Question
i have heard from a friend that it is possible to combine human feaces and ash, and after a time a fertilizer is developed? i am hoping to use this information, if it is true and correct, to develope a programme in rural africa to help combat sanitation problems. Can you offer your expertise in this matter? any information or recommendations on where to research this topic would be greatly appreciated!

Answer
'Humanure' is the term for composting human waste.  It was coined in 1994 in The Humanure Handbook by Joseph Jenkins.  The World Health Organization ('WHO') publishes guidelines on the subject, 'Guidelines for the Safe Use of Wastwater, Excreta and Greywater: Excreta and Greywater Use in Agriculture', available for download:

http://www.who.int/water_sanitation_health/wastewater/gsuweg4/en/index.html

The key risks seem to be two-fold.  One is the group of human handlers who collect, treat or apply the sewage; the other is the consumers who receive potentially contaminated food.  There are several ways the materials can be treated to remove pathogens, but unless the people who handle the waste are familiar with precautions they need to take, it is certain to lead to outbreaks of all kinds of ugly diseases.  There are however numerous ways to treat the waste that will effectively purify it and make it safe to use as agricultural fertilizer or even in some cases as drinking water.  Local materials (wood shavings, coconut husks, etc) are used in each case as part of the process.  

The IslandWood School on Bainbridge Island, Washington, designed its facilities exclusively with ultra-green technology that included compost toilets along with solar power and cumputer-modelled air-flow to replace a/c.  Matsuzaki Wright Architects designed the C.K. Choi Building at Univ. of British Columbia with compost toilets and urinals among its ultra-green award-winning features.  

Most authorities agree that effective composting of human waste takes time -- 6 years is reasonable -- with breakdown by Bacteria, Fungi and other specialized microbes.  That said, this is most certainly the shape of things to come.  We should all get used to it.  As they've been saying lately, We do not inherit the Earth from our ancestors; we borrow it from our children.  The Third World is not the only place that should be implementing these concepts.  Thanks for writing.