Urine-diversion composting latrines

I come from Iran, and I would like to receive information on separation toilets.

In response to your request for information on separation toilets, I hope the following information and references help you.

This response is based on providing information around urine-diversion composting latrines, which often comes under the broader banner of Ecological Sanitation, or ecosan.

From the diagram below you can see that composting latrines are one among a wide range of options for sanitation – and only a few examples are indicated here. Their selection should be based on careful consideration, taking into account the range of factors discussed here.

Diagram sanitation options

Use – past and present

Human excreta has been used for many centuries as a fertiliser and soil conditioner. In a number of countries in Asia (e.g. China) and central/south America (e.g. Mexico) the practice of excreta re-use is still widely practised. Where systems have been put in place to remove waste from the user with a water-borne system (typically flush latrines and sewerage system), the practice of handling excreta has gone out of favour. In other countries, it has never been culturally acceptable to handle human excreta, although in certain projects this is changing through much social input and promotion – with a range of successful and not so successful results.

Why ecological sanitation?

The selling points of ecological sanitation (of which urine diversion composting latrines is a part) are given as:

• nutrients in human excreta can be reclaimed and used in plant/crop growing when composted;
• urine can be used as a soil conditioner / fertilizer;
• treating and handling human waste on-site protects the environment from the pollution potential from untreated waste, or waste that is transported off-site and then treated; and
• ecological sanitation latrines are easier to empty that other on-site options (such as pit latrines).

And why not?

Those who promote the use and philosophy of ecological sanitation do not always provide a balanced argument that considers aspects of the technical, social, cultural, health and cost implications that have to be addressed for the principle to work to the benefit of the user (usually females).

Design

“Composting latrines consist of a single or double vault construction with a system to ensure that urine is kept separate from faeces. This aims to reduce the odour. The urine is an effective fertiliser, while the faeces contain most of the disease-causing micro-organisms. The faeces are collected in the vault (box) and need to be mixed regularly with earth, wood ash or other organic waste material to deodorize them and to control the moisture content. The accumulated compost waste needs to be left at least a year in order to ensure that all pathogenic organisms have died off. (Note from the author: Recent studies recommend the excreta should be left to compost for 2 years, to ensure the material is safe to handle.)

Collection box

The collection box can be constructed either above or below ground and so in theory the system is suitable for regions with shallow groundwater or risk of flooding. However, the composting latrine has caused a good deal of controversy and discussion amongst experts around the world and there are many arguments against using the system. In particular there are health risks associated with poorly managed composting latrines and there is also a low level of user acceptance in many countries and cultures. It is not therefore recommended that composting latrines are constructed unless there is a proven track record of operation and acceptance in the project area or region.” From WELL fact sheet, Low-cost sanitation in areas with a high groundwater table, by Sarah Parry-Jones

The design and arrangement of urine-diversion composting latrines varies from place to place and country to country. Two arrangements are shown below.

Anaerobic bacteria

The first makes use of anaerobic bacteria to decompose the excreta, with two vaults alternatively storing excreta and a separate receptacle for storing urine. The urine should be diluted with 3-6 parts water before being used. This can be done by pouring a small amount of water on to the urine collection area (squatting plate, or specific part of the pedestal) after use. In many applications the urine is then diverted directly to a plot of land where it acts as a soil conditioner for plants and/or crops.

Control of moisture content in the stored excreta is vital for correct operation of the latrine. Such latrines are therefore not appropriate where water is used for anal cleansing.

An advantage of this type of latrine is that since the vault contents are kept dry, there is no pollution to the surrounding ground provided the system is correctly operated and maintained.

Double-vault composting latrine

A system of this type is being piloted in Nepal and a paper due to be presented at the next WEDC Conference explains the findings of the pilot project and implications for the further use of urine diversion composting latrines. A factor in favour of the success of this system is that people currently use human waste as a fertiliser, so there does not have to be a change in cultural practice to enable this improved technique to be acceptable. The draft paper is attached for your information.

The second type is a continuous composting latrine, which makes use of aerobic bacteria to break down the excreta. These tend to be more “commercially” manufactured systems that incorporate the full functioning of the latrine into a single unit, or can be built using local materials under good supervision and with experienced builders.

Continuous composting latrine

Such latrines have proved to be successful in installations in European countries, but in developing countries they have proved to be expensive to construct and also difficult to ensure correct operation in relation to moisture control.

In a case in South Africa, a pedestal is placed over a bucket, which is then emptied into a compost heap in the garden of the house. This is a form of on-site sanitation, with “off-site” composting!

Technical challenges

The method of separating the urine from the faeces at the squatting plate or pedestal is something of a technical challenge and a number of designs have been tried and tested. Many, such as that used in South Africa and in Nepal, work on the “split defecation hole” principle. The pedestal, or squatting plate, is divided into two sections that allow faeces to go one way and urine another (an example for a pedestal latrine is from a WEDC conference paper written in South Africa – see references below).

Social implications

Handling human excreta is not acceptable in many cultures, for a variety of reasons which could be linked to cultural beliefs. Where excreta is handled, it may be viewed as the role of women, those of a lower caste and often the poorest, to perform. This increases their burden and can impact negatively on their position in society.

Health considerations

Although fully composted excreta is relatively safe to handle, incorrect handling – or handling excreta that has not been left long enough under the right conditions – introduces a significant health risk. This is of particular concern in situations where those handling excreta are likely to also be affected by HIV/AIDS and therefore have a lower immunity to disease.

Cost

Both financial and economic costs need to be taken into account. The designs currently used are more expensive to build than other forms of on-site latrine. Also composting latrines require more user time to operate and maintain in terms of adding ash to the pit, keeping the pedestal or squatting plate clean, handling the collected urine and emptying vaults. This has economic implications where time has a financial dimension. Financial gains derived from increased crop production have to be balanced against these other costs. Consideration should also be given to the fact that the costs and benefits may not accrue to the same person. For example, it may be the wife’s task to empty the latrine vaults, but the husband’s role (and therefore source of income) to sell produce at the local market.

Use for collected urine and excreta

As composted excreta and urine are intended to be collected and used, there needs to be a place for application of these end products. Where households have their own small gardening plots, direct application at the household level is possible, with no transport or third-party handling involved. If this is not the case, some form of household- or community-level collection by farmers, or a commercial user of compost, is needed. Without such a collection system, households will not be in a position to dispose of the composted excreta and the latrine will fill up and become unusable. Without a suitable disposal point for the urine, this could also become a problem to dispose of and may end up polluting adjacent watercourses.

Providing choice

Use of ecological sanitation is often promoted on the basis that it is a better option than pit latrines, as it is reported to deal more effectively with smells, flies and end use of excreta. In some cases, ecosan is the only sanitation option offered to households or communities. As with the introduction of any one technique, there are limitations with this approach.

Pit latrines are a safe and effective system of excreta management if correctly designed, built, operated and maintained. They should not be dismissed on the basis of incorrect, or poor, operation. Similarly for urine-diversion composting latrines. There are situations where the use of ecosan is more appropriate than other forms of sanitation, however it should be offered as a way to achieve improved sanitation as one of a range of options - from a simple hole in the ground with a sanitary platform on top to a more advanced water-borne system, if this is appropriate.

Links to further information

A wide range of information is available on the concept of urine diversion and pilot studies, while there is very limited information available reporting the successful use of urine diversion composting latrines in developing countries based on experience beyond the pilot phase.

Here are a few references:

General information on composting latrines, with an introduction to considering technical and social factors, plus links to other websites about ecosan: http://peacecorps.mtu.edu/erda/index.html

Parry-Jones, S. (?). Low-cost sanitation in areas with a high groundwater table. WELL Fact sheet.

A couple of relevant conference papers presented at the 25th WEDC Conference (1999) are:

A discussion of the application of ecosan in Ethiopia – looking at constraints and benefits:

A case study of piloting urine diversion into South Africa (with a photo of a urine-diverting pedestal)

From the 23rd WEDC Conference (1997) a paper that evaluated a particular model of composting latrine in an urban informal settlement in South Africa. Considers both social and technical aspects.

More details can be found in the WHO publication (1992) “A guide to the development of on-site sanitation”

I hope this information is of benefit to you. If you would like additional, specific information, do let me know and we can respond accordingly.

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Rebecca Scott, WEDC, 9th July 2004

This response is provided by WELL, a DFID funded resource centre aiming to improve access to information and provide support in water, sanitation and environmental health. The views expressed are not necessarily those of DFID