Thursday, 21 February 2013

We need to talk about poo

Like most of you, until recently I had never paid too much attention when I went to the toilet. I did my business, pressed the flush and never saw it again. Out of sight is out of mind. When I was living in Rwanda I heard from friends about a German man who no longer flushed and instead used a bucket. My immediate reaction was to laugh, and then laugh some more. When I met Jan, the man in question, I laughed yet again at his idea. How could that be sensible? Does it not stink and attract flies? After a few months I visited his house and saw his toilet. I was surprised that it looked pretty normal and that there was no smell and no flies. In the end I moved in with Jan and was able to become a 'bucketeer' rather than the 'flusher' I had been before (and unfortunately am again) for a few months. The system was extremely low-tech, essentially a bucket and sawdust:

When the bucket was full it was emptied into a compost heap that heats up to around 60 °C, killing any pathogens in it.

So why am I writing about my intimate experiences with a bucket on a blog about farming? Every day we each empty around 15 grams of nitrogen into the toilet, whilst this doesn't sound much, it adds up to 5 kg per year. Recalling from my previous post that globally we each use 15 kg of nitrogen fertiliser of which 50 % is wasted, you can see that we are throwing away a resource that could be used to grow a considerable portion of our diet.

After a few months on the compost heap, mine was ready to fertilise the coffee crop that I will be drinking next year:

Before sewers were developed, most of the human waste cities produced was returned to the land. Doing so allowed Chinese farmers to farm the same land for four millenia and in Tudor England Gong farmers would empty latrines and transport the 'night soil' to the fields. Doing that had it's drawbacks, mainly because it was very effective at spreading disease. Incredibly, 1 million people in India are still being paid to empty latrines by hand. Society has benefited massively from the development of sewers, but they are not the optimal way to deal with our waste. As well as all the nutrients lost, flushing the toilet uses a lot of water - around 10,000 litres a year which is around 25 % of our water use. This isn't just a waste of water, but it also makes retrieving the nutrients from the sewage more difficult as they are so diluted. Putting it into perspective, every day the water and nitrogen we waste could grow about 3 kg of potatoes.

The nitrogen cycle of the UK. The top right arrow labelled '???' shows just how much nitrogen is being wasted. (And no I don't have a scanner)
You can see in the diagram above that a tiny part of the nitrogen we eat does end up back in the soil for crops to use. This is as sewage sludge though which is very different to compost. We put all kinds of nasty substances into the sewer system and these end up in the sludge - it's not a great idea to start adding heavy metals to farmland. Speaking from personal experience (it used to be dumped close to my house) it also stinks since it doesn't have the correct carbon:nitrogen ratio like a compost.

Precious little has been written about recycling human waste in the scientific literature. Geographers have written about it recently but seemingly microbiologists and agronomists have not. As a result, we have little idea of how to handle our waste safely while maximising its value. I am 99% certain that a system as simple as Jan's will never catch on widely here in the developed world. Our fecophobia is so severe that people aren't going to be persuaded to swap their flushing toilet for a bucket. What's needed is a radical redesign of the toilet so that it looks vaguely similar but is no longer wasteful. You might have read in the news that people are starting to think about reinventing the toilet, stimulated by funding from Bill Gates. They are concentrating on the developing world where the need for sanitation is the main priority, but hopefully some of them could be transferred here. It would certainly take some savvy marketing to get people to change their habits... perhaps Apple can get behind it and develop the iCrap? There are already some interesting products out there such as this freezer toilet but that still leaves the composting problem. I don't feel completely crazy envisaging a future where we freeze our waste and it is then collected from the kerbside with the rest of our rubbish. Other people have had more barmy ideas like powering robots with it, feeding it to maggots to make food for livestock or even turning it into burgers (you thought horse was bad)!

The recycling of our waste is a perfect example of an old technology that has almost been abandoned but which could substantially improve the sustainability of our farming system. Since I began writing this months ago, some interesting articles have been written by Fred Pearce about a few scientists that are working in this field. The future is looking brighter. In my next post I'll discuss genetic modification which in many ways is the polar opposite - comparatively a very young technology which, although widely used is feared and ill-understood by large portions of society.


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