2 GTZ Datasheet on Composting Toilets (2006)

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technical data sheets for ecosan components ecosan program - Deutsche Gesellschaft fr Technische Zusammenarbeit (GTZ) GmbH

03 Composting Toilets

A General Description

Waterless toilet systems

Receive mainly faeces, but treatment of urine and solid biowaste is possible as well

Dry organic bulking material should be added

Produce a valuable soil conditioner with low pathogen content

Suitable for both industrial and developing countries

COLLECTION

TREATMENT

UTILIZATION

URINE FAECES

SOLID BIOWASTE

GREY

WATER

RAIN

WATER

A General description

A.1 Basic principles

The basic principle of a composting toilet system is the biological degradation of excreta and toilet paper in a specially designed container. Urine is usually collected separately, or in some types of composting toilets collected and treated together with faeces. Organic food waste can be added too.

The decomposition process is called composting, which is the degradation of organic matter by thermophilic aerobic bacteria and other micro organisms. These bacteria rely on a good aeration of the material, on optimal moisture content and a specific carbon to nitrogen ratio.

Human excreta and food waste alone do not provide those optimum

conditions since their water content and the nitrogen content are too high. Therefore an additive or so-called bulking agent is recommended to lower the water content, to improve aeration and to increase the carbon content of the material. Wood, chips, bark chips, sawdust, paper and other substances are commonly used.

Figure 1: Schematic of continuous composting toilet (Davison, 2001)

Since good aeration is very important, the container is usually equipped with a ventilation system that improves aeration of the material and provides odour control. Moreover, with bulking agents, the pore spaces of the composting pile can be increased; hence it will be less compact, leading to better aeration. However, too much air flow can remove too much heat and moisture, therefore the condition within the composter should not be too cool or dry.

Another benefit of adding bulking materials is to increase C/N ratio in order to attain the optimum composting condition. Sometimes these bulking materials also have an additional effect on odour control by binding the

substances causing bad odours.

One main effect of the decomposition process in a composting toilet is the considerable volume reduction (10-30% of the original mass), thus allowing the prolonged storage of waste in the container. The emptying frequency depends on the size of the container, the feeding rate and the composting rate (volume reduction).

The decomposition process in a composting toilet is rarely a real thermophilic composting with temperature rising above 50C, which would guarantee complete pathogen destruction and hygienization of the waste. The pathogen content is reduced considerably in a composting toilet. However, complete pathogen destruction can only be achieved if good process conditions can be guaranteed, e.g. by using an advanced toilet design with insulation for maintaining a high temperature within the whole composting chamber.

The end product of a composting toilet is an odourless stabilized material, which is very valuable as soil conditioner. It can be used directly for non-food plants or for agriculture use. Further treatment for hygienization such as additional heap-composting or prolonged storage (see box 2) increases hygienic safety of agicultural use.

A.2 Available technologies

Although there are many different composting toilet designs that continue to evolve, the basic concept of composting remains the same.

Box 1: Optimum conditions for thermophilic composting, allowing temperature to rise up to 50-70C:

Good aeration

Moisture content 50-60%

C/N ratio 30-35

Note that optimum conditions are rarely achieved in composting toilets.

A General Description

B Detailed information on different types of Composting Toilets

B.1 Single-vault composting toilets B.2 Multiple-vault composting

toilets B.3 Movable bucket / bin

composting toilets B.4 Composting toilets with mixing

devices

C Manufacturers and commercially available composting toilets



A composting toilet has two basic elements: a place to sit (or to squat) and a composting chamber. Apart from those basic elements, a ventilation system is highly recommended in order to stimulate aeration and prevent odour.

Available systems can be distinguished is as follows:

Toilet seat and composting container in the same unit, or separate

Some composting toilet systems have the seat and the composting container spatially separate, e.g. the toilet seat is in the ground floor and the container is situated below in the basement, connected by a vertical tube. Other systems have the toilet seat in the same unit with the container. In that case, containers are usually smaller and have to be emtied more often.

Urine diversion or not

The toilet can be designed either with or without urine diversion.

Detailed information on urine diversion can be found in the GTZ technical data sheet for urine diversion (01) on http://www.gtz.de/en/themen/umwelt-infrastruktur/wasser/9397.htm

It should be noted that without urine diversion, more bulking agent needs to be added in order to significantly lower moisture level and increase C:N ratio to attain the optimum treatment conditions. Urine adds more water than is necessary and it has a very high nitrogen content. The moisture content of faeces without urine (66-80%), plus the addition of toilet paper and bulking material are sufficient for good processing.

Many composting toilets also have a drainage system to allow evacuation of liquids. These liquids are called leachate and have very high concentrations of nutrients, organics and also contain pathogens. Leachate needs to be collected, treated and reused if possible. Urine diversion usually allows to avoid or to considerably reduce leachate production.

Self-constructed or commercially procured

There are many designs and models offered by manufacturers all over the world with a large range of prices. However composting toilets can also be self-constructed. Manufactured toilets are often more expensive than self-constructed systems.

Low-tech or high-tech

The systems range from low-tech (simple, non-electric, but more care is required) to high-tech (complex, electric, very low labour work, but higher cost) systems. Low-tech composters are simple reactors in which all is collected and allowed to decompose in at ambient temperature. They require the user to take a more active role in the day-to-day maintenance of the unit. High-tech units can be equipped with electric fans, automatic mixers and thermostatically controlled heaters and require very low level of user intervention.

Single-vault (continuous) or multiple-vault (batch)

Either multiple chambers batch com-posting, e.g. EcoTech Carousel, or sin-gle chamber continuous composting process shown in figure 1, e.g. Clivus multrum, Clivus minimus, BioLet, etc. are feasible to use.

On-site or off-site composting

Most composting toilets process the material on-site in a composting cham-ber that is located directly under in the toilet seat or in the basement of the building. Other systems however use movable collection bins or containers that are emptied frequently and where the material is then transported to an external site for treatment.

A.3 Applicability

Composting toilets eliminate the need for flushing water. No water supply (no expensive installation for infrastructure like water supply line and sewerage) is necessary. Furthermore, it allows for the recycling of valuable plant nutrients via compost products.

This technology is suitable for both industrialized and developing countries, especially in arid regions and regions without piped water or sewers. It works without water and wastewater connection.

With proper management the toilet is easy to use and to maintain, and the final product is a high-quality compost soil conditioner for garden or agriculture.

Compared to dehydration toilets, composting toilets require higher costs in term of excreta management. The most important difference between this technology and that of dehydration is the moisture content of faeces within the vault (around 50% comparing to 25% in dehydration toilet). Composting toilets need organic bulking materials to increase carbon content whereas dehydration toilet can use also other dry absorbents as ash or dry soil to lower the moisture content. The nutrients in products from composting toilet are more readily available to plants than those from dehydration toilet.

Compared to VIP/pit latrines, composting toilets can be built above ground level as permanent structure. There is no need for digging deep pit and periodical replacement of the facility when pits are full.

Composting toilets are sealed systems that exclude any infiltration of contaminated liquids into the groundwater or other harmful emissions into the environment.

Composting toilets can close the nutrient cycle, turning a dangerous waste product into safe compost, without smell, hassle, or fly problems.

They are usually less expensive than conventional septic systems or sewered systems (if costs for sewerage and wastewater treatment are considered) treatment and they will reduce household total water consumption by at least 25%.

In several projects composting toilets have also been successfully implemented in houses with several floors.

In term of operation and maintenance, composting toilets are most suitable

Box 2: Suggested alternative recommendations for primary treatment of dry faeces before use at household level. No addition of new material. (Schnning and Stenstrm, 2004)

Treatment Criteria Comment

Storage (only treatment) at ambient temperature 2-20C

1,5-2 years Will eliminate most bacterial pathogens, substantially reduce viruses, protozoa and parasites, some soil-b ova may persist

Storage (only treatment) at 20-35C

>1 year As above

Storage and alkaline treatment

pH >9 during > 6 months

Temperature 25 or lower pH will prolong the time for absolute elimination



when users are committed to operate the system carefully. Composting toilets need more care than dehydration toilets in the case of low-tech systems.

A.4 Further reading

Esrey, St. A., et. al., 1998, Ecological sanitation. Department for Natural Resources and the Environment, Sida, Stockholm, Sweden.: Well-illustrated book concerning different types of composting toilet as well as performance and health issues.

Del Porto, D. and Steinfeld, C., 2000, The composting toilet system book. The Center for Ecological Pollution Preven-tion (CEPP), 1st ed. with additions.: in-formation on several types of compost-ing toilet system, including practical ap-plication and maintenance.

Jenkins, Joseph, 2005, The Humanure handbook a guide to composting hu-man manure, Joseph Jenkins Inc, Grove City, USA.

lain, Christophe, 2005, Un petit coin pour soulage la plante Toilettes s-ches et histoires deau, ditions Goutte de Sable, Athe, France.

A.5 References

Crennan, L., waterless toilets, Home, Technical Manual: design for lifestyle and the future, www.greenhouse.gov.au

Davison, L. and Schwizer, B., 2001, Waterless composting toilets, septic safe, Environment & Health Protection Guidelines: On-site Sewage Manage-ment for Single Households.

Esrey, St. A., et. al., 1998, Ecological sanitation. Department for Natural Re-

sources and the Environment, Sida, Stockholm, Sweden.

Montgomery, T., 1990, On-Site waste-water treatment systems, Technical Bul-letin No. 6, The New Alchemy Institute.

Peasey, A., 2000, Health aspects of dry sanitation with waste reuse. Task No. 324, WELL.

Reed, B. and Shaw, R. Using human waste, technical brief no. 63, WELL.

2006, GTZ

technical data sheets for ecosan components

authors: GTZ ecosan team (Christine Werner, Nathasith Chiarawatchai, Florian Klingel, Patrick Bracken)

Deutsche Gesellschaft fr Technische Zusammenarbeit (GTZ) GmbH

ecosan program

Dag-Hammarskjld-Weg 1-5 65760 Eschborn, Germany T +49 6196 79-4220 F +49 6196 79-7458 E [email protected] I www.gtz.de/ecosan

2 GTZ Datasheet on Composting Toilets (2006)

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