NSWAI

LANDFILL GAS RECOVERY

Landfill gas production results from chemical reaction and microbes acting upon the waste as the putrescible material begins to break downin the landfill. The rate of production is affected by waste composition and landfill geometry, which in turn influence the microbial populations within it , chemical make-up of waste, thermal range of physical conditions, and the biological ecosystems co-existing simultaneously within most sites.

Landfill gas is the natural by-product of the decomposition of solid waste in landfills and is comprised primarily of carbon dioxideand methane, which is then combusted to generate electricity .

Landfill gas is composed of a mixture of hundreds of different gases. By volume, landfill gas typically contains 45% to 60%Methane and 40% to 60% carbon dioxide. Landfill gas also includes small amounts of nitrogen, oxygen, ammonia, sulfides, hydrogen, carbon monoxide, and nonmethane organic compounds (NMOCs) such as trichloroethylene, benzene, and vinyl chloride.

Methane is a primary constituent of landfill gas (LFG) and a potent greenhouse gas when released to the atmosphere. Reducing emissions by capturing LFG and using it as an energy source can yield substantial energy, economic, and environmental benefits. The implementation of landfill gas energy projects reduces greenhouse gas emission and air pollutants, leading to improved air quality and reduced possible health risks. LFG projects also improve energy independence, produce cost savings, create jobs, and help local economies. Internationally, significant opportunities exist for expanding landfill gas energy.

LFG is extracted from landfills using a series of wells and a vacuum system,and collected the gases through pipes. Once the landfill gas is processed, it can be combined with natural gas to fuel conventional combustion turbines.Instead of allowing LFG to escape into the air, it can be captured, converted, and used as an energy source. Using LFGE helps to reduce odors and other hazards associated with LFG emissions, and it helps prevent methane from migrating into the atmosphere and contributing to local smog and global climate change. LFG is extracted from landfills using a series of wells and a blower/flare (or vacuum) system. This system directs the collected gas to a central point where it can be processed and treated depending upon the ultimate use for the gas. From this point, the gas can be simply flared or used to generate electricity, replace fossil fuels in industrial and manufacturing operations, fuel greenhouse operations, or be upgraded to pipeline quality gas.

How is landfill gas produced?

Most landfill gas is produced by bacterial decomposition, which occurs when organic waste is broken down by bacteria naturally present in the waste and in the soil used to cover the landfill. Organic wastes include food, garden waste, street sweepings, textiles, and wood and paper products. This process is known as bacterial decomposition. Landfill gases can be created when certain wastes, particularly organic compounds, change from a liquid or a solid into a vapor. This process is known as volatilization. Nonmethane organic compounds (NMOCs) in landfill gas may be the result of volatilization of certain chemicals disposed of in the landfill. Landfill gas, including NMOCs, can be created byt he reactions of certain chemicals present in waste. For example, if chlorinebleach and ammonia come in contact with each other within the landfill, a harmful gas is produced.

Conditions affect landfill gas production

Waste composition - The more organic waste present in a landfill, the more landfill gas (e.g., carbon dioxide, methane, nitrogen, and hydrogen sulfide) is produced by the bacteria during decomposition. The more chemicals disposed of in the landfill, the more likely NMOCs and other gases will be produced either through volatilization or chemical reactions.

Age of refuse - Generally, more recently buried waste (i.e., waste buried less than 10 years) produces more landfill gas through bacterial decomposition, volatilization, and chemical reactions than does older waste (buried more than 10 years).

Presence of oxygen in the landfill- Methane will be produced only when oxygen is no longer present in the landfill.

Moisture content- The presence of moisture (unsaturated conditions) in a landfill increases gas production because it encourages bacterial decomposition. Moisture may also promote chemical reactions that produce gases.

Temperature- As the landfill's temperature rises, bacterial activity increases, resulting in increased gas production. Increased temperature may also increase rates of volatilization and chemical reactions.

Links for Reports and Research Paper

http://pdf.usaid.gov/pdf_docs/PNADK799.pdf
http://www.swlf.ait.ac.th/IntlConf/Data/ICSSWM%20web/FullPaper/Session%20IX/9_02%20_Rachel%20Goldstein_.pdf
http://www.anl.gov/PCS/acsfuel/preprint%20archive/Files/38_3_CHICAGO_08-93_0895.pdf
http://www.nrbp.org/pdfs/pub08.pdf
http://pdf.usaid.gov/pdf_docs/PNACA056.pdf
http://www.nrdc.org/air/energy/lfg/lfg.pdf
http://www.caricom.org/jsp/projects/landfill_gas_technology.pdf
http://www.energyjustice.net/lfg/factsheet-lfg.pdf
http://www.go-worldlee.com/resources/landfill_south_africa.pdf
http://www.bvsde.paho.org/bvsacd/cd48/landfill_gas.pdf
http://www.lei.lt/Opet/pdf/Willumsen.pdf