v>EPA
United States
Environmental Protection
Agency
Office of Water
Washington, D.C.
EPA 832-F-99-066
September 1999
Water Efficiency
Technology Fact Sheet
Composting Toilets
DESCRIPTION
Originally commercialized in Sweden, composting
toilets have been an established technology for more
than 30 years, and perhaps longer in site-built forms.
As they require little to no water, composting toilet
systems can provide a solution to sanitation and
environmental problems in unsewered, rural, and
suburban areas and in both developed and
underdeveloped countries.
A composting (or biological) toilet system contains
and processes excrement, toilet paper, carbon
additive, and sometimes, food waste. Unlike a septic
system, a composting toilet system relies on
unsaturated conditions where aerobic bacteria break
down waste. This process is similar to a yard waste
composter. If sized and maintained properly, a
composting toilet breaks down waste 10 to 30% of
its original volume. The resulting soil-like material
called "humus," legally must be either buried or
removed by a licensed septage hauler in accordance
with state and local regulations.
Public health professionals are beginning to
recognize the need for environmentally sound
human waste treatment and recycling methods. The
composting toilet is a nonwater-carriage system that
is well-suited for (but is not limited to) remote areas
where water is scarce, or areas with low
percolation, high water tables, shallow soil, or rough
terrain. Because composting toilets eliminate the
need for flush toilets, this significantly reduces water
use and allows for the recycling of valuable plant
nutrients.
Although there are many different composting toilet
designs that continue to evolve, the basic concept of
composting remains the same.
The primary objective of composting toilet systems
is to contain, immobilize, or destroy pathogens,
thereby reducing the risk of human infection to
acceptable levels without contaminating the
environment or negatively affecting the life of its
inhabitants. This should be accomplished in a
manner that is consistent with good sanitation
(minimizing the availability of excrement to disease
vectors, such as flies, and minimizing human contact
with unprocessed excrement), thus producing an
inoffensive and reasonably dry end-product that can
be handled with minimum risk.
A composting toilet is a well-ventilated container
that provides the optimum environment for
unsaturated, but moist, human excrement for
biological and physical decomposition under
sanitary, controlled aerobic conditions. Some are
large units that require a basement for installation.
Others are small self-contained appliances that sit on
the floor in the bathroom. In the composting
process, organic matter is transformed by naturally
occurring bacteria and fungi that break down the
excrement into an oxidized, humus-like end-
product. These organisms thrive by aeration,
without the need for water or chemicals. Various
process controls manage environmental
factors—air, heat, moisture—to optimize the
process.
The main process variations are continuous or batch
composting. Continuous composters (including such
brands as CTS, Clivus Multrum, Phoenix, Biolet,
SunMar, etc.) are single chambers where excrement
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is added to the top, and the end-product is removed
from the bottom. Batch composters (including
Carousel, Vera, and nearly all of the site-built
composters worldwide) are actually two or more
composters that are filled and then allowed to cure
without the continuous addition of new potentially
pathogen contaminated excrement. Alternating
concrete double-bins are the most common batch
system, although several systems use polyethylene
55-gallon drums that contain the process.
APPLICABILITY
Composting toilet systems can be used almost
anywhere a flush toilet can be used. They are
typically used for seasonal homes, homes in remote
areas that cannot use flush toilets, or recreation
areas, etc. Application advantages for composting
toilet systems are listed below:
• It is more cost-effective to treat waste on-
site than it is to build and maintain a central
sewer system to which waste will need to be
transported.
• Water is not wasted as a transport medium
to flush toilets.
• Nutrients (nitrogen and phosphorus) are
kept in tight biological cycles without
causing problems to receiving waters.
There have been many reports of successful use of
waterless (composting, incinerator, chemical, and
privy) toilets. Below are some examples of
successful stories.
Replacement of Existing Disposal Systems
A family of four had a failing wastewater disposal
system in their urban home. They lived on a small
lot with insufficient land area to construct a disposal
system for their water use. A waterless toilet was
installed in conjunction with a 35% smaller disposal
system to handle the remaining graywater.
Rejuvenation of an Existing Disposal System
A disposal system in a residential neighborhood had
a history of surface breakouts due to overloading.
The load was reduced when a waterless toilet was
installed along with water conservation devices on
plumbing fixtures.
Remodeling
A waterless toilet was installed in a basement near
a family room because it was more practical than
installing plumbing and a pump to lift the waste to
a septic tank.
Waterless, Solar Toilets in Colorado Park
The Colorado Health Board was faced with the task
of providing adequate toilets to the outlying
portions of a 18,000-acre recreation area. The
options considered were running a sewer and water
line or installing chemical toilets and vault latrines.
However, these options added to the problem with
continual maintenance requirements, high chemical
costs, expensive excavations and pump-outs, and
the potential to pollute groundwater. Faced with
this dilemma, the Colorado Health Board installed
composting toilets to decompose wastes without
water, chemicals, pollution, or odor.
The compost produced from the decomposed waste
was similar to topsoil and reduced considerably in
volume. Directly below the toilet chute was a large
tank in which organic material such as lawn
clippings, paper, and leaves was placed. The waste
decomposed slowly along the tank floor by the
natural bacteria present in the waste material. A fan
powered by a small photovoltaic cell on the roof of
each brick and concrete restroom was installed to
draw out all vapors produced in the tank. Both the
men's and the women's stalls were accommodated
by a tank unit each to handle up to 40,000 uses per
year, thus providing much-needed toilet facilities in
outlying areas.
ADVANTAGES AND DISADVANTAGES
Some advantages and disadvantages of composting
toilet systems are listed below:
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Advantages
Composting toilet systems do not require
water for flushing, and thus, reduce
domestic water consumption.
These systems reduce the quantity and
strength of wastewater to be disposed of
onsite.
They are especially suited for new
construction at remote sites where
conventional onsite systems are not feasible.
Composting toilet systems have low power
consumption.
Self-contained systems eliminate the need
for transportation of wastes for
treatment/disposal.
Composting human waste and burying it
around tree roots and nonedible plants keeps
organic wastes productively cycling in the
environment.
Composting toilet systems can accept
kitchen wastes, thus reducing household
garbage.
In many states, installing a composting toilet
system allows the property owner to install
a reduced-size leachfield, minimizing costs
and disruption of landscapes.
Composting toilet systems divert nutrient
and pathogen containing effluent from soil,
surface water, and groundwater.
Disadvantages
Maintenance of composting toilet systems
requires more responsibility and
commitment by users and owners than
conventional wastewater systems.
Removing the finished end-product is an
unpleasant job if the composting toilet
system is not properly installed or
maintained.
• Composting toilet systems must be used in
conjunction with a graywater system in most
circumstances.
• Smaller units may have limited capacity for
accepting peak loads.
• Improper maintenance makes cleaning
difficult and may lead to health hazards and
odor problems.
• Using an inadequately treated end-product
as a soil amendment may have possible
health consequences.
• There may be aesthetic issues because the
excrement in some systems may be in sight.
• Too much liquid residual (leachate) in the
composter can disrupt the process if it is not
drained and properly managed.
• Most composting toilet systems require a
power source.
• Improperly installed or maintained systems
can produce odors and unprocessed
material.
DESIGN CRITERIA
The main components of a composting toilet (see
Figure 1) are:
• A composting reactor connected to a dry or
micro-flush toilet(s).
• A screened air inlet and an exhaust system
(often fan-forced) to remove odors and heat,
carbon dioxide, water vapor, and the by-
products of aerobic decomposition.
• A mechanism to provide the necessary
ventilation to support the aerobic organisms
in the composter.
• A means of draining and managing excess
liquid and leachate (optional).
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• Process controls to optimize and facilitate
management of the processes.
• An access door for removal of the end-
product.
The composting unit must be constructed to
separate the solid fraction from the liquid fraction
and produce a stable, humus material with less than
200 MPN per gram of fecal coliform. Once the
leachate has been drained or evaporated out of the
unit, the moist, unsaturated solids are decomposed
by aerobic organisms using molecular oxygen.
Bulking agents can be added to provide spaces for
aeration and microbial colonization.
The compost chamber in some composting toilets is
solar or electrically heated to provide and maintain
optimum temperature requirements for year-round
usage.
PERFORMANCE
There are several factors that affect the rate of
composting. Discussed below are the predominant
factors:
• Microorganisms: The microbiology is
dominated by the presence of a mixed
population of bacteria and fungi. The
presence of these microorganisms is directly
related to the environmental conditions in
the compost material.
Temperature: As the microorganisms grow,
heat is generated by the energy released
during aerobic microbial respiration. The
temperature of the compost is significant
from a public health perspective because of
the need for destruction of pathogens.
Temperatures typically never become high
enough to rapidly destroy pathogens, so
time and optimum environmental factors are
more significant.
Moisture: Moisture enables microorganisms
to hydrolize complex organic compounds
into simpler compounds before they are
metabolized. The moisture should be
maintained within the range of 40 to 70%,
with the optimum being about 60%.
pH: In composting toilet systems, pH is not
typically a concern to the owner/operator,
although the pH will initially drop as organic
acids are formed. Other biochemical
processes buffer the final end-product,
bringing it to a neutral level. In general, the
optimum pH is between 6.5 and 7.5.
Composting Pile
Inspection Hatch
Source: Adapted from Clivus Multrum, Inc., 1994.
FIGURE 1 COMPOSTING TOILET
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The two main parameters in the composting process
that account for the destruction of pathogens are:
• Antibiosis: Microbial and other higher order
aerobic organisms develop in the compost
pile during the decomposition process,
resulting in the synthesis of substances that
are toxic to most pathogens.
• Time: When exposed to an unfavorable
environment for an extended period of time,
most pathogenic microorganisms will not
survive. However, caution is essential when
using the compost end-product and liquid
residual in case some pathogens survive.
Table 1 gives typical pathogen survival
times at 20 to 30 °C in various
environments.
The standard governing minimum materials, design,
construction, and performance of composting toilet
systems is the American National Standard/NSF
International Standard ANSI/NSF 41-1998: Non-
Liquid Saturated Treatment Systems.
TABLE 1 TYPICAL PATHOGEN SURVIVAL TIMES AT 20 TO 30°C IN VARIOUS
ENVIRONMENTS
Carbon to nitrogen ratio (C/N): For
complete utilization of the nitrogen in urine,
an adequate amount of carbon (about 30
parts of carbon for each part of nitrogen) is
required. However, as most urine drains to
the bottom of the composter and is
removed, this is less of a problem than is
usually reported in literature.
Aeration: Maintaining an aerobic
environment in the composting chamber is
the most important factor for the growth of
microorganisms, reducing high moisture
content, and minimizing nitrogen loss
through ammonia volatilization. Aeration
can be improved by mechanical mixing or by
adding wood chips or sawdust to the
composting material.Management: As with
all wastewater treatment systems,
management is critical to the efficiency of
the system.
Pathogen
Bacteria
Fecal conforms3
Salmonella (spp.)3
Shigella*
Vibrio choleraeb
Protozoa
E. histolytica cysts
Helminths
A. lumbricoides eggs
Viruses3
Enterovi ruses0
Survival Time, Days
Fresh Water and Wastewater Crops
< 60 but usually < 30
< 60 but usually < 30
< 30 but usually < 10
< 30 but usually < 10
< 30 but usually < 15
Many months
< 120 but usually < 50
< 30 but usually < 15
< 30 but usually < 15
< 10 but usually < 5
< 5 but usually < 2
< 10 but usually < 2
< 60 but usually < 30
< 60 but usually < 15
Soil
< 120 but usually < 50
< 120 but usually < 50
< 120 but usually < 50
< 120 but usually < 50
< 20 but usually < 10
< Many months
< 100 but usually < 20
a In seawater, viral survival is less and bacterial survival is very much less than in fresh water.
b V. cholerae survival in aqueous environments is a subject of current uncertainty.
c Includes polio, echo, and coxsackie viruses.
Source: Adapted from: Crites and Tchobanoglous, 1998.
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OPERATION AND MAINTENANCE
Handling raw waste has historically been a problem
from a management standpoint. Removing vault or
pit type waste has led to accidental spills and is
always a difficult task. This is why managers
appreciate the concept of composting human waste.
Management considerations for composting toilets
include gathering information on how much
maintenance is needed annually, administration and
operation, quality control and assurance, record-
keeping, and training.
In general, operation and maintenance (O&M) for
composting toilet systems does not require trained
technicians or treatment plant operators. However,
regular O&M is of the utmost importance since any
system depends on responsible administration. In
cold climates, all composting toilet systems should
be heated to levels specified by the manufacturer or
designer.
Composting toilet systems may require organic
bulking agents to be added, such as grass clippings,
leaves, sawdust, or finely chopped straw. The
agents composting by providing a source of carbon
for the bacteria, as well as keeping the pile porous
for proper air distribution. If the facility is used
every day, it is recommended to add bulking
material at least every other day. Periodic mixing or
raking is suggested for single-chamber continuous
systems.
The other required maintenance step is removing the
finished end-product (anywhere from every 3
months for a cottage system to every 2 years for a
large central system). If proper composting has
taken place, the end-product should be inoffensive
and safe to handle. Adequate precautions should be
taken while handling the humus material. All waste
materials should be disposed of in accordance with
the state and local regulations.
COSTS
The cost of a composting toilet system depends on
the manufacturer and their type of design. Although
the principle of waste treatment is the same, there
are design variations in the containment of the
waste, aeration, and other features of the system.
The main factors that determine costs are the cost of
the equipment, the building foundation, electrical
work, and installation labor.
For a year-round home of two adults and two
children, the cost for a composting toilet system
could range anywhere between $1,200 and $6,000,
depending on the system. Cottage systems designed
for seasonal use range from $700 to $1,500. Large-
capacity systems for public facility use can cost as
much as $20,000 or more. However, site-built
systems, such as cinder-block double-vault systems
are as expensive as their materials and construction
labor costs. A septic tank and soil absorption or
subsurface irrigation system to manage graywater
will usually be required.
REFERENCES
1. Clivus Multrum, Inc. 1994. "When Nature
Calls... It Calls Clivus®." Clivus Multrum,
Inc. Lawrence, Massachusetts.
2. Cook, B. 1981. "Field Evaluation of
Compost Toilets." Individual Onsite
Wastewater Systems: Proceedings of the
Seventh National Conference, pp. 83-98.
3. Crites, R. and G. Tchobanoglous. 1998.
Small and Decentralized Wastewater
Management Systems. The McGraw-Hill
Companies. New York, New York.
4. Del Porto, D. A. and C. J. Steinfeld. 1998.
The Composting Toilet Book. Chelsea
Green Publishing, Inc. Whiteriver Junction,
Vermont.
5. Felton, D. (editor). 1981. "State-Of-The Art
Assessment of Compost Toilets and
Greywater Treatment Systems." The
Winthrop Rockefeller Foundation. Little
Rock, Arkansas.
6. Guttormsen, D. 1979. "Evaluation of
Compost Toilets—A Field and Laboratory
Update." Individual Onsite Wastewater
Systems: Proceedings of the Sixth National
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Conference. Ann Arbor Science Publishers,
Inc. Ann Arbor Michigan.
7. Hoxie, D. C. and W. W. Hinckley. 1977.
"Factors Affecting Acceptance of Waterless
Toilets—The Maine Experience." Individual
Onsite Wastewater Systems: Proceedings of
the Fourth National Conference. National
Sanitation Foundation (NSF).
8. Jacobson, A. R. January 1982. "Waterless,
Solar Toilets for Colorado Park." Public
Works, vol. 113.no. 1. p. 85.
9. Rockefeller, A. 1980. "Separated
Treatment: Composting Toilets and
Greywater." Conference Proceedings.
pp. 104-118. Environmental Policy Institute
and Clean Water Fund. Cambridge,
Massachusetts.
10. Scholze, R. J. 1984. "Appropriate
Technology for Army Waste Management:
Applications for Remote Sites and
Mobilization." DAEN-ZCF Technical Note
No. 84-2. Department of the Army, Office
of the Chief of Engineers. Washington, D.C.
11. Scholze, R. J. September 1985. "Innovation
in Remote Site Waste Treatment."
BioCycle. pp. 37-38.
12. Scholze, R. J.; J. E. Alleman; S. R. Struss;
and E. D. Smith. December 1986.
"Technology for Waste Treatment at
Remote Army Sites." USA-CERL Technical
Report N-86/20. USA-CERL. Champaign,
Illinois.
Installations: Preliminary Findings." USA-
CERL Technical Report N-160. USA-
CERL. Champaign, Illinois.
ADDITIONAL INFORMATION
Creative Energy Technologies
Carsten Ginsburg
lOGerty'sPath
Summit, NY 12175
Jade Mountain Inc.
Wes Kennedy
P.O. Box 4616
Boulder, CO 80306
Sun-Mar Corporation
Fraser Sneddon
5035 North Service Road, Unit C9-C10
Burlington, ON L8N 2Y9
Trisynergy Inc.
Tevan Riedel
P.O. Box 27015
San Diego, C A 92198-1015
The mention of trade names or commercial products
does not constitute endorsement or recommendation
for use by the U.S. Environmental Protection
Agency.
13. Seabloom, R. W. and J. Engeset. March 1 &
2, 1978. "An Appraisal of Composting
Toilets." Proceedings of the Second
Northwest On-Site Wastewater Disposal
Short Course. University of Washington.
Seattle, Washington.
14. Smith, E. D.; C. P. C. Poon; S. R. Struss; J.
T. Bandy; and R. J. Scholze. April 1984.
"Appropriate Technology for Treating
Wastewater at Remote Sites on Army
For more information contact:
Municipal Technology Branch
U.S. EPA
Mail Code 4204
401 M St., S.W.
Washington, D.C., 20460
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