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The Composting Toilet - an ecologically responsible solution
by Flemming Abrahamsson, "Mikroben" nr. 7, 1994
translated from the Danish by "Renewable Energy"
The composting toilet solves with one blow the problems
of "black waste water" and loaded nutrient salts in the
recipient and overuse of our precious water resources.
Our daily consumption of water is 180-200 litres which
translates to approximately 70,000 litres
of drinking water/person/year. Ordinary flush toilets are
responsible for 15-20,000 litres of this amount. Composting
toilets do away with this water wastage and at the same time
keep feces, paper and even urine out of the sewage system.
When one mentions the word "composting toilet"
or "mulch latrine", people immediately
protest and come up with such comments as,
"you don't mean you expect us to go back to the use of stinky latrines ?!" and
"doesn't it smell like slurry ?!" But on this matter
I must be firm - today we have an odourless and comfortable solution
very suitable for installation inside the home.
In contrast to many so-called "ingenious" solutions such as
incineration toilets, freezer-bag toilets,
dry toilets and the like, which often require the use of large amounts of
energy, a genuine composting toilet consists of
a large container in which a composting process takes place before
the contents are removed, and a toilet
stool + seat very similar in appearance to
that of an ordinary flush toilet. The end product of the composting toilet is
an odourless humus material totally unlike
manure or the contents of a latrine. (there is no danger in handling it and
it can be used as fertilizer for shrubs and
decorative plants as long as it has had soil contact for 19 months)
Denmark's neighboring countries
During the past few decades, individuals in Norway and Sweden have been
continuously working on the development of composting
toilets, so that today we have a new generation of
composting toilets. In 1982, according to the Nordic Ministercounsil,
there were 300,000 composting toilets installed
throughout Scandinavia. I suppose that Denmark accounts
for only about 100 of these. Development has continued
at a fast rate in the neighbouring countries and the
latest encouraging news is that Tannum "municipality", near
Goteborg, Sweden, has recently forbidden flush toilets
from the year 2000 and currently builds 70% of their new
housing without flush toilets.
Because of the fact that 7% of Danish housing
(in rural areas) aren't connected to central
sewage systems, some research on composting toilets
has been undertaken at The Danish Technical University
and the most current news in this field is that a
project called "Kompost-toiletter 1994" by Simon Wris-Berg and
Peter Friis Moller has been awarded a prize by Denmark's
agricultural school. Some Danish firms have experienced
an increase in inquiries about
composting toilets during the past few years
due both to increasing environmental awareness as well as ever
increasing water costs.
The design of a composting toilet
Composting toilets vary in appearance depending upon the manufacturer, but
common for them all, is that they have a collection
container for feces, paper, in some cases kitchen garbage, while
some separate urine into a second container. The contents of
the feces container are composted by aerobic
process, which takes about one year, into a humus like material.
In the company "Renewable Energy", we have
developed a year-round model called the "Eco-composter"
for family homes. The collection container of our toilets is
made of fibre reinforced concrete which makes for a
reduction in use of fibreglass and epoxy. The toilet stool,
which is made of either fibre-concrete or porcelain, is designed
so that urine and feces are kept separate. The feces,
paper and kitchen garbage drop vertically down into one
tank, while the urine is collected at the front - a design
appropriate for both female and male use. In this way the urine
can, without coming into contact with the feces, be
collected in a tank and because there is no danger of disease,
be used as liquid fertilizer when mixed with 4-5 times
its amount in water. The urine can also, of course, be mixed
with household "grey waste water". But this must be
regarded as the second solution. Our porcelain stool is designed
in such a way that the urine compartment can be
flushed with 0.1 litres of water.
The tank has ventilation channels to enable the oxidizing process
to take place, and all air is drawn up through a
vent which reaches up through and over the roof of the house.
This means that the composting toilet itself functions
as a ventilation system for the entire toiletroom,
keeping out unwanted smell. This makes for quite an advantage -
there is never any unpleasant smell connected with a "visit"
to the toiletroom.
As indicated in table 1, a family's
yearly production of compost humus is approximately
100-200 litres (the original amount of uncomposted feces
having been greatly reduced after composting).
Table 1 Yearly production per adult human:
400-500 litres urine which contains:
5 kg nitrogen
0.4 kg phosphate
0.9 kg potassium
50-60 litres feces which contains:
0.1 kg nitrogen
0.2 kg phosphate
0.2 kg potassium
Table 2
substance unit sewage sludge human manure animal manure soil
--------- ---- ------------- ------------ ------------- -----
N kg/t 30 250 25 1-2
P kg/t 20 35 10 0.4
K kg/t 2 45 17 0.5
Ca kg/t 25 30 12 25
Mg kg/t 4 7 4 7
Zn g/t 1750 200 100-800 26
Cu g/t 250 30 20-350 8
Ni g/t 20 2 1-36 5
Cd g/t 7 0.4 0.3 0.2
Pb g/t 300 1 5-15 17
Hg g/t 5 0.5 0.05
____________________________________________________________________________
table 2: The amounts of nutrients & heavy metals in manure and soil
source: J.Aa. Hansen and J.C. Tjell, 1982 w/Jacob Vester
____________________________________________________________________________
The components of our composting toilet take
up the same amount of space as a traditional flush toilet in the
toiletroom itself, while the collection-container and
ante-chamber are located beneath the floor of the toiletroom or
from a connected "lightbox" located outdoors.
Infection and the authorities
The Danish authorities require that the same minimum
criteria are fullfilled as with
sludge delivery, due to a risk of
disease-carrying bacteria and parasites,
although the compost can always be spread on the ground because the
amount of heavy metals in human feces + urine is extremely
low when not mixed with other wastewater (see table 1)
The compost-humus could of course be pasteurized at 70
degrees for a minimum of 1 hour, but this holds no
interest for us, because we want to avoid the use of
large amounts of energy and retain the good balance with
nutrients which are present in the compost-humus. We don't
want to use energy for no reasons. We require that the
compost is brought in contact with soil bacteria and kept
behind a little fence for yet another year before being
spread out on gardens or fields. This requirement
is easy to live with in cases where here is a complete plan for the
composting toilet and the "grey wastewater", for
instance first via a microbiological
cleaning in a sandfilter and finally by means of
gravitation in an "energy-forest draining system" so that we really can
put the compost in the "energy-forest". Today we are
no longer confronted with the same resistance to this
installation design as 10 years ago, due to greater
environmental awareness and stricter wastewater treatment
requirements.
We will experience fast and hopefully creative
development in the area of composting toilets combined
with more research which initially can find support in
the results of our neighbouring countries. Because the lack of
fresh water is a global problem, these solutions are
quite suitable for export to other countries.
Price: around 12000 d.kr. incl. toilet stool, compost container and ventilation
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