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OPINION - Confusing Cause and Effect


Incorporating

Founder : Len Abrams
Water Policy International

Ecological Sanitation

Content

Introduction
Linear Flow Systems
Circular Flow Systems
Toilet Designs and Operation
Health Risks & Benefits
Food Security
Links

Prepared by Anton Earle, October 2001

Introduction

Conventional forms of centralised sanitation are coming under increasing criticism. Especially because of the enormous investment involved, the huge operating and maintenance costs, high water consumption and other drawbacks, they are not suitable as a blanket solution for developing countries, particularly in arid zones. Even conventional individual disposal systems, such as latrines and cesspits, make poor alternatives - especially in view of increasing population densities and the substantial groundwater pollution they can cause. Moreover, all conventional types of wastewater and sewage disposal systems usually deprive agriculture, and consequently food production, of the valuable nutrients contained in human excrement.

A more holistic approach towards ecologically and economically sound sanitation is offered by the concepts referred to as "ecological sanitation". Ecological sanitation technologies take the principle of environmental sanitation a step further: Environmental sanitation means keeping our surroundings (the environment) clean and safe and preventing pollution. It includes wastewater treatment and disposal, vector control and other disease-prevention activities. Ecological sanitation, on the other hand, is premised on recycling principles. The key objective of this approach is not to promote a certain technology, but rather a new philosophy of dealing with what has been regarded as waste in the past. The systems of this approach are based on the implementation of a material-flow-oriented recycling process as a holistic alternative to conventional solutions. Ideally, ecological sanitation systems enable the complete recovery of all nutrients from faeces, urine and greywater to the benefit of agriculture, and the minimisation of water pollution, while at the same time ensuring that water is used economically and is reused to the greatest possible extent, particularly for irrigation purposes.

This web page draws freely from the publication "Closing the Loop: Ecological Sanitation for Food Security" by Esrey et al, 2001: SIDA.

Special Introduction by Steven Esrey


Linear Flows

Most families in the North make use of 'flush and discharge' systems - the regular waterborne sewerage toilet. These are designed on the premise that human excreta are a waste, suitable only for disposal. This approach also assumes that the environment has an infinite capacity to absorb and assimilate these wastes (see diagram).

Adapted from Esrey et al, 2001

On average, 15,000 litres of treated, safe, drinking water is used to flush 35 kilograms of faeces and 500 litres of urine per person every year. This conversion of cleanwater into 'blackwater' is a massive waste of water for arid regions. In developing countries 90 percent of this sewage is flushed into surface waters, polluting rivers, lakes and coastal areas. This can contribute to the spread of disease, as well as lowering the oxygen content of the water bodies, leading to increased algae growth and eutrophication.

In developing countries the most common sanitation system is the pit latrine, based on the 'drop and store' principle. Although this uses much less water than flush systems it also has its drawbacks. Due to the large volume of the underground pit needed it is not suitable for densely populated urban areas. If the groundwater table is high, or the ground is very hard it is not possible to construct these toilets.

In areas where they are used there is the risk that the surrounding groundwater will be contaminated from seepage or from water flowing in during floods. This has implications for health as pathogens can contaminate drinking water supplies. Due to the high humidity levels in the pits disease vectors breed rapidly, producing diseases such as filariasis, yellow fever and cholera.

As mentioned above, all linear systems have the other major disadvantage that nutrients and organic matter are wasted. Nutrients, such as nitrogen, phosphorous and potassium are plentiful in urine and faeces provide carbon and condition the soil.

Summary of Linear systems:

Advantages
Disadvantages

Removal of pathogens from the domestic environment.

Elimination of foul odours - if properly constructed.

Convenient & easy to use.

Nutrients are wasted.

Downstream areas potentially receive pollution.

Lots of water wasted.

Hormones and antibiotics enter the drinking water system.

Very costly to construct and maintain effective sewerage network.

The energy contained in the organic carbon from faeces is lost.

Pit latrines can't be used in high density areas.

Pit latrines can't be constructed in areas with hard ground or high water tables.

 


 

Circular Flows

Ecological sanitation is a safe method of recovering nutrients from human excreta, then recycling them back into the environment and productive systems (see diagram alongside).

A human being produces exactly the amount of nutrients that is needed for growing his or her food (measured in crops) 7.5 kg of nitrate, phosphorus and potassium for 250 kg of crops. Urine hardly contributes at all to the spread of diseases (e.g. bilharziasis) and contains approximately 88% of the nitrogen, 67% of the phosphorus and 71% of the potassium carried in domestic wastewater. Faeces contain 12% of the nitrogen, 33% of the phosphorus, 29% of the potassium and also 46% of the organic carbon, as well as most of the pathogens.

If separated, urine can easily serve as a fertiliser after it has been diluted with water. After faeces have been dessicated (dried-out), they are free from pathogens, diseases and odour. They can then serve as a soil conditioner for agriculture, returning a significant part of the nutrients and trace elements to the soil.

The remaining treated greywater may be used for irrigation and also for recharging the local aquifer. This closes local cycle, helping to improve food security and to conserve soil fertility. At the same time, human health is improved due to the removal of disease sources from the domestic environment.

 

Summary of Circular flow systems:

 

Advantages
Disadvantages

Removal of pathogens from the domestic environment.

Elimination of foul odours - if properly constructed.

Diseases are destroyed, not just contained.

No potential to contaminate other water sources.

Use very little, or no water.

Nutrients and organic matter is recovered.

Very cheap to build and operate, with very few components which can malfunction.

Users do need to be taught how to use them properly.

Faeces need to be treated in the correct manner, otherwise they pose a health risk.

High density urban areas don't always have the capacity to use the byproducts produced.

 


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