P from Pee

P from Pee

Busting for a leak? Dying for a crap? These expressions may well take on new meaning in a not too distant future where our food is grown from the nutrients we excrete as by-products of our metabolism.

Phosphorus (P), a plant nutrient that we rely upon heavily for global food production, is a FINITE resource with nothing that will ever replace it. Plants need P to grow, we can’t substitute this nutrient like we can substitute coal fired power for solar. Peak Phosphorus is, by all accounts around 40 years away. At this point, Phosphorus will begin to cost a lot more than it currently does, as the easy to mine mineral deposits will have all but disappeared. Planning the transition to nutrient recovery needs to begin now, and the first thing we can do is ask ourselves how we can reduce the consumption of P in the first place. Stangely enough, the best answer is to eat more plants, since 80% of P fertilizer is used to grow feed for meat and it isn’t rocket science to realize that meat doesn’t account for 80% of the full feeling in our bellies. Reducing consumption of meat to say, Victorian times, (about a sausage a week) would go a long way to helping prevent climate change and preserving our Phosphorus deposits for future generations to use on their crops. It wouldn’t do our overall health a disservice either.

Another way that we can reduce P consumption is to increase the value of the food grown by not being too fussy about its shape, size, colour etc. So much food is de-valued because it does not meet the standards that we as consumers have unwittingly set for ourselves. At best, ‘ugly food’ ends up being used for a lower value product, at worst, it goes to landfill where it produces more greenhouse gas emissions whilst it rots. Eat ugly and send the message to the market that it’s ok for food to be ugly.

Once we have cooked up our favourite ugly vegetarian delight, there will always be the bits we can’t eat. The best way to recover the nutrients from food scraps is to either feed them to a worm farm or compost them so as the P becomes food for microorganisms which benefit the soil into which the compost is used. The soil food web then shares back all the nutrients with the plants and the cycle is completed.

Of course it doesn’t stop at the table. One person excretes enough nutrients (N, P and K) to grow their yearly supply of bread, so best we find a way to get at that before the bakery runs out of flour. The simplest approach is to have a composting toilet, which is fine if you have enough garden and space for one. Again, the nutrients feed the compost food web, which in turn feed the garden and plants. At some stage though, we will have to recover bulk human and animal urine and mix it up with some fancy (luckily abundant) minerals to produce a cystalised fertilizer called Struvite.

So one day when you ask me if I am taking the piss, the answer will be most definitely yes.


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