Composting toilet

Public composting toilet facility on E6 highway in Sweden

A composting toilet is a dry toilet that uses a predominantly aerobic processing system to treat human excreta, typically with no water or very small volumes of flush water, by composting or managed aerobic decomposition. Composting toilets may be used as an alternative to flush toilets in situations where no suitable water supply or sewer system and sewage treatment plant is available to capture the nutrients in human excreta in the form of compost. For example, they are in use in many of the roadside facilities and national parks in Sweden, US, Uk and Australia.

The human excrement is usually mixed with sawdust, coconut coir or peat moss to enable aerobic processing, liquid absorption, and odor mitigation. Decomposition is generally faster than the anaerobic decomposition used in wet sewage treatment systems such as septic tanks.

Composting toilets yield soil compost that can be used for horticultural or agricultural soil enrichment as local regulations allow.

Terminology

Schematic of the composting chamber which is located below the toilet seat

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

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.

Composting container of "TerraNova" composting toilet, showing open removal chamber (town house at the ecological settlement Hamburg-Allermöhe, Hamburg, Germany)

The term "composting toilet" is used by many people and manufacturers quite loosely, and may also have a different meanings in different countries. For example, in English-speaking countries, the term "anaerobic composting" (equal to anaerobic decomposition or digestion) is used as well, wheras for example 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 the action of a microbial community or with the action of earth worms like in vermicomposting.

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 have also been called "sawdust toilets" which can be a more appropriate term if the amount of aerobic composting taking place in the toilet's container is very limited.

Appropriateness

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).

Basics

Main article: Compost

Components

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:

1. a reactor which is the storage or composting chamber
2. a ventilation unit to provide air to ensure aerobic conditions, to allow carbon dioxide and water to evaporate and to reduce odour
3. a leachate collection system to drain excess liquid
4. 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 amounts 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.

Pathogen removal

Excreta-derived compost may be deemed safe for humans to use on crops if handled in accordance with local health regulations, and composted properly. This means that thermophilic composting must heat the compost pile sufficiently to destroy harmful pathogens, or enough time must have elapsed since fresh material was added that biological activity has killed any pathogens. To be safe for crops, a curing stage is often needed to allow a second mesophilic phase to reduce potential phytotoxins.

Excreta-derived compost aids in the return of nutrients in fecal matter to the soil, but it can carry and spread a number of human pathogens. These pathogens can be killed by composting both by the extreme heat of the composting and the extended amount of time (1 to 2 years) that it is allowed to decompose.

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.

An influential source in the US states that complete pathogen destruction may be achieved if the entire compost heap heats itself to 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. Other composting experts regards this as being overly optimistic.

Design considerations

Environmental factors

There are four main factors that affect the decomposition process:

1. Oxygen: There has to be enough oxygen to ensure aerobic composting
2. Moisture: Proper moisture content of 45 to 70 percent
3. Internal heap temperature: ideally between 40 to 50 °C (achieved through proper chamber dimensioning, and possibly mixing)
4. 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."

External composting chamber of a composting toilet at a house in France

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.

Leachate management

Composting toilet with a seal in the lid in Germany

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.

Types

Many companies are offering their composting toilet models, and construct-it-yourself systems are also popular.

Main types

There are four main types of composting toilets:

• Single-vault
• Multiple-vault
• Mobile bucket or bin toilets followed by external composting of the excreta
• Composting toilets with mechanical devices

Variations

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.

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.

As an example, the slow composting toilets that have been installed by the Green Mountain Club for use in the backcountry of Vermont, USA, are constructed with multiple vaults and a movable toilet platform. When one of the vaults is filled up, the toilet seat can be slid across to be over the empty vault. The full vault is left untouched for up to three years before it is emptied. A shorter time period is used if red worms are employed in a vermicomposting type arrangement. With these composting toilets, users are asked by the Club to deposit their urine directly into the toilet rather than in the forest, in order to add the needed moisture to the compost pile. In contrast, users of the Club's other types of dry toilets - like pit latrines and simple bucket toilets with woodchips and external composting - are asked not to urinate in the toilets but rather in the forest in order to reduce odors in these toilets. This is because the latter types of toilets generally require dryer conditions.

While the slow low temperature composting process utilized in the Club's moldering toilets is not able to kill off helminth eggs, such as Ascaris lumbricoides, this is not a huge concern due to the fact that helminth infections are relatively uncommon in the U.S. population, although they do exist.

Manufactured systems

"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.

One type of composting toilet model from Sweden which is relatively well known is called the "Clivus Multrum" model. Many other models exist on the market.

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.

Maintenance

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 odor. 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

Main articles: Uses of compost and Reuse of excreta

Henry Moule's earth closet, patented in 1873 (not a true composting toilet). Example from around 1875. Rear chamber for dispensing cover material

Henry Moule's earth closet design, circa 1909.

Soil conditioner

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.

The nutrients in compost from a composting toilet have a higher plant availability than the product (dried faeces) from a urine-diverting dry toilet.

By disposing of feces and urine through composting, the nutrients contained in them are returned to the soil. This aids in preventing soil degradation. Human fecal matter and urine have high percentages of nitrogen, phosphorus, potassium, carbon, and calcium. In this regard their compost is equivalent to many fertilizers and manures purchased in garden stores.

Pharmaceutical residues

The excretion of prescription pharmaceuticals into excreta-derived compost, just as in conventional sewage and sewage sludge processing, is a potential source of contamination of 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 pharmaceutical medications are excreted by the human body. Many of these medications were directly dumped into municipal sewage supplies; those medications that are lipophilic (dissolved in fats) are more likely to reach groundwater by leaching from fecal wastes. Regular sewage treatment removes an average of 60% of these medications. The percentage of medications degraded during composting of excreta has not been studied.

Advantages and disadvantages

The advantages and disadvantages of composting toilets are similar to those of urine-diverting dry toilets compared to pit latrines or flush toilets.

Advantages

Comparison with pit latrines

The advantage of composting toilets compared to pit latrines is the conversion of feces into a dry odorless material and therefore an avoidance of the issues surrounding liquid fecal sludge management (e.g. odor, fly attraction, difficulties in pit emptying). A well-maintained composting toilet is an odor and insect free toilet which is appreciated by users and allows simple removal and far less offensive and safer handling of the fecal material once the feces vault has filled up. Moreover, the risk of water pollution is minimised through the safe containment of faces in above-ground vaults and this allows the toilets to be constructed in locations where pit-based systems are not appropriate.

Comparison with flush toilets

Flush toilets dilute excreta and create wastewater streams, something that composting toilets do not. The installation of composting toilets in all households connected to a common sewer would result in vastly reduced volumes of water, nutrients and organic matter arriving at the associated wastewater treatment plant.

Disadvantages

Comparison with pit latrines

Disadvantages of composting toilets compared to pit latrines include: higher capital costs (although whole-of-life costs might be lower), more awareness required by the user who has to use it properly (for instance, adding covering materials, ensuring the right moisture content which may mean collecting urine separately).

Comparison with flush toilets

The pathogen destruction rate in composting toilets that are not connected to external, secondary composting, is usually very low, particularly with regards to the difficult to destroy helminth eggs, like Ascaris eggs. If the users or the caretakers are unaware of this fact, and do not protect themselves and their environment accordingly, this could lead to spreading of diseases, especially if the compost from the composting toilet is directly used in gardening activities. In this context, the exaggerated claims of many composting toilet manufacturers as well as well-known composting experts regarding the safety of the compost produced from composting toilets is not helpful and potentially even dangerous to public health.

History

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 type 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

Regulations

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. 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 tack 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 (Massachusetts) 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 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 "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 conjunction 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.

Germany

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 consists 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.

Finland

Numerous sparsely settled villages in rural areas in Finland are not connected to municipal water supply or sewer networks and homeowners must maintain 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, composting toilets are common at holiday homes, often located near sensitive bodies of water. For these reasons, many manufacturers of composting toilets are based in Finland, for example the companies 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 figures for composting toilet use in Finland in 2014:

• About 4% of single-family homes in sparsely settled areas not connected to any public sewer network are equipped with a composting toilet. It may be the only toilet in the house or a second one when there is also a flush toilet available.
• In holiday homes composting toilets, as well as other types of dry toilets, are more common: almost 200 000 composting toilets are thought to serve holiday homes in Finland. This figure refers solely to commercial models, both simple ones and more sophisticated models. In addition, at least an equivalent number of other types of dry toilets serve holiday homes. The simplest ones are often not placed inside the house but in a separate toilet hut or outhouse.

External links

• "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