Robyn Williams: This is the sound of flowing water of course. I'm sitting next to a pair of rather nice fountains, and with me is Dr Amanda Ellis who is actually working on desalination techniques which we've heard about a great deal and they usually involve membranes and quite a lot of technology and expense even. But Amanda, you're working on a nano-system involving carbon tubules, is that right?

Amanda Ellis: That's right. They're carbon nanotubes, and essentially they're rolled up pieces of graphite. So graphite is atomistically smooth, so when you roll it up into a cylinder the inside of the nanotube is atomistically smooth, obviously, that means that it's very hydrophobic, so it hates water. So once we can put water inside it, it just shoots straight through, and we call that ballistic transport.

Robyn Williams: 'Ballistic', that sounds very violent.

Amanda Ellis: It is. Well, if you imagine firing a gun, the bullet doesn't touch the side walls of the barrel of the gun, and that's pretty much what water does, it doesn't touch the side walls, there's no interaction, no drag, and so there's no energy transfer to the walls or from the walls and so it just fires straight through.

Robyn Williams: But doesn't it take the salt with it?

Amanda Ellis: No. That's a good question. You can make nanotubes of all sorts of diameters. So essentially we'll have nanotubes that are around about 0.6 of a nanometre, about 100,000 times smaller than the diameter of a human hair. And so what will happen is the water will enter but that will cause the sodium ions and the chloride ions to remain outside of the tube because they've got a hydration shell around them.

Robyn Williams: I see, so they are separated from the water. But won't they accumulate pretty quickly and stuff things up?

Amanda Ellis: Yes, they will, and that's the idea. So the idea is that we have these carbon nanotubes in a polymer membrane, the carbon nanotubes are vertically aligned, so they pass the salt water over the top, the water will ballistically transport through at about 1,000 times faster than conventional membranes. The only thing we need to do is apply pressure to start the water flowing, after that we don't need to apply any pressure, the water will just pop straight through. And because we've got the sodium chloride ions remaining on the surface, then we just have a cross flow. So we just flow them off and...

Robyn Williams: Skim them off.

Amanda Ellis: Skim them off, so to speak, yes, kind of.

Robyn Williams: I see. And what kind of purity of water do you get out the other end?

Amanda Ellis: You would get pure water, 100% pure water. We'd expect the exclusion of sodium and chloride ions to be almost 100%. It's easier obviously to model this than it is to actually do it experimentally. At the moment we're doing it on a reasonably small scale, so we only get a couple of millilitres of water coming through and so we can test the conductivity of that water and it's usually nothing.

Robyn Williams: So it's a case of scaling up from very tiny to extremely big.

Amanda Ellis: But one of the advantages of what we're doing compared to other people throughout the world is that we're using chemical methods to create these membranes, we're not using conventional chemical vapour deposition of carbon nanotubes, that's usually how they're made...what happens is you put a vapour into a furnace, say toluene or some sort of organic solvent, and then that will nucleate on tiny little particles in the system and the nanotubes will grow like grass.

Robyn Williams: Are you suggesting the nanotubes come cheaply?

Amanda Ellis: They do now, yes. The Chinese can make them in kilogram quantities. Say if you've got a membrane a metre squared you might have ten milligrams of carbon nanotubes, so they're cheap, yes. If you want a kilo you can buy it for easily $50 or something like that.

Robyn Williams: That sounds most impressive. Surely someone has done the estimate, if you were to scale up to make a plant that would serve, say, half of Adelaide, providing water, how much money would you save on conventional desalination plants in terms of energy and money?

Amanda Ellis: In terms of energy you'd probably be lowering it by 90% because you're not having to apply pressures. In terms of cost, savings, again you're probably talking about 50%. The advantage of what we're going to be doing is that we're going to be producing water...instead of 86 litres per metre squared of a traditional membrane, it's 86,000 litres per metre squared from a membrane, given the same time period. So we're going to be using less energy to do that and obviously less material. One thing that the membranes now...they're around about, let's just say, 0.5 of a centimetre in thickness, we're talking now about making membranes that are about at least 1,000 times thinner than that. So we're using less polymer, therefore there's less polymer waste which means that we'd need less transport, so less energy in terms of transporting around the waste membranes or transporting them in. I can't really put a particular number on it but there's definitely considerable...

Robyn Williams: Big benefit. At what point will you actually scale up from your mini laboratory model to something that might be able to do the job out in the world?

Amanda Ellis: Well, if the world was a perfect place and everything goes smoothly, definitely we would be looking at within the next five years to actually having an extended membrane system that we would be testing in just like a portable desalination plant. Basically after that point it's about manufacturing, can manufacturers upscale.

Robyn Williams: Any rivals in the world?

Amanda Ellis: At the moment, no.

Robyn Williams: So you've got the field to yourself. Do you think you might have given the game away by telling the secret of how it might work?

Amanda Ellis: No, I don't think so because at the moment, like I say, most people are concentrating on the chemical vapour deposition, so the growing of the nanotubes, and then somehow getting them into a polymer. The problem with that is there's not a very strong binding between the carbon nanotube wall and the polymer, and so water can leak down through them. So that's one of the disadvantages. Our system, we're growing the polymer from the carbon nanotube wall.

Robyn Williams: What made you think of it in the first place?

Amanda Ellis: That's a very good question. What we were doing was we were putting in a grant, and the three of us...so there was myself, Professor Joe Shapter and Professor Nico Voelcker at Flinders University, we sat down and we came up with the idea and the concept of it, we put in a grant, we got funding for it, and so we're going from there.

Robyn Williams: I know that lots of people have been wondering about the future of nano and thinking, well, if we've got something so close to us, as in our water, what if lots of little bits of nano come off into the water, will they affect our health? Do you know about the answer to that?

Amanda Ellis: That's a very good question and many people have asked me that, in fact. The answer to that is in two parts really. The first part is that when carbon nanotubes are functionalised, so when we change the outside of the tube, the graphene tube, it tends to be end up being less cytotoxic. There's been demonstrated research that in fact these are less cytotoxic when they're functionalised. They can't enter into a cell. And the other thing is that our nanotubes that are in the membrane are very short, so if you're talking about asbestos (because I think that's where you're leading), asbestos...is mainly based on its aspect ratio, it has a very long length to the width of it, whereas with our carbon nanotubes we're talking about a much shorter length to the width. And so to try and get them to spear into cells to cause damager is a lot more difficult, and when they're functionalised it almost doesn't happen at all.

Robyn Williams: Congratulations, it sounds intriguing.

Amanda Ellis: Thank you very much.

Robyn Williams: Dr Amanda Ellis from Flinders University in South Australia, ballistic water, purified at half the cost and tens times the speed, if they get the theory to work in practice.