Not Wasting Our Waste
Large-scale agriculture needs plenty of nitrogen, phosphorus, and potassium.
By 2010, world demand for nitrogen fertilizer climbed above
100 million tonnes per year.
Industrial operations and mining can provide the needed chemical fertilizers,
but at enormous costs in money and pollution.
Could recycled urine play a significant role in making agriculture
a more "green" undertaking?
Possibly.
Studies indicate
that urban waste water contains enough nitrogen, phosphorus, and potassium
to offset more than 13% of the agricultural fertilizer demand.
The value of those possibly recovered nutrients would total
US$ 13.6 billion annually.
The problem, we're told, is that we are wasting our waste products.
Urine is 91–96% water.
A typical adult urinates six to eight times a day,
producing about 1.4 liters of urine each day.
That urine contains dissolved salts, urea, uric acid, creatinine,
proteins, hormones, and trace amounts of enzymes, hormones, and
other chemicals.
That 1.4 liters of urine contains about 59 grams of total solids.
Urine makes up just 1% of household waste water,
but it contains 80–90% of the nitrogen
and at least 50% of the phosphorus and potassium.
That 59 grams for one person in one day sounds small,
but collected through the year in a city it adds up.
One study found
that waste water adds 6.2 million tonnes of nitrogen to coastal water
annually.
"Nutrient pollution" is a big problem.
Simply dumped into nearby waterways, it can fertilize unwanted algae blooms.
Wildlife officials in Florida
reported
that hundreds of manatees had starved to death along the state's east
coast in 2021 because algae blooms had killed the seagrass they feed on.
What's In Your Pee?
What we would like to extract, in terms of elements, is primarily the
nitrogen, phosphorus, and potassium.
The phosphorus and especially the nitrogen will be bound in molecules,
requiring multiple chemical steps to yield the desired compounds.
The chemical profile of typical human urine is, in addition to
the roughly 95% water or H2O:
| Urea |
NH2–CO–NH2 |
9.3 to 23.3 g/L |
| Chloride |
Cl- |
1.87 to 8.4 g/L |
| Sodium |
Na+ |
1.17 to 4.39 g/L |
| Potassium |
K+ |
0.750 to 2.61 g/L |
| Phosphate |
PO43- |
1.20 g/L |
| Creatine |
C4H7N3O |
0.670 to 2.15 g/L |
| Sulfur |
S |
0.163 to 1.80 g/L |
Urine is slightly acidic,
with the pH ranging from 5.5 to 7 and averaging around 6.2.
For comparison, the pH of orange juice is 3.3–4.2,
black coffee is about 5.0,
and milk is 6.5–6.8.
Urea is the main nitrogen source in fresh mammal urine.
A high protein diet leads to high urea levels in urine.
If you save your urine,
emulating Howard Hughes who famously saved his pee
in a large collection of jars,
biochemical decomposition converts its urea into ammonia and ammonium.
A jar in Howard's pee collection wouldn't have smelled too bad when
it was fresh, but ammonia and its derivative ammonium are pungent.
Urea, NH2–CO–NH2.
Biochemical decomposition of urea as urine ages
converts urea into ammonia and ammonium.
Ammonia is toxic, so fish excrete it immediately,
birds convert it into uric acid,
and mammals convert it into urea.
Or at least that's the overly simplified explanation.
The qualifier "most of" needs to be added to all three cases.
Aged urine is called lant,
a word which comes from Old English.
If someone asks you "What's in all these jars?",
you could answer "Lant" in the hopes that they wouldn't know what
you're talking about.
Or just say "It's my pee!" and see what they make of that.
Maybe they'll assume you're a titan of the aeronautics industry.
Over 90% of the world's industrial urea production is used as
nitrogen-release fertilizer.
It is relatively cheap to transport given the amount of nitrogen
per unit of solid material.
It breaks down to ammonium or NH4+ in the soil,
and is taken up by plants.
Urea is produced in factory settings on a large scale.
Worldwide urea production capacity in 2012 was estimated at 184 million tonnes.
Urea is produced in an industrial setting by starting with
a fossil fuel — usually natural gas,
sometimes other petroleum derivatives,
less often coal.
That is used to produce ammonia with a large amount of carbon dioxide
byproduct.
The ammonia and CO2 are then used to produce urea.
Typically a urea plant is built next to a synthetic ammonia plant,
making one large complex that turns hydrocarbons into urea.
Ammonia, NH3.
Ammonium, NH4+,
formed from ammonia plus an extra hydrogen atom.
Uric acid is another possible constituent of human urine.
It's created in humans when the body breaks down purines, present in
high concentrations in meat and meat products, especially internal organs.
Uric acid dissolves into the blood and travels to the kidneys,
and is passed out in urine.
A normal level is 250 to 750 milligrams per 24 hours,
meaning only about 0.18 to 0.54 g/L to use the units of the above table.
Too much of it and you get gout, "The Disease of Kings".
Uric acid, C5H4N4O3
Phosphate is present in the body,
especially in bones and teeth,
and some is excreted through urine.
Phosphate, PO43-
Inorganic phophates for use in agriculture are mined.
The island nation of Nauru and the nearby Kiribati island of Banaba
are small isolated islands.
For thousands of years, birds landed on those islands, pooped,
and later flew on.
The deposits accumulated until the islands were
largely formed from bird droppings.
Guano.
The phosphate deposits were noticed in 1899 and mining started soon after.
Mining came to be controlled by Britain, Australia, and New Zealand,
with the natives put to work digging phosphate for very little pay.
The glories of colonialism.
80% of the two islands' surfaces have been strip-mined away,
and the phosphate was almost completely gone by 2000.
Finally, creatine is another
nitrogen-bearing component of human urine.
Creatine, a breakdown product from muscle and protein metabolism.
Using the Stored Pee
The traditional method is to store the urine until it has aged into lant
and the urea has mostly converted to ammonia and ammonium.
Then you apply it to plants, often after diluting it with water.
The buzzwords include ecosan, short for
ecological sanitation.
Or as a slogan, "Closing the cycle of agricultural nutrient flows".
The problem is one of collection.
Individuals or families could use a waterless urinal,
possibly as simple as a jug with a funnel.
Urine-diverting toilets with dedicated drain lines
could collect urine on an urban scale.
A group of undergrad students at the University of Florida did the math.
Estimate how much urine could be collected in a season of home games
at the football stadium,
calculate the nitrogen and phosphorus in the collected pee,
and estimate the cost of the modified toilet and urinal systems
plus the urine storage system.
The final conclusion is that in one football season,
fans would produce more than enough nutrients to fertilize
the field for that season.
See their paper for all the details:
Nutrient Recovery Potential from Stadium Wastewater for Use
as Turfgrass Fertilizer
The University of Michigan studied so-called "peecycling" at a city scale,
publishing the results in the Environmental Science and Technology
journal:
Life Cycle Assessment of Urine Diversion and Conversion to
Fertilizer Products at the City Scale
Some news stories reported on peecycling in 2022.
A news feature article in Nature appead in February 2022:
The urine revolution:
how recycling pee could help to save the world
The New York Times reported on the Rich Earth Institute's project:
Meet the Peecyclers. Their Idea to Help Farmers is No. 1.
See the
Rich Earth Institute website
for more information, including how to get involved.
Human urine has been collected for industrial applications for over two
millennia:
Making Textiles? You'll need Urine, Seaweed, and Shale
Gratuitous picture of Bill Gates drinking water recovered from human urine.
Large-scale urine collection to extract drinking water and valuable chemicals
needs to be careful about other urine content, especially hormones,
and to a lesser extent, excreted pharmaceuticals:
How Your Pee Can Change The Sex Of Fish And Reptiles
You Can Flush But You Can't Hide
To take a more sophisticated approach than simply saving your pee
and pouring it into the garden, see:
Recovery of Phosphorus and Potassium from Source-Separated
Urine Using a Fluidized Bed Reactor:
Optimization Operation and Mechanism Modeling
Phosphorus and Potassium Recovery from Human Urine Using a
Fluidized Bed Homogeneous Crystallization (FBHC) Process
Advancing the Design and Operating Conditions for
Block Freeze Concentration of Urine-Derived Fertilizer
Next article:
The Worm-Riddled Friars of Medieval Cambridge
