Reducing the emissions of our greenhouse gases is thought to be the most effective way to mitigate global warming. But while adapting our industrial and agricultural activities to achieve that is very important, we should not forget how waste generated and disposed by humans also contributes to global warming. In 2002, a survey revealed that greenhouse gas emissions from waste were highest in North America, at over 200 million tonnes, in Europe they amounted to over 100 million tonnes while in Japan, Australia and New Zealand they were over 50 million tonnes .
Today, the 7 billion residents of planet Earth generate 1.2 kg of waste per person per day; this amounts to about 1.3 billion tonnes per year. By 2025, this is likely to rise to about 2.2 billion tonnes per year . A very significant chunk of this waste – about 59% for both higher and lower income countries – ends up in landfills .
In landfills, waste is generally placed underneath the ground surface in an area of the land which is first lined with clay and then covered with a sheet of flexible plastic. Drains and pipes are also placed to collect a liquid which seeps out from the trash. This liquid, called leachate, is a contaminated fluid which is then treated as wastewater. In 2008, New York’s landfills released about 276 million gallons of leachate . Modern landfills require soil to be added to cover fresh additions of waste every day and once the landfill has reached its capacity, the trash is covered with clay and another plastic sheet.
While landfills were not designed to break down waste, since their primary function is to simply “store it,” the trash placed in landfills does decompose slowly in an oxygen-free environment. Due to the lack of oxygen, bacteria found in organic waste produce methane gas, a highly flammable and dangerous gas if allowed to collect underground. Methane is also a potent greenhouse gas – about 25 to 72 times more potent than carbon dioxide - and contributes to global warming. Given that about half of our trash is mostly food and paper which means it is organic trash, landfills have a very high methane emitting potential .
It is however claimed that a lot of modern landfills can collect methane through a layer of pipes placed on top of the waste layer, whereas others vent the methane into the air or collect it and burn it to produce energy. This is welcomed as best practice for the industry, but sadly it does not reflect the situation on the ground.
The Intergovernmental Panel on Climate Change (IPCC) reviewed the waste sector in its 2007 Fourth Assessment Report. The IPPC acknowledged that the best and more modern landfills might achieve very high capture rates of methane when there is functioning gas collection and the site is well-sealed. But, it also highlighted that that in contrast to the best operations, “some sites have less efficient or only partial gas extraction systems and there are fugitive emissions from landfilled waste prior to and after the implementation of active gas generation” . Moreover, it added that “it estimated that ‘lifetime’ recovery efficiencies may be as low as 20%”, which means that the vast majority of methane gas escapes .
It is, therefore, not surprising that this makes landfill the fourth largest contributor to climate change after electricity generation, transport and manufacturing .