Integrated Environmental Biotechnology - Environmental Biotechnology: Theory and Application - page 243

than two years, came at the same time as a fall in sugar revenue following a slump
in the world market. The Brazilian sugarcane industry, which had shortly before
invested heavily in an extensive national programme of modernisation, faced
collapse. Against this background, the production of fuel from the newly available
biomass crop became a sound commercial move, simultaneously reducing the
country's outlay on purchased energy and buoying up one of its major industries.
The keynote of this chapter is the potential for integrating biotechnologies.
In the preceding discussion of biogas, this involved the marrying together of
the goals of biowaste treatment and energy production. In a similar vein, as was
described in an earlier chapter, there have been various attempts, over the years, to
produce ethanol from various forms of waste biomass, using naturally occurring
microbes, isolated enzymes and genetically modified organisms (GMOs). The
appeal to obtaining renewable energy from such a cheap and readily available
source, is obvious.
In many respects, the situation which exists today with biowaste is very sim-
ilar to that which surrounded Brazil's sugarcane, principally in that there is an
abundant supply of suitable material available. The earlier technological barri-
ers to the fermentation of cellulose seem to have been successfully overcome.
The future of ethanol-from-biowaste as an established widespread bioindustrial
process will be decided, inevitably, on the long-term outcome of the first few
commercial projects. It remains fairly likely, however, that the fledgling industry
will depend, at least initially, on a sympathetic political agenda and a support-
ive financial context to succeed. While this application potentially provides a
major contribution to addressing two of the largest environmental issues of our
time; energy and waste, it is not the only avenue for integrated biotechnology in
connection with ethanol production.
As has already been mentioned, specifically grown crops form the feedstock
for most industrial fermentation processes. The distillation which the fermen-
tate undergoes to derive the final fuel-grade alcohol gives rise to relatively large
volumes of potentially polluting byproducts in the form of 'stillage'. Typically
high in BOD and COD, between six and 16 litres are produced for every litre
of ethanol distilled out. A variety of end-use options have been examined, with
varying degrees of success, but dealing with stillage has generally proved expen-
sive. Recently developments in anaerobic treatments have begun to offer a better
approach and though the research is still at an early stage, it looks as if this
may ultimately result in the double benefit of significantly reduced cost and
additional biomass to energy utilisation. The combination of these technologies
is itself an interesting prospect, but it opens the door for further possibilities
in the future. Of these, perhaps the most appealing would be a treatment train
approach with biowaste fermentation for ethanol distillation, biogas production
from the stillage and a final aerobic stabilisation phase; an integrated process on
a single site. There is, then, clear scope for the use of sequential, complementary
approaches in this manner to derive maximum energy value from waste biomass