What are the similarities and differences in composting
systems that can be operated in open or in-vessel
systems - with or without worms?
Reference and sighting researched by: Tanya
Vece
(Re-print of media material from BioCycle April
1997, pages 57-59)
THE IMPORTANCE of biological processes
in the management of animal organic wastes has
been widely recognized. Within the broad range
of bioprocesses available, this report deals with
the two which are the most efficient for converting
solid organic residuals into useful products -
composting and vermicomposting. The purpose is
to compare the advantages and disadvantages of
the two processes.
COMPOSTING METHODS
Open systems of composting can be summarized as
follows: Windrow composting consists of placing
the mixture of raw materials in long narrow piles
or windrows which are turned mechanically on a
regular basis to aerate the piles. Turning alone
often does not ensure consistent oxygenation.
Within an hour after turning, oxygen levels in
a pile often drop drastically, and microbial activity
is correspondingly reduced. For this reason, the
pile must be turned frequently, leading to technical
and economic problems.
Moreover, pile size is another important consideration,
because piles higher than three meters become
difficult to aerate. In forced aerated static
piles, a blower provides air to the composting
mass. No turning of the materials is needed once
the pile is formed. There are basically two ways
to oxygenate the piles: Bottom suction draws air
through the pile by the imposition of negative
pressure. In this kind of ventilation, height
is a critical factor. With piles greater than
2.5 to three meters, it becomes almost impossible
to get uniform aeration.
These piles must be blanketed with an insulating
layer (usually cured compost) to ensure a uniform
distribution of temperature. Bottom blowing is
used where aeration is provided by blowing air
through the pile (positive pressure). This method
tends to cool and dry the bottom layers of the
pile, leaving the outer layers warm and moist.
In alternative ventilation systems, bottom blowing
aeration is alternated with bottom suction aeration.
The alternative air movement leads to a homogenization
of temperature and moisture throughout the pile.
