Hi Isis,

Sorry, should have explained further - the membrane is also hydrophobic so is not wetted.

Thanks Alisson for this. However, in order to form a biofilm in addition to the obvious microbes, a surface, moisture and a substrate are needed. It seems to me that all of these "ingredients" will be present on the retentate side of your membrane. What you are describing is not very different from most conventional membrane applications. Not sure I follow how there will be "no risk of biofouling."
From what you describe it seems that once the water passes it will be in the form of vapour, but before that it could be potentially available for a biofilm, no?

Hi Isis,

Yes, we'll exclude all microns - they are much too big to fit through the membrane! There is no risk of biofouling as the water passes through the membrane as a vapour.

We see the business operating as a franchise. There will need to be a certain number of toilets within a geographical area for it to be profitable, so I think they would have a monopoly for that geographical area.

Alison

Hi Alisson,
Thanks for your email. Your idea sounds amazing, btw!
So, from what I got from your explanation, the pervaporation process is akin to a membrane filter. In this case, as you are excluding most microbes, what is the risk of "biofouling" your pervaporator? How will this be addressed?
Nanotechnology, pervaporation and electrohydrodynamic spray atomisation aside, how easy will this design be scalable? That is, do you envision someone being able to replicate it as an open source technology or will there be a "monopoly" of the market by the business that has the specialised knowhow? (not that a monopoly is necessarily a bad thing)

Hi Isis,

Yes, I'm the PI, so I'll try to answer your questions.

There's a photo of our works-like prototype on our blog:

nanomembranetoilet.blogspot.co.uk/2013/1...nearly-finished.html

The looks-like protoype is in the final stages of the design so I'll post an image of it soon.

To define the terms simply:
Pervaporation is a process by which water molecules are transported through a thin membrane wall. Pathogens and large molecules are excluded. This allows us to extract almost pure water from the waste, though that water is a vapour.
Super hydrophilic nanobeads are glass beads with a nanotechnology coating to which water vapour is attracted. When enough water has been attracted it forms a droplet which then drains downwards through gravity. We collect this water so it can be used in the home.
Electrohydrodynamic spray atomisation is a process by which very small bits of plastic (polymer) are sprayed onto the sludge. This stops odour and pathogens escaping.

The cost of the toilet is estimated at $750, though this does not include the gasifier that we are hoping to develop in the next phase of the project to extract the energy from the waste and complete the pathogen kill. However, we don't expect households to shell out this money upfront, rather it will be recouped through a service plan which as well as covering the capital costs will also cover the removal of the sludge, the servicing of the membrane and beads and the replacement of the polymer.

Compromises - I think the main one is the realisation that the dewatered material from the membrane may not have sufficient structure to stay together as a briquette. We've added a dewatering screw press (we needed this to move the material through the toilet anyway) and we're now going to collect the sludge in a bag rather than as a fully sprayed briquette that could be handled. We would also like to develop a community scale gasifier which will be fed by this waste so we don't really see this as a compromise. The remaining challenge is to reduce the energy demand of the whole system so it can truly operate off grid eelctricity, powered by our human generators .

I hope this answers your questions but happy to answer more!

Hi Alisson,
Are you the principal investigator?
"The university received $810,000 funding from the Bill & Melinda Gates Foundation in August 2012 to produce a prototype in the UK by the end of November 2013."
Can you give us a sneak preview of the prototype? We are almost in November...
How would you explain "pervaporation", "super hydrophilic nanobeads" and "electrohydrodynamic spray atomisation" to a layman?
Do you have an idea of the projected range this is expected to cost?
Also, this project seems very ambitious (and it should considering the scope of the challenge), but I'd like to know, now that you are a year in, what compromises have you had to make in view of the initial idea and the practicalities of making this into a real system?
Thanks in advance...

Hi Naomi,

Thanks for your question. Actually, we are now moving towards combustion/gasification as our final treatment method for the sludge so the biodegradability of the polymer will not be an issue. But you're right - using recycled bags would be a problem for biodegradability.

Alison

PS Keep up to date with what we're doing on our blog:

nanomembranetoilet.blogspot.co.uk/

Hi Alison,

I shortly want to go back to Massimo’s comment on the introduction of plastic to the ground through the briquette coating.

You mentioned that the coating you are using is biodegradable and that you were also considering recycling plastic bags as a coating. Those are generally not braking down fast and are not “biodegradable”. Are you still considering the recycling option bearing this in mind? Or would it require additional treatments to make the plastic biodegradable?

I have little knowledge in this field thus the answer might be obvious – still I am curious!

All the best,

Naomi

See the latest blog post about the team's trip to Ghana to see sites where the Nano Membrane Toilet might be used:

nanomembranetoilet.blogspot.co.uk/2013/0...o-see-challenge.html

The video of my presentation in Durban is now online if anyone wants to see it:

Please do stay in touch. We have an extensive research activity on membranes so may be able to help out with your future research.

Thank you for your answer.

It is interesting to notice that you can concentrate urine with your membrane.
I work myself to develop a urine separation toilet without problem. I know that urine treatment (reuse or other) is the problem now in my case.
I keep that in mind when I try to star new research on urine treatment.
Thank you

Emmanuel
Ecodomeo