Op-Ed: The value of urine in a water-sensitive future

By now, most Capetonians will know what stored urine smells like – a strong ammonia smell which we try to eliminate using detergents or even precious water. But how does this smell develop? Urine is approximately 95% water and the other 5% has many components, the most abundant being urea. Urea degrades when bacteria are present and this reaction forms ammonia gas. Fortunately, we can prevent this reaction from occurring by adding vinegar or bleach.

But other than having a bad smell, urine is very valuable because it has high concentrations of nitrogen, phosphorus and potassium, the three key ingredients needed to make inorganic fertilisers. It also has calcium, magnesium and other minerals necessary for plant growth. Shockingly, the urine that we flush away in a toilet only makes up about 1% of the sewage from our homes, yet it contains over 80% of the nitrogen, 56% of the phosphorus and 63% of the potassium in sewage. We literally pee away these valuable nutrients and spend vast amounts of money and energy trying to remove them (not recover them) in sewage plants. If left untreated, these nutrients can enter the environment resulting in algae blooms in natural water bodies. This has already happened at the Hartbeespoort dam in the North West Province and the Wildevoelvlei in Cape Town.

What should be happening is that the urine should be recovered and used to make fertiliser. This approach would also offset the need to pursue the costly and energy intensive effort of mining for limited phosphates and producing synthetic fertilisers. Recovering fertiliser from urine closes the nutrient cycle and has the potential to create a more sustainable future.

In addition, we use drinking water to flush our toilets and urinals. Just flushing our urine away can use as much as 25% of our daily water consumption, depending on how strict you are with your water saving activities. Last year, a final year Civil Engineering student, Tinashe Chipako, calculated that the University of Cape Town (UCT) uses about eight Olympic size swimming pools just to flush its urinals each year. UCT has since implemented water saving initiatives by reducing the number of urinal flushes and putting signage encouraging users to limit the number of flushes. This shows the huge potential for reducing our water consumption by implementing “simple” initiatives. I was encouraged to see similar signage at malls and shopping centres in Cape Town. Coastal cities could even consider sea water flushing for their urinals and toilets, but this requires significant investment to install dual reticulation systems, replace existing pipes and retrofitting waste water treatment plants. Encouragingly, Hong Kong has been using sea water for toilet flushing since the 1950s.

First, we need to collect the urine. This collection could happen at a household level using containers or new office blocks could install no-mix toilets and urine collection systems. The urine can then be treated in three potential ways: (i) we can add calcium hydroxide, which would produce calcium phosphate and prevent ammonia from forming, (ii) we can add a magnesium compound to produce magnesium ammonium phosphate (otherwise known as struvite) or (iii) we can dilute the urine and use it as is.

The addition of calcium hydroxide (lime) or magnesium sulphate (Epsom salt) to your urine produces a solid which is the fertiliser. You would need to filter the solid from the liquid component, which can be done using a simple cloth or bag filter. It might be a good education exercise for your children, showing them that our “waste” can produce valuable fertiliser.

The fertilisers would be produced locally, by entrepreneurs and private companies, thus reduding our need to import fertilisers or mine for natural phosphate rock. For example, UCT currently purchases about four tons of fertiliser a year for its sports field yet it has the potential to produce seven tons of fertiliser from urinals alone. It is clear that systems need a drastic rethink.

How can we save water when we need to pee?

• You can pee into a container, dilute the urine as needed using shower water or washing machine water and use this as a liquid fertiliser in your garden. It’s recommended that you dilute the urine 1:3.
• You could also pee directly into the garden but don't pee in the same place as salts will eventually build up.
• If you live in an apartment block, you can add vinegar to your toilet to prevent any bad smells while it mellows and flush periodically with shower water.
• Be open to nutrient recycling initiatives. For example, imagine if we had a company that collected filled urine containers from your home on a weekly basis at a minimal cost or at no cost (the company would make money from the sale of the fertiliser produced). This urine could then be transported to a Resource Recovery Plant where different fertilisers and resources could be manufactured. Or imagine that you transported filled urine-fertiliser containers to recycling depots, much like you would for glass recycling. These household systems would require no water and any bad smell would be prevented by prior calcium hydroxide addition.

Initiatives like this will probably be more widely accepted now (at least in Cape Town) as a result of this drought and that is our blessing in disguise. There are clearly many entrepreneurship opportunities in this space.

Moving to a more sustainable and circular economy, recycling initiatives such as recovering value from urine and faeces becomes pertinent. In addition, rethinking conventional sanitation systems, questioning how they work and how they can be improved is extremely important because not only can we save water but we can also recover resources in a more efficient manner. Be open to change and embrace it because our very future might depend on it. DM

Other articles:

• Greenovate Award for recycled urine project
• Futurewater
• SAICE award for urine research project

Dr Dyllon Randall is a senior lecturer, Department of Civil Engineering, University of Cape Town

Photo: Residents of Cape Town collect drinking water in the early morning from a mountain spring collection point in Cape Town, South Africa, 31 January 2018. EPA-EFE/NIC BOTHMA