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Waste

By Email author - Sun, 22 May 2011 11:10:01 GMT
Waste

During the year 2008/2009, 37% of UK household waste was recycled, compared to only 14% in 2000/2001 and during that period the amount sent to landfill fell from 78% to 50%. According to DEFRA (Department of Environment, Food and Rural Affairs) waste management accounted for an estimated 3.6% of the UK's green house emissions during 2008. 89% of this came from landfill, 9% from wastewater handling and 2% from waste incineration.

Vast amounts of domestic and industrial waste are generated each year and landfill remains a common means of waste disposal in most countries. Traditionally this was simply dumped into holes in the ground and sites were located in former quarries, mining voids or borrow pits.

If properly designed and well managed, landfill can provide a hygienic and relatively inexpensive method of waste disposal. On the other hand, poorly designed or poorly managed landfill sites can create wind blown litter, attract vermin and allow contamination to leach into the soil. In addition as the waste breaks down methane and carbon dioxide are produced, which are greenhouse gases and can cause odour problems and kill surface vegetation.

These problems can largely be overcome by lining the pit with clay to prevent leaching; compacting the waste to increase density and stability; covering the material to prevent attracting rats and mice; and installing gas extraction systems.

In spite of this, landfill is becoming more controversial, partly due to the ever-decreasing number of suitable sites, but largely for the fact that it encourages the dumping of materials that could be reused or recycled.

People are beginning to look for other solutions and attention is turning to ways in which all this waste can be put to good use. Incineration of waste has always been fairly common in a domestic context, but it is also carried out on an industrial scale. It is useful for disposing of residue of both solid waste management and solid residue from wastewater management. The process reduces volumes of solid waste to between 20% and 30% of its original volume.

Incineration can be used for the disposal of solid, liquid and gaseous waste and is recognised as being a practical method of disposing of certain hazardous waste materials such as biological medical waste.

It is a particularly common method of waste disposal in highly populated countries such as Japan where land is scarce. Again, this is a controversial means of waste disposal. Often these incineration furnaces are used to generate, heat, steam or electricity, but combustion is not always perfect and there is concern about the emission of gaseous pollutants and the harm that they might do to the environment.

Recycling can be a very cost-effective way of disposing of waste materials by collecting them for reprocessing into new products. Many items of domestic and industrial waste can be recycled. Aluminium from beverage cans, steel food or aerosol cans, copper wire, old cars, plastic bottles, glass bottles, scrap paper, newspapers, magazines and cardboard are just some examples.

Materials such as glass, steel and aluminium can be recycled an infinite number of times and reprocessed using a fraction of the amount of energy that is needed to create a new product. It should be pointed out that if glass is put in landfill it will take about 4,000 years to break down.

Computers and electronic equipment can also be recycled, but this usually involves painstaking dismantling. For this reason, combined with lack of regulation, this type of e-waste (ewaste or electronic waste), is often shipped to developing countries where labour costs are lower; much of it ending up in large e-waste dumps.

Biological reprocessing of waste is really another name for composting, where the aim is to recycle material to produce a mulch or compost for agricultural or landscaping purposes. Quite often the waste gas, such as methane, that is generated as part of the process will be captured and used for generating electricity or heat, thus maximising efficiencies.

Composting is very common in the domestic situation and has been popular with generations of gardeners, where vegetable matter such as garden waste is rotted down on the traditional compost heap.

Anaerobic digestion is the next step. Each year the UK produces 100 million tonnes of waste suitable for anaerobic digestion. Most of this, 80 to 90 million tonnes, is made up of manures and slurries, but 12 to 20 million tonnes is food waste.

It is estimated that by 2020 this could generate at least 10 to 20 TWh (terawatt hours - thousand million kilowatt hours) of heat and electricity per year, or 27 TWh if converted into biomethane for injection into the gas grid. Putting this into perspective, 27 TWh represents about 7% of current UK domestic gas demand.

It is also suggested that this gas could be further refined to produce hydrogen for use in stationary cogeneration fuel cells. If used in this way it would eliminate the pollution from products of combustion.

In the UK 66% of sewage sludge is already treated by anaerobic digestion and in 2008 this produced 0.7 TWh of electricity.

A further bonus of anaerobic digestion is that diversion of biodegradable waste from landfill can achieve a significant reduction in greenhouse gas emissions. Capturing biogas from one tonne of food waste will save the equivalent of 0.5 to 1 tonne of carbon dioxide.

Waste products always contain energy and this can be harnessed either by using them as direct combustion fuel or indirectly by processing them into another kind of fuel. Anaerobic digestion is an excellent example of this indirect process.

In the years of plenty our society became a ''throw away'' society; when something broke or wore out it was simply thrown away. An important part of waste management is to prevent the creation of such waste material. This includes repairing broken items rather than simply replacing them with new ones; reusing cotton shopping bags rather than using throwaway plastic ones; avoiding the use of disposable products and designing products that use less material while serving the same purpose, such as lightweight drink cans and bottles.

The cornerstone of most waste management strategies is the waste hierarchy, also known as the ''3 Rs'' - reduce, reuse, recycle. The aim is to extract the maximum practical benefit from products and to generate the minimum amount of waste.

It can be compared to a six-layer pyramid.

  • At the peak is the ultimate aim - the prevention of waste.

  • The next layer is minimisation, where you generate as little waste as possible.

  • Below this is reuse, where you repair rather than throw away.

  • The next layer is recycling where waste materials are processed into new products.

  • Fifth from the top is energy recovery where energy is extracted from remaining waste.

  • Finally, the bottom line, the disposal of anything that is left.

    Various strategies have been considered to deal with waste. Producer responsibility is a strategy designed to promote the integration of all costs associated with a product up to its eventual disposal. Manufacturers, importers or vendors of a product are required to be responsible for its end-of-life disposal. The costs of this would obviously be reflected in the purchase price.

    Another strategy is the polluter pays principle. In this case the polluting party is responsible for paying for the impact caused to the environment. With respect to waste management, this will generally mean being required to pay for appropriate disposal of waste.

    An example of this principle would involve the kerbside collection vehicle weighing each bin as it was being emptied and the consumer subsequently being billed accordingly.

    One of the most critical issues with respect to waste management is education and awareness. The world's natural resources are in grave danger. Environmental pollution and degradation are occurring at an unprecedented scale and speed.

    Waste material represents a fantastic resource that in many cases is simply there waiting to be tapped. To simply bury it in the ground or burn it is not a realistic option in the 21stcentury.

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    Topics: Waste