||The examples and perspective in this article may not represent a worldwide view of the subject. (March 2015)|
A composting toilet is a dry toilet that uses a predominantly aerobic processing system to treat human excreta, by composting or managed aerobic decomposition. These systems generally use little to no water.[page needed] Composting toilets may be used as an alternative to flush toilets. They have found use in situations where no suitable water supply or sewer system and sewage treatment plant is available to capture the nutrients in human excreta. They are in use in many roadside facilities and national parks in Sweden, US, UK and Australia. They are used in rural holiday homes in Sweden and Finland.
The human excreta is usually mixed with sawdust, coconut coir or peat moss to enable aerobic processing, liquid absorption, and odor mitigation. Most composting toilets use slow, cold composting conditions, sometimes connected to a secondary external composting step.
Composting toilets produce a compost that can be used for horticultural or agricultural soil enrichment if the local regulations allow this. A curing stage is often needed to allow mesophilic composting to reduce potential phytotoxins.
- 1 Terminology
- 2 Applications
- 3 Basics
- 4 Pathogen removal
- 5 Design considerations
- 6 Types
- 7 Maintenance
- 8 Uses of compost
- 9 Comparison
- 10 History
- 11 Regulations
- 12 Notes
- 13 References
- 14 External links
The term "composting toilet" is used quite loosely, and its meaning may vary by country. For example, in English-speaking countries, the term "anaerobic composting" (equivalent to anaerobic decomposition) is used. In Germany and Scandinavian countries, composting always refers to an aerobic process. This aerobic composting takes place either with an associated increase in heat due to microbial action or with the action of earth worms as in vermicomposting.
Composting toilets differ from pit latrines, arborloo or tree bogs, 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 also differ from urine-diverting dry toilets (UDDTs) where pathogen reduction is achieved through dehydration (also known by the more precise term "desiccation") and where the faeces collection vault is kept as dry as possible. Composting toilets target a certain degree of moisture in the composting chamber.
Composting toilets can be used to implement an ecological sanitation (ecosan) approach for resource recovery, however ecosan is an approach and not a specific technology. Therefore, these toilets should not be called "ecosan toilets".
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.
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 be help to increase the resilience of existing sanitation systems in the face of possible natural disasters such 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.
- storage or composting chamber
- a ventilation unit to provide air to ensure aerobic conditions, to allow water to evaporate and to vent odorous gases, such as hydrogen sulfide, ammonia and methane
- a leachate collection system to remove excess liquid
- an access door for extracting the compost
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 a large amounts of ammonia that inhibits microbiological activity.
Composting toilets greatly reduce human waste (excreta) volumes through psychrophilic, thermophilic or mesophilic composting. Keeping the composting chamber insulated and warm protects the composting process from slowing due to low temperatures.
Excreta-derived compost recycles fecal nutrients, but it can carry and spread pathogens if the process of reuse of excreta is not done properly.
Internal pathogen destruction rates are usually low, particularly helminth eggs, such as Ascaris eggs, risking disease absent proper system management. Compost from human excreta processed under only mesophilic conditions or taken directly from the compost chamber is not safe for food production. 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 sufficiently, or enough time (1–2 years) must elapse since fresh material was added that biological activity has had the same pathogen removal effect.
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. An alternate 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, although others regard this as overly optimistic.
Four main factors affect the decomposition process:
- Sufficient 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.")
- Temperature between 40 to 50 °C (achieved through proper chamber dimensioning and possibly active mixing)
- Carbon-to-nitrogen ratio (C:N) of 25:1
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 mixed with feces. Additives or “bulking material”, such as wood chips, bark chips, sawdust, ash and pieces of paper can absorb moisture. The additives improve pile aeration and increase the carbon to nitrogen ratio. Bulking material also covers faeces and reduces insect access. Absent sufficient bulking material, the material may become too compact and form impermeable layers, which leads to anaerobic conditions and odour.
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
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.
Slow composting (or moldering) toilets
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 offer a framework for safe reuse of excreta, using a multiple barrier approach.
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. Slow composting toilets rely on long retention times for pathogen reduction and for decomposition of excreta or on the combination of time and/or the addition of red wriggler worms for vermi-composting. Worms can be introduced to accelerate composting. Some jurisdictions of the US consider these worms as invasive species.
Example in Vermont woods
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. 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.
"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, 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.
"Remote" "central" or "underfloor" units collect excreta via a toilet stool, either waterless, vacuum or micro-flush, from which it drains into 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.
Some units employ roll-away containers fitted with aerators, while others use sloped-bottom tanks.
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 more often), 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. Active, hot composting may span months only while passive, cold composting may require years. Properly managed units yield output volumes of around about 10% of inputs.
Uses of compost
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 faeces that result from a urine-diverting dry toilet.
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.
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 excreta-derived compost must consider the risk of pathogens.
Excreta-derived compost may contain prescription pharmaceuticals. Such residues are also present in conventional wastewater treatment effluent. 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, caffeine, carbamazepine, fibrates and cholesterol-reducing medications. 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. Wastewater treatment plants remove an average of 60% of these medications. The percentage of medications degraded during composting of excreta has not yet been reported.
Unlike pit latrines, composting toilets convert feces into a dry, odorless material, avoiding the issues surrounding liquid fecal sludge management (e.g. odor, insects and disposal). These toilets minimize the risk of water pollution through the safe containment of faces in above-ground vaults, which allows the toilets to be sited in locations where pit-based systems are not appropriate.
However, composting toilets face higher capital costs (although lifecycle costs might be lower) and greater complexity (for instance, adding covering materials and managing moisture content).
Unlike flush toilets, composting toilets do not dilute excreta and create wastewater streams which must be treated before disposal. On the other hand, wastewater treatment plants can centralize waste management for an entire community, with potentially greater efficiency.
Urine-diverting dry toilets
Composting toilets are more difficult to maintain than other types of dry toilets, like urine-diverting dry toilets (UDDT) with which they are often confused. This is due to the need to maintain a consistent and relatively high moisture content. Apart from that, composting toilets are quite similar to UDDTs, sharing many of the same advantages and disadvantags.
Dry earth toilet
Before the flush toilet became accepted in the late 19th century in developed countries, some inventors, scientists and public health officials supported the use of "dry earth closets", a type of dry toilet with similarities to composting toilets. However, the collection vessel for the human excreta was not designed to compost. Dry earth closets were invented by English clergyman Henry Moule, who dedicated his life to improving public sanitation after witnessing 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 patented his device (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 public support as attention turned to the water-flushed toilet connected to a sewer system.
In Germany, a similar dry toilet with a peat dispenser was marketed until after the second World War (it was called "Metroclo" and was manufactured by Gefinal, Berlin).
International Organization for Standardization (ISO)
The International Organization for Standardization (ISO) is currently preparing a "management standard". As of 2015 this was in a draft state as ISO 24521, under the heading "Activities relating to drinking water and wastewater services — Guidelines for the management of basic onsite domestic wastewater services". The standard is meant to be used in conjunction with ISO 24511. It deals with toilets (including composting toilets) and toilet waste. The guidelines are applicable with 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 Officials
The International Association of Plumbing and Mechanical Officials (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." 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.
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.
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.
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 dating to 1982. The settlement consists of 36 single-family houses with approximately 140 inhabitants and 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 m³ water savings per year for the whole settlement.
No performance standards for composting toilets are universally accepted in the US. Seven jurisdictions in North America use American National Standard/NSF International Standard ANSI/NSF 41-1998: Non-Liquid Saturated Treatment Systems. An updated version was published in 2011.[note 1] Systems might also be listed with CSA, cETL-US, and other standards programs.
Regarding byproduct regulation, several US states permit disposal of solids from composting toilets (usually a distinction between different 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. 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."
- 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."
- Rhode Island−"solids produced by alternative toilets may be buried on site," while, "residuals shall not be applied to food crops."
- 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."
- 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]."
- Washington−models its extensive regulations for what it refers to as "waterless toilets") on the federal regulations that govern sewage sludge.
The Environmental Protection Agency has no jurisdiction over the byproducts of a dry toilet as long as excreta 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.
- 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.
- Hill, B. G. (2013). An evaluation of waterless human waste management systems at North American public remote sites. PhD thesis, University of British Columbia (Vancouver), Canada
- 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
- Stenström, T.A., Seidu, R., Ekane, N., Zurbrügg, C. (2011). Microbial exposure and health assessments in sanitation technologies and systems - EcoSanRes Series, 2011-1. Stockholm Environment Institute (SEI), Stockholm, Sweden, page 88
- National Small Flows Clearinghouse, West Virginia University, Composting toilet technology
- WHO (2006). WHO Guidelines for the Safe Use of Wastewater, Excreta and Greywater - Volume IV: Excreta and greywater use in agriculture. World Health Organization (WHO), Geneva, Switzerland
- Allen, Lee (2013). "Long Trail News: Quarterly of the Green Mountain Club, Fall 2013. Article titled: "A Privy is a Privy is a Privy...or is it? To Pee or Not Pee."". Green Mountain Club. Green Mountain Club. Retrieved 31 January 2013.
- Antos-Ketcham, Pete (2013). "Long Trail News: Quarterly of the Green Mountain Club, Fall 2013. Article titled: "Batch-Bin/Beyond-the-Bin (BTB) Composting Privies"". Green Mountain Club. Green Mountain Club. Retrieved 31 January 2015.
- 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
- Drugs in the Water. Harvard Health Letter. 2011.
- Encyclopedia of Quantitative Risk Analysis and Assessment, Volume 1, edited by Edward L. Melnick, Brian S. Veritt, 2008
- "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.
- Global Dry Toilet Association of Finland (2011) Dry Toilet Manufacturers in Finland, Leaflet in English and Finnish
- "Global Dry Toilet Association of Finland". Global Dry Toilet Association of Finland - Company and association members. 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)
- 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.
|Wikimedia Commons has media related to Composting toilets.|
- "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