Time to stop flushing good fertiliser down the drain?

Round and round the toilet bowl… no, please don’t stop reading, this is actually a lead-in to a fascinating proposal by one wastewater scientist to add urine to the circular economy.

Products are traditionally made in such a way that they cannot be easily repaired, upgraded or refurbished and which is made from materials that cannot be recycled, being designed with built-in obsolescence to encourage repeated purchases as part of a linear path from mining to landfill. The circular economy is a revolutionary concept where instead of the traditional wasteful process of mining raw materials from the earth and manufacturing something that is finally dumped as rubbish in landfill, products are designed so that there is no waste produced at any stage, the product being designed to eliminate waste at every stage of its manufacture, with products being shared, repaired, refurbished and only when they can no longer be used, completely recycled, so that the limited quantities of materials in man-made systems are recycled just as they are in nature. In some ways, it is a step back in time to the days of make do and mend, but updated to include upgrades and making products as new and more capable than before while minimising waste. Why throw out your computer and buy another if you could just swap out components and refurbish the supporting mechanisms for another five years of life? What if you could repeat the process and save money and the environment?

Now, what if you were part of another circular economy, one that recycles the leftovers of what you have consumed into fertiliser to grow more commercial plants. What if your bodily wastes were recycled and turned into high-quality fertiliser rather than ending up in streams and rivers, killing entire ecosystems through eutrophication (a process where increasing the naturally very low levels of nitrogen and/or phosphorous in watercourses turns them from clear babbling brooks teeming with life and splashing with fish into sluggish, silty bywaters populated only by mosquitoes, midges and bloodworms, all other life suffocated as algal blooms suck the life from the waterway). Urine is particularly rich in phosphorous, making it both a particularly dangerous pollutant of freshwater and going some way to explain why you find stinging nettles (Urtica dioica L.) along the side of disturbed paths, where man and beast relieve themselves, although stinging nettles do prefer disturbed/recently cleared ground because of the reduced plant competition as well. Traditional sewage treatment plants struggle to extract enough of the nitrates and phosphates from sewage to make the treated water they release harmless but what if urine could be turned into a rich fertiliser?

It turns out it could. It turns out that stale urine is an inhospitable environment for spoilage microbes and can be turned both into a nutrient slurry or even a desiccated powder that is about 20% nitrogen by weight, making it an ideal fertiliser for farmer’s fields. This aspect of the circular economy – spreading human waste on crops – goes back to the Middle Ages, but with just a few intervening steps, we now know how to put nutrition back into the soil without contaminating our food with raw sewage! We might even expect sewage treatment companies to offset the cost to consumers of wastewater treatment with the profits from these fertiliser sales.

So, after all that, it turns out that the circular economy is all just a little bit of history repeating.

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