Fertilizer from Urine

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Importance

Human urine contributes most of the nutrients to wastewater, but is typically less than 1% of its volume (Maurer, Pronk, & Larsen, 2006). Nitrogen is the most abundant nutrient in urine. Urine contains 89% of the nitrogen that is excreted from the human body (Vinneras & Jonsson, 2002). For treatment plants using activated sludge processes approximately 50% of the energy consumed is for ammonia as N₂ to the atmosphere (Goldstein & Smith, 2002). Simultaneously, 1% of world energy is used to turn atmospheric N₂ into ammonia for fertilizer and other products (Maurer, et al., 2006). The release of this nitrogen has caused eutrophication of many waterways(Rockstrom et al., 2009). The potential benefits from reusing the nitrogen in urine are substantial. Reusing the phosphorus in urine is equally important. Urine contains 82% of the phosphorus excreted from the body(Vinneras & Jonsson, 2002). Phosphorus fertilizer is mined from rocks, which are non-renewable and are expected to peak in 2030 (Cordell, Drangert, & White, 2009). Phosphorus released into aquatic systems also contributes to eutrophication of waterways (Rockstrom, et al., 2009). Urine offers a renewable source of phosphorus. Higher tech solutions for urine reuse have been explored by NASA, but at an expense (Subbarao, Wheeler, & Stutte, 2000). Lower tech urine reuse has been researched and proven by the world health organization, in soil based agriculture, however this process is open to release of nutrients to the wider ecosystem the same as conventional fertilizers (Schönning, 2001).

Principles of Operation

Urine is often free of pathogens, however pathogens can be present in the urine of unhealthy people, or pathogens can be introduced via contamination from feces during collection. Applying urine directly to crops introduces the risk of humans consuming pathogens, therefore a simple treatment of storing urine is recommended prior to exposing crops to urine.

Typically urine is separated at the source by urine separating toilets (aka partitioned toilets) or Urinals. Urine is collected, preferably in undiluted form to reduce the storage volume needed. Urine is stored to allow urea to hydrolyze which in turn raises the the pH to ~9 (Maurer, et al., 2006). The high pH will inactivate pathogens over time, especially under warmer conditions. Storing for six months above 20°C reduces the risk of contracting an illness to 5.4x10^-4 per instance of direct ingestion (Schönning, 2001).

Urine contains nutrients in similar ratios to what plants need with some exceptions. Urine is low in metals as these are typically routed to the feces during digestion, however many metals are needed in low enough quantities that plants can accumulate them from the surrounding soil or in the water source. Urine is also high in salt (NaCl) because we as humans have a greater need and consumption of salt beyond what plants provide. Therefore urine fertilization has been studied specifically on halophytes (salt tolerant) and natrophillic (salt assimilating) crops (https://pubs.acs.org/doi/full/10.1021/jf0717891).

Operating Requirements and Conditions

Storage Conditions

Condition	Optimum	Operating Range	Units	Notes
Temperature	<20	-	°C	-
pH	9	8-9.5	-	-

Ratios of Inputs to Outputs

The average person excretes 1.25 liters of urine a day (Schönning, 2001). It is difficult to link exact inputs to outputs because storage conditions will determine water loss which can concentrate the nutrients and some nitrogen may be lost as ammonia goes through nitrification and denitrification to form nitrogen gas. The treated urine is typically diluted after storage treatment and dilution rates of one to two parts water per part urine are common (http://www.who.int/water_sanitation_health/wastewater/urineguidelines.pdf).

Major Nutrients excreted in kg/person/year from people in Sweden and Kenya. Both Urine and Faeces shown for comparison.

Country, Excrement	Nitrogen	Phosporus	Pottasium
Kenya, urine	2.1	0.23	0.8
Sweden, urine	4	0.37	0.9
Kenya, faeces	0.3	0.12	0.3
Sweden, faeces	0.6	0.18	0.4

http://www.who.int/water_sanitation_health/wastewater/urineguidelines.pdf

Concentration of Nutrients in Urine. A dilution of 2:1 is shown for typical soil agriculture application while a dilution of 14:1 is shown to achieve concentrations suitable for hydroponics for most nutrients. All concentrations in g/L. Concentration of Urine from (Kirchmann and Petterson, 1995) Typical Concentrations needed for Hydroponics (Raviv and Lieth, 2007)

Nutrient	Stored Urine (2:1 Dilution)	Stored Urine (No Dilutioon)	Stored Urine after dilution of 14:1	Min Concentration for Hydroponics	Max Concentration for Hydroponics
Nitrogen	2.2	6.6	0.44	0.05	0.2
Phosphorus	0.2	0.6	0.04	0.005	0.05
Pottassium	1.0	3.0	0.2	0.05	0.2
Sulphur	0.2	0.6	0.04	0.005	0.2
Calcium	0.02	0.04	0.003	0.04	0.2
Magnesium	0.0015	0.0046	0.0003	0.01	0.05
Chlorine	2.37	7.1	0.47	N/A	N/A
Zinc	0.00009	0.00027	0.00002	0.00005	0.00005
Copper	0.00015	0.00047	0.00003	0.000001	0.00001
Boron	0.00044	0.0013	0.00009	0.0001	0.0003
Iron	0.00019	0.00056	0.00004	0.0005	0.003
Manganese	0	0	0	0.0001	0.001
Nickel	0.00012	0.0003	0.00002	N/A	N/A
Molybdenum	N/A	N/A	N/A	0.00001	0.0001
Sodium	0.96	2.8	0.19	N/A	N/A

Maintenance and Repair

Maintenance Schedule

Frequency	Action	Who Performs?	Time to Complete
(state the frequency)	(state the action)	(User, Professional, Manufacturer, Anyone)	(Number and unit of time)

Known Failures and Solutions

Problem	Symptom (s)	Fundamental Cause	Solution
A goal the user cannot achieve	Usually a measurable or observable attribute	Connect to a more fundamental principle	Action that can be taken

System Variations

Soil Based Agriculture

Cabbage Production

Urine fertilized cabbage has been shown to be a comparable substitute to industrial fertilizers. Levels of chloride were higher compared to industrial-fertilized plots applied with the same amount of overall nitrogen. Brassica's, including cabbage, are known to be more salt tolerant and could therefore be more suited to urine fertilizer (Marschner, 2012). Tastes of the produced cabbage was reported to be similar. (https://pubs.acs.org/doi/full/10.1021/jf0717891).

Instances of the System

Make	Model	Dates of Production	End of Production	Number Produced
(Insert Company)	(Insert Model)	(State a Date)	(State a Date)	(State a unitless quantity)