In-vessel composting refers to a group of methods
which confine the composting mass within a building,
container or vessel. There are a variety of
in-vessel methods with different combinations
of vessels, aeration devices, and turning mechanisms.
Among these, the most widely utilized are continuous
vertical reactors, and horizontal reactors.
In continuous vertical reactors, the materials
usually are loaded through the top of the reactor
and discharged from its bottom. Oxygenation
is provided by forcing air up from the bottom
through the composting mass. These reactors
can process large amounts of material (as much
as 2,000 cubic meters) and may be as high as
nine meters. However, the height is extremely
critical and masses higher than three meters
lead to a serious problems in ventilation.
In horizontal reactors, the materials are arranged
along the length of the unit and the depth never
exceeds two or three meters. The principal advantage
of these systems is the possibility to control
the process, resulting in a shorter duration
of the thermophilic stage than in the open systems.
Because oxygen is supplied either by turning
or by aeration, the composting mass can be uniformly
oxygenated and the temperature can be readily