Welcome to the May 2010 issue of Waste and Resource Management which is being compiled as the United Kingdom anticipates a general election with uncertainty as to which party will be in power after May. Whoever wins, there is, however, no uncertainty that one important task facing the new government is to incorporate the revised European waste framework directive within both English and Scottish law by December 12th 2010.
The waste management hierarchy has been a guiding principle within the various national waste strategies published in the British Isles for a number of years. With the incorporation of the forthcoming waste framework directive into British legislation, a new version of the hierarchy will gain legal status as a ‘priority order’. It is therefore appropriate that this issue of Waste and Resource Management leads the way by presenting four papers in a sequence that respects that hierarchy.
Recycling of construction waste materials has been the subject of a number of recent papers in Waste and Resource Management and has been a major focus of attention – notably from WRAP and some of the ‘zero waste’ programmes. Wimalasena et al., (2010) record a study into the economic viability of construction waste recycling in Calgary, Alberta.
Following a discussion on the composition of construction waste in Canada compared to that studied in Calgary, and the impact of landfilling the materials concerned, the authors report the costs involved, comparing recycling with landfill disposal. The authors conclude that recycling is more time consuming and expensive than landfilling in the short-term, but such costs are outweighed by the long-term environmental, social and economic benefits. They then propose a number of suggestions on how to improve recycling practices at the construction sites. The conclusion drawn is that while recycling may seem a burden, when thought is applied to the subject, it can be turned to positive advantage.
Continuing the theme of recycling, the paper by Nehdi and Arif (2010), adds to the body of knowledge on the recycling of specific material streams by describing work carried out at the University of Western Ontario on a major hazardous household waste-stream – namely latex paint. The study investigates the recycling of the paint by using it as a partial replacement for water in Portland cement – a product known as ‘paintcrete’.
Incorporation of hazardous materials into concrete matrices to facilitate disposal has been common practice for many years. The key to success lies in the ability of the matrix to resist leaching of pollutants into the environment, as described in the paper. If the paint is to be successfully recycled, the glycols and heavy metals within it must be contained, even when the concrete is subjected to harsh environmental conditions such as wetting and drying and freeze–thaw ageing, subjected to both fresh and salt-water. The authors conclude that paintcrete is a robust product even under such diverse conditions.
At the bottom of the hierarchy is landfill. While now seriously out of favour, the fact is that it will remain in use for many years to come. Until mankind develops de-materialisation, the only way matter can ultimately be disposed of is in landfill. While recycling is favoured in almost every case to landfill, the laws of thermodynamics tell us that even after energy recovery, there will always be some level of wastage in whatever system we deploy. Yet despite this, landfill is still only too often portrayed as simply burying matter in ‘a hole in the ground’. This is a gross simplification, as landfill is in fact a complex technology involving multiple engineering disciplines and sciences. It is important that we understand landfill behaviour – particularly if the concept of their use develops from a place of ultimate disposal to one of temporary storage of resources that can later be recovered.
One important aspect of landfill operations with municipal (MSW) and many commercial and industrial wastes is compaction of the waste mass to optimise the utilisation of the void space. Zhang et al., (2010) examine the compressive behaviour of MSW and challenge the traditional industry approach to void ratios. Using one-dimensional compression testing they examine the volume loss not only between particles, but also the compression of voids within particles. Mathematical relationships are developed describing the compressive behaviour and comparisons made between analytical results and physical tests, taking into account linear and elastic-plastic phase relationships.
Much of the reasoning behind the waste management hierarchy and the avoidance of landfill lies in mitigating climate change impacts by reducing greenhouse gas emissions arising from waste management practice. The foremost and most commonly known of the greenhouse gases produced is carbon dioxide, a significant by-product of combustion processes. Although conceived primarily to enable the advent of clean-coal power stations, the sequestration or storage of carbon dioxide in saline rock formations is a developing technology that may be equally applicable to the combustion of waste.
In the final paper in this issue, Garcia et al., (2010) present an easy reference guide to the technology to date. The paper provides a short, but complete description of the process along with the trapping mechanisms that can be applied, before exploring its macro-economics. Usefully, the paper presents a wealth of references that can be followed up by the interested reader.
Whether or not storage of carbon dioxide is an ultimate disposal route or whether it will one day become just a temporary repository from where the gas is reclaimed and recycled, remains to be seen. Just like the general election, the answer lies in the future and is there to be made. It just depends on what we do with it.
