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The Human Body as Recycling Machine

Originally appears in the Summer 2014 issue

ALTHOUGH URINE makes up only 1% of the total volume of wastewater, it can pose serious risks to human (and non-human) health if left untreated. In this context, separate collection and treatment of urine could make significant contributions to water pollution control and nutrient recycling worldwide for both urban water management and sustainable agricultural purposes. However, this valuable and relatively new technology—which presumes the human body to be a recycling machine—remains unknown to most people.

The primary purpose of this article is to introduce two interrelated practical classroom activities meant to enable high school science teachers and students to appreciate the importance of using alternative ways of collecting and recycling human urine for the production of natural fertilizers. More so: through a series of calculation exercises, it demonstrates how environmental education is intrinsically connected with different areas of the school curricula—biology, mathematics, chemistry—and beyond, like global food production and distribution issues.

Why recycle urine?

Most people would agree that technology is an intrinsic and fast-evolving part of our society. Many things that we barely even consider to be technology were developed to help us live longer and healthier lives: toilets, for example. Nowadays, the presence of toilets is considered a symbol of economic progress, high civility, and even social status. Not surprisingly, both public defecation and urination are considered
offenses in many countries. In terms of the two most ordinary excrements flushed down the toilet, I have opted here to address the usually neglected importance of urine. (Yuck! I know.)

Urine is more than waste that is washed away from your blood by our kidneys. Historically, it has been used in the Inuit culture for animal skin tanning and was once employed to wash clothes in ancient Rome. Additionally, unusual changes in the colour or odour of urine and urination frequency can suggest a number of diseases, like diabetes.

In freshly excreted urine, nitrogen is mostly in the form of organic nitrogen (urea) – or CO(NH2)2. Indeed, urine is responsible for over 80% of nitrogen and 50% of both potassium and phosphorus in conventional domestic wastewater. Hence, resource-intensive processes at wastewater treatment plants are used to clean the water off any unnecessary nutrients and residues of medicines before it can be released back into the environment.

In the face of growing worldwide urbanization rates and the associated rise in wastewater production, the separate processing of urine could reduce the size of wastewater treatment plants and allow for the recovery of important nutrients – like nitrogen and potassium. These nutrients, in turn, are essential in the manufacture of fertilizers, considered a crucial commodity in the current food distribution
efforts aimed at reducing global hunger.

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Giuliano Reis is an Associate Professor of Science Education in the Faculty of Education, University of Ottawa. His research interests include science teacher education and environmental education.