This section of exploration of potential energy sources is only meant as an indication for further investigations. For me it was important to get an idea about the potential of this energy source and to be familiar with its exploitation method. Nevertheless, I do not want to explore this matter in depth, because this would certainly break the frame of this project.
The landfill "lixao do Alvarenga" is, due to the ongoing de-composting processes within the fill, continuously producing a methane/CO2 cocktail gas. This gas can be used for cooking purposes (difficult!!) and to drive compressors for electricity production. The 114,778-m2 area of landfill hold approximately 2.295,569 m3 of waste. At least 30% of this waste is of organic origin and partially transforms into gas. As a rule of thumb, one can say, that 1 Kg of solid organic matter produces 1 m3 of methane.
This landfill gas, as it comes out of the ground is 21 times as harmful to the environment as CO2. The methane contents have to be higher than 40% in order to be used for electricity production. The share of methane can be manipulated through the application of anaerobic bacteria. Landfill gas with a share of methane higher than 40% produces 1,5 kW electricity per m3. In order to cover the electricity demand for Sitio Joaninha, 480.000 m3 landfill gas is required per year, which is equivalent to 480 t of solid organic matter or 55 m3/h. The total of organic matter deposited within the landfill "lixao do Alvarenga" should be around 68,876 t. I do not know, who much of this is already composted but according to the following table, the available gas, with a capturing level of 70% should give electricity to Sitio Joaninha until approx. the year 2025. Until then, a variable surplus between 100 - 800% annually can be expected.
Source: with permission of: Tallner@t-online.de
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The exploitation of the gas is done through gas wells, which are vertically adjustable, because of the setting of the landfill. One should not forget, that gas is matter transformed and therefore equivalent to a certain mass volume, which will be slowly subtracted from this huge pile of waste. |
 Source: http://entsorgungszentrum.de/Service /Technik/Bhkw/Gas.htm |
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The number of gas wells, are interconnected by a pipe system, which leads to an either mobile or fixed station. Here the gas flow from each well is controlled and the quality differences adjusted, so that the gas mixture always has the same share of methane. This allows the combustion engines to run better. As These engines not only produce gas but also heat, this heat can be used to dry fruits. |
 Source: http://entsorgungszentrum.de/Service /Technik/Bhkw/Gas.htm |
But before one can think about the gas harvesting, one has to solve the problem, that the landfill is due to its continuous production of leachate a great hazard to the environment and in particular to the nearby water reservoir of Billings.
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The physical stability of the landfill has to be first examined and then, if necessary reinforced. The geographical situation of the landfill does permit in my opinion, that the landfill receives only a surface seal, which reduces the cost for its regeneration immensely. Nevertheless, this seal is necessary to prevent any further rainwater penetration and therefore the reduction of leachate. But, the reduction of humidity within the landfill can also lead to an early stop of de-composting and therefore to an end of methane production. To seal the ground of the landfill is a far more expensive operation but a lot more effective. The leachate could be used for further production of methane and drained under supervision in order to clean it. Thus the pollution of the Billings reservoir from this source could finally come to an end. |
 Source: www.uni-weimar.de/Bauing/wbbau /studium/zusatz/ww63k09schnupper.pdf |
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Which kind of seal will be deployed, depends on the final classification of the landfill. There is also the possibility of deployment of different materials for the actual seal layer. Traditionally the use of soils rich in clay and silt are recommended. Field studies though, showed, that the persistence of such layers as far as sealing is concerned is limited. A capillary system out of layers of sand with different coarseness has been developed during the 90´ in Germany and found to be very successful. During the final planning, costs, effectiveness and environmental impact of both solutions have to be considered. |
 Source: www.uni-weimar.de/Bauing/wbbau /studium/zusatz/ww63k09schnupper.pdf |
A final word on the destiny of the landfill in urban planning terms has to be made. Once all the technical work is done, the landfill should be replanted with medium high trees and bushes. Part of the huge space should give room for a football field and other sport activities.
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