Reuse of human excreta
The intended reuse applications for the nutrient content may include: soil conditioner or fertilizer in agriculture or horticultural activities.
[3] The resources available in wastewater and human excreta include water, plant nutrients, organic matter and energy content.
[1] Various technologies and practices, ranging in scale from a single rural household to a city, can be used to capture potentially valuable resources and make them available for safe, productive uses that support human well-being and broader sustainability.
[26] The general limitations to using urine as fertilizer depend mainly on the potential for buildup of excess nitrogen (due to the high ratio of that macronutrient),[20] and inorganic salts such as sodium chloride, which are also part of the wastes excreted by the renal system.
[16] It was reported in 1995 that urine nitrogen gaseous losses were relatively high and plant uptake lower than with labelled ammonium nitrate.
[29] One low-tech solution to odor is to add citric acid or vinegar to the urine collection container, so that the urease is inactivated and any ammonia that do form are less volatile.
[27] Besides concentration, simple chemical processes can be used to extract pure substances: nitrogen as nitrates (similar to medieval nitre beds) and phosphorus as struvite.
[29] The health risks of using urine as a source of fertilizer are generally regarded as negligible, especially when dispersed in soil rather than on the part of a plant that is consumed.
Urine can be distributed via perforated hoses buried ~10 cm under the surface of the soil among crop plants, thus minimizing risk of odors, loss of nutrients due to votalization, or transmission of pathogens.
[31][32] In developing countries, the use of raw sewage or fecal sludge has been common throughout history, yet the application of pure urine to crops is still quite rare in 2021.
[22][33] Since about 2011, the Bill and Melinda Gates Foundation is providing funding for research involving sanitation systems that recover the nutrients in urine.
Examples of onsite technologies include pit latrines, unsewered public ablution blocks, septic tanks and dry toilets.
[39] Work by the International Water Management Institute and others has led to guidelines on how reuse of municipal wastewater in agriculture for irrigation and fertilizer application can be safely implemented in low income countries.
[41] Sludge treatment liquids (after anaerobic digestion) can be used as an input source for a process to recover phosphorus in the form of struvite for use as fertilizer.
For example, the Canadian company Ostara Nutrient Recovery Technologies is marketing a process based on controlled chemical precipitation of phosphorus in a fluidized bed reactor that recovers struvite in the form of crystalline pellets from sludge dewatering streams.
The resulting crystalline product is sold to the agriculture, turf, and ornamental plants sectors as fertilizer under the registered trade name "Crystal Green".
The concept is also used in water supply and food production, and is generally understood as a series of treatment steps and other safety precautions to prevent the spread of pathogens.
[45][35] Exposure of farm workers to untreated excreta constitutes a significant health risk due to its pathogen content.
[51] The nutrients, especially nitrates, in fertilizers can cause problems for ecosystems and for human health if they are washed off into surface water or leached through the soil into groundwater.
[52] Black soldier fly (BSF) bio-waste processing is a relatively new treatment technology that has received increasing attention over the last decades.
Larvae grown on bio-waste can be a necessary raw material for animal feed production, and can therefore provide revenues for financially applicable waste management systems.
That is a far higher gold content than Japan’s Hishikari Mine, one of the world’s top gold mines, [...] which contains 20–40 grammes of the precious metal per tonne of ore."[62] This idea was also tested by the US Geological Survey (USGS) which found that the yearly sewage sludge generated by 1 million people contained 13 million dollars worth of precious metals.
[64] The terms "sanitation economy" and "toilet resources" have been introduced to describe the potential for selling products made from human feces or urine.
[67] The compost produced at these facilities is sold to farmers, organizations, businesses, and institutions around the country to help finance SOIL's waste treatment operations.
[70] When considering drivers for policy change in this respect, the following lessons learned should be taken into consideration: Revising legislation does not necessarily lead to functioning reuse systems; it is important to describe the “institutional landscape” and involve all actors; parallel processes should be initiated at all levels of government (i.e. national, regional and local level); country specific strategies and approaches are needed; and strategies supporting newly developed policies need to be developed).
[71] In the United States, the EPA regulation governs the management of sewage sludge but has no jurisdiction over the byproducts of a urine-diverting dry toilet.
It is also used for making an alcohol-based bio-pesticide: the ammonia within breaks down lignin, allowing plant materials like straw to be more easily fermented into alcohol.
In Mukuru, Kenya, the slum dwellers are worst hit by the sanitation challenge due to a high population density and a lack of supporting infrastructure.
[80] In Tororo District in eastern Uganda—a region with severe land degradation problems—smallholder farmers appreciated urine fertilization as a low-cost, low-risk practice.
Linking up of public toilets with biogas digesters as a way of improving communal hygiene and combating hygiene-related communicable diseases including cholera and dysentery is also a notable solution within Ghana.
