Biomedical Engineering Reference
In-Depth Information
The removal of organic sulphur from coal has been investigated by using
model organic substrates, most commonly dibenzothiophene (DBT). In labo-
ratory experiments, a number of organisms have been shown to be able to
remove organic sulphur, including heterotrophs (Rai and Reyniers, 1988) like
Pseudomonas , Rhizobium and the fungi Paecilomyces and chemolithotrophs
like Sulfolobus , mentioned earlier. These all act aerobically, but there is evidence
to suggest that some microbes, like Desulfovibrio , can employ an anaerobic route
(Holland et al ., 1986). While the use of such model substrates has some validity,
since thiophenes are the major organic sulphur components in coal, how well
their breakdown accurately reflects the situation for the real material remains
much less well known. However, this knowledge base is growing, particularly in
the light of successful experiments using Trametes versicolor ATCC 200801 and
Phanerochaete chrysosporium ME 446 to desulphurise Tun¸bilek lignite, which
has a typically high average sulphur content of around 2.59% (Aytar, Sam and
¸ abuk, 2008).
A range of putative bioreactor designs for desulphurisation have been put for-
ward, involving treatment systems of varying complexity, which may ultimately
provide an economic and efficient method for removing sulphur from these fuels
prior to burning. However, the state of the art is little advanced beyond the lab-
oratory bench and so the benefit of large scale commercial applications remains
to be seen.
Biological Control
The use of insecticides and herbicides, particularly in the context of agricultural
usage, has been responsible for a number of instances of pollution and many of
the chemicals implicated are highly persistent in the environment. Though there
has been a generalised swing away from high dosage chemicals and a widespread
reduction in the use of recalcitrant pesticides, worldwide there remains a huge
market for this class of agro-chemicals. As a result, this is one of the areas
where biotechnological applications may have significant environmental impact,
by providing appreciably less damaging methods of pest management. The whole
concept of biological control took a severe blow after the widely reported, dis-
astrous outcome of Australia's attempts to use the Cane Toad ( Bufo marinus )to
control the cane beetle. However, in principle, the idea remains sound and con-
siderable research effort has gone into designing biological systems to counter
the threat of pests and pathogens. Some of these, in respect of soil-borne plant
pathogens and bio-pesticides, are discussed elsewhere in this work and, accord-
ingly, do not warrant lengthy reiteration here.
The essence of the specifically environmental contribution of this type of bio-
intervention lies in its ability to obviate the need for the use of polluting chemicals
and, consequently, lead to a significant reduction in the resultant instances of
contamination of groundwater or land. However, one of the major limitations
on the effective use of bio-controls is that these measures tend to act more
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