Written by Max Burns: PhD Candidate, James Cook University
for the National Science Communication Challenge
Phosphate is a non renewable resource.
It is essential for all agriculture.
Your urine is full of it.
By recovering this phosphate we could offset 20% of Australia's agricultural demand.
When you are using the toilet, having that hopefully private moment, do you ever wonder what happens to your poo and pee after you flush?
It goes to a treatment plant, where the water is cleaned, but there are lots of valuable nutrients which could be recovered. One of these nutrients is phosphorus, an essential fertilizer for all agriculture, and a non-renewable resource.
Recycling all of this wastewater phosphorus, could meet 40% of import demand and 20% of our agricultural demand in Australia.
This is a lot for an industry which makes up 12% of Australia’s gross domestic product. Unfortunately, we don’t actually recover these nutrients in a useful form.
Don’t despair though, because in the not too distant future, the term wastewater will be down the toilet, as we are entering the age of resource recovery!
The best way to recycle phosphate is to form phosphate crystals called struvite which can be used directly and safely as a slow release fertiliser.
The way these crystals form is like scale in a kitchen jug or an iron. But this is a complicated process: crystals can be born into existence, they can grow and they can stick together. By understanding and controlling how these things happen, crystal size can be controlled, making the product easier to manage.
Crystallization is usually done in batches, but by having a continuous inflow and outflow, lots of data can be gathered.
This data can be related to other systems using a computer model to describe fluid flows and the number and size of crystals as they grow.
Complicated equations describing these things can be simplified by breaking them up into lots of simple equations in a grid.
To begin with, they give a picture like an 8bit computer game, but as the resolution is increased, the picture becomes more like an HD movie.
We stop at the point where we can’t tell the difference between what the computer tells us and what we see in real life. So far, by telling the computer what conditions we’ve used, we’ve been able to predict the size of crystals to within 1/60th of a millimetre, which is pretty good. By reversing this process, we can tell the computer what size crystal we want and it can tell us the best way to make them.