Composting toilets

A composting toilet is a system for removing feces away from humans and living areas to safely store and treat it, so that it can be reused safely for local agriculture. It comprises of a toilet, which is usually (but not always) a dry toilet or urine diversion dry toilet together with (almost always) some kind of storage system beneath, often called a latrine. This is in contrast to a pit latrine, where there is no barrier to the surrounding environment and material leaches out. This is a very important document that attempts to define clearly common terms used in the sector.

It is a very common WASH system aiming to give better health to communities than they have with open defecation and with less of the problems sometimes associated with a single pit latrine, which may leak exposing groundwater and drinking water to harmful microbes which cause illness.

Appropriate technology toilet systems can be high risk activities, see below regarding strategies to minimise risk of infection.

What is ecosan?

Ecological sanitation (ecosan) is the general term used in WASH circles to describe sanitation systems which are dispersed (rather than being based on sewers and large municipal wastewater treatment works ) and which aims to encourage people to view their own waste as a potential resource rather than a problem. This has wide applicability in countries that have complex sewerage systems as the 'flush and forget' mentality is found almost everywhere.

Ecosan and composting toilets are terms that are often used interchangably and can be poorly defined. It is probably best to consider composting toilets as part of Ecological Sanitation, which can and should contain a range of other processes.

How are they supposed to work?

Human feces is a major pathway for micobial pathogens which cause diarrhea and other diseases which are a major cause of death, particularly of infants. The pathogens are able to survive in the feces when it is kept near body temperature, but even in circumstances where the feces is dried out completely, they may still pose a danger.

The composting process aims to encourage a situation whereby the pathogens are destroyed by competition from other 'healthy' soil micobes. This environment is created by adding carbon-rich material, reducing moisture levels and increasing oxygen by aeration.

A composting toilet is therefore a low technology method to encourage the best possible conditions to destroy the pathogens and usually involves adding available carbon-rich materials after defecation - usually ash or sawdust. There are often modifications to standard pit latrines to make them smaller, more watertight and better aerated (see below). This means that a composting toilet is usually emptied more regularly than a pit latrine might have been.

In many, but not all, systems the urine is separated from the feces as the urine is much less likely to be a source of infection and can be used more easily as a direct form of fertiliser. The composting process is usually considered to be more efficient when the feces is drier and the risk of leakage is reduced.

Toilets and latrines may also be used for temporary storage and feces removed for local secondary treatment.

Advantages

Toilet systems that dispose (processed or raw) human feces directly into the soil (ie pit latrines and flush toilets hooked upto a septic tank connected to a drain field) can contaminate waterlogged and high water table areas. This puts people at risk of catching cholera, dysentery, diarrhoea, jaundice, typhoid, polio and intestinal worms.

In waterlogged areas where there was previously no satisfactory sanitation system operating, the benefits that compost toilets provide are clear. They can prevent ground and surface water contamination and protect people's health in areas where open defecation on the ground or directly into water bodies has been the norm. The production of safe compost and effective use of the urine and wash water are also a significant benefit.

Composting toilets also protect surface and ground water from sewage pollution. Unlike flush toilets, composting toilets do not produce raw/untreated sewage should not smell. They save huge quantities of water.

The use of compost toilets means that cities and peri-urban areas do not need to extend capital intensive sewerage networks and sewage treatment plants. In addition, at least in theory, the lack of septic tanks should mean that emptying is a safer process. The recurring cost of maintaining additional infrastructure is also avoided. Both these factors represent a huge saving. Also, in areas where toilets would be flushed with municipal water there is an enormous saving in water requirements.

Cross contamination between water mains and sewers is (or should be) eradicated where compost toilets are well established as the standard sanitation technology. Soils are steadily improved by the regular addition of good quality compost.

The technology also lends itself extremely well to areas with hard rocky soils where excavation of pits is difficult, expensive or inappropriate. Again the compost is valuable and can help to provide a better chance of establishing plant cover on thin and fragile soils.

Additional advantages finally are that composting toilets can be and do not produce flies or smell if properly constructed. It also does not provide a breeding ground for mosquitoes. Septic tanks and pit latrines often have poorly fitting covers or the covers are not carefully replaced after emptying. These places then become prime breeding sites for mosquitoes which should, in theory, not exist in a composting toilet

Disadvantages

One major disadvantage is that compost still needs to be moved manually by the user to the agricultural field for deposit, which represents a major potential source of infection.

Efficient composting and sanitisation of feces requires consistent temperatures of over 30°C and ideally over 50°C for an extended period of time. The materials in a composting toilet may never reach that temperature or there may be limited consistency within the material so that there may be some that is not properly sanitised even where the majority is. This can be a potential problem as surviving microbes can reinoculate the remaining material.

The most efficient form of sanitation is in aerobic conditions, but in practice conditions in a given composting toilet system may be a mix of anaerobic and aerobic zones - or even largely anaerobic. This has important implications as to the effectiveness of the process as most microbial pathogens are anaerobic and are destroyed in aerobic conditions. Anaerobic digester systems have been shown to be effective at treating feces and outdoor co-composting of sludge is known to be effective, so a composting toilet may actually represent the worst of all options.

Hill and Baldwin[1] write, convincingly:

The limited body of literature on [composting toilets], especially field versus laboratory studies, generally does not prove them reliable for decomposition or sanitation of fecal matter. Adequate temperatures are seldom, if ever, attained eliminating this reliable mechanism of pathogen destruction. Storage alone is unlikely to be a reliable pathogen destruction mechanism.

In addition, most composting systems only have storage for material for 6-12 months. Poor management or unforeseen circumstances may mean that the toilets need to be emptied more regularly, which may have important consequences on the overall pathogen risk to users.

Are composting toilets safe?

Stenström et al [2] tried to assess the risk of microbial exposure from a range of WASH sanitation systems. They concluded that there were risks associated with both the operation and emptying of the facilities. If the toilet was kept clean, forms of dry toilet offered medium to low risk of infection for users and cleaners/workers. However, manually handling the material generated from these systems can be high risk.

Composting toilets are designed to destroy pathogens to produce a safe compost. However, studies have indicated that in different situations, pathogens are not necessarily destroyed. The general feces advice is that composts should not be handled for at least a year, and that they should not be necessarily considered to be fully sanitised even then. Ideally all composts from toilet pits should undergo additional treatment before being added to agricultural land.

For a fuller discussion of the academic literature on this subject, please see Infection risk from Ecosan.

In countries where the prevalence of infectious disease is very low and where there are extremely good healthcare is available, these risks may exist but the effects on individuals may be far lower. Good practice suggests, however, carefully considering the risks and pathways for infection wherever the technology is used.

Creating community support

It is important to realise that any composting toilet programme also requires an education programme to ensure that the principals of use and maintenance are clearly understood and accepted by the user group.

Adequate awareness raising and training needs to be given to the users in the early stages of establishing the composting toilet. It is essential that the toilet is correctly designed and built and that there has been a very interactive and participative approach to its introduction. If these steps are taken, there is a far greater chance of the compost toilet being "owned, understood and accepted" by the community which is essential if it is to be successful.

The need for interactive training and awareness raising is to unravel and dispel the misunderstandings and confusion that often surrounds sanitation, health, hygiene, water and the environment. For example, in one project the main interest in the compost toilet was for the privacy it gave rather than because it was safer and more hygienic than open defecation. At the same time, the greatest fear of the users and neighbours was that it would smell. By knowing the fears and misconceptions, the hygiene awareness raising can be tailored to suit the needs of a specific community.

Training of the awareness team must also be done very carefully and interactively as they may have the same misconceptions as the community. It is often beneficial to build the team from amongst women and youths already active in development in the community and who are held in good regard locally. Some methods that have been effective in reaching the community are the performance of street dramas explaining the many faecal-oral routes that give rise to disease and relating them to every day events and habits. Illustrated leaflets can be distributed, games played and songs sung with children and adults, both in school and leisure time. House visits should be made to follow up the messages and discuss the dramas and leaflets. These visits can be particularly effective since people are generally more willing to express any doubts in private.

See also community-led total sanitation, which is an effort to stimulate demand for better sanitation from communities themselves.

Types of composting toilet

Composting toilets should be understood as whole systems, intended to produce safe compost which can be used as a soil amendment. So it can be helpful to consider parts of the system to include a collection vessel (toilet or urinal), a storage area (latrine, pit or storage tank) and treatment.

Sometimes composting toilets are described as small pit latrines, often with urine diversion dry toilets. Sometimes single VIP and double VIP latrines or variations are considered to be composting toilets because it is considered that useful sanitation of microbial pathogens will be occurring in the latrines.

Whilst these modifications may be helpful, particularly regarding odors and flies, the conditions in latrines are not ideal and the effect on pathogens is highly variable. All material generated by these systems should therefore be considered partially-treated at best, even if additional sawdust or ash has been added to the feces and it has been left for the recommended storage times.

The only two types of composting toilet systems that matter are therefore those which adequately destroy harmful pathogens and those that do not. Full treatment of feces within a toilet or latrine is unlikely to happen without some kind of mechanical stirring and forced aeration.

To reduce risk, material from composting toilets should never be put directly onto food crops. Storage for at least a year is highly advisable in a latrine, after which material should be removed (ideally with minimum handling) and taken for secondary treatment. The simplest secondary treatment systems are community scale co-composting or vermiculture, which have shown to be effective at sanitisation if managed properly.

During this treatment, workers may be at high risk of infection, so need to wear protective clothing. Even after treatment, feces compost should not be used on any food crop which will come into direct contact with humans - such as leaves or tubers. Ideally the compost should never be used on food crops at all.

Case studies and how-tos available on Appropedia

Ole Ersson's sawdust toilet how-to explains how to make a simple collection system and outside composting with sawdust.

The Pedregal Permaculture Demonstration Center how-to explains the form and function of their urine diversion double pit composting toilets.

The New Dawn composting toilet how-to explains how the Costa Rican herbalism school constructed and operate their single pit composting toilet.

The Noyemberyan composting toilet page does not have much information about the system installed by Peace Corps in Armenia, but there are some good photos which show a form of single ventilated improved pit design.

Humboldt State University's CCATBox is a form of single ventilated pit latrine but with forced air pumped through it and rotating drums to ensure mixing and sanitation of the compost.

The Duchamp de Loo is another student project from Humboldt State which created a mobile toilet for use on a barge. It comprises of a urine diversion and collection system for feces which are moved elsewhere for composting.

Alternatives to consider

Notes and references

  1. ↑ Hill, G. B., & Baldwin, S. A. (2012). Vermicomposting toilets, an alternative to latrine style microbial composting toilets, prove far superior in mass reduction, pathogen destruction, compost quality, and operational cost. Waste Management.
  2. ↑ Stenström TA, Seidu R, Ekane N, and Zurbrügg C. Microbial Exposure and Health Assessments in Sanitation Technologies and Systems (2011). EcoSanRes

Further reading

See also

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