(Luận văn thạc sĩ) research on hydrothermal carbonization (htc) of paper mill sludge, food and forestry wastes effects of process parameters on properties of hydrochar

VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY KARUNASENA DHANUKA NAYOMAL RESEARCH ON HYDROTHERMAL CARBONIZATION (HTC) OF PAPER MILL SLUDGE, FOOD AND FORESTRY WASTES h EFFECTS OF PROCESS PARAMETERS ON PROPERTIES OF HYDROCHAR MASTER'S THESIS VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY KARUNASENA DHANUKA NAYOMAL RESEARCH ON HYDROTHERMAL CARBONIZATION (HTC) OF PAPER MILL SLUDGE, FOOD AND FORESTRY WASTES h EFFECTS OF PROCESS PARAMETERS ON PROPERTIES OF HYDROCHAR MAJOR: ENVIRONMENTAL ENGINEERING CODE: 8520320.01 RESEARCH SUPERVISORS: Associate Prof Dr CAO THE HA Dr VU NGOC DUY Hanoi, 2021 ACKNOWLEDGMENTS The work documented in this report was only possible to achieve with the guidance, support and patience of a number of people that I have the privilege to interact and learn from First of all, I would like to express my sincere gratitude towards Associate Professor Cao The Ha and Doctor Vu Ngoc Duy for the enthusiastic instructions and encouragement throughout this current study Secondly, I take this opportunity to express my gratitude to all the professors, lecturers and students at the Environmental Engineering program, VNU Vietnam Japan University for their inspiration during this project Finally, I would like to thank my parents for their support and encouragement during this long period h Karunasena Dhanuka Nayomal TABLE OF CONTENTS h LIST OF TABLES i LIST OF FIGURES ii LIST OF ABBREVIATIONS v CHAPTER : INTRODUCTION 1.1 Hydrothermal Carbonization of Lignocellulosic Biomass CHAPTER : LITERATURE REVIEW 2.1 Historical overview of HTC process 2.2 Biomass And Thermochemical Processes 2.2.1 Thermochemical processes 2.2.2 Biomass: definition, properties, and comparison 12 2.3 Overview of HTC Process 15 2.3.1 Reaction mechanism of HTC with biomass 15 2.3.2 The role of water in HTC 19 2.3.3 Effect of process parameters 20 2.3.4 Advantages of HTC 24 2.3.5 Potential uses of HTC coal 25 2.3.6 Products of HTC 27 CHAPTER : MATERIALS AND METHODS 35 3.1 HTC applicable industries 35 3.1.1 Food and Beverage industry 35 3.1.2 Paper industry 36 3.1.3 Forestry 38 3.2 Materials 40 3.3 Description of the HTC reactor 41 3.4 Experimental methods and principles 42 3.4.1 pH 43 3.4.2 Electrical Conductivity (EC) 44 3.4.3 Total Nitrogen (NCASI Method TNTP-W10900) 44 3.4.4 Total phosphorus (NCASI Method TNTP-W10900) 45 3.4.5 Chemical Oxygen Demand (EPA Method 410.3) 46 3.4.6 Sample treatment: Moisture removal 47 3.4.7 Ash content and volatile matter calculation 48 3.4.8 Calculating gross calorific value 49 CHAPTER : RESULT AND DISCUSSION 51 4.1 Moisture Removal 51 4.2 Hydrochar 54 4.2.1 Restaurant Food waste (RFW/R) hydrochar 54 4.2.2 Paper mill sludge (PMS/P) hydrochar 57 4.2.3 Saw dust (SD/ S) hydrochar 61 4.3 Characteristics of hydrochar process water 66 4.3.1 Restaurant food waste (RFW/ R) process water 66 4.3.2 Paper mill sludge (PMS/P) process water 71 4.3.3 Saw dust (SD/ S) process water 76 CONCLUSION 80 REFERENCES 84 APPENDIX 89 h LIST OF TABLES h Table 2.1 Characteristics of biomass torrefaction Table 2.2 Characteristics of biomass pyrolysis Table 2.3 Characteristics of biomass gasification 10 Table 2.4 Characteristics of biomass Hydrothermal carbonization 12 Table 2.5 Chemical analysis and properties of selected types of biomass (Canzana, 2011) 14 Table 2.6 Saturated steam table (Kruse et al.,2013) 22 Table 2.7 Summary of process parameters for HTC process 23 Table 2.8 Comparison of reaction conditions and product distributions (Libra et al.,2011) 28 Table 2.9 Distribution of the carbon fraction in the HTC product phases (Marchetti, 2012) 29 Table 2.10 Examples of solid yields and elementary compositions of HTC-coal from different substrates (Libra et al.,2011) 30 Table 2.11 Composition of the process water resulting from HTC (Robbiani, 2013) 33 Table 4.1 Moisture content, Amount of dry solid Volatile, ash and Gross caloric values calculated by equation (5) of biomass feeds 51 Table 4.2 Proximate analysis of biomass after the hydrothermal carbonization gross caloric values were calculated by equation (5) n = 52 Table 4.3 Comparison of gross calorific value from the research with literature review 64 Table 4.4 GCVs of the feed and chosen hydrochar samples from ultimate analysis 64 i LIST OF FIGURES h Figure 1.1 Garbage dump in Giong Rieng district, Kien Giang province and Binh Tu landfill, Phan Thiet city, Binh Thuan province.( Ministry of Natural Resources and Environment Report, 2019) Figure 1.2 Friedrich Bergius Figure 2.1 Differences between primary and secondary cell wall in plants 15 Figure 2.2 Degradation products and sub products during hydrolysis of lignocellulosic biomass (Qadariyah et al.,2011) 16 Figure 2.3 Comparison of different energy and carbon exploitation schemes for carbohydrates (Titrici et al.,2007) 25 Figure 2.4 Percentage of each product in HTC process 28 Figure 2.5 Van Krevelen diagram (Marchetti, 2012) 31 Figure 2.6 Correlation carbon content and calorific value for different substrates (Oliveira et al.,2013) 32 Figure 3.1 Food waste collecting site, Canada 35 Figure 3.2 Paper mill sludge, Peninsular Malaysia 36 Figure 3.3 Forestry waste Terrace Community Forest, Northwest British Columbia 38 Figure 3.4 Raw dried restaurant food waste, raw dried paper mill sludge and raw dried saw dust 40 Figure 3.5 Hydrothermal carbonization reactor with Teflon inner compartment and stainless steel outer cover 41 Figure 3.6 Carbolite gero laboratory furnace 42 Figure 3.7 Calibration curve for total nitrogen 45 Figure 3.8 Calibration curve for total phosphorus 46 Figure 3.9 Calibration curve for Chemical oxygen demand 47 Figure 3.10 Thermal analysis procedure for Biomass fuel (Hydrochar) Fixed solid, Ash, Volatile solid 49 Figure 4.1 Raw biomass feed samples and subsequent hydrochar samples 53 Figure 4.2 The dependence of yield of RFW hydrochar from dried food waste with temperature and time (n = 3, triplicate) 54 Figure 4.3 Percentages of total solid content and moisture content of RWFHC with time and temperature (n = 3, triplicate) 55 Figure 4.4 Percentages of Volatile solid content and ash of RWFHC with time and temperature (n = 3, triplicate) 55 ii h Figure 4.5 Gross calorific values of RFWHC with time and temperature (n = 3, triplicate) 56 Figure 4.6 Percent conversion of PMS hydrochar with time and temperature (n = 3, triplicate) 57 Figure 4.7 Total solid content and moisture content of PMSHC with time and temperature (n = 3, triplicate) 58 Figure 4.8 Percentages of Volatile solid content and ash of PMSHC with time and temperature (n = 3, triplicate) 59 Figure 4.9 Gross calorific values of PMSHC with time and temperature (n = 3, triplicate) 59 Figure 4.10 Yield of SD hydrochar with increasing time and temperature at 220oC (n = 3, triplicate) 61 Figure 4.11 Total solid content and moisture content of SDHC with time and temperature at 220oC (n = 3, triplicate) 62 Figure 4.12 Percentages of Volatile solid content and ash of SDHC with time and temperature at 220oC (n = 3, triplicate) 62 Figure 4.13 Gross calorific values of SDHC with time and temperature at 220oC (n = 3, triplicate) 63 Figure 4.14 pH of RFW process water with time and temperature (n = 3, triplicate) 66 Figure 4.15 COD of RFW process water with temperature and time (n = 3, triplicate) 67 Figure 4.16 Electrical conductivity of restaurant food waste process water with temperature and time (n = 3, triplicate) 68 Figure 4.17 Total nitrogen of RFW process water with temperature and time (n = 3, triplicate) 69 Figure 4.18 Total phosphorus of RFW process water with temperature and time (n = 3, triplicate) 70 Figure 4.19 pH of PMS process water with temperature and time (n = 3, triplicate) 71 Figure 4.20 Electrical conductivity of PMS process water with temperature and time (n = 3, triplicate) 72 Figure 4.21 COD of PMS process water with temperature and time (n = 3, triplicate) 73 Figure 4.22 Total nitrogen of PMS process water with temperature and time (n = 3, triplicate) 74 Figure 4.23 Total phosphorus of PMS process water with temperature and time (n = 3, triplicate) 75 Figure 4.24 pH of SD process water with time and temperature at 220oC (n = 3, triplicate) 76 iii Figure 4.25 Electrical conductivity of SD process water with time and temperature at 220oC (n = 3, triplicate) 77 Figure 4.26 COD of SD process water with time and temperature at 220oC (n = 3, triplicate) 78 Figure 4.27 Total nitrogen of SD process water with time and temperature at 220oC (n = 3, triplicate) 79 h iv LIST OF ABBREVIATIONS Carbon-13 Nuclear Magnetic Resonance American Society for Testing and Materials Chemical Oxygen Demand Electrical Conductivity Energy Dispersive X-ray Spectroscopy Fixed Solid Gas Chromatography–Mass Spectrometry Gross Calorific Value Greenhouse Gas Hydrochar Higher Heating Value Hydrothermal Carbonization Moisture Content Municipal Solid Waste National Council for Air and Stream Improvement Paper mill Sludge Initial Sample of Paper mill Sludge Paper mill Sludge Hydrochar Restaurant Food Waste Restaurant food waste hydrochar Initial Sample of Restaurant Food Waste Saw dust Saw dust Hydrochar Scanning Electron Microscopy Initial Sample of Saw dust Total Nitrogen Total Organic Carbon Total Phosphorus United States Environmental Protection Agency Volatile Solid h 13C-NMR: ASTM: COD: EC: EDS: FS: GC-MS: GCV: GHG: HC: HHV: HTC: MC: MSW: NCASI: P/PMS: PINI: PMSHC: R/RFW: RFWHC: RINI: S/SD: SDHC: SEM: SINI: TN: TOC: TP: US EPA: VS: v of secondary char in the liquid phase Therefore, it can be assumed that the recycling process enhances the yield of hydrochar However when it moves to third recycling the yield drastically surges V Data of Moisture, Total solid, Volatile solid, Ash, GCV M% 180oC 200oC 220oC 220oC Ash% GCV 3.76953681 96.19920714 91.186318 8.8136816 26.844017 18R4 2.81683562 97.36653646 89.976932 10.430945 26.868991 18R6 2.70437984 97.54887465 91.744417 8.2555829 27.224046 20R3 2.70584813 97.56570302 76.750059 23.526045 24.81761 20R4 2.57179587 97.72787058 91.733118 8.4182901 27.248108 20R6 1.1091257 98.25066138 78.358184 25.470365 24.922042 22R3 1.96830433 98.01626661 86.090872 13.909128 26.424955 22R4 1.54810793 98.08841494 88.566139 11.773814 26.805889 22R6 0.97129498 98.77339152 100.83013 26.876987 26.599897 h 200oC VS% 18R3 M% 180oC S% S% VS% Ash% GCV 18P3 3.0981932 97.168593 60.6472 39.35275941 22.191952 18P4 2.6854883 97.4860877 60.3133 39.6867014 22.207294 18P6 2.5565901 97.5937744 59.6437 40.35632069 22.123938 20P3 2.3389171 97.7827995 60.3041 39.69588371 22.269848 20P4 1.5256192 98.241865 59.6006 40.39944631 22.256899 20P6 1.9872878 98.1553904 58.4302 41.56982535 22.051941 22P3 1.6030647 98.4399831 60.2168 39.78321033 22.397735 95 VI 22P4 1.2371191 98.5676531 58.7004 41.29956968 22.183906 22P6 1.1855571 98.6264004 56.4533 43.54668774 21.838884 Data of COD Sample Name Singlet Duplicate Triplicate Average Abs Abs Abs Abs 0.053 0.057 0.048 0.053 PMS initial 0.000 0.015 0.011 0.009 SD initial 0.062 0.019 0.011 0.031 18R3 0.168 0.108 0.163 0.146 18R4 0.164 0.162 0.200 0.175 18R6 0.139 0.180 0.168 0.162 20R3 0.181 0.249 0.184 0.205 20R4 0.145 0.186 0.126 0.152 20R6 0.083 0.106 0.116 0.102 22R3 0.111 0.194 0.186 0.164 22R4 0.106 0.098 0.104 0.103 22R6 0.096 0.110 0.088 0.098 18P3 0.025 0.028 0.035 0.029 18P4 0.030 0.043 0.044 0.039 18P6 0.052 0.054 0.059 0.055 20P3 0.032 0.040 0.041 0.038 20P4 0.047 0.060 0.048 0.052 20P6 0.058 0.073 0.055 0.062 22P3 0.042 0.052 0.032 0.042 22P4 0.058 0.064 0.054 0.059 22P6 0.069 0.083 0.075 0.076 22S3 0.045 0.046 0.034 0.042 22S4 0.076 0.054 0.057 0.062 h RFW initial 96 22S6 VII 0.083 0.078 0.089 0.083 Data of total phosphorus Singlet Sample N Abs Duplicate Err% Abs Triplicate Err% Abs Err% Averag e RFW initial 0.1220 9.6608 0.0427 0.1120 8.8935 0.0427 0.1170 18R3 0.1750 13.7277 0.1358 0.2300 17.9481 0.1358 0.2025 18R4 0.3070 23.8567 0.0623 0.2710 21.0942 0.0623 0.2890 18R6 0.3380 26.2354 0.0289 0.3190 24.7775 0.0289 0.3285 20R3 0.2410 18.7922 0.1529 0.3280 25.4681 0.1529 0.2845 20R4 0.2660 20.7106 0.1271 0.2060 16.1065 0.1271 0.2360 20R6 0.1700 13.3441 0.0968 0.1400 11.0421 0.0968 0.1550 22R3 0.2960 23.0126 0.0296 0.2790 21.7081 0.0296 0.2875 22R4 0.2030 15.8763 0.1185 0.1600 h 12.5767 0.1185 0.1815 22R6 0.1420 11.1955 0.0923 0.1180 9.3539 0.0923 0.1300 PMS initial 0.0050 0.6829 0.0909 0.0020 0.4527 0.6364 0.0060 0.7597 0.0909 0.006 18P3 0.0080 0.9131 0.0000 0.0100 1.0666 0.2500 0.0080 0.9131 0.0000 0.008 18P4 0.0160 1.5270 0.2800 0.0090 0.9899 0.2800 0.0530 4.3662 3.2400 0.013 18P6 0.0220 1.9874 0.0233 0.0060 0.7597 0.7209 0.0210 1.9107 0.0233 0.022 20P3 0.0160 1.5270 0.0000 0.0110 1.1433 0.3125 0.0160 1.5270 0.0000 0.016 20P4 0.0300 2.6013 0.1111 0.0240 2.1409 0.1111 0.0170 1.6037 0.3704 0.027 20P6 0.0280 2.4478 0.1200 0.0040 0.6062 0.8400 0.0220 1.9874 0.1200 0.025 22P3 0.0210 1.9107 0.0500 0.0100 1.0666 0.5000 0.0190 1.7572 0.0500 0.020 22P4 0.0120 1.2201 0.6190 0.0360 3.0617 0.1429 0.0270 2.3711 0.1429 0.032 22P6 0.0030 0.5295 0.5385 0.0060 0.7597 0.0769 0.0070 0.8364 0.0769 0.007 97 VIII Data of total nitrogen Singlet Sample N Duplicate Triplicate Err% Abs Err% Abs Err% Average RFW initial 0.124 0.418 0.228 0.070 0.198 0.070 0.213 PMS initial 0.052 2.467 0.013 0.133 0.017 0.133 0.015 SD initial 0.029 0.673 0.015 0.135 0.008 0.538 0.017 18R3 0.576 274.219 0.020 0.576 274.219 0.020 0.611 291.309 0.040 0.588 18R4 0.675 322.559 0.009 0.675 322.559 0.009 0.694 331.836 0.019 0.681 18R6 0.654 312.305 0.014 0.659 314.746 0.007 0.668 319.141 0.007 0.664 20R3 0.792 379.688 0.073 0.684 326.953 0.073 0.395 185.840 0.465 0.738 20R4 0.461 218.066 0.012 0.450 212.695 0.012 0.472 223.438 0.036 0.456 20R6 0.319 148.730 0.002 0.320 149.219 0.002 0.554 263.477 0.734 0.320 22R3 0.740 354.297 0.008 0.892 428.516 0.215 0.728 348.438 0.008 0.734 22R4 0.625 298.145 0.004 0.620 295.703 0.004 0.863 414.355 0.386 0.623 22R6 0.673 321.582 0.086 0.613 292.285 0.011 0.573 272.754 0.075 0.620 18P3 0.134 29.199 0.116 0.220 50.195 0.452 0.169 37.744 0.116 0.152 18P4 0.260 59.961 0.154 0.215 48.975 0.046 0.201 45.557 0.108 0.225 18P6 0.466 110.254 0.341 0.367 86.084 0.056 0.328 76.563 0.056 0.348 20P3 0.345 80.713 0.025 0.328 76.563 0.025 0.281 65.088 0.165 0.337 20P4 0.374 87.793 0.005 0.371 87.061 0.003 0.371 87.061 0.003 0.372 20P6 0.482 114.160 0.072 0.417 98.291 0.072 22P3 0.344 80.469 0.086 0.409 96.338 0.086 0.307 71.436 0.185 0.377 22P4 0.355 83.154 0.054 0.406 95.605 0.082 0.365 85.596 0.028 0.375 22P6 0.370 86.816 0.169 0.300 69.727 0.052 0.333 77.783 0.052 0.317 22S3 0.022 1.855 0.228 0.035 5.029 0.228 0.029 22S4 0.048 8.203 0.103 0.059 10.889 0.103 0.054 h Abs 0.450 98 22S6 IX 180oC 200oC 220oC 180oC 0.069 13.330 0.140 0.081 16.260 0.339 0.052 9.180 0.140 0.061 Data of Weight, pH, EC, W% W1 Ph EC W% Unit g mScm-1 % 18R3 1.81 0.20 4.08 0.22 3.78 0.21 45.3 4.93 20R3 1.64 0.05 3.87 0.09 4.96 0.45 40.9 1.40 22R3 1.85 0.09 3.20 0.08 6.84 0.28 46.3 1.61 18R4 1.46 0.06 3.68 0.23 5.33 0.30 36.5 1.24 20R4 1.95 0.17 3.32 0.23 5.29 0.63 48.6 4.27 22R4 1.94 0.07 3.05 0.36 5.35 0.66 48.4 3.85 18R6 1.72 0.06 3.10 0.17 5.75 0.48 43.1 2.18 20R6 1.92 0.11 3.35 0.12 4.42 0.18 48.0 3.18 22R6 1.96 0.03 3.65 0.11 5.18 0.25 48.9 2.52 18P3 3.74 0.04 6.26 0.12 0.92 0.00 93.5 1.09 20P3 3.66 0.04 6.03 0.17 1.04 0.03 91.5 1.04 22P3 3.64 0.02 5.36 0.17 1.00 0.08 91.0 0.32 18P4 3.71 0.04 5.98 0.15 0.97 0.08 92.7 1.05 20P4 3.57 0.04 5.48 0.26 1.38 0.06 89.4 0.98 22P4 3.46 0.04 4.91 0.09 1.61 0.02 86.6 0.87 18P6 3.63 0.01 5.37 0.19 1.29 0.00 90.7 0.54 20P6 3.44 0.03 5.12 0.03 1.80 0.08 86.0 1.12 22P6 3.22 0.05 4.55 0.06 1.96 0.08 80.6 1.22 22S3 3.19 0.04 3.00 0.08 0.22 0.01 79.7 0.88 22S4 3.07 0.04 2.77 0.04 0.35 0.04 76.6 0.99 22S6 2.91 0.02 2.69 0.03 0.45 0.01 72.7 0.59 h Sample 200oC 220oC 220oC 99 X EDS analysis of raw restaurant food waste sample h 100 XI EDS analysis of 18R6 hydrochar sample h 101 XII EDS analysis of raw papermill sludge sample h 102 XIII EDS analysis of 22P3 hydrochar sample h 103 XIV EDS analysis of raw saw dust sample h 104 XV EDS analysis of 22SD3 hydrochar sample h 105 VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY SOCIALIST REPUBLIC OF VIETNAM Independence – Freedom – Happiness Hanoi, date 12 month 07 year 2021 CONFIRMATION OF THE MASTER’S THESIS REVISION Fullname: Karunasena Dhanuka Nayomal Student ID: 19110070 Date of birth: 16/ 09/ 1993 Place of birth: Sri Lanka Master Program in: Environmental Technology Defense date: 21/ 06/ 2021 Based on the recommendation of the Master’s thesis evaluation committee, the thesis has been revised as follows: Comments, recomendations Revised content/ explain Chapter Introduction: not a chapter, should be shorten, some can be moved to Literature Review, add Research Objectives and Contents Section 2.3: should be move Moved section 2.3 into the material Chapter 2, Section to material (research section 2.3 objects) Section 3.3.6: Sample Added the description of the Chapter treatment: “sample” here is pretreatment processes that carried out an HTC product? Input during the research to the section 3.3.6 wastes should be pretreated? Remove junk before grinding process? Should write more clear h NO Created the “Historical overview of Chapter & HTC process” section in the literature review by using the parts of introduction Added the research objectives and contents to the introduction 106 Check reaction time of HTC Fixed the reaction time of the HTC Chapter 2, Table 2.4 in page 10 and table 2.4 (1 process following single reference to 72 hrs or 0.5 to 24 hrs.?) Correct the explanation of f, Corrected the t and T in equation (1): page parameters 18 HTC process should be The “HTC process” section moved into Chapter separated from section 3.3 the literature review and separated from “Analytical methods” the analytical methods Analytical methods: should Cited the standards that followed during Chapter cite the standard methods the analytical methods (TCVN or EPA) Fig 4.2: n=? based on the results of conversion percentages: what time you select and why? Fig 4.6: n=?, explain why time increased conversion % reduced at all temperatures; check at 200oC, 22P6 or 20P6? Correct Other Figures with error Add n values for all of the figures Chapter bars should add n value? contain error bars Fig 17-23,… descriptions of the Chapter Add the n values of each experiment Chapter 4, section Gave the reasons for the selection of the 4.2 & 4.6 reaction times and conversion reduction for 4.2 and 4.6 h 10 Conclusion:should Remove the citations and table from the Conclusion conclude according to the conclusion and modified the conclusion research contents, should not put citation and table in conclusion 107 11 Spelling mistakes (pages Fixed the spelling mistakes 9, Fig 2.2, etc.), correct corrected the chemical formula chemical formula and All the chapters 12 Correct abbreviation Fixed the mistakes in the abbreviation List of abbrevation (GHG), add CE (conversion section efficiency?) 13 Websites citation: should Corrected the website citation following References add access date the APA standards 14 The format of the whole Followed the VJU format and guidelines All the chpaters thesis should be revised and it is recommended that student have to strictly follow the format guideline of VJU h 15 There are many typos and Fixed the grammar and typo errors All the chapters grammar mistakes in the writing The student rarely Fixed the ambiguity in usage of comma uses the comma and and full stop wrongly uses the dot in the sentence Thus, it is very difficult to understand the idea of student 16 Due to the copy and paste Changed the name of the materials into Chapter without corrections, in the correct ones some parts the name of the material is incorrect 17 All the references should be Followed the VJU guideline for References section cited in the correct format references and single style of citation and the reference list should and referencing follow the guideline Student should use only style to cite the reference in the thesis 108 18 Some information is lacked Add the lacked references to the relevant All the chapters of source(reference) sections 19 The literature review Arrange the literature review section Chapter section is not well written following logical format and removed and not logical Students the section 1.2 from the thesis need to revise this section It can be considered that part 1.2 is not related with the thesis 20 The conclusion needed to Modified the conclusion section along Conclusion be rewritten with the comments of Assoc Prof Nguyen Thi Ha SUPERVISOR'S CONFIRMATION SIGNATURE OF STUDENT h CONFIRMATION OF MASTER’S THESIS EVALUATION COMMITTEE (Chairman) 109