Biotechnology and Waste - Environmental Biotechnology: Theory and Application - page 199

in a later chapter and accordingly, a consideration of the wider implications of
biogas fuel will be deferred until then. However, it is worth pointing out in the
waste-specific context that, though much has been made of the apparent dual
benefit of biowaste treatment and energy production, in an actual application, it
is a practical impossibility to optimise both simultaneously.
Other Biotechnologies
Although composting and AD between them account for by far the bulk of
biological waste treatment globally and each has a well established track record,
as is so often the case with practical applications of environmental biotechnology,
neither is a clear winner. Dependent on the specifics of the situation, the particular
waste composition, local factors, and so on, either can have clear benefits to offer
and, as we have seen, both can form adequate responses to the growing demand
for biowaste diversion. At the same time, each has its limitations also. For AD, the
air-tight nature of the reactor, the gas handling arrangements needed to guarantee
that the potentially explosive methane produced can be safely managed and the
demands of internal environmental control contribute heavily to the overall capital
cost of the plant. In addition, on a practical note, there are certain inherent limits
on the levels of contamination by other waste fractions that can be tolerated.
Clearly, for some applications, these factors may prove major barriers to use.
On the other hand, composting is essentially less of an engineered solution
and in many of the versions often seen at local authority sites, it is a very
simple process. The major practical limitation, at least as a sole method of bulk
treatment, lies in the physical amount of material, since the typical retention
period for composting is longer than AD and the final volume of product derived
is greater. Consequently, a relatively large area of land is required for processing
and a sizeable market capacity or disposal arrangement is necessary for the
compost. In certain circumstances, these issues may be significant blocks to
its adoption.
Applications for which neither of the major technologies is an immediately easy
fit have, at times, led to interest in the potential of other methods of biowaste
treatment. It is beyond the scope of this topic to discuss the wider political and
economic issues surrounding biowaste initiatives, though it should be clear that
such factors commonly play an indivisible part in their implementation. Suffice
it to say that these local modalities can often form the most critical deciding
factors in determining the suitability of a given approach. This is something of a
mixed blessing, since, though it can make direct comparisons between individual
methods exceedingly difficult to do in a meaningful way, it does leave space for
novel or less-well-known technologies to play a role.
Annelidic conversion (AC)
The use of a variety of annelid worm species is one alternative approach that
has received fairly regular re-awakenings of interest over the years, having been