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Evaluation of the Efficiency of Methane Oxidation Layers

The gas building level of older landfills is decreasing continuously. Below a lower limit of CH4-content an active gas utilization systems can’t be used and a passive system for methane elimination has to be implemented. An effective and cost efficient method is the utilization of the restoration layer to implement an adequate system composed of a landfill gas distribution layer and covering layer. The landfill gas will be distributed below the covering layer and will slowly migrate through the surface. If there is an adequate migration rate the methane will be completely oxidized. The implementation of such a methane oxidation system during surface sealing of landfills is easy to realize and there is mostly sufficient available area.

The efficiency of different methods and kinds of methane oxidation systems in the restoration layer of landfills is analyzed in the given report. In Saxony there are more than ten surface sealed landfills with a methane oxidation system with operation experiences. Basically five different systems of landfill gas distribution into the restoration layer with different thickness of covering layers were examined. Beside the utilization of the drainage layer for gas distribution also special systems with distribution layers located in different distances from the surface are executed. These special layers can be subdivided into single areas, into several horizontal trenches or as a mixture of the different variants as well.
In addition different soil-mechanical tests and air flow tests through different driving rod samples were carried out. Finally there is one important result. Although nearly all samples will be suited according the effective guidance in the soil mechanical test, the air flow rate at varying pressures (0 - 10 mbar) is very different. Hence the landfill gas migration rate will also be different and finally the methane conversion rate as well.
To compare the efficiency of the five examined systems special parameters were measured and evaluated during a long test period. Beside the methane content of the different gas wells the gas volume stream from the gas wells into the gas distribution layer was measured. At the same time the CH-content at the surface was measured using a flame ionization detector (FID). By mathematical method the unconverted flow rate of methane was calculated for each of the five different systems. Considering the medium value of all measurements the conversation rate of each system was calculated finally.

Copyright:	© Lehrstuhl für Abfallverwertungstechnik und Abfallwirtschaft der Montanuniversität Leoben
Quelle:	Depotech 2012 (November 2012)
Seiten:	8
Preis:	€ 4,00
Autor:	Dr.-Ing. Arnd Seyfert
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