Toilets Emerge as Viable Alternatives
by Carol Steinfeld
January 25, 2001
Composting toilets are finding their
way into mainstream homes due to tightening wastewater regulations,
awareness of pollution, and compatible gray-water systems.
When Rob Okun took steps to sell his home in western Massachusetts
last summer, he triggered a town review process that ultimately
condemned the house. His septic system was located in high groundwater
and in a town water supply district – a clear pollution threat.
The Board of Health wouldn’t allow him to install just a holding
tank, which can be expensive to pump out (hence holding tanks have
a history of “developing” holes of suspicious origin).
The only acceptable solution was a zero-discharge system, one that
used up the home’s effluent. And they had one in mind: an
integrated composting toilet and wastewater system. In this case,
an engineered garden system that manages household washwater would
be enclosed in a greenhouse; built off the living room, it would
offer the added benefit of passive solar heat. The home’s
three toilets would be replaced with micro-flush toilets that flowed
to a composting reactor. Okun ultimately got his asking price from
a couple who were intrigued by the system. “The prospective
owners love the idea,” says David Del Porto, whose firm, Sustainable
Strategies, designed the system. “They didn’t realize
that this was possible. They’re really enthusiastic.”
Composting toilets – once only the toilet choice of parks
and owners of remote homes – are finding their way into
mainstream homes. Tightening wastewater regulations, growing awareness
of pollution sources, and compatible gray-water systems and flush
toilets are making them a viable alternative to septic systems
and central sewage treatment in many areas.
Think of a composting toilet as an air-breathing septic tank. Inside
the composting reactor, excrement, urine, toilet paper, and sometimes
kitchen scraps are transformed into compost by mostly aerobic microorganisms,
which break down the material to 10% of its original volume. In
fact, these microbes process 10 to 20 times faster than the anaerobic
bacteria at work in a septic tank.
“It’s nature’s way,” says Del Porto,
who has sold and designed several types of composting toilets
for 25 years. “You can compost in a teacup; it’s not
rocket science. What is science is managing the process for a
minimum of odors, cost, safety, and pathogen destruction.”
Just like commercial and backyard composting of organic wastes,
composting toilets must control the primary process factors: oxygen,
temperature, moisture, and a nutrient balance of 30 parts carbon
to one part nitrogen, he says.
A Warmer Reception
But the prospect of maintaining these systems turns off many potential
buyers, says Bill Wall of Clivus Multrum New England. Nearly all
of his customers now opt for his company’s service contract.
Service is available on an annual basis for about $200 and on a
four-times-annually basis for about $600 (prices depend on location).
It usually includes checking all parts, leveling the compost, and
removing it, if necessary. “This makes the operation and maintenance
easy now, so it’s a viable solution for more people,”
Property owners are also reconsidering this alternative due
to skyrocketing sewer rates and holding tank pumping costs. Others
like the fact that they allow them to reduce the size of their
leaching beds. Wall notes that some of his customers opted for
his systems to avoid cutting trees to make way for leaching beds.
Perhaps the most important change in the public’s reception
of composting toilets is that they can be coupled with micro-flush
toilets. “Many people don’t like the ‘black
hole’ concept,” says Wall, referring to what some
users of simple compost toilet systems see when they lift the
lid of a waterless toilet stool. “Now you can have a flush
toilet connected to your composter. It’s more traditional.
And you don’t have to have a straight chute,” he says.
Compatible micro-flush toilets include the SeaLand, which uses
one pint of water flushed with a foot pedal, and Evac and SeaLand
vacuum toilets, such as those used on airplanes and trains. The
new Vera Waterless Toilet uses the mass of the waste itself with
simple fluidic engineering to move the waste, and the Nepon toilets
from Japan use foam.
The extra water from these toilets must be treated by evaporation,
disposal, or utilization. AlasCan, Clivus Multrum, Phoenix, and
EcoTech offer wastewater systems to treat this liquid, as well
as the rest of a home’s washwater, or “gray water.”
Clivus Multrum and EcoTech offer gray-water irrigation systems
that treat the water through garden beds. These systems must be
approved by states on a case-by-case basis. Gray-water irrigation
has gained acceptance in many states, such as California and Arizona,
according to Del Porto. Other companies offer evaporators. AlasCan
offers a home-sized three-chambered aerobic wastewater treatment
One of the major obstacles to installing a composting toilet
is getting permits. Composting toilets usually require permits
from town, county, or state officials, and the ease of permitting
them varies widely across the country. Many health officers are
simply unfamiliar with these systems. Some fear that zero-discharge
systems will allow building in previously undevelopable areas.
Some states require backup conventional wastewater systems. States
that are more amenable than others include Massachusetts, Maine,
New Mexico and Washington. Permits are rarely granted for owner-built
composting toilets, unless they have rigorous monitoring or maintenance
plans. Many states require certification by NSF International,
essentially the “UL” of the public health industry.
Types of Composting Toilets
In terms of how they operate, most composting toilet designs are
based on either “batch” or “continuous”
composting. Batch composting is processing done in more than one
compost chamber, which are interchanged as they fill up. The advantage,
some say, is that older or finished compost is not contaminated
by the new nutrients and potential disease-causing organisms in
fresh waste. In some systems, the chambers can be removed from the
toilet to take outside to empty.
“Continuous” composting takes place in a single-chamber
composter, where fresh waste is continually deposited at the top
of a composting chamber, and finished compost is removed from
the other end of the unit.
Composting toilets are usually either “self-contained”
or “central” systems. In a central composting system,
the composting reactor is separate from the toilet bowl –
usually located in the basement or in its own enclosure to the
side of the building. All include fans; heaters are usually optional.
Commonly the choice of year-round homes and facilities with multiple
toilets, they range in price from $1,400 to $8,000 and higher
for large systems.
Among the central composters, the Clivus Multrum and the CTS
are inclined vault composters, essentially large inclined boxes
where waste moves down the incline, which slows its passage to
the bottom, helping to aerate it. Compost is removed through an
access hatch at the bottom of the tank. The Phoenix is a tall
vault with a stacked three-part system. Waste falls to a high
area, where rotatable tines act as a mixing device to break it
up and aerate it. It then falls to a grate, then to a collection
box. The AlasCan is a highly mechanized composter with power-driven
auger-agitators and high-velocity air flow via a fan. The Bio-Sun
system is a large canister tank in which a powerful air compressor
moves large volumes of air across the excrement. Increasingly,
Bio-Sun is designing the composting reactor right into the foundations
Occasional leveling of the material with a pitchfork is required
in some of these systems. Users also turn the compost at the removal
hatch end to prevent compaction and promote aeration. In all of
these models, urine and other liquids – called “leachate”
– drains to the bottom, where it is evaporated or must be
drained for disposal or utilization. All but the CTS employ a
leachate-recirculating system that pumps liquid from the bottom
and spritzes it on the top of the composting material.
The EcoTech Carousel is a fiberglass cylindrical container consisting
of an outer container that holds a rotatable inner container divided
into four compost chambers. This keeps liquid separate from the
compost, and compost in batches. When one chamber fills up, the
next is rotated into position. The Vera Toga 2000 is a system
of roll-away interchangeable 60-gallon compost reactors. Extra
containers can be purchased, giving it as much capacity as one
has containers. Sun-Mar’s new Centrex Plus features a two-chamber
version of its patented “bio-drum,” a rotatable canister,
and a finishing drawer. Sun-Mar’s Centrex, a smaller unit
featuring a smaller bio-drum and just one collection tray, is
typically only used in cottages.
Advantages of central systems: Larger units have long-term retention
(two years or more), allowing longer composting periods and more
capacity. Disadvantages: Their large sizes – a few are six
to 10 feet high – require special installation considerations.
The larger single-chamber units are also more susceptible to compaction
of the composting mass.
“Self-contained” toilets are single-unit composters
whereby the toilet seat and the compost reactor are all part of
the same appliance. These can sit in the bathroom. Due to their
small size, these are typically used in cottages and seasonal
homes. Their capacity typically ranges from two to six adults,
varying with the model. Prices range from about $850 for a Vera
Cottager to $1,470 for a BioLet XL.
Sun-Mar’s series of composting toilets all feature a revolving
bio-drum – a canister-like composter mounted horizontally.
A hand-crank allows users to periodically rotate the bio-drum
to mix and aerate the material. BioLet’s XL uses a mixing
arm to slice through the composting waste and push it through
a grate. Vera’s Toga series all feature interchangeable
composting chambers, as does the BioLet NE. Sancor’s Envirolet
has a moveable grate – called a “mulcherator”
– that can be manually pulled to break up, mix, and aerate
Advantages to self-contained units: These are lower-priced and
small, ensuring fewer installation issues. Disadvantages: Users
must constantly remove the finished compost while adding new material.
Due to their small size, they are often overloaded, and processing
can be incomplete. Excess leachate is the bane of the smaller
ones, and one must guard against letting the material bake and
dry into a hard mass.
There’s also the do-it-yourself option. “There’s
a rich history of owner-built composting toilets, from knock-offs
of commercial models to various innovative uses of industrial
containers,” says Del Porto, who has developed several site-built
designs himself. Site-built designs range from systems using 55-gallon
drums and a scissors jack to concrete-block chambers to toilet
seats placed over five-gallon pails. These often cost less, but
they can be difficult to get permitted. “If they provide
adequate aeration and heat, they all work about as well as the
amount of care their owners put into their operation and maintenance.
It’s the commercial manufacturers that have to develop user-friendly
technologies,” he says.
Nearly all toilets are available with fans (electrical or solar-powered)
and optional heaters. Supplementary heat speeds up the composting
process, although too much heat can dry out and halt composting.
Care and Feeding
Composting human waste needs added carbon to transform the nitrogen
in urine, as well as to help aerate the material and absorb some
excess moisture. Bill Wall recommends finely mulched wood, composted
leaves, planar shavings or gerbil bedding and pine bark mulch. Although
he sells an additive mix, Del Porto recommends using stale popped
popcorn or dime-sized wood chips. “It has the ideal shape
to create air spaces, nooks and crannies for bacteria to grow and
good nutrients that are totally consumed in the composting process,”
he says. Both discourage using peat moss alone. “It doesn’t
really decompose,” Wall says.
Finished compost – called “humus” –
has the consistency of composted leaves, and should smell earthy
but not offensive. Most states require sending it to a treatment
facility or burying it under at least six inches of soil, preferably
within the root zones of non-edible plants that can use the nutrients.
If any leachate is emptied from composters, it must, by law,
be disposed of in an approved wastewater system. It cannot be
drained to the ground untreated. The nutrient value of urine is
such that it can be added to gray water and safely applied to
plants in a sub-surface irrigation system (approved by a local
board of health, of course).
There’s no getting around it, says Del Porto: composting
toilets require proper care and feeding. “Many people overload
them,” he says. “Or they take material out too soon.
Or lose the manual, and pretty soon they’re putting dirt
in the composter. Then they’re on the phone, saying, ‘this
thing doesn’t work!’ That’s classic.”
Long-time composting toilet owner Patti Nesbitt says maintaining
her system is as easy as adding an occasional handful of wood
mulch and emptying it once a year. A wastewater consultant to
the Environmental Protection Agency, Nesbitt installed a Carousel
composting toilet in her Stroudsburg, VA, house 15 years ago,
to allow her to reduce the size of her septic tank system and
leaching bed. Her composting reactor is located in her kitchen
pantry, right underneath the toilet stool on the second floor.
“It stays warmer there, and it’s more convenient to
empty,” she explains. “There’s no odor. It works
Mainstreaming this technology, however, may require more compromises
with this country’s “flush and forget” mentality.
Harvard University recently developed a simple prototype “Smart
Composting Toilet” with sensors that automatically control
temperature, air and moisture. “That’s the future
of these systems,” Del Porto says. “More and more,
they will be automated and maintained by service providers - just
like a septic system or any other appliance in the house.”