180 Environmental Biotechnology
Table 8.2 General range of values
for landfill leachate
Determinand Value range
pH 5.5–8
BOD 5–80 000
COD 50–100 000
Nitrate 0.1–1 000
Sulphate 1–1 000
VFAs 150–50 000
Concentrations expressed in mg/l, pH in
pH units.economic forces in the commercial arena, this means that waste biotechnologies
seem certain to assume greater importance in the coming decades.
Biological Waste Treatment
The aims of biological treatment are relatively straightforward and can be summed
up in the following three points:
- Reducing the potential for adverse effects to the environment or human health.
- Reclaiming valuable minerals for reuse.
- Generating a useful final product.
Broadly speaking, this effectively means the decomposition of the biowaste by
microbes to produce a stable, bulk-reduced material, during which process the
complex organic molecules originally present are converted into simpler chemi-
cals. This makes them available for literal recycling in a wider biological context.
To some extent these three aims can be seen as forming a natural hierarchy,
since removing environmental or health risks, and deriving a stable product,
forms the bottom rung of the ladder for all biological waste treatment technolo-
gies. Clearly, whatever the final use of the material is to be, it must be safe
in both human and ecological terms. The recovery of substances, like nitrogen,
potassium and phosphorus, which can be beneficially reused, forms the next level
up, and is, in any case, closely linked to stabilisation, because these chemicals,
if left untreated within the material, would provide the potential for unwanted
microbial activity at a later date. The final stage, the generation of a useful end-
product, is obviously dependent on the previous two objectives having been met
with some degree of efficiency. The possible uses of the final material, and just
as importantly, its acceptability to the market, will largely be governed by the
certainty and effectiveness of the preceding processes of stabilisation and recla-
mation. Thus, while the hierarchical view may, in some ways, be both a natural
and a convenient one, these issues are not always as clear-cut, particularly in
respect of the implications for commercial biowaste treatment, as this approach
might lead one to believe.