Composting toilets
From: Neena Jud (
Date: Thu, 19 Dec 2013 05:12:30 -0800 (PST)
I happen to be writing an article this month about my experience with
designing a composting toilet facility for a nature preserve in southern
Kentucky. So let me take a few minutes to summarize (sorry - it is long):
Toilet systems that use water to carry the waste product away have recently
come under scrutiny due to concerns about availability of water. This is of
greater concern in the arid west, but all may be subject to some cost of
treatment of the effluent. There are two primary wet systems: connected into
a municipal sewer or a septic system. For a septic system, one must be
concerned about percolation rates AND the depth to the groundwater. In
Kentucky there is a lot of porous limestone, fairly near the surface (i.e.
Mammoth Cave). If the bacteria and microbes haven't finished their job by
the time the liquid seeps into the groundwater, your neighbors downstream
will not be happy.
Dry systems are worth considering. Pit type outhouses are the oldest
"system". They are inexpensive because they are temporary. After a while
that pit will fill up. You can move the whole structure or build new. Plus
there is the potential for leaching contaminants into the groundwater. And
in the heat of the summer there is an odor. There are Incinerating toilets.
Very compact, but they require gas or electricity to operate. A little bit
of ashes need to be removed occasionally. Most of these are very small and
appropriate for a cabin in the woods - not heavy use. Composting systems
seemed tome to be the best choice for my project of all the dry systems.
(You may know this already but.) when a bear shits in the woods, there are
organisms and microorganisms in the leaf litter and top layer of the soil
which break down the animal wastes into nutrients for the plants. Composters
require an initial inoculation of microorganisms and a layer of wood
shavings to take the place of the leaf litter. After each use another scoop
of wood shavings is added. After some period of time, the decomposers
happily turn what we consider waste matter into the same type of compost
that you can get from the community scrap food pile next to the vegetable
garden. And anyone who has messed with the compost pile knows that there is
an optimal ratio of autumn leaves, grass clippings, vegetable scraps,
eggshells and water to get the proper nitrogen-carbon mix.
There are choices amongst composting systems - large scale use and small
scale like in a home. They all use wood shavings to provide the plant matter
component and there must be some space below the toilet for the composting
to occur (frequently downstairs). Most of the small scale systems are
homemade, and therefore less expensive, but also subject to being more
One system is called "Owner built 2 chamber". Downstairs there must be two
miniature rooms (chambers) side by side, with access doors in a front wall.
Upstairs is a large toilet room over the top of both chambers with a hole in
the floor. The toilet is secured over one hole while the one chamber is
accepting contributions. The other hole is closed off. When the first
chamber is full, switch the toilet over to the other side and contribute to
the second side, letting the material in the first chamber decompose. There
needs to be a vent pipe for each chamber and a convenient container of wood
shavings proximate to the toilet. The floor of the chambers needs to pitch
in one direction to collect excess liquid. This can be piped out to a
graywater bed that has other water sources contributing to it (i.e.laundry).

Another system is called the "Carousel". At one time they could be purchased
from Scandinavia, but I think these days one must construct their own based
on that design. There is a rotating drum divided into quadrants. The center
of the drum is offset from the toilet chute above so the contributions go
into one quarter. When that quadrant is full, rotate the drum and contribute
to the next space. By the time three quadrants are filled, the material in
the first quadrant is composted, and it can be removed to the garden or
The final homemade system I will describe is the "Big Batch - EKAT". This
relies on two (or more) wheely bins, or demolition carts that have a sinuous
sculpture of perforated pvc pipes for ventilation - which must be connected
to a vent pipe. One receives the contributions while the other is
processing. And once it is ready to be emptied, take it straight out to the
For my project, I didn't think our volunteers would be willing to deal with
any of the homemade systems, and I didn't think they had the necessary
capacity, so I went up in scale to the pre-engineered, manufactured systems.
One big advantage is that they are more likely to be accepted by regulatory
authorities like Health Departments. All these require a vent pipe which
takes away the odor, sometimes fan assisted which requires electricity -
either from the grid or from a Photo Voltaic panel. There also must be a
method to collect & remove excess liquid. This can be either with an
evaporation chamber or into a graywater garden. Depending upon your usage
(liquid contributions vs solids) and your ambient humidity, there may be a
need for additional water into the composter.
Someone else mentioned Clivus Multrum. They have been around a long time,
make good quality systems, spend a lot on advertising and continuing
education which contributes to a higher cost. I think another aspect is they
are located in the northeast (higher land cost and higher employee pay).
Definitely worth looking at their products!
I chose the Phoenix 200 system from Advanced Composting in Whitefish,
Montana. Their unit is more vertical than the Clivus, and has a slightly
different way of moving the material down to the removal door. Cost of unit
was 75% of the big brand name.
There are at least two other large scale systems manufacturers. One is
Composting Toilet Systems in Newport, Washington. I can't find my records on
the other, but it is also closer to the Pacific Ocean. Their systems are
similar in design to the Clivus Multrum base line model. I'm not sure of the
costs of these, since the footprint of their composters did not fit my
design as well as the Phoenix.
My design has been in operation for almost two years, and amazingly the
compost is not ready to be removed. We keep adding shavings and the level
doesn't rise. I don't know what is going on, but it is not a problem, so I
will let the microorganisms keep doing their thing.
Well, that is enough for today. Search the internet for "composting toilet
systems" and you will find plenty of additional reading.
Neena Jud, AIA LEED AP
Harmony Architecture
Cincinnati, Ohio
harmony [at]

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