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Struvite recovery

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[[Image:Struvite.jpg|thumb|right|150px|A jar of Struvite]]

[[Image:urine collection.jpg|thumb|right|150px|Man collecting urine in jerrycans on his bicycle]]

Urine is often used as a low cost liquid fertilizer in rural areas due to its highly concentrated nutrient content. It The main minerals required by plants are nitrogen, potassium and phosphorus. Urine contains roughly 80% of the nitrogen , 60% of the potassium and 5055% of the phosphorus which that humans excrete. Further it While nitrogen is very sustainablerelatively easy to obtain from other sources, since through urine separation, approximately 350L potassium and phosphorus are more scarce. The only readily available organic source of these is urine can be collected annually for any adult. However [[application of urine ]] is often unwanted since it is required in large volumes, is inconvenient to transport and has a bad odourodor. Also it cannot be applied through irrigation systems.

When urine is reacted with magnesium (bittern) it produces stored, a spontaneous reaction occurs, forming the precipitate: magnesium ammonium phosphate, also known as struvite. The precipitate However only 30-50% of the phosphate precipitates naturally. By reacting the urine with magnesium, over 90% of the phosphorus can be recovered. This can be filtered out and dried to produce a valuable powder fertilizer in powder form. The remaining effluent contains most of the urine’s nitrogen and potassium. Since there are no precipitates and can be applied to crops through irrigation systems.

It Struvite can be produced locally using a locally manufactured reactor. Currently the capital costs of the reactor are quite high and it must be built by skilled workers. So , so struvite production is not economically viable in all communities. However research is still being done to improve designs of the reactor and develop low cost business models.  If production becomes cheap struvite can potentially replace many artificial fertilizers.

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==History and social context==

Pilot studies were conducted by eawag Eawag and UN-Habitat in a peri-urban farming community called Siddhipur in the Kathmandu Valley in Nepal. This was done to investigate the feasibility of urine separation and local struvite production.

Here urine was collected from homes using jerry cans and a bicycle. The urine was separated using the already existing EcoSan toilets in each household. Cyclists went around the neighborhood to collect the urine and transport it to the reactor. 400L of urine was used for struvite production daily.

The study showed that struvite recovery is indeed feasible and a community wide production programme could generate around 170kg of struvite per year .

==Suitable conditions ==

For the production of struvite, firstly urine is needed. This can be collected from markets, urinals, public buildings. It must be separated from other sanitation products using [[urine diverting toilets]] or other EcoSan technologies. Then magnesium must be obtained. This can come from bittern from salt production, which contains 3-10% magnesium, or magnesium sulphate from fertilizer powder, containing 5-10% magnesium.

For production using Using the STUN reactor:

First the reactor is filled with urine. Then the magnesium is added. The molar ratio of magnesium to phosphorus in the urine should be 1:1. Hence the phosphorus concentration needs to be determined and depending on the magnesium source, the appropriate amount added. The mixture stirred manually by rotating the crank handle. This is done for about 10 minutes as the struvite precipitates. After the struvite has settled, the valve is opened to filter out the struvite. This is then sundried. The leftover effluent can be used for irrigation. It is suitable for drip irrigation systems.

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