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
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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