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

soil, decomposition is aerobic, the organic material being mineralised and carbon
dioxide (CO 2 ) released as the major gaseous product. However, though biowaste
awaiting collection in dustbins and even, to some extent, when only recently
delivered to landfill, initially begin to breakdown in this way, older putrescible
material, buried deeper, experiences conditions effectively starved of oxygen. In
this environment, the degradation process is anaerobic and mineralisation con-
tinues with broadly equal amounts of methane (CH 4 ) and carbon dioxide being
produced. This resultant mix is known as landfill gas and typically 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 syner-
gistic substances, enzymes or other catalysts. Methanogenesis is discussed more
fully elsewhere, but it is possible to simplify the overall process thus:
Organic material −→ CH 4 + CO 2 + H 2 + NH 3 + 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 (CO 2 ). It was precisely because of these concerns that the
European Union began its drive to produce statutory controls on the amount of
biodegradable 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. Established figures from the Environment
Agency 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, pushing 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 non-combustibles 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 law can
afford to ignore this material.