International Review of Waste Management Policy - Department of ...

4. The degree to which materials (especially metals) are recovered, and recovered in
a useful form for recycling; and
5. The degree to which other potential hazards associated with landfills are likely to
be problematic in future, and he degree to which stabilization might minimize
these.
Each of these issues influences the degree to which stabilization contributes
positively to the outcomes.
Examining one of these more closely, it is clear that as regards greenhouse gas
emissions (GHGs), when compared to landfilling of untreated waste, basic
stabilization processes, with residues being landfilled, exhibit the following
performance characteristics:
� Less of the carbon is transformed into methane, and the majority is transformed
into carbon dioxide, a far less potent greenhouse gas. Other things being equal,
this means that the greenhouse gas emissions from the process (including the
landfilling of the residues) will not be so harmful;
� The absence of methane generation for subsequent capture for energy recovery
implies no displacement of fossil carbon by the stabilization process by means of
energy generation. Other things being equal, this means that the greenhouse gas
emissions from the process (including the landfilling of the residues) will be more
damaging than for untreated landfilling;
� On the other hand, stabilization processes would, typically, recover some
materials such as steel even in their most basic configuration. This would imply
recovery of energy embodied in materials, improving the greenhouse gas balance
of the stabilization process;
� Finally, the degradation of carbon is likely to occur more quickly under the more
controlled conditions in a stabilization process. Hence, the time profile of
emissions is such that proportionately more of the emissions occur earlier in time.
The effect of discounting will tend to make the impact of these earlier emissions
more important. Consequently, this would tend to increase the impact of the
stabilization process relative to landfill of untreated waste where GHGs are
concerned.
It can be seen that a fairly complex range of issues affects performance in this one
area. What is clear, however, is that in the overall system – stabilization plus
landfilling – the majority of GHG emissions is shifted into the stabilization process.
The emissions in the landfilling phase are likely to be less significant, and are likely to
occur further into the future (because the remaining carbon is, by definition, of a
more slowly degrading nature). Consequently, it seems reasonable to argue that
landfilling stabilized waste is less harmful than landfilling treated waste.
61.2.4.3 MBT (dry stabilisation, RDF to cement kiln)
In this configuration, it is assumed that input materials are first treated mechanically
(to render the material easier to treat aerobically) and then subjected to a process
where the material is dried using both the heat from aerobic degradation processes,
and the air from the aeration of the total mass of material.
The performance of dry stabilisation processes are likely to be improved, in relative
terms, if:
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