A good waste management system will minimise the generation of waste, maximise recycling and other reuse of materials, and separate residual waste for safe disposal, according to type. The options for the final disposal of unusable waste include:
Burying waste has been practised for millenia. The modern method involves a lined (plastic or clay) pit, where solid waste is compacted and eventually covered by earth.
When organic material decomposes, it can create two problems: leachate and methane gas. Leachate is a liquid which accumulates at the bottom of the landfill. It has no economic value, and must be siphoned out for special treatment and separate disposal.
Landfill gas is mostly methane, and rises through the waste mound, or may enter escape paths in the ground system around the landfill site. In badly managed landfill sites this has led to explosions and groundwater contamination. Landfill gas can be allowed to escape into the air at non-dangerous concentrations, or, ideally, captured and used as a fuel.
Pilot plants in, for example Düsseldorf, Germany, have demonstrated that practically all waste can be incinerated, so that the mass is reduced, energy is recovered, and volatile substances made inert. Gaseous emissions, however, must be controlled. These can be many types, among which persistent organic compounds, such as dioxins, furans and PAHs.
Other air pollutants which may arise are $NO_x$, $SO_x$, which cause acid rain, CO, ozone, and the greenhouse gas, $CO_2$, as well as some VOCs (although it is reasonable to assume that most organics will be removed by the oxidation process), and particulate matter.
The resulting solid furnace slag, if inert, might find some applications, such as aggregate, or simply landfilled.
Incineration plants which generate electricity from the heat of the process are termed waste-to-energy (WtE).
Recycling became popular in the 1980s and 1990s, also because it was a practical and local way to foster public engagement. However, the value of recycling depends greatly on a calculation of the energy needed, and available applications for the recyclable material.
If the alternative raw material is imported great distances, then reclaiming the used material may be advantageous economically. If the material cannot be reused for the original purpose (such as PET), then collecting the material may be a net cost, and the value of the recycling scheme may be more political than economic.
An example of where economic thinking prevails over environmental criteria is New York City, which recently decided to reduce non-economic recycling. The city generates 36,000 tonnes of waste every day, with very low separation rates. New York City now spends c. 1.5 billion dollars a year on collecting and transporting its waste outside its region, with very little investment in local solutions. With federal pressure rising to comply to the minimisation, separation and disposal-at-source principles, this is a policy which has major economic and political liabilities.
The easiest materials to recycle are aluminium, copper, steel, glass, paper. Now, plastics can be more efficiently recycled: PET, polyethylene are two common ones.
Many councils encourage reuse of construction materials, provided they do not contain toxic or banned substances, such as asbestos.
Market prices, such as for copper and aluminium, as well as energy prices, have a significant impact on the level of interest in recycling.
Content © Renewable-Media.com. All rights reserved. Created : October 5, 2015 Last updated :February 16, 2016
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1871 - 1937
Ernest Rutherford, 1871 - 1937, was a New Zealand chemist and physicist, who worked in Canada and England. His work pioneered our understanding of the atom.
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