We are all quite used to the idea of fertilizing the soil with the manure of animals and usually don't think twice about it. But imagine using human manure -- even your own -- to help grow the food that you eat. Some might scoff at the idea, but it's one that many have been researching, including Jörgen Fidjeland who discussed the use of faecal sludge as fertilizer at this year's Tropentag conference at the University of Hohenheim in Stuttgart, Germany... (read more) What a Waste! Consider that untreated sewage from over 4 billion people is being dumped into rivers and oceans all over the world and that humans have been, and still are, using human faeces -- known as night soil -- and urine as a fertilizer source. Hence why Fidjeland and his colleagues find it necessary to look at new methods of making faecal sludge safe to use and to reduce the number of pathogens within the final product in order to take full advantage of its positive aspects. A messy situation? The most common counter argument to the use of human waste as a fertilizer source is that harmful substances are present, such as pathogens, unmetabolized pharmeceuticals and heavy metals. Until now, the most common technique has been to compost the waste, allowing the high temperatures over a period of time to kill some pathogens. But Fidjeland and other scientists at the Swedish University of Agriculture Sciences are looking at a new method called ammonia sanitisation in order to rid the fertilizer of the most problematic pathogens. Ammonia sanitisation is a technique which simply requires the application of an ammonia source and a sufficient period of airtight storage. Ammonia has been shown to be an effective chemical disinfectant, able to inactivate pathogens like viruses, bacteria, and worm eggs. Lucky for humans, our urine makes the perfect source of ammonia -- when the urine is combined with faeces, which contains the enzyme urease, ammonia is produced. But there are a few conditions which are required for this process to work. Putting a Lid on the Situation In normal flush toilets and pit latrines, the addition of too much water during the flush or the extended contact of the urine to air renders the beneficial substances ineffective. Therefore, sewage systems would have to be redisgned in order to decrease the amount of water used in flush toilets and to provide a sufficient period of airtight storage -- sometimes over a month. Such an overhaul to waste systems would be difficult, but not impossible. Pilot projects are already underway in parts of Europe and Africa, says Fidjeland. Nevertheless, if such methods and systems would be adopted the benefits would be numerous, especially in urban areas of low income regions where untreated waste is especially hazardous and problematic (think of the recent cholera outbreak in Haiti). In addition, if some scientists' assertions are correct, phosphate rock, which is the world's main source of phosphorous fertilizer, is becoming increasingly scarce meaning phosphorous may become a limiting factor in agricultural production. But because human waste is rich in the three vital nutrients for plant production -- Nitrogen, Phosphorous, Potassium -- such methods of human waste sanitisation could address both current and possibly drastic future problems.