From Volume 7, No. 6 -- June 1998
For years, Clivus Multrum has
been the de facto standard
for composting toilets in North America. Clivus was
introduced in North America from Sweden during the
1970s by Abby Rockefeller. Almost single-handedly,
the Clivus established composting toilets as a viable
alternative to conventional flush toilets. While Clivus
remains an active player in the composting toilet
field, the product's dominance in the field could
be threatened by the growing popularity of a challenger:
the Phoenix Composting Toilet from Advanced Composting
Systems of Whitefish, Montana.
The Phoenix Composting Toilet has one to three shafts
with tines for aeration. Compost is removed at the
bottom. Photo: Advanced Composting Systems
Glenn Nelson founded Advanced Composting Systems
in the mid-1980s. Prior to that he was a licensed
manufacturer of Clivus toilets (one of two in the
U.S.) and played a key role in improving the Clivus
design. Through working on the Clivus design, he gained
a great deal of insight into the workings of composting
toiletsthen, with the Phoenix, he designed a very
different product.
Advantages of composting toilets
Composting toilets allow human wastes to be converted
into nutrient-rich compost, which
can be used to fertilize plants though most experts
recommend against fertilizing food crops with composted
human waste. Composting toilets save a lot of water
by eliminating the use of water for toilet flushing
(or at least eliminating most of the water). This
reduces extraction pressures on aquifers or surface
waters and (with systems connected to municipal sewage
treatment plants) educes the energy and environmental
costs of treating wastewater. Compared with standard
on-site wastewater disposal systems (septic tank and
leach field), a composting toilet reduces nutrient
loading of the aquifer and lower-elevation surface
waters fed by groundwater.
How the Phoenix toilet
works
The residential-scale toilets come in three sizes,
rated for two people, four people, or eight people.
These have either two or three modular compartments.
The larger models are taller but have the same footprint
as smaller models. On initial set-up, the composting
chamber is "charged" with wood shavings,
peat moss, and water to provide an environment that
will be conducive to biological decomposition. During
use, waste enters the top either through one or more
12"-diameter (300 mm) chutes from waterless toilets
located directly above the tank, through 4"-diameter
(100 mm) sloped pipes from micro-flush toilets not
positioned directly above the tank, or through 11/2"-diameter
(38 mm) hoses from vacuum-flush toilets located below
the top of the tank. A separate shaft from the kitchen
can also be used to deliver compostable kitchen waste
to the composting tank. During normal usage, a bulking
agent (typically wood shavings or sawdust) is regularly
added to the composting toilet to assist in the decomposition
process.
Waste gradually builds up in the tank and decomposes
through the action of aerobic bacteria. A shaft with
tines on it is manually rotated with a crank to periodically
mix the decomposing waste, ensuring adequate oxygenation.
In the smallest model, there is only one mixing shaft;
on the larger models there are either two or three.
The manufacturer recommends turning the crank weekly,
but one user EBN spoke with turns it daily partly
for the exercise (it takes significant effort, he
said). Decomposed waste that has been there the longest
is at the bottom of the tank, where it can be periodically
removed typically once a year. Optimal decomposition
occurs when the insulated tank is in a space that
stays at about 65F (18.3C).
With a properly operating family-sized composting
toilet, less than a cubic foot
of composted waste is removed
annually. This is because most
of the mass of the human waste
is converted into carbon dioxide
and water vapor (the primary
products of decomposition), which
are volatile gases. In public
facilities, the amount of compost
removed can be far greater (see
below). ACS Note. This paragraph
is not correct. For a Phoenix
that is operated and maintained
correctly, the annual amount
of compost removed will be approximately
12 cubic feet.
An electric fan and vent pipe are located at the
top of the tank to pull fresh
air into the tank through specially
designed air baffles in the sides and to remove gases
and odors. This vent usually extends up through the
roof, and the five-watt fan operates continually,
using about 45 kWh per year. Sustainable building
expert Jorg Ostrowski, of Calgary, Alberta added a
small light by the fan that attracts fruit flies (often
an unwanted member of the compost ecosystem), which
are then ejected from the composter. Both fan and
light can easily be operated with a photovoltaic panel
and battery. Liquids are separated from solids through
a drain at the bottom of the tank and either resprayed
over the pile or removed. With vacuum-flush and micro-flush
toilets, excess liquid may need to be removed; however,
with waterless toilets, liquids are more commonly
recirculated back into the pile using the manual respray
system supplied with the unit. Depending on the conditions,
it is sometimes necessary to
add additional water to keep the pile moist enough
for optimal decomposition.
Comparisons with Clivus Multrum
Those readers familiar with the Clivus Multrum composting
toilet know that this system has a large tank (significantly
longer than that of the Phoenix, though ot as tall)
with a sloped bottom. The idea is that waste entering
the tank at the uphill end will gradually slump downward
as it decomposes. The problem, according to Nelson,
is that decomposed waste at the bottom of the pile
in a Clivus doesn't slide along as it is supposed
to. Recently added waste often flows over the top
of the older waste. The result is that waste that
has not been adequately decomposed may get removed
during cleanout. That's not good from a health and
safety standpoint.
Nelson knows this because he has done extensive
testing of both Clivus and Phoenix toilets. Every
six months he puts a layer of dated tags, such as
color-coded marbles, in his composting toilets (there
must be a joke in here somewhere about "anal
retentive," but we're not going to touch it).
With the Clivus he found that some of these would
never come out. "People work with just one-half
or one-third of the compost pile [with the Clivus]," he
told EBN. With the Phoenix design, on the other hand,
Nelson's marked tags stay right on track first-in,
first-out.
Another problem Nelson had with
the Clivus was pooling of
liquid waste at the bottom of the tank, often becoming
anaerobic (a smelly type of decomposition that occurs
when insufficient oxygen is available). This led to
his liquid-separation system in the Phoenix that allows
manual respraying of the liquids onto the top of the
composting pile. Alternately, the liquid can be drained
awayeither into a conventional (downsized) septic
system or a peat filtration bed.
Barry Greese, director of operations at Clivus,
admitted that some of the compost remains in the rear
pocket of the tank, but said this isn't a problem.
He told EBN that the company is making continual improvements
to their line of composting toilets and welcomes the
more active role Phoenix is playing in the industry. "If
there are more companies out there talking up human
waste recycling, it's a better thing all the way around," he
said. "The more the merrier."
User experience
Jorg Ostrowski, of Calgary, Alberta installed a
Phoenix Composting Toilet in 1994 and is, so far,
very happy with its operation. He has not yet begun
removing composted waste, because the toilet typically
takes several years to build up enough compost that
some needs to be removed. Ostrowski and his family
use the toilet as a household composter, adding kitchen
waste, weeds from the garden, even dust from the vacuum
cleaner "anything biodegradable."
At Grand Canyon National Park, the Phoenix Composting
Toilet is quite popular, with eight toilets currently
in use and several more going in. The Indian Garden
facility at the bottom of the Canyon has had several
Clivus composting toilets in use for about 15 years
and one Phoenix toilet for eight or nine years. "I
like the Phoenix much better than the Clivus toilets," Indian
Garden manager Larry Simkins told EBN. "It's
much easier to remove the compost from the Phoenix," he
said, which is an important issue given the high usage
the toilets get. In 1995, the last year for which
they have usage records (automatic counters on toilet
stalls), the Phoenix averaged 100 uses per day, with
peak usage significantly higher. The park removes
four to six 55-gallon drums of compost from the Indian
Garden Phoenix toilet each year, flying it out by
helicopter. Simkins also feels that the Phoenix does
a better job at composting the wasteprobably because
of the aeration that occurs when the tines are rotated.
Since the park first began using the Phoenix, all
new composting toilets installed have been Phoenix
models, according to Simkins.
Details
The Phoenix Composting Toilet is manufactured out
of rotationally molded polyethylene. The polyethylene
used in the interior baffles is post-industrial recycled,
but the plastic for the tank itself is made from virgin
resin. Nelson has tried to incorporate more recycled-content
plastic, but it just hasn't been cost-effective, he
told EBN.
Be aware that the Phoeix toilet
is not cheap. The list price ranges from $3,500 for the smallest residential model
to about $6,000 for the largest unit (designed for
a public facility). In suitable soils, this can equal
the cost of putting in a septic tank and leach field,
but it is generally less expensive than a conventional
in-ground system on poor soils. And of course there
is no water use, which can save money over time. We
don't attach a value to keeping groundwater uncontaminated,
so our economic analyses don't factor that in. All
products are shipped directly from the manufacturing
facility in Whitefish, Montana, though there are several "sales
associates" throughout the U.S. and Canada. To
date the company has produced and sold just over 300
toilets.
For more information:
Glenn Nelson
Advanced Composting Systems
195 Meadows Road
Whitefish, MT 59937
406/862-3854, 406/862-3855 (fax)
Weblink: www.compostingtoilet.com