technology waste

How is Bill Gates getting on at reinventing the toilet?

A few years ago I wrote disparagingly about Bill Gate’s Reinvent the toilet challenge, after it declared a hydrogen fuel cell toilet the best innovation to bring toilets to the 2.4 billion people without one. I haven’t come back to the competition since, but there have been further rounds and the Gates’ have invested millions in alternative toilets of one kind or another since. I thought I’d better check in again, and there are now some really good ideas on the list. I was also pleased to see that there are a variety of local challenges and trials in various locations, as there isn’t going to be a one size fits all solution.

2.4 billion people without a toilet is a huge challenge, especially since we can’t roll out flushing toilets everywhere. There isn’t enough water, and the sewers and treatment plants would be prohibitively expensive. If climate change brings more drought, those lucky enough to have a flushing toilet today might start to wonder why such a wasteful technology became so commonplace.

I’ve featured a bunch of waterless toilets before, and there are quite a few in the Gates programme that I could mention. I’m going to go with this one because it’s from Cranfield University, which is practically local. It’s called the Nano Membrane Toilet, and here’s how it works:

I have a few questions about this still. The challenge was to build something that doesn’t need a water, sewage or electrical connection. Is it powered by the poo? Because I see an incineration process in there, and that must be energy intensive. I don’t suppose paper can go through the archimedes screw, and if it got jammed it would be a nightmare to unblock.

On the plus side, I love the simplicity of closing the lid, and all those cogs flip round underneath to clean it. If it does work self-contained, then you could deliver it and stick it in an appropriate room like a piece of furniture – no plumbing or installation required. If I ever live the middle class dream and install a downstairs toilet in my house, I’d like one of these.


  1. Thanks – interesting. I think the aspirational aspect is very important. I spent time with some very knowledgeable indigenous NGO leaders in Nigeria, who told me there are many ‘long drop’ toilets there (far more hygenic than defecating in the open) but people are rarely willing to use them. So the motivation aspect is crucial. Dried faeces would have a high energy value, so combustion should be self sustaining, but would require some electrical or other power to get it started; there’s also the issue of carbon monoxide from indoor combustion, and the mechanical complexity; will it really be maintanable. I guess I need to study the small print of technical/operational feasibility studies…

    1. Compost toilets are smelly in hot countries (unless very well designed and constructed, maybe) and people often don’t like them (see comments above). Also (again depending on design and construction) they can be a health risk unless the right management procedures are rigorously followed. It’s one thing to advocate them among healthy affluent people, but among people with already fragile nutrition and health, where life is often very chaotic, you really have to be careful to ‘first do no harm’. People often do die of diaorhhea.

      1. I was reading about sea level rise recently, and one of the big issues is flooding of cess-pits and septic tanks. The polluted water creates a massive health risk. In any place where there is a risk of flooding, you want a toilet that processes waste on the spot rather than letting it build up. Composting or dehydrating toilets will be a good solution in some places, and in others something more like this would be safer.

  2. I have the same question regarding the incineration process. And the paper. Are they assuming this would be used primarily in locations where paper isn’t? All paper wouldn’t sink with the poo, so how is it guaranteed that the paper wouldn’t block the pee filters?
    I did hear that they collect the filters for regeneration, which means they must be reusing them. That’s a very cool feature.
    Overall, I like the idea. I would like to learn more about it. Go do some investigation, Jeremy…

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