A composting toilet is a type of dry toilet that treats human waste by a biological

process called composting. This process leads to the decomposition of organic

matter and turns human waste into compost-like material. Composting is carried out
by microorganisms (mainly bacteria and fungi) under
controlled aerobic conditions.[2] Most composting toilets use no water for flushing and
are therefore called "dry toilets".

In many composting toilet designs, a carbon additive such as sawdust, coconut coir,
or peat moss is added after each use. This practice creates air pockets in the human
waste to promote aerobic decomposition. This also improves the carbon-to-nitrogen
ratio and reduces potential odor. Most composting toilet systems rely
on mesophilic composting. Longer retention time in the composting chamber also
facilitates pathogen die-o . The end product can also be moved to a secondary
system – usually another composting step – to allow more time for mesophilic
composting to further reduce pathogens.

Composting toilets, together with the secondary composting step, produce a humus-
like end product that can be used to enrich soil if local regulations allow this. Some
composting toilets have urine diversion systems in the toilet bowl to collect the urine
separately and control excess moisture. A vermifilter toilet is a composting toilet with
flushing water where earthworms are used to promote decomposition to compost.

Composting toilets do not require a connection to septic tanks or sewer

systems unlike flush toilets.[2] Common applications include national parks, remote
holiday cottages, ecotourism resorts, o -grid homes and rural areas in developing
countries.

Terminology

[edit]

Schematic of the composting

chamber which is located below the toilet seat [2]
The term "composting toilet" is used quite loosely, and its meaning varies by country.
For example, in Germany and Scandinavian countries, composting always refers to a
predominantly aerobic process. This aerobic composting may take place with an
increase in temperature due to microbial action, or without a temperature increase in
the case of slow composting or cold composting. If earth worms are used
(vermicomposting) then there is also no increase in temperature.

Composting toilets di er from pit latrines and arborloos, which use less controlled
decomposition and may not protect groundwater from nutrient
or pathogen contamination or provide optimal nutrient recycling. They also di er
from urine-diverting dry toilets (UDDTs) where pathogen reduction is achieved through
dehydration (also known by the more precise term "desiccation") and where the feces
collection vault is kept as dry as possible. Composting toilets aim to have a certain
degree of moisture in the composting chamber.

Composting toilets can be used to implement an ecological sanitation approach

for resource recovery, and some people call their composting toilet designs "ecosan
toilets" for that reason. However, this is not recommended as the two terms (i.e.
composting and ecosan) are not identical.[3][4]

Schematic of a composting toilet with urine diversion

Composting toilets have also been called "sawdust toilets", which can be appropriate
if the amount of aerobic composting taking place in the toilet's container is very
limited.[5] The "Clivus multrum" is a type of composting toilet which has a large
composting chamber below the toilet seat and also receives undigested organic
material to increase the carbon to nitrogen ratio. Alternatives with smaller composting
chambers are called "self-contained composting toilets" since the composting
chamber is part of the toilet unit itself.

Applications

[edit]
 This is the pedestal for a split-system composting toilet
where collection/treatment chambers are located below the bathroom floor.

Inexpensive do-it-yourself compost toilet at Dial

House, Essex, England, utilizing an old desk as the toilet unit.

Public composting toilet at a park in Helsinki, Finland

Composting toilets can be suitable in areas such as a rural area or a park that lacks a
suitable water supply, sewers and sewage treatment. They can also help increase
the resilience of existing sanitation systems in the face of possible natural disasters
such as climate change, earthquakes or tsunami. Composting toilets can reduce or
perhaps eliminate the need for a septic tank system to reduce environmental
footprint (particularly when used in conjunction with an on-site greywater treatment
system).

These types of toilets can be used for resource recovery by reusing sanitized feces and
urine as fertilizer and soil conditioner for gardening or ornamental activities.

Basics
[edit]

Main article: Compost

Components and use

[edit]

A composting toilet consists of two elements: a place to sit or squat and a

collection/composting unit.[3] The composting unit consists of four main parts: [2]

 storage or composting chamber

 a ventilation unit to ensure that the degradation process in the toilet is

predominantly aerobic and to vent odorous gases

 a leachate collection or urine diversion system to remove excess liquid

 an access door for extracting the compost

Many composting toilets collect urine in the same chamber as feces, thus they do
not divert urine. Adding small amounts of water that is used for anal cleansing is no
problem for the composting toilet to handle.

Some composting toilets divert urine (and water used for anal washing) to prevent the
creation of anaerobic conditions that can result from over saturation of the compost,
which leads to odors and vector problems. This usually requires all users to use the
toilet in a seated position. O ering a waterless urinal in addition to the toilet can help
keep excess amounts of urine out of the composting chamber. Alternatively, in rural
areas, men and boys may be encouraged just to find a tree.

Construction

[edit]

The composting chamber can be constructed above or below ground level. It can be
inside a structure or include a separate superstructure.

A drainage system removes leachate. Otherwise, excess moisture can cause

anaerobic conditions and impede decomposition. Urine diversion can
improve compost quality, since urine contains large amounts of ammonia that inhibits
microbiological activity.[6]

Composting toilets greatly reduce human waste volumes

through psychrophilic, thermophilic or mesophilic composting. Keeping the
composting chamber insulated and warm protects the composting process from
slowing due to low temperatures.

Odorous gases

[edit]

The following gases may be emitted during the composting process that takes place in
composting toilets: hydrogen sulfide (H2S), ammonia, nitrous oxide (N2O) and volatile
organic compounds (VOCs).[7] These gases can potentially lead to complaints about
odours. Some methane may also be present, but it is not odorous.

Pathogen removal

[edit]

Waste-derived compost recycles fecal nutrients, but it can carry and spread
pathogens if the process of reuse of waste is not done properly. Pathogen destruction
rates in composting toilets are usually low, particularly of helminth eggs (such as
those from the genus Ascaris).[5] This carries the risk of spreading disease if a proper
system management is not in place. Compost from human waste processed under
only mesophilic conditions or taken directly from the compost chamber is not safe for
food production.[8] High temperatures or long composting times are required to kill
helminth eggs, the hardiest of all pathogens. Helminth infections are common in
many developing countries.

In thermophilic composting bacteria that thrive at temperatures of 40–60 °C (104–

140 °F) oxidize (break down) waste into its components, some of which are consumed
in the process, reducing volume and eliminating potential pathogens. To destroy
pathogens, thermophilic composting must heat the compost pile su iciently, or
enough time (1–2 years) must elapse since fresh material was added
that biological activity has had the same pathogen removal e ect.

One guideline claims that pathogen levels are reduced to a safe level by thermophilic
composting at temperatures of 55 °C for at least two weeks or at 60 °C for one
week.[3] An alternative guideline claims that complete pathogen destruction may be
achieved already if the entire compost heap reaches a temperature of 62 °C (144 °F) for
one hour, 50 °C (122 °F) for one day, 46 °C (115 °F) for one week or 43 °C (109 °F) for one
month,[6] although others regard this as overly optimistic.[3]

Design considerations

[edit]
 Composting toilet with a seal in the lid in Germany

Environmental factors

[edit]

Four main factors a ect the decomposition process:[6]

 Su icient oxygen is necessary for aerobic composting

 Moisture content from 45 to 70 percent (heuristically, "the compost should feel

damp to the touch, with only a drop or two of water expelled when tightly
squeezed in the hand".[3])

 Temperature between 40 °C (104 °F) and 50 °C (122 °F), which is achieved

through proper chamber dimensioning and possibly active mixing

 Carbon-to-nitrogen ratio (C:N) of 25:1

Additives and bulking material

[edit]

Human waste and food waste do not provide optimum conditions for composting.
Usually the water and nitrogen content is too high, particularly when urine is mixed
with feces. Additives or "bulking material", such as wood chips, bark chips, sawdust,
shredded dry leaves, ash and pieces of paper can absorb moisture. The additives
improve pile aeration and increase the carbon to nitrogen ratio. [3] Bulking material also
covers feces and reduces insect access. Absent su icient bulking material, the
material may become too compact and form impermeable layers, which leads to
anaerobic conditions and odour.[3]

Leachate management

[edit]

Leachate removal controls moisture levels, which is necessary to ensure rapid,

aerobic composting. Some commercial units include a urine-separator or urine-
diverting system and/or a drain at the bottom of the composter for this purpose.

Aeration and mixing

[edit]

Microbial action also requires oxygen, typically from the air. Commercial systems
provide ventilation that moves air from the bathroom, through the waste container,
and out a vertical pipe, venting above the roof. This air movement (via convection or
fan forced) passes carbon dioxide and odors.

Some units require manual methods for periodic aeration of the solid mass such as
rotating the composting chamber or pulling an "aerator rake" through the mass.

Comparisons with other types of toilets

[edit]

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Pit latrines

[edit]

Main article: Pit latrine

Composting toilets convert feces into a dry, odorless material which is very di erent
to the wet fecal sludge produced in pit latrines which has to be taken care of through
a fecal sludge management system. Composting toilets do not cause groundwater
pollution due to their safe containment of feces in above-ground vaults compared to
pit latrines, allowing composting toilets to be sited in locations where pit-based
systems are not appropriate.

Composting toilets may have higher capital costs than pit latrines, but lower lifecycle
costs. They require more involvement by the user than the "drop and forget" approach
of pit latrines.

Flush toilets

[edit]

Main article: Flush toilet

Unlike flush toilets, composting toilets do not require a sewerage system and do not
mix flushing water with urine and feces. They require more involvement by the user
than the "flush and forget" approach of flush toilets connected to sewage treatment
plants.

Urine-diverting dry toilets

[edit]

Main article: Urine-diverting dry toilet

Composting toilets, although similar to and sharing many advantages and

disadvantages with urine-diverting dry toilets (UDDT), are more complex and require
more maintenance to keep a consistent and relatively high moisture content. Some
composting toilets are designed with urine diversion.

Types

[edit]

External composting chamber of a composting toilet at

a house in France
Commercial units and construct-it-yourself systems are available. [9] Variations
include number of composting vaults, removable vault, urine diversion and active
mixing/aeration.[3]

Slow composting (or moldering) toilets

[edit]

Most composting toilets use slow composting which is also called "cold composting".
The compost heap is built up step by step over time.

The finished end product from "slow" composting toilets ("moldering toilets" or
"moldering privies" in the US), is generally not free of pathogens. World Health
Organization Guidelines from 2006 o er a framework for safe reuse of waste, using a
multiple barrier approach.[10]

Slow composting toilets employ a passive approach. Common applications involve

modest and often seasonal use, such as remote trail networks. They are typically
designed such that the materials deposited can be isolated from the operational part.
The toilet can also be closed to allow further mesophilic composting. [11] Slow
composting toilets rely on long retention times for pathogen reduction and for
decomposition of waste or on the combination of time and/or the addition of red
wiggler worms for vermi-composting. Worms can be introduced to accelerate
composting. Some jurisdictions of the US consider these worms as invasive
species.[10]

Active composters (self-contained)

[edit]

"Self-contained" composting toilets compost in a container within the toilet unit. They
are slightly larger than a flush toilet, but use roughly the same floor space. Some units
use fans for aeration, and optionally, heating elements to maintain optimum
temperatures to hasten the composting process and to evaporate urine and other
moisture. Operators of composting toilets commonly add a small amount of
absorbent carbon material (such as untreated sawdust, coconut coir, or peat moss)
after each use to create air pockets to encourage aerobic processing, to absorb liquid
and to create an odor barrier. This additive is sometimes referred to as "bulking agent".
Some owner-operators use microbial "starter" cultures to ensure composting bacteria
are in the process, although this is not critical.

Vermifilter toilet
[edit]

A vermifilter toilet is a composting toilet with flushing water where earthworms are
used to promote decomposition to compost. It can be connected to a low-flush or a
micro-flush toilet which uses about 500 millilitres (17 US fl oz) per use. Solids
accumulate on the surface of the filter bed while liquid drains through the filter
medium and is discharged from the reactor. The solids (feces and toilet paper) are
aerobically digested by aerobic bacteria and composting earthworms into castings
(humus), thereby significantly reducing the volume of organic material. [12]

Other

[edit]

Some units employ roll-away containers fitted with aerators, while others use sloped-
bottom tanks.

Maintenance

[edit]

Maintenance is critical to ensure proper operation, including odor prevention.

Maintenance tasks include: cleaning, servicing technical components such as fans
and removal of compost, leachate and urine. Urine removal is only required for those
types of composting toilets using urine diversion.

Once composting is complete (or earlier), the compost must be removed from the
unit. How often this occurs is a function of container size, usage and composting
conditions, such as temperature.[3] Active, hot composting may require months, while
passive, cold composting may require years. Properly managed units yield output
volumes of about 10% of inputs.

Uses of compost

[edit]
 Finished compost from a composting toilet ready for
application as soil improvement in Kiel-Hassee, Germany

Main articles: Uses of compost and Reuse of excreta

The material from composting toilets is a humus-like material, which can be suitable
as a soil amendment for agriculture. Compost from residential composting toilets can
be used in domestic gardens, and this is the main such use.

Enriching soil with compost adds substantial nitrogen, phosphorus, potassium,

carbon and calcium. In this regard compost is equivalent to
many fertilizers and manures purchased in garden stores. Compost from composting
toilets has a higher nutrient availability than the dried feces that result from a urine-
diverting dry toilet.[3]

Urine is typically present, although some is lost via leaching and evaporation. Urine
can contain up to 90 percent of the residual nitrogen, up to 50 percent of
the phosphorus, and up to 70 percent of the potassium.[13]

Compost derived from these toilets has in principle the same uses as compost
derived from other organic waste products, such as sewage sludge or municipal
organic waste. However, users of waste-derived compost must consider the risk of
pathogens.

Pharmaceutical residues

[edit]
Waste-derived compost may contain prescription pharmaceuticals. Such residues are
also present in conventional sewage treatment e luent. This could contaminate
groundwater. Among the medications that have been found in groundwater in recent
years are antibiotics, antidepressants, blood thinners, ACE inhibitors, calcium-
channel
blockers, digoxin, estrogen, progesterone, testosterone, Ibuprofen, ca eine, carbama
zepine, fibrates and cholesterol-reducing medications.[14] Between 30% and 95% of
pharmaceuticals medications are excreted by the human body. Medications that
are lipophilic (dissolved in fats) are more likely to reach groundwater by leaching from
fecal wastes. Sewage treatment plants remove an average of 60% of these
medications.[15] The percentage of medications degraded during composting of waste
has not yet been reported.

History

[edit]

Further information: Dry toilet § History

In the late 19th century in developed countries, some inventors, scientists and public
health o icials supported the use of "dry earth closets", a type of dry toilet with
similarities to composting toilets, although the collection vessel for the human
waste was not designed to compost.[16]

Society and culture

[edit]

Regulations

[edit]

International Organization for Standardization (ISO)

[edit]

In 2016, the International Organization for Standardization (ISO) published the

standard "Activities relating to drinking water and wastewater services — Guidelines
for the management of basic on-site domestic wastewater services". [17] The standard
is meant to be used in conjunction with ISO 24511. [18] It deals with toilets (including
composting toilets) and toilet waste. The guidelines are applicable to basic
wastewater systems and include the complete domestic wastewater cycle, such as
planning, usability, operation and maintenance, disposal, reuse and health.
International Association of Plumbing and Mechanical O icials

[edit]

The International Association of Plumbing and Mechanical O icials (IAPMO) is a

plumbing and mechanical code structure adopted by many developed countries. It
recently proposed an addition to its "Green Plumbing Mechanical Code Supplement"
that, "...outlines performance criteria for site built composting toilets with and without
urine diversion and manufactured composting toilets." [19] If adopted, this composting
and urine diversion toilet code (the first of its kind in the United States) will appear in
the 2015 edition of the Green Supplement to the Uniform Plumbing Code. [20][21]

United States

[edit]

No performance standards for composting toilets are universally accepted in the US.
Seven jurisdictions in North America[22] use American National Standard/NSF
International Standard ANSI/NSF 41-1998: Non-Liquid Saturated Treatment Systems.
An updated version was published in 2011.[23] Systems might also be listed with the
Canadian Standards Association, cETL-US, and other standards programs.

Regarding byproduct regulation, several US states permit disposal of solids from

composting toilets (usually a distinction between di erent types of dry toilets is not
made) by burial, with varying or no minimum depth mandates (as little as 6 inches).
For instance:

 Massachusetts: "Residuals from the composting toilet system must be buried

on-site and covered with a minimum of six inches of clean compacted
soil.[24] Massachusetts requires that any liquids produced but, "not recycled
through the toilet [itself, be] either discharged through a greywater system on
the property that includes a septic tank and soil absorption system, or removed
by a licensed septage hauler."[24]

 Oregon: "Humus from composting toilets may be used around ornamental

shrubs, flowers, trees, or fruit trees and shall be buried under at least twelve
inches of soil cover."[25]

 Rhode Island: "Solids produced by alternative toilets may be buried on site"

while "residuals shall not be applied to food crops." [26]
  Virginia: "All materials removed from a composting privy shall be buried," and
"compost material shall not be placed in vegetable gardens or on the ground
surface."[27]

 Vermont: "Byproducts may be disposed via "...shallow burial in a location

approved by the Agency that meets the minimum site conditions [required for
an onsite septic tank-based sanitation system]."[28]

 Washington: models its extensive regulations for what it refers to as "waterless

toilets" on the federal regulations that govern sewage sludge.[29]

The Environmental Protection Agency has no jurisdiction over the byproducts of a dry
toilet as long as waste are not referred to as "fertilizer" (but instead simply a material
that is being disposed of). Federal rule 503, known colloquially as the "EPA Biosolids
rule" or the "EPA sludge rule" applies only to fertilizer. Thus, individual states regulate
composting toilets.[30][31]

Germany

[edit]

The regulations for composting toilets and other forms of dry toilets in Germany vary
from state to state and from one application to another (e.g. use in allotment gardens
or use in family homes and settlements). In the di erent states of Germany, it is the
"Landesbauordnung" (translates to "state civil engineering regulations") of the
respective state that regulates the use of such alternative toilets. [32] Most of them
stipulate the use of flush toilets, however there are many exceptions, for example in
the states of Hamburg, Lower Saxony, Bavaria, Mecklenburg-Western
Pomerania, Rhineland-Palatinate, Saxony-Anhalt and Thuringia.[32] These generally
make exceptions for the use of composting toilets in homes provided that there are no
concerns for public health.

Regulations governing the use of compost and urine from composting toilets is less
clear in Germany but it seems generally allowed provided it is used on one's own
property and not sold to third parties.[32]

Examples

[edit]

Finland

[edit]
Numerous sparsely settled villages in rural areas in Finland are not connected to
municipal water supply or sewer networks, requiring homeowners to operate their
own systems. Individual private wells, i.e. shallow dug wells or boreholes in the
bedrock, are often used for water supply, and many homeowners have opted for
composting toilets. In addition, these toilets are common at holiday homes, often
located near sensitive water bodies. For these reasons, many manufacturers of
composting toilets are based in Finland, including Biolan, Ekolet, Kekkilä, Pikkuvihreä
and Raita Environment.[33][34]

Estimates made by leading Finnish composting toilet manufacturers and the Global
Dry Toilet Association of Finland provided the following 2014 figures for composting
toilet use in Finland:

 About 4% of single-family homes not connected to a public sewer network are

equipped with a composting toilet.

 Some 200,000 manufactured composting toilets are thought to serve holiday

homes, matched by the number of other dry toilets. The simplest ones are sited
in an outhouse.

Germany

[edit]

Composting container of "TerraNova" composting

toilet, showing open removal chamber (town house at the ecological settlement
Hamburg-Allermöhe, Germany)
Composting toilets have been successfully installed in houses with up to four
floors.[3] An estimate from 2008 put the number of composting toilets in households in
Germany at 500.[35] Most of these residences are also connected to a sewer system;
the composting toilet was not installed due to a lack of sewer system but for other
reasons, mainly because of an "ecological mindset" of the owners.

In Germany and Austria, composting toilets and other types of dry toilets have been
installed in single and multi-family houses (e.g. Hamburg, Freiburg, Berlin), ecological
settlements (e.g. Hamburg-Allermöhe, Hamburg-Braamwisch, Kiel-Hassee, Bielefeld-
Waldquelle, Wien-Gänserndorf) and in public buildings (e.g. Ökohaus Rostock, VHS-
Ökostation Stuttgart-Wartberg, public toilets in recreational areas, restaurants and
huts in the Alps, house boats and forest Kindergartens). [35]

The ecological settlement in Hamburg-Allermöhe has had composting toilets since

1982. The settlement of 36 single-family houses with approximately 140 inhabitants
uses composting toilets, rainwater harvesting and constructed wetlands. Composting
toilets save about 40 litres of water per capita per day compared to a conventional
flush toilet (10 liter per flush), which adds up to 2,044 m 3 water savings per year for the
whole settlement.[36]

United States

[edit]

Slow composting toilets have been installed by the Green Mountain Club in Vermont's
woodlands. They employ multiple vaults (called cribs) and a movable building. When
one of the vaults fills, the building is moved over an empty vault. The full vault is left
untouched for as long as possible (up to three years) before it is emptied. The large
surface area and exposure to air currents can cause the pile to dry out. To counteract
this, signs instruct users to urinate in the toilet.[37] The club also uses pit latrines and
simple bucket toilets with woodchips and external composting and directs users to
urinate in the forest to prevent odiferous anaerobic conditions. [38]

Worldwide

[edit]

Composting toilets with a large composting container (of the type Clivus Multrum and
derivations of it) are popular in US, Canada, Australia, New Zealand, Sweden and
Finland. They can be bought and installed as commercial products, as designs for self
builders or as "design derivatives" which are marketed under various names. It has
been estimated that approximately 10,000 such toilets might be in use
worldwide.[citation needed]