Biotechnology and Waste - Environmental Biotechnology: Theory and Application - page 205

greater than about 10% which means that, in order to derive higher concentra-
tions, approaches relying on distillation or fractionating are required. In a wider
context, ethanol, either as the typical hydrated form (95% ethanol, 5% water) or
as azeotropically produced anhydrate, makes a good fuel with excellent general
combustion properties.
Historically, the realisation of the huge energy source locked up in the sugars
of the cellulose molecule has always been a practical impossibility. The combi-
nation of the β 1-4 linkage in cellulose itself, coupled with its typically close
association with lignin, making large-scale hydrolysis to sugars a costly and
difficult prospect. Some early attempts employed enzymes from wood-rotting
fungi working on a feedstock of old newspapers or pulp, though the energy
involved in actually making the process work often became a limiting factor. In
the mid-1990s, various researchers began to investigate the potential of genet-
ically modified bacteria, by inserting appropriate sequences from a variety of
naturally occurring wood-rotting organisms. In the following years, a number of
technologies have emerged, based both on whole-organism and isolated-enzyme
techniques, and the commercial processing of cellulose to alcohol now appears
to be about to become a mainstream reality.
A number of countries have begun to show an interest in the potential gains
to be had from developing a biowaste-based ethanol industry. Within the USA,
many individual states have started to undertake feasibility studies for their own
areas. A recent California Energy Commission Report, for example, has estab-
lished that the state-wide annual generation of biowaste exceeds 51 million dry
tonnes, comprising forestry residue, MSW and agricultural waste. The same doc-
ument estimates the resultant maximum ethanol yield at more than 3 billion
gallons (US).
There are several thriving biomass-to-ethanol production plants elsewhere in
the USA and the world, though most of these make their alcohol from primary
crop plants, rather than biowaste. As with biogas, further discussion of the wider
aspects of ethanol and the role of biotechnology in energy production appears in
a later chapter.
Eutrophic fermentation (EF)
Eutrophic fermentation was the name given by one of the authors to the experi-
mental, wet, in-vessel, aerobically enhanced biodegradation process he designed
to investigate accelerated decomposition, principally as an alternative to anaero-
bic digestion. Fermentation in this context relates to the wider application of the
word to encompass all microbial breakdown and not simply the anaerobic pro-
duction of alcohol and eutrophic refers to the nutrient-rich environment within
which it takes place.
The process arose as a result of research into the enhanced aerated remediation
of post-anaerobic digestion liquor. The idea of introducing air into liquid or
slurrified waste, as was discussed in Chapter 6, is well established as a means