Integrated Environmental Biotechnology - Environmental Biotechnology: Theory and Application - page 241

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 bio-industrial
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 by-products in the form of 'stillage'. Typically
high in BOD and COD, between 6 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 remains at a relatively early stage, it looks as
if this may ultimately result in the double benefit 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, complimentary
approaches in this manner to derive maximum energy value from waste biomass
in a way which also permits nutrient and humus recovery. Thus, the simultane-
ous sustainable management of biologically active waste and the production of a
significant energy contribution becomes a realistic possibility, without the need
for mass-burn incineration. In many respects this represents the ultimate triumph
of integration, not least because it works exactly as natures does, by unifying
disparate loops into linked, cohesive cycles.
Clearly, both AD and ethanol fermentation represent engineered manipulations
of natural processes, with the activities of the relevant microbes optimised and
harnessed to achieve the desired end result. In that context, the role of biotechnol-
ogy is obvious. What part it can play in the direct utilisation of biomass, which
generates energy by a quite different route, is less immediately apparent. One
of the best examples, however, once again relates to biological waste treatment
technologies, in this instance integrated with short rotation coppicing (SRC).