Applications of Nanobubbles

Hello, welcome back to Nanobubbles 101. And once again, I'm Niall English, co-founder of AquaB and Chief Technology Officer, as well as a professor in chemical engineering at University College Dublin. And my research interests and commercial interests now in many cases revolve around Nanobubbles.

So in this particular episode, I want to discuss applications of Nanobubbles, of this platform-wide technology, and in such a way convince you as to why I believe Nanobubbles are very important, not only for the environment, but for wider industry and industrial applications. So before we delve into too much detail on industrial applications, we can do a quick recap on the history. I don't really have a lot to say here because there really hasn't been much extensive history of Nanobubbles research.

And as I said in the first introductory episode, it's really only the past 10 to 15 years since around 2010, that has been more in-depth research done on Nanobubbles. For many years, they weren't taken seriously, I would say, due to the Epstein-Plessé theory of bubbles. Predicting their stability for perhaps no more than micro to milliseconds.

However, we all know now, belatedly, only in the past 10, 15, 20 years, that that's not necessarily true at all, and that Nanobubbles may well persist for minutes to perhaps months in certain situations due to their meta-stability. And their lifetime, as we discussed in the previous episode, the second episode, depends on many, many different things, such as zeta potential, the overall population, perhaps the level of salinity and pH of the water, as well as just their structural makeup and electrostatic personality and their own density as well. So really, a whole suite of different factors influences their lifetime.

We're really sort of dependent upon laser light scattering methods to show that Nanobubbles are there. There are other variants and other methods, but those are the ones that are most popular. And then quite often we can get mistake particulates for Nanobubbles and can't see the one for the trees.

So sometimes there is always that sort of question mark. And sometimes we're always a bit of a doubting Thomas to wonder if there really are Nanobubbles present. So one has to be very careful to say that definitively.

But in all of these applications that I'm going to discuss in the current episodes, exciting as they are, they all hinge upon essentially one or two really important physical characteristics, such as the level of dissolved gas. So the dissolved gas might be dissolved oxygen, or it could be dissolved carbon dioxide, or whatever other gas we wish to deliberately and willfully introduce into the system for our particular application. It could be hydrogen, it might be nitrogen, et cetera, et cetera.

So, I mean, an obvious place to start is dissolved oxygen, and quite often oxygen in water, that definitely accounts for many, many different applications, both environmentally and industrially. So dissolved oxygen, or DO for short, is something that we typically want to boost. In many cases, the level of DO is below its thermodynamic level that it should be at, at the given temperature.

In other words, Henry's Law. So for air in contact, just the atmosphere, in contact with water and atmospheric pressures, the DO level should perhaps be at 25 degrees Centigrade, about 8.5 milligrams per liter. At higher temperatures, it would fall at 35 or 40 degrees.

It should fall down to the order of 5 to 6 milligrams per liter and so on. And that's why we often see fish kills, for example, happening in the summertime. As I said in the first episode, as temperature goes up, the level of Henry's Law, DO goes down.

And that's quite often why we see, say, fish, for example, trout dying at extreme heat in the summertime. So if we could really add nanobubbles of air, oxygen, but air is cheaper than oxygen, at least it's free for now, we can then introduce air to boost the level of DO in, for example, reservoirs, estuaries, lakes, or wherever there might be fish as well, for example, in fish farms. And it's similar for in agriculture where we want to grow plants and vegetables and so forth, crops, we can boost the level of DO.

Because quite often water isn't actually at its thermodynamic law, Henry's law level. So for example, if Henry's law, eight and a half milligrams per liter at 25 centigrade is the level for air, that would be 100% DO. In many cases, we're way below 100% saturation and the level of DO may be 50, 60%, sometimes less of what it should be at a given temperature.

So for example, in an activated sludge water treatment plant, a good level of DO that we would wish to maintain would be of the order of three or maybe three and a half milligrams per liter to have a reasonable level of aeration to feed the microbes in the activated sludge process. And quite often, because of the very strong biological oxygen demand, BOD, by definition present in these activated sludges, we need to really boost the level of oxygen going in, which is why we have these big mammoth blowers at water treatment plants, spending probably about several percent of the world's electricity just on aerating bubbles into water, and those larger bubbles leave the water within a minute or less than a minute and just aren't there for long enough to transfer their sacred cargo or their sacred treasure of oxygen into the regular dissolved state. And the oxygen transfer efficiency there for established aeration methods may only be 3, 4, 5, 6, 7 percent.

If you're using microbubble generators in situ, it might be of the order of 10 to 15 percent, which is clearly better than 3, 4, 5 percent, but it's still very energy intensive in generating with current microbubble generation technology. So being able to use nanobubbles that we generate, say, by whatever method, especially with the energy efficient electric field method, can really boost the level of oxygen transfer efficiency, not because nanobubbles themselves are inherently better at transferring their cargo of oxygen by fixed law into the surrounding regular dissolved oxygen phase, but simply that they're around for longer. So if nanobubbles persist, perhaps for the limit of their lifetime, which could be minutes, it could be months or anything in between, many hours, then at least nanobubbles are simply there in the water for much longer than 30 seconds and actually have ample time to transfer as much of their treasure, if you like, of oxygen by fixed law from themselves to the surrounding water where they can be gobbled up by the hungry chemistry or biology that is feeding the chemical or biological oxygen amount, in other words, the COD or BOD.

And one could say the same thing about, say, dissolved carbon dioxide. For example, if we are growing algae, certain strains of algae were involved in algal culture, we want to just have carbon dioxide being fed into the water in the form of bubbles, but rather than larger bubbles of carbon dioxide that are millimeters in size or fractions of a millimeter, these macroscopic bubbles, if we can convert a fraction of those into nanobubbles and have those stay in the water for much longer, again, they simply have more time to transfer their pressures, cargo of carbon dioxide, into the regular Henry's Law level of CO2, simply because they're around in the water for much longer. So in that way, we have to input less CO2 into the system, less CO2 escapes the atmosphere, and we have a much better gas transfer efficiency.

So whatever the dissolved gas, whether it's hydrogen, oxygen, nitrogen, carbon dioxide, ozone, etc., etc., we can really boost the lifetime and the stability in the form of nanobubbles and these nanobubble reservoirs, if you like, transferring their precious cargo or treasure into the dissolved gas phase, the regularly dissolved gas phase from the nanodesolved gas phase to replenish, if you like, in a self-correcting feedback loop, the level of Henry's law dissolved gas by Fick's law, which is the chemical potential driving force gradient from the nanodesolved phase into the regular dissolved phase.

Now, whilst we've spoken about some of the bedrock scientific principles, and I have no wish to alienate more sort of layman type listeners with that, I think it's essential for us to start talking about applications, which I want to do now. So a good place to start is perhaps with the bodies. We can talk about maybe human bodies, we can talk about maybe animals.

So it's actually been found in some, I think, trials of cyclists in the past couple of years that if they were drinking air, I think it was oxygen, it was either oxygen or air nanobubbles in water, that their cycling performance went up, I believe, of the order of three, four percent, something like that, which of course is hugely important in elite cycling circles, that the performance could be boosted by several percent in terms of racing times by nanobubbles, because the nanobubbles that were there in the water they drank was able to pass directly into the bloodstream, where you have this extra cargo, if you like, of oxygen being available from this reservoir to pass into effectively saturate beyond normal levels, the normal levels of dissolved oxygen in the blood, so the hemoglobin was enhanced in terms of its performance. Equally, if we look at, say, animals, there's some preliminary evidence that nanobubbles in drinking water for animals may help out potentially with the gut microbiome reactions and can help with rumination reactions, for example, in cattle as well. It can help with the thermodynamics and kinetics of some of those rumination chemical reactions going on in cattle's stomach as well, which of course mimics anaerobic digestion plants that we have on the go as well ourselves, which are a bit mimicking like what happens in a cow's stomach.

So we can just look at animals and humans' response to nanobubbles to get a good idea of how this reservoir effect, where we can impart our sacred cargo of gas, how this can have immediately beneficial effects. Moving on to environmental and industrial applications, maybe we can start off with environmental, because that's an area very close to my heart personally. I'm very much a green environmentalist at heart.

But I think we can achieve, using Nanobubbles, very strong environmental returns without necessarily sacrificing economic growth either, which is what really excites me as well about Nanobubbles in terms of sustainability. And for me, of course, a big area is water treatment. So if we can reduce to, say, 4 to 5% of electricity demand that water aeration is currently using worldwide, especially when we add in some fish farms and irrigation, I mean, we're putting, by William, in mankind, we're putting in about 4 or 5% of global electricity into bubbles that just rise out of the water and escape into the under of the atmosphere within a minute or so.

So if we can have Nanobubbles being produced in conjunction with the set point, say, for a dissolved oxygen level that we wish to maintain, the set point, or perhaps Goldilocks, we might call it, of about desired level of about 3 mg per litre, then the Nanobubble generator can be there, and the regular water blowers and aeration infrastructure should still stay there, of course. That can just be switched on and off on a feedback control system or relay switch, as and when the DO level would drop below the desired set point, for example, 3 mg per litre. But the point is that these blowers will be on for less often, because if the Nanobubbles are residing in the water and aren't escaping by Stokes law, so they have long enough to prop up Henry's law, if you will, then that very much is a good thing that can reduce the energy demand for water aeration, especially activated sludge tanks, very substantially.

Also in terms of dissolved air flotation, because Nanobubbles are so small, they have a much better surface area to volume ratio, and therefore can really enhance the level of flotation very, very substantially, because effectively what happens is that the Nanobubbles are electrostatically active, and they effectively attract things in the water. Now, what might things be? Well, it can often be charged species, salt ions, particulates, nanoparticulates, microparticulates, pieces of electrostatic dirt, if you will, and impurities.

And they all cling on to, let's say, virgin naked Nanobubbles to create a microscale colony. And then these microscale colonies can rise up and float up to the top much more easily. Because if something is on the microscale, well, you can't evade buoyancy and Stokes law forever.

So once you get to the micron scale, the Nanobubble is now the center of a micron size colony, and that rises up all the more easily. And this, of course, can be very important for downstream flotation operations in mining, where we want to separate, say, various tailings from water coming out of mining operations. Of course, being able to harness the reactive oxygen species that we have from Nanobubble generation, especially by electric field methods or electrostatic methods, then that can really boost the level of plants and plant growth and also help to fight some infections, for example, sea lice and so forth.

That's a benefit to both agri and aquaculture. Other areas would include, for example, ozone nanobubbles. So we found, and that could be anyway, that we can effectively increase the half-life of ozone eight to tenfold from its regular half-life of 20-odd minutes in water when it's in standard molecular form.

So this can also help out with disinfection and water cleaning and pesticides possibly as a pesticide alternative. So there really is quite a wide variety of areas in the environmental space and industrial space. Looking at oil and gas, for example, we can use nanobubbles that can be infused into frac water or frac juice alongside our surfactants or our multiplying agents, our salts and so forth.

And that can be injected by the high-pressure wellhead pump into the well. That can, I suppose, penetrate rock more easily due to lower surface tension. There's a thermodynamic effect of shifting the thermodynamic goalposts if you have a higher level of dissolved gas, for example, dissolved CO2 in nanobubble form.

The kinetic effect of reaching intercalated oil in the rock and sediments much more easily in the pore structure by lower surface tension. And this can lead to well stimulation, faster kinetics of oil liberation, gas liberation to really help fracking and ultimately the ultimate yield as well of the hydrocarbon release. So this is another very important area.

Fermentation, of course, boosting dissolved oxygen level there and some reactive oxygen species. It's very important. It can be used in alcohol production.

Even nitrogen nanobubbles as a preservative for beer or milk or other downstream operations where we can really extend the shelf life of beverages as well. Not to mention reactive oxygen species helping to oxidize various forms of reactive nitrogen and sulfur. So, for example, especially in wastewater from anaerobic digestion or wastewater from agriculture, we can really tackle ammonia levels, nitrites, hydrogen sulfide, etc.

Whereas the reactive oxygen species of Ross tend to make short work of that. In other words, to oxidize these into less innocuous forms of hydrogen sulfide, nitrates, and so forth, to help us also comply with nitrates directives, which is very important in agriculture as well. So, there's such a wide variety of environmental applications and industrial applications.

I mean, if we look at the chemical industry per se, we can boost hydrogen levels for hydrogenation reactions. We may be able to make synthetic methane from the liquid phase reaction of hydrogen and CO2 in water as being another area. We could use less expensive catalysts in industrial hydrogenation reactions as well.

So, there really is a wide variety of industrial processes across vast waves of industries, pharmaceuticals, chemical industry, synthetic gas, renewable gas, oil and gas, oil extraction. And then, of course, there's fuels. We can put nanobubbles into fuels, whether at the inlet manifold of an engine or in fuel retention tanks, for example, kerosene, marine diesel, terrestrial diesel, petrol, calorific fuels, and various other alternative fuels that are being explored at the moment, biofuels as well.

So the nanobubbles, for example, of air or perhaps oxyhydrogen or oxygen, really effectively, once you aerosolize the fuel inside the engine block, they tend to burn from the inside out as well as from the traditional outside in, because you have all these trapped nanobubbles of gas, which is waiting to combust on the inside as well as on the outside. And it can also tend to reduce NOx and SOx emissions from the exhaust gas profiles. So really, in this episode, I've tried to give you this type of high-level flavor of the myriad of different applications there are for our nanobubbles.

This is just really scratching the surface of all of these applications. I wanted to thank you again for joining me. A quick recap is that in this particular episode, we've just discussed some of the scientific principles underlining the usage of nanobubbles, some of these nanouniversal features of dissolved gas level and fixed-in-all gas transfer to the biological or chemical gas demand that wants to use it, the whole concept of transferring this sacred cargo, some of the mass transfer aspects, and how this can play into and manipulate and control different aspects of how these are actually used in various applications.

So in our next episode, the fourth episode, that is, in our Nanobubbles 101 series, we're going to be looking at how Nanobubbles are generated, including some of the challenges, problems, difficulties. That will give me a bit more time to talk about, I suppose, my own lead invention and some of that discovery work, and how that originated. I gave a brief outline of that, I believe, in the introductory first episode.