Seasonal Variation of Landfill Methane Emissions from ... - JGSEE

The 2 nd Joint International Conference on “Sustainable Energy and Environment (SEE 2006)”
D-026 (O) 21-23 November 2006, Bangkok, Thailand
Seasonal Variation of Landfill Methane Emissions from Seven Solid Waste Disposal Sites in Central
Thailand
Komsilp Wang-Yao 1,* , Sirintornthep Towprayoon 1 , Chart Chiemchaisri 2 , Shabbir H. Gheewala 1 and
Annop Nopharatana 3
1 The Joint Graduate School of Energy and Environment, King Mongkut’s University of Technology Thonburi, Bangkok, Thailand
2 Department of Environmental Engineering, Faculty of Engineering, Kasetsart University, Bangkok, Thailand
3 Pilot Plant Development and Training Institute, King Mongkut’s University of Technology Thonburi, Bangkok, Thailand
Abstract: Landfill gas (LFG) consists of 50 – 60 vol. % methane, 30 – 40 vol. % carbon dioxide and trace amounts of numerous
chemical compounds. Pressure, concentration and temperature gradients that develop within the landfill result in gas emissions to the
atmosphere and in lateral migration through the surrounding soil. Measurements were performed at seven solid waste disposal sites,
located in central Thailand including 3 sanitary landfills, and 4 open dumps. The methane emission measurements were conducted
from September to November 2005 for wet season data and from January to February 2006 for dry season data. Emissions fluxes of
methane at each point were calculated in g/m 2 /d. 88.4% of sampling runs fulfilled the R 2 >0.5 criterion for dC/dt (75% had values of
R 2 > 0.9). From 188 closed flux chamber results in wet season, the spatial variability of the local emissions is quite high (ranging
between 0 – 825.79 g/m 2 /d) but the average spatial emissions ranged between 5.45 – 129.79 g/m 2 /d. The spatial variability of the local
emissions in dry season is lower than emissions in wet season (ranging between 0 – 686.93 g/m 2 /d) but the average spatial emissions
ranged between 1.00 – 23.40 g/m 2 /d. Thus, the amount of LFG collected by extraction in dry season may be lower than in the wet
season.
Keywords: Landfill Gas, Methane Emission, Flux Chamber
1. INTRODUCTION
Landfill gas (LFG), originating from the anaerobic biodegradation of the organic content of waste, consists of 50 – 60 vol. %
methane, 30 – 40 vol. % carbon dioxide and trace amounts of numerous chemical compounds [1]. One ton of municipal solid waste
results in approximately 160 – 250 m 3 of landfill gas. Pressure, concentration and temperature gradients that develop within the
landfill result in gas emissions to the atmosphere and in lateral migration through the surrounding soils [2,3]. The migration and
emission of LFG may potentially lead to negative effects in the surrounding such as explosion hazards, health risks, damage to
vegetation, odor nuisances, groundwater contamination, and global climate effects [4]. The total global methane emissions have been
estimated at 500 Tg/year and landfills contribute 40 Tg/year, 8% of the total [5]. The IPCC estimates that landfill emissions are 7% of
the total global methane emissions [6]. Moreover, landfills are the rank third in anthropogenic methane sources, right after rice
paddies and ruminants [7].
Emissions are dependent on annual rates of waste generation, composition of the solid waste, landfill burial practice,
methanotrophic methane oxidation, and methane recovery for commercial use. Previous studies have indicated that rates for landfill
methane emissions and oxidation range over 6-7 orders of magnitude with optimum rates for both processes exceeding observed rates
for other methane sources. Field measurements of net methane emissions range from 4000 g m -2 day [8]. There are few
available landfill methane emissions measurements to compare sites with different waste age, season, and landfill management
practices in Thailand.
The objective of this study is to investigate the landfill methane emissions characteristics for the seasonal and to use the model to
predict the total amount of LFG generated. Three major aspects have been studied. Firstly, surface methane emissions were observed.
Secondly, emissions ratio between wet season and dry season were studied. Finally, the results obtained from field investigation have
been modeled with the first order decay model (FOD) to obtain the decay rate constant.
2. METHODOLOGY
2.1 Site Description
Landfilling and open dumping are the most common ways of municipal solid waste (MSW) disposal in developing countries. In
Thailand, about 30% of MSW is disposed by landfilling, 70% by open dumping, and 1% by incineration. Measurements were performed
at seven solid waste disposal sites, located in central Thailand including 3 sanitary landfills, and 4 open dumps. The study sites selected
are summarized in Table 1. The methane emission measurements were conducted from September to November 2005 for wet season
data and from January to February 2006 for dry season data. The location of study sites are shown in Figure 1.
Corresponding author: komsilp@gmail.com
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The 2 nd Joint International Conference on “Sustainable Energy and Environment (SEE 2006)”
D-026 (O) 21-23 November 2006, Bangkok, Thailand
Table 1 Characteristics of study sites
Site Disposal practice Began
operation
Waste stream
(tons/day)
Waste in place
(tons)
Landfilling area
(hectares)
Pattaya sanitary landfill 2002 245 ~350,000 22.4
Cha Am sanitary landfill 2000 56 ~50,000 19
Hua Hin sanitary landfill 1998 68 ~160,000 12
Nonthaburi open dump 1986 850 ~5,500,000 29.8
Nakhonpathom open dump 1997 180 ~590,000 5
Samutprakan open dump 1999 80 ~180,000 2.5
Rayong open dump 1998 70 ~114,000 3.5
Fig. 1 Location of sanitary landfill sites
2.2 Methane emission rates and gas analysis
Flux chamber technique consists of trapping the gas as it leaves the soil surface, either by allowing the gas to build up in a closed
enclosure (closed or static chamber technique), or by removing and measuring the gas as it leaves the enclosure (open or dynamic
chamber technique) [9]. Methane emission rates from the landfill surface in this study were determined using the static chamber
technique. Static chambers are the most frequently used technique for the measurement of gas fluxes from soils. The chamber
technique is low in cost, and simple to operate but extremely labor and time intensive [10]. The chambers used in this study were
constructed with 0.40 m. - PVC pipe, 0.25 m. in height having PVC cap at the top of chamber. To protect the air intrusion,
chambers were sealed to the ground by firming soil around the outside. Methane samples were collected from a chamber after1, 2, 3,
and 4 minutes using 60-mL plastic syringes fitted with plastic valves. These gases were contained in 10-mL vacuum tube. Samples
were analyzed on a gas chromatograph equipped with a flame ionization detector. Methane flux was determined from concentration
data (C in ppmv) plotted versus elapsed time (t in minutes). The data generally showed a linear relationship, in which case dC/dt is
the slope of the fitted line. The methane flux, F (g/m 2 /d), was then calculated in Equation 1 as follows:
F = V/A (dC/dt) Equation 1
Where V is chamber volume and, A is the area covered by the chamber. The slope of the line, dC/dt, was determined by linear
regression between CH 4 concentration and elapsed time.
In order to conduct the flux chamber measurements, numerous samples were collected across the landfill or open dump surface on
a regular grid pattern at 30 – 40m intervals. Precipitation was absent and barometric pressure and ambient wind speed, factors which
are known to affect emissions, were relatively constant during this period.
2.3 Geospatial distribution
The major disadvantage of the chamber measurements having a small footprint so a large number of sampling points should be
provided for detailed spatial distribution study. However, in order for the geospatial analysis to be of value, proper interpolation
methodology must be applied. These methods offer the potential of calculating whole site emission estimates from limited point
measurements, which could lead to improving overall national inventories for global landfill methane emission estimates [11].
Geospatial distributions of the methane emissions in this study were estimated by Kriging method. Kriging refers to the process of
using the spatial dependency to predict the value of a property at unknown location from the relationship observed in the sampling
location. The weight for the kriging analysis was decided by semivariogram. Mapping software Surfer by Golden Software was used
to analyse the geospatial distribution in this study. The kriging model was applied to map the results, and the volumetric value of the
contour map was estimated by volume and area integration algorithms in Surfer.
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The 2 nd Joint International Conference on “Sustainable Energy and Environment (SEE 2006)”
D-026 (O) 21-23 November 2006, Bangkok, Thailand
2.4 LFG generation model
There are a variety of methods that can be used to evaluate the feasibility and potential benefits of collecting and using the
generated landfill gas for energy recovery or other uses. However, the Mexico Landfill Gas Model (Mexico LFG Model) is generally
recognized as being the widely used approach. The landfill gas generation rates are estimated by the model along with estimates of
the efficiency of the collection system in capturing generated gas, known as the collection efficiency. The model provides landfill gas
recovery estimates by multiplying the landfill gas generation by the estimated recovery efficiency as follows in Equation2:
n
−kt Q = ∑2
( i
M
kLoM
i
e ) Equation 2.
i=
1
Where:
n
∑ = sum from opening year+1 (i=1) through year of projection (n)
i = 1
Q
M
= maximum expected LFG generation flow rate (m 3 /yr)
k = methane generation rate (year -1 )
L
o
= potential methane generation capacity (m 3 /Mg)
M
i
= mass of waste accepted in the i th year (Mg)
t
i
= age of the waste disposed in the i th year (years)
The L o value is dependent on the composition of the waste, and in particular, the fraction of organic matter present. The L o value is
estimated based on the carbon content of the waste, the biodegradable carbon fraction, and a stoichiometric conversion factor.
According to IPCC, a variation from less than 100 to more than 200m³ of CH 4
per ton of waste is indicated [12]. Normally, L o
adapted to European waste, with approximately 30% of organic matter, is 100 m³/ton of waste. By using average study site waste
composition and landfilling practice with IPCC method, 100 m³ of CH 4
per ton of waste is obtained for Pattaya, Cha-Am and Hua-
Hin landfill site. 80 m³ of CH 4
per ton of waste is obtained for Nakhonpathom dump site. 40 m³ of CH 4
per ton of waste is obtained
for Rayong dump site.
The methane generation rate constant (k) determines the rate of generation of methane for refuse in the landfill. The k value is a
function of a number of factors including refuse moisture content, availability of nutrients for methanogens, pH, and temperature.
The values of k can range from 0.003 per year to 0.21 per year [13]. In Thailand, a larger fraction of readily biodegradable organic
matter and high moisture content could be a reason to expect a larger value of k. The k value of 0.15 per year was calculated based on
Thai waste composition [14].
3. RESULTS AND DISCUSSION
3.1 Methane emissions
Studies were carried out at 7 sites as mentioned earlier. Measured methane emissions from different waste disposal techniques are
presented in Table 2 for both wet season and dry season. Emissions fluxes of methane at each point were calculated in g/m 2 /d. 88.4%
of sampling runs fulfilled the R 2 >0.5 criterion for dC/dt (75% had values of R 2 > 0.9). Mapping software Surfer was used to analyse
the geospatial distribution and average spatial emissions in all study sites.
Table 2 Methane emissions at 7 disposal sites in wet season and dry season
CH 4 emissions in wet season
CH 4 emissions in dry season
Average
spatial
emissions
(g/m 2 /d)
Average
spatial
emissions
(g/m 2 /d)
Emission ratio
(wet season/dry
season)
Site
Range
Number
of test
points
Range
Number
of test
points
Pattaya 0.38 – 697.85 40 129.79 0.00 – 686.93 41 23.40 5.55
Cha-Am 0.00 – 58.24 30 5.45 0.00 – 8.45 31 1.00 5.45
Hua-Hin 0.00 – 295.82 30 51.79 0.00 – 117.00 40 10.31 5.02
Nakhon Pathom 0.00 – 825.79 30 7.89 0.00 – 38.09 32 4.17 1.89
Nonthaburi 0.00 – 358.22 20 3.94 0.00 – 19.94 20 1.64 2.40
Rayong 0.00 – 22.79 22 2.44 0.00 – 2.89 20 1.00 2.44
Samutprakan 0.00 – 724.09 16 12.21 0.00 – 14.28 16 4.82 2.53
From 188 closed flux chamber results in wet season, the spatial variability of the local emissions is quite high (ranging between 0
– 825.79 g/m 2 /d) but the average spatial emissions ranged between 5.45 – 129.79 g/m 2 /d. It can be seen from Table 2 that the
methane emission for wet season is 5 times that for dry season in landfill whereas it is only 2 times in open dump.
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The 2 nd Joint International Conference on “Sustainable Energy and Environment (SEE 2006)”
D-026 (O) 21-23 November 2006, Bangkok, Thailand
3.2 Methane generation rate
The study site’s information including L o , disposal area and waste disposal history were used to evaluate the value of k by fit with
experimental data in the Mexico LFG Model. The obtained values of k are summarized in Table 3. It is clear that the values of k are
higher in wet season than dry season by about 7.5 – 9.6 times for landfills but varied between 2.1 – 11.5 times for open dump sites.
Table 3 The obtained value of methane generation rate (k)
Site Landfilling Condition k-wet season (yr -1 ) k-dry season (yr -1 )
Pattaya Managed - Deep 0.192 0.020
Cha-Am Managed - Shallow 0.040 0.005
Nakornprathom Unmanaged - Deep 0.005 0.002
Hua-Hin Managed - Deep 0.138 0.016
Nontaburi Unmanaged - Deep 0.0003 0.0001
Rayong Unmanaged - Shallow 0.013 0.004
Samutprakan Unmanaged - Deep 0.013 0.001
4. CONCLUSION
Measurements for methane emission were performed at seven solid waste disposal sites, located in central Thailand including 3
sanitary landfills, and 4 open dumps. 88.4% of sampling runs fulfilled the R 2 >0.5 criterion for dC/dt (75% had values of R 2 > 0.9).
The spatial variability of the local emissions in wet season is quite high (ranging between 0 – 825.79 g/m 2 /d) but the average spatial
emissions ranged between 5.45 – 129.79 g/m 2 /d. The spatial variability of the local emissions in dry season is lower than emissions in
wet season (ranging between 0 – 686.93 g/m 2 /d) but the average spatial emissions ranged between 1.00 – 23.40 g/m 2 /d. The obtained
values of k that used for methane emissions calculation ranged from 0.04000 – 0.19200 and 0.00530 – 0.02000 in landfills for wet
season and dry season, respectively. The obtained values of k for open dump sites ranged from 0.00030 – 0.01340 and 0.00012 –
0.00420 for wet season and dry season, respectively. The emissions in wet season are much higher than dry season. The moisture
content in waste disposal body might be the main cause for these phenomena.
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