When the Gates Foundation first announced its $42 million Reinvent the Toilet Challenge I took so much abuse for my post Gates Foundation Throwing $42 Million Into The Toilet. Fortunately we changed commenting systems and all of them were flushed away. Then the first winner was announced and it confirmed everything I worried about- it was so complex, a standard toilet on top of a sewage system that would be at home on the Space Station.
Now we have another new toilet design from Cranfield University in the UK, described as "a household scale off-grid toilet which produces clean water and ash." It has also been described as a " power-generating ‘super-toilet’ that doesn’t need mains water and can charge your phone." I will confess that I have spent quite a few hours trying to figure out how it works; the Cranfield site explains it thusly:
The toilet flush uses a unique rotating mechanism to transport the mixture into the toilet without demanding water whilst simultaneously blocking odour and the user’s view of the waste.
Well, not exactly. The mechanism is clever, maintaining a constant seal, but while you are using it the poop is sitting right under you without any water covering it, and it is going to smell during the process of elimination. Anyone who has used a German shelf-style toilet or a squat toilet will know what I mean. One is not, as they show in their photo, going to put this in your living room. Once you are done and close the lid, it does rotate and seal any smells from below.
Solids separation (faeces) is principally accomplished through sedimentation. Loosely bound water (mostly from urine) is separated using low glass transition temperature hollow-fibre membranes. The unique nanostructured membrane wall facilitates water transport in the vapour state rather than as a liquid state which yields high rejection of pathogens and some odorous volatile compounds.
The video explains that somehow pure water floats on top of the poop and then filters through the membrane. The blog suggests that "faeces will settle to the bottom of the holding talk and urine will be removed from the top using a weir."
A description on the SuSanA site describes a vacuum pump to lower pressure, which would create vapour from liquid:
Unlike with conventional membrane separation, the pervaporation process requires only a low vacuum pressure to be applied. The water that crosses the polymer membrane is then condensed on super hydrophilic nanobeads and flows to a distillate store for later use in washing or irrigation.
Earlier reports on the toilet claimed that "heat from burning the waste produces enough electricity to power the unit, and could even produce a little extra for mobile phone charging" and the drawing shows a "gasifier to combust water (?) and generate power"; The most current version on their site appears to say otherwise:
the residual solids (around 20-25% solids) are transported by mechanical screw which drops them into into a coating chamber lined with a replaceable bag. Once inside the coating chamber, the solid matrix is periodically coated with a biodegradable nano-polymer. The nanopolymer coating serves to block odour and acts as a barrier to pathogen transport. The toilet will be powered using a modular hand crank or bicycle power generator supplied for household use that can also power other low voltage items (eg mobile phones).
In fact, the video explains that the poop balls are coated in paraffin wax which are then picked up by the guy with the service contract and taken away to "a locally sited small scale gasifier sized to accommodate around 40 toilets."
As for the pee that has been separated through those nano-structured membrane walls,
A novel nano-coated bead enables water vapour recovery through encouraging the formation of water droplets at the nanobead surface. Once the droplets form a critical size, the water drains into a collection vessel for reuse at the household level in washing or irrigation applications.
Does this all make sense?
Now the Cranfield team has done a lot of work on this, and has put together a group of serious experts on membranes and other technologies. But I go back to the arguments that I have made since the Gates program started.
Let's start with the pee; had it been separated in the first place, it could have been used directly for irrigation, and the valuable phosphorus in it could have been put to work. There is absolutely no need to put it through nano this and nano that- it is useful stuff in its original form.
Then there is the poop, also useful stuff. Had it been collected in a standard composting toilet, it could have been used as... compost. Or there are many other designs where the poop is collected and taken to a digester and turned into fuel. I does not need to be dried, turned into little balls and coated with wax. Really.
On Gizmag they describe this as "a cheap waterless toilet that turns waste into clean water and power " But lets get real: It will not be cheap; It has batteries and generators and pumps and "nano-coated hydrophilic beads". It is an extremely high tech device. It has also been over-hyped; everyone is excited by the fact that is purported to charge your phone. It's clear that the gang at Cranfield University have worked really hard and there is some sophisticated stuff going on here with semipermeable membranes, but it seems that the PR department has got out of control.
Building a toilet shouldn't be rocket science. But so many of the Reinvent the Toilet Challenge treat it like it is. The Nano Membrane toilet definitely is rocket science and I hope I am wrong, but I fear it will suffer from a failure to launch.