Mohammed F.M. Abushammala

Regional landfills methane emission inventory in Malaysia

The decomposition of municipal solid waste (MSW) in landfills under anaerobic conditions produces landfill gas (LFG) containing approximately 50—60% methane (CH4) and 30—40% carbon dioxide (CO2) by volume. CH4 has a global warming potential 21 times greater than CO2; thus, it poses a serious environmental problem. As landfills are the main method for waste disposal in Malaysia, the major aim of this study was to estimate the total CH4 emissions from landfills in all Malaysian regions and states for the year 2009 using the IPCC, 1996 first-order decay (FOD) model focusing on clean development mechanism (CDM) project applications to initiate emission reductions. Furthermore, the authors attempted to assess, in quantitative terms, the amount of CH4 that would be emitted from landfills in the period from 1981—2024 using the IPCC 2006 FOD model. The total CH4 emission using the IPCC 1996 model was estimated to be 318.8 Gg in 2009. The Northern region had the highest CH4 emission inventory, with 128.8 Gg, whereas the Borneo region had the lowest, with 24.2 Gg. It was estimated that Pulau Penang state produced the highest CH4 emission, 77.6 Gg, followed by the remaining states with emission values ranging from 38.5 to 1.5 Gg. Based on the IPCC 1996 FOD model, the total Malaysian CH 4 emission was forecast to be 397.7 Gg by 2020. The IPCC 2006 FOD model estimated a 201 Gg CH4 emission in 2009, and estimates ranged from 98 Gg in 1981 to 263 Gg in 2024.

Empirical gas emission and oxidation measurement at cover soil of dumping site: example from Malaysia

Methane (CH4) is one of the most relevant greenhouse gases and it has a global warming potential 25 times greater than that of carbon dioxide (CO2), risking human health and the environment. Microbial CH4 oxidation in landfill cover soils may constitute a means of controlling CH4 emissions. The study was intended to quantify CH4 and CO2 emissions rates at the Sungai Sedu open dumping landfill during the dry season, characterize their spatial and temporal variations, and measure the CH4 oxidation associated with the landfill cover soil using a homemade static flux chamber. Concentrations of the gases were analyzed by a Micro-GC CP-4900. Two methods, kriging values and inverse distance weighting (IDW), were found almost identical. The findings of the proposed method show that the ratio of CH4 to CO2 emissions was 25.4xa0%, indicating higher CO2 emissions than CH4 emissions. Also, the average CH4 oxidation in the landfill cover soil was 52.5xa0%. The CH4 and CO2 emissions did not show fixed-pattern temporal variation based on daytime measurements. Statistically, a negative relationship was found between CH4 emissions and oxidation (R2u2009=u20090.46). It can be concluded that the variation in the CH4 oxidation was mainly attributed to the properties of the landfill cover soil.

Modeling of methane oxidation in landfill cover soil using an artificial neural network

Knowing the fraction of methane (CH4) oxidized in landfill cover soils is an important step in estimating the total CH4 emissions from any landfill. Predicting CH4 oxidation in landfill cover soils is a difficult task because it is controlled by a number of biological and environmental factors. This study proposes an artificial neural network (ANN) approach using feedforward backpropagation to predict CH4 oxidation in landfill cover soil in relation to air temperature, soil moisture content, oxygen (O2) concentration at a depth of 10 cm in cover soil, and CH4 concentration at the bottom of cover soil. The optimum ANN model giving the lowest mean square error (MSE) was configured from three layers, with 12 and 9 neurons at the first and the second hidden layers, respectively, log-sigmoid (logsig) transfer function at the hidden and output layers, and the Levenberg-Marquardt training algorithm. This study revealed that the ANN oxidation model can predict CH4 oxidation with a MSE of 0.0082, a coefficient of determination (R 2) between the measured and predicted outputs of up to 0.937, and a model efficiency (E) of 0.8978. To conclude, further developments of the proposed ANN model are required to generalize and apply the model to other landfills with different cover soil properties. Implications: To date, no attempts have been made to predict the percent of CH4 oxidation within landfill cover soils using an ANN. This paper presents modeling of CH4 oxidation in landfill cover soil using ANN based on field measurements data under tropical climate conditions in Malaysia. The proposed ANN oxidation model can be used to predict the percentage of CH4 oxidation from other landfills with similar climate conditions, cover soil texture, and other properties. The predicted value of CH4 oxidation can be used in conjunction with the Intergovernmental Panel on Climate Change (IPCC) First Order Decay (FOD) model by landfill operators to accurately estimate total CH4 emission and how much it contributes to global warming.

Evaluation of methane generation rate and potential from selected landfills in Malaysia

Methane emissions and oxidation were measured during the wet and dry seasons at the Air Hitam, Jeram, and Sungai Sedu landfills in Malaysia. The resulting levels of methane emissions and oxidation were then modeled using the Inter-governmental Panel on Climate Change 1996 first order decay (FOD) model to obtain methane generation rate and potential values. Emissions measurements were performed using a fabricated static flux chamber. A combination of gas concentrations in soil profiles and surface methane and carbon dioxide emissions at four monitoring locations in each landfill was used to estimate the methane oxidation capacity. The methane potential value was 151.7xa0m3xa0t−1 for the Air Hitam and Jeram sanitary landfills and 75.9xa0m3xa0t−1 for the Sungai Sedu open dumping landfill. The methane generation rate value of the Jeram and Air Hitam sanitary landfills during the wet season was 0.136xa0year−1, while that of Jeram during the dry season was 0.072xa0year−1. The methane generation rate values of the Sungai Sedu open dumping landfill during the wet and dry seasons were 0.008 and 0.0049xa0year−1, respectively. The observed values of methane generation rate and potential assist to accurately estimate total methane emissions from Malaysian landfills using the Inter-governmental Panel on Climate Change FOD model.

Assessment of methane emission and oxidation at Air Hitam Landfill site cover soil in wet tropical climate.

Methane (CH4) emissions and oxidation were measured at the Air Hitam sanitary landfill in Malaysia and were modeled using the Intergovernmental Panel on Climate Change waste model to estimate the CH4 generation rate constant, k. The emissions were measured at several locations using a fabricated static flux chamber. A combination of gas concentrations in soil profiles and surface CH4 and carbon dioxide (CO2) emissions at four monitoring locations were used to estimate the CH4 oxidation capacity. The temporal variations in CH4 and CO2 emissions were also investigated in this study. Geospatial means using point kriging and inverse distance weight (IDW), as well as arithmetic and geometric means, were used to estimate total CH4 emissions. The point kriging, IDW, and arithmetic means were almost identical and were two times higher than the geometric mean. The CH4 emission geospatial means estimated using the kriging and IDW methods were 30.81 and 30.49xa0gxa0m−2xa0day−1, respectively. The total CH4 emissions from the studied area were 53.8xa0kgxa0day−1. The mean of the CH4 oxidation capacity was 27.5xa0%. The estimated value of k is 0.138xa0year−1. Special consideration must be given to the CH4 oxidation in the wet tropical climate for enhancing CH4 emission reduction.