稼働中の準好気性廃棄物処分場における上昇温度とガス成分に関する研究
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公開日: 2020-12-15
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https://doi.org/10.15118/00010332

STUDY ON ELEVATED TEMPERATURE AND GASCOMPONENT WITHIN AN OPERATING SEMIAEROBIC LANDFILL
By
Vu Quang Huy

Submitted to
Muroran Institute of Technology
Department of Civil Engineering and Architecture

In partial fulfilment of the requirements for the Degree of Doctor of Philosophy

Supervisor: Professor Yukihiro Kohata

Hokkaido, Japan
2020

STATEMENT OF AUTHENTICITY

I hereby certify that all of the work described within this thesis is the original work of
the author. Any published (or unpublished) ideas and/or techniques from the work of others are
fully acknowledged in accordance with the standard referencing practices.
Name: Vu Quang Huy
Date: August 2020

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ABSTRACTIn this study, the performance of an operating semi-aerobic landfill in the northern part of Japan
has been investigated. Observation and data analysis have been conducted simultaneously
aiming to evaluate the performance of the operating semi-aerobic landfill based on the landfillgas (LFG) temperature and LFG concentration. This study is summarized as follows.
1. A series of surveys has been carried out on-site to collect the temperature distribution
and gas concentration data of LFG venting pipes (VPs) in about 10 years (including 9
main LFGVPs, 39 branch LFGVPs, and 5 monitoring LFGVPs). The observation results
showed that the average temperature at the exit of surveyed main LFGVPs, branch
LFGVPs, and monitoring LFGVPs are >25oC, 20oC, and 20oC, respectively. Especially,
the highest LFG temperature was above 60oC within the main LFGVP M2. Methanegas (CH4) concentration of most of the main LFGVPs was below 10%, while others
were above 10%. The distributions of LFG concentration and temperature showed thebiodegradation by aerobic or anaerobic. For about 10 years those distributions changed
largely by the aerobic or anaerobic biodegradation. Especially clogging resulted in theincrease of CH4. If the ratio of CH4 to CO2 is below 1, aerobic biodegradation is active.
This ratio in all LFGVPs was below 1.0 and was below 0.5 in main LFGVPs. So thissemi-aerobic landfill has been operated appropriately.
2. The temperature of geomembrane liner at the bottom of the semi-aerobic landfill wasmonitored continuously from 2002 to 2017. The geomembrane temperatures graduallyrose up 30-35oC and remained over 30oC for 10 years (2006-2016) before dropping
down less than 30oC in 2017. The temperature rise was due to the biodegradation oforganic solid waste or the heat of hydration of incinerated bottom ash which is the main
factors caused the generation of heat in the landfill. Recently, the geomembrane
temperatures are gradually decreasing year by year because less landfilling organic
wastes for biodegradation results in a small amount of heat generation. The risk of ahigh-temperature effect on barrier systems may decrease.
3. The numerical simulation has been used for modeling the movement of gas flow withina semi-aerobic landfill. In addition, the influence of clogging phenomena on the gas
flow has been also considered by using the numerical simulations.
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ACKNOWLEDGEMENTSFirst and most importantly, I would like to thank Prof. Yukihiro Kohata and Assoc. Prof.
Yoshida Hideki, my supervisors, for their continuous support, guidance, creativity andunlimited patience during my study period at Muroran Institute of Technology (MIT). I havelearned a great deal from them. I also extend thanks to Prof. Kimura Katsutoshi and Prof.
Nagatsukawa Makoto for serving as members of my Ph.D committee. Their helpful comments
and wonderful recommendations have improved my work.
Special thanks are also given to all members of International Relations Center of MIT
for their support on my living conditions.
Lastly, I would like to thank all of my family and friends for their support,
encouragement, patience and love, without which, this would not have been possible.

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TABLE OF CONTENTSStatement of Authenticity............................................................................................................ i
Abstract ..................................................................................................................................... iii
Acknowledgements .................................................................................................................... v
Table of Contents ..................................................................................................................... vii
CHAPTER 1: Introduction ......................................................................................................... 1
1.1 Background ................................................................................................................... 1
1.2 Research Objectives ...................................................................................................... 2
1.3 Organization of the Dissertation ................................................................................... 2
CHAPTER 2: Literature Review................................................................................................ 5
2.1 Introduction ................................................................................................................... 5
2.2 Biological Degradation Processes in MSW Landfill .................................................. 10
2.2.1. Landfill Gas (LFG) Generation........................................................................ 11
2.2.2. Heat Generation ............................................................................................... 13
CHAPTER 3: Methodology ..................................................................................................... 17
3.1 Introduction ................................................................................................................. 17
3.2 Description of the landfill ........................................................................................... 17
3.2.1. Gas venting pipes ............................................................................................. 18
3.2.2. Leachate Collection Pipes (LCPs) ................................................................... 23
3.2.3. Leachate Pond .................................................................................................. 24
3.2.4. Barrier Systems ................................................................................................ 25
3.3 Survey methods ........................................................................................................... 27
3.3.1. LFG temperature and LFG concentration ........................................................ 27
3.3.2. Geomembrane temperature .............................................................................. 30
3.4 Numerical simulation .................................................................................................. 32
3.4.1. Basic goal of the simulation ............................................................................. 32
3.4.2. Various properties needed for the simulation .................................................. 32
3.4.3. Governing equations and geometry ................................................................. 33
3.4.4. Input parameters ............................................................................................... 38
CHAPTER 4: Results and Discussion ..................................................................................... 41
4.1 Observation results ...................................................................................................... 41
4.1.1. Spatial distribution of LFG .............................................................................. 41
4.1.2. Influence of the type of gas VPs on LFG concentration and temperature ....... 42
4.1.3. The main gas VP M2 ....................................................................................... 42
4.1.4. The branch gas VP B10 ................................................................................... 46
4.1.5. The average values of the gas temperature, CH4 concentration and the ratio of
CH4/CO2 ..................................................................................................................... 48vii

4.1.6. Long-term temperature monitoring of geomembrane liner ............................. 51
4.2 Simulation results ........................................................................................................ 58
CHAPTER 5: Conclusion ........................................................................................................ 65viii

CHAPTER 1: INTRODUCTION

Today, landfill sites still play an important role in solid waste management (SWM)
system in all over the world. However, landfilling is facing some serious problems such as
shortage of land, the need for long-term maintenance for stabilization and environmental
pollution from its emissions (leachate, landfill gases…). The necessity of surveying thephenomena happening within a landfill is critical to give solutions dealing with its negative
impacts on our environment.
1.1 BackgroundIn recent years, landfill aeration has been considered to be one of the most important
options for the concept of sustainable landfill. The conventional landfills are considered to beunsustainable. Landfill aeration is considered to be an indispensable tool for the controlled andsustainable conversion of conventional anaerobic landfills into a biological stabilized state.
The main benefits of landfill aeration are to reduce methane gas accumulation whichcauses the greenhouse effects, improve the leachate quality, accelerate biological stabilizationof the organic fraction of waste, and decrease the period of time after closure.
Landfill aeration is mainly used in old landfills to convert conventional anaerobic
landfills into biological stabilized state. However, landfill aeration is not widely applied so far,it has already been successfully applied to several landfills in Europe, North America and Asia
(M. Ritzkowski, 2012). Landfill aeration concepts include high pressure aeration where air is
supplied by a compressed air distribution network with operating pressure greater than 0.3 bars,
low pressure aeration is implemented with the range of operating pressure from 20 – 80 mbar
by air compressors and semi-aerobic uses the natural convection in order to supply air into thelandfill.
The concept of high-pressure aeration is mainly associated with the implementation oflandfill mining projects. Low pressure aeration aims to accelerate biological waste stabilizationin situ and reduce the greenhouse gas emissions. And semi-aerobic concept is mainly used inJapan and some other Asian countries for long-term reduction of GHG emissions andimprovement of leachate quality and for landfill remediation of old landfills. Furthermore, the1cost of construction and operation of the semi-aerobic landfills is lower than other concepts
because it uses no mechanical equipment for aeration.
Studies on landfill aeration began from the late 1990s. However, there is a little ourunderstanding of the processes occurring inside the landfill implemented by aeration methods
so far. Therefore, the necessary demand for surveying and collecting the data in full-scale iscritical to evaluate what happens inside an aerated landfill.
1.2 Research Objectives
Heat, gas and leachate are the primary products of decomposition process of organic
wastes due to physical, chemical and biological reactions that occur within the wastes.
Temperature and gas components are the constituents that have an interaction.
In addition, temperature is a good index to evaluate or detect an aerobic biodegradationin semi-aerobic landfills which have been widely used in Japan from 1975. The Japaneseguideline for MSW landfill revised in 1989 also states that stabilization of landfill may be
confirmed by 4 indexes, which are settlement, quality of leachate, quality and quantity oflandfill gas and temperature in landfills (M.O.E, 1989). Therefore, the purpose of this study
focuses on surveying and monitoring the landfill gas components and temperatures in a semiaerobic landfill.
1.3 Organization of the Dissertation
The thesis includes five chapters. Chapter one introduces the background and purposesof research. This research focuses on evaluating the stabilization of an operating semi-aerobic
landfill based on surveying and monitoring landfill gas components and temperatures.
Chapter two summaries briefly the structure, mechanism, and our understanding ofsemi-aerobic concepts so far.
Chapter three presents the methodology, the surveyed site and how to survey and collectthe data in-situ.
Chapter four analyzes the collected data and give the evaluation about what happens
inside an operating semi-aerobic landfill.
Chapter five is to focus on making a numerical modeling. Based on the collected data,a simulation is proceeded in order to predict the trend of landfill gas components and2

temperatures in the future by COMSOL Multiphysics software. Then, comparing the modeling
results to observed data.
Finally, chapter six sums up what the study got achievements and future plans.

Bibliography
Berge N. D., R. D. (2007). The status of aerobic landfills in the United States. In M. R. R.
Stegmann (Ed.), Landfill Aeration (pp. 257-271). CISA Publisher.
Heijo Scharff, A. V. (2011). Landfill sustainability and aftercare completion criteria. Waste
Management & Research 29, 30-40. doi:10.1177/0734242X10384310
M.O.E. (1989). Japan waste management for plan, design of MSW landfill sites. JWMS
Publication.
M. Ritzkowski, R. S. (2012). Landfill aeration worldwide: Concepts, indications and findings.
Waste Management 32, 1411-1419.
Matsufuji, Y. (2004). A road to semi-aerobic landfill: Experience of semi-aerobic landfills inJapan and Malaysia. The Third Intercontinental Landfill Research Symposium .
Hokkaido, Japan.
Nobutoshi Tanaka, Y. T. (2005). Past, present, and future of MSW landfills in Japan. J Mater
Cycles Waste Manag. doi: 10.1007/s10163-005-0133-6
Theng Lee Chong, Y. M. (2005). Implementation of the semi-aerobic landfill system (Fukuoka
method) in developing countries: A Malaysia cost analysis. Waste Management 25, 702711.
Y. Masufuji, A. T. (2007). The history and status of semi-aerobic landfills in Japan and
Malaysia. In I. T. aeration, & M. R. R. Stegmann (Ed.), Landfill aeration (pp. 109-116).
CISA.
Yi He, L. G. (2012). The Advantages and Mechanism of Semi-aerobic Landfill. Energy
Procedia 17 , 391-396.

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CHAPTER 2: LITERATURE REVIEW

2.1 Introduction
Landfilling technology continues to be one of the main methods used in future modern
municipal solid waste (MSW) strategies (Cossu, 2012), particularly in developing countries,
because of low construction and operation costs as compared to other technologies. It is anecessary and unavoidable step in closing the material cycle (Cossu, 2009; Cossu et al., 2016).
At present, there are 4 types of main landfilling concepts: anaerobic, aerobic, semi-aerobic, andhybrid. Each type has its own advantages and disadvantages. The choice of a specific type
depends on many factors (i.e., cost, regulations, climate, waste characteristics). Also, the goalsof waste treatment (i.e., energy recovery, increasing the waste stabilization) play a role inlandfill type selection (Grossule et al., 2018). One of the biggest challenges of landfilling
technology is to maintain the performance of a landfill as its initial design purposes to minimize
the risks to the surrounding environment. A good design, together with an appropriate operationmode, will significantly reduce the negative impacts on the environment and public health(Hrad et al., 2013; Stegmann and Ritzkowski, 2007).
The rapid development of science and technology during the last decades helped
researchers to propose the “sustainable landfill” concept (Antonis and Haris, 2009; Cossu,
2005) with the aim of (1) reducing waste volume, (2) accelerating the stabilization of waste, (3)minimizing landfill gas production which leads to greenhouse effect, (4) rapid biogas
production, and (5) decreasing the leachate organic load. In 2002, a special Task Group ofInternational Waste Working Group (IWWG) was established to achieve these targets througha project named “Landfill Aeration”. By means of the research projects all over the world,
researchers realized that aerobic conditions process faster the waste degradation and reduce
more significantly emissions than the anaerobic environment. Besides, the “Landfill Aeration”
project has paved the way for the recovery of valuable resources through landfill mining.
Therefore, in recent years, in situ landfill aeration projects have received much attention. It has
been considered as a useful tool for the sustainable conversion of conventional anaerobic
landfills into a biologically stabilized state. It has also shown a minimized emission potential(Ritzkowski and Stegmann, 2012).

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Many years ago, in some places in America, Europe and Japan the air and moisture havebeen added into a landfill to create the optimized aerobic conditions which help aerobic
microorganisms degrade biodegradable organic matter. The concept of semi-aerobic landfill
might be the oldest method for landfill aeration.
The semi-aerobic landfill concept is based on passive aeration. This concept wasdeveloped in 1975 by researchers at Fukuoka University, Japan, when it was given the namesemi-aerobic landfill. In semi-aerobic landfills, waste is aerated naturally by atmospheric air
via a network of horizontal leachate collection pipes (LCPs) connected to vertical landfill gas(LFG) venting pipes (VPs). The outlet of the main LCP in the leachate pond is always open.
Air is drawn into the main LCP due to a buoyancy effect, and the LFG is discharged into theatmosphere (Matsufuji and Tachifuji, 2007). Because of both the limited strength of the passive
aeration induced by natural ventilation and anaerobic zones remaining inside the semi-aerobic
landfill, the process of biological stabilization occurs more slowly in semi-aerobic landfill thanthat in actively aerated landfill. For this reason, semi-aerobic landfill has partial aeration aroundthe wells and pipes.
In Japan, the semi-aerobic landfill is the standard design for landfills. In this system,
waste is naturally aerated by oxygen supplied through a network of leachate collection pipes(LCPs) and gas collection pipes.
Semi-aerobic landfill is an unique structure for landfill aeration. Landfill gas (LFG)
extraction wells are connected to leachate collection pipes in a semi-aerobic landfill and air is
induced to the landfill body through the wells and pipes passively because the top of those wells
and the end of those pipes are always open to the air.

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Figure 1 Schematic diagram of semi-aerobic landfill
Figure 1 shows the schematic concept of semi-aerobic landfill. Semi-aerobic landfill isa passive aeration system because it acts by means of air flow via LFG extraction wells and
LCPs. Oxygen can be penetrated into waste layer from the top and bottom of landfill and resultsin aerobic biodegradation around the wells and pipes. Such aerobic biodegradation will generatea large amount of heat and then landfill temperature will increase. However, these zones where
far away from LFG extraction wells and LCPs will become anaerobic conditions. That’s why
it is called the “semi-aerobic landfill”.
Because the landfill layers are partially exposed to the air around the wells and pipes.
Such aeration may contribute to reduction of leachate intensity and methane emission throughthe operation period of landfilling. However, passive aeration has lower performance thanactive aeration. Then semi-aerobic system should be characterized by monitoring data inlandfill sites. Active aeration always produces heat by biological and chemical reactions andcarbon dioxide. So temperature and gas component are appropriate indices for evaluating theperformance of semi-aerobic landfill.
In semi-aerobic landfills, the leachate collection system consists of a central perforated
pipe (main collection pipe) with perforated branch pipes on either side of it laid at a suitableinterval. The pipes are embedded in graded gravel (5-15 cm) and installed with adequate slope.
7The main collection pipe ends in open leachate collection pond. The pipes are designed in awaythat only one-third of the section is filled with liquid. At each intersection of the main collection
pipe with the branch pipes, and at the end of each branch pipe, vertical gas ventilation wells
enclosed in graded gravel (eventually packed inside a wire netting) are erected.

GravelPerforated pipe

Figure 2 Main leachate collection pipe8Perforated pipe

GravelFigure 3 A typical landfill gas venting pipe (venting pipe)
Since the two piping systems are connected, ambient air and landfill gas flows throughthe leachate collection pipes and the gas ventilation wells, thus, enhancing the intrusion of the
air into the inner part of the landfilled wastes occasionally. Due to higher temperature in thewaste (compared to the ambient air), the gas inside waste tends to rise and gets vented throughthe gas wells, thus, generating a negative pressure siphoning effect that draws more air into
LCPs.
The majority of landfills in Japan, over half of the number of the landfills in Korea anda few landfills in Malaysia have been constructed and operating according to the semi-aerobic
concept. Semi-aerobic landfills exhibit reduced methane gas generation rates and an enhanced
leachate quality in comparison to anaerobic landfills. The key concept of a semi-aerobic landfill
is the connection of a leachate collection pipe with gas vents that directly connect to theatmosphere. However, due to the limited intensity of aeration induced by natural ventilationand the remaining anaerobic zones inside the landfill waste, the biological stabilization occurs
rather slowly in comparison to actively aerated landfills.
9During recent years, the semi-aerobic concept has been recognized for its potential
towards landfill remediation. As a part of remediation works, passive gas vents could beinstalled in closed landfills, however, each vent is installed separately, and they do not connect
to each other. (H.Yoshida, 2007).
Although numerous studies have focused on the semi-aerobic landfill concept(Ahmadifar et al., 2016; Cossu et al., 2016; Grossule and Lavagnolo, 2017; Hanashima et al.,
1981; Hirata et al., 2012; Huang et al., 2008; Matsuto et al., 2015; Morello et al., 2017;
Ritzkowski et al., 2006; Shimaoka et al., 2000; Theng et al., 2005; Wu et al., 2017; Yang et al.,2012), most of them were conducted using a lysimeter either in a laboratory or at pilot scale.
Those demonstrated significant achievements of the semi-aerobic landfill concept, including(1) accelerating the biodegradation of organic matter, (2) improving leachate quality, (3)reducing methane (CH4) gas emission, and (4) entailing lower construction and maintenancecosts (Ishigaki et al., 2011). The current study has been carried out over many years to monitor
and evaluate the aerobisation within a full-scale operational semi-aerobic landfill based on
measurements of the LFG temperature and concentration.
LFG temperature is regarded as a good index for assessing the decomposition of
biodegradable waste. Both aerobic and anaerobic decomposition processes generate heat [seeEquations (1) and (2)]. Rees (1980) measured a temperature range of 40°C–45°C in a waste
layer that was 4 m thick. High temperatures, in the range of 60°C–90°C, have also beenmeasured in other parts of the world (Bouazza et al., 2011; Yesiller et al., 2015, 2011; Yoshida
and Rowe, 2003). Moreover, several studies have been aimed at determining the heat generation
value through theoretical analyses of biochemical decomposition of waste. Pirt (1978) and Rees
(1980) reported a heat generation value of 632 kJ/kg glucose for anaerobic digestion. Cooneyet al. (1969) reported a heat generation value of approximately 110 kcal/mol oxygen (O2)(15,400 kJ/kg glucose) for aerobic digestion. Thus, it is clear that aerobic decomposition
generates a larger amount of heat from waste decomposition than does anaerobic decomposition.

2.2 Biological Degradation Processes in MSW Landfill
Semi-aerobic is a combination of aerobic and anaerobic decomposition. Biologicaldecomposition is classified into aerobic and anaerobic one. Glucose (C6H12O6) is thought to be
the most popular organic waste. The aerobic process may be expressed by:
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Degradable waste + Oxygen  CO2 + H2O + biomass+ heat + partially degraded materials
The process of anaerobic decomposition may be expressed by:Degradable wastes  CH4 + CO2 + organism growth + partially degraded organics
2.2.1. Landfill Gas (LFG) Generation

Landfill gas is a mixture of many gas components which results from the decompositionof wastes. The most common gas components including methane (CH4), carbon dioxide (CO2),
oxygen (O2), nitrogen (N2). The amount of gas generated depends on the amount andcomposition of the organic content of the waste. The rate of gas generation depends on thecomposition of the organic waste and the biochemical environment in the landfill (plenty ofwater, no inhibitors present). The gas moves out of the waste by the pressure that it builds.
Inside the semi-aerobic landfills, there are always two reaction zones existing at various
locations simultaneously which are aerobic zone and anaerobic zone. The areas around theperforated gas vents and leachate collection pipes are aerobic zone because the air flow
(oxygen) is supplied from the bottom of LCPs and from the top of gas vents. Therefore, oxygen
is utilized by aerobic microorganisms. At the locations which are far from LCPs and gas vents,
oxygen cannot reach these points or be limited, the anaerobic reaction becomes dominant.
2.2.1.1. Aerobic Decomposition
Aerobic processes require the presence of oxygen. Thus, aerobic decomposition occurs
on initial placement of the refuse, while oxygen is still available. In addition, the aerobic
reactions also occur around the landfill gas venting pipes where oxygen is provided from the
LCPs and from the top of gas vents. When there is enough oxygen for aerobic microorganisms,
the aerobic reaction will happen until the organic matter disappears. During the stage ofdecomposition, aerobic microorganisms degrade organic materials to carbon dioxide (CO2),
water (H2O), partially degraded residual organics, and considerable heat. Aerobic
decomposition is characteristically rapid, relative to subsequence anaerobic decomposition.
C6H12O6 + 6O2  6CO2 + 6H2O + Heat (1)In this stage, the main gas components is CO2 and water vapor.
112.2.1.2. Anaerobic Decomposition
As the biodegradation of the refuse progresses, the oxygen becomes depleted, the redox
potential is reduced, and the anaerobic methanogenic bacteria becomes dominant. These
organisms produce carbon dioxide, methane, and water, along with some heat.
Characteristically, these organisms work relatively slowly but efficiently over many years todecompose remaining organics.
C6H12O6  3CH4 + 3CO2 + Heat

(2)

In this stage, nitrogen (N2) and hydrogen sulfide (H2S) may also be produced due to themicrobial process of denitrification, in which the nitrate ion is reduced. Hydrogen sulfide is
produced by sulfate-reducing microorganisms.
Landfill gas production rate gradually decrease over time due to the decrease of organic
materials. Gas production rate (consumption) is the rate of oxygen in a landfill in the case of
aerobic decomposition or the rate of production of methane in a landfill in the case of anaerobic
decomposition. The rate at which landfill gas is generated depends on many factors, the mostimportant factors are moisture content, nutrient content, bacterial content, pH level, temperature,
particle size of waste. Therefore, a great deal can be learned about the status of landfill
decomposition by monitoring the gas components and leachate.
In practice, LFG is considered to be a mixture of the gases CH4, carbon dioxide (CO2),
O2, and nitrogen (N2). LFG is composed 45% to 60% methane and 40% to 60% carbon dioxide(ATSDR, 2001). In conventional sanitary anaerobic landfills operating under normal conditions,the ratio is typically from 0.8 to 1.4 (Benson, 2017). Theoretically, if the ratio of CH4 to CO2 iseither greater than or equal to 1 [from Equation (1)], the anaerobic condition predominates(Barlaz et al., 2010; Jafari et al., 2017; Martin et al., 2013). Thus, it can be derived that if theCH4/CO2 ratio is less than 0.8, anaerobic and aerobic conditions are coexisting simultaneously
within the landfill. Matsufuji et al. (1996) created a semi-aerobic landfill model in a lysimeterand found the CH4/CO2 ratio to be 1.0. IPCC (2006) calculated the ratio to be 0.33 by using
default values. Kim et al. (2010) measured the ratio at 1.0 in a closed landfill site that had been
undergoing remediation to accelerate landfill stabilization through installing numerous passive
LFGVPs that were not connected to the LCPs. Yang et al. (2012) found the CH4/CO2 ratios foranaerobic landfills and semi-aerobic landfills to be 1.9 and 0.8, respectively. Zhang and Matsuto
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(2013) reported a CH4/CO2 ratio between 1.0 and 1.5 for a semi-aerobic landfill site that was
not being operated correctly. Jeong et al. (2015) measured LFG from VPs in five semi-aerobic
landfills in South Korea. However, the ends of LCPs in all five landfill sites were closed, andthe CH4/CO2 ratio ranged from 1.08 to 1.46, averaging 1.30. Thus, a CH4/CO2 ratio below 1.5
might be an indicator of landfills with a semi-aerobic design.
The CH4/CO2 ratio is regarded as an indicator for evaluating the proportions ofanaerobic decomposition and aerobic decomposition. Semi-aerobic landfill is a partial
aerobisation system because passive aeration works only around LFGVPs and LCPs, and there
is limited penetration of O2 into waste mass.
If the ratio of CO2/CH4 > 1.0, it means that the aerobic reactions become dominant thananaerobic reactions.
2.2.2. Heat Generation

Significant amounts of heat are generated in MSW landfills due to the decompositionof the organic fraction of the waste mass. The heat generated results in long-term elevated waste
temperatures with respect to local air and ground temperatures (Nazli Yesiller, 2015).
Heat is one of byproducts of waste decomposition process.
Heat generation due to biological processes was provided for varying phases ofdecomposition including aerobic phase, anaerobic phase and total decomposition. Rates of heatgeneration were higher for the aerobic phase than the anaerobic phase (H. Yoshida R. K., 2003).
Many researchers have been pointed out that temperatures is an important factor ofchemical, physical and biological phenomena in a sanitary landfill. Ree (1980) proposed thatmethane production in landfills can be optimized by temperature control. Cecchi (1993)
indicated that anaerobic digestion of MSW can be accelerated more actively in thermophilic
condition than in mesophilic one. Collin (1993) indicated that the maximum temperature in thebottom of a landfill reached to about 65C and such temperature rising may induce a crack inclay liners. Hasegawa (1979) indicated that gas temperature in the landfill rose up to about 70C
rapidly during landfilling. Then the temperature drops to 40-50C gradually several months
later and stabilized at 25-35C five or six years later. It was concluded that the temperature rise
was caused by the heat generation of aerobic decomposition. Nakamura (1987) observed that13

the temperature began to rise 50-100 days later after landfilling and methane gas produced
actively at the same time.
However, if landfill temperature rise above 70-80C, microbiology may become extinct.
So, 70-80C may be maximum for landfill temperature.
In this study, we surveyed several important indicators, including the LFG temperature andconcentration and ratio of CH4 to CO2, of an operating semi-aerobic landfill at full-scale. Our
observations indicated that the passive aeration happened effectively. The aerobic condition
occurred around the main LFGVPs. The highest LFG temperature was over 60oC and remained
above 40°C for over 5 years. The average CH4 concentrations were below 15%. These above
analyses also showed that high temperature and the CH4/CO2 ratio less than 1.0 potentially areuseful indicators of the type of landfill processes. They can help landfill operators realize thepredominance of aerobic biodegradation within the landfill. Oxygen (O2) is supplied naturally
into the waste mass without the need for a blower, promoting aerobisation within the landfill
through the buoyancy effect. This leads to significantly reducing the costs of construction andoperation. The aerobic biodegradation performance of the branch LFGVPs was not as efficientas the main LFGVPs.
Although our study focuses only on the analysis of LFG components and LFG temperatures,
these are useful indicators that can be measured easily on-site to identify the aerobic conditionof operating semi-aerobic landfills. Besides analyzing the leachate quality, monitoring the LFG
concentration and temperature periodically is required to detect the sudden rise in CH4
concentrations in semi-aerobic landfills. This monitoring should play a key role in evaluating
the passive aeration performance of semi-aerobic landfills.
This paper is the first step in a series of our research. We will develop the research infurther works by conducting the coupling analysis. Next steps, the numerical simulations will
be used for modeling the gas production, temperature distribution, gas concentrations and wewill compare the numerical simulations with the real data and evaluate the gas and heattransport phenomena within the semi-aerobic landfill.

14

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Nobutoshi Tanaka, Y. T. (2005). Past, present, and future of MSW landfills in Japan. J Mater
Cycles Waste Manag. doi:DOI 10.1007/s10163-005-0133-6
R. Kerry Rowe, Y. Y. (2012). Clogging of finger drain systems in MSW landfills. Waste
Management 33, 2342-2352.
Theng Lee Chong, Y. M. (2005). Implementation of the semi-aerobic landfill system (Fukuoka
method) in developing countries: A Malaysia cost analysis. Waste Management 25, 702711.
Toshihiko Matsuto, X. Z. (2015). Onsite survey on the mechanism of passive aeration and air
flow path in a semi-aerobic landfill. Waste Management, 204-212.
Y. Masufuji, A. T. (2007). The history and status of semi-aerobic landfills in Japan and
Malaysia. In I. T. aeration, & M. R. R. Stegmann (Ed.), Landfill aeration (pp. 109-116).
CISA.
Yi He, L. G. (2012). The Advantages and Mechanism of Semi-aerobic Landfill. Energy
Procedia 17 , 391-396.
Yoshida, H. (2007). Landfill temperatures in semi-aerobic landfills. In M. R. R. Stegmann (Ed.),
Landfill aeration (pp. 136-142). CISA.

15

16

CHAPTER 3: METHODOLOGY

3.1 Introduction
This chapter introduces briefly an operating semi-aerobic landfill site in Hokkaido,
Japan and the survey methods were implemented to collect the temperature and gas component
data at the site.
3.2 Description of the landfill

Figure 4 Aerial view of the operating semi-aerobic landfill in the northern part of Hokkaido,
Japan (in 2003)
17

This semi-aerobic landfill site is located in the northern part of Hokkaido, Japan (Figure4). It has been designed following the canyon/depression method, and the waste is filled in
multiple lifts (sandwiched method). The area of the landfill is 12.3 ha, and its volume isexpected to reach 1,840,000 m3 over a 27-year period (2003–2030). Each waste type, such as
mixed waste, incombustible waste, bottom ash, and fly ash, is placed into the site in different
lifts. The operation began in 2003 and is expected to proceed until 2030.
3.2.1. Gas venting pipes

According to the design, the Asahikawa municipality will install 73 gas venting pipesclassified three types including main wells, branch wells and monitoring wells. A typical gas
venting pipe contains two main parts: a venting pipe and a gravel layer. The material used forventing pipes is high-density polyethylene (HDPE) and the venting pipes are perforated along
the pipe body, the diameter of a small hole is from 5mm to 10mm. Table 1 summaries thequantity of gas wells of Yoshino landfill and Figure 6 shows the map of gas venting pipes atthe site.
After that the perforated pipe is enclosed by a gravel layer with the average diameter ofstones or gravel from 150 mm to 200 mm. The thickness of the enclosed gravel layer is about
300 mm. To fix the gravel layer embedding the venting pipe, a steel wire mesh is used. Figure
8 presents the structure of a typical gas venting pipe at the site.
Table 1 The quantity of gas venting pipes of the landfill
Main wells
Design9Installed

9

Branch wells
59

Monitoring wells
55

Figure 3 shows a typical landfill gas venting pipe in the landfill site. The LFGVP
arrangement consists of a 200 mm high-density polyethylene pipe surrounded by a verticalgravel layer measuring 1,200 × 1,000 mm. The VP is perforated along its length with small
holes measuring 5–10 mm in diameter. The average diameter of the gravel (stone) is 15–20 cm.
Wire netting is used to support and embed the vertical gravel layer. The purpose of surrounding
the VP with this vertical gravel layer is to (1) protect the VP from deformation due to wastecompaction and other external forces, (2) reduce clogging of the perforations on the body of18

the VP, (3) enable the leachate head to quickly, and (4) create another pathway for ambient air
to penetrate waste layers.
Apart from the monitoring LFGVPs, which are not connected to the LCP network, all
the LFGVPs (e.g., main LFGVPs and branch LFGVPs) are connected to the LCPs to take theair flow into the waste layers. Currently, 53 of 73 LFGVPs have been installed, including 9
main LFGVPs, 39 branch LFGVPs, and 5 monitoring LFGVPs (Figure 6). The unique structureof the semi-aerobic landfill generates passive aeration because its mechanism is based entirelyon the buoyancy effect resulting from the temperature difference between the waste mass andthe outside air. Thus, a negative pressure siphoning effect is created to draw air into the pipes,
and air penetrates the waste mass (Matsufuji and Tachifuji, 2007).
The leachate is collected via an LCP network at the bottom of the landfill and isconveyed to the leachate pond (Figure 4 and Figure 6). The diameters of the main LCP andbranch LCP are 700 and 400 mm, respectively. The average leachate discharge is 600 m3/day,and the volume of the leachate pond is 12,700 m3. As for the water quality of the leachate, thesuspended solids' concentration is less than 890 mg/L, and the biochemical O2 demand is lessthan 1,900 mg/L. As mentioned above, in addition to collecting leachate, LCPs convey air into
the waste layers. Therefore, the main end of an LCP is always open to the atmosphere.
To date, 53 LFGVPs have been installed in the landfill site. Some of these LFGVPs
were built when the landfilling began, whereas others have been installed more recently.
Currently, the landfill site is divided into two zones: A and B.

19

Figure 5 Structure of the operating semi-aerobic landfill

Figure 6 The layout of landfll gas venting pipes and the leachate collection system inthe surveyed operating semi-aerobic landfill.

20

In Zone A, the landfilling operation was completed in 2010 (Figure 6). By 2014, thevolume of waste deposited was 730,550 m3. Zone A contains 28 LFGVPs (4 main LFGVPs, 21
branch LFGVPs, and 3 monitoring LFGVPs), and the waste mass has reached the designed
height. The heights of the waste at the main gas VPs M1, M2, M3, and M4 are 17.6, 26.6, 30.8,
and 33.0 m, respectively. Waste is still being placed in Zone B. Consequently, our analysis
focuses on the LFGVPs in Zone A. Figure 7 is the cross-section through some LFGVPs in Zone
A and depicts the waste layers buried from before 2005 to 2014. It should be noted that, before
2005, the landfill accepted organic waste because the city's incineration plant could not accept
all combustible wastes. However, since 2005, the landfill has accepted only incombustible
waste, bottom ash, and fly ash.
Ideally, we should consider all the LFGVPs in Zone A. However, we focus only on
measuring the LFG temperature and concentration to identify whether aerobization is occurring
within the semi-aerobic landfill. Therefore, the LFGVPs installed in cells containing only
bottom ash and fly ash are not considered in this analysis. The monitoring LFGVPs are also notconsidered in this study because the bottom of these LFGVPs are not connected to the LCPs
network and the positions of these LFGVPs are so close to the main LFGVPs or LCPs (i.e.,
MH2, MH3), the performance of monitoring LFGVPs can be affected by the main LFGVPs.

21

Figure 7 Cross-section of waste layers through the landfill gas venting pipes.
The distance between the gas venting pipes is designed adequately in order that thenatural aeration happens efficiently. Clearly, the distance is more short more efficient, however,the cost of construction also becomes higher.

22

Soil

Waste

Soil
Waste

Figure 8 A typical gas venting pipe

Figure 9 Mechanism of a gas venting pipe

As mentioned above, the duty of a gas venting pipe is mainly to discharge the landfill
gases generating during the waste decomposition into the atmosphere and supply oxygen foraerobic reactions caused by microbial activities.
3.2.2. Leachate Collection Pipes (LCPs)

The leachate collection pipe network is designed to be responsible for the collection andtransport of the leachate, which flows from the bottom of the landfill. Leachate is a byproductof waste decomposition or percolation through waste. Rainwater percolates through the landfill
cover into the waste playing an important role in leachate generation. The composition ofleachate varies in each landfill depending on waste composition, amount of water available andlandfill age.
The function of the LCPs is to lower the leachate mound, reduce hydraulic head on theliner system, and reduce the amount of contaminants available for transport through the barriersystem.

23

Figure 10 Base gravel layer

Figure 11 Main leachate collection pipe
(perforated pipe)

3.2.3. Leachate Pond

Leachate pond is designed to store the liquids collected by leachate collection pipes
before transporting to wastewater treatment plant. Treated leachate meets the requirements ofenvironmental standard then could be discharged into local waterways or streams.

Figure 12 Leachate pond in Yoshino landfill, Asahikawa City, Hokkaido

24

3.2.4. Barrier Systems

3.2.4.1. Cover Layer
The cover is a material layer used to separate the waste with the environment forprotection of public health. During landfill operation, there are two types of cover will be used.
The one is daily cover used to cover the top of waste at the end of the working day to reduceodors and vermin. Figure 13 shows the material used to be daily cover in Yoshino landfill.

daily cover (soil)

Figure 13 Daily cover by soil
The other is final cover which is a multilayer barrier, the function of the final cover isto reduce or prevent infiltration of precipitation into the landfill in order to minimize leachate
generation.
3.2.4.2. Liner
Liner system is also a multilayer system to control contamination transport forprotection of the subsurface water and soils. Advection and diffusion are the main mechanismsof contaminant transport through the liner. During advection, suspended solids or dissolved
material moves with water or leachate and can be transported through pores of a liner based on25

the hydraulic head. Diffusion may be a significant transport process in low permeability liner
systems. HDPE geomembrane is the main material used for liner system in Yoshino landfill.
The bottom barrier system of the semi-aerobic landfill was designed according to theregulation promulgating by the Ministry of Health and Welfare in 1998. The landfill used asingle geomembrane with impervious soil layer and geotextiles used as a protection mat on the
top of the geomembrane.
In Japan, the amount of natural clay is not available, therefore, to deal with the challenge,
bentonite was mixed with soil to create two low-permeability material layers with thecoefficient of permeability less than 10-7 cm/s. The thickness of each bentonite-soil layer is 250
mm. Sandwiched between two bentonite-soil mixture layers, a bentonite sheet with a thicknessof 3.5 mm was placed for the protection. Upper of the bentonite-soil mixture layer is bentonite
sheet (t=3.5 mm), geomembrane (t=1.5 mm) and geotextile (t=10 mm). The thickness of theprotective soil layer and gravel layer are 700 mm and 300 mm, respectively (Fig.13).

700 mm

1500 mm

300 mm

Waste
GravelProtective
Soil
Geotextile, t=10 mm

500 mmGeomembrane, t=1.5 mm
Clay liner

Bentonite sheet, t=3.5 mm

Clay liner

Figure 14 A cross-section of the bottom barrier system
The municipal solid waste is directly above the gravel. Before 2005, the landfill
accepted organic waste because the city's incineration plant could not accept all combustible

26wastes. However, since 2005, the landfill has accepted only incombustible waste, bottom ash,and fly ash.
The landfill site has been constructed in a temperate climate region. The air temperaturefluctuates from −20°C in winter to 25°C in summer. The mean annual temperature is 6.7oC.
Precipitation is distributed throughout the year with maximum amounts of during the latesummer. The mean annual precipitation for the region is 1103 mm. The yearly average amountof snowfall ranges widely from 300 cm to 750 cm.
3.3 Survey methods
3.3.1. LFG temperature and LFG concentration

Temperatures at the Yoshino landfill were measured by lowering thermo-couple sensor
into the vertical gas wells open to the atmosphere during specific monitoring events (Figure15). Gas concentrations also were measured at the same locations as the temperature
measurements in the gas wells using a portable gas analyzer (Figure 16).

27

Figure 15 Temperature analyser

Figure 16 Gas analyser

Figure 17 Methods collecting the LFG temperature and LFG concentration
Air and gas movement occur in the gas wells and the measured temperatures may not
fully represent the adjacent waste mass temperatures at a given measurement location.
Nevertheless, these temperature measurements provide representation of temperature trends
and variations in temperatures due to changing decomposition conditions in the waste mass andwere used in the analysis presented herein (N. Ysiller, 2011).
As shown in Figure 15 and Figure 16, the temperature was measured using athermocouple recorder (Graphtec GL200A, measurement range of thermocouple type T), andthe gas component was measured using a portable LFG analyzer (Geotech GA5000, Portable
28

Landfill Gas Analyzer). The analyzer was equipped with a pump working at a sampling rate of
550 mL/min. Typically, a gas sampling tube and a thermometer sensor were lowered into
LFGVPs to sample the air at 1-m-depth intervals from ground level, and measurements wererecorded after 90 s of sampling. Three different gases—CH4, CO2, and O2—were detectedoccurring simultaneously. The N2 content was determined from the balance of CH4, CO2, andO2. The accuracy of the measurement after calibration for CH4, CO2, and O2 was ±0.5%, ±0.5%,
and ±1%, respectively.

Figure 18 In-situ collecting data
Temperature and gas data at the Yoshino landfill have been obtained since 2010 inwastes with ages 2 years to over 13 years. The initial data set at each well represents temperatureand gas conditions prior to the placement of the gas wells.
Since 2006, gas temperatures and gas component data have been measured in waste
layers aged from 2 years to >11 years. There are movements of air and gases in the gas wells,
and the temperatures measured may not fully represent the adjacent waste mass temperatures
at a given measurement location. Nevertheless, due to employing a consistent measurement
method, these temperature measurements are representative of temperature trends andvariations in temperatures due to changing decomposition conditions in the waste mass andhave been used in the analysis presented herein (Yesiller et al., 2011).
29

Carbon monoxide (CO) concentration was also measured by the Portable Landfill Gas
Analyzer. The CO concentration was below 30 ppm. Therefore, the concern about the potential
for subsurface combustion was not significant in this study (FEMA, 2002).
3.3.2. Geomembrane temperature

Geomembrane temperature under the LFGVP M2 have been monitored for more than
10 years (Figure 19).

Figure 19 The position of measuring the LFG temperature and liner temperature on site

30

WasteGravelProtective
Soil
Geotextile

Position oftemperature
sensorGeomembrane
Clay liner

Bentonite sheet

Clay liner(b)Figure 20 Scheme of measuring the liner temperature
Geomembrane temperature has been measured by using an integrated temperature
sensor below the geomembrane. The Type T Thermocouple (BT-100) with a temperature rangeof -30oC - 70ºC has been installed below the primary bentonite sheet in the liner system. The
geomembrane temperature has been measured 4 times per day (6-hour intervals) and thetemperature data have been collected 2 times per year from the data logger. The operation of
the thermocouple bases on the thermoelectric effect which produces a temperature-dependent
voltage. Then this voltage is interpreted to measure temperature. The temperature measurement
has started since October 2002.
LFG temperature is measured by a temperature recorder (Graphtec GL200A, themeasurement range of thermocouple type T). A temperature probe was lowered into the LFGVP
M2 at 1-m-depth intervals from ground level, and measurements were recorded after 90 s ofsampling. The measurement of LFG temperature has started since January 2006. However, the
LFG temperatures only have been measured 4 times per year. The measured temperatures may
not fully represent the adjacent waste mass temperatures at a given measurement location.
However, these temperature measurements provide a representation of temperature trends andvariations in temperatures due to changing decomposition conditions in the waste mass and31were used in the analysis presented herein. Besides, air temperature also has been recorded at
the same time as measuring the LFG temperature.
3.4 Numerical simulation
The finite element method (FEM) is the most widely used method for solving problemsof engineering and mathematical models. Typical problem areas of interest include thetraditional fields of structural analysis, heat transfer, fluid flow, mass transport, andelectromagnetic potential.
COMSOL Multiphysics is a finite element analysis, solver and simulation software/
FEA software package which is used for various physics and engineering applications,especially coupled phenomena, or multiphysics.
In this study, a cross-platform finite element analysis named COMSOL Multiphysics
Modeling was utilized to simulate the biodegradation process happening within the landfill
which cannot be seen in reality.
3.4.1. Basic goal of the simulation

This part of research only focuses on simulating the transport of phenomena of landfill
gas. A 2D model represents the venting pipe, gravel layer, cover soil and waste layer. Heattransport, mass transfer and momentum transport are considered as the main transportphenomena happening during the biodegradation of organic matter.
In addition, the simulation also considers the effects of clogging phenomena on thegeneration and distribution of LFG concentration, and temperature within the semi-aerobic
landfill. As the venting pipe is clogged, the air cannot migrate into the venting pipe from thebottom of the LCP, therefore, there is no air flow at the bottom.
3.4.2. Various properties needed for the simulation

3.4.2.1. Density
The landfill gas is a mixture of many gases, however, the main gas components
including methane gas (CH4), carbon dioxide (CO2), oxygen (O2) and nitrogen (N2). And thedensity of landfill gas is a function depends on the temperature, internal pressure, and gas
concentration.
32

3.4.2.2. Porosity
Porosity is defined as the fraction of the control volume that is occupied by pores. Thus,
porosity can vary from zero for pure solid regions to unity for domains of free flow.
3.4.2.3. Permeability
Permeability is defined as the ability of a porous material to allow fluids to pass throughit. The unit for permeability is m2
The permeability of a medium is related to the porosity, but also to the shapes of thepores in the medium and their level of connectedness.
3.4.3. Governing equations and geometry

Waste matrix is a heterogeneous porous medium. A detailed description down to every
pore is not practical. Therefore, to simplify the problems, a combination of the porous (waste)
and fluid (landfill gas) media into a single homogeneous medium is a common alternative
approach.
The geometry of model is modeled including 3 blocks: waste block, gravel block andpipe block with the dimensions as follow:

33

Figure 21 The geometry of model
3.4.3.1. Continuity equation    .  u   Qm
t34

3.4.3.2. Darcy’s Law equation
To model low-velocity flows or media where the permeability and porosity are verysmall, and for which the pressure gradient is the major driving force and the flow is mostly
influenced by the frictional resistance within the pores, Darcy’s law together with the continuity
equation and equation of state for the pore fluid (or gas) provide a complete mathematical modelsuitable for a wide variety of applications involving porous media flows. With Darcy’s law, themomentum is so small it can be neglected, pressure alone drives the flow
Darcy’s law states that the velocity field is determined by the pressure gradient, the fluid
viscosity, and the structure of the porous medium:

u


p


Inserting Darcy’s equation into the continuity equation:     .   p   Qmt
 where:
 = landfill gas density (kg/m3)
 = dynamic viscosity of LFG (Pa.s)= porosity (a dimensionless number between 0 and 1)

 = permeability of the media (m2)
Qm = mass source (kg/(m3.s))p= LFG pressure (Pa)t= time (s)In the landfill, the transformation of organic matter to the landfill gas component andother products mainly based on the aerobic and anaerobic reactions caused by microorganism
activities. The consumption of organic matter and oxygen, the generation of methane gas andcarbon dioxide have to be considered. Hence, mass source (Qm) will be added into the above
equation.
Qm = (RCH4+RCO2)*(xO2_initial/Kfactor)/[xO2_initial/Kfactor + wO2]
Where:

35

RCH4 = the methane gas generation rate from waste layer (kg/(m3.s))
RCO2 = the carbon dioxide generation rate from waste layer (kg/(m3.s))
wO2 = mass fraction of oxygen (a dimensionless number between 0 and 1)
xO2_initial = initial oxygen concentration (mol/m3)
Kfactor = a coefficient (dimensionless)3.4.3.3. Heat transfer equations in fluid and solid
The heat transfer equation for porous media is derived from the mixture rule on energies
appearing in solid and fluid heat transfer equations. For solid medium:

where:
 = solid density (waste, soil, gravel) (kg/m3)
Cp = specific heat capacity of solid (waste, soil, gravel) (J/m3/kg)
T = temperature (K)q = conductive heat flux
Q = heat source or sink
For fluid medium:

where:
 = fluid density (kg/m3)
Cp = specific heat capacity of fluid (J/m3/kg)
T = fluid temperature (K)q = conductive heat flux
Q = heat source or sink
The local thermal equilibrium hypothesis assumes equality of temperature in both fluid andsolid phases:
Heat source is the heat generation of biodegradation of organic materials within thelandfill resulting from microorganism activities and chemical reactions. In this simulation, heatsource is considered as a function mainly depending on the biological reactions.
36

Q0 = Raero*dHaero*wO2/(xO2_initial/Kfactor+wO2)
where:
Raero = heat generation rate of aerobic decomposition (J/(m3.s)))dHaero = heat generation value aerobic decomposition (J/(m3.s)))3.4.3.4. Transport of landfill gas concentration equations
The basic equation for the conservation of mass of a species i is:

Where:
 = the density of landfill gas mixture (kg/m3)
ωi = mass fraction of gas component i (dimensionless)u = the mass averaged velocity of the mixture (m/s)
ji = the mass flux relative to the mass averaged velocity (kg/(m2.s))
Ri = heat the rate expression describing its production or consumption (kg/(m3.s))
3.4.3.5. Organic matter (glucose) consumption equation
To model the solid waste biodegradation (glucose), the Monod equation was used:f
Where:
f= - RCH4*xO2_initial/Kfactor/(xO2_initial/Kfactor+xO2)/MCH4- RO2*xO2/(xO2_initial/Kfactor + xO2)/MO2u= the concentration of the biodegradable of solid waste (kg/m3)

f= solid waste biodegradation rate (kg/(m3.s))t= time (s)RCH4 = the methane gas generation rate from waste layer (kg/(m3.s))
RO2 = the oxygen consumption rate (kg/(m3.s))
xO2 = mole fraction of oxygen (mol/m3)
xO2_initial = initial oxygen concentration (mol/m3)
37

Kfactor = a coefficient (dimensionless)
MCH4 = molecular weight of methane (kg/mol)
MO2 = molecular weight of oxygen (kg/mol)
3.4.4. Input parameters

Input parameters
Atmospheric pressure, p0
Initial temperature, T0
Porosity, εTortuosity, τ
Density of landfill gas, ρg
Density of waste, ρw
Density of soil, ρsPermeability of waste, 𝜅w
Permeability of soil, 𝜅sPermeability of gas, 𝜅g
Dynamic viscosity of gas
The methane gas generation rate, RCH4
The oxygen consumption rate, RO2
The carbon dioxide generation rate, RCO2
Molecular weight of methane, MCH4
Molecular weight of oxygen, MO2
Molecular weight of carbon dioxide, MCO2
Molecular weight of nitrogen, MN2
Molecular weight of glucose, Mglucose
Initial temperature, Tinit
Thermal conductivity of waste, kw
Thermal conductivity of soil, ks
Thermal conductivity of gas, kg
The initial methane gas concentration, xCH4_initial
The initial oxygen concentration, xO2_initial
The initial carbon dioxide concentration, xCO2_initial
The initial nitrogen concentration, xN2_initial
The half saturation constant for the oxygen, Kfactor
The gas constant, Rg
Specific heat capacity of gas mixture, Cp,gas
Specific heat capacity of waste, Cp,w
Specific heat capacity of soil, Cp,sHeat generation rate of aerobic decomposition, Raero
Heat generation value aerobic decomposition, dHaero
The effective specific capacity of gas, Ceff
The effective density of porous media, 𝜅eff
The effective thermal conductivity of gas, kg

Unit

Value

atm
K
kg/m3
kg/m3
kg/m3
m2
m2
m2
Pa.s
kg/(m3.s)
kg/(m3.s)
kg/(m3.s)
kg/molkg/molkg/molkg/molkg/moloCW/(m.K)
W/(m.K)
W/(m.K)
mol/m3mol/m3mol/m3mol/m3kg/m3J/(mol.K)
J/(kg.K)
J/(kg.K)
J/(kg.K)
J/(m3.s)J/(m3.s)J/(kg.K)
kg/m3
J/(kg.K)1
273.15
0.1
1.5
1.293
1200
1800
1e-13
1e-12
1e-4
1.78e-5
1.6e-73.2e-82.93e-7
0.016
0.032
0.044
0.028
279
20
0.95
0.86
0.02
0
0.21
0
0.79
20
8.314
1524
1000
1109
1e-6
4.67e5
1939
1157
0.35

38

* These parameters are determined by the reference # H.Yoshida, doctoral degree dissertation, Hokkaido
Univ. (1999). The reference shows the characteristics of the wastes which were not incinerated and landfilled.

As mentioned above, porosity is defined as the fraction of the control volume that is
occupied by pores. Therefore, the porosity is one of the most representative parameters of void
space structure. For natural media, porosity does not normally exceed 0.6 and for theexperimented waste layers, porosity varied widely within the range 0.03 to 0.6 (Amjad Kallel
N. T., 2004).

39

40

CHAPTER 4: RESULTS AND DISCUSSION

4.1 Observation results
Temperatures at the Yoshino landfill were measured by lowering thermo-couple sensor
into the vertical gas wells open to the atmosphere during specific monitoring events from 2010
until now.
4.1.1. Spatial distribution of LFG

Figure 22 (a) Gas components and (b) ranking map of CH4 concentration at the exit ofsurveyed landfill gas venting pipes (Zone A) on September 10, 2013.
Figure 22(a) describes the main LFG components, including CH4, CO2, O2, and N2, atthe exit of LFGVPs surveyed on September 2013. It can be seen that the CH4 concentration at
the exit of the surveyed LFGVPs is below 10% (blue color), apart from the case of the branch
LFGVP B10 (24.4%). Figure 22(b) shows the range of CH4 concentrations at the exits of thesurveyed LFGVPs. Here, we rank the CH4 concentration using four colors: green represents a
CH4 concentration either less than or equal to 5%, blue represents a concentration greater than41

5% and either less than or equal to 10%, yellow represents a concentration greater than 10%
and either less than or equal to 20%, and red represents a concentration greater than 20%. Mostof the main LFGVPs (M1, M2, M3, and M4) have a CH4 concentration below 10%, whereas
the CH4 concentration of branch LFGVPs ranges from 1.4% (B12) to 24.4% (B10). The ranking
map of CH4 concentration [Figure 22(b)] shows that most of the LFGVPs with high CH4
concentration are branch LFGVPs (B6, B9, B10, and B13). This could be due to the branch
LFGEWs are far away from the main LCP; the air flow is difficult to move to these branch
LFGEWs through the main LCP at the bottom of the landfill.
4.1.2. Influence of the type of gas VPs on LFG concentration and temperature
4.1.3. The main gas VP M2

Zone A (landfilling completed) contains four main LFGVPs: M1, M2, M3, and M4. Our
analysis focuses on the main gas VP M2, where the height of the organic waste (approximately
20 m) was the largest in the landfill site (see Figure 7).
Figure 23 shows the LFG concentration and temperature and the CH4/CO2 ratio at theexit of the main LFGVP M2. The air temperature fluctuated from −20°C in winter to 25°C insummer. Though the air temperature was always below 0°C in the winter months, the hightemperature trend of LFG remained at >40°C for more than 5 years before declining to 20°C in
the most recent observation. This means that there was a continuous active aerobic condition
around this LFGVP. Over the observation period, the CH4/CO2 ratio was below 1.0 (from 0.34
to 1.04). This shows that aerobisation was active in this LFGVP, and the aerobic condition
became dominant. The trend of this ratio increased slightly from the 1,200th day to the 2,450th
day (from 2006 to January 2010) from the commencement of the landfilling operation and thendeclined gradually to less than 0.5 by the 3,800th day (February 2014). The CH4 concentration
at the exit ranged from 5% to 15%. The CH4 concentration increased slightly, from 7% to 15%,in the early observation and then decreased gradually to 5%.

42Figure 23 Landfill gas concentration and temperature and the CH4/CO2 ratio at the exit of themain landfill gas venting pipe M2
The findings reveal that, during the 7 years from December 2006 (3 years after thelandfilling operation commenced) to February 2014, the CH4 concentration of the LFGVP M2
varied from ~7% to ~15% from December 2006 to August 2010 and then declined gradually.
This decline may have been due to the gradual disappearance of organic waste. Obviously, thetrend of reduction of LFG temperature, CH4 concentration, and the CH4/CO2 ratio may be usefulindicators of the landfill stabilizing.
As the CH4 concentration data were recorded only at the exits of LFGVPs, the measured
CH4 content could be diluted by air. However, even when we measured the CH4 and O2
concentrations since 2010 along the depths of the LFGVP M2, the CH4 concentration of this43

LFGVP was always less 20% from 2010 to 2013, and it then declined to below 10% in 2014
[Figure 24(a)].

Figure 24 (a) CH4 concentration profile of the main landfill gas venting pipe M; (b) O2
concentration profile of the main landfill gas venting pipe M2; (c) Temperature profile of themain LFG venting pipe M2.
44

The CH4 concentrations were always below 20% at all depths, whereas the O2
concentrations ranged from ~1% to ~15%. The waste mass at the LFGVP M2 reached thedesigned elevation of 211 m in 2008. Most of the measurements were obtained in winter(January and February), and the surface of the landfill was covered with a thick layer of snow(the average annual snowfall is around 0.8 m). This meant that it was impossible for air tomigrate into the landfill body through the soil cover layers. However, the O2 concentrations
inside the VP fluctuated around 8–15%. During the summer and autumn months (August,
September, and October), when there was no snow, the O2 concentrations dropped to below
5%, and the CH4 concentrations increased to 20% [Figure 24(a,b)]. Such phenomena provedthat the semi-aerobic mechanism was functioning. O2 is supplied into the waste mass from the
LCPs at the bottom due to the buoyancy effect, which is a product of the temperature difference
between the inside and outside of the landfill, and then it migrates to the waste layers near the
LFGVPs. The more the temperature difference increases, the greater the amount of O2 drawn
into the pipe network. As a result, aerobisation happens strongly at the waste layers close to the
LFGVPs.
The aim of semi-aerobic landfill is to promote aerobic biodegradation of organic wastes
within the landfill. To assess the aerobization of the semi-aerobic landfill, LFG temperatures of
LFGVPs should be measured. Figure 24(c) depicts the LFG temperature profiles of the main
LFGVP M2. The LFG temperatures have been monitored since 2010 (7 years after thelandfilling operation commenced).
The main LFGVP M2 showed the highest gas temperature of all the LFGVPs installedin the landfill area. The highest temperature recorded was 63.2°C at −4 m depth in January
2011, and the high-temperature trend continued until 2014. Figure 24(c) also indicates theelevated temperature of above 40°C from January 2010 to 2014. The high temperatures wereobserved particularly in early January and February. At that time, it was winter at the study site,
and the average daily ambient temperature was from −20°C to −5°C. The temperature
difference between the inside and outside of the LFGVP was greater than 60°C (Figure 23).
This affirms that the driving force of air flow in the semi-aerobic landfill increases in winter.
Yanase et al. (2010) measured the rate of air flow into the LCP for 1 year and found a high flowrate in winter and no air flow in summer. That explains why our measurements recorded hightemperatures in the landfill over the observation period.

45

4.1.4. The branch gas VP B10

The branch LFGVP B10 is located near the main LFGVP M2. At this location, theheight of the waste layers, including organic waste, was ~10 m. However, the average CH4
concentration of this branch LFGVP was highest (18.9%) among the surveyed LFGVPs.
Figure 25 shows that the gas temperatures at the exits were affected by air temperatures.
The LFG temperatures ranged from 7.1°C to 32.4°C. Meanwhile, the CH4 concentrations
ranged from 15% to 38% at the exit during 2,000 days (approximately 6 years) before declining
to 0% at the most recent observation. Clearly, the CH4 concentration of the branch LFGVP B10
was 2–3 times higher than that of the main LFGVP M2 (see Figures 20, 21, and 22).

Figure 25 The Landfill gas concentration and temperature and the CH4/CO2 ratio at the exitof the branch landfill gas venting pipe B10.
The ratio of CH4/CO2 ranged from 0.8 to 1.2 for 6 years before decreasing to 0. The factthat the LFG concentration was 0 in the most recent observation could be due to the46

disappearance of organic waste. In this case, the anaerobic condition could become more
dominant than the aerobic condition.
Figure 26(a,b) shows the CH4 and O2 concentration profiles of the branch LFGVP B10.
The CH4 concentrations ranged from 20% to 45%, whereas the O2 concentrations ranged,
approximately, from 0% to 10%. Apart from the measurement obtained in August 2010, the O2
concentration reached 0% and the CH4 concentration reached 45%. In other measurements, theCH4 concentration fluctuated from 20% to 38%, whereas the O2 concentration ranged from 3%
to 10%, and the temperature ranged from 10°C to 30°C [Figure 26(c)]. These indicators revealthat the anaerobic condition became dominant.

47

Figure 26 (a) CH4 concentration profile of the branch landfill gas venting pipe B10; (b) O2
concentration profile of the branch landfill gas venting pipe B10; (c) Temperature profile ofthe branch landfill gas venting pipe B10.
Figure 26(c) depicts the temperature profile of the branch LFGVP B10. The highest
temperature was 40°C at 0 m depth (at ground elevation) in September 2012, and a hightemperature trend was recorded in August 2010, when the gas temperature ranged from 22°C
to 32°C, with the highest value being at ground level. In general, the shape of the gas
temperature line of this LFGVP was different from the shape of the temperature line of the
LFGVP M2 (see Figure 24). In this case, as the O2 concentration remained between 3% and
10% inside the LFGVP [Figure 26(b)], it may be that the organic wastes near the LFGVP were
exhausted and the CH4 moved to the LFGVP from distant areas where anaerobic conditions
existed.
4.1.5. The average values of the gas temperature, CH4 concentration and the ratio of CH4/CO2

Figure 27 shows the average values of the gas temperatures, the CH4 concentrations,and the CH4/CO2 ratios at the exits of the surveyed LFGVPs (from December 2006 to February2014). The average LFG temperatures of the main LFGVPs (M1, M2, M3, and M4) were higher
than those of the branch LFGVPs. The average CH4 concentrations of the main LFGVPs were48

below 10%. In particular, the CH4/CO2 ratios of the main LFGVPs were below 0.8, whereas
the CH4/CO2 ratios of the branch LFGVPs ranged from 0.9 to 1.1. This means that there wasmore effective aerobic biodegradation at the main LFGVPs than that at the branch LFGVPs.

49

Figure 27 The average values of (a) the gas temperature and (b) CH4 concentrationsand (c) the CH4/CO2 ratio at the exit of the surveyed landfill gas venting pipes during theperiod from December 2006 to February 2014.
Although the branch LFGVPs B1, B2, and B3 showed average CH4/CO2 ratios of below
0.4 and average CH4 concentrations below 7%, the average LFG temperatures were below 20°C.
Thus, it may be that the anaerobic condition was still dominant. Another reason could be dueto the amount of organic matter within the waste mass exhausted.

50

4.1.6. Long-term temperature monitoring of geomembrane liner

In recent years, modern sanitary landfills have been designed with modern engineered
facilities to reduce the negative impacts on the environment and community. A barrier system
is one of the key components in waste disposal facilities. The main duties of the barrier system
are to isolate waste from the surrounding environment. The top barrier is to minimize thenuisance of waste disposal facilities from the community. The bottom one helps to protect the
groundwater and subsoil from contaminants of waste.
For modern waste disposal facilities, designing appropriately the bottom barrier (liner)
is very important to prevent dissolved contaminants from migrating to the underneath. Materials
for constructing the bottom liner could be low-permeability material layers such as naturalclayey deposits, compacted clay liners, geosynthetic clay liners. Recently, geomembrane liners
have been used in many applications over the world. Geomembranes (high-density
polyethylene) have been used as bottom liners in landfills for almost 30 years because of theiradvantages such as extremely low permeability (10-14 m/s), physical, biological and chemical
resistance.
Using the geomembrane liner at the bottom barrier layers of landfills showed significant
effectiveness in minimizing the migration of contaminants into groundwater. Nevertheless, if
the geomembrane liners have not been installed properly, technical faults during construction
lead to risks to the environment. In addition, geomembrane is a type of polymeric plastic
material (e.g., high-density polyethylene (HDPE) and polyvinyl chloride (PVC)), its physical,
mechanical and chemical properties are easily weakened as it exposed to high temperatures.
Heat is a primary byproduct of biodegradation of organic materials and also due tochemical and biochemical reactions occurring within the waste mass. The biological reactions
happening inside a typical landfill are exothermic by virtue of mechanisms of aerobic andanaerobic decomposition processes and expressed as below:
Anaerobic condition:

C6H12O6 → 3CO2 + 3CH4 + Heat

Aerobic condition:

C6H12O6 + 6O2 → 6CO2 + 6H2O + Heat

(1)
(2)

51

Pirt (1978) and Rees (1980) reported a heat generation value of 632 kJ/kg glucose foranaerobic digestion. Cooney, Wang and Mateles (1968) reported a heat generation value ofapproximately 110 kcal/mol oxygen (O2) (15,400 kJ/kg glucose) for aerobic digestion. Thus, it
is clear that aerobic decomposition generates a larger amount of heat from waste decomposition
than does anaerobic decomposition.
Heat or temperature affects engineering properties of wastes and properties andperformance of earthen and geosynthetic components of cover and bottom liner systems.
Temperatures within solid waste landfills in some areas with the different climatic conditions
over the world were recorded up to 60-90ºC (Yesiller et al, 2015). Incineration and combustion
ash-related reactions can generate temperatures up to 150oC (Calder et al, 2010). Such elevatedlandfill temperatures also affect the chemical, physical and biological processes in the landfill
and may have a significant impact on the service life of components of any engineered barriersystem [(Southen and Rowe, 2004), (Rowe, 2005), (Jafari et al, 2013), (Rowe et al, 2009).
HDPE and PVC geomembranes are sensitive to high temperatures which makemechanical and chemical properties change. This leads to a decrease in the bending stiffness,
reduction in resistance to chemicals, an increase in the process of thermo-oxidation which willcause antioxidant depletion in a geomembrane, potential desiccation in clay liners beneath ageomembrane, and an increase diffusion and/or moisture movement through liners (Rowe,1998).
Koerner and Koerner (2006) monitored the in situ temperature of geomembrane liners
at a dry cell and a wet cell of an MSW landfill in Pennsylvania, USA. The average temperature
was from 20oC – 30oC for the dry cell. For the wet cell, the temperature ranged from 25oC –46oC over a period of observation. Klein, Baumann, Kahapka and Niessner (2001) reported thatthe temperature of the geomembrane over clay (composite liner system) rose to 46oC and the
maximum temperature in the waste was 85oC within an MSW incinerator bottom ash landfill
in Ingolstadt, Germany. Yoshida and Rowe (2003) observed in situ landfill temperature ofTokyo Port Landfill where the waste was placed directly on the surface of a natural clayey liner
without geomembrane liners. The temperature ranged from 25oC – 50oC. And there is evidenceof landfill temperature above ambient temperature for more than 40 years. In some cases,
temperatures up to 80oC have been measured (Martin et al, 2013). The elevation of temperaturefrom 25oC to 90oC in bentonite-sand mixture layer reduces free swelling potential and strain

52

about 20 percent, this causes increasing in compressibility rate and quantities for this layer(Shariatmadari and Saeidijam, 2012).
In Japan, the first sanitary landfill with a geosynthetic liner was constructed in the
Nakata landfill in Chiba City in 1977. However, the final regulations requiring the barriersystems for all new sanitary landfills promulgated in October 1998 (Imaizumi et al, 2006). The
semi-aerobic landfill is a unique technology that was discovered in Fukuoka, Japan in 1975
(Shimaoka et al, 2000) and it became the compulsory standard for planning new landfills. There
has been a dozen of researches on the effective performance of semi-aerobic landfill technology
so far including both in lab-scale and full-scale. These advantages are (1) reducing methane
emissions, (2) reducing leachate intensity, (3) aerobic biodegradation happens effectively, (4)high landfill temperature which could speeds up the stabilization process, (5) cost-effectiveness.
However, there have been not so many researches about the influence of liner
temperature on the service life of the barrier system in semi-aerobic landfills. Therefore, thispaper discusses the observed LFG temperature and the temperature of the landfill barrier system
within an operating semi-aerobic landfill with the point of view of practical management oflandfills.

Figure 28 Air temperature and LFG temperature at the exit of LFGVP M2 over theobservation period
Figure 28 shows the results of air and LFG temperatures at the exit of LFGVP M2
during 2006-2018. The air temperature fluctuated from −20°C in winter to 25°C in summer.

53

The LFG temperatures rose to over 50oC (2 years after starting to place the waste) as a result of
the biodegradation of wastes in the landfill.
60
Air temperature
50

Temperature[ºC]

40
30
20
10
0
-10
-20

Dec-2019

Dec-2018

Dec-2017

Dec-2016

Dec-2015

Dec-2014

Dec-2013

Dec-2012

Dec-2011

Dec-2010

Dec-2009

Dec-2008

Dec-2007

Dec-2006

Dec-2005

Dec-2004

Dec-2003

Dec-2002

Dec-2001

Figure 29 Variations of average air temperatures
60
Leachate temperature
50

Temperature[ºC]

40
30
20
10
0
-10
-20
Dec-2019

Dec-2018

Dec-2017

Dec-2016

Dec-2015

Dec-2014

Dec-2013

Dec-2012

Dec-2011

Dec-2010

Dec-2009

Dec-2008

Dec-2007

Dec-2006

Dec-2005

Dec-2004

Dec-2003

Dec-2002

Dec-2001

Figure 30 Variations of average leachate temperatures versus time54

60
Geomembrane temperature
50

Temperature[ºC]

40
30
20
10
0
-10
-20
Dec-2019

Dec-2018

Dec-2017

Dec-2016

Dec-2015

Dec-2014

Dec-2013

Dec-2012

Dec-2011

Dec-2010

Dec-2009

Dec-2008

Dec-2007

Dec-2006

Dec-2005

Dec-2004

Dec-2003

Dec-2002

Dec-2001

Figure 31 The average observed geomembrane temperature under the LFGVP M2 with time
The measurement of temperatures (air, leachate, and geomembrane) has been started inearly July 2003. That time was summer in the region; therefore the average air temperatures
were from 12oC – 22oC. After that, the air temperature gradually decreased to less than -15oC
in winter (Figure 28). The lowest air temperature was -18oC in January 2008 and the highest
air temperature was 28oC in August 2010. Although the differences in air temperatures between
summer and winter were so large, there were no significant differences in temperaturebackground among years.
Figure 30 and Figure 31 show the average temperatures of leachate and geomembraneover the observation period. The average leachate temperatures ranged from 8oC (March 2004)
to 34oC (the end of August and early September 2012).
In the winters of the observation, the leachate temperatures and the geomembrane
temperature still remained over 8oC and 20oC, respectively (Figure 30 and Figure 31). During
the first 3 months from the beginning of the measurements, the leachate temperature increased
from 15oC to 22oC and the geomembrane temperature increased from 15oC to 25oC. The
increase in temperatures could be due to the aerobic decomposition of organic wastes happening
in the landfill.

55During the first 3 years from July 2003 to June 2006, the leachate temperatures only
fluctuated from 10oC to 25oC before increasing over 30oC in August 2006. The leachate
temperature often ranged from 20oC – 25oC in summers and from 8oC – 12oC in winters. It canbe seen that the leachate temperatures were affected by the air temperatures.
From 2004, the geomembrane temperature gradually increased to 35oC and remained
stable over 8 years before declining to 30oC in recent years. Obviously, the geomembrane
temperatures varied without any effect by the air temperature. As the unique structure of thesemi-aerobic landfill, the elevated temperature in the semi-aerobic landfill is a result of aerobic
biodegradation of organic materials caused by the buoyancy effect (Shimaoka et al, 2000). The
cause of the elevated temperatures in geomembrane is mainly due to the biodegradation oforganic solid waste or the heat of hydration of incinerated bottom ash which is the main factors
causing the generation of heat in the landfill [(Yesiller et al, 2015), (Koerner and Koerner, 2006),(Yoshida and Rowe, 2003)].
The aerobic decomposition within this semi-aerobic landfill strongly effected on waste
layers and geomembrane. Barrier systems were exposed to high-temperature conditions. Suchtemperature rise may result in degradation of geomembrane made by plastic and desiccation ofclay layer which composed of bentonite clay sheets. Elevated temperatures can reduce service
life HDPE geomembranes by accelerating antioxidant depletion of geomembranes and polymer
degradation. Rowe (2005) estimated the service life of HDPE geomembrane as exposed to hightemperatures.
Table 2 The service life of HDPE geomembrane based on an estimation of Rowe (2005)
Temperature (oC)Service life (years)

20565 – 90030

205 – 31535

130 – 190

40

80 – 12050

35 – 50

60

15 – 20

The temperature range under HDPE geomembrane at the operating semi-aerobic landfill
has remained from 30-35ºC. Therefore, according to the estimations of Rowe (2005), thelifetime of the geomembrane is from 130 to 315 years (see Table 2). Recently, thegeomembrane temperatures are gradually decreasing year by year because of less landfilling56

organic wastes for biodegradation. The risk of a high-temperature effect on barrier systems may
decrease, however, monitoring temperatures in LFG extraction wells and geomembrane is very
important for practical management of an operating semi-aerobic landfill.
The surveyed operating semi-aerobic landfill in Hokkaido shows the elevatedtemperatures in landfill gas and geomembrane under the LFGVP M2. The LFG temperature
increased over 40oC after 2 years from the beginning of placing the waste. The maximum of
LFG temperature was approximately 60oC. The high-temperature trend of LFG remained over
40oC in 7 years (2006-2013) as a result of the aerobic biodegradation of organic wastes. The
temperature of the geomembrane also rose to 30-35oC due to the effect of aerobic
biodegradation within the landfill. Such temperature rise may result in the risk of degradationof geomembrane made by plastic and desiccation of the clay layer of the barrier system. The
lifetime of HDPE geomembrane composed of a bottom barrier system could be reduced
significantly as exposed to high temperatures. Monitoring geomembrane temperature or thetemperature of the bottom barrier is very important for semi-aerobic landfill management.

57

4.2 Simulation results
This simulation focusing on calculating the pressure distribution, landfill gas
concentration and temperature distribution within the landfill body. To verify the quality of thesimulation, the calculated results will be compared to the observation results, for example thelandfill gas concentration at the exit of the landfill gas venting pipe M2.
4.2.1.1. Landfill gas pressure distribution

Figure 32 Simulated landfill gas pressure distribution in August 2014 (t=7 years after starting
the operation)
Gases accumulating in a landfill create areas of high pressure. Figure 32 indicated thatthe high LFG pressure is at the corner of the model, far awar from the surface and the gas well.
The LFG pressure near the vertical venting pipe or vertical gravel layer and near the surface isequal to the atmospheric pressure.

58

4.2.1.2. Landfill gas temperature distribution 2D

Figure 33 Simulated temperature distribution in August 2014 (t=7 years after starting theoperation)

Figure 34 Simulated landfill gas temperature distribution in 3D in August 2014 (t=7 years
after starting the operation)
59

Figure 33 showed that high temperature area are along the venting pipe, the verticalgravel layer and areas near the surface. The maximum temperature is 41.5oC. The aerobic
biodegradation happen effectively near surrounding the gas venting pipe or the vertical gravel
layer. Clearly, the imigration of oxygen concentration is the main driven promoting the aerobic
bacteria activities.
4.2.1.3. Gas concentration at the exit

Figure 35 Comparing the simulated LFG concentration and the observed LFG
concentration at the exit of the LFG venting pipe M2 (from 2006 to August 2014)
The calculated methane gas and carbon dioxide concentration are less than 10%. The
calculated methane gas looks fit with observed data.

60

4.2.1.4. The distribution of gas component around the LFG venting pipe

61

Figure 36 The distribution of gas component (a) CH4 concentration, (b) O2
concentration, (c) CO2 concentration, (d) N2 concentration in in August 2014 (t=7 years after
starting the operation)
High oxygen concentration only distributes along the venting pipe, the vertical graveland near the surface. Other areas far away from the gravel layer, the oxygen concentration is 0.
It means that the aerobisation only happens in the limited areas.
62

Methane gas and carbon dioxide concentration still maintain more than 30% from about
3-meters far from the vertical gravel layer and from 5-meters far from the surface. It can beconcluded that anaerobic condition is dominant.
From these above results, the usage of numerical simulation to predict the behaviors oflandfill such as LFG temperature and LFG concentration is applicable. This helps operators anddesigners be able to calculate the appropriate distance between the LFG venting pipes toimprove the stabilization of the landfill, for example, in landfill aeration projects.

63

64

CHAPTER 5: CONCLUSION

The dissertation attempted to survey the elevated temperature and gas components
inside an operating semi-aerobic landfill during 6 years from 2010 until 2018. Based on thiswork it is concluded that:-High landfill temperature can be observed in the landfill. The maximum
temperature is over 60C.

-

Aerobic biodegradation happens effectively in semi-aerobic landfill.

-

The temperature increase of one LFG extraction well will affect on the other if the
distance between 2 well is not so large.

-

Clogging phenomenon causes the high increase in methane concentration.

-

If clogging happens in many wells, a semi-aerobic landfill will be changed into
anaerobic landfill.

-

Need to prevent the clogging phenomena.

In addition, a basic simulation was implemented in order to model the movement of
LFG flow from waste layers through gravel layer, venting pipe discharging into atmosphere,
the heat transport and the mass transfer within the landfill body.
-

Simulation results showed the distribution of LFG pressure, the temperature
distribution, and the gas concentration at the exit of the gas venting pipe M2.

-

The simulated gas concentration looks fit with the observation gas concentration at
the exit of the gas venting pipe M2.

-

Gas well contributes to aerobisation from the top to the bottom surrounding thevertical gas well.

-

The visualized maximum temperature is 41.5˚C. The aerobic biodegradation happen
effectively near surrounding the gas venting pipe.
Numerical simulation can helps us predict (1) the biodegradation process happening
within the landfill which cannot be seen in reality; (2) the influence of factors on thestabilization of the landfill. This will help improve the design goals.
65

In the near future, the author will try to make a simulation of temperature distribution
and movement and transport of concentration of gas component within a landfill. In thesimulation, we will consider the effects of surrounding environmental conditions, oxygen
consumption, and water vapour transport on the heat generation and gas transport and how toaccelerate the high temperature inside a landfill. Further research will consider the effects oftemperature on the material of liner at the bottom of an operating semi-aerobic landfill.

----------------------------------------------------The end --------------------------------------------------

66