Biotechnology and Waste 181In practical terms, the application of this leads to two major environmental
benefits. Firstly, and most obviously, the volume of biowaste consigned to landfill
is decreased. This in turn brings about the reduction of landfill gas emissions to
the atmosphere and thus a lessening of the overall greenhouse gas contribution,
while also freeing up space for materials for which landfill genuinely is the most
appropriate disposal option. Secondly, good biological treatment results in the
generation of a soil amendment product, which potentially can help lessen the
demand for peat, reduce the use of artificial fertilisers, improve soil fertility and
mitigate the effects of erosion.
As has been mentioned previously, stabilisation is central to the whole of bio-
logical waste treatment. This is the key factor in producing a final marketable
commodity, since only a consistent and quality product, with guaranteed free-
dom from weeds and pathogens, will encourage sufficient customer confidence
to give it the necessary commercial edge. As a good working definition, stabil-
isation is biodegradation to the point that the material produced can be stored
normally, in piles, heaps or bags, even under wet conditions, without problems
being encountered. In similar circumstances, an incompletely stabilised mate-
rial might well begin to smell, begin renewed microbial activity or attract flies.
Defined in this way, stability is somewhat difficult to measure objectively and,
as a result, direct respirometry of the specific oxygen uptake rate (SOUR) has
steadily gained support as a potential means to quantify it directly. Certainly,
it offers a very effective window on microbial activity within the matter being
processed, but until the method becomes more widespread and uniform in its
application, the true practical value of the approach remains to be seen.
The early successes of biowaste treatment have typically been achieved with
the plant matter from domestic, commercial and municipal gardens, often called
‘green’ or ‘yard’ wastes. There are many reasons for this. The material is readily
biodegradable, and often there is a legal obligation on the householder to dispose
of it separately from the general domestic waste. In the UK alone, the production
of this type of biowaste is estimated at around 5 million tonnes per annum (DETR
1999b), making this one area in which biological waste treatment can make very
swift advances. Nowhere is the point better illustrated than in the USA, where
the upsurge in yard waste processing throughout the 1990s, led to a biowaste
recovery rate of more than 40%, which made an effective contribution of nearly
25% to overall US recycling figures. In many respects, however, discussions of
waste types and their suitability for treatment are irrelevancies. Legislation tends
to be focused on excluding putrescible material from landfills and, thus, gener-
ally seeks to make no distinction as to point of origin and applies equally to
all forms. The reasons for this are obvious, since to do otherwise would make
practical enforcement a nightmare of impossibility. In any case, the way in which
waste is collected and its resultant condition on arrival at the treatment plant is
of considerably greater influence on its ease of processing and the quality of the
derived final product.