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landfill waste management

来源: 作者: 发布时间:2011-01-15  

Landfills are areas of land built up with layers of solid waste and covered with soil or other types of covering. They are different to dumps or tips, which are what most people think of when they hear about landfills, because they of their careful construction using special lining and covering systems to contain the waste.

Landfill sites comprise:

 A liner system

Storage space for the waste, usually arranged in cells

A leachate collection system

A gas collection system

A cover or capping

The lining of a landfill has a crucial role in preventing the waste escaping into and contaminating the soil and water around the site. There may be chemicals or unpleasant substances in the waste that need containing within the sealed area.

        Every ton of household waste contains approximately 150 to 250 kg organic matter that is biologically decomposable. Under oxygen-restricted conditions, bacterial degradation of the organic matter takes place through four phases yielding landfill gas.Landfill gas consists of the following main components:

Methane

CH4

approx. 50¸¸65 Vol. %

Carbon dioxide

CO2

approx. 35¸¸45 Vol. %

Water vapour

H2O

saturated

When  the landfill gas is pumped from a landfill under controlled and sustainable conditions, the following average values will be measured:

Methane

CH4

approx. 40-50 Vol. %

Carbon dioxide

CO2

approx. 35-45 Vol. %

Nitrogen (from Air)

N2O

approx. 5-15 Vol. %

Oxygen (from Air)

O2

approx. 1-3 Vol. %

Water vapour

H2O

saturated

Dangers

The composition of landfill gas clearly illustrates its potential danger to the environment. The potential harm that can be caused by the gas can be categorised as follows:

a)  Physiological

Danger of asphyxiation which is caused by the displacement of oxygenated air by landfill gas. There is a particularly high risk in confined spaces and trenches in the body of the landfill.

Nausea and intoxication, through the inhalation of toxic components in the gas. Damage to vegetation on and around the landfill site.

b)  Physical

Danger of explosion through the formation of methane-air mixtures, above all within the explosion limits of the methane (5 to 15 % by volume of methane in air). This is a high risk in underground services such as sewers, storm water drains and other pipelines routed through areas that are near or on landfills. The pipeline system of the degassing plant (operating at sub-atmospheric pressure), leachate control systems on the landfill and enclosed space on or near landfills are particularly high risk areas!

Landfill or smouldering fires, caused through the flammability of the landfill gas.These hazards are particularly treacherous when the unpredictable migration of landfill gas through the strata below the landfill is considered. It has been documented that landfill gas has collected several hundreds of meters away from landfill sites in the cellars of buildings and caused serious explosions. The gas migrates either in association with landfill leachate or independently due to barometric pressure changes brought about by the movement of cold fronts and other weather systems over the landfill area.

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