect of initial concentration on the percentage removal of TCA onto PETAC and PETMAC 86 4.8 SEM images of PETAC and PETMAC after adsorption 89 4.9 EDX diagrams of PETAC and PETMAC after adsorption on raw water sample 90 4.10 EDX diagrams of PETAC and PETMAC after adsorption on treated water sample 91 4.11 FT-IR spectrum of PETAC and PETMAC after adsorption on influent raw water 92 4.12 FT-IR spectrum of (a) PETAC (b) PETMAC after adsorption on influent treated water 93 4.13 Langmuir adsorption isotherms for the adsorption of TCA using Cocoa husk alkaline-PET and chitosan modified-PET 97 4.14 Freundlich adsorption isotherms for the adsorption of TCA using cocoa husk alkaline-PET and chitosan modified-PET 98 4.15 TCA adsorption isotherms employing (a) cocoa husk alkaline-PET and (b) chitosan modified-PET (Tempkin adsorption isotherms) 99 4.16 TCA adsorption isotherms utilizing (a) Cocoa husk alkaline-PET and (b) Chitosan modified-PET, as determined by Dubinin-Radushkevich 100 4. 17 Pseudo-first order for the adsorption of TCA by (a) Cocoa husk alkaline-PET (PETAC) (b) chitosan modified-PET (PETMAC) 102 xviii 4.18 Pseudo-second order for the adsorption of TCA by (a) cocoa husk alkaline-PET (PETAC) (b) chitosan modified-PET (PETMAC) 103 4.19 The reusability efficiency of TCA onto PETAC and PETMAC at 2.5 mg/L initial concentration 106 xix LIST OF ABREVIATIONS AND ACRONYMS APHA American Public Health Association DO Dissolved Oxygen BOD Biological Oxygen Demand COD Chemical Oxygen Demand et al. et alli ( and others) hr Hour mL Millilitres NTU Nephelometric Turbidity Units oC Degree celcius OH Hydroxyl ion OM Organic Matter Pt.Co Platinium Cobolt TDS Total Dissolved Solids TOC Total Organic Carbon TSS Total Suspended Solids WHO World Health Organisation TCA Trichloroacetic Acid PET Polyethylene Terephthalate xx PETAC Polyethylene Terephthalate Activated Carbon PETMAC Polyethylene Terephthalate Modified Activated Carbon pH Power of Hydrogen SwWECh Sold waste, Water and Environmental Chemistry SEM Scanning Electron Microscope FT-IR Fourier Transformed-Infrared Spectroscopy EDX Energy Dispersive X-ray UNICEF United Nations Children’s Fund AC Activated Carbon USEPA United State Environmental Protection Agency CAC Commercial Activated Carbon ANOVA One-way Analysis of Variance OSC Oscillation UV-Vis Ultraviolent Visible EC Electrical Conductivity xxi ABSTRACT The study determined the physicochemical parameters and trichloroacetic acid concentrations of the water samples before and after conventional treatment at the Obafemi Awolowo University, Ile-Ife water treatment plant. It also investigated the adsorption efficiencies of chitosan modified and unmodified adsorbent prepared from polyethylene terephthalate waste and periwinkle shells for the removal of trichloroacetic acids in the water samples. The study further compared the adsorption efficiencies of commercially available activated carbon with the chitosan modified and unmodified adsorbents. These were with a view to providing information on the adsorption efficiencies of polyethylene terephthalate waste carbon and periwinkle shells-based chitosan with commercially available activated carbon for the removal of trichloroacetic acid from water. Polyethylene terephthalate was obtained from the Obafemi Awolowo University Campus, while the periwinkle shell utilized for chitosan extraction was obtained from the Eket Main Market in Akwa- Ibom State. Caustic alkali produced from cocoa pod husk was used to activate the PET. The activated carbon was made by carbonizing the caustic alkali impregnated Polyethylene Terephthalate (PET) in a furnace at 500 °C for 1 hour. For elemental and surface morphology determinations, the activated carbon was evaluated using Energy Dispersive X-ray (EDX) and Scanning Electron Microscope (SEM). The Fourier Transform-Infrared (FT-IR) spectroscopic technique was used to determine the structural chemical functional groups in activated carbon. Chitosan was made by deproteinizing, demineralizing, decolourizing, and deacetylating the periwinkle shell. Using a UV- vis Spectrophotometer, the level of trichloroacetic acid (TCA) in water samples was detected at 530 nm. Batch adsorption tests were conducted to investigate the removal of TCA under a variety of conditions, including the effect of concentration, adsorbent dosage, pH, and agitation time. Adsorption isotherms were calculated using experimental data from various initial TCA xxii concentrations. The adsorption kinetics were also used to identify a potential rate-limiting phase during the adsorption process. The results showed that the TCA levels were 0.9900 mg/L in raw water and 2.8900 mg/L in conventionally treated water. The PETAC, PETMAC, and commercial activated carbon (CAC) gave mean TCA concentrations of 0.1900±0.0000, 0.0900±0.0000 and 0.0900±0.0000 mg/L before adsorption and 0.1400±0.0707, 0.0900±0.0000 and 0.0000±0.0000 mg/L after adsorption on raw water and conventionally treated water, respectively. There was significant (p < 0.05) difference when raw and conventional treated water were subjected to the three adsorbents. The TCA removed by the two adsorbents (PETAC and PETMAC) required 4 minutes, 1.2 g/L adsorbent dose, and a pH of 9. At 4 minutes of contact time, the highest adsorption efficiencies were 80.286 and 98.286% for PETAC and PETMAC, respectively. The reusability efficiencies of PETAC and PETMAC were 78.4 and 82.4%, respectively. The PETAC with R2 = 0.9377, showed that Langmuir model best fit the TCA adsorption in the isotherm models. The PETMAC with R2 = 0.9986 indicated that the pseudo-second order fitted the kinetic data. This study concluded that activated PET carbon was effective to remove TCA from water supply and could be improved by adding chitosan. 1 CHAPTER ONE INTRODUCTION 1.1 Background of the Study Water covers three-quarters of the earth's surface (75%), and it remains very important. Notably, water (H2O) is a common substance existing naturally in three common states of matter (Mohammad, 2015). It is a key requisite of life, and enormously significant for existence of all living organisms (Gupta and Deshpande, 2004). Living cells comprises approximately 80% of water (Shepherd, 2006). In man, three-quarters of the fluid are made of water, and forms the essential medium in which the chemical reactions of the cells occur, hence human activities and settlements hinge on its availability (WHO and UNICEF, 2017). However, extensive human activities have led to the accumulation of toxic wastes which pollute fresh water bodies (UNEP, 2016). Water is classically denoted as unfit for use domestically or in support of aquatic life, when compromised by human-derived or other waste (WHO and UNICEF, 2017). Consequently, diverse approaches have been exploited to remove pollutants from water. Water treatment or disinfection is the method of removing, deactivating or killing pathogenic microorganisms (Mezzanotte et al., 2007). Water treatment entails a number of processes and operations to get rid of soluble and insoluble contaminants in water. These processes include sedimentation, precipitation, oxidation, carbon adsorption, ion-exchange, membrane filtration, among others (Okoya et al., 2020). Chemical disinfectants when in excess could by means of organic and inorganic contaminants lead to the materialization of other hazardous by-products (WHO, 2000). Disinfectants utilized for potable water comprises chlorine (Cl), chloramines (NH2Cl), ozone (O3), chlorine dioxide (ClO2), 2 and ultraviolet radiation, all of which can kill or prevent replication of microorganisms in water supply (Mezzanotte et al., 2007). Chlorine occurrences significantly injure bacterial cells, cell permeability dislocation and nucleic acids and enzymes damage (Mitch et al., 2019). Toxicological researches have revealed that most haloacetic acids (HAAs), especially trichloroacetic acid (TCA) could be hazardous to human health, because they are hydrophilic and highly acidic (Dickenson et al., 2008). Trichloroacetic acid (TCA) is one of the by-product formed when naturally occurring organic matter, for example, fulvic and humic acids derived from breakdown of vegetative material, or other organic materials, such as chemical pollutants, react with antimicrobial oxidizing agents or with halides in water (Richardson and Postigo, 2015). The composition of by-products varies with the source and properties of the water, the disinfection method used, and variety of reactants present in the water. Most common exposure route for disinfection by products (DPBs) is the consumption of chlorinated water (Wang et al., 2014). Other potential exposure sources include swimming pools and spas that use chlorine for disinfection (Cardador and Gallego, 2011). Trichloroacetic acids and other DBPs can bring about adverse effects in humans if ingested through drinking water. Humans could likewise be exposed to TCA through the consumption of food, and some beverages made with water that is disinfected with chlorine. The presence and quantities of DBPs have been found in drinking water, restricted as a result of this concern (USEPA, 2011). TCA has a maximum contamination level of 200 µg/L (USEPA, 2011). Numerous techniques have been described for quantification of TCA in different matrices. The Fujiwara method was utilized by Bernauer et al. (1996) and Raaschou-Nielsen et al. (2001). This method is proven as the interaction between pyridine molecules and TCA in basic medium (UV-vis spectrophotometric determination). 3 Methylation techniques, utilizing either boron trifluoride (BF3) or methanol diazomethane or a methanol/sulfuric acid esterification techniques (Froese et al., 2002) all accompanied in gas chromatography (GC). Thus, Fujiwara techniques used by Raaschou-Nielsen, et al. (2001) with some modifications will be utilized. Drinking water especially in Nigeria comes in polyethylene pack, known as table water, and it is one of the booming business in Nigeria. This goes for either 50 or 70 Naira, depending on the area. Over the past few years, polyethylene materials have substituted leaves, glasses and metals as a low cost and more efficient means of packaging. However, on the downside the polyethylene materials are non-biodegradable which make them persist in the urban area, clogging drains, threatening small animals, soil detriment and Oceans pollution (Ozobu and Omal, 2010). Currently, three options are available for the disposal of polyethylene material i.e. incineration, landfilling and recycling, however, all of these methods have certain limitations (Grover et al., 2015). For example, during the thermal decomposition of polyethylene waste, toxic gases are produced and released directly into the atmosphere which could result in breathing problem or other respiratory difficulties (Grover et al., 2015). Land filling is performed for the degradation of polyethylene waste, however this technique pose its own hindrance which time consuming for degradation of polyethylene due to anaerobic environment. A trending difficulty related with the incineration treatment is the release of pollutants in the form of toxic and harmful compounds, which may have numerous health implications in humans including cancer (Grover et al., 2015). Inclusively, polyethylene are highly resistant to microbial degradation due to its hydrophobicity and high molecular weight (Grover et al., 2015). Hence, reuse of polyethylene material remains eco-friendly, and inexpensive method for polyethylene waste management. 4 Domestic waters for human consumption and utilization are now limited due to the high level of contamination from all kinds of wastes from both organic and chemical compounds. Raw water purification becomes necessary for maintaining water quality measures (UNICEF/WHO, 2004). At OAU water treatment plant, low lift pump is used to pump water from the reservoir to the treatment plant. This is followed by aeration, coagulation, sedimentation, filtration and disinfection. Adsorption techniques using activated carbon (AC) remains commonly recognized method to get rid of hazardous substances present in water. In addition, AC surface modification becomes of interest, as modified AC gives better adsorption efficiency than commercially available AC (Okoya et al., 2014). Currently, chitosan (produced by deacetylation of chitin) has high utilization for hazardous compounds removal, the presence of OH- and NH2 make it coordination and electrostatic interaction site (Ding et al., 2007). As a result, the goal of this research is to find out more about adsorption performances of chitosan modified activated carbon produced from polyethylene terephthalate on trichloroacetic acids. 1.2 Statement of the Research Problem Trichloroacetic acids remain toxic compounds formed during photolysis of halogenated hydrocarbons and chlorination of water. The conventional water treatment has not been effective for its removal. There is scanty information on the use of polyethylene terephthalate waste carbon and periwinkle shells-based chitosan as adsorbent for its removal; hence this study. 1.3 Specific Objectives of Research The specific objectives of this study are to 5 (a) determine the physicochemical parameters and trichloroacetic acid concentrations of the water sample before and after conventional treatment at the Obafemi Awolowo University water treatment plant, Ile-Ife; (b) investigate the adsorption efficiencies of chitosan modified and unmodified adsorbent prepared from polyethylene terephthalate waste and periwinkle shells in order to remove trichloroacetic acids from water samples; and (c) compare the adsorption efficiency of commercially available activated carbon with modified and unmodified chitosan adsorbents. 6 CHAPTER TWO LITERATURE REVIEW 2.1 Water Resources Water remains top world’s natural resource with great significance. All living organisms depend entirely on it for their survival (Gupta and Deshpande, 2004). Water is being used by humans for various purposes, such as drinking water, domestic purposes and economic activities (APHA, 2012). A sustainable and efficient utilization of water resources is therefore necessary for healthy living and other ecosystem services. Leading sources of water includes; lake, ponds, stream, and groundwater. In general, freshwater bodies are of diverse types, they include ponds, streams, rivers, lakes, and reservoir. Freshwater bodies are very important as they produce drinking water and ensure stability of microclimate of the area, ground water recharge, creating employment by boosting tourism, fisheries, recreation, etc. (Mini et al., 2003). However, freshwater resources all across the globe are under sustained anthropogenic pressure owing to increase in human activities. The contamination of such biotypes with acute concentrations of pollutants is the outcome of dumping of domestic, agricultural, municipal and industrial waste into these water bodies (Hasan et al., 2007; Zuber and Sharma, 2007). 2.2 Water Chemistry Water (H2O) is made up of H+ and OH-. Both hydrogen atoms of H2O are attached by chemical bonds to the same side of the oxygen atom, which gives H2O a bent configuration. The tetrahedral structure of water is as shown in Figure 2.1. 7 Figure 2.1: Tetrahedral Structure of Water Source: https://chem.libretexts.org 8 Generally, organisms survive in water of a particular pH and could be endangered when the pH is altered. At extremely low or high pH, water becomes harmful to most organisms (Bolawa et al., 2018). pH consideration is important because of how it influences the distribution of other pollutants existing in water. Water with extremely low pH level attracts accumulation of trace elements. Metals such as aluminum and copper are stored on fish gills and biomagnifies across the food chain. Also, when water is basic, ammonia compounds are transformed to a toxic form. i.e basic water is highly toxic if ammonia is present (Kurniawan et al., 2006). 2.3 Water Quality The quality of the water we drink, as well as the cleanliness of lakes, streams, rivers, and the ocean, is critical to our survival. The usefulness of water is determined by its quality. Water pollution is caused by a variety of human activities, rendering it unfit for the purposes for which it was previously intended (Alao et al., 2010). Human activity, on the other hand, may have an adverse effect on surface water. As microorganisms grow, dissolved oxygen (DO) levels decrease when organic matter, such as raw human and animal waste, enters surface water (utilizing the available oxygen as the energy source). Total dissolved solid (TDS) levels may rise as a result of untreated wastewater discharged by industries, urban runoff, and increased erosion as a result of land use and drainage basin changes. As a result, water quality standards and criteria are guidelines that set specific limitations on the water quality that can be used for a specific purpose (Chapman and Kimstach, 1996). 2.3.1 Water quality parameters Access to good water is so important for preserving quality of life, it's critical to research the different physical and chemical factors used to determine water quality in depth. 9 2.3.1.1 Physical characteristics of water 2.3.1.1.1 Odour and Taste The decomposing water weeds and dead aquatic animals cause the water to stink. Discharged sewage water, for example, may contribute to the production of hydrogen sulphide odor. The threshold odour number is used to quantify odor (TON). This is the dilution ratio of the sample at which smell can only be measured. The water sample is diluted with odourless water until the tester detects at least some odour. The lower the TON value, the better the water quality (Okoya et al 2020). 2.3.1.1.2 Turbidity Natural water turbidity is as a result of fine particles that are suspended matter such as, Organic Matter (OM). Turbidity gives the photosensitive property (Tyndall effect) which indicate scattering of light as a result of the particles suspended in the water. The amount of light dispersed is determined by the size and form of the particles. Turbidity marks water in poor condition for home purposes, food making and several other uses. Regular method for determining turbidity is the Jackson Candle Turbid meter (Gray, 1994). 2.3.1.1.3 Temperature Invading solar radiation and atmospheric pressure cause convection currents and thermal stratification by causing regional and temporal thermal changes in water resource availability. The release of heated effluents causes thermal changes in accessible water supplies as well. Microbial growth in water are all influenced by water temperature, As the temperature rises, chemical reactions speed up, gas solubility decreases, tastes become more intense, and so on (Thomas et al., 2012). 10 2.3.1.2 Chemical characteristics of water 2.3.1.2.1 Hydrogen ion concentration The amount of hydrogen ions present in a solution, known as pH, determines whether the solution is acidic or alkaline (Radwan, 2005). Chemical and biological reactions take place in a pH range that is moderate. For waste water treatment, pH determination is critical. Higher pH values can cause scale to build in equipment that transports water for heating, as well as reduce the efficiency of chlorine in killing bacteria. When the pH in water pipes falls below 6.5, hazardous metals including Zn, Pb, Cd, and Cu are released, causing corrosion. Water conductivity and total alkalinity are also affected by pH. (Gupta, 2004). A pH range of 6.5 to 8.5 is recommended for drinking water (WHO, 2008). 2.3.1.2.2 Alkalinity Alkalinity is defined by the presence of hydroxyl ions capable of reacting with hydrogen ions. Alkalinity (measured in mg/l CaCO3) is determined by the amount of calcium, magnesium, sodium, and potassium bicarbonate, carbonate, and hydroxide compounds in natural water. (APHA, et al., 2012). 2.3.1.2.3 Acidity Water's acidity relates to its ability to neutralize strong bases in the presence of free carbon dioxide, mineral acids such as sulphuric acid, and dissociated acids. Acidity is important because it causes corrosion and alters chemical and biological responses (Manivaskam, 2000). 2.3.1.2.4 Electrolytic conductivity This occurs when an electric current passes through water. The presence of inorganic elements (ions that carry a negative or positive charge) contribute to conductivity in water (Fondriest, 2014). The 11 dissolution of ions in water is largely influenced by temperature; warm water have higher conductivity than cold water (Okoya et al., 2020). 2.3.1.2.5 Sulphate (SO4 2-) Due to the great solubility of sulphate in water, it is possible that it is present in the water and hence does not precipitate. Transformations to sulphur and hydrogen sulphide, it could, on the other hand, be based on water's redox potential. It has long been assumed that the amount of sulphate in surface water correlates with the amount of sulphur dioxide in anthropogenic emissions. Sulphate levels of roughly 500 parts per million (ppm) can have a laxative effect. By converting sulphate to hydrogen sulphide, bacteria can use it as an oxygen source (H2S) in the pre-oxidation process (Finlayson et al., 2000). 2.3.1.2.6 Chloride (Cl-) Chloride levels in the water might make it unsafe to drink (Chapman and Kimstach, 1996). Chloride can be found in a variety of waters. Domestic sewage is a source of chlorides in the water. Most naturally occurring cations do not precipitate with chloride, which is very soluble. Mohr's and Volhard's techniques are commonly used to determine chloride levels (Ademiluyi and Odugbesan, 2008). Chloride concentrations should be fewer than 10 mg/L in most circumstances, and even less than 2 mg/l in other cases (Brandt et al., 2017). 2.3.1.2.7 Nitrate (NO3 -) Due to its inability to percolate through the soil, the nitrate anion (NO3 -) flows with water. Nitrate is commonly found in water, particularly in locations where agricultural fertilizer is excessive. In field crops, nitrogen fertilizers are utilized in massive volumes. Because plants cannot use all of the nitrogen applied to the fields, it remains in the soil and is washed into surface water. One of the most water soluble anions is nitrate. The condition known as methamoglobinemia, commonly known as 12 "blue baby syndrome," is caused by nitrate, which is a possible human hazard, especially to infants. In the intestines, nitrate is transformed into nitrite, which binds to hemoglobin to generate methamoglobin, reducing the blood's ability to circulate oxygen. Blood cells have been altered, and they can no longer transfer oxygen, resulting in brain injury or suffocation (WHO, 2004). High nitrate in women have been related to bladder cancer in some recent studies. For human consumption, International authorities have suggested that nitrate levels in consumption water be reduced to 10 mg/L. (USEPA, 2016). 2.3.1.2.8 Dissolved Oxygen (DO) The dissolved oxygen concentration (DO) of water is critical for all biota. Temperature, salinity, and water velocity all affect oxygen availability. In water, DO is essential for survival. The best way to determine whether an aerobic or anaerobic environment influences biological changes in living organisms is to look at DO. When oxygen interacts with manganese hydroxide, it liberates iodine equivalent, which is used to calculate DO in water. This results in oxygen fixation. The iodine emitted is titrated using a typical sodium thiosulphate solution with starch as an indicator. As a result, maintaining aerobic conditions in receiving waters, as well as sewage with aerobic bacteria and industrial waste water treatment, necessitates monitoring DO levels. (Umeham and Onyeagba, 2001). Anaerobic decomposition produces odiferous compounds due to a lack of DO in incoming fluids. Aerobic organisms oxidize wastes to harmless compounds if enough DO is supplied. Anaerobes participate in waste conversion when DO is low, typically resulting in unacceptable end products. 2.3.1.2.9 Biochemical Oxygen Demand (BOD) The amount of oxygen utilized by bacteria to oxidize organic molecules is known as biochemical oxygen demand. The BOD method is used to determine how much oxidizable organic matter is 13 existing in water. The measurement of dissolved oxygen concentration in a water sample before and after five days of incubation at 20°C is the most fundamental value of BOD determination. (Samer, 2015). The acceptable value of 10.0 mg/L as a drinking water standard has been endorsed by the WHO. 2.3.1.2.10 Chemical Oxygen Demand (COD) This is the quantity of dissolved oxygen necessary for a potent chemical oxidant in water to oxidize organic molecules. COD levels are more essential than BOD readings because the presence of toxins and other factors can inhibit microbial development. COD levels are used as a criterion for releasing industrial/domestic effluents into different sorts of water, as well as a standard for determining a treatment plant's competency. The drinking water standard has been proposed as a range of approximately 10.0 mg/L (Tyagi et al., 2003). 2.4 Pollution of Water When contaminants are poured into water bodies, either directly or indirectly, without being properly cleaned to remove harmful substances, water pollution occurs. Water pollution is a worldwide issue that is one of the most common causes of death and illness. Changes in water quality are caused by human anthropogenic acts, either directly or indirectly (Renu, 2020). Algal blooms land tremors, volcanic eruptions, urban runoffs, and earthquakes are all natural phenomena that generate substantial changes in water quality and ecological status (Sharma et al., 2013). In both emerging and developed countries, industrialization is a key contributor to water contamination issues. According to a statewide water quality survey conducted in the United States, 45 percent of evaluated stream miles and 32 percent of assessed bay and estuarine square miles are contaminated. (WHO, 2011). 14 2.4.1 Water pollution causes 2.4.1.1 Natural pollution Natural elements, such as organic molecules from plants and viruses, may create natural pollution of the biotic environment by polluting nature with hazardous chemicals such as poisons, germs, and oxygen-depleting substances (Coliform bacteria are widely utilized as a bacterial indicator of water contamination, but they are not disease-causing bacteria). Salmonella, Burkholderia pseudomallei, Cryptosporidium parvum, Giardia lamblia, Novovirus and other viruses, as well as parasitic worms (helminthes), are some of the bacteria and parasitic worms that have been found in surface water and have caused injury to humans (Sharma, 2013). 2.4.1.2 Chemical pollution a. Organic pollutants in water • By-products of disinfection, such as haloacetic acids and trihalomethane, found in treated drinking water • Detergent for laundry • Food processing waste, such as fats and grease (oxygen-demanding chemicals) • A wide spectrum of organo-halides (insecticides and herbicides) and other chemical compounds • Fuel combustion byproducts (Petroleum hydrocarbons) • Because volatile organic compounds (VOCs) do not mix well with water and are denser, they may settle to the bottom of reservoirs • Infinite chemical compounds derived from personal hygiene and cosmetic items (UNICEF and WHO, 2017). b. Contaminants in the water that are not organic • Sulfur dioxide is emitted by power plants. • Heavy metals in stormwater runoff from agricultural activities 15 • Nitrates and phosphorus in fertilizer (WHO/UNICEF, 2017). 2.5 Treatment Processes for Drinking Water 2.5.1 Physical treatment These are mostly determined by the physical characteristics of the pollutants to be eliminated, such as particle size, density, viscosity, volatility, and so on. 2.5.1.1 Coagulation and flocculation Coagulation and flocculation eliminate turbidity, algae, and microbes from surface water. When a chemical coagulant is mixed with water, it produces a floc, which traps contaminants. The flocs are separated by sedimentation and/or filtering after water treatment, with flotation methods being utilized as an alternative to sedimentation (Crini et al., 2019). The most often utilized coagulants are aluminum sulfate and ferric sulfate. Coagulants are dosed in solution at a rate dictated by raw water quality at the input of a mixing tank or flocculator (Butkus et al., 2003). Coagulation has the benefit of speeding up the settling of suspended solids, and it is especially effective in removing small particles that are difficult to remove via flotation (Okoya et al., 2020). Bench scale coagulation tests are frequently performed to determine the optimum coagulant to employ and the most effective conditions for a certain raw water sample (Oladoja, 2016). Coagulation and flocculation are the most successful treatments for lowering color and turbidity, but they may not be suitable for limited water supplies due to the high level of control required and the need to inject substantial amounts of sludge. 16 2.5.1.2 Sedimentation Simple sedimentation reduces turbidity and suspended particles (i.e. unassisted by coagulation). Purpose of gravity sedimentation tanks is to slow the flow of water. This permits gravity to settle suspended particles (Jakubowski and Craun, 2002). 2.5.1.3 Filtration Turbidity and algae are kept out of the water using screens, gravel filters, slow sand, quick gravity filters, or cartridge filters. Slow and rapid sand filtration differ not only in filtration speed, but also in the underlying design of the treatment process. Although rapid sand filtration is a physical therapy technique, slow sand filtration is primarily a biological process. Cartridge filters, which consist of a woven or spun filter in a conventional housing, will be used by many small private water systems (Cornwell et al., 2003). Figure 2.2 depicts a typical water treatment procedure. 2.5.1.4 Aeration Eliminate volatile organic molecules (VOCs), oxygen stripping is utilized. Aeration occurs during the oxidation stage of the iron and manganese removal process (Korich et al., 1990). Air stripping aeration systems strive to ensure efficient oxygen mass transfer into water while also eliminating gases and volatile contaminants. A simple cascade or diffusion of air into water can normally be used to transfer oxygen without the requirement of sophisticated apparatus (USEPA, 2012). 2.5.2 Chemical treatment 2.5.2.1 Control of pH The determination of water pH may need to be attuned in the process of treatment and earlier than distribution for a variety of reasons, including; ensuring that the pH value fulfills water quality 17 Figure 2.2: Flow Chart of Water Treatment Processes Source: Google image 18 criteria, regulating corrosion in the flow system as well as users' installations, increasing disinfection efficiency and allowing iron and manganese to be excluded. Sulphuric acid, hydrochloric acid, sodium hydrogen sulphate, or carbon dioxider are examples of appropriate acids, can be used to lower the pH, when necessary (Ademoroti, 1996). 2.6 Water Disinfection Uncontrolled microbial contamination of drinking water sources is well-known in Sub-Saharan Africa, and it continues to be a public health risk. Disinfection is a crucial phase in the water purification process that protects the public from hazardous microbes and diseases spread by water (Lee, 1992). Disinfectants like chlorine, chlorine dioxide, and chloramine, as well as ozone and ultraviolet (UV) irradiation, have been used to kill harmful bacteria in water (Mitch et al., 2003). Contamination of drinking water by sewage or animal excrement is the most serious threat. This is due to the fact that sewage from either human or animal sources can damage the environment and contain germs that cause a variety of infectious diseases (Ali et al., 2014). If pathogenic bacteria are present in the raw water, disinfection is obligatory to kill or incapacitate them. Water treatment employs a variability of disinfection techniques. For big water sources, chlorine disinfection is the most widespread approach, while it is less popular in small water supplies. The most dominant disinfection method seen in private supply is ultraviolet irradiation. Disinfectants have fluctuating vulnerabilities to different bacteria, and disinfectants have different effectiveness. Certain microbe, disinfectant concentration and contact duration, as well as the disinfecting condition of the water, pH, and temperature, all affect disinfection efficiency (Aggazzotti et al., 2014). 19 2.6.1 Chlorination For a long time, chlorine has been used successfully to treat aquatic infectious diseases, and it is one of the most active public health initiatives ever (Hua and Reckhow, 2007). Chlorine, either as a gas (Cl2) or as hypochlorite ions, is used to disinfect water. Hypochlorous acid (HOCl) is formed when any form of chlorine combines with water, and it soon dissociates to form hypochlorite. H+ + OCl- → HOCl Disinfection efficacy varies across a wide range of bacteria, in addition to variances in oxidizing capacities across kinds of chlorine. The most resistant organisms include protozoans, helminths, and viruses, followed by bacterial pathogens, with resistance varying by species. When it comes to enteric bacteria like E. coli, chlorine is quite powerful, however, it is less efficient against other types of bacteria (Richardson, 2003). 2.6.2 Chloramination Chloramines are created by combining chlorine (Cl2) and ammonia (NH3). HOCl + NH3 →NH2Cl + H2O Chloramines are amines that are linked together by at least one chlorine atom and one or more nitrogen atoms. When dissolved chlorine and ammonia combine, inorganic chloramines are formed. Chlorine and chloramine are linked in a variety of ways. The objective is that they both provide good residual disinfection while posing little public health risks. Monochloramine on the other hand as a disinfectant, it's 200 times less effective (Guay et al., 2005). Chlorine, on the other hand, interacts with a number of substances to form trihalomethanes (THM) and other by-products, whereas chloramine produces far fewer THMs and HAAs (Choi and Valentine, 2002). 20 2.7 Disinfection By-products Disinfection byproducts are chemical, organic, and inorganic compounds generated when a disinfectant reacts with naturally occurring organic materials in water (Sayess et al., 2017). When disinfectants, such as chlorine, combine with naturally occurring molecules in water, disinfection by-products can arise. Organic molecules such as humic acid and fulvic acid are required in the processes that lead to the creation of these chemicals (Nikolaou et al., 2004). Disinfectant type, dose, disinfection residue, reaction time, temperature, and pH all have an impact on the sorts of disinfection byproducts that are produced. Table 2.1 shows the disinfection By-products (DBPs) of different disinfectants When the dose and residue are both high, the disinfection by product is high. Due to the short reaction period. Trihalomethanes (THM) and halogenic compounds may be formed in large amounts (Liang and Singer, 2003). The breakdown of tribromine acetic acids is likewise accelerated when the temperature rises (Karanfil et al., 2008). Hypochlorite ions are formed when the pH level is high, limiting the effectiveness of chlorine disinfection and resulting in the development of more THM. More HAAs are generated when the pH level is low. (Liang and Singer, 2003). 2.8 General Information on Haloacetic Acids Haloacetic acids are acids that contain haloacetic groups. Disinfectants HAAs, which are DBPs, are produced when natural chemical molecules in raw water react with them. Acetic acid referents with one, two, or three hydrogen atoms of the methyl group substituted by chlorine or bromine are known as HAAs (Karanfil et al., 2008). Acetic acids come in a variety of structural forms, including mono- , di-, and trichloroacetic acids, as well as mono-, di-, and tribromoacetic acids. Animal studies have indicated that HAAs are harmful to the liver and embryos, as well as having mutagenic, carcinogenic, and reproductive properties. Long-term exposure to high quantities of 21 Table 2.1: Disinfection By-products (DBPs) of different Disinfectants Source: Cardor and Gallego (2011) Disinfection Organohalogenic disinfection by-products Inorganic disinfection by - products non-halogenic disinfection by-products Chlorine (Cl2)/underchloric acid (HOCl) Trihalomethanes, halogenic acetic acid, haloacetonitriles, Chlorine hydrates, Chlorophenols etc. Chlorate (particularly the application of hypochlorite) Aldehydes, alkanic acids, benzene, carboxylic acids Chlorine dioxide (ClO2) - Chlorite, Chlorate - Chloramines (NH2Cl) Haloacetonitriles, cyanochlorine, organic chloramines etc. Nitrite, nitrate, chlorate, hydrazine Aldehydes, ketons Ozone (O3) Bromoform, monobromine acetic acid, dibromine acetic acid etc. Chlorate, iodate, bromate, hydrogen peroxide. Aldehydes, ketons, carboxylic acids 22 haloacetic acids has been linked to a number of health problems, including cancer, birth defects, and skin irritations (Pan, 2014). 2.8.1 Occurrence surveys of haloacetic acids Haloacetic acids HAAs occur at very low concentrations in natural waters, including surface waters and precipitation. In unpolluted ground water, HAAs are generally below detection limits. In contrast, disinfection of water drastically increases HAAs levels, and the overall concentration as well as the HAAs speciation depend on multiple factors, including disinfection method, residual disinfectant concentration, organic carbon content of water, halogen levels, temperature, pH, time in the distribution system, etc. Chloramination is believed to reduce HAAs levels in comparison with chlorination (Krasner et al., 2010). In certain uses necessitating higher residual disinfectant, such as in swimming pool water, very high concentrations of individual HAAs have been conveyed in certain studies (Ye et al., 2011). This may be of concern due to human exposure from ingested pool and drinking water. (Goslan et al., 20012). The halogens are a group of reactive elements in the periodic table that form a family. The presence of halogen atoms indicates a haloacetic acid's reactivity, specifically, the reactivity of the alpha carbon to which the halogens are bonded, as well as the ionizability of the carboxylic group. Physical- chemical features of halogens such as the reactivity of haloacetic acid is influenced by electronegativity, polarizability, atomic size, and associated properties like the strength of the halogen- carbon atom bond and the halogen's inclination to act as a leaving group (Stalter et al., 2016). The high electronegativity of halogenated chemicals renders them extremely reactive and amplifies their toxicity within living cells. From chlorine to bromine to iodine, as the halogens moves down the periodic table. The strength of the negative charge created by carboxylic acid ionization, the magnitude 23 of the negative log of the acid dissociation constant (pKa), and the reactivity of the alpha carbon in a substitution reaction are all affected by the presence of one or more halogen atoms in a haloacetic acid. As a result, the type and amount of halogen atoms in each haloacetic acid determine its physical- chemical properties (Stalter et al., 2016). The physical-chemical characteristics of HAAs determine their toxicity (because they describe a molecule's ability to penetrate cells as well as its potential reactivity with other molecules within a cell). All haloacetic acids exist in their ionized form at physiological pH, however the pKa also indicates that the acid form's strength grows as the pKa decreases. (Schultz and Shangraw, 2006). Table 2.2 lists the physicochemical properties of haloacetic acid. 2.9 Trichloroacetic Acid (TCA) TCA is made up of acetic acid, which is a monocarboxylic acid. Chlorine takes the place of all three methyl hydrogens (Figure 2.3). TCA is a type of haloacetic acid that only exists in its ionized state and does not breakdown (Lawson et al., 2003). TCA has been found to be positive in cancer bioassays, and it is thought that TCA causes liver cancer through a different mechanism than other haloacetic acids (Bull, 2000). Trichloroacetic acid (TCA) belongs to the haloacetic acid family. Trichloroacetic acid is almost solely ionized, and it does not degrade (Lawson et al., 2003). TCA has been shown to cause liver cancer by processes separate from those found in other haloacetic acids (Bull, 2000). 24 Table 2.2: Physical and Chemical Properties of Haloacetic Acid Source: Karafil et al., 2008 Monochloro acetic acid Dichloro acetic acid Trichloro acetic acid Monobromoac etic acid Dibromoaceti c acid Formula CH2ClCOOH CHCl2COOH CCl3COOH CH2BrCOOH CHBr2COOH Molecul ar weight (g/mole) 94.497 128.942 163.387 138.948 217.844 Physical state at ambient temperat ure colorless to white crystalline (hydroscopic) colorless to yellowish liquid colorless to off-white crystalline colorless crystalline beige crystalline (hydroscopic) Boiling point (oC) 189 194 195.5-198 208 128-130 Solubilit y in water (g/L) 858-3170 (25 oC) 1,000 (20 oC) miscible 44 (25 oC) 82 (20 oC) very high in some sources (miscible) 94 (25 oC) 2110 (25 oC) Vapor pressure (mm Hg) 0.065 0.179 0.06 0.119 0.023 Acidity, pKa 2.87-2.97 1.26-1.41 0.51-0.66 2.89-2.96 1.39-1.48 25 Cl Cl Cl OH O Figure 2.3: Chemical Structure of Trichloroacetic acid Source: Google image 26 2.9.1 Sources of trichloroacetic acid The sources of trichloroacetic are as follows; 1. Water The photocatalytic breakdown of tetrachloroethylene in water produces trichloroacetic acid as a major chlorinated by-product (IARC, 1995). As a result, it can be found in drinking water and swimming pools after raw waters with natural organic components have been disinfected with chlorine (Hargesheimer and Satchwill, 1989). TCA has around a 40-day residence period in pond water (Ellis et al., 2001). 2. Food After being employed as an herbicide, TCA deposits have been discovered in wheat, barley, and oat seed (Kadis et al., 2011). Trace concentrations (0.01–0.20 ppm [0.01–0.20 mg/kg]) were observed in vegetables and fruits from fields irrigated with TCA-containing water; slightly higher levels (0.13– 0.43 mg/kg) were found in field bean pods and seeds (Demint et al., 2010). 2.9.2 Application of trichloroacetic acid a. Medical application Therapeutic usages of TCA take into justification of use as an antibacterial and a peeling agent. It has shown to be effective in removing tattoos and curing genital warts. It's also used in microscopy as a decalcifier and fixative, also as a protein precipitant in chemical analyses of bodily fluids and tissue extracts (Gennaro, 2000). 27 b. Industrial application TCA is also utilized as a solvent in the plastics sector and as an inscription and soaking agent for the surface cleaning of metals (HSDB, 2001). c. Agricultural application The agricultural use of TCA, generally it has been used as a selective herbicide as its sodium salt and soil Purifier (Koenig et al., 2011). 2.9.3 Trichloroacetic acid metabolism in animals and humans TCA is easily absorbed by rats and humans via the cutaneous and oral routes into the gastrointestinal system (USEPA, 2012). TCA binds significantly to plasma and also metes out to liver proteins after digestion in rats (Schultz et al., 2006). In the liver, a tiny percentage of TCA is metabolized (Yu et al., 2011). Rats and mice produced carbon dioxide, glycoxylic acid, oxalic acid, glycolic acid, and dichloroacetic acid after receiving 20 or 200 mg of TCA per kg of body weight. (Hunter et al., 2006). Figure 2.4: The oxidative metabolic activity that does occur is predominantly cytochrome P450 converting trichloroacetic acid through a dichloroacetic acid radical into Benzoyl glycine (hippuric acid). 2.9.4 Trichloroacetic acid's health effects The bioaccumulation of various forms of Trichloroacetic acid in humans has resulted in carcinogenic and mutagenic effects in humans, including cancer and other pregnancy difficulties (Anandharihara et al., 2005). Despite the fact that epidemiological studies had yet to establish a definitive link between chlorinated surface waters and bladder cancer, USEPA (1999) The weight of evidence from toxicological and epidemiological investigations showed a potential causal connection, according to the researchers. In urinalysis, the kidneys are known to expel pollutants from the body in order to 28 Figure 2.4: Metabolism of Trichloroacetic Acid (Larson and Bull, 1992). 29 keep the bloodstream and other body fluids in a homeostatic equilibrium. Increased levels of contaminants in the urine have been linked to one of four factors: hormonal imbalance, increased urine production, a likely malfunctioning kidney caused by diseases such as inflammation, and a higher- than-normal pollutant content in the body and bodily fluids (Plewa et al., 2010). 2.10 Adsorption Techniques The process of a gaseous or liquid material (adsorbate) adhering to a solid surface is known as adsorption. This is because spongy materials with broad surfaces can selectively trap chemicals on the solid's surface (adsorbent) (Attia et al., 2003). 2.10.1 Physical adsorption Electron exchange is replaced by Van der Waals forces, dipole interactions, and hydrogen bonding. All contribute to physical contact between the adsorbent and the adsorbate. Physical adsorption requires no activation energy, hence the time it takes to reach equilibrium is quite brief. As a result, Physical adsorption is a reversible and non–specific process (Rio, 2006). 2.10.2 Chemical adsorption Chemical adsorption is both selective and irreversible due to the chemical interaction between the adsorbent and the adsorbate molecule. Weak chemical adsorption is caused by covalent bonds between the adsorbent and the adsorbate, whereas strong chemical adsorption is caused by ionic bonds (Okada et al., 2003). 2.11 Adsorbent Physical Characteristics 2.11.1 Adsorbent pores The adsorbent's adsorption capacities and even active adsorption rate are determined by the number of pores, their shape, and their magnitude (Radovic, 1999). 30 2.11.2 Specific surface area of adsorbent Micropores make up the bulk of the overall pore volume and cover the majority of the activated carbon's interior surface. The sample's outer surface is made up of mesopores, macropores, and the nonporous surface (Figure 2.5). Despite the fact that micropores are responsible for the bulk of adsorption, meso- and macropores are required in every adsorption process because they serve as a conduit for the adsorbate into micropores. In addition, multilayer adsorption takes place in meso and macropores (Suhas and Carrot, 2007). 2.12 Activated Carbon Activated carbon is the most important adsorbent for industrial use. The porous, black carbonaceous substance known as activated carbon (AC) has a porous look. Since 1500 B.C., carbonized wood and charcoal have been employed as water filters, medical adsorbents, and purifying agents. Activated carbons are generated from carbonaceous solid precursors that are either synthetic or natural. Coconut shells, peat, black ash, charcoal, lignite, bituminous coal, and petroleum coke, to mention a few ingredients, can be used to make it. Because of its large internal surface area and pore volume, in gas and liquid phase processes, AC works effectively as an adsorbent, catalyst, or catalytic support (Radovic, 2001). 2.12.1 Activated carbon preparation The two most popular methods for producing activated carbon are physical and chemical activation (Figure 2.6). 31 Figure 2.5. External and Internal Adsorbent Surface (Mohamed, 2011). 32 Figure 2.6: Scheme of the Process of Activated Carbon Manufacturing. Source: Mohamed (2011) 33 2.12.1.1 Physical activation a. Carbonization Carbonization is a thermal process that converts a carbonaceous precursor to solid char while removing any remaining liquids or gases (Chattopadhyaya et al., 2006). This occurs when there is no air present and the temperature is between 600 and 800 degrees Celsius. b. Activation By increasing the porosity of the char, activation increases activated carbon's surface area (Turmuzi et al., 2004). Rio et al., (2005b), Physical activation is defined as the high-temperature gasification of the resultant char with an activating source, CO2, steam, or air are examples of such activating substances (800-1000 oC); the char develops a porous structure. Because activated carbon produced with steam has a larger adsorptive capacity and wider pore size dispersion than activated carbon produced with CO2, it is the most widely used activating gas (Khalil et al., 2001). 2.12.1.2 Chemical activation Chemical activation consists of two phases (carbonisation and activation) that are conducted simultaneously. In an inert atmosphere, the raw material is impregnated with a chemical agent such phosphoric acid, sulphuric acid, potassium hydroxide, or zinc chloride (Tay et al., 2001). The impregnated product is heated to (500-800 oC) under steam flow and kept at that temperature for a short period before being rinsed to get rid of the activator. The chemical process of activation strategy provides a better yield than the physical activation method, which can be up to 30% higher (Dabrowski et al., 2005). Chemical activation provides the following advantages: (a) simplicity, as the raw material does not need to be carbonized first; (b) reduced activation temperatures; and (c) good porosity structure formation. 34 2.13 Activated Carbon Chemical Structure 2.13.1 The textural properties The carbon atoms align to create graphite crystallites, consisting of three to four parallel hexagonal carbon ring layers form during the carbonization of the raw material (Figure 2.7 a). These characteristics make AC highly porous, making it ideal for a wide range of compound catalysis and adsorption (Figure 2.7b). 2.13.2 Functional groups on the surface The adsorption potential and textural qualities of an AC's surface are affected by its chemical environment (Bansal et al., 2005). The activation process is primarily responsible for controlling the chemical functional groups on the surface. The two principal kinds of surface functional groups include acidic groups (carboxylic, lactones, and phenols) and basic groups (pyrone, chromene, ethers, and carbonyls) (Boehm, 1994; Yang, 2003; Shen et al., 2008). (Figure 2.8). The type of surface functional groups has a big impact on liquid-phase adsorption, changing the way solutes interact with carbon surfaces (Moreno-Castilla, 2004; Derylo-Marczewska et al., 2008). Thus, the acidic or basic compounds formed on the adsorbent surface explain the charge, hydrophobicity, and electrical density of the graphite layers (figure 2.9), illuminating the adsorbent activity differences toward a variety of compounds. When the amount of acidic surface groups is reduced, adsorption increases (Radovic et al., 2001; Moreno-Castilla, 2004). Carbonic's hydrophilic character is enhanced by increased acidic surface functional groups, which reduces its affinity for non-polar organic compounds while boosting its polar molecules' adsorption capacity (Kim and Park, 2007; Huang et al., 2008). Basic function groups, on the other hand, lead to hydrophobic carbons and have a strong affinity for water-insoluble organic compounds such as phenols (Stoeckli and Hugi-Cleary, 2001). Furthermore, the pH significance at which the surface 35 Figure 2.7. Carbon Atom Arrangement in Graphite Crystal (a); Activated Carbon Microstructure (b) Source: Mohamed, 2011 36 Figure 2.8: Chemical Structure of Activated Carbon Source: Wikipedia Figure 2.9: Surface Functional Groups of the Activated Carbon Mohamed (2011). 37 charge is zero affects the pH of the solution and the surface charge of carbon (pHPZC). Amphoteric carbons have a positively charged carbon surface at pH ˂ pHpZC and a negatively charged carbon surface at pH>pHPZC. A negative charge will emerge from the breakdown of acidic surface oxygen complexes, such as carboxylic and phenolic groups. The positive surface charge could be explained by the presence of electron-rich patches within the graphene layers that act as Lewis basic centers, drawing protons from the aqueous solution. Alternatively, it could be caused by the presence of basic surface oxygen complexes such as pyrones or chromenes (Moreno-Castilla, 2004). 2.14 Polyethylene Terephthalate PET is a thermoplastic polymer that is utilized in a variety of applications, including clothing fibers, tanks, and bottles, as well as construction components. Plastic has many uses in everyday life, yet it is harmful to the environment when it is recycled. As a result, hazardous chemicals remain. Plastics are widely used in a range of products due to their durability, light weight, ease of molding, and low cost of production. As a result, the use of plastic has continuously increased over the previous 50 years (Alighiri et al., 2019). Amorphous PET is used to produce bottles and packaging because of its great transparency, which is comparable to that of glass. A semi-crystalline polymer, which is foggy and has a milky white hue, is used in other cases. (Awad and Khalaf, 2018). However, massive volumes of PET products (bottles, spinning, and packaging films) significantly contaminate the environment. PET is included in approximately 12% of municipal plastic waste (Williams, 2006). 38 Separating PET bottles from municipal rubbish is, in reality, one of the most successful polymer recycling instances (EPA, 2015). There are numerous methods for recycling disposable beverage bottles, including chemical recycling (hydrolysis, aminolysis, glycolysis, etc.) and physical recycling (re-melting). Plastic recycling is significant for two reasons: first, it helps to reduce the overall volume of plastic trash, and second, it helps to create value-added materials from low-cost sources by transforming them into materials that are appreciated (Badia et al., 2012). The need to expand the usage of recycled plastics prompted researchers to look at new processing processes that would result in higher-value goods. PET is made up of repeated (C10H8O4) units polymerized from the monomer ethylene terephthalate. Figure 2.10 depicts the chemical structure of PET. 2.14.1 Preparation of activated carbon from polyethylene terephthalate waste ACs are porous solids that have desired properties like chemical resistance, thermal stability, and surface area (Cardoso et al., 2008). Inside the material, many pore networks create a large surface area. The material preparation, pore sizes and volumes are influenced by the pretreatment of the precursor prior to carbonization, the carbonization process itself, and the activation step conducted after or concurrently with the carbonization process (El-Hendawy, 2009). Steam activation (physical activation) has been considered in the manufacturing of polyethylene activated carbon. (Esfandiari et al., 2012). Chemicals such as KOH and NaOH have also been used in the carbonization process, either before or after. Chemical activation has a number of advantages, including the ability to be applied in a single step and the production of a more porous structure (Cardoso et al., 2008). 39 Figure 2.10; Chemical make-up of Polyethylene Terephthalate (PET) Source: Wikipedia 40 2.15 Chitosan Chitosan is made when chitin is deacetylated (D-glucosamine connecting to N-acetyl D-glucosamine via a 1,4-glycosidic bond) (Figure 2.11). The most plentiful sources of chitin are crab and shrimp shells. Organic and inorganic contaminants have been removed from water using chitosan and its derivatives. (Bhatnagar and Sillanpaa, 2009). The high adsorption potential of chitosan is due to four factors: (1) Due to the enormous amount of hydroxyl groups in glucose units, it has a high hydrophilicity (2) a huge number of functional groups are present (3) these groups' strong chemical reactivity, and (4) the polymer chain's flexible structure Chitosan, as opposed to activated charcoal, is more effective in removing organic pollutants. (Venugopal, 2011). 2.16 Adsorption When using activated carbon to treat drinking water and wastewater, adsorbates fight for adsorption sites on the carbon surface. As a result, it's vital to have a full grasp of the impacts of carbon adsorption of different organic molecules. Designing such feasible systems, particularly those containing a large number of solutes, is extremely difficult. (Lu and Sorial, 2007). Site competition and pore obstruction are two key processes through which natural organic matter (NOM) competes (Li et al., 2003). NOM molecules that are small, powerfully adsorbing, and have a size that is similar to the preferred compound are primarily responsible for continuous site competition, which reduces a component's adsorption capacity (Liding et al., 2008). 2.16.1 Factors affecting the adsorbent/adsorbate interactions Traditional AC adsorption capacity for organic compounds is heavily influenced by a variety of parameters, including not just the adsorbent's nature as well as the adsorbate type. The pKa, functional groups, polarity, water solubility, molecular size, and weight of the chemical are all 41 Figure 2.11: Chemical Structure of Chitosan Source: Wikipedia 42 important considerations (Terzyk 2004; Zhang et al., 2006a). Furthermore, in the adsorption process, variables such as solution pH, ionic strength, and temperature play a role in the interactions between the adsorbent and the adsorbate (Canizares et al., 2006; Vasiljevic et al., 2006; Al-Degs et al., 2008). 2.16.2 Nature of the adsorbate's influence Although the substituent groups aren't thought to be engaged in interactions with the carbon surface (Dabrowski et al., 2005), they do change molecular characteristics, which affect adsorption progression. a. The effect of electron donor/acceptor substituent groups Interfaces are formed by the connections between the electrons in the carboxylic group of Trihaloacetic acid. The graphene layers contain charge transfer, dispersive force, and polar electrostatic components. Electron removing groups are hypothesized to increase interactions by lowering electron density, hence diminishing gross electrostatic interactions between Carboxylic groups. The interfaces are enriched when the number of bromo (-Br) and chloro (-Cl) groups is increased because they are both electron-withdrawing groups (Liu Q-S et al., 2010). b. Solubility The solubility and chemical structure of organics have an impact on adsorption. In one sense, it is palpable that a compound's adsorption capacity decreases as its solubility in water increases. The polarity of an adsorbate is usually related to its dissolution; the more polar an adsorbate is, the more soluble it is in a polar solution. Kumar et al. (Kumar et al., 2007). 43 c. Hydrophobicity Adsorbates with a higher hydrophobicity tend to be assimilated and stick to the carbon surface or the pores, in aqueous solution. Hydrophobic chemicals are forced to the adsorbent surface more than hydrophilic compounds, resulting in more adsorbed hydrophobic compounds (Moreno-Castilla, 2004). d. The solution's pH Changes in pH in adsorption coordination can have an impact on the chemical characteristics of activated carbon surfaces as well as the shape of the adsorbate, making it a significant factor in the process. Acidic or alkali species can alter the surface chemistry of the adsorbent by reacting with the surface groups. As a result of the pH, these factors could induce considerable changes in adsorption symmetry. Garcia-Araya and colleagues (Garcia-Araya et al., 2003). The adsorbate is primarily deprotonated at pH > pKa and protonated at pH ˂ pKa. As a result of these influences, the adsorption equilibrium may be considerably altered (Laszlo and colleagues, 2007). 2.17 Isotherm of Adsorption As a function of the adsorbate's equilibrium concentration, the adsorption isotherm describes the quantity of material adsorbed per unit mass of adsorbent. The mass balance equation is used to calculate the equilibrium concentration in solution when a ce