Human urine usually goes in septic tanks before ending in costly water treatment facilities. Americans produce 30 billion of urine annually and a person typically uses 400 gallons of drinkable water a year to flush urine away. Seems like even urine leaves an ecological footprint.
Several experts and studies have made an interesting suggestion to tackle the environmental impact of urine: Use human urine as fertiliser in agriculture.
H. Kirchmann and S. Pettersson in 1994 made a bold move to understand the chemical composition of human urine in an attempt to compare it with commercial organic fertiliser. They initially mentioned the absence of literatures exploring the use of urine as fertiliser, except for earlier studies that probed the agricultural value of urine along with feces.
Understanding the literatures
In their study published by Fertilizer Research, Kirchmann and Pettersson found out that stored human urine contained critical constituents similar to commercial fertilisers. These include nitrogen, potassium, calcium, and phosphorus. The study also revealed urine has lower heavy metal concentrations than organic fertilisers.
Several relatively recent studies subsequently contributed to the growing body of literature about the use of urine as fertiliser. For instance, H. Heinonen-Tanski, S. K. Pradhan, and P. Karinen in 2010 reviewed related studies detailing the effectiveness of urine in cereal and vegetable yields.
Published in the journal Sustainability, the review suggested plants fertilised with human urine might have produced higher, similar, or slightly lower yields than plants fertilised with commercially available minerals. Still, urine-fertilized plants had higher yields than non-fertilised plants.
Researcher and resource-recycling specialist Carol Steinfeld authored the book Liquid Gold: The Lore and Logic of Using Urine to Grow Plants. It essentially provides not only a definitive guide to using urine to grow plants for domestic or commercial use but also an extensive discussion about the valuable applications of urine throughout history and across several purposes.
Agricultural application of urine
According to the World Health Organization, although human urine comprises less than a percent of domestic wastewater, it still contains a substantial amount of nitrogen and phosphorous—about 80 and 55 percent respectively. Urine contamination of rivers and streams runs the risk of algal blooms that can choke off aquatic life.
It is also worth mentioning that the world is facing a shortage in phosphorus, especially shortage of phosphate rocks, due to excessive mining to meet the demands of the agriculture industry. This shortage could create food insecurity and promote hunger further in large parts of the world. Nonetheless, this phosphorus shortage can be mitigated by using urine as a fertiliser.
Rich Earth Institute, meanwhile, has initiated the collection of urine instead of letting it go in septic tanks and water treatment facilities. This endeavour also promotes the use of urine as an alternative to commercial fertilisers.
Founded in 2011, the people behind Rich Earth Institute have dedicated themselves to advancing and promoting the use of human waste as a resource. Their goal is to bring together sanitary engineers, farmers, water quality advocates, businesspeople, agricultural scientists, and regulators. Together, they would demonstrate the valuable uses of human waste. The Urine Project is their first flagship initiative.
“Since 2012, we have been collecting urine from over 170 volunteer participants in and around Brattleboro, Vermont. After sanitising the urine, we apply it to farmland that is producing hay. Throughout the process, we collect detailed data on the effect of urine fertiliser on the quantity and quality of the hay harvest and on the properties of the soil,” said Rich Earth Institute.
The Netherlands, especially the city of Amsterdam, had also ventured into a similar undertaking. Dubbed as the Green Urine Campaign that ran during the International Water Week in 2014, the city government placed public urinals that served as urine collection sites. The goal of the campaign was to raise awareness of the benefits of using urine as fertiliser.
Waternet, the water company of Amsterdam, is currently on the process of building a facility that would create 1,000 tons of fertilisers from the wastewater of 1 million people.
Researchers H. Heinonen-Tanski, S. K. Pradhan, and P. Karinen have also come up with a suggestion for better integrating domestic sewage system with urine collection. In their paper, they suggested instalment of separate or exclusive toilets for urinating, especially in poor rural areas or farm communities.
Problems in using urine as fertiliser
There is downside to using urine in agriculture however. Take note that undiluted urine can chemically burn the roots of some plants which is why it is usually applied diluted with water, which also reduces odour development during application.
In addition, using urine as fertiliser has one critical limitation involving the potential for buildup of excess nitrogen and other constituents such as inorganic salts. It is worth mentioning that the degree of the impact of this factor depends on usage, salinity tolerance of the plant, soil composition, addition of other fertilising compounds, and quantity of rainfall or other irrigation.
But the aforementioned downsides are actually dependent on lack of proper knowledge in incorporating urine in farming techniques. These downsides are manageable as long as farmers are knowledgeable about the proper use of urine in agriculture. They should have an understanding of urine quality, the nutritional needs of their crops, and soil composition of their farms.
The real challenge to using urine as fertiliser centres on collecting urine. It is unclear whether source separation, urine diversion, and on-site urine treatment can be made cost effective. Furthermore, some might consider the collection and reuse of urine in agriculture as unorthodox. These challenges require intervention from governments or other influential organisation.
Further details of the research of Kirchmann and Pettersson are in the article “Human Urine: Chemical Composition and Fertilizer use Efficiency” published in 1994 in the journal Fertilizer Research. Further details of the study of Heinonen-Tanski et al are in the article “Sustainable Sanitation—A Cost-Effective Tool to Improve Plant Yields and the Environment” published in 2010 in the journal Sustainability. Photo credit: Rich Earth Institute