Reuse of faeces and urine from ecological sanitation
Practical Action
Table 2: Factors affecting micro organisms in the environment
[Adapted from Schonning and Strenstrom, 2004]
Temperature
Most micro organisms will survive well at low temperatures (<5 ºC), die
off occurs at high temperatures (40-50 ºC). Unfortunately many ecosan
composting processes do not reach these temperatures throughout the
entire volume of the compost.
pH Micro organisms survive best at pH neutral (7), if a mixture becomes
very acidic or alkaline pathogens will die off. Therefore lime is added to
ecosan toilets to increase pH (a pH >9 is required), the higher the pH
the higher the die off rate (if pH >11-12).
Ammonia
High levels of ammonia kill off pathogens, chemicals can be added.
Moisture
A low moisture content will kill pathogens, this is the reasoning behind
dehydrating ecosan latrines. A satisfactory moisture content target
would be <25%.
Solar/UV light
UV-light reduces pathogen numbers, therefore the die off of pathogens
after application to fields will increase.
Other organisms
Micro organisms live longer in sterilized material, therefore when soil
(as well as other materials) is added the competing bacteria encourage
die off.
Nutrients
Due to the nature of the dangerous pathogens they are unable to
compete with other pathogens for scarce nutrients resulting in die off
of pathogens from excreta.
Others
Oxygen availability can also affect pathogen survival, as can the
presence of various organic and inorganic compounds.
This table shows the factors that kill pathogens, the particular pathogens located within
faeces and urine will not be listed in detail. The following sections looks into the best way to
treat each component, both separately and when they are mixed together, along with
guidelines on application practices.
Faeces
When separated from urine, faeces contain a minimal level of nutrients and high level of
pathogens. Despite this it contains the bulk of organic material and makes a very good soil
conditioner.
Pathogens
The pathogens found within faeces can be split into four categories, bacteria, viruses,
parasitic protozoa and helminths. This brief will not describe the pathogens in any great
detail; diseases which can be transmitted include cholera, typhoid and hepatitis A.
Treatment of faeces
There a numerous means of reducing the pathogen content in faeces, some can be advised as
primary treatment (on-site; within the sanitation systems itself), whereas others should be
recommended as a secondary (off-site) treatment. The main reason for employing primary
treatment is to reduce volume and weight of faecal sludge this facilitates simpler storage,
transport and secondary treatment, and in some cases reduces pathogen content to make
further handling safer. Secondary treatment makes the faeces safe enough to return to the
soil. The following are the main treatment methods.
Storage – Through storage of faeces a number of the processes within table 2 will take place.
Storage is often recommended as a primary treatment method, the success displayed in
practice is variable. The pH of the material, the moisture content, ambient temperature and
biological competition will all affect die off, since these factors will vary continuously the
level of pathogen die off will also vary. Different studies have shown the required storage time
to be different however the WHO guidelines (WHO, 2006) suggests that if the ambient
temperature is between 2 – 20 ºC a storage period of 1.5 – 2 years will be sufficient, and for
an ambient temperature of 20 – 35 ºC a storage duration of 1 year or more is needed. Storage
is best applied alongside other measures and is limited by the die off of Ascaris eggs.
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