The Nano Membrane Toilet

Current toilet designs are not meeting the needs of 2.6 billion people on earth who currently lack access to safe and affordable sanitation. Many of these also have non-existent or unreliable water, sewage and electricity supplies. The team at Cranfield University has been challenged to "Reinvent the Toilet". They propose a concept for a Nano Membrane Toilet which will be able to treat human waste on-site without external energy or water, allowing it to be safely transported away and potentially reused.

The toilet will accept faeces and urine as a mixed stream. Volume reduction of urine and faeces will be undertaken using dense polymeric membranes that enable extraction of the water content as a vapour through the membrane wall. These membranes will be used to thicken the sludge to a target solids content of between 20% and 25%. The membrane wall comprises a low glass transition temperature (GTT) dense polymeric structure which enhances the membrane’s permeability for water vapour. Unlike with conventional membrane separation, these membranes separate water vapour through a solute-diffusion mechanism which requires only a very small vacuum pressure to be applied. This vacuum pressure will be generated by a user-operated handle. Since the membrane is nonporous, the resultant distillate (transported water vapour) will be pathogen-free water. The resultant sludge will move downwards through the toilet under gravity before encapsulation as a briquette with fuel or soil nutrient potential. The recovery of water and unionised ammonia from the vapour is made possible by the application of nanotechnology-derived super hydrophilic beads to process the extracted water vapour from the vacuum distillation unit.

The sludge briquettes will be encapsulated using Electrohydrodynamic spray atomisation. The polymer to be sprayed will be ε-caprolactone and will also incorporate a nanomaterial with bactericidal properties (e.g. Ag or TiO2). This will establish a physical barrier between the sludge and the environment as well as killing some of the bacteria. The advantage of encasing the sludge with a fibre mesh, compared to an impervious coating, is that water vapour is able to escape from the briquette facilitating further drying. An alternative to using virgin polymer would be to use disposable plastic bags. Plastic bags are widely used in peri-urban areas, and make up a large proportion of solid waste.

Overall the output from the toilet would be pathogen-free water and sludge briquettes for combusting or applying to land as a fertiliser or combusting.