Biotechnology and Waste - Environmental Biotechnology: Theory and Application - page 202

weight per day. This influx of material is turned into increased worm biomass,
both in terms of individual growth and population increase. As a result, AC has
tended to make use of redworm species such as Dendrobaena, Helodrilus and
especially Eisenia as the mainstay of these operations. In nature, these animals
are naturally found amongst the fallen plant material of woods and forests,
where they are commonly associated with the production of leaf litter. Their
use in worm beds stands as another example of making use of an organism's
natural abilities to achieve the biotechnologist's desired result. When the
artificial environment of the worm bed is well enough managed and conditions
suitably optimised, the redworms decompose and mineralise the biowaste
extremely efficiently, effectively reprising their role in nature under these
engineered conditions.
Despite the predominance of redworms within vermiculture for the reasons out-
lined, there have been a number of cases that have used true earthworm species,
with varying degrees of success. Thus, members of the genera Lumbricus and
Amynthas have featured, but perhaps one of the most notable successes was with
Pheretima elongata , a deep burrowing worm, native to India, which was used to
great effect as part of the Bombay plague prevention project, which was founded
in 1994 in response to an earlier outbreak of the disease. The growing amount
of waste in the city had been strongly implicated in attracting and harbouring
the vector rats. The use of vermiculture proved very effective in reducing the
biowaste problem (Menon, 1994) and hence was seen as a major preventative
measure against a recurrence of the plague.
The use of worms to break down waste is not a particularly novel idea, though
like many aspects of environmental biotechnology, it frequently seems to fall first
in and then out of favour on a fairly regular basis. The advantages of worm-based
biowaste treatment are fairly easy to see. In the first instance, vermiculture offers
a high potential volumetric reduction, often exceeding 70% while producing a
well-stabilised final product. Secondly, this product itself is rich in potassium,
nitrogen, phosphorous and other minerals, which is presented in an ideal form
for plant uptake, and hence represents a high fertiliser value. The market for
this product has already been successfully established in some parts of the world
and many others seem set to follow. This is an important issue, as it has been
estimated that for every 1 tonne of biowaste deposited on the bed, around half a
tonne of worm casts is produced (Denham, 1996).
Finally, the rapid growth potential of worms under idealised conditions has
the potential to provide a harvestable biomass resource, typically either as seed
populations for other vermiculture operations or for direct sale into the fishing
market. The reputation of the bait outlet has been tarnished in the light of various
spectacular collapses, most notably the Californian pyramid franchise back in
the 1970s and other similar operations in the UK more recently. Often aimed at
farmers seeking diversification ventures, it is unlikely that worm production will
truly be the salvation for all of them. However, the fact remains that there are