Biotechnology and Waste - Environmental Biotechnology: Theory and Application - page 200

to the growing demand for biowaste diversion. At the same time, each has its
limitations also. For AD, the airtight nature of the reactor, the gas-handling
arrangements needed to guarantee that the potentially explosive methane pro-
duced 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 practi-
cal 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 reawakenings of interest over the years, having been
variously termed worm composting , vermicomposting, vermiculture or our pre-
ferred annelidic conversion , a term first attributed to H. Carl Klauck of Newgate,
Ontario. The description worm composting and its like is somewhat misleading,
since the process from both biological and operational criteria is quite distinct
from true compost production in two significant ways.
Firstly, as we have seen, in traditional composting, breakdown is brought
about by the direct actions of a thriving microbial community. Within a worm-
based system, while micro-organisms may contribute in some way to the overall
biodegradation, their role in this respect is very much incidental to that of the
worms themselves.
Secondly, in worm systems, biowaste is typically laid in much shallower layers
than is the case for windrows or static piles, frequently being deposited on the