202 Environmental Biotechnology
achieved without waterlogging, since this reduces pile aeration and may, further
actively drive the resident worms to leave in search of drier conditions. Unsur-
prisingly, many commercial scale systems make use of extensive drainage works
to help avoid this. Well-ventilated covers are also often used, particularly in out-
door installations, which help overcome the rigours of the weather while also
producing continuously dark conditions. Accordingly, the worms are encouraged
to be active for much more of the day than would otherwise be the case. This
brings additional bonuses, since the burrowing of the animals themselves both
promotes enhanced aeration and has beneficial effects on odour control, partic-
ularly in respect of sulphide concentrations, which have been reported as being
reduced by a factor of 100 or more.
In common with trends in many other biotechnological interventions, there
has been some interest over the years in developing in-vessel systems. This
principally arises as an attempt to create circumstances in which process control
can be maximised, but has the additional benefit of also giving rise to a modular
and highly portable approach, which has helped annelidic conversion penetrate
areas that might otherwise have remained closed to it. One of the reasons for this
is that this approach gets around the need for a permanent installation, which may
be an important consideration for some applications. However, the unit processing
cost is consequently higher than would be the case for a simple land-based system
of similar operational capacity.
A number of different species of worms are used in vermicultural operations
around the world, but in general terms all of them can be placed into one of
two broad categories, namely redworms and earthworms. Although some uncer-
tainty exists as to the absolute validity of this division, it is a useful tool, at
least at the functional or morphological level, to aid understanding of the whole
approach. The true earthworms are burrowers, and generally speaking consume
dead biological material from within the soil itself rather than directly assimi-
lating the biowaste. The nutrient value of the organics so treated is returned via
worm casts. Hence, initiatives reliant on earthworms are probably best regarded
as a form of worm-enhanced composting. By contrast, redworms, which are
also sometimes termedmanureor compostworms, rapidly and directly feed
on the biowaste, consuming half or more of their own body 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, annelidic conversion
has tended to make use of redworm species such asDendrobaena, Helodrilus
and especiallyEisenia 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 lit-
ter. 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 condi-
tions suitably optimised, the redworms decompose and mineralise the biowaste