Climate Change Corner

Reducing Carbon Footprint with Innovative Ways of Managing Waste

When organic waste decomposes anaerobically in landfill, one of the end products of the decomposition process is landfill gas which is a mixture of approximately 60% methane and 40% carbon dioxide. Methane has more than 20 times the greenhouse effect of carbon dioxide when the gases are released into the atmosphere. Traditionally, therefore, landfill gas has been treated by collecting it from the landfill and burning it in a flare, in the presence of air, to produce carbon dioxide thereby reducing the overall greenhouse effect of the landfill gas.

To further reduce the carbon footprint, in modern landfills and restored closed landfills in Hong Kong and elsewhere, thermal energy released by the burning of methane is put to beneficial uses:

§  Landfill gas is used to power generators which provide all the electricity required on the landfill sites.

§  The power released by burning methane in the landfill gas is also used as a source of thermal power for treating leachate; the heavily contaminated wastewater collected at the base of landfills as one of the other end products of the decomposition of organic waste.

§  At NENT Landfill, for the past three and a half years, gas collected from the landfill has been purified by the removal of carbon dioxide and other contaminant gases to produce a synthetic natural gas (SNG) with very high methane content. This SNG is used by Towngas in their Tai Po plant to provide energy for the production of domestic towngas from naphtha and/or LNG. Similar projects are now under consideration at both WENT and SENT Landfills.

All three of these beneficial uses of landfill gas not only destroy methane and thereby reduce the greenhouse effect of landfill gas but also provide energy which would otherwise be obtained from fossil fuels thereby further reducing the overall greenhouse gas emissions and promoting sustainability of fossil fuels.

Other techniques adopted by Hong Kong waste management companies to reduce global warming include:

§  the collection of municipal solid waste by an automatic vacuum collection system which eliminates the need for refuse vehicles to collect the waste from bins thereby reducing emissions from the collection vehicles and also reducing traffic congestion.

§  at an incineration plant for the treatment of hazardous chemical waste, the heat produced from the waste is used to raise steam which is used by the waste producers as a source of energy thereby reducing their consumption of fossil fuels.

§  other plants for the treatment of domestic, industrial and commercial solid waste convert the thermal energy produced by the incineration of the waste into electrical power which is supplied to the national grid.

Innovative methods of waste management are already making a significant contribution to combat climate change and further employment of the techniques described above, among others, can provide an increased contribution in the future.

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This article is contributed by Mr Barry Adcock of Swire SITA Waste Services Ltd. with the co-ordination of the Environmental Division.