Composting toilet

Composting toilet at Activism Festival 2010 in the mountains outside Jerusalem

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. 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.

Terminology

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

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 usually do not divert urine. 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 ecosan is an approach and not a specific technology. Therefore, composting 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.

Applications

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

Inexpensive do-it-yourself compost toilet at Dial House, Essex, England, utilizing an old desk as the toilet unit.

Public composting toilet at a highway rest facility in Sweden

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).

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

Basics

Main article: Compost

Components

A composting toilet consists of two elements: a place to sit or squat and a collection/composting unit. The composting unit consists of four main parts:

• storage or composting chamber
• a ventilation unit to provide air to ensure aerobic conditions, to allow water to evaporate and to vent odorous gases
• a leachate collection system to remove excess liquid
• an access door for extracting the compost

Construction

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.

Pathogen removal

Excreta-derived compost recycles fecal nutrients, but it can carry and spread pathogens if the process of reuse of excreta is not done properly.

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.

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.

Design considerations

Composting toilet with a seal in the lid in Germany

Environmental factors

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 management

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.

Types

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

Commercial units and construct-it-yourself systems are available. Variations include number of composting vaults, removable vault, urine diversion and active mixing/aeration.

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 backcountry

File:Moldering Toilet based on Green Mountain Club design.jpg

Composting toilet (called moldering privy in the US) located on the Appalachian Trail in New Hampshire, USA

Slow composting toilets have been installed by the Green Mountain Club in the Vermont's backcountry. 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.

Active composters

Self-contained

"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

"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.

Other

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

Maintenance

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.

Composting toilets are more difficult to maintain than other types of dry toilets, like urine-diverting dry toilets with which they are often confused. This is due to the need to maintain a consistent and relatively high moisture content.

Uses of compost

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

Main articles: Uses of compost and Reuse of excreta

The material from composting toilets is a humus-like material, which can be suitable as 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 composting toilets has in principal 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 in the compost. Compliance with local regulations that govern such materials is therefore also required.

Pharmaceutical residues

Excreta-derived compost may contain prescription pharmaceuticals, just as in conventional sewage and sewage sludge processing. This can be a point of concern as it could lead to groundwater pollution. 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 toilets, thus mixing with the domestic wastewater in this way. Those medications that are lipophilic (dissolved in fats) are more likely to reach groundwater by leaching from fecal wastes. Regular sewage treatment plants remove an average of 60% of these medications. The percentage of medications degraded during composting of excreta has not yet been reported.

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 simpler toilets

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 water-flushed 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 simpler toilets

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).

In-situ pathogen destruction rates

The pathogen destruction rate in the composting toilets themselves, i.e. without 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. Compost from human excreta processed under only mesophilic conditions or compost taken directly from the compost chamber of the toilets should not be applied directly to crops as this cannot be considered a safe practice. Therefore, the often exaggerated claims of composting toilet manufacturers regarding the safety of the compost produced from composting toilets may be dangerous to public health.

History

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.

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 that as long as the excreta in question is not ever referred to as "fertilizer" (but instead simply a material that is being disposed of) 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

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