The
VCU is an in-vessel, aerobic composting system suited
to processing biological waste in small to medium sized
municipal and industrial applications.
Composting takes place inside modular, insulated, stainless
steel-lined composting chambers, measuring 4.5 metres
high and 2.5 metres square. With a maximum throughput
of 10 tonnes per day per chamber, subject to nature of
feedstocks. Chambers are linked together to form systems
of any capacity. The VCU system is typically favoured
for facilities processing between 5,000T and 40,000T/annum.
Biological waste must have sufficient structural material
(or bulking agent) to allow the passage of air through
the waste when it is in the chamber. Bulking agent is
typically shredded green waste or wood waste. The proportion
of bulking agent required depends on the kind of waste
being processed and typically varies between 15% and 50%
by mass. These wastes are mixed in a large batch mixer
before being fed into the chamber by a series of sealed
conveyors.
The processing chambers operate continuously on a 'plug-flow'
principle. As product is removed daily from the base,
waste is fed into the top of the chamber. Typical retention
times vary between 4 and 14 days. Retention time used
depends on the plant's requirements.”
[click
image to enlarge]
[click
image to enlarge]
The
VCU's working principle is a re-engineering of the traditional
composting process, with air drawn up through the decomposing
waste as it moves down through the chamber. Heat is generated
by the metabolic activity of microbes at the chamber's lower
levels.
Rather than let this metabolic heat energy dissipate to
atmosphere, it is harnessed to help create a natural chimney
effect that draws in cool air at the open base of the chamber.Due
to the rising heat, temperatures vary between 40°C at
the base of the chamber and in excess of 70°C at the
top. Effectively, daily waste input is heat treated before
the degradation process begins.
Based on natural principles, this system is very energy-efficient
and does not require agitation, bio-filtration, external
heating or air injection. With minimal moving components,
maintenance and operating costs are very low.
