204 Environmental Biotechnology
There are many of advantages to this method, most obviously in that it allows
for the input biowaste to undergo established sanitisation procedures without
detriment to the worms themselves, which are, as discussed previously, temper-
ature sensitive. A less commonly appreciated benefit of this approach is that
the period of initial composting significantly reduces worm ammonia exposure,
to which, again, they are very sensitive. However, as with so much of these
combined approaches, there is a need to manage the treatment conditions care-
fully to produce the optimisation desired. There is evidence to suggest that a
precomposting phase has a negative effect on worm growth and reproduction
rates (Fredericksonet al. 1994) which obviously represents a direct reduction in
the overall rate of worm biomass increase. Obviously this has an effect on the
overall rate of stabilisation and processing, particularly since it has been demon-
strated that the enhanced waste stabilisation achieved under worm treatment is
only attained under conditions of high resident worm biomass (Fredericksonet al.
1994). It seems reasonable to suggest, then, that to maximise the effectiveness
of the combined treatment approach, the initial composting period should be no
longer than the minimum necessary to bring about pathogen control of the input
biowaste. Though this represents the kind of compromise balancing act so typical
of much of environmental biotechnology, it is one which holds much promise.
The combination of annelidic conversion with composting permits both enhanced
stabilisation rate and product quality, with the additional bonus that the volatile
organic content is also significantly reduced. It is also possible that the natural
ability of worms to accumulate various hazardous substances within their bodies
will also have implications for waste treatment, particularly if it proves possible
to use them deliberately to strip out particular contaminating chemicals.
Annelidic conversion is currently very clearly a minority technology in this
role, but the potential remains for it to play a role in the future biological treatment
of waste, either as a standalone or, as seems more likely, as part of an integrated
suite of linked processes. This seems particularly likely if the characteristically
superior product derived from this process can be shown to be consistent, since
specialist materials in the horticultural and gardening market generally tend to
offer better returns. However, only time will tell whether this will prove to be
sufficient financial incentive to offset the costs of production and encourage wider
adoption of the technology.
Biowaste to ethanol
Around half of the total dry matter in plant origin biomass is cellulose, and
since this makes up the majority of the biowaste component in MSW, it rep-
resents a huge potential source of renewable energy. As is widely appreciated,
sugars can be broken down by certain micro-organisms to produce alcohols, of
which ethanol (C 2 H 5 OH) is the most common. This is, of course, a well-known
application for the production of alcoholic beverages across the world, typically
using fermentative yeasts. These organisms are poisoned by ethanol accumulation