A composting toilet is a dry toilet that uses a predominantly aerobic processing system that treats human excreta, typically with no water or very small volumes of flush water, via composting or managed aerobic decomposition. Composting toilets may be used as an alternative to flush toilets in situations where there is no suitable water supply or sewer system and sewage treatment plant available, or to capture nutrients in human excreta as humanure. They are in use in many of the roadside facilities and national parks in for example Sweden, USA, United Kingdom and Australia.
The human excrement is normally mixed with sawdust, coconut coir or peat moss to support aerobic processing, absorb liquids, and to mitigate odor. The decomposition process is generally faster than the anaerobic decomposition used in wet sewage treatment systems such as septic tanks.
Composting toilets yield a soil amendment that can be used in horticultural or agricultural applications as local regulations allow.
- 1 Terminology
- 2 Appropriateness
- 3 Design considerations
- 4 Types
- 5 Maintenance
- 6 Use of compost
- 7 History
- 8 Society and culture
- 9 Notes
- 10 References
- 11 External links
Composting toilets should not be confused with the pit latrine, arborloo or tree bog, all of which are forms of less controlled decomposition, and may not protect groundwater from nutrient or pathogen contamination or provide optimal nutrient recycling. They should also not be confused with urine-diverting dry toilets (UDDTs) where pathogen reduction is achieved through dehydration (also known by its more precise term "desiccation") and the faeces collection vault is therefore kept as dry as possible (whereas in a composting toilet a certain degree of moisture is aimed for in the composting chamber).
Composting toilets are usually set up without urine diversion but can also include urine diversion. Offering a waterless urinal in addition to the composting toilet can help keep excess amounts of urine out of the composting chamber.
Composting toilets can be used to implement an ecological sanitation (ecosan) approach for resource recovery, however it would be wrong to call a composting toilet an "ecosan toilet" as ecosan is an approach and not a specific technology.
Composting toilets can be suitable in areas with no suitable water supply, sewer system and sewage treatment plant. They can be used for resource recovery by reusing sanitized feces and urine in agriculture as fertilizer and soil conditioner.
Furthermore, composting toilets can also be suitable in situations where:
- An individual, family or community wants to increase the resilience of their existing sanitation system in the face of possible natural disasters (i.e. climate change, earth quakes) or possible rising energy prices; and
- Following approval by local building inspectors and health department authorities, an individual or family seeks to reduce or perhaps eliminate the need for a septic tank system to reduce their environmental footprint (particularly when the UDDT is used in conjunction with an on-site greywater treatment system).
A composting toilet consists in principle of two elements: a place to sit or squat and a collection and composting unit. The actual composting unit of the composting toilet consists of four main parts:
- a reactor which is the storage or composting chamber
- a ventilation unit to provide air to ensure aerobic conditions, to allow carbon dioxide and water to evaporate and to reduce odour
- a leachate collection system to drain excess liquid
- an access door for withdrawing the mature product
The composting chamber can be constructed below or above ground, indoors or outdoors with a separate superstructure. A drainage system should be installed to ensure the removal of leachate. Otherwise, too much moisture can cause anaerobic conditions and impede the degradation. Urine diversion can improve the compost quality since urine contains a large ammounts of ammonia that inhibits microbiological activity.
Composting toilets greatly reduce the volume of excreta on site through psychrophilic, thermophilic or mesophilic composting. In cold climates the composting chamber should be indoors so that the composting process is not inhibited due to low temperatures.
Rapid aerobic composting will be thermophilic decomposition in which bacteria that thrive at high temperatures (40-60 °C or 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. Compost from composting toilets is hygienically harmless (i.e. pathogen levels reduced to a safe level) if thermophilic composting occurs at temperatures of 55 °C for at least two weeks or at 60 °C for one week.
There are four main factors that affect the decomposition process:
- Oxygen: There has to be enough oxygen to ensure aerobic composting
- Moisture: Proper moisture content of 45 to 70 percent
- Internal heap temperature: ideally between 40 to 50 °C (achieved through proper chamber dimensioning, and possibly mixing)
- Carbon-to-nitrogen ratio (C:N): ideally 25:1
With regards to optimum moisture content, one source recommends: "The compost should feel damp to the touch, with only a drop or two of water expelled when tightly squeezed in the hand."
Additives and bulking material
Human excreta and food waste do not provide optimum conditions for composting. Usually the water and nitrogen content is too high, particularly when urine is not separated and is mixed with the other material in the vault. Additives or “bulking material”, such as wood chips, bark chips, sawdust, ash and pieces of paper, are used to absorb moisture. The additives also improve the aeration of the pile and increases the carbon to nitrogen ratio by adding carbon-rich material. Bulking material also serves as cover of the fresh faeces and reduces access of flies and other insects. If sufficient bulking material is not added, the organic matter in the composting vault may get too compact and form impermeable layers, which leads to anaerobic conditions and odour.
Drainage of excess liquid or leachate 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: too dry, and the mass decomposes slowly or not at all; too wet and anaerobic organisms thrive, creating undesirable odors (cf. Anaerobic digestion). This separated liquid may be diverted to a blackwater system or collected for other uses. Some units include a urine-separator or urine-diverting system.
Aeration and mixing
The other requirement critical for microbial action, as well as drying, is air. 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 convection 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.
Many companies are offering their composting toilet models, and construct-it-yourself systems are also popular.
There are four main types of composting toilets:
- Mobile bucket or bin toilets followed by external composting of the excreta
- Composting toilets with mechanical devices
Slow composting toilets, moldering toilets
In slow composting toilets (also referred to as "moldering toilets" or "moldering privies" in the U.S.), the temperatures that are achieved are not high enough to destroy pathogens. Slow composting or cold composting happens in most of the composting toilets, because the heap is built up step by step and not at once, regarding humidity, carbon to nitrogen ratio and other process parameters. So a second composting is normally necessary to destroy e.g. potential helminth eggs. Nevertheless, slow composting toilets are composting toilets, as "composting" in English means decompostion in general.
Such composting toilets are usually designed for modest and often seasonal use and employ a more "passive" approach to the composting process (rather than a more actively managed approach) like those that serve remote trail and hiking networks. Mouldering toilets are typically designed and constructed such that the materials deposited can, at a certain point, be isolated or segregated from the operational portion of the toilet (or the entire toilet itself can be closed-off from use) in order to undergo low temperature mesophilic composting. Slow composting toilets rely either solely on long retention times for pathogen reduction and to fully decompose excreta or on the combination of time and the addition of red wriggler worms for vermi-composting. The slow composting toilets utilized in the backcountry of Vermont, USA, are left untouched (once full) for up to three years before they are emptied (less if red worms are employed). However, this would still not be sufficient to kill off helminth eggs, such as Ascaris lumbricoides. As helminth infections are however not common in the population of the U.S. this is not an important problem.
"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 500 millilitres (17 US fl oz) 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.
Self built units
Site-built or self-built composting toilet designs vary, ranging from roll-away containers fitted with aerators to large concrete sloped-bottom tanks.
The emptying frequency of the composting container depends on the size of the container, the amount of material added per day and the composting conditions. 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 health regulations.
Maintenance of composting toilets, whether they are in private or in public settings, is critical to ensure they operate well and without odour. Maintenance tasks include: Cleaning, checking of technical components of the composting toilet (such as the fan) as well as safe treatment, handling and use of the compost and leachate (and urine if it is collected separately).
Composting toilets require greater management efforts than urine-diverting dry toilets due to the need to maintain a consistent relatively high moisture content.
Use of compost
Compost derived from composting toilets (where organic kitchen waste is in some cases also added to the composting toilet), has in principal the same uses as compost derived from other organic waste products, such as sewage sludge or municipal organic waste. One limiting factor may be legal restrictions due to the possibility that pathogens remain in the compost. In any case, the use of compost from composting toilets in one's own garden can be regarded as safe and is the main method of use for compost from composting toilets. Hygienic measures for handling of the compost must be applied by all those people who are exposed to it, e.g. wearing gloves and boots.
Some of the urine will be part of the compost, although some urine will be lost via leachate and evaporation. Urine can contain up to 90 percent of the nitrogen, up to 50 percent of the phosphorus, and up to 70 percent of the potassium present in human excreta.
Before the flush toilet became universally accepted in the late 19th century, there were inventors, scientists, and public health officials who supported the use of "dry earth closets", a typle of dry toilet with some similarities to the modern composting toilets. However, the collection vessel for the human excreta was not designed to achieve composting at the toilet level. Dry earth closets were invented by the English clergyman Henry Moule, who dedicated his life to improving public sanitation after witnessing the horrors of the cholera epidemics of 1849 and 1854. Impressed by the insalubrity of the houses, especially during the Great Stink in the summer of 1858, he invented what he called the 'dry earth system'.
In partnership with James Bannehr, he took out a patent for the process (No. 1316, dated 28 May 1860). Among his works bearing on the subject were: "The Advantages of the Dry Earth System", 1868; "The Impossibility overcome: or the Inoffensive, Safe, and Economical Disposal of the Refuse of Towns and Villages", 1870; "The Dry Earth System", 1871; "Town Refuse, the Remedy for Local Taxation", 1872, and "National Health and Wealth promoted by the general adoption of the Dry Earth System", 1873.
His system was adopted in private houses, in rural districts, in military camps, in many hospitals, and extensively in the British Raj. Ultimately, however, it failed to gain the same public support and attention as the water-flushed toilet connected to a sewer system.
In Germany, there was a similar design of a dry toilet with a peat dispenser on the market until after the second World War (it was called "Metroclo" and was manufactured by Gefinal, Berlin).
Society and culture
United States of America
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 2011.[note 1] Systems might also be listed with CSA, cETL-US, and other standards programs.
Regarding regulation of the byproducts of a composting toilet, several U.S. states permit disposal of solids from composting toilets (usually a clear distinction between different types of dry toilets is not made) by burial, with some mandating lesser minimum depths, as little as 6 inches, and others not specifying any minimum depth at all. For instance:
- The Commonwealth of Massachusetts requires that, "residuals from the [composting toilet] system must be buried on-site and covered with a minimum of six inches of clean compacted soil.
- In Oregon the applicable regulations state that, "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."
- Rhode Island, meanwhile, acknowledges that, "solids produced by alternative toilets may be buried on site," but specifies that, "residuals shall not be applied to food crops."
- Likewise, the Department of Health of the Commonwealth of Virginia requires that, "...all materials removed from a composting privy shall be buried," and that, "compost material shall not be placed in vegetable gardens or on the ground surface."
- The State of Vermont permits users to dispose of the byproducts 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]."
- The State of Washington takes a wholly different tact in choosing to model its extensive regulations that oversee the use of dry toilets (what it refers to as "waterless toilets") in large part on the federal regulations that govern sewage sludge.
At least one state goes so far as to distinctly regulate the "liquids" produced by a composting toilet, requiring 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."
For dry toilet users users in the United States, an important distinction to keep in mind - and one that is supported by the aforementioned existence of numerous state regulations that make no mention of, and also diverge widely from, the requirements of the federal regulations that govern the management of sewage sludge - is the fact that the federal 503 rule, known colloquially as the the "EPA Biosolids rule" or the "EPA sludge rule", has no jurisdiction over the byproducts of a dry toilet and that all oversight of these materials falls to the individual states.
International Organization for Standardization (ISO)
The International Organization for Standardization (ISO) is currently preparing a "management standard" which is in a draft state as ISO 24521, currently under the heading "Activities relating to drinking water and wastewater services — Guidelines for the management of basic onsite domestic wastewater services". The new standard is meant to be used in conjuction with ISO 24511 standard. More than conventional wastewater it will deal with toilets (including composting toilets) and toilet waste. The guidelines are applicable with privately or publically owned and/or operated basic wastewater systems and include the aspects of the whole life span of domestic wastewater such as planning, usability, operation and maintenance, disposal, reuse and health.
International Association of Plumbing and Mechanical Officials
The International Association of Plumbing and Mechanical Officials (IAPMO), a plumbing and mechanical code structure currently utilized by many western states has 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." If adopted, this new far reaching 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.
In some projects in Germany composting toilets have been successfully implemented in houses with up to four floors.
The ecological settlement in Allermöhe, Hamburg, is a reference project with a history reaching back to 1982. The settlement consits of 36 single-family houses with approximately 140 inhabitants and uses composting toilets besides rainwater harvesting and constructed wetlands. The waterless toilet system saves 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 m³ water savings per year for the whole settlement.
Numerous sparsely settled villages in rural areas in Finland are not connected to municipal water supply or sewer networks and the house owners must themselves take care of their own systems. Individual private wells, i.e. shallow dug wells or boreholes in the bedrock, are often used for water supply, and several house owners have opted for composting toilets. In addition, composting toilets are common at holiday homes, located often near sensitive water bodies. These are the reasons why there are many Finnish manufacturers of composting toilets, for example the companies Biolan, Ekolet, Kekkilä, Pikkuvihreä and Raita Environment.
- A listing of the most current NSF/ANSI standards can be found in PDF format at NSF International's Standards subdomain.
- Tilley, E., Ulrich, L., Lüthi, C., Reymond, Ph., Zurbrügg, C. Compendium of Sanitation Systems and Technologies - (2nd Revised Edition). Swiss Federal Institute of Aquatic Science and Technology (Eawag), Duebendorf, Switzerland. ISBN 978-3-906484-57-0.
- Berger, W. (2011). Technology review of composting toilets - Basic overview of composting toilets (with or without urine diversion). Deutsche Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH, Eschborn, Germany
- National Small Flows Clearinghouse, West Virginia University, Composting toilet technology
- Appalachian Trail Conservancy (2014). Backcountry Sanitation Manual, 2nd Edition. Appalachian Trail Conservancy, Green Mountain Club, USDA Forest Service, National Park Service, USA
- Berger, W. (2009). Appendix of technology review of composting toilets - List of manufacturers and commercially available composting toilets. Gesellschaft für Internationale Zusammenarbeit (GIZ) GmbH
- J.O. Drangert, Urine separation systems
- Oregon Onsite Advisory Committee "Final Report of Recommended Changes to Rules Governing Onsite Systems", OR DEQ, February 8, 2010, accessed May 8, 2011.
- "PUBLICATIONS - Standards and Criteria - March 21, 2013" (PDF). NSF International. p. 4. Retrieved 24 March 2013.
Wastewater Treatment Units … NSF/ANSI 41 – 2011: Non-liquid saturated treatment systems (composting toilets)
- "Regulatory Provisions for Composting Toilets and Greywater Systems". The Official Website of the Massachusetts Executive Office of Energy and Environmental Affairs. Office of Energy and Environmental Affairs. Retrieved 13 January 2015.
- "Department of Consumer and Business Services, Building Codes Division, Division 770, Plumbing Product Approvals". Oregon Secretary of State. State of Oregon. Retrieved 13 January 2015.
- "State of Rhode Island and Providence Plantations Department of Environmental Management, Office of Water Resources: "Rules Establishing Minimum Standards Relating to Location, Design, Construction and Maintenance of Onsite Wastewater Treatment Systems"". State of Rhode Island Department of Environmental Management. STATE OF RHODE ISLAND AND PROVIDENCE PLANTATIONS. July 2010. Retrieved 13 January 2015.
- "SEWAGE HANDLING AND DISPOSAL REGULATIONS (Emergency Regulations for Gravelless Material and Drip Dispersal), 12 VAC 5-610-10 et seq.". State of Virginia Department of Health. Commonwealth of Virginia. 14 March 2014. Retrieved 13 January 2015.
- "Environmental Protection Rules, Chapter 1: Wastewater System and Potable Water Supply Rules". State of Vermont Drinking Water and Groundwater Protection Division. State of Vermont. 29 September 2007. Retrieved 14 January 2015.
- "Recommended Standards and Guidance for Performance, Application, Design, and Operation & Maintenance: Water Conserving On-Site Wastewater Treatment Systems". State of Washington Department of Health. State of Washington. July 2012. Retrieved 14 January 2015.
- "Water Efficiency Technology Fact Sheet: Composting Toilets". United States Environmental Protection Agency, Office of Water, Washington, D.C., EPA 832-F-99-066. United States Environmental Protection Agency, Office of Water. September 1999. Retrieved 13 January 2015.
- "TITLE 40—Protection of Environment, Chapter I—Environmental Protection Agency (Continued), Subchapter O—Sewage Sludge, Part 503—Standards for the Use or Disposal of Sewage Sludge". Electronic Code of Federal Regulations. United States Government Publishing Office. Retrieved 13 January 2015.
- "ISO/DIS 24521. Activities relating to drinking water and wastewater services -- Guidelines for the management of basic onsite domestic wastewater services". International Organization for Standardization (ISO). Retrieved 15 January 2015.
- "ISO 24511:2007. Activities relating to drinking water and wastewater services -- Guidelines for the management of wastewater utilities and for the assessment of wastewater services". International Organization for Standardization (ISO). Retrieved 15 January 2015.
- "Recode September 2014 Newsletter". Recode. Recode. September 2014. Retrieved 15 January 2015.
- "IAPMO Proposed Composting and Urine DIversion Toilet Code". The IAPMO Group. International Association of Plumbing and Mechanical Officials. Retrieved 15 January 2015.
- Cole, Daniel (January 2015). "IAPMO GPMCS raising the bar for water, energy efficiency". Plumbing Engineer. Plumbing Engineer. Retrieved 15 January 2015.
- Rauschning, G., Berger, W., Ebeling, B., Schöpe, A. (2009). Ecological settlement in Allermöhe Hamburg, Germany - Case study of sustainable sanitation projects. Sustainable Sanitation Alliance (SuSanA)
- Global Dry Toilet Association of Finland (2011) Dry Toilet Manufacturers in Finland, Leaflet in English and Finish
- "Global Dry Toilet Association of Finland". Global Dry Toilet Association of Finland - Company and association members. Retrieved 15 January 2015.
- Humanure Handbook online (PDF also available)
- "What is a Composting Toilet System and How Does it Compost?"
- Composting toilet description (Sustainable Sanitation and Water Management Toolbox)
- Composting systems (documents in library of Sustainable Sanitation Alliance)
- More photos of composting toilets in Flickr photo database of Sustainable Sanitation Alliance