Browsing by Author "Ranasinghe, RHK"

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item: Thesis-Abstract
Effect of compaction and moisture content on gas transport and water retention in landfill cover soil : Maharagama landfill as a case study
Ranasinghe, RHK; Nawagamuwa, UP; Kawamato, K
In Sri Lanka, Engineered landfills are not being used and only very few controlled landfills are available. The usual procedure is to cover the waste with a good cover soil without providing gas venting facilities. This can be found at Maharagama dumpsite too. Hazardous gaseous and liquid landfill emissions are major problems of landfills. Since gas venting facilities are not provided, pressure inside the waste layer is very high compared to the atmosphere. Hence cover soil of the waste disposal site plays a major role in emission of landfill gases. Once the solid waste is covered with soil these gases are released to the atmosphere with high pressure, through this cover soil. Therefore studying the cover soil parameters are of paramount importance in evaluating and predicting its future gas emission. The Soil gas diffusion coefficient (Dp) and Air Permeability (ka) govern transport and emission of gases to the atmosphere such as of green house gases and volatile organic chemicals in the unsaturated zone. Further, considering gas diffusion coefficient in free air (Do) in this study, soil gas diffusivity (Dp/Do) and air permeability (ka) were measured in the soil which was used as the cover soil of Maharagama waste disposal site. The objectives of the research study were (a) to study about the gas transport parameters of landfill cover soil and (b) to understand effect of compaction and moisture content of the soil on the gas diffusivity (Dp/Do) and air permeability (ka). Measurements were done in 100cm3 repacked soil samples at different compaction levels with the existing moisture contents( normal compacted samples) and soil water matric potentials from pF= 1, 1.5,2,3,4.1 ( pF = -log,!" If'matric potential in em H20), air dried and oven dried conditions( pF controlled samples). In-situ air permeability was measured at the field in order to compare the laboratory and field measurements. At the same time the methane concentration in the research area was measured and a methane concentration contour map was produced. The air permeability changes from 0 to 100 flm2 while the soil air content varies from 0 to 0.35 m3 m", For the pF controlled samples kavaries from 0 to 100 flm2 and soil air content varies from 0.02 to 0:35 m3 m-3. In the case of normal compacted sojl sample leavaries from 0 to 80 Jlm2 while the soil air content varies from 0 to 0.28 m3 mo3. The soil gas diffusivity changes from 0 to 0.09 for the pF controlled samples and o to 0.07 for the normal compacted samples. The increase of dry density and reduction of water content increases the amount of soil air content and hence increased the soil gas transport parameters. At the fully dry condition and the with the maximum soil air content and the gas diffusion is around 9% of the gas diffusion coefficient in free air. With dry conditions the changes of soil structure properties also affects the soil gas transport, especially for the soil air permeability. According to the methane concentration contour map the methane concentration is very close to the atmospheric methane concentration all around the ground area except at few hot spots. Considering the results of this research, Maharagama waste disposal site final cover soil can be expressed as a very less gas exchangeable material. However, it is a very good capping material and the produced landfill gas from the waste layer is trying to migrate through the loosely compacted points around the ground area (high methane concentration was observed in few loosely compacted points). Methane concentration contour map further verifies the experimental results. At the same time, due to low gas exchange through the cover soil, the waste layer will be maintained in an anaerobic condition and hence the green house gas (methane) production is definitely enhanced. In the future, methane emission could be increased through the loose compacted points. These points can become (hotspots) and the formation of the cracks around the ground area would also be possible with time.A long term study is needed to observe the future gas emission at this location.
item: Article-Abstract
Gas exchangeable properties of "Maharagama" open dump cover soil
Ranasinghe, RHK; Nawagamuwa, UP; Wickramarachchi, PNK; Kawamoto, K
In Sri Lanka, normal practice is to dump waste in low lands and cover with a good compacted soil without providing gas venting facilities. This can be found at 'Mahargama' dumpsite too. Once municipal solid waste is placed in landfills, complex sequence of biologically, chemically and physically mediated events occur relating to hazardous gaseous and liquid landfill emissions. Hence, cover soil of landfills/ open dumps plays a major role in emission of landfill gases, because gases are released to atmosphere with high pressure, through cover soil. Therefore, studying gas transport parameters of cover soil are of paramount importance in evaluating its future gas emission. Soil gas diffusion coefficient (Dp)and Air Permeability (ka) govern transport and emission of gases through soil. In this study, these parameters were measured in repacked samples at different water matric potentials. Methane concentrations were measured in site and a methane concentration contour map was produced to identify the gas emission from landfill. According to the observed data, the Maharagama cover soil can be expressed as a less gas exchangeable material (but a good capping soil). In the future methane emission can be increased through the loose compacted points and this can become hotspots. Further, formation of cracks around the ground area will also be possible.
item: Article-Abstract
Measurement of gas transport parameters for final cover soil at Maharagama landfill in Sri Lanka
Wickramarachchi, PN; Ranasinghe, RHK; Nawagamuwa, UP; Kawamoto, K
To make a proper evaluation and better understanding of gas component movement inside a landfill site, investigation of the different parameters related to gas flow is important. In this study, air permeability (ka) and gas diffusivity (DP/Do; where Do is the gas diffusion coefficient in free air) were measured as a function of soil air content (D} in final cover soil at Maharagama landfill in Sri Lanka. The ka and D, were measured at different gravimetric water content in some samples and another set of samples were treated under different pF conditions (pF= log (-'¥) where '¥ is the soil water matric potential in H2O a) and water blockage parameter (.i..) were calculated accordingly.
item:
Study on gas transport and water retention In landfill cover solI : a Sri Lankan case study
Ranasinghe, RHK; Nawagamuwa, UP; Wickramarachchi, PN; Kawamoto, K; Komatsu, T
In Sri Lanka, engineered landfills are not usually available and the common procedure is to cover the waste with a good cover soil without providing gas venting facilities. Hazardous gaseous and liquid landfill emissions are major problems of landfills. Hence cover soil of the landfill plays a major role in emission of landfill gases, because once the solid waste is covered with soil these gases are released to atmosphere with high pressure, through this cover soil. Therefore, studying the cover soil parameters are paramount importance in evaluating its future gas diffusion. The Soil gas diffusion coefficient (Dp) and permeability (ka) govern the transport and emission gases in the unsaturated zone. In this study, "V>ll'I'.0'" diffusivity (DplDo, Do is gas diffusion coefficient in free air) and k, was measured for the soil ofMaharagama landifill final cover soil at different soil water matric potentials
item: Conference-Extended-Abstract
Study on gas transport and water retention in maharagama land fill cover soil
(2009) Ranasinghe, RHK; Nawagamuwa, UP; Kawamoto, K
In Sri Lanka there are few controlled landfills available and usual procedure is covering the waste layer with a good toil as a final cover. The Soil gas diffusion coefficient (Dp) and Air Permeability (Kcl) govern the transport and mission of gases in unsaturated zone. In this study, Dp and Ka in soil which was used to construct Maharagama yandfdl site cover filling at different soil water matric potential were measured. With the soil air content, it is found hat, Dp monotonically increases and Ka gradually increases.