A perspective on the discussion of Aerobic Landfills at the International Landfill Symposium 2003, Cagliari, Sardinia
A key topic raised in many papers at the year’s symposium was the issue of “final storage quality” (FSQ) for wastes being landfilled, criteria for defining FSQ, and approaches to achieving it.
Countries now recognise that existing pre-treatment methods do not approach FSQ, and that the landfilled residues still require continuing aftercare.
There was widespread recognition that a notional aftercare period of 30 years is meaningless in terms of reaching FSQ and that for landfills constructed according to modern standards, the period is likely to be measured in centuries or even millennia. The need to accelerate the washing out of soluble pollutants from landfills and to accelerate the degradation of biodegradable wastes was raised by a much larger number of renowned speakers, from a much wider spectrum of countries, than at any previous Sardinia symposium.
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“The results presented at this symposium shifted this topic from the level of ‘interesting idea with potential’ to that of serious technology”
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Another related area that attracted many papers and much discussion was research and full scale practice of aerobic remediation of old landfills. This involves the injection of air via one set of wells and extraction of gas via another set. It might be said that this topic ‘came of age’ at Sardinia 2003.
It has become well established from the published research now available that definite benefits can be realised from aerobic landfill remediation in some circumstances, including:
- Conversion of the microbial ecology from a methanogenic system to an aerobic system, similar to composting, leading to an odour-free landfill gas containing only CO2, N2 and O2 but no methane, and requiring no further treatment;
- Large reductions in leachate ammoniacal nitrogen concentrations.
Smaller scale research and field trials have been presented at previous conferences. However, the quantity of papers and the results presented at this symposium shifted this topic from the level of ‘interesting idea with potential’ to that of serious technology, which will undoubtedly be of great importance in future.
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“Risks of damage to thermoplastic infrastructure, sub-surface fires and generation of carbon monoxide. Clearly these are areas for further research.”
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Even so, much remains to be discovered: successful application has so far been limited to relatively shallow sites, and it remains unclear what would be needed to adapt the technique to deeper sites; successful application has also been limited to sites that are known to be close to the end of their gas generation curves, and applying aeration techniques to a site containing too much degradable matter could be ineffective in changing the overall microbial régime and might carry a risk of generating very high temperatures, with consequent risks of damage to thermoplastic infrastructure, sub-surface fires and generation of carbon monoxide. Clearly these are areas for further research.
Proceedings of Sardinia 2003, the Ninth International Waste Management and Landfill Symposium, 6-10 October 2003, are available by e-mail from www.eurowaste@tin.it or via www.sardiniasymposium.it .
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