TENHUNEN@finujo.bitnet (03/29/89)
From: Lasse Johansson, Engineer
Firm Ekodesign
Pallastunturinkuja 7 G 25
SF-01280 Vantaa
FINLAND
Tel: Int. 358-0-3920186
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*EXCESSIVE AERATION - A COMMON ERROR IN COMPOSTING*
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In literature and in practical composting applications, the
importance of powerful aeration has been generally stressed.
Air exchange is of course inevitable, but in a considerable
less degree than in the current practice.
This can be cleared by comparing the two areas inside the
compost that has just been made and mixed so that its mois-
ture and nutrient proportions are suitable, and it has just
reached the optimum temperature area.
In this situation the INNER PART produces heat actively, and
the convection of the heat is prevented by a thick layer of
compost biomass around it. This same layer also SLOWS DOWN
the excessive gas exchange and reduces its chilling effect.
The SURFACE PART again receives continuously excess heat
from the warmer inner part, and it is chilled and dried by
the surrounding, freely moving air.
The reactors made according the current recommendations for
forced composting have been constructed mainly to imitate
the conditions of this surface part. A good example of this
are the electric, so called "rapid composting privies",
where the aeration has been forced by a blower, and the mis-
sing heat insulation is aimed to compensate by electric hea-
ting. These two actions - that both need extraneuous energy
- aim in a great deal to cancel each other. So the wished
effect, the promotion of the composting process, becomes
difficult.
This disadvantage will again be accentuated, if the mixing
will work badly or is wholly missing. The moisture and the
composting aid can be distributed in the mass very unevenly.
The particles with deviating specific mass - e.g. paper -
can even be left wholly unmixed, because the surface dried
by the too efficient air exchange will lose part of its
sticking and covering properties.
The same errors can be found in the unheated containers of
direct composting privies and - in general - in household
waste composters. The drawback effects of incomplete mixing
will be aimed to compensate by the too effective aeration.
The chilling effect will delay the process, and this makes
one again to scale up the size of the unit, so that the
price will rise and operation and maintenance will become
more difficult.
The process could be forced by reducing aeration and by inc-
reasing heat insulation and mixing. So, the unit size could
be scaled down. Joining this with good technical and ergo-
nomical planning practice, a product can be designed that
will both be a bestseller and add the proportion of ecolo-
gical alternatives in our waste management practice.
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*Theory for a NEW COMPOSTING PRIVY DESIGN:*
*******************************************
By imitating the conditions where the INNER PART of the
well-working compost will reach its momentary temperature
maximum and by aiming to maintain this stage as a continuous
process, it is possible to develop a small and energy self-
sufficient composting process.
***
ORGANIZER'S COMMENT:
Please send your possible comments to the BIO-CONVERSION
bulletin board / newsgroup / teleconference system you'll
use - or straight to me:
Organizer: Juhani Tenhunen, M. Sc. (Eng.)
University of Joensuu
Karelian Institute, Section of Ecology
Laboratory of Environmental and Energy Biotechnology
P.O. Box 111
SF-80101 Joensuu
FINLAND
Telefax: Int. 358-0-1513590
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Mail copy (incl. original in Finnish): Jarmo Louvo
Tapio Raita
Arto Salokangas
Mirja Salkinoja-Salonen
Arja Vuorinen
Arto Stenroos
Sirkka Malkki
George Woolston
Raimo Lilja
Rainer Lahti