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Gas generation from one landfill can provide electricity to more than 200 apartments and become a new inexhaustible source of energy. What is the catch with landfill gas and why are the garbage kings in no hurry to extract it from landfills?

From the history of production

Household waste began to be used as a source of energy relatively recently. The first experimental landfill using special engineering facilities opened in California in 1937. Research and use of landfill gas in the United States intensified after the adoption in 1965 of the law on disposal of solid waste. Landfill gas utilization efforts accelerated during the oil crisis of the 1970s. Since 1980, the US government began to provide tax incentives to landfill gas producers. As early as 1985, more than 30 plants were operating in the United States using biogas from landfills.

The US is currently the world leader in landfill gas production. Of the 1812 landfills, 427 have gas generation projects. Most of them are concentrated in the Midwest and California. The number of projects to generate gas from US landfills does not correlate with the number of all landfills in the country. The region of the south, the leader in terms of the number of landfills, is lagging behind among gas projects. The Midwest region, the backbone of heavy industry, is in the lead. The industrial development of the lakeside states has made it possible to implement complex technical projects for the extraction of gas from landfills and its further use. More than 70% of projects in the states of the West are in California. This is not surprising, because it ranks first in the production of waste - 36 million tons per year.

How is landfill gas obtained?

Waste in landfills as a result of anaerobic (in the absence of oxygen) decomposition releases landfill gas. Waste decay occurs under the influence of bacteria belonging to two large families: acidogens and methanogens. Acidogens produce the primary decomposition of garbage into volatile fatty acids, namely, from fat, the maximum yield of methane is obtained. Methanogens convert volatile fatty acids into methane CH₄ and carbon dioxide CO₂. As a result, landfill gas consists of approximately 50% methane CH₄, 50% CO₂, including small impurities H₂S and other organic substances.

Landfill design

In order to obtain gas from landfills, a special design of the landfill is required, which would not only allow collecting gas for its further use, but would also meet environmental standards without polluting soils and groundwater.

The bottom of the excavated pit is covered with a geomembrane, and then covered with a meter thick clay. Geomembrane is a modern waterproofing material that can also perform drainage functions. Such protection is created to prevent the penetration of leaching products into the soil and groundwater. Garbage is brought in in layers, compacted by rollers at the end of each day and covered with a daily coating - a layer of clay 15-30 cm thick. This is necessary to reduce stench and prevent debris from being dispersed by wind and birds. After filling the pit with debris, it is covered with a roof and a protective coating. Roofing consists of compacted clay, more heavily laid on top of debris than daily roofing and geomembranes. The protective cover is a layer of soil and vegetation cover.

The pit is equipped with engineering structures for the removal of liquid and gaseous products of waste decomposition. Wells, pipes are laid in the body of the pit, pumping equipment is installed. Methane formed as a result of the decomposition of garbage is collected from a landfill and enters a scrubber - a gas cleaning device used to clean gaseous media from impurities in various chemical and technological processes. The method of cleaning gas coming from a landfill is based on washing the gas with a liquid, usually water. This method makes it possible to remove dust and aerosol particles from the gas.

After cleaning in the scrubber, the gas enters the compressor, after which it can already be used. Landfill gas is used directly to generate heat and steam, and also as a vehicle fuel. The resulting gas can also be used as a fuel for electricity generation. For this, gas turbine and gas piston installations are used.

Negative impact of landfill gas

With extensive use of landfill gas and the obvious positive aspects of its use, this gas also has a number of disadvantages. It contains a huge amount of toxic and harmful substances that are extremely dangerous for human health and life. Landfill biogas has a detrimental effect on the vegetation around and on the landfill. In the absence of proper management of its formation and collection, the destruction of the body of the landfill occurs due to the release of gas pressure inside it. Finally, landfill gas is a greenhouse gas.

The issues of landfill gas formation at MSW landfills and minimization of its impact on the environment are very relevant. Production and further use of gas from landfills are the most acceptable, promising and justified solutions from an environmental and economic point of view. The development of landfill gas requires a whole complex of expensive measures for its extraction, purification and transportation.

Worldwide landfill gas production

The volumes of annual gas production are presented in Table 1, from which it follows that the global utilization of landfill gas is approximately 1,2 billion m³ per year, which is equivalent to 429 thousand tons of methane or 1% of its global emission. The volume of extracted gas compared to the volume of its formation is negligible. At the moment, it is too early to talk about landfill gas as a new alternative fuel. However, the presence of colossal deposits of garbage and the improvement of technologies for the extraction and purification of landfill gas suggests that its importance will grow in the future.

Author: Lyubov Melnikova, Faculty of Geography, Moscow State University

Information sources

1. International Energy Agency iea.org
2.worldenergyoutlook.org
3. Gonopolsky A. M. On the issue of the market use of biogas generated at landfills

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