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Low-flush Toilets

Author/Compiled by
Beat Stauffer (seecon international gmbh)
Executive Summary

A low-flush or low-flow toilet is a flush toilet that is adapted in order to use significantly less water than a full-flush toilet. Low-flush toilets use a special design of the cistern and the siphon in order to allow the removal of faeces and excreta with less water. Most often, they also include a dual flush system, with one flush being designed for urine only, using even less water than the other designed for faeces. Today, there exist many suppliers of different models of low-flush toilets all over the world. Low-flush toilets reduce the water consumption, however, low-flush toilet still require large amounts of fresh water and with certain models, users have to flush even twice in order to achieve the complete removal of faeces from the bowl.

Advantages
Ultra-low-flow toilets reduce water consumption and costs to the consumer
They contribute to preserving the environment by protecting ground water from depletion and possible contamination
Easy to use and clean
Disadvantages
Some ultra-low-flow models may require flushing more than once to adequately clean the toilet bowl
Risk of clogging/plugging
It still requires a constant source of water, it will not function without it
In Out

Freshwater, Urine or Yellowwater, Faeces, Excreta

Blackwater

Basic Design Principles

Low-flush toilets work with a very small amount of water. The exact amount of water varies between less than a litre (for urine only) up to 6 or 8 litres. These toilets can operate by gravity or vacuum. You can read more on vacuum toilets here. Gravity toilets have special requirements regarding the slope of the pipe. Large water savings are thus possible, which even facilitate the source separation of greywater and blackwater. If the gradient to the public sewer systems is steep enough, low-flush toilets can also be retrofitted into existing buildings. However, there is a risk of pipe clogging (HEEB et al. 2007).

In some cases, the volume of water used per flush is not sufficient to empty the bowl and consequently the user is forced to use two or more flushes to adequately clean the bowl, which negates the intended water saving (TILLEY 2008). Thus, many users were disappointed and frustrated with performance problems of the first generation of low-flush toilets. Since  then, the manufacturers have solved these problems by modifying passageways to move a reduced amount of water more vigorously around the bowl. To make these toilets even more efficient, dual-low-flush toilets where developed. This type of toilet saves water by offering different flush volumes: a full-flush for solids (faeces) and a half-flush for liquids (urine) (JCSA n.y.).

 With a toilet dual flush button, users have the possibility to choose between two volumes either for solids or for liquids. Source: ROUS WATER (2011)

With a toilet dual flush button, users have the possibility to choose between two volumes either for solids or for liquids. Source: ROUS WATER (2011)

 

 

 

Nowadays, products vary in that they may have narrower bowls with a smaller water surface, manually controlled water flow (via a foot pedal) into the bowl, or water pumps to assist in bowl emptying and cleaning. One model eliminates the “S” trap of a conventional toilet design, enabling waste to be washed down using less water. Another product flushes by opening a hinged flap to let wastes and a small amount of water fall into a lower chamber. After several seconds the flap reseals, and a blast of compressed air forces the wastewater over the trap and out a discharge line from the toilet (PIPELINE 2000).

Drain Lines

     This low-flush toilet from Microphor in Willits, California, uses approximately 4.8 litres of water per flush. Source: PIPLINE (2000)

This low-flush toilet from Microphor in Willits, California, uses approximately 4.8 litres of water per flush. Source: PIPLINE (2000)

There are discussions about the performance of low-flush toilets to transport the waste trough the building drains to the public sewer system. As already mentioned, there is a risk of pipe clogging. Especially in older buildings, drain lines (slope, diameter, length) were designed for common flush toilets. More information and researches can be found in the document “Evaluation of Low-Flush-Volume Toilet Technologies to Carry Waste in Drain lines” (GAULEY and KOELLER 2005).

     


Reuse of Faecal Sludge as Fertiliser

The toilet waste or blackwater (urine and faecal matter) contains the majority of the nutrients in wastewater. A century ago, toilet waste was collected in major European cities and used as fertiliser in near urban agriculture. Ordinary flush toilets use much water and the blackwater becomes diluted. Modern toilet technology (vacuum or low-flush gravity) have flush volumes below 1 litre. With these toilets collection and separate treatment of the concentrated blackwater is more interesting in order to treat and reuse it (JENSSEN et al. 2004).

Costs Considerations

Costs are not higher than a common flush toilet system. But the huge savings of flush water and the smaller volume of generated blackwater reduce operation costs significantly.

Operation and Maintenance

Although flushing water rinses the bowl, the toilet should be scrubbed clean regularly. It is important that no other object than faeces or urine are tried to flush away, because in this case the risk of clogging is even higher and could lead to expensive cleanout costs.

Health Aspects

The low-flush toilet itself is safe and comfortable to use provided it is kept clean. There are no real problems with odours if used correctly (TILLEY et al. 2008). If the flush performance is bad, the bowl should be cleaned more often. Furthermore, in the absence of an appropriate (semi-)centralised treatment system, toilet wastewater flows through a sewer system directly into the environment without any treatment. This spreads pathogens and can endanger the health of residents (see also health and hygiene issues).

At a Glance

Working Principle

Human excreta is flushed away by a minimised amount of water.

Capacity/Adequacy

Basically, it can be built everywhere, urban and rural areas. A constant source of water and an appropriate sever system and (semi-)centralised treatment system must be available.

Performance

Depends on type, but there are many models with a high performance available.

Costs

Not higher than a common flush toilet system. Minimised flushed water and blackwater reducing operation costs.

Self-help Compatibility

Low, it might be difficult to find spare parts.

O&M

Easy to use and clean. Beside human excreta and toilet paper, no other objects should be flushed.

Reliability

If well maintained and constructed, high.

Main strength

Comfortable and hygienic for the user. Saves large amounts of water in comparison with common flush-toilets.

Main weakness

Still requires water. The risk of water pollution in sequence of unprofessional wastewater discharge is high.

Applicability

A flush toilet should not be considered unless all of the connections and hardware accessories are available locally. The low-flush toilet must be connected to both a constant source of water (can be a big problem and controversy in arid climates) for flushing and a collection and storage/treatment or conveyance technology to receive and treat the blackwater. The flush toilet is suitable for both public and private applications and can be used in every climate (TILLEY et al. 2008).

Library references

Sustainable Wastewater Management in Urban Areas

A document about sustainable wastewater management in urban areas.

JENSSEN, P.D. ; GREATOREX, J.M. WARNER, W. S. (2004): (= Kapitel 4. Kurs WH33, Konzeptionen dezentralisierter Abwasserreinigung und Stoffstrommanagement ). Hannover: University of Hannover

M3: Ecosan Systems and Technology Components. M 3-2: Ecosan Technologies to Close the Water Loop

This presentation is adapted from the Ecosan Curriculum 2.2. The ecosan curriculum was created in order to compile the large amount of information on ecological sanitation in a structured and comprehensive way. This is a summary about the various Ecosan (or more: sustainable sanitation) systems.

HEEB, J. ; JENSSEN, P. ; GNANAKAN, K. ; CONRADIN, K. ; (2007): HEEB, J. ; JENSSEN, P. ; GNANAKAN ; CONRADIN, K. ; (2008): Ecosan Curriculum 2.3. Switzerland, India and Norway: .

WaterSense High-Efficiency Toilet Guide

This guide mentions all important points if someone wants to buy a low-flush toilet.

JCSA (n.y): Williamsburg: James City Service Authority (JCSA) URL [Accessed: 14.03.2011]

Compendium of Sanitation Systems and Technologies

This compendium gives a systematic overview on different sanitation systems and technologies and describes a wide range of available low-cost sanitation technologies.

TILLEY, E. ; LUETHI, C. ; MOREL, A. ; ZURBRUEGG, C. ; SCHERTENLEIB, R. ; (2008): Duebendorf, Switzerland: Swiss Federal Institute of Aquatic Science and Technology (EAWAG) and Water Supply and Sanitation Collaborative Council (WSSCC) URL [Accessed: 15.02.2010]
Further Readings

Sick Water? The central role of wastewater management in sustainable development

This book not only identifies the threats to human and ecological health that water pollution has and highlights the consequences of inaction, but also presents opportunities, where appropriate policy and management responses over the short and longer term can trigger employment, support livelihoods, boost public and ecosystem health and contribute to more intelligent water management.

CORCORAN, E. ; NELLEMANN, C. ; BAKER, E. ; BOS, R. ; OSBORN, D. ; SAVELLI, H. (2010): A Rapid Response Assessment. United Nations Environment Programme (UNEP), UN-HABITAT, GRID-Arendal URL [Accessed: 05.05.2010]

M3: Ecosan Systems and Technology Components. M 3-2: Ecosan Technologies to Close the Water Loop

This presentation is adapted from the Ecosan Curriculum 2.2. The ecosan curriculum was created in order to compile the large amount of information on ecological sanitation in a structured and comprehensive way. This is a summary about the various Ecosan (or more: sustainable sanitation) systems.

HEEB, J. ; JENSSEN, P. ; GNANAKAN, K. ; CONRADIN, K. ; (2007): HEEB, J. ; JENSSEN, P. ; GNANAKAN ; CONRADIN, K. ; (2008): Ecosan Curriculum 2.3. Switzerland, India and Norway: .

WaterSense High-Efficiency Toilet Guide

This guide mentions all important points if someone wants to buy a low-flush toilet.

JCSA (n.y): Williamsburg: James City Service Authority (JCSA) URL [Accessed: 14.03.2011]

Sustainable Wastewater Management in Urban Areas

A document about sustainable wastewater management in urban areas.

JENSSEN, P.D. ; GREATOREX, J.M. WARNER, W. S. (2004): (= Kapitel 4. Kurs WH33, Konzeptionen dezentralisierter Abwasserreinigung und Stoffstrommanagement ). Hannover: University of Hannover

Guidelines for the safe use of wastewater excreta and greywater. Volume IV. Excreta and Greywater Use in Agriculture

Volume IV of the Guidelines for the Safe Use of Wastewater, Excreta and Greywater recognizes the reuse potential of wastewater and excreta (including urine) in agriculture and describes the present state of knowledge as regards potential health risks associated with the reuse as well as measures to manage these health risks following a multi-barrier approach.

WHO (2006): Geneva: World Health Organisation URL [Accessed: 26.02.2010]

How to Manage Public Toilets and Showers

The purpose of this decision-making aid is to provide practical advice and recommendations for managing toilet blocks situated in public places. It is primarily aimed at local decision-makers in developing countries and at their partners (project planners and managers).

TOUBKISS, J. ; (2010): (= Six Methodological Guides for a Water and Sanitation Services' Development Strategy , 5 ). Cotonou and Paris: Partenariat pour le Développement Municipal (PDM) and Programme Solidarité Eau (pS-Eau) URL [Accessed: 19.10.2011]
Case Studies

Case Study 4. Dual-Flush Toilet

This case study estimates the annual water consumption and savings that can be realised by a family of four using a dual-flush toilet instead of a conventional 13-litre or 6-litre toilet.

ATLANTIC ECOWORKS (n.y): Charlottetown: Atlantic EcoWorks URL [Accessed: 15.03.2011]

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