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

VIETNAM NATIONAL UNIVERSITY, HANOIVIETNAM JAPAN UNIVERSITYTO HOANG NGUYEN ARSENIC LEACHING POTENTIAL FROM FLY ASH OF COAL POWER PLANT IN VIETNAM MASTER'S THESIS Environmental Engineering

VIETNAM NATIONAL UNIVERSITY, HANOIVIETNAM 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, HANOIVIETNAM JAPAN UNIVERSITY

Prof Dr TRAN HONG CON Prof Dr TAKASHI HIGUCHI

1 3 5 Behavior of Arsenic in Fly Ash and its release

2 5 Leaching Test under strong acid condition (pH = 1)……… 34

2 6 Leaching Test under strong alkali condition (pH = 10)……… 36

1

2 7 Leaching test under acid rain condition……… 37

2 8 Leaching test under seawater

4 1 Method Validation and Quality Control……… 66

4 2 Arsenic Distribution in surveyed

3

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 2 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

Thermal Power PlantWorld Health OrganizationUnited States Environmental Protection AgencyScanning Electron Microscope

Limit of DetectionQuality Control

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.

1.Research Motivation and Literature Review

1.1 Introduction of Coal Power Development in Vietnam

After nearly four decades of effort and development, Vietnam’s economy has beenachieving new thriving milestones, especially 6.5-7.0% predicted GDP growthrate over the 2016-2020 period, which successfully puts the nation into dynamiceconomy and attractive investment group (VCCI & PwC, 2017) In order toincrease and sustain the domestic production, however, the country has requiredgigantic power consumption of high reliability but more importantly, of goodaffordability Among all types of high-capacity energy source such as nuclear,wind, solar, hydro, thermal; Thermal energy with focus on coal (from now onreferred as Coal Power) seemed to outweigh the rest due to three main reasons.Firstly, the conventional hydropower installed in Vietnam’s river network hasalmost reached its maximum potential due to exploitation since 1960s (VCBS,2016) Besides, the more complexity in multi-stakeholder governing of MekongRiver Basin and unpredictable water patterns of climate change has recently madehydropower less keen toward policy makers Secondly, Coal Power offers cheaperinitial investment and maintenance if removing environmental cost and thus bringmore reasonable price for the majority of people in short term Thirdly, in vision

to 2030/2050, Vietnam will prioritize the development of renewable energy togradually replace other kinds of conventional power, but in the meantime toguarantee energy security, Coal Power will still be on its watch (GeneralDirectorate of Energy, 2017)

According to the Power Development Plan VII, until 2020, the total general capacityoff all power sources is expected to reach 60,000MW, in which 21,600MW belongs

to Hydro Power (36%) and 26,000 MW belongs to Coal Power (43.3%) This energytrend will abruptly be adjusted in the manner which double the capacity of coalpower into 47,600 MW of total 96,500 MW (49.3%) while hydropower proportionreduce to 23% in 2025 By 2030, to meet up with high

energy demand of 129,500MW, all power sources must enhance their productionleading to the soar of Coal Power into 55,300MW (Approval of the RevisedNational Power Development Master Plan for the 2011-2020 Period with theVision to 2030; General Directorate of Energy, 2017).

Higher power must accompany with higher responsibility in terms of economic as well as environment Yet this is when two edges of the blade appear

social-On one hand, the coal power ensure a stable input with reasonable cost fordomestic production without too much investment to renewable energy at a time

On the other hand, latent pressure of coal-combustion-derived pollutions withvibrant precursors is becoming a real threat for sustainability of Vietnam Amongthem, hazardous effects to surrounding ecosystem of heavy metals in fly ashunder open, inadequate storage and management are drawing substantial attentionfrom Vietnamese researcher Under the range of this Master’s Thesis, aninsightful study toward leaching potential and distribution of Arsenic from fly ash

of thermal power plant will be provided The first half of part 1: Introduction

will help shed light on the practical situation, urgent necessity in Vietnam that led to the conduct of this study.

1.2 Fly Ash Management Practice in Vietnam

For many years using Coal-fired Power Plants effectively, although not beingaudited carefully, the estimated amount of fly ash (coal-derived combustion by-product in solid form) accumulated has reached approximately 30 million tons,yet in which less than 4 million have been treated The majority of fly ash fromThermal Power Plant is being stored at open areas surrounding each plant.Nonetheless, under open condition, the light-weight, particulate properties of flyash make it extremely prone to dispersing, causing air pollution to thesurrounding environment To mitigate the effect, fly ash is usually transported towater bodies of proximity named “ash pond” to store This method is referred aswet disposal or wet impoundment (B Stapp, 2015)

(1) Most ash pond are relatively large with the purpose of long-timeholding fly ash inside, making most of them impossible to have protective bottomlayer and ,therefore, pond water containing high content of Heavy Metals tend toleak to nearby regions, causing damage to both people’s health and reduce

economic values (Vietnamnet, 2016)

(2) The input water sometimes has inconsistent quality and source, eg.Sea water, normal rain, acid rain, fresh water, etc., causing it more difficult tocontrol the behavior of heavy metals during aging process

(3) The different types of coal ash product also have different behaviors during wet impoundment, which will be discussed in the next chapter

Figure I.2.1 Ash impoundment of Hai Phong Thermal Power Plant I & II,

Thuy Nguyen District, Hai Phong (Source: Google Earth)

Many countries who used to use coal power in the past has been struggling with thisissues for decades and eventually come up with new solutions to avoid wet disposal.The most leading country to refer in this realm is Japan According to Sato andFujikawa in 2015 and reports from the Japan Coal Energy Center (JCOAL), there arevarious solution derived to suppress the controversial impacts of coal ash or wasteincineration ash The most important initiative is to reuse them

as materials for other building purposes Secondly, the country is approachingtoward coal gasification, which produce syngas (Carbon monoxide + Hydrogen +Carbon Dioxide + Methane) to apply for higher efficiency combustion process.Furthermore, more improvements for flue gas treatment were carried out withmore strict regulations to ensure the quality of living environment as Japan hasrecently been in a serious power reform after the earthquake at Fukushimanuclear power in 2011.

In another so-called developed country of the region such as India, a lot ofemphasis has been put into materializing of fly ash Based on types of coal andcontent of lime (CaO), fly ash can be classified into two main types: C (>20%CaO), and F (< 10% CaO) Class C fly ash with self-cementing property is usedmore widely with construction purposes: Fly Ash-Based Cement, Brick,Embankment, Concrete or Ceramics (Dwivedi and Kumar Jain, 2014; Senapati,2011) With lower lime content, Class F fly ash need activator additives likePortland Cement or quicklime to start cementing or can be mixed with SodiumSilicate to form geopolymer (Dwivedi and Kumar Jain, 2014) Additionally, somestudies shows that fly ash can be used for agriculture to improve permeability,fertility, texture of soil, stabilize some HMs and optimize pH value (Kumpiene,Lagerkvist and Maurice, 2007; Alam and Akhtar, 2011)

The above pathways all lead to a bright end for thermal power that inflict littleharms to ambient air and minimize the volume of fly ash disposed in developedcountries But for now, the lack of technology and economic potential is holdingVietnam back though all limitation has been realized Hopefully, with morescientific paper plus practice in environmental pollution, Vietnam’s policy makerwill have a different look into the situation

Beside of technological factor, the second main reason is due to coal type variationleading to inconsistence of fly ash quality With mentioned demand for energyproduction in the next few decades, Vietnam is predicted to face serious needs for

coal to supply the entire system Table I.2.1 will depict the coal demand in severalperiods.

Table I.2.1: Estimation of coal demand/supply for Vietnam over different periods

of time (Source: Vietnam’s Power Development Plan, Ministry of Industry and Trade, 2017)

Demand

Domestic Supply

Import Coal (5,500 Kcal.kg)

Import for Coal-fired Power Plant

From the table, it can be easily seen that by 2030 the annual consumption of coalwill triple at 156.6 million tons, comparing to 2017’s data However, as Vietnam’snatural reserve for coal has been drained out and most of coal sources will beprovided from other countries In 2030, the domestic capacity is expected to meetaround 30% of total needs, and Coal-operated thermal power will utilize more than80% of imported amount Hence, it will be even more challenging in the future toidentify exact type of fly ash to apply appropriate treatment technology

To finalize, it can be concluded from the situation that:

(1) The higher the coal consumption will be, the more fly ash will be created;leading to much more serious environmental burden, especially if simple wetdisposal method continues

(2) The inconsistent of coal quality and originality will make it more challengingfor treatment of fly ash Hence, in the meantime of developing new technology,

wet disposal will still be regarded as a temporary solution This process might take years to eliminate all fly ash accumulated.

(3) Therefore, to obtain good understanding on the influences of fly ash aging inwet impoundment, research for availability/release potential of hazards from flyash is urgent

(4) The most toxic component of fly ash in storage are Heavy Metals, includingArsenic This Master’s Thesis put emphasis on the Arsenic Leaching Potential(ALP) in various conditions and arsenic distribution in surrounding areas as abaseline study for assessing hazard level imposed by fly ash

1.3 Characteristic of Arsenic in Fly Ash

Fly Ash is the fine-particle particle byproduct of combustion process, mostly byCoal-Power Plant or Biomass Power Plant aiming to generate power and WasteIncineration Plant This study only concentrates to Coal Fly Ash, which is ofgreatest concerning for Vietnam at the moment Based on physical properties andoriginality, Fly Ash can be divided into two main groups: Class C and Class F.The following parts will describe more of their characteristic and explain whythey are important information

1.3.1 Physical and Chemical Properties of Class C Fly Ash

Basically, there are 4 major types of coal often utilized in combustion process:Anthracite, Bituminous, Sub-bituminous and Lignite Anthracite is regarded as thehighest rank of coal which contains approximately 95% of carbon, making it hardand shining black color and lower volatile content Bituminous is soft coal,containing higher moisture content (up to 20%) and volatile content (up to 40%).Sub-bituminous is also soft black coal, less superior than the other above, but can befound more common in thermal power Lignite, as being ranked lowest in value,contain highest moisture proportion and lowest heat value Class F Coal is group

name for Anthracite and Bituminous coal while Class C composes of

Sub-bituminous and Lignite coal

Therefore, in terms of originality, Class C Fly Ash is the combustion byproduct ofClass C Coal

In terms of major composition, class C and Class F difference can be defined using SiO2-Al2O3-CaO Diagram (SAC-Ternary Diagram) as in Figure I.3.1

Figure I.3.1 SAC Ternary

60%-in wet impoundment (Catalano et al., 2012), which is very important for choos60%-ingappropriate leaching method of this study Other than major components, othermetals and Heavy Metals such as Fe, Ni, Mg, Cr, Pb, As, Se, Cd, Cu, Zn also present

in fly ash as a result of co-mineralization in coal deposit (Catalano et al., 2012;Deonarine et al., 2016) However, the occurrence of these HMs does not depend ontype of fly ash but rather their deposit location and other variables

1.3.2 Physical and Chemical Properties of Class F Fly Ash

The most significant difference between class C and class F Fly Ash lying in theirCaO proportion (Guo and Shi, 2013; Bankowski, Zou and Hodges, 2004) Bycombusting class F coal: Anthracite and Bituminous, class F Fly Ash is obtained.Specifically, there are around 80% SiO2, 18-40% Al2O3, and 2-18% CaO in class

F This difference makes it harder for class F ash to self-solidify under normalcondition and need supplementary additive like pozzolan cement to makeconcrete Additionally and more importantly, in reverse with class C fly ash, class

F produce more acidic condition during aging process based on its low limecontent (Catalano et al., 2012; Deonarine et al., 2016) This will greatly affect therelease potential as well as behavior of many substances inside the matrix, inwhich most significantly to this study, Arsenic

1.3.3 Overview of Arsenic

Arsenic (As) is the 33th element of periodic table with atomic weight of 74.92.Arsenic is a metalloid, usually occur in nature under mineral forms (in whichmostly of sulfur and other metals) Arsenic is abundant in Earth’s crust (ranked

53th), making it ubiquitously available in many country, especially South EastAsia and can be found in both soil and water environment Beside naturaloccurrence, Arsenic is used directly in agricultural products (pesticide, herbicide,insecticide), wood preservatives, batteries, pigment production, ammunition andpresent indirectly in coal ash from Thermal Power Plants

There are two main form of Arsenic: organic and inorganic Organic arsenichappens through bioaccumulation when organism consume food with highercontent of Arsenic Organic Arsenic is regarded as less toxic than its counterpart,inorganic Arsenic

1.3.4 Toxicity of inorganic Arsenic to human health and regulation in Vietnam

According to World Health Organization (WHO), inorganic Arsenic is considered

as highly toxic Major diseases relating to arsenic poisoning (Arsenicosis)includes acute immediate symptoms, skin, bladder and lung cancer

In short term, the direct exposure to high concentration of Arsenic might causenausea, vomiting, abdominal contraction and diarrhea if non-lethal dose isabsorbed When lethal enough, Arsenic poisoning can make victim feel extremetingling, numbness and finally death (WHO, 2018) In many countries, Arsenichas been used as one of the quickest poison for centuries and the small amount ashalf of a pea size can instantly cause mortality to a person

In long term, it has been reported that the contact with Arsenic-contaminatedwater of more than 50 mg/L (50 ppm) for a long duration will increase 1% ofcancer in population (National Research Council (US) Subcommittee on Arsenic

in Drinking Water, 1999) The most common cancer type is skin cancer,nonetheless lung cancer and bladder cancer are also found related to the situation

In fact, the death by Arsenic poisoning is not unexpected Patients will sufferfrom skin lesion, “Black Foot Disease”, hyperkeratosis, heart attacks and kidneyfailure for a long period of time before the death penalty (WHO, 2018) Theseprecursors are not only painful but also affect greatly to the victims’ livelihood.Arsenic exists in two oxidation states, Arsenic trivalent: As(III) and pentavalentAs(V) It is also widely known that As(III) is 60 times more toxic than As(V)(Ratnaike, 2003)

In our body, Arsenic can deactivate several hundreds of vital enzymes, disruptingparticularly to which coordinate DNA replication, DNA repair and cellular energypathway ATP, the most vital energy holding compound, will be destroyed bysubstituting Phosphorous by Arsenic (Ratnaike, 2003) DNA damage, lipidperoxidation and reactive oxygen production that harm organs’ function are by-products of Arsenic reduction-oxidation process and metabolic activation process(Cobo and Castiñeira, 1997)

Acknowledging the deleterious consequences of Arsenic contamination and theessential of prevention, WHO, U.S EPA and many countries has establishedsafety limits for Arsenic uptake as well as Arsenic concentration in soil and waterenvironments Table I.3.1 shows some typical standard values for Arsenic withcomparisons to Vietnam.

Table I.3.1 Comparison of typical Standard Values for Arsenic in some

environments (Soil, Hazardous Waste, Surface water, Ground water, Drinkingwater)

Arsenic in Soil

Arsenic in Hazardous Waste

Arsenic in Surface Water

Arsenic in Ground Water

Arsenic in Drinking Water

1.3.5 Behavior of Arsenic in Fly Ash and its release potential

Because of Arsenic’s extreme toxicity, it is necessary for any country to evaluate thepresence of this substance in any industrial activities that prone to increase the totalamount of Arsenic in the region Vietnam in its own direction to expand Coal Powerscale is not an exception Though total Arsenic (T-As) is an important target

of examination, it will be inconsiderate if its mobility or release potential (alsocalled leaching potential) is taken lightly (Azam et al., 2008).

To have a good insight toward FA’s Arsenic characteristic and behavior, it issignificant to know the chemical transformation during combustion process of coal.Under high temperature in boiler, most substances existing in coal undergo thermaldenaturing: volatilization of VOC, molecular breakdown (disintegration), re-fusion

to form new compounds (Pandey et al, 2011) Coal pulverized to maximize heatconversion breakdowns into much finer, spherical FA particles and act as a coolersurface for condensing volatile inorganic compounds (Pandey et al, 2011) Manymetal elements obey gradation theory and be divided into several groups Someexperience little concentration increase with decreased particle size (“Litho” Group);some, including “Pb, As, Se, Cd, Sb”, increase their concentration with decreasedparticle size (“Chalco” Group) while some shows milder manners between twogroups (Davison et al., 1974; Klein et al., 1975) The enrichment of these newcompounds takes place in spherical outer layer and speedily extractable from 5%-40% in water (Linton et al., 1976) Hence, since 1980, USEPA in their publication

“Ambient water quality criteria for arsenic” has observed considerable concentration

of soluble salts, toxic compounds and Arsenic in Fly Ash

As mentioned, Arsenic is mostly abundant in co-existence of Iron and Sulfur,which possess mineral form of Pyrite (FeS2) Jacob et al in 1970 conceived animproved rate of arsenic adsorption in presence of iron or aluminum oxide,especially Arsenate (As-V) Furthermore, the capture ability of iron can even beenhance with support of Calcium, forming [Ca2.Fe3(AsO4)3.(OH)4.10H2O]complex (Pandey et al, 2011) Fortunately, this can be perceived as an advantage

as lime (CaO/Ca(OH)2) is frequently added during operation of power plant to act

as principal desulfurizer Goodarzi, 2006 and Zielinski et al, 2007 have proved theCa-capturing theory when highest amount of trace elements were found in bagfilter, in which more forms were found

There are two dominant fates in which Thermal Power Plant’s proximities become exposed with Heavy Metals in Fly Ash in general and Arsenic in specific:

(1)Particulate Matter transport through dispersion and sedimentation; and(2)leaching in soluble form from fly ash impoundment (Pandey et al., 2011; Catalano et al., 2012; Deonarine et al., 2016; Azam et al., 2008)

(1) Particulate Matter transport through dispersion and sedimentation: to understand the principle of this pathway, the emission and

pollution control mechanism of Coal Power Plant should be explained first.Figure I.3.2 demonstrates the operating process of a typical power plant.Starting from input material, coal will be delivered by conveyor tocombustion chamber Theoretically, the heat conversion from burning coal iscalculable precisely, however in practice the actual efficiency is even lowerand be dependent on the version of combustion technology as well asmaintenance status The incomplete burning of coal will result in fly ash withmore carbon content and might have different behavior with ideal fly ash.However since researching every aspect will be resource-consuming, thismaster thesis will assume fly ash as completely burnt

After going through combustion chamber and heat conversion process, the fluegas containing emission gases and fly ash is directed to filter system when single

or multiple technologies applied For particulate phase, the most popular systemscan be listed as Gravitational settle/Cyclone which take advantage of kinetic loss

in collision with chamber’s wall to settle coarse particle; Bag

Filter/Membrane Filter for finer particle that escaped cyclone; Liquid treatmentusing water to adsorb/absorb dust; and Electrostatic Precipitator (ESP) in whichparticulate matters will be electrostatically charged and collected For gas phase,the most harmful gas/greenhouse gas is SO2, therefore the Flue GasDesulfurization chamber, using lime (CaO/Ca(OH)2) to capture SO2 effectively

Figure I.3.2 Main Technologies used in a typical Coal Power Plant and pathway

of flue gas (Source: Liberty Hygiene, www.libertyhygiene.com)

Although these technologies plays an important role in mitigating the effect of

serious pollution and is competent to achieve dust removal yield from 95% to

99.5% (Meikap, 2004), the amount of fly ash escaped through stack and entering

atmosphere are still relatively large, especially with local communities

surrounding Thermal Power Plants According to data, it is estimated that a

500MW plant can produce up to 500 tons of fly ash per day Thus a common

1200MW Power complex in Vietnam, in both scenarios, can produce:

If 95% removal yield achieved

1200

Some part of P.M can travel very far distance but many, depending on wind,

particle size and moisture, stay closely to the power plant The amount of free

fly ash can varies with technological improvement but in either situation, the

pressure to environment and public health is of great question Acid rain andother weathering condition might be a factor to increase the release of solubleArsenic Rain washout, surface runoff and infiltration can transport thesepotential contamination to water bodies that used by communities for domesticuse (Pandey et al, 2011).

(2) Arsenic leaching from wet impoundment: for decades, researcher has tried to evaluate the mobility and toxicity of Arsenic in various leaching

condition, both in-lab and in-situ since they are key factors of Arsenicbehavior and As-containing water are most likely to be consumed by humanand related living organisms Yet, the leaching manner has so far not clearlyexplained (Pandey et al, 2011) Several theories of interaction wereintroduced, in which pH, reduction-oxidation state, ionic strength of solutionmeet high consensus for their importance (Kirby and Rimstidt, 1994; Azam etal., 2008; Catalano et al., 2012; Deonarine et al., 2016)

Arsenic Release Potential (ARP) or Arsenic leaching potential (ALP),however, receives most attention from pH approach as it can interpret some,but not to all extent, mechanisms Based on classification of coal, fly ash isalso divided into class C and class F There is a strong belief among scientiststhat class C fly ash during aging process produce alkaline environment due tohigher Ca content, though gradually get neutralized by CO2 intake from theatmosphere (Catalano et al, 2012; Deonarine et al., 2016) On the other hand,class F with much lower level of Ca, have tendency to produce acidicenvironment in contact with water (Catalano et al, 2012; Deonarine et al.,2016) Wide range of studies also suggested that the pH range for minimumrelease is pH 3-7 and pH ranges for increasing ARP are pH < 3 and pH 7-11(Wang et al., 2009; Pandey et al., 2011; Izquierdo and Querol, 2012; Bednar etal., 2010) In his study, Wang et al, 2009 also indicated that Bituminous coal(Class F) leached relatively more than Sub-bituminous coal (Class C)

The difference in ARP by pH can be explained by two major mechanisms:adsorption/desorption to iron oxide and Calcium precipitation The sharprising of arsenic concentration in low pH leaching test is possibly attributed

by non-adsorbable As from neutral region and FA particle dissolution itself instrong acidic condition (Wang et al., 2008; Wang et al., 2009) In contrast, thehypothesis for the increasement of ARP in alkaline condition might beprotonated surface annihilation in high pH, leading to loss binding site for As-anions thus making them more available (Wang et al., 2008; Wang et al.,2009) Nonetheless, when pH reach 9 or more, formation of AsO4 3-

commence Since this form of Arsenic is most preferred by free Ca for precipitation, the ARP now exhibits decrease comparing to acidic condition.The higher the pH becomes, the more insoluble calcium arsenate gains andthe less Arsenic is released to leachate (Wang et al., 2009) Yet if pH canbreakthrough extreme alkaline value ( pH ≥ 11), Ca will prioritize hydroxideion to precipitate in form of Ca(OH)2, weakening Ca-As bond and enablingmore Arsenic to be released (Wang et al., 2009)

co-1.4 Research Approach

Most of the mentioned studies are able to distinguish the originality of coal(lignite, sub-bituminous, bituminous, anthracite) and types of FA they arefocusing (class F, class C), but so far most of research in Vietnam have encounter

a serious problem of mixing coal from various sources in each Thermal PowerPlant, caused by the shortage in domestic supply and leading to uncertainty in flyash type The accurate mixing ration between class C and class F coals remainunknown in reality, therefore it is even more challenging for researcher to predictthe behavior of Arsenic during wet aging The As toxicity to local communitiesand release potential from then are different to previous studies and need a newapproach to evaluate these parameter again

Therefore, this study aims to re-assess the release potential of Arsenic in Fly Ashfollowing practice in Vietnam; also evaluate the toxicity of this substance from

power plant, ash storage site to local community by determining total-arsenic, leaching potential as well as its distribution in both soil and water samples.

The research approach can be separated into 3 main phases:

❖ Pre-phase (From May - July, 2018): Proceeded meeting with supervisors: Prof Tran Hong Con, Hanoi University of Science (HUS);

Prof Takashi Higuchi, Ritsumeikan University Collected information ofthe topic and related documents from professors

❖ Phase 1: Preliminary Examination (From July - September,

2018):

o Establish detail research procedure, including time and budget management

o Research scope, site selection and methodology selection

o Sample Collection for Rain Season (August) and Dry Season (December)

❖ Phase 2: Sample Analysis (September 2018 – March 2019):

o Total As content in samples to provide baseline for evaluation

o Quality Control + Method Validation

o Acid condition (pH =1) Leaching Test (rain + dry season)

o Alkaline condition (pH = 10.08) Leaching Test (rain + dry season)

o Acid rain condition (pH = 4.20) Leaching Test (rain + dry season)

o Seawater condition (pH = 7.76) Leaching Test (rain + dry season)

o Distribution of toxicity

❖ Phase 3: Data Treatment + Interpretation (April 2019)

❖ End-Phase: Writing (April – May 2019) + Defense (June 2019)

24

2 Methodology and Apparatus

2.1 Sampling and Collection

2.1.1 Introduction of Pha Lai Thermal Power Plant

Pha Lai Thermal Power Plant (PLTPP) is one of the oldest coal power facility inVietnam It was originally designed with USSR’s combustion technology andwent into operation in 1980 as one of the symbols for friendship between twonations The initial capacity was only 440 MW, powered by 4 turbines (110 MWeach) During 1980s-1990s, such capacity contributed in greatest amount to theelectricity grid of Northern Vietnam and only became second when Hoa BinhHydropower Plant (1,920 MW) was installed in 1994 In late 1990s, the position

of Pha Lai Thermal Power Plant was recovered with new expansion of two moremodern turbines, 300 MW each, raising total electric capacity to 1040 MW in

2001 However, as new standards for coal Power are frequently promulgated,both in terms of technical improvement and environmental well-beings, Pha LaiPower Plant has been regarded as one of the most backward station in the North

of Vietnam Yet this facility is also one of the most representative examples formany similar Power Plants that has been serving for long period of time andbeyond The accumulated fly ash produced by these stations also holds a verylarge proportion in total national fly ash reserve Therefore, PLTPP has all virtue

to be chosen as target of this study

Table II.1.1 gives information on detail technical design of Pha Lai Thermal

Power Plant

TECHNICAL DESIGN

Capacity

Total Electricity Generation

Power for Self-operation

Dust Removal Efficiency

Steel pipe:

ɸ = 4.5m

With regard to geographical characteristic, Pha Lai Thermal Power Plant (both1&2) is located in Pha Lai Ward, Chi Linh City, Hai Duong Province (65km fromHanoi) The area is lying at the crossroad of 3 rivers: Cau River (flowing in fromNorth West), Luc Nam River (flowing in from North-East) and Duong River(going nearby, from West to South) The population of Pha Lai ward is 21.309people (updates in 2010) spreading in the area of 13.825 km2 There are two mainwind directions: North East and North West The open terrain plus wind comingfrom both directions help disperse flue gas from Plant’s stack to surrounding arearobustly Pha Lai Thermal Power Plant possesses several ash ponds scatteringaround community areas The biggest impoundment is located up in a mountain3.2 km from the Plant, while some smaller storage site are placed in the North,near Luc Nam tributary where fly ash and coal slag can be transferredconveniently in pipeline As the area is surrounded by rivers, it can be suggestedthat groundwater table remains relatively adequate and therefore, the leachingactivities are more likely to impose effects to the adjacent community

2.1.2 Sampling Method

Based on weather patterns, our group conducted 2 sampling periods in Rain Season(16-17th August 2018) and Dry Season (13-14th January 2019) For each point, wecollected the same amount of sample in both sampling trip The accurate coordinatesare logged with GPSMAP® 78, Garmin (visit Annex for more detail)

Equipment for sampling trip includes: PET Bottles (sufficient for water sampling),connection cord (x1), bucket (x1), parafilm (sufficient), clinging film (sufficient),shovel (x1), plastic zip bag (sufficient), filter paper with pore size = 8 µm (ɸ =

125mm, Whatman), plastic funnel (x3) All equipment were provided by

VJU-MEE laboratory, Environmental Chemistry Laboratory, HUS and personal funding

Figure II.1.1 Sampling Map for both Rain Season and Dry Season (Source: All copyright of original capture

belongs to Google Map; edited and labeled by To Hoang Nguyen)

The overall strategy could be divided into 4 separate tasks:

• Task 1: River Sampling

➢ Survey area, select sampling points following water streams (approx 200m in distance)

➢ There are 2 complementary samples that were notcollected in Rain Season trip: Cau River and Luc Nam River Thesesamples were taken only in Dry Season trip

• Task 2: South West Soil Sampling

➢ Survey area, select sampling points based on thepredicted path of wind dispersion: North East → South West(approx 200m – 250m in distance)

➢ Soil samples were taken by removing 10cm of top soil, then taking 1-2kg of soil into zip bag, sealed

➢ South West (SW) samples are denoted from No.8 -No.17

in map

• Task 3: North West Soil Sampling

➢ Similar to Task 2 in terms of Procedure

➢ North West (NW) samples were taken in the river bank ofopposite site to PLTPP, therefore there will be no connection withground water of Pha Lai area The major factor contributing to

31

➢ North West samples are denoted from No.18 – No.22 in map.

• Task 4: Ash Pond Sampling

➢ Ash Pond sediment samples were collected in the same manner with soil sample

➢ Ash Pond samples were collected in 3 different areas toensure the representative for the whole area However some sectors,which were too far with no transport available, could not beexamined

➢ Fly Ash samples are denoted from No.5 to No.7 in map

Table II.1.2 Summary of sample types and season variation.

2.2 Storage and Preservation

All soil and sediment samples after being taken from ground were enclosedimmediately in plastic zip bag Raw water samples were collected and filtered

32