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Newsletter and Technical Publications

<Sourcebook of Alternative Technologies for Freshwater Augumentation
in Small Island Developing States>


PART B - ALTERNATIVE TECHNOLOGIES

1. TECHNOLOGIES GENERALLY APPLICABLE TO ISLAND STATES

1.3 Wastewater Treatment Technologies and Reuse

1.3.1 Alternative (Dry) Sanitation

There are a number of different types of sanitation that are generally used on small islands, including simple pit latrines; ventilated improved pit (VIP) latrines, in which a ventilation stack is introduced to reduce nuisance from flies and odours; the pour flush toilet where a water seal is installed to completely eliminate odours, fly nuisances and mosquito breeding in the pit; septic tanks and effluent disposal pipes; and composting toilets. Detailed information on these technologies is readily available in the general literature, and the emphasis here is on their application in SIDS.

Contamination of water supplies by human and animal excrement is a recognised means of transmission of diseases. In addition, the high nutrient loading from such contamination can also negatively affect human health and cause ecological damage. For these reasons it is advisable to take all measures possible to prevent human and animal excrement from reaching freshwater sources. Faecal contamination of groundwater from human sources can also occur due to the percolation of the effluents from septic tanks or pit latrines into the groundwater, or through infiltration of faecal material into the groundwater from the land surface. One way to avoid faecal contamination of groundwater is to use a composting toilet which is a sanitation technique that is capable of converting excrement and organic material into a soil-like substance that has a pleasant earthy odour, and which can be safely disposed of in the environment after an adequate composting period. This section focuses on the dry sanitation technology used in composting toilets as this technology both conserves water and protects the groundwater. The protection of the groundwater is of particular importance to the very small islands, where the groundwater lens is very limited and close to the land surface.

Technical Description

The features of a composting toilet include on-site dry biological treatment; one or more containers under the toilet pedestal to receive human excrement (faeces and urine) and other bodily discharges; use of a bulking agent containing accessible carbon that is added to the containers regularly to keep the pile aerated; ventilation either passively or by electric fans; storage of the solids in the containers while they are being broken down by composting; disposal of excess liquid in an appropriately designed evapotranspiration trench adjacent to the toilet building (or, in the case of some commercial units, disposal by evaporation using an electric heater or a solar array); and reduction of pathogens. The material in the containers undergoes primarily aerobic decomposition through the process of mesophyllic composting; (i.e., mesophyllic microorganisms that thrive in a temperature range of 19oC to 40oC contribute to the decomposition of organic matter in the system). Composting toilets can be purchased as prefabricated units or constructed as owner-built units from a number of designs that have been developed over the last 50 years.

There are three main types of composting toilets; namely, (1) the continuous system with a single container in which excrement is deposited by the user from the top of the system and from which compost is removed from the base after an extended period of time, (2) the batch system with two or more containers that are alternated so that an active container is in use in the system while a fallow container has time to compost without the addition of further excrement, and (3) a separation system which separates liquids from the solids which are collected in a moveable container. This latter type is still being developed.

The Clivus Multrum (Figure 12), which originated in Scandinavia, is a continuous system. The material which is deposited in the toilet slides down the inclined bin over time and is emptied from the end-product chamber in a composted form. In practice, blockages or compacting of waste can occur if the material does not slide down the incline. To rectify this, the pile should be raked or stirred to move the material further down into the bin. Another commercial continuous system is the Dowmus which uses worms to assist with the decomposition process.

The alternating batch system (Figure 13), available commercially as the Rota-Loo, the Nature-loo and the Wheelibatch toilet, is based on the original "two holer" used in rural areas of Viet Nam, and has two or more containers which are alternated. The advantage of the alternating batch system is that it allows a period of time when no new material is being deposited in the toilet, thus preventing re-contamination of the composting pile. There is usually no requirement for raking the pile or having any contact with the material during the composting period, but the bins do have to be changed with both the mobile system and fixed pedestal units when they become full. Some designs use turning devices to aerate the pile, but these should not be necessary and often cause difficulties.

Figure 12

Figure 12. Schematic of a composting toilet (of Clivus Multrum).

Extent of Use

Composting toilets are currently being used experimentally on Christmas Island, Kiribati (see Part C, Case Studies), as well as in the Federated States of Micronesia. In Australia, the United States, Canada, and Europe, composting toilets are used by managers of public recreational areas such as national parks, state reserves, water-supply catchment areas, and forestry reserves, and are particularly favoured in areas of high-conservation value and at remote sites.

Figure 13

Figure 13. Wheelibatch toilet.

Operation and Maintenance

Composting toilets require a certain amount of attention and involvement by the householders or maintenance staff. A small quantity of bulking agent has to be added to the toilet regularly. Operators must collect the bulking agent from the bulk store and provide small quantities in a container beside the toilet for users to add after using the system. When the bin that is in use is full, it must be changed by the operator so that the pile can lie fallow to compost the excreta while the alternate bin is in use. This should happen approximately every four months, depending on household size. In a tropical climate, the excreta is fully composted, and all pathogens have been eliminated, in a four month period. If the system is a mobile system like the Nature-loo or the Wheelibatch toilet (see Part C, Case Studies), the bins must be manually changed. If the system is a static system like the Cage Batch toilet, the pedestal must be shifted from the full bin to the empty bin. When the pile in the fallow bin is composted, the compost must be extracted and dug into the garden. Placing the compost around a fruit tree is a common use for the treated product.

Level of Involvement

As each household and/or group of houses is encouraged to participate in the construction of the unit, and, as each is responsible for the operation and maintenance of the toilets, there is a high level of involvement by the user.

Costs

The Australian products range in price from $1 500 to $3 500 for the unit, to which must be added the cost of an outhouse, or the cost of retro-fitting a bathroom or pre-existing building. Some companies offer a range of sizes to meet differing intensities of usage, and prices vary accordingly. Those constructed in 1995 on Christmas Island, Kiribati, cost approximately $2 200 (Table 3). The very high cost of these units is due to the fact that most of the construction materials are imported, and the costs reflect the high transportation costs incurred.

Effectiveness of the Technology

There is a considerable amount of water to be saved by using a composting toilet. Composting toilets in a typical home can reduce residential water consumption by up to 28% from that of a home served by flush toilets (Chapman, 1993). On low-lying atolls and in those parts of larger islands where even properly functioning septic systems can pollute the groundwater, composting toilets offer a potential means to reduce the risk of groundwater contamination (although, as the use of composting toilets is not yet widespread, no conclusive results have been documented).

Suitability

Composting toilets are particularly suited for use on small, low-lying islands where there is a shortage of water, and where the groundwater is very sensitive to contamination.

TABLE 3. Construction Costs of a Composting Toilet.

ITEM COST ($)
Cement $120
Concrete blocks 120
Fibreglass fittings 220
PVC fittings 80
Frame timber 500
Other timber 120
Trenches and fittings 230
Fittings 150
Cladding 300
Labour 180
Contingencies 180
Total $2 200

Advantages

Composting toilets are an onsite sewage management technology that can offer significant protection for water quality and quantity since the toilets provide dry, biological treatment of human excrement and do not generate quantities of contaminated water that must be discharged into the environment. The excrement in a composting toilet is contained in bins that are installed at ground level so the waste is not in contact with the groundwater. The liquid that drains through the pile is of a sufficiently small quantity that it can be adequately isolated and treated in a sealed trench adjacent to the toilet. This technology also avoids the use of scarce groundwater or rainwater supplies for flushing toilets. Also, use of manufactured toilet paper in composting toilets is not required, resulting in a cost savings within the household. Any organic material that can be decomposed is suitable for personal cleansing (e.g., leaves, coconut fibre, writing paper, cardboard, and rags). The systems can also accommodate washwater to the extent that the quantity of water introduced into the bins does not saturate the pile. Composting toilet design can be adapted to local social and physical circumstances as long as the basic conditions for composting are maintained and the protection of public health and the environment is assured. About 4 months is required for effective composting and treatment of disease-causing organisms, at the end of which period, the excrement has changed its appearance and odour to that of compost which can be used as a fertiliser and dug in around fruit trees. Because composting toilets rely mainly on aerobic decomposition, the material in the bins does not have a faecal or unpleasant odour while it is breaking down. Consequently, it is not necessary to remove the material from the site while it is being treated, saving money, time, and resources and avoiding the risk of contact during transportation. Composting toilets are designed be easily maintained by the householder, and there are no chemicals involved or moving parts that can break down. As the composting toilet is a dry method of treatment, and the material is contained immediately below the pedestal, it is very difficult for the system to become blocked or obstructed even if a large object is dropped into the toilet. Therefore, repair rarely required and seldom require contact with fresh sewage. The only pipe on the system is a short 50 mm fitting from the liquid drainage area at the base of the bin to the trench, which should be easily accessible should there be reason to clear it. The composting toilet involves a simple, self-sufficient, recycling of waste material that can have added benefit through the practical demonstration of these principles on a daily basis as well as significant long term educational value, particularly for children.

Disadvantages

Because the bins of the composting toilets are generally installed at ground level, the toilet enclosure is elevated, and stairs or a ramp are required for access. This could be a problem for the elderly or disabled. Also, this requirement often means that the toilet building is taller than the surrounding buildings and can be quite obvious. However, these difficulties can be alleviated by building the toilet room close to a one storey, pre-existing house, by growing trees around the enclosure, or by designing a house that has an elevated verandah area under which the bins can be installed. Likewise, while composting toilets are capable of providing protection of the public health and environment by preventing contamination and waste of precious water resources, they can become a health hazard if not designed appropriately or maintained properly. For example, liquid from the drainage trench may surcharge and come in contact with people or waterbodies. Similarly, if the compost is removed from the fallow bin before it has had time and/or the right conditions to fully compost, disease organisms may be transmitted to those who handle the material, especially if they are careless. Simple precautions and guidelines for using and maintaining the systems can overcome these limitations, but must be taught to users as part of the information programme that must accompany the introduction of composting toilets (or any other sanitation strategy, for that matter).

Insects are attracted to human excrement and decomposing organic matter. Although certain insects or invertebrates play an important role in breaking down the material into a more accessible for the microbial digesters, some insects can act as vectors of disease. It is important that these insects, especially common houseflies, do not enter the bin and breed. This requires that the lid of the toilet be kept closed, a courtesy that people often forget. Spring loading the seat so that it closes automatically after each use has been tried, but, in practice, suffers from a number of drawbacks. Use of the bulking agent after each use should use a sufficient quantity of the material to cover the fresh excreta and minimize its attractiveness to insects.

Finally, when compared to the standard pit latrines which are widely used on small islands, composting toilets are too expensive for most island people to afford. Locally manufactured designs may be one way to make composting toilets more affordable. Also, being a new technology, it may be difficult to persuade people to use dry techniques instead of the more traditional water-borne methods of sewage treatment. People may be sceptical, and technology transfer of composting toilets should be undertaken cautiously and with maximum community participation. Use of the composting toilet also requires that separate treatment be provided for water used for washing, laundry and other household or personal needs.

Cultural Acceptability

Every culture has taboos relating to human excrement. Most of these taboos are based upon an understanding that ill-health can be caused by contact with faeces, especially faeces from a diseased person or stranger. For some, there are issues of sorcery involved or religious restrictions. These taboos may initially cause people to be concerned about using a composting toilet since the excrement is contained and treated on-site, and the compost can be recycled as a soil improver. This is in contrast to septic tank and sewerage systems which remove the excrement from the immediate surrounds and requires little or no further user involvement. For this reason, conduct of a demonstration project using a well-functioning composting toilet system in which the transformation of excrement to an acceptable compost can be observed may be necessary before a final opinion can be formed in the user community. If the prospect of using the end-product, however transformed it may be, remains a cultural obstruction to the use of the composting toilet, then some other, acceptable method of disposal of the compost must be found if composting toilets are to be an effective sewage treatment option.

Another concern is that, because the waste material is contained and treated in bins under the toilet, some people may feel that the use of a composting toilet is like using a pit latrine and, therefore, a backward step in sanitation practice. This caution and scepticism can only be allayed by direct experience with a well-functioning composting toilet. As with any technological introduction, informational programmes will be necessary to explain the risks and benefits. Health and environmental problems caused by a variety of sanitation practices are universal. However, it can be demonstrated that the composting toilet is sometimes preferred by people in countries where water-borne sewerage systems are readily available. This can help people understand that appropriately-designed, composting toilets are one of the latest developments in sanitation practice, and in certain situations they may be the only sensible choice

Further Development of the Technology

There is a need to develop this technology further to comply with the conditions of the islands where composting toilets are installed. Developments are especially needed to reduce the cost of the units, perhaps through the use of local materials for construction. Also, design improvements are needed to better conform the units to their surroundings and minimise the aesthetic and societal impacts of the toilets.

Information Sources

Anda, M., K. Mathew, and G. Ho 1991. Appropriate Technology Hygiene Facility for Small Communities. Water Science and Technology, 24(5):163-173.

Berg, G., et al. 1976. Viruses in Water. American Public Health Association, Washington.

Canter, L.W. and R.C. Knox 1985. Septic Tank Effects on Groundwater Quality. Lewis Publishers, Boca Raton, Florida.

Chapman, P. 1993. Compost Toilets: an Option for Human Waste Disposal at Remote Sites. MSc Thesis, Lincoln University, Canterbury, New Zealand.

Crennan, L. 1995. Wet and Dry Conservancy: the Politics and Practicalities of On-site Sanitation. PhD Dissertation, Centre for Environmental Studies, University of Tasmania, Hobart, Australia.

Gotaas, H. 1956. Composting, Sanitary Disposal and Reclamation of Organic Wastes. World Health Organisation, Geneva.

Handreck, K. 1993.Composting: Making Soil Improver from Rubbish. Division of Soils, CSIRO, Australia.

Lewis, W.J., S.S.D. Foster, and B.S. Drasar 1980. The Risk of Groundwater Pollution by On-site Sanitation in Developing Countries: A Literature Review. International Reference Centre for Waste Disposal, Duebendorf.

Marjoram, T. 1983. Pipes and Pits under the Palms: Water Supply and Sanitation in the South Pacific. Waterlines, 2(1):14-17.

Markell, E.K. and V. Marietta 1981. Medical Parasitology. W. B. Saunders Company, London.

Rogers, E. 1995. Diffusion of Innovations, Fourth Edition. The Free Press, New York.

Safton, S. 1993. Human Intestinal Parasites in Composting Toilet Systems. MSc Thesis, Medical Laboratory Science, Charles Sturt University, Wagga Wagga, Australia.

Winter, S.J. 1988. Construction Manual for a Water-sealed Toilet. United Nations Development Programme, New York.

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