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

treatment may give rise to damages, some reduction in the external costs of
landfilling such residues could be achieved;
3. As regards the energy efficiency of such processes, some have taken the view that
unless gas engines are used to generate energy from the energy carrying gases
derived from pyrolysis / gasification, the net conversion of energy may be less
than is the case with conventional mass burn incineration. Energy efficiencies are
significant in the analysis, the more so if it is assumed that the source of energy
which might be displaced is ‘less clean’. If gases are used in co-firing of power
stations, higher efficiencies may be achieved;
4. The design of the process itself may lead to lower emissions into raw flue gas with
the result being that either emissions of cleaned flue gas are, other things being
equal, improved relative to incineration, or that the expenditure on flue gas
cleaning to achieve a given standard may be lower with ATT than with
conventional incinerators.
It should be made clear that because the processes being considered tend to be
proprietary ones, the above comments are intended to apply to ‘possible
configurations’, and they do not necessarily apply equally to all ATT processes.
Furthermore, as stated earlier, the track record of ATT facilities for treating raw
residual waste is not well established in Europe.
61.2.4.2 MBT (basic stabilisation)
Basic stabilization systems rely, in the main, on reducing the biodegradability of
material prior to landfilling. In this system, it is assumed that following mechanical
treatment, the waste materials are subjected to an aerobic stabilization process with
the aim being to reduce the potential for gas generation when the material is
deposited in, or possibly on, a landfill. Some ferrous metals and perhaps some nonferrous
metals may be extracted during the process, but the mass of material
landfilled is essentially equal to the mass of material received minus the loss of
moisture and the mass loss due to the degradation of, principally, more rapidly
degraded carbon fractions.
The degree to which this represents an improvement on sending materials to landfill
in an untreated form depends upon:
1. The extent to which one believes that landfills fail to operate in a well-behaved
manner, in particular, whether one believes that they:
a. Do generate problematic emissions before gas capture systems are
effectively operational;
b. Fail to capture the majority of methane emitted over the time during
which emissions from the waste occur;
c. Generate relatively little energy from waste as a result;
d. Generate problematic leachate;
2. Whether the level of stabilization attained through the process is sufficient to
ensure that residual methane emissions from landfilled waste are effectively
reduced to close to zero (and this may imply active management);
3. The level of abatement of, in particular, ammonia and more harmful VOCs (as
opposed to less harmful ones emitted by biofilters) during the stabilization
process; and
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International Review of Waste Policy: Annexes