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

variously termed worm composting , vermicomposting , vermiculture or our pre-
ferred annelidic conversion (AC), 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
surface of an underlying soil bed. This is a major difference, principally because
it reduces the natural self-heating tendency within the decomposing matrix.
Worms of various species can be present in traditional compost heaps, even in
thermophilic piles, but they avoid the genuinely thermophilic core, being found
at the significantly cooler edges of the heap. In addition, under such conditions
the resident annelid population is, in any case, many magnitudes smaller than
in the deliberately high-biomass levels of AC systems. While in common with
all poikilothermic organisms, worms do require some warmth to remain active,
which for most species means a lower limit of 10 ◦ C, they do not generally
tolerate temperatures in excess of 30 ◦ C and death occurs above 35 ◦ C. Most
species have an optimum range of 18-25 ◦ C, which makes the point very clearly
that the highly exothermic conditions encountered as part of the 'true' compost-
ing process would be impossible for them to survive, and certainly not in any
sizeable numbers.
Annelidic conversion is similar to composting in the sense that it can be scaled
to meet particular needs and, as a result, it has been promoted in various forms for
both domestic and municipal applications over the years. Again, like composting,
particularly in respect of home bins, this has not been entirely free of problems,
since all the difficulties regarding bin design, operator diligence and issues of
compliance apply if anything, more rigorously to AC as to traditional composting.
While some recycling officers have found that these projects have been widely
welcomed and effective, others report 'considerable' drop-off rate in usage.
In the case of commercial scale treatment, worm systems have sufficient in-
built flexibility to be tailored to suit. However, since the beds must be significantly
shallower than an equivalent windrow, accommodating the same amount of mate-
rial for treatment necessitates a much larger land requirement, which may itself
prove a constraining factor. Thus, for each tonne of biowaste to be deposited
weekly, the typical bed area required is around 45m 2 . Hence, for a typical Civic
Amenity Site annual production of 4000 tonnes, and allowing for the seasonal
nature of its arising, around half a hectare, or one and a quarter acres, of ground
is required simply for the beds themselves. This rises to more than double to
provide the necessary service access between and around the wormeries.