Agriculture Reference
In-Depth Information
(Price and Phillips 1990; Fletcher 1991; Edwards 1995a,b). These systems use large containers
raised on legs above the ground ( Figure 18.3 ) . This allows organic wastes to be added in thin layers
to the surface from mobile gantries at 1- to 2-day intervals, and the vermicomposts can be collected
mechanically through mesh floors at the bottom using manual power or electrically driven breaker
bars, which travel up and down the length of the system on a winch. Waste released on the floor
can be brought from under the reactor to one end by hydraulically driven flap scraper systems of
the kind used to collect manure from dairy cows in barns. Such reactors can range from medium-
technology systems using manually operated loading and waste collection systems to large (40 m
long, 2.8 m wide, 1 m deep or 1 m long legs) processes that are completely automated, electrically
hydraulically driven, continuous flow reactors, which have operated successfully in the U.K., United
States, and Australia for several years (Edwards 1998). The earthworm populations in such reactors
tend to reach an equilibrium biomass of about 9 kg per m 2 . Such reactors can fully process the
whole 1-m depth of suitable organic wastes they contain in about 30 to 45 days (Edwards 1995b,
1998). Economic studies have shown that such reactors have a much greater economic potential
to produce high-grade plant growth media with few losses very quickly and much more efficiently
than do windrows or ground beds.
C OMPLETE R ECYCLING V ERMICOMPOSTING S YSTEM
A complete, vermiculture-based, urban waste recycling system has been developed in France. This
involves putting waste through a selector that breaks up plastic wastes and removes them, followed
by manual sorting, sorting of rolling objects such as bottles, and separation of ferrous metal objects
with magnets. The waste is then transported to a thermophilic compost system for 30 days, followed
by vermicomposting in a very deep continuous flow system for about 60 days before removing
earthworms, storing, and packaging. This system can turn as much as 27% of the total urban waste
stream into vermicompost. This was sold and added to the commercial potential of the recycling
considerably.
C OMMERCIALIZATION AND E CONOMICS OF V ERMICOMPOSTING S YSTEMS
The use of organic wastes to grow earthworms is an extensive cottage industry in the United
States and other parts of the world. Many of these small-scale producers market the castings
they produce for growing plants. Most operations in the United States are based primarily on
windrow systems, which have many economic and environmental drawbacks, as discussed here.
They are ground based and require large areas of land, with potential for groundwater pollution
with nutrients and other contaminants because they are watered regularly and usually have no
protection against leaching. The process is slow, taking 4 to 12 months to complete. The
harvesting of the vermicompost is laborious and time consuming because the earthworms in
the waste have to be separated, usually by a screening process, before marketing. Although the
initial capital outlay, other than land, is low, its labor costs are high at all stages of operation.
The wedge system designed by Edwards and colleagues described in this section has been used
by a number of organizations. Although it uses an innovative but relatively inexpensive tech-
nology and requires less equipment, it overcomes many of the labor, economic, and environ-
mental drawbacks associated with windrows. In particular, it uses less land, there is no leaching
into groundwater, and there is no need to separate earthworms from the vermicompost. The
processing time is shorter (3 to 4 months).
The automated continuous flow reactor system designed by Edwards and colleagues (Edwards
1995b, 1998) and used by the Oregon Soil Corporation since 1992 has totally different environ-
mental, operating, and economic characteristics. The equipment has to be under cover to maintain
controlled environmental conditions, and the waste compartment is raised above the floor and is
maintained at 80% moisture content and 20 to 32AC with no leaching. The retention or processing
 
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