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Feces, faeces, excrement or dung is a waste product from an animal or human. Feces is an extremely rich source of soil nutrients and soil microorganisms, and treating it as waste discards a valuable resource. (See No such thing as garbage) However it is also a potent source of human pathogens, and attractive to disease vectors such as flies, making it dangerous to public health. Therefore it must be appropriately treated in most cases and applied according to safety guidelines.
Feces, when used as a resource is referred to as manure. Similarly, human waste, when treated in the same context is referred to as humanure. Humanure must be handled with particular care is it is more likely to carry human pathogens, compared to animal manure.
Feces can be used for several purposes:
- it can be used as is, as an organic fertilizer in agricultural fields (the feces is then called "manure") Use as is (as night soil) however is known to cause illness, especially among those not accustomed to eating food grown in this way.
- it can be composted to form humus (ie using a composting toilet): this is slightly more environmentally friendly
- rather than using it in pure form or as compost, only the phosporus too can be extracted by adding magnesium to form struvite and then collect the struvite (less environmentally friendly)
- it can be used in biodigesters to form biogas and manure (= residue)
Note that water-based systems require sewage treatment and use of this is best avoided (see Wastewater and Category:Wastewater ). Also note that manure can also be allowed to be digested by composting worms (e.g. for feeding fish).
Feces as fuel
Dung is considered to be one of the best fuels for the traditional mud stove for the following reasons:
- it burns slowly
- cooks fast
- generates powerful heat compared to other sources of fuel found locally
- easy to store
- Less toxic compared to other sources of fuel
Problems related to dung as a fuel are:
- there is a scarcity of dung
- cattle owners do not permit collection form their fields
- as dung is being dried there is a risk that it could be stolen
- It burns faster than wood when it is not properly compressed
Making Clean Dung Briquettes from feces
Dung washing is a simple process whereby the dung is washed with water, organic matter, fermented paper, sawdust or other additives mixed into the slurry and then the liquid removed via compression. The benefits of washed compressed dung as a fuel source are three fold.
- The chlorine and the silica present in the dung are water soluble and hence can be removed prior to burning. These components contribute a serious health risk for users when burnt.
- The water-soluble fraction of the dung also constitutes the “agriculturally nutritious” aspects of dung and thus can be retained for fertiliser.
- Removal of the silica content, lowers the ash content which inturn allows for the proper flow of air which overall translates to a reduction in the formation of the harmful carbon monoxide.
A briquette press is a tool that can be used to remove the liquid and bind the slurry into solid briquettes. A two stage press has been designed with a hybrid lever and screw compression that produces briquettes fast and efficiently with the minimum of effort. Initially a lever is depressed to a comfortable operating level, then the lever mechanism is locked in place and a secondary screw system further depresses a plunger and applies the additional force necessary to to remove additional moisture. The steel briquette press can be manufactured locally, is easily maintenaned and simple to use. The Briquette chamber can produce four briquettes simultaneously. Having two briquette chambers and base stands allows for increased speed an efficiency as one chamber can be filled whilst the other is being compressed. Briquettes take on average 6 days to dry in dry temperate conditions. 
Safe use of humanure
It is an important principle in risk management to take several safety measures together, to minimize risk. Although humanure is relatively safe, extra precautions should be taken for the possibility of pathogens surviving the composting process, and for those with weakened immune systems.
The key safety measures involve:
- Processing: ensuring pathogens are killed, through temperature, time and pH [verification needed])
- Separation: ensuring that the humanure and any remaining pathogens don't touch or enter food.
- Food treatment: Washing, peeling and/or cooking reduce the risk further, if necessary.
For food safety, it is recommended to apply mature humanure to an empty garden bed first, then apply layers of safer soil and mulch.
Variations in treatment requirements
Treatment and application requirements will be less strict where the soil will not be used for food crops for months or years, and where there is little exposure to humans and human disease vectors. In such cases, appropriate precautions are still important, such as mixing with soil or covering with a later of soil, to speed breakdown. Mulch adds physical protection, and compost tea might be expected to affair the breakdown and suppression of pathogens.
The Humanure Handbook by Joseph Jenkins explains how to compost human feces in such a way as to kill the pathogens. A summary of the method is:
- Use sawdust to bury manure. Sawdust provides carbon and this balances the nitrogen in the faeces. A good carbon-nitrogen balance is needed for composting. The Sawdust also keeps bad smells in and keeps flies away.
- Do not separate urine and feces, as the urine provides moisture the microorganisms need.
- As well as adding the buckets from the toilet to the compost heap, throw on chunky materials like straw. This traps air pockets in the compost heap.
- Optionally, skewer the compost heap with sticks or pipes to provide more aeration.
- Let it sit for a year before using on plants
Note that most approaches however emphasize separating the urine, as otherwise the nitrogen content becomes too high for proper composting (requires a specific carbon/nitrogen ratio).
Notes and references
- Source: Mohammed Aslam, Practical Action Bangladesh
- Source: EWB NAMUNA Clean Cooking Initiative Nepal (2011)
- The 3rd edition of the Humanure Handbook is free on the web here: http://jenkinspublishing.com/humanure_contents.html
- Elephant dung as a sustainable raw material
- Fuel Gas from Cow Dung
- Greywater reuse