The more waste we generate, the more we have to dispose of. Some methods of waste disposal release air pollutants and greenhouse gases into the atmosphere. Waste recycling offers one means of reducing the impacts of waste disposal on the atmosphere, but there are other methods of waste disposal which are more environmentally friendly.
The most common disposal methods, particularly in the UK, are landfill and to a lesser extent incineration. Each year approximately 111 million tonnes of controlled waste (household, commercial and industrial waste) are disposed of in landfill sites in the UK. Some waste from sewage sludge is also placed in landfill sites, along with waste from mining and quarrying. There are over 4000 landfill sites in the UK. As landfill waste decomposes, methane is released in considerable quantities. Currently it is estimated that over 1.5 million tonnes of methane are released by landfill sites in the UK each year. Methane is a strong greenhouse gas and contributes to global warming. Furthermore, the leachate fluids formed from decomposing waste can permeate through the underlying and surrounding geological strata, polluting groundwater which may be used for drinking water supplies. Containment landfills however, can limit the spread of this waste leachate.
Incineration is the second largest waste disposal method in most countries. In the UK, approximately 5% of household waste, 7.5% of commercial waste, and 2% of industrial waste is disposed of by incineration. When burning waste, a large amount of energy, carbon dioxide and other potentially hazardous air pollutants is given off. Modern incinerators however, can use this waste energy to generate electricity and hence prevent the energy from being wasted. Incineration plants range from large scale, mass-burn, and municipal waste incinerators to smaller clinical waste incinerators used in hospitals. During the 1990s many UK hospital incinerators were forced to close owing to tougher emissions legislation introduced by the 1990 Environmental Protection Act. Today, hospitals tend to share one large incinerator to dispose of the wastes for a number of hospitals.
A less common but more sustainable method of waste disposal is anaerobic digestion. In this process waste decomposes in an enclosed chamber, unlike in a landfill site. Digestion takes place in an oxygen-free environment. Bacteria thrive in this environment by using the oxygen that is chemically combined within the waste. They decompose waste by breaking down the molecules to form gaseous by-products (methane) and small quantities of solid residue. Anaerobic sewage plants produce significant quantities of methane, which can be burnt to generate electricity. Liquid and solid organic fertilisers are also formed, and can be sold to cover operating costs. For several years, sewage sludge and agricultural waste has been treated by anaerobic digestion, and the process is now being used for municipal solid waste. It requires the biodegradable section of the waste to be separated from other material and put into digestion chambers. Currently, the UK has only a small number of plants, and each can handle only a few hundred tonnes of waste each year. However, the usage of anaerobic digestion as a sustainable waste disposal method is forecast to increase. Many other countries already utilise anaerobic digestion to dispose of large amounts of waste. Denmark for example, treats 1.1 million tonnes of waste by anaerobic digestion every year.
As well as recycling waste, individuals can adopt more sustainable ways of disposing it. One way is to compost any organic waste such as food and garden waste. Organic waste breaks down over a few weeks into a mulch which can be used as a soil fertiliser. Individual households have practiced small-scale composting for many years, and the UK Government is now encouraging this on a wider scale. Large-scale composting schemes are also being developed, with the collection of organic waste from parks and civic amenity sites. Garden and food wastes are collected directly from households in separate kerbside collections. Large central facilities can then compost the collected organic waste. These schemes are to help the UK meet its target of recycling and composting 33% of household waste by 2015.