United States
                       Environmental Protection
                       Office of Water
                       Washington, D.C.
EPA 832-F-99-066
September 1999
Water  Efficiency
Technology  Fact  Sheet
Composting  Toilets

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
                      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

                      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

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.


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

•      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.


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.


Some advantages and disadvantages of composting
toilet systems are listed below:

       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

       They   are  especially  suited   for  new
       construction  at  remote   sites  where
       conventional onsite systems are not feasible.

       Composting toilet systems have low power

       Self-contained systems  eliminate the need
       for  transportation   of   wastes   for

       Composting human  waste  and burying it
       around tree roots and nonedible plants keeps
       organic wastes productively cycling in the

       Composting  toilet  systems can  accept
       kitchen wastes, thus reducing  household

       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.
       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
•      Composting toilet systems must be used in
       conjunction with a graywater system in most

•      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


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).

•      Process controls to optimize and facilitate
       management of the processes.

•      An  access door for removal of the  end-

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


There are several factors that affect  the rate  of
composting. Discussed below are the predominant

•      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

                                               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

                                               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.
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.
Fecal conforms3
Salmonella (spp.)3
Vibrio choleraeb
E. histolytica cysts
A. lumbricoides eggs
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

< 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.


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

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

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.


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.


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,

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

       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,

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,
       Installations: Preliminary Findings." USA-
       CERL  Technical  Report  N-160.  USA-
       CERL. Champaign, Illinois.


Creative Energy Technologies
Carsten Ginsburg
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
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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