Methane Recovery from Landfills
Utilization as a Potential Energy Source and Impact on Reduction of Green House Gasses
According to The Conference Board of Canada, current Canadian municipal solid waste (MSW) generation levels are approximately 30 million tonnes per year, with a rate of 894 kg per capita, 67 percent of which is landfilled. (Jones L. et al. 2002) Sanitary landfills burry MSW under soil, sanctioning a complex series of reactions to occur, where anaerobic microorganisms decompose a portion of the organic fraction of the waste producing methane and carbon dioxide. Methane generation and emission from landfills are topics of major interest due to methane's role in the greenhouse effect, migration of hazard potential, health and safety issues and energy applications. The objective of this literature review is to provide a concise relationship between MSW and landfill gasses (LFG), details of potential methods used for capturing methane as appose to emitting the gas as well as the benefits of doing.
Rendering to information written by D.R. Reinhart and T.G. Townsend (1998), MSW contains approximately 50 – 70 % of biodegradable material, such as food, paper, wood, and garden trimmings. Once MSW is deposited into a landfill, it undergoes a number of biological, physical and chemical changes. These changes are greatly dependent on site conditions, waste characteristics, temperature, quantity of oxygen, moisture content and other factors. (Nozhevinikova et al. 1993)
The most important reactions occurring within the landfill are those involving the microbes which begin to consume the carbon in the organic material, in turn causing the decomposition and eventually leading to the evaluate of LFG.
In sanitary landfills, the process of burying waste and regularly covering deposits with a low permeability material creates an internal anaerobic environment that favors
methane producing bacteria since the presence of oxygen is lacking. Pathways leading to the production of methane and carbon dioxide from anaerobic digestion of organic fraction of solid waste are briefly described bellow: 1)
Decomposition of organic matter- In this preliminary process, compounds of higher molecular mass (Lipids, proteins, nucleic acids etc.) are transformed into intermediate mass compounds making them much more suitable for the microorganisms as a source of energy and cell carbon 2)
Conversion of decomposed matter to Organic Acid- In this phase, the existing microorganisms convert the intermediate molecular mass compounds into lower molecular mass compounds such as compel organic acids. 3)
Conversion of Acetic Acid to Methane Gas- During this stage, the microorganisms transform the acetic acid into methane (CH4) and carbon dioxide (CO2) gasses.
(Cassia de Brito Galvao, T. and Pos, W.H. 2002)
As the solid waste decomposes in landfills, the gas which is emitted is composed of approximately 50 percent CH4 and 50 percent CO2, both of which are green house gasses (GHG) (Bingemer, H G., & Crutzen, P. J. 1987)
With Landfilling being the primary source of disposal of MSW around the world, (Encyclopedia Britanica 2012) methane emissions from landfill represent the largest source of GHG emissions from the waste sector, contributing around 700 Mt CO2-e. (United Nations Environmental Programme 2012) As recorded by Environment Canada (2010), similar trends exist nationally with emissions from Canadian landfills accounting for 20% of the total national methane emissions. Information gathered in a thesis prepared by Palananthakumar, B. (1991) outlines the proportion of methane produced world wide from landfills, and can be seen illustrated graphically below in Figure 1.0.
Figure 1.0: % of Methane Production Contributions Worldwide from Landfill
Existing research leads to the...
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