Municipal Solid Waste (MSW) Landfills are very unpopular due to the many environmental problems which have been attributed to landfills. In Europe there is massive investment underway to reduce substantially our reliance on landfills. In many areas worldwide landfill space is running out, due to public hostility arising from public perception of landfills and environmental problems.
To protect the environment, landfill sites were lined with clay, to contain any liquid, and a thick plastic lining, which allows leachate to be collected and removed from site. Also, landfills provide ideal conditions for methanogenesis, with lots of organic material and anaerobic conditions prevalent. Globally, landfills contribute to the “greenhouse effect”, due to landfill gas emissions. The Greenhouse Effect is caused by so called “greenhouse gases” (such as carbon dioxide, methane, and water vapour) in the atmosphere. It is thought that even with the best landfill gas extraction systems installed about half of the total methane produced by any landfill site escapes without being burnt, either in a flare, or in a generator to supply energy. The escape of the methane into the atmosphere is much more damaging in terms of its Greenhouse Effect than if it is burnt. The huge amounts of waste that are buried in landfill sites can mean that methane is produced for years after the site is closed, due to the waste slowly decaying under the ground.
During landfill operations the waste collection vehicles are weighed at a weighbridge on arrival. After waste loads are deposited, compactors or bulldozers are used to spread and compact the waste on the working face. Typically, in the working face, the compacted waste is covered with soil daily. Alternative waste-cover materials are several sprayed-on foam products and temporary blankets. Blankets can be lifted into place with tracked excavators and then removed the following day prior to waste placement. Chipped wood and chemically “fixed” bio-solids may also be used as an alternate daily cover. The space that is occupied daily by the compacted waste and the cover material is called a daily cell. Waste compaction is critical to extending the life of the landfill. Factors such as waste compressibility, waste layer thickness and the number of passes of the compactor over the waste affect the waste densities.
The lifetime of a site depends on its size. It is possible to calculate the volume of waste that the site will be able to accept. Once this waste volume has been reached, the site will be closed and restored. The rubbish is covered and the top of the site is sealed. Sites used to be sealed with clay but now heavy-duty plastic liners are used. Soil is then placed on top allowing the site to be grassed over and trees planted. The Landfill Directive (99/31/EC) includes targets to:
• Reduce biodegradable municipal waste sent to landfill by 65% by 2015
• Ban landfill of hazardous and non-hazardous wastes together from 2002
• Ban liquid waste, and certain hazardous wastes from 2002
• Ban landfill of whole tyres by 2003 and shredded tyres by 2006