A
composting toilet is a dry
toiletA toilet is a sanitation fixture used primarily for the disposal of human excrement, often found in a small room referred to as a toilet/bathroom/lavatory...
that using a predominantly aerobic processing system that treats excreta, typically with no water or small volumes of flush water, via composting or managed aerobic decomposition. Composting toilets may be used as an alternative to
flush toiletA flush toilet is a toilet that disposes of human waste by using water to flush it through a drainpipe to another location. Flushing mechanisms are found more often on western toilets , but many squat toilets also are made for automated flushing...
s in situations where there is no suitable water supply or waste treatment facility available or to capture nutrients in human excreta as humanure. They are in used in many of the roadside facilities in
SwedenSweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
, in National Parks both in the United States and the United Kingdom.
The human excrement is normally mixed with
sawdustSawdust is a by-product of cutting lumber with a saw, composed of fine particles of wood. It can present a hazard in manufacturing industries, especially in terms of its flammability....
,
coconutThe coconut palm, Cocos nucifera, is a member of the family Arecaceae . It is the only accepted species in the genus Cocos. The term coconut can refer to the entire coconut palm, the seed, or the fruit, which is not a botanical nut. The spelling cocoanut is an old-fashioned form of the word...
coir, peat moss to support aerobic processing, absorb liquids, and to reduce the odor. The decomposition process is generally faster than the anaerobic decomposition using in wet
sewage treatmentSewage treatment, or domestic wastewater treatment, is the process of removing contaminants from wastewater and household sewage, both runoff and domestic. It includes physical, chemical, and biological processes to remove physical, chemical and biological contaminants...
systems such as septic tanks.
Operating process
Although there are many designs, the process factors at work are the same. Rapid
aerobicAn aerobic organism or aerobe is an organism that can survive and grow in an oxygenated environment.Faculitative anaerobes grow and survive in an oxygenated environment and so do aerotolerant anaerobes.-Glucose:...
composting will be thermophilic decomposition in which bacteria that thrive at high temperatures (40-60 °C / 104-140 °F) oxidize (break down) the waste into its components, some of which are consumed in the process, reducing volume, and eliminating potential pathogens.
Drainage of excess liquid or
leachateLeachate is any liquid that, in passing through matter, extracts solutes, suspended solids or any other component of the material through which it has passed....
via a separate drain at the bottom of the composter is featured in some manufactured units, as the aerobic composting process requires moisture levels to be controlled (ideally 50% +/- 10): too dry, and the mass decomposes slowly or not at all; too wet and anaerobic organisms thrive, creating undesirable odors (cf.
Anaerobic digestionAnaerobic digestion is a series of processes in which microorganisms break down biodegradable material in the absence of oxygen. It is used for industrial or domestic purposes to manage waste and/or to release energy....
). This separated liquid may be diverted to a
blackwaterBlackwater is a term dating to at least the 1970s used to describe wastewater containing fecal matter and urine. It is also known as brown water, foul water, or sewage...
system or collected for other uses. Some units include a urine-separator or
urine-diverting-Urine diversion:Urine diversion refers to the separation of urine from feces at the point source, i.e at the toilet or outhouse. A toilet fixture used to help facilitate the separation is called a urine diversion toilet or UDT. The bowel has two separate compartments which may or may not be...
system.
Where solar heat is used, this might be called a "solar" toilet. These systems depend on desiccation to achieve sanitation safety goals features systems that make use of the separated liquid fraction for immediate area fertilization.
Urine can contain up to 90 percent of the N (nitrogen), up to 50 percent of the P (phosphorus) and up to 70 percent of the K (potassium) present in human excreta. In healthy individuals it is usually pathogen free, although undiluted it may contain levels of inorganic salts and organic compounds at levels toxic to plants.
The other requirement critical for microbial action (as well as drying) is oxygen. Commercial systems provide methods of ventilation that move air from the room, through the waste container, and out a vertical pipe, venting above the enclosure roof. This air movement (via
convectionConvection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
or fan forced) will vent carbon dioxide and odors.
Some units require manual methods for periodic aeration of the solid mass such as rotating a drum inside the unit or working an "aerator rake" through the mass. Composting toilet brands have different provisions for emptying the "finished product," and supply a range of capacities based on volume of use. Frequency of emptying will depend on the speed of the decomposition process and capacity, from a few months (active hot composting) to years (passive, cold composting). With a properly sized and managed unit, a very small volume (about 10% of inputs) of a
humus-like material results, which can be suitable as soil amendment for agriculture, depending on local
public healthPublic health is "the science and art of preventing disease, prolonging life and promoting health through the organized efforts and informed choices of society, organizations, public and private, communities and individuals" . It is concerned with threats to health based on population health...
regulations.
Composting toilets greatly reduce the volume of excreta on site through psychrophilic, thermophilic or mesophilic composting and yield a soil amendment that can be used in horticultural or agricultural applications as local regulations allow. In combination with a
Constructed wetlandA constructed wetland or wetpark is an artificial wetland, marsh or swamp created as a new or restored habitat for native and migratory wildlife, for anthropogenic discharge such as wastewater, stormwater runoff, or sewage treatment, for land reclamation after mining, refineries, or other...
these even require only the half area.
These should not be confused with the pit latrine,
arborlooAn Arborloo is a simple and ecological type of toilet. Its concept is to compost directly the feces in a pit, and to grow subsequently a fruiting tree on this very fertile soil....
or
tree bogA tree bog is a form of outside toilet which has willows, nettles and other nutrient-hungry plants planted around it. The fæces are held in a chamber open to the air which allows it to decompose rapidly, feeding the trees around it. Unlike a conventional compost toilet, a tree bog should never need...
all of which are forms of less controlled decomposition, and may not protect ground water from nutrient or pathogen contamination or provide optimal nutrient recycling.
Manufactured composting toilet systems
Several manufactured composting toilet models are on the market, and construct-it-yourself systems are also popular.
"Self-contained" composting toilets complete or begin the composting in a container within the receiving fixture. 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, peat moss) after each use to create air pockets for better 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.
"Remote," "central," or "underfloor" units collect excreta via a toilet stool, either waterless or micro-flush, from which it drains to a composter. "Vacuum-flush systems" can flush horizontally or upward with a small amount of water to the composter; "micro-flush toilets" use about 0.5 litre (0.879877380288283 imp pt) per use. These units feature a chamber below the toilet stool (such as in a basement or outside) where composting takes place and are suitable for high-volume and year-round applications as well as to serve multiple toilet stools.
"Desiccating toilets" dry the excreta to destroy pathogens, though one study suggested that drying can result in rehydration of pathogens when in contact with moisture later.
Self built unit
Site-built or self-built composting toilet designs vary, ranging from rollaway containers fitted with aerators to large concrete sloped-bottom tanks.
Regulation
There are no universally accepted performance standards for composting toilets in the United States, although seven jurisdictions in North America rely on testing of manufactured systems to
American National Standard/NSF International Standard ANSI/NSF 41-1998: Non-Liquid Saturated Treatment Systems. An updated version of ANSI/NSF Standard 41 was published in 2005. Systems might also be listed with CSA, cETL-US, and other standards programs.
See also
- Chemical toilet
A chemical toilet is a toilet which uses chemicals to deodorize the waste instead of simply storing it in a hole, or piping it away to a sewage treatment plant. Common types include aircraft lavatory, some passenger train toilets and the portable toilets used on construction sites and at large...
- Ecological sanitation
Ecological sanitation, also known as ecosan or eco-san, are terms coined to describe a form of sanitation that usually involves urine diversion and the recycling of water and nutrients contained within human wastes back into the local environment....
- Humanure
- Urine diversion dessication toilet (UDDT)
-Urine diversion:Urine diversion refers to the separation of urine from feces at the point source, i.e at the toilet or outhouse. A toilet fixture used to help facilitate the separation is called a urine diversion toilet or UDT. The bowel has two separate compartments which may or may not be...
- Vermicomposting
External links