Biotechnology and Waste - Environmental Biotechnology: Theory and Application - page 177

biowaste awaiting collection in dustbins and even, to some extent, when only
recently delivered to landfill, initially begins to break down in this way, older
putrescible material, buried deeper, experiences conditions effectively starved of
oxygen. In this environment, the degradation process is anaerobic and miner-
alisation continues with broadly equal amounts of methane (CH 4 ) and carbon
dioxide being produced. This resultant mix is known as landfill gas and typi-
cally contains a number of trace gases of varying chemical composition. At the
functional level, the mechanism of this reaction is very complex, with hundreds
of intermediary reactions and products potentially involved and many requiring
additional synergistic substances, enzymes or other catalysts. Methanogenesis is
discussed more fully elsewhere, but it is possible to simplify the overall pro-
cess thus:

−−−→

CH 4 + CO 2 + H 2 + NH 3 + Organic material H 2 S

The production of methane is a particular worry in environmental terms since,
although there is some disagreement as to the exact figure, it is widely accepted
as more than 30 times more damaging as a greenhouse gas than a similar amount
of carbon dioxide. It was precisely because of these concerns that the European
Union began its drive to produce statutory controls on the amount of biodegrad-
able material permitted to be disposed of by this route. Without going into lengthy
descriptions of the final legislation adopted, or the history of its stormy 10-year
passage into European law, it is fair to say that the elements of the Landfill
Directive which relate to biowaste require considerable changes to be made in
waste management practice. This is of particular importance for those countries,
like the UK, with a previously heavy traditional reliance on this method. A
series of stepped major reductions in the amount of material entering landfill are
required and a timetable has been imposed for their implementation. By 2020
at the latest, all EU member states must have reduced their biowaste input into
landfill by 65% of the comparable figure for 1995. According to the Directive,
'biodegradable' is expressly defined as any 'waste that is capable of undergoing
anaerobic or aerobic decomposition, such as food and garden waste, and paper
and paperboard ' (DETR 1999a). This has particular implications for currently
landfill-dependent nations. The most recent Environment Agency figures show
that 32% (by dry weight) of MSW production in the UK is paper. This represents
its single largest biodegradable component, using the Directive definition, push-
ing the traditional biowaste element into second place by 11% (DETR 1999a).
Taking into account the additional contributions of 1% textiles, 3.5% 'fines',
4% miscellaneous combustibles and noncombustibles at 1%, the grand total of
'biodegradable' inclusions in the UK waste stream comes to 62.5%, based on
figures from this same study (DETR 1999a). Making up more than half of the
total on its own, paper is, then, of great potential importance, and it is clear that
no attempt at reaching the levels of reduction demanded by the new law can
afford to ignore this material.