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

1. As described above (for basic stabilisation), the landfilling of untreated wastes
performs relatively poorly;
2. Again as described above, the abatement of ammonia and VOCs is efficient;
3. Because the energy recovery process gives rise to ash and air pollution control
residues in the form of clinker, the performance relative to incineration is
improved where it is believed that landfilling of air pollution control residues from
incinerators gives rise to environmental damage;
4. Where the process of energy recovery through RDF utilisation clearly displaces
less clean energy sources, this may improve relative performance. This issue is
not straightforward as many cement kilns are beginning to utilise a range of
wastes (so the time may come where one waste simply replaces another, at the
margin);
5. Where the cement kiln itself is equipped with quality flue gas abatement. This may
be of concern regarding more volatile heavy metals such as mercury, though
equally, the significance of this must be contextualised by the mercury content of
incoming wastes;
6. Some materials (e.g. ferrous metals, non-ferrous metals) are recovered with the
ability to substitute for primary materials whose production incurs environmental
damages;
7. Any landfilled residues are biologically stable.
These issues are among the key variables likely to affect the environmental
performance of a treatment / disposal method based around dry stabilisation.
Evidently, the nature of input wastes is also important in determining the nature of,
for example, the RDF fraction which may be derived, and hence, the potential for, for
example, energy recovery through combustion of the RDF.
61.2.4.4 MBT (separation of some dry recyclables, AD of biowaste, and possibly
RDF to third party)
Several facilities are now in operation where the biological treatment aspect of the
MBT process involves anaerobic digestion (AD). Facilities utilising dry and wet AD
processes now exist. Evidently, in such processes, there may be advantages in
ensuring that the costs of the AD equipment itself are reduced through the separation
of a fraction consisting primarily of organic wastes suitable for digestion. This may
occur through, for example, using screen undersieves for the digester since, for
example, the food waste fraction of waste tends to be concentrated in small particle
size fractions.
As mechanical separation processes improve, it is becoming possible to consider
facilities where residual waste is treated:
1. Mechanically to separate out:
a. fractions for recycling. Fractions may include metals, glass, other inert
materials, and some plastics;
b. fractions for subsequent biological treatment;
c. fractions for subsequent use as an RDF;
2. Biologically (anaerobic), with a small size fraction being digested to produce
biogas;
3. Thermally, with an RDF fraction derived for subsequent use either in dedicated
waste facilities, or existing industrial facilities;
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International Review of Waste Policy: Annexes