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|  |  | | (This debate is closed and is a read-only archive) | Sustainable waste management
[29-Jan-2003]
| | Waste outputs should be more effectively used as resource inputs. |  | | | The generation of waste is part of a resource cycle that includes extracting materials and energy from the environment, refining raw materials and producing goods, consuming and using goods and, eventually, returning materials to the environment.
| The processes of refinement, manufacture and consumption each have inputs (materials and energy) and outputs (products, energy and waste). Waste outputs from one process may in some cases be used as resource inputs to another, or even the same, process. Closure of the cycle, ie, the return of waste or used resources to the environment in a way that enables them to be extracted and used again, rarely happens except in a haphazard way and on a geological timescale.
| Julie Hill has mentioned the waste hierarchy, which places waste avoidance (through reduced consumption and re-use) ahead of recycling, energy recovery and disposal. It is difficult to argue with this order of priority, but the creation of waste seems inevitably to accompany consumption, and increased consumption is the basis for the conjuring trick that passes for the UK economy. So waste avoidance through reduced consumption will be difficult, and on current trends is unlikely to be achieved. We could probably do more to encourage and facilitate re-use but there are limitations. If you no longer want your avocado-coloured bathroom suite, why should someone else?
| Much has been done over the past decade or more to promote recycling, but we should look very carefully at the overall resource, environmental and human implications of collecting, transporting and reprocessing materials before deciding that recycling must automatically be the most appropriate way of dealing with a particular waste stream. For example, recycling paper involves substantial transport costs (and presumably its share of casualties), recycles the most eminently renewable component (fibre), and leaves a residue of filler and de-inking sludge that is, in itself, a major and problematic waste stream.
| High-energy wastes such as mixed plastics and paper are probably best used as a replacement for non-renewable fuels such as oil and gas: combustion of mixed plastic and paper wastes linked to power and heat recovery efficiently recycles the energy that started as oil.
| There is, in any case, little point in recycling materials unless there is a demand for the resulting recyclate, and the UK government, through the Waste and Resources Programme (WRAP), is at least now addressing the issue of market development.
| Prolonging the useful life of materials can be achieved by recovering them from the waste stream at any stage of the resource cycle, and the European Union's recent and impending 'end-of-life' directives are to be welcomed as facilitating the de-manufacture of complex goods such as cars and electrical or electronic devices for maximum component and material recovery. But as a society we will always create waste that has to be disposed of, and progress towards sustainable development requires us to focus not only on prolonging the useful life of materials, but also on their return to the environment in a way that maximises benefit and minimises harm.
| The two main routes for final disposal are currently combustion (incineration) and landfill.
| Combustion has an important role to play in both waste and energy policy. As already stated, combustion of high-energy wastes, linked to power and heat recovery, is an efficient and appropriate means of energy recovery. Some wastes, for example clinical waste and some hazardous wastes, must be disposed of by high-temperature incineration in order to destroy potentially harmful pathogens and other substances.
| Combustion of mixed waste, however, is a waste of natural resources. Wet organic waste is unsuitable for combustion as it can contain up to 80 percent water. Although it will burn with other waste, net energy production will be low and in some cases negative due to the amount of energy required simply to evaporate the water. Gasification is a fashionable idea at present as an alternative to combustion but cannot overcome the inherent stupidity of trying to use a material that contains up to 80 percent water as a fuel.
| Traditional, mixed landfill is undoubtedly a waste both of recoverable material resources and of a potential supply of energy. As the organic fraction of a mixed waste degrades, it produces landfill gas which, if untapped for energy production, is released into our environment. But old landfills are neither designed nor managed to generate and extract this gas quickly or efficiently. An added bonus of doing this would be to return the landfill to a stable state with minimal pollution potential within the timescale of a generation.
| Organic waste has the potential to produce 150-300m3 (885-1770 megajoules) of gas per tonne from anaerobic digestion of bio-waste, plus an organic soil conditioner as an end product. This resource should therefore neither be burnt nor wasted in landfill. Composting is equally inappropriate, as instead of energy being recovered it is consumed in the process and greenhouse gases are released.
| There is no reason why large-scale bio-digestion facilities could not be constructed throughout the UK to harness this energy. Biogas is already collected from many traditional landfill sites, with some producing over 7000 kiloWatthours (kWh) of energy for the national grid, but in most cases the heat is still wasted. Unfortunately, despite their sustainable nature, low-cost engineered anaerobic digestion facilities could fall foul of EU legislation if they are considered a form of landfill.
| And finally, even in a world where we avoid waste, re-use goods, and recover as much material and energy as we can before final disposal, there will always be a need for landfill, both for combustion ash and for residuals that cannot readily be burned. Problems with existing landfill sites, although remarkably few, often stem from previous bad design, inadequate construction techniques and poor operational control. Modern, well-engineered and managed landfill sites need not suffer from the same shortcomings, and they will continue to have an important role to play in the future, even if the nature and volume of what enters the site are expected to change dramatically.
| In summary, sustainable waste management involves the appropriate treatment (re-use, materials recovery, energy recovery or safe disposal) of each component of the potential waste stream at an appropriate stage in the resource cycle. Different components will require different treatments, so the way forward has to involve separation of wastes, probably mainly at source, to ensure an effective overall contribution to the energy and carbon balance.
| Above all, we need a waste strategy that is founded on scientific understanding and analysis, engineering feasibility, and socioeconomic reality rather than vested interest, anecdote, uninformed emotion and political expediency - as is the case at present.
| William Powrie is head of the department of Civil and Environmental Engineering, University of Southampton
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