MECHANICS AND SETTLEMENT OF POST LANDFILL DIRECTIVE RESIDUAL WASTES

Landfill has been the principal method of waste disposal throughout most of the developed world for the last 100 years or more. More than 80% of the UK's waste is currently disposed of to landfill, but changes in legislation and resource management philosophy - in particular the EU Landfill Directive - are already beginning to change this. For example, the Directive requires a reduction in the amounts of biodegradable municipal waste (BMW) being disposed of to landfill in the UK to 75% of 1995 levels by 2010, 50% by 2013 and 35% by 2020. The Directive also requires that wastes are subjected to pre-treatment prior to landfilling, therefore a major role for landfill in the disposal of residual (i.e., post treatment or energy recovery) wastes will remain. Implementation of the EU Landfill Directive will have major implications for the nature of the waste that is disposed of to landfills throughout Europe, and hence for the way in which the receiving landfills should be managed. In particular, the Directive will require the large-scale treatment of municipal solid waste (MSW) to reduce the biological content. European experience suggests that treatment is likely to take one of two forms; either incineration, which has always been unpopular with the public in the UK, or a treatment comprising both mechanical and biological elements, together known as mechanical-biological treatment or MBT. MBT typically involves shredding or grinding of wastes prior to accelerated aerobic (often referred to as composting) or anaerobic degradation. Processing will leave a residue which, though much less biodegradable than MSW, will still produce gas (up to 20% of that from an untreated waste) and have the potential to pollute the environment.It is thought by some that there will be commercial or land improvement uses for the compost-like treated waste residues; however European experience and UK research has shown that it is likely that much of this waste residue will be suitable only for landfill for the foreseeable future. The residual wastes have very different properties to untreated wastes in terms of their mechanical behaviour (which impacts on the physical stability of landfills and hence their risk of landslides and pollution), the amount of gas and fluid which will be produced and the timescales over which gas and fluid production will occur. Unless the properties of residual wastes are understood and appropriate changes in working practice implemented, the consequences in terms of slope failure (landslide), increased risk of environmental pollution and potential loss of life could be severe. The aim of this research is to establish the mechanical and biological properties of waste residues so that design and management policies can be tailored to the waste's properties.