Arsenic leaching potential from fly ash of coal power plant in vietnam

VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY TO HOANG NGUYEN ARSENIC LEACHING POTENTIAL FROM FLY ASH OF COAL POWER PLANT IN VIETNAM MASTER'S THESIS Environmental Engineering Hanoi, 2019 VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY TO HOANG NGUYEN ARSENIC LEACHING POTENTIAL FROM FLY ASH OF COAL POWER PLANT IN VIETNAM MAJOR: Environmental Engineering CODE: Experimental RESEARCH SUPERVISOR: Prof Dr TRAN HONG CON Prof Dr TAKASHI HIGUCHI Hanoi, 2019 Table of content Research Motivation and Literature Review…………………….……… 1 Introduction of Coal Power Development in Vietnam……………………9 Fly Ash Management Practice in Vietnam……………………………… 10 Characteristic of Arsenic in Fly Ash………………………………………14 Physical and Chemical Properties of Class C Fly Ash………………14 Physical and Chemical Properties of Class F Fly Ash………………15 3 Overview of Arsenic………………………………………………….16 Toxicity of inorganic Arsenic to human health and regulation in Vietnam………………………………………………………………16 Behavior of Arsenic in Fly Ash and its release potential……………18 Research Approach……………………………………………………… 23 Methodology and Apparatus………………………………………………26 Sampling and Collection………………………………………………… 26 1 Introduction of Pha Lai Thermal Power Plant…………………….26 2 Sampling Method………………………………………………… 28 2 Storage and Preservation………………………………………………… 32 Physical Characteristic of Fly Ash……………………………………… 33 Solid-Liquid Ratio (SLR) Examination………………………………… 33 Leaching Test under strong acid condition (pH = 1)…………………… 34 Leaching Test under strong alkali condition (pH = 10)………………… 36 Leaching test under acid rain condition………………………………… 37 Leaching test under seawater condition………………………………… 38 Sample Digestion………………………………………………………… 39 10 Quantitative Analysis…………………………………………………… 40 11 Method Validation……………………………………………………… 44 Result……………………………………………………………………… 45 Physical Properties of Fly Ash…………………………………………… 45 Calibration curve………………………………………………………… 46 3 Method Validation and Quality Control………………………………… 47 3 AAS Comparison………………………………………………… 49 3 Pack Test comparison………………………………………………51 3 Precision Test………………………………………………………54 Arsenic Distribution in surveyed area…………………………………….55 Distribution of rain season…………………………………………56 Distribution of dry season………………………………………….68 Arsenic Leaching Potential (ALP) in different condition……………… 64 Acid Condition (pH = 1)……………………………………………62 Alkali condition (pH = 10)………………………………………….63 Acid rain condition (pH = 4.20)…………………………………….64 Seawater condition (pH = 7.76)…………………………………….65 Discussion………………………………………………………………… 66 Method Validation and Quality Control………………………………… 66 Arsenic Distribution in surveyed area…………………………………….66 Arsenic Leaching Potential (ALP) in different condition……………… 68 Conclusion………………………………………………………………… 70 Limitation………………………………………………………………… 71 REFERENCE……………………………………………………….72 List of Table Table I.2.1: Estimation of coal demand/supply for Vietnam over different periods of time ……………………………………………………………………………………14 Table I.3.1 Comparison of typical Standard Values for Arsenic in regard to some environments …………………………………………………………………… … 19 Table II.1.1 will give information on detail technical design of Pha Lai Thermal Power Plant……………………………………………………………………………………27 Table II.1.2 Summary of sample types and season variation………………………….33 Table III.3.1 Specific samples used for each kind of validation/QC test…………… 49 Table III.3.2 Comparison of analytical results between HgBr2 Method and AAS Method……………………………………………………………………………… 50 Table III.3.3 Chi-square Test for Goodness of Fit between HgBr2 and AAS results….51 Table III.3.4 Comparison of results between Pack Test and HgBr2 Analysis…… …53 Table III.3.5 Precision Test Result for HgBr2 method…………………………… …55 Table III.4.1 Detail information of Arsenic content in soil sample (rain season)…… 57 Table III.4.2 Detail information of Arsenic concentration in water sample (rain season)…………………………………………………………………………… ….59 Table III.4.3 Detail information of Arsenic content in soil sample (dry season)…… 60 Table III.4.4 Detail information of Arsenic concentration in water sample (rain season).……………………………………………………………………………… 62 Table IV.2.1 Average monthly rainfall of Bai Chay monitoring station, Quang Ninh province, 2017…………………………………………………………………………67 List of Figure Figure I.2.1 Ash impoundment of Hai Phong Thermal Power Plant I & II, Thuy Nguyen District, Hai Phong.……………………………………………………………………12 Figure I.3.1 SAC Ternary Diagram of materials …………………………………… 16 Figure I.3.2 Main Technologies used in a typical Coal Power Plant and pathway of flue gas…………………………………………………………………………………… 22 Figure II.1.1 Sampling Map for both Rain Season and Dry Season……………… …31 Figure III.1.1 SEM image of Fly Ash at x500 magnification………………………….45 Figure III.1.2 Composition of Fly Ash……………………………………………….46 Figure III.2.1 Calibration curve for Mercury (II) Bromide method (Low concentration: 10-100ppb)…………………………………………………………………………….47 Figure III.2.2 Calibration curve for Mercury (II) Bromide method (High concentration: 100-1000ppb)………………………………………………………………………….48 Figure III.3.1 Histogram for frequency distribution of difference percentage between data sets……………………………………………………………………………… 53 Figure III.3.2 Correlation between HgBr2 and Pack Test results…………………… 54 Figure III.4.1 Distribution map of Arsenic in Pha Lai Thermal Power Plant area for rain season …………………………………………………………………………….57 Figure III.4.2 Distribution map of Arsenic in Pha Lai Thermal Power Plant area for dry season………………………………………………………………………………….60 Figure III.5.1 Arsenic Leaching Potential (ALP) for acid condition……………….…63 Figure III.5.2 Arsenic Leaching Potential (ALP) for alkali condition…………… …64 Figure III.5.3 Arsenic Leaching Potential (ALP) for acid rain condition…………… 65 Figure III.5.4 Arsenic Leaching Potential (ALP) for seawater condition………….…66 Abbreviation List F.A (or FA) Fly Ash ARP/ALP Arsenic Release/Leaching Potential H.M Heavy Metal TPP Thermal Power Plant WHO World Health Organization USEPA United States Environmental Protection Agency SEM Scanning Electron Microscope LOD Limit of Detection QC Quality Control Acknowledgement First and foremost, I would like to express my greatest appreciations to Prof Tran Hong Con, Hanoi University of Science and Prof Takashi Higuchi, Ritsumeikan University, my principal supervisors whose expertise, generosity and thorough guidance have enormously contributed to the completion of this thesis as well as my understanding of the topic that is of my great interest There is no such honor being comparable to working with them I would like to sincerely thank Prof Jun Nakajima, my special academic advisor at Vietnam-Japan University for spending his precious time in busy schedule to share advices and helpful support in the progress of implementing and writing this thesis Importantly, I would like to spend my most sincere gratitude to Prof Cao The Ha - Director of MEE program, Prof Hiroyuki Katayama, Prof Ikuro Kasuga, Dr Nguyen Thi An Hang and the entire MEE Department for valuable support during the implementation of thesis as well as my stay in VJU Thank you for everything we have experienced together I would also like to express my gratefulness to Ms Tran Dieu Linh, my fellow student in MEE and Mr Dao Trung Duc, MNT student for their kind and dedicate assistance in my study Without directive support and coordination from all Departments of VJU and specially Department of Academics and R&D as well as Japan International Cooperation Agency, this internship could not be completed in such successful and exhaustive manner Therefore I would like to humbly offer my thankfulness to the efforts of the University and JICA South West 4_1 15.16 67.1% South West 4_2 15.16 67.1% South West 5_1 28.55 126.3% 31.67 140.2% South West 5_2 67.1% 133.2% Table III.4.4 Detail information of Arsenic concentration in water sample (rain season) The A and B values are regulated in QCVN 40-2011/BTNMT for wastewater Note: N.D is non-detectable Arsenic Conc Arsenic Conc A value B value (µg/L) (mg/L) (mg/L) (mg/L) Ash Pond 31.12 0.03 Ash Pond 36.99 0.04 Ash Pond 51.66 0.05 Cau River N.D N.D Luc Nam River N.D N.D Cooling Stream 10.12 0.01 0.05 0.1 River N.D N.D River N.D N.D River 19.39 0.02 River 24.08 0.02 Sample Name On the contrary to rain season, the dry season experienced a different patterns of distribution Regarding water, all of water samples now possess much smaller concentration, denoted by green color, than in rain season Both river site and ash pond site share this common patterns Regarding soil-sediment, the Arsenic content has risen remarkably comparing to the basis of rain season None sample shows green indicator, because most of them 61 has already turns to purple (hazardous) Ash pond and North West + samples are in red color, denoting highly hazardous, especially North West 5, which possess Arsenic content up to 133.2% of Original Fly Ash Luc Nam river and Cau river are not the exception when their Arsenic content are 56.9% and 50.9% of Original F.A, respectively 3.5 Arsenic Leaching Potential (ALP) in different condition Leaching potential were measured by taking ratio of released concentration over absolute concentration of Arsenic in samples then apply grouping method to determine the ratio range where the majority of sample fall into This method provides the most intuitive approach to compare leachability of sample in different environment The condition has the highest range of majority will be regarded as most potential for leaching and reverse 3.5.1 Acid Condition (pH = 1) Figure III.5.1 Arsenic Leaching Potential (ALP) for acid condition After extraction, the concentration of leached Arsenic versus absolute content in soil-sediment samples are relatively high Around a half of the rain season samples 62 has ALP between 1:2 and 1:32, and one fifth belongs to the group of 1:2 to 1:8 The dry season shows a slightly better performance in leaching test with samples in near 1:1 region and most of the samples are above 1:32 ratio The exact ratio for samples under 1:32 region will be non-specifiable due to resolution limits of the graph In overall, it can be assessed the ALP of acid condition as very good for high ratio between released and absolute content Samples which possess 1:1 ratio release almost all of their As 3.5.2 Alkali condition (pH = 10) Figure III.5.2 Arsenic Leaching Potential (ALP) for alkali condition For rain season of alkali condition, there are only samples locating in 1:20 to 1:100 region and 10 more locating in 1:100 to 1:200 region which adding up to half of the population On the other hand, dry season sees much sharper increases of each individual with approximately 18 samples (equally 60% of population) ranges between 1:20 to 1:100 and up to 80% of the population stands between ratio of 1:20 to 1:200 However in either situation, no sample could break through the upper 63 bound of 1:20 Also, the exact ratio for samples under 1:200 region will be nonspecifiable due to resolution limits of the graph Based on the lower ALP for majority of sample, it can be assessed the leaching potential of alkali condition as not as good as acid condition 3.5.3 Acid rain condition (pH = 4.20) Figure III.5.3 Arsenic Leaching Potential (ALP) for acid rain condition The leaching test under acid rain condition (pH =4.20) observes similar patterns toward its counterpart, alkali condition Regarding rain season, samples are found in 1:20 to 1:50 region, in 1:50 to 1:100 and more in 1:100 to 1:200, which cumulatively build up more than 60% of the total population Similarly, dry season experience the same number of 17 samples ranging from ratio 1:20 to ratio 1:200 The exact ratio for samples under 1:200 region will be non-specifiable due to resolution limits of the graph 64 It can be inferred from the graph above that both rain and dry season samples might behave in the same pattern More importantly, from analogous ARP ratio range of 1:20 to 1:200, alkali condition and acid rain condition show little difference in extracting performance to each other 3.5.4 Seawater condition (pH = 7.76) Figure III.5.4 Arsenic Leaching Potential (ALP) for seawater condition Having regard to seawater condition, there are three ratio ranges are to examine: 1:25, 1:50 and 1:400 In both season, there are very limited number of samples having ratio near 1:25 or 1:50 region (5 in rain season + in dry season) The majority of population shows very low performance toward leaching test by staying under 1:400 region Among all condition, the ARP of seawater condition is the lowest 65 Discussion 4.1 Method Validation and Quality Control From accepted hypothesis that “there is no significant difference between two data sets of HgBr2 and AAS method” by Chi-square test for goodness of fit, plus good correlation/fitness between HgBr2 and Molybdenum Blue results, we can conclude that there is enough accuracy for Mercury(II) Bromide to be main analytical method for the study Empirically, with environmental sample analysis, the average relative standard deviation (RSD) of 9.37% for precision test is very good as some circumstances allow up to 300% Therefore, the precision goal is achieved Since both accuracy target and precision target are accomplished, the trueness of the method is considered as valid 4.2 Arsenic Distribution in surveyed area To begin with the seasonal pattern, according to the observation of both soil and water samples, the content of Arsenic in dry season soil is higher than in rain season soil This phenomenon can be explained by higher precipitation during rain season that impose several effects onto soil such as upper layer erosion, soil washout, or infiltration into ground Table IV.2.1 represents the average monthly rainfall rate of Quang Ninh province (in proximity to Hai Duong province; Hai Duong has no monitoring station) to support the above hypothesis Table IV.2.1 Average monthly rainfall of Bai Chay monitoring station, Quang Ninh province, 2017 (Source: General Statistics Office of Vietnam) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 171.1 351.7 623.1 646.0 264.1 384.4 14.5 21.6 Unit: mm 26.4 53.3 45.1 38.9 66 In six months of rain season, from May to October, the total rainfall amount is 2440.4mm while the total rainfall of six months of dry season, from November to April, is 199.8mm The gap of 10 times higher in precipitation can bring robust effect to soluble Arsenic in soil The easy-to-access Arsenic, when contacting with rain water for a certain amount of time will be dissolved then follow runoff water to nearby receptor bodies (pond, lake, river, channel), increasing the Arsenic concentration of such bodies (1); or infiltrate into ground and stay idle inside water table (2) The (1) hypothesis is supported by actual As concentration in water samples The higher concentration of As in rain season than follows above expected pathway In this case, the direct water source of community has been affected by this external source of Arsenic If local residents use this water directly for domestic purpose, the content of Arsenic might be dangerous in both short and long term as the concentration is far higher than safety standard The (2) scenarios has not yet been confirmed by scientific data due to time limitation of this study However, it is possible that the accumulation of Arsenic in ground water is even more toxic to human health than Arsenic in river Under anaerobic condition underground, As(V) tend to be reduced to As(III), which possess more toxicity The intake to this water source of local people by wellaccessing can get them exposed to more unwanted negative health effects Secondly, the As content in river water might also be influenced by rivers’ seasonal patterns The source of Arsenic might originate partly from upstream sources that need more exhaustive examination to confirm Thirdly, due to long time operation of Pha Lai Thermal Power Plant, since 1980, the soil condition has changed drastically, leading to being unable to acquire 67 original soil sample to establish baseline As level in the region However, with many sample containing abnormally high amount of As, e.g ≥ 50% of Original Fly Ash, we can conclude that the area surrounding Pha Lai Thermal Power Plant prone to be impacted by external source of Arsenic, in this case is fly ash Finally, to assess the effect of wind direction to the dispersion of fly ash, we must see if there is any gradient trend in soil samples of North West and South West Basically, the dispersion region is defined by flying radius when particle remains in atmosphere; and the settling area where particle lose kinetics and falls down The concentration in flying radius tend to be lower than in settling region and the outbound of dispersion region also tend to be lower than both flying radius and settling region From distribution map of either rain or dry season (Figure III.3.1 and III.3.2), the As content in soil increases over distance in South West samples, which peak at SW_4 and SW_5 From data, it seems that the flying radius of South West direction ranging below 1.0km distance from the power plant whereas the settling region locating around 1.0 - 1.2km There is a possibility that at distance beyond sampling points, the concentration of As might still increase Therefore, in the next studies, this information should be clarified again This type of trend in North West samples for dry season is not as sharply visible as South West, however for rain season they still follow a suggested trend The concentration of As in soil peaks at SW (1.0km from power plant), decreases over distance at SW 4,3,2 (1.2km, 1.4km, 1.8km from power plant, respectively) and drop to minimum at SW1 (2.0km) Conceivably, below 1.0km is dispersion region and above 1.0km in North West direction is outbound of dispersion 4.3 Arsenic Leaching Potential (ALP) in different condition Among all conditions, the acidic condition (pH = 1) expresses highest leaching potential With majority of ALP ranging from 1:1 to 1:32, the release of substance 68 is relatively easy with this pH Ranked 2nd are equally alkali condition (pH = 10) and acid rain (pH = 4.20) with most of ALPs ranging between 1:20 to 1:200 And the least leachable condition title belongs to seawater when its vast majority falls behind 1:400 ratio There are several possible explanations for this observation As already mentioned in literature review, the main mechanism for the variation of Arsenic concentration by pH are redox potential and adsorption Several studies carried out by Wang et al, 2008; 2009 and Azam et al, 2009 suggested that the good pH for desorption of As are below pH for dissolution of FA particles and above pH as As being replaced by OH- in Fe-binding site This explains the relatively good leaching result for alkali condition At extremely high or low pH such as (strong acid dissolution) or more than 11 (formation of more Ca(OH)2 leading to release more As from CaAs bonding), the desorption of As is robustly higher Also, because both soil and sediment collected (5-20cm depth) are in frequent contact with open air (oxidation), the dominant form or Arsenic is As(V), which prefer lower pH for dissolution These explain why at acidic condition, the ALP of Arsenic is remarkably good According to previous studies, the pH 3-7 might be weakest for extraction However as artificial acid rain in this study consists solely of NO3- and SO42- ions, it can bring about the dissolution of Fe-containing complex thus free As from bound The artificial seawater, on the other hand, is different Consisting of mostly neutral weak ions, the extracting capability of solution is no stronger than normal water From ALP results of ash pond samples, we can come up with the suggestion for behavior Arsenic in each fly ash scenarios As mentioned in the introduction, since Vietnam is currently using various sources of coal for electricity generation, it is infeasible for a particular power plant to use single type of coal but rather mixed source In case that there is more dominant proportion of class F Fly Ash, the ash 69 pond water tend to be more acidified, leading to more release of Arsenic during wet aging process In case that class C Fly Ash prevails, alkalization of water tends to take place and reduce the content of releasable As for a certain amount of time Yet in long term, atmospheric CO2 and acid rain will gradually have neutralization impact to this alkalinity To derive better solution that help tackle the consequences of Arsenic, each power plant should put more emphasis on coal type management and counteraction to deal with pH of water during wet impoundment Finally, to answer the question regarding “if some power plants near coastal area using seawater to keep the moisture of fly ash (avoid scattering by wind) can have some negative impact to local community or not”, the question is seawater itself has limited capability to desorb As from soil for short term However in long term, the acidification or alkalization, one way or another, will happen under idle wet impoundment which will have As behave differently from beginning Therefore, rather than let seawater stay idling in ash pond, the system that spray and circulate seawater to keep ash particle moist enough to adhere to each other but not long enough to be denatured to acid/alkaline solution should be recommended Conclusion The operation of thermal power plant in Vietnam has been raising more and more concerning in terms of Arsenic contamination From data collected, there seems to be a tight relationship between improper fly ash management, either in official storage area or in surrounding environment, and the abnormal content of Arsenic in local community of Pha Lai Although the leachability of this substance varies upon natural climate condition, geographical property (wind, river, soil), type of fly ash and even preventive technology, the current situation with human health is certainly at dangerous level In due course of many possibility, people will 70 gradually get exposed to this contamination that eventually leaves undesirable repercussion The different in Arsenic Leaching Potential of each solvent also suggest an approach for experts and researcher in this area to find novel solution for this problem Limitation This study carried out by student To Hoang Nguyen, MEE class intake cannot avoid limitations Due to time constraint, the full scale for sampling has still been at primary stage, leaving some hypothesis left unexamined Some parameters relating to geographical characteristic, proximity area of Pha Lai TPP, upstream sources of Arsenic in Luc Nam river and Cau river also need more survey Furthermore, the lack of specialized equipment to collect deep soil has led to being unable to obtain true original soil If the sample is available, more information of the natural As occurrence will be 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of combustion process, mostly by Coal- Power Plant. .. for installing facilities, especially ash retaining sector Some Power Plants even use seawater to maintain submersion of fly ash to avoid wind scattering It is usually reported that fly ash are