Composting Toilets
Composting is an aerobic process—it takes place with the presence
of air. That means that properly operating composting toilets do not
produce unpleasant smells or gases. The temperatures reached inside
the compost, along with the time the compost spends “curing”,
kill the disease organisms that might be present. Composting toilets
also conserve the nutrients in the feces and urine, so that they can
be returned to the land. Compost itself contains valuable organic
matter that does wonders for soil life and gardens, a topic which
will be expanded on in future writings on gardening.
Some people are worried about the fact that one might have to handle
material containing human feces. This is a valid concern, but it shouldn’t
be a problem if proper handwashing and other simple precautions take
place. After all, most of us are quite literally full of poop all
the time, and use the toilet on a regular basis, and it doesn’t
harm us. As long as you wash properly, a composting toilet is no more
dangerous than any other kind of toilet.
For extensive information on the subject of composting toilets, please read the well-written and thoroughly researched Humanure Handbook,
by Joseph Jenkins. You can visit his website at www.jenkinspublishing.com/humanure.html,
where the entire text is available online. He uses the term “humanure”
to refer to human poop.
Composting is a process in which microorganisms, normally present
in the soil and all around us, break down organic materials like kitchen
scraps, straw, poop, and so on. Essentially, they eat it. As they
do this, they also generate heat, the same way that our bodies generate
heat all the time. This heat builds up in the pile, and the increased
temperatures kill pathogens present. There is a special class of microorganisms
called “thermophilic microorganisms.” These microbes love
high temperatures. If you can get the pile up to thermophilic temperatures,
above 45°C (113°F), these microbes will love it. The composting
process will happen very rapidly, and all pathogens will quickly be
killed.
A well made compost will not smell, and will be quite warm. The essential
ingredients of a good compost are sufficient moisture, oxygen, a warm
enough temperature, and a good balance between carbon and nitrogen.
The compost should not be too dry, or too
wet. If it is too dry, the microorganisms will not be able
to grow properly, and valuable nitrogen will be lost to the air. If
it is too wet, than the air won’t be able to get in, and the
compost will become anaerobic (and smelly). A compost should be about
as damp as a wrung-out sponge. If your compost is too dry, just add
household wastewater. If it is too wet, you need to add more bulky
material like straw, or other roughage materials discussed below.
Giving a compost pile oxygen means giving it air.
This is why bulky materials are so important. You can use sawdust,
leaf mould, peat moss, weeds, hay, straw, leaves, rice hulls, shredded
paper or cardboard, or similar materials. If something in the compost
pile smells bad, cover it with this bulky material.
Temperature is important because the thermophilic
composting microbes need a certain minimum temperature to operate,
and because the elevated temperature kills pathogens (just as a fever
kills pathogens in our bodies). In cold climates, they will sleep
over winter, but the compost pile will come alive again in the spring.
This freezing also kills some pathogens. You can continue to add compost
to the pile even if it is frozen.
A good carbon to nitrogen ratio helps the compost
to heat up, by giving the microbes a healthy, balanced diet. The bulky
materials listed above are very high in carbon. Adding manure and
urine equalize the nitrogen ratio. You want to have a ratio of carbon
to nitrogen somewhere between 20:1 and 35:1. If you have too much
nitrogen in your compost, it will release that nitrogen as ammonia
gas, which you don’t want. Not only will you lose nitrogen,
but it smells bad.
Many people do not pee in their composting toilets, because it causes
a smell for them. This smell comes from excess nitrogen and water,
and adding roughage compensates. Jenkins recommends including urine
in a well-balanced compost, but most of the people I know simply apply
their urine (diluted with 3 to 6 parts of water) to their garden or
orchard. (Urine is almost universally free of pathogens. Only urinary
schistosomiasis can be spread by urine, and it exists only in a few
tropical locations.) See what works for you with your climate and
soils. If putting urine in your composting toilet isn’t working,
your nose will tell you quickly.
Separating urine may also be a good idea in situations where the
nitrogen content is required immediately for gardening, and the gardener
can not wait several years for the compost to cure.
See the books in the notes at the end of this section for comprehensive
tables of the carbon and nitrogen contents of different foods and
organic materials.
There is a wide variety of home made and commercial compost toilets,
but, of course, we will discuss those you can make yourself.
The two discussed here are the two-chamber mouldering toilet, and
the Jenkins sawdust toilet.
The Jenkins Sawdust Toilet
Described by Joseph Jenkins in the Humanure Handbook, the sawdust
toilet is a convenient method of composting your humanure while still
having a toilet inside your home. This method consists of two parts,
a toilet receptacle inside, which is filled with sawdust or other
roughage, and regularly emptied into a set of composting bins outside.
The toilet receptacle inside is simple to construct, and can be made
in a variety of different ways. Using 5-gallon buckets as the receptacle
is easy, since they are so common. Jenkins recommends not using a
larger size than that, since the contents would be very heavy to carry
out to the pile. You can build a toilet seat on top of it, or a platform
to squat on.
After each “deposit”, add roughage to cover the feces
and urine. This toilet does not require an airtight or fly-proof lid,
since the roughage keeps out flies and cuts smells.
When the receptacle is full (or almost too heavy to carry) it can
be dumped in the compost bin and buried in the top layer of the compost
pile.
There are a number of designs for the compost bins, many of which
vary by climate. People in hot, dry climates, may need to dig a pit
to put their compost in to conserve valuable moisture. People in very
rainy climates may need to build a roof over their compost pile to
keep it dry enough, and prevent nutrients from leaching away.
Jenkins suggests a simple rotating multi-bin system, as shown. Remember
that you will need at least two bins, one for this year’s compost
pile (still being built), and one for last year’s which is composting.
If climate or other constraints prevent your compost pile from reaching
thermophilic temperatures, you will want to add a third bin to let
the compost mature for a full two years. You may also want an extra,
sheltered bin to keep roughage such as straw, grass, or hay in.
When starting a new humanure compost pile, put down at least 18 inches
of roughage. This "sponge" will soak up any fluid leaching
from the pile to prevent contamination.
If you don’t have any smells, hopefully you won’t have
any trouble with animals digging into the pile. If this is a problem,
you should put wire or other barriers around the pile, to prevent
animals from accessing the pile and spreading pathogens.
The Two Chamber Toilet
This composting toilet is essentially an outhouse version of the
general system described above. The “bathroom” is located
directly above the composting chamber, as shown. There are two seats
(or holes, if you prefer to squat), one for each chamber. The chambers
are used one at a time. While one chamber is composting and closed
off, the other is in use. After each deposit, roughage is dropped
into the chamber.
You can make the chamber out of cement, wood, or other materials
that you have available. However, it need not be air or fluid-tight.
You will need a door on the “back” to access the compost
for checking on it and eventually emptying the chamber. You may need
to smooth the pile, check the moisture, and add more roughage.
Variations
There are plenty of variations on simple and homebuilt composting
toilet designs. To increase the composting temperature, some toilets
use solar energy to heat the pile and accelerate decomposition. You
can enhance the two-chamber design above by facing the chambers towards
the south and placing glass or translucent plastic on the wall to
let in sunlight. You could even include reflectors to heat things
up even more.
Some designs also include perforated pipes or other means of increasing
the air supply to the compost pile. Others creatively incorporate
reused barrels or other materials in their toilets. You can check
out a variety of designs on the web, and experiment for yourself.
Composting Toilet Notes
www.compostingtoilet.org/
The Humanure Handbook, by Joseph Jenkins
The Toilet Papers, by Sim Van Der Ryn
More information on composting in general will be covered in future
writings. In the meantime, check out excellent books on the subject
like “The Real Dirt: The Complete Guide to Backyard, Balcony,
and Apartment Composting” by Mark Cullen and Lorraine Johnson.
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