Background...

Municipal solid waste comprises waste generated in households and assimilated waste generated in commercial establishments, institutions, and businesses. It is also defined as solid waste that is collected by or on behalf of a Local Authority. MSW includes used paper and cardboard, waste wood, plastic bottles, metal packaging and drink cartons, organic waste such as green waste, vegetable, fruit and garden waste and non-recyclable residual waste.

A typical municipal waste management option consists of Waste Minimisation/Reduction, Re-use, Recovery and Waste Disposal

Waste minimisation/reduction

This involves reduction in the generation of waste and use of natural resources. Source reduction actually prevents the generation of waste in the first place, so it is the most preferred method of waste management and goes a long way toward protecting the environment.

Re-use

The reuse of waste involves using a product or packaging more than once, thereby extending the lifetime of the material, and reducing the quantity of waste for disposal. Re-use means that items do not need to be reprocessed before they can be used again.

Waste Recovery

Waste recovery is a broad term used to represent the process by which waste is converted either into a usable form or energy is derived out of the waste. This includes recycling, composting and energy from waste recovery through suitable technologies like landfilling and incineration. The choice between these should be based on the environmental options available for a particular waste stream

Waste Disposal

Waste disposal is usually the last resort in a typical waste management hierarchy. Disposal routes include amongst others, landfilling and incineration. The options for waste disposal however, depend on the waste stream. Wastes with high volatile or toxic contents are not suitable for landfilling. Likewise, wastes with low calorific value are not suitable for incineration. Municipal incineration is not usually considered acceptable because of its adverse environmental and health effects and the destruction of materials that could be conserved while saving energy through other management methods

Landfill

A secure landfill is a carefully engineered depression in the ground into which wastes are put. The aim is to avoid any hydraulic [water-related] connection between the wastes and the surrounding environment, particularly groundwater

Landfills are a vital component of any well-designed MSWM system. They are the final storehouse of the Municipal Solid Waste of a community after all other Municipal Solid Waste Management options have been fully exhausted. The safe and effective operation of landfills depends on the sound planning, administration, and management of the entire MSWM system. This begins with an institutional and policy environment that views MSWM as an important component in the sustainable development plans of a city and country. It continues with MSWM regulations that are designed to protect human health and the environment. It ends with the coordination of MSWM programs, from waste reduction and resource recovery through collection, transfer, and ultimate disposal, into an integrated system. This system must provide a vital public service without compromising human health or the environment.

Landfills range in type from uncontrolled open dumps to secure sanitary landfills. Uncontrolled, open dumps are not a sound practice, but controlled dumps and sanitary landfills can provide effective disposal of a city's MSW in accordance with appropriate local health and environmental standards

Landfill Gas

Landfill gas is generated during the natural process of bacterial decomposition of organic material contained in municipal solid waste landfills. By volume, landfill gas is about 50 percent methane and 50 percent carbon dioxide and water vapour, and also contains small amounts of nitrogen, oxygen, and hydrogen, less than 1 percent non-methane organic compounds, and trace amounts of inorganic compounds.

Once a landfill site has been capped with soil, the breakdown of biological matter creates huge quantities of hydrocarbon gases, particularly methane - which is 21 times more damaging to the atmosphere than CO2, but can be easily burned in an internal combustion engine.

The formation of gas is affected by a number of factors such as the materials contained in the landfill, the depth of the tip, the density of the tipped material, water content, air temperature, atmospheric pressure and volume of precipitation.

The decomposition process in a landfill generating significant amounts of gas lasts about 15-25 years. The volume of gas decreases steadily over this period of time

LFG use

The Methane arising from LFG finds useful application in the following ways:

• Direct use as heat in kilns, boilers, and furnaces.

• For electricity generation

• For upgrading to a higher quality fuel such as LNG