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Human waste is an extremely rich source of soil nutrients and soil microorganisms, and treating it as waste discards a valuable resource. (See also 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.
While water-based systems require sewage treatment, composting toilets produce humanure, ready for use (with care). The humanure can be used as is or can also be allowed to be digested by composting worms (e.g. for feeding fish).
Massive amounts of human waste are produced by human settlements. Taking sustainability seriously means addressing where this waste goes. What do you do with your feces? Most of us on the West operate on the out of sight, out of mind system. It is wasted.
Historically, human societies took two opposing directions.
- Some developed hygiene laws to ensure separation from human waste and the disease it carries.
- Some used night soil, untreated human waste, as fertilizer. However this is known to cause illness, especially among those not accustomed to eating food grown in this way.
However in the twentieth century[verification needed] with an undemanding of pathogens and the effectiveness of thorough composting, humanure became possible closing the nutrient cycle by reusing human waste, while still minimizing exposure to dangerous pathogens.
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 other approaches emphasize separating the urine.
Notes and references
- The 3rd edition of the Humanure Handbook is free on the web here: http://jenkinspublishing.com/humanure_contents.html
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