TechStuff Gets Salty

Published Oct 1, 2012, 8:25 PM

What is desalination? What are some of the methods used to get salt out of water? Why isn't desalination in wider use? Join Jonathan and Chris as they explore the tech behind desalination in this episode with Erik Hanson of General Electric.

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Brought to you by the two thousand twelve Toyota Camera. It's ready. Are you hey there, tech stuff listeners, This is Jonathan Strickland, and I wanted to talk to you a little bit about something cool going on at how stuff works right now. I know all of you guys are really creative and you love technology. Well, now you can show us what you're made of because Toyota is sponsoring a new photo upload widget over at how stuff works dot com. You can share your gadget ideas, modifications, hacks, some great tech ideas. Show us what you're made of. Let us know how creative you are. You can go to www dot how stuff works dot com, slash upgrade your tech and upload those photos. Now we want to see what you got. Get in touch with technology with tech Stuff from how stuff works dot com. Hello again, everyone, and welcome to tech stuff. My name is Chris Poulette and I am an editor at how stuff works dot com. Sitting in for me, as is typical, is senior writer Jonathan He there right, So, Chris, one of the big issues facing the world today is access to clean, drinkable water, and so we wanted to talk to someone who's an expert in a particular form of processing water to make something that isn't drinkable into drinkable water, and we have with us from ge Eric Hansen. Eric, welcome to the to the podcast. We're excited to have you here, and we're going to talk a bit about desalination, which is a process where we're removing things like salt and other minerals from water so that you have clean drinking water as an as a byproduct, really the other one being the the salt, the salute. So we want to talk a little bit about the process that you guys use over at g the things that you're looking into, and um, how that has changed over the years. So to really start off, what what are the greatest benefits of desalination? UM? A great question. You know, the world today bases you know, ever increasing challenges and stresses on water supplies. But you know, the good news behind that is the Earth's surfaces water. So even though less than one percent of that is accessible as fresh water today, the rest of it is is seawater, and we do have the technologies today to turn that into usable water. So in fact, those technologies have been around for a really long time. You know, even hundreds of years ago, people would boil water, capture the steam from that water, and use the condensation from that that steam as purified water. So the concepts of of desalinating water using heat or thermal technologies, those aren't new concepts. They've been around for a while. Desalination has been going on for a long time, and even up through the most of the nineties, thermal technologies were still very prevalent, albeit a little bit more advanced than just simply boiling water, but the concepts were still the same, heating of the water, capturing the steam, and condensing it. In the in the nineties, different technologies started being applied. UH. Instead of heating up the water and boiling it, what we started doing was applying membranes, special kinds of of very advanced filters. UH. These membranes are able to remove the salts from the water UH with much less energy. It takes a lot of energy to boil water, so using membrane technologies, we've been able to reduce the amount of energy it takes to remove the salt from water. And over the last twenty years there have been just a lot of advances in that in that field, which I'm sure we'll go into a little bit more in our conversation. Sure, making the cost of the salinating water come down, you know, every year, right, And so you're talking about these these semi permeable membranes. Essentially we're looking at a process of reverse osmosis really um forcing the using pressure essentially to force water that has various minerals and salt in it through this membrane. The membrane separates out the minerals the salts, and the water passes through. Normally, when you have a membrane between a solute and a solvent, the solvent is going to pass through the membrane until there's a an equilibrium there and osmosis pressure is osmotic pressure is built up. So in this case, we're actually applying energy on one side so that we get water on one end of the membrane and everything else is on the other. Is that that sort of a bird's eye view of what that technology is all about. Yeah, you described it very well. You know. One of the biggest difference between membrane filtration and the types of filtration that most people are familiar with is when most people think of a filter, they imagine a barrier of some kind with one stream of water flowing into it, things being removed by that barrier, and then one stream of water flowing out the other side, and then after a while you have to do something to get all this stuff you've removed off that barrier. So membrane technology doesn't exactly work that way. You still have a barrier and it's the membrane, but in membrane technology, the feed stream is actually flowing across the membrane, so you have one stream in, but then you're applying pressure, so some waters making it through the membrane, and that's the purified water without much salt in it, and all the salt, all the salt is staying on the other side of the membrane. So in membrane technology, instead of one stream in and one stream out, you actually have one stream in but two streams out purified the saltier stream, so that salt here stream the brine. I know that that has caused some problems in the past, simply because Brian, you know, what do you do with that after you've gone through the desalination process? Now, Brian, because it has this concentrated amount of salts and minerals, and it's actually denser than sea water. So if you were to simply dump that Brian into the sea, then it would it would sink to the bottom of the sea floor where it could potentially cause damage depending upon the environment that you're in. Uh, can you talk a little bit about some of the approaches to to take care of that problem. I know there's some about mixing the brian in with other water that's going to be running into the sea, so it it dilutes it. So I mean, if you step back and look at the desalination process, you know from from feet, uh, it can simply be considered really part of the normal water cycle, the hydrological cycle. So yes, there's water with more salt going back into the ocean, but the water that's purified and it is then used ultimately that goes back into the ocean as well, whether it comes through municipal wastewater and sanitary sewers and it's treated you know in many other ways. You know that water all does essentially return to the hydrological cycle at some point. So you know, from a high level, the mass balance is fine. The oceans aren't going to get saltier because of this because we are returning the purified water back to the oceans at some point as well. So really the the more immediate concern is just that very point at which you're introducing the brine back into the ocean, and depending on the characteristics of the seabed and what's living in that area, UH, sometimes there are special considerations that are taken. UH. And you know, there are many different ways you can return the brine back into the ocean. You can just have a pipe that puts it right into the ocean. You can create an elaborate grid of pipes underneath the seabed to uh, to blend it a little bit better. There's a number of different methods and UH, even though the salination may seem like a niche to some people, there are actually quite a few specialties within it. And UH, you know, really thinking through how the brine is going back into the ocean and how it's going to affect marine life is uh is quite a science in itself. But you know, there's been a ton of progress on that really in just the last ten years. And you know, I think in nearly all cases we're now able to come up with with special schemes and the right technology to blend U without harming marine life. Fantastic. Uh. Well, moving on to another question, what what's the greatest barrier to adoption of desalination? I mean, why, uh, what's keeping this technology from being more widespread it and used in more areas of the world. You know, I think there are you know, you could probably classify it into two different barriers. One of one of them is, uh is more perception. Uh. You know, there are some areas where the public still isn't really that on board with it yet, just for you know, things they've read in the news and their own ideas about it. Other parts of the world are doing this uh often, you know, in the Middle East or in Southeast Asia. You find de cell plants all over the place. They have largely solved all the environmental issues that people should be worried about. Um. You know, but some people are slower to adapt than others, and it takes a while to to come to terms with with some of that mentally. UM. So that you know, that's a harder problem to solve. The easier problems to solve really are are the energy problems. Because when you do desalination, it isn't the cheapest way to get water. If there's other uh subs lies of water available to you UH that don't have so much salt in them, they're most likely going to be less expensive than desalination. So today people are doing desalination really only in areas where they don't have a lot of other alternatives, where they're in a water scarce area and they simply need to do it. So driving down the energy cost is really the primary goal and desalination, and it has been for the last twenty years, and there have been a lot of different improvements over the last really fifteen years that have really made progress in driving that down UH, and they're in a number of different areas. Obviously, the amount of energy that you need to drive the salt out of the water is a big deal, and you can lower that through advances in the membrane chemistry, so actually improving the membranes. You can do it through advances in the efficiencies of pumps UH, and you can also do it through advances in energy recovery devices. So there's a you know a number of different areas that people are working on. And then in addition to that, you know, simply the operation of these plants. You know, it requires a the amount of manpower just to keep these things running. So we've also been making a lot of improvements and innovations in the pre treatment to these plants. So as as the pre treatment to the water gets better, they're lower operating costs as well. So lots of different levers to pull in order to lower the operating costs. You know, I was wondering a little bit about the equipment itself. I mean, the process itself seems pretty uh, pretty straightforward, but um, you know, is the is the equipment itself large? Does it take up a lot of space or or does it require a lot of high pressure to make it work? Yeah, that two different things. In terms of size. It doesn't take up really any more space than a traditional water treatment plant for the same capacity would. But the big difference is pressure. The more salt that have dissolved in any in any given amount of water, the higher the osmotic pressure of that water, something Jonathan referred to in his earlier explanation. So the more salt, higher the osmotic pressure, the more pressure you need to apply to the water to drive the salt out of it. So take for example, the middle East, in the Gulf, in the Middle East, that's really some of the saltiest water in the world. So on on detail plants, they're we're running them as high as eight p s i, which is pretty high pressure. Uh. In other parts of the world, like say the Caribbean, the water is a little less salty, still absolutely seawater, but it's not quite as stalene as as the Middle East. So there you because it has slightly less salt, you can use slightly less less pressure. Now, are these plants often um sort of piggybacked onto other plants like power generation. That was wondering if there was a lot of cogeneration going on with desalination plants. Yeah, that's a great question. Uh. And this is actually one of the reasons that g is is uh, you know, so active in this market. Uh. You know, there's just an inex Uh. There's a there's a obvious tie between energy and water. So to produce energy, you know, power plants need water to produce energy. Infect almost ten percent of all global water withdrawals go to the production of water, so that's a pretty significant amount. Uh. And then the reverse of that is to desalinate water, you need energy to do it. So power plants and deesel plants are are are very linked. In the past, when the technologies were more thermal based, that was another advantage of tying the plants together because many power plants, especially power plants in the past, had a lot of waste heat, so they could use some of that heat uh for the thermal desalination. Power Plants today are much more efficient, so there isn't so much waste heat coming from them. Uh. And the membrane technologies come to a point where really that's the propolan technology for desalination. So we're not seeing them tied together as much anymore because of waste heat from the power plant, but we are seeing them tied together simply because the power plant needs water uh and the decail plant needs power. Excellent, So what is GE doing to make desalination more feasible to address water scarcity issues? So we're working in a number of different areas. We've worked a lot in the past on the membranes and uh, you know, there are really some very high quality membranes now used in desalination. Uh. They're not an entitlement yet. There are still some games to be made there. UM. But they're they're getting close. The membranes are very efficient today. UM pre treatment is very important. So when when we talk about membranes and how they take this all out of water, they're great at taking the salt out of water, but they aren't great at taking suspended solids out of water. So you don't want to put salt or sticks or stones or anything like that into a membrane. That's bad for it. So pretty much every membrane plant in the world has some kind of pre treatment in front of it to take the suspended solids out before it gets to the membranes. UH and G has been leading in this area as well. We have some terrific advanced prefiltration another type of membrane called an ultrafiltration membrane, and it it provides really superior UH suspended solids removal, so that the water that gets to the the reverse us most of the membranes is as clean as it can be, still salty, but it's had everything else removed and that makes the life of those membranes lasts a lot longer, which in turn lowards the overall cost of ownership UM. Then the other pieces of the pumping side there are a lot of different kinds of pumps in the marketplace. The most fishing types of pumps are positive displacement pumps. If you think of pumping water, you can imagine you have a fixed geography fixed geometry of water. The most efficient way to raise the pressure of it is just to push on it um and that works today in in relatively small sizes, but as plants get larger and larger, uh, there aren't so many good positive displacement pumps. So instead what people use their centrifugal pumps. So that's more like spinning the water. The water that gets thrown to the outside has a higher pressure. So you know, we've been working developing a new pump which is a positive displacement style pump, but it's much larger than other positive displacement style pumps on the marketplace. That's a pretty new product for us, but we expect that within the next year we're gonna start seeing more of more of that pump out in de cel plant and that's going to knock as much as another ten percent of the energy off, so that when we get that fully commercialized, not in the marketplace, it's gonna lower the electrical costs by about ten percent more, which is really significant when you're talking about, you know, the cost of desalination. Sure. So, so that's where it leads into what do you see as the future of desalination? Where do you see us going in another few years, like another decade or two decades. Yeah, that's a great question and a hard question because there are many many technologies out there today. Uh, you know, I I think most people in the industry, myself included, really see reverse osmosis as continuing to be the most prevalent technology for at least the next five or seven or ten years. Um. It's certainly possible that some other technologies could could come along, and you know, honestly, if there are other technologies that will dramatically lower the cost of desalination, that would be great for the planet. Um. But I I you know, I think over the next five or seven years, what we're going to see is people figuring out how to link the cell plants more to other renewables. So already we're starting to see people thinking about how do you combine a de cell plant with wind turbines and a wind farm, or how do you combine a de cil plant with a solar farm. You know, it turns out that a lot of places in the world, the neat desalination, places that are water scarce, are also places that have quite a bit of sun. So there there's some nice natural links between you know, combining solar with de cell. In some ways, there's also challenges because you know, in addition to having on his sun, you know, some of these places also have a lot of sand and it's dusty, and and dust and solar don't don't always pair so well, but dust coats the panels and may become less efficient. But you know, now we're talking about some pretty um discreete challenges. You know, people are doing us now, they're learning, they're getting better at it. There's not a lot of solar plus D cell or wind plus D cell out there today, but I think in the next five to ten years we're probably gonna start to see a lot more about Yeah, it's really exciting and to give our listeners an idea of the impact that these sort of technologies have made so far. Uh, it wasn't that long ago that the estimated population that could not get access to clean water was around twenty but according to the World Health Organization, they had a two thousand twelve report which took numbers from two and took a look at that. Uh, they said that it's is still a massive problem. Still seven million people lack access to safe drinking water, according to this report, and that's a you know, that's a sobering number. But the silver lining here is that that's that's half of what it was before, so that the numbers of people who are getting access to safe and water there on the rise, which I mean, that's obviously the way we want to see this trend go. So it's exciting to see this sort of technology combined with the efforts of other organizations out there dedicated to making sure that that people across the world get access to this water. Yeah. I couldn't agree more. You know, one of the statistics that that I often hear is that today it's one and every six people today doesn't have access to clean water, which is, as you said, really a sobering number. Um. You know, I think there's an interesting combination here where you read a lot about this today. You know, ten years ago you didn't generally see water articles in mainstream media, and today, you know, every week you're going to see an article in mainstream media talking about water scarcity, and you know, it is a serious problem and it is alarming. But the plus side of this publicity is that they're more entrepreneurs, more large companies like GE, just more people out there starting to think about what are some possible solutions, uh, And there's lots of them. You know. The salination is a great example of ways that we can solve water scarcity. Water reuse is another great example of ways that we can solve water scarcity. Water reuse is just taking water that's already been used for one purpose, uh, and treating it and cleaning it up and finding a way to use it for another purpose. So, you know, I think all the current press that we hear about water scarcity is actually helping to feed a pipeline of new innovations and new ideas that will actually help solve the problem in the long rust. Fantastic, Eric, Uh. That that's a great look at the desalination process and what g E is doing to to really push this technology forward. And we really appreciate you coming on the show and talking with us. It's been a really educational experience for me and especially as as as liberal arts majors whose background and engineering is saying, Wow, that's cool. Uh, it's really great to get people like you on our show to talk about this and and give our listeners this uh this sort of Uh look, is there anything else you would like to say before we wrap up? Well, you know, Jonathan Chris, I'd just like to say thanks, thanks for having me on the show. Um. You know, at GE, we're doing a lot of really interesting and innovative things to solve the very problems that we were just talking about for the last half hour. Uh. You know, one of the great things about being in this kind of business is when you come up with innovations, you can actually see that they're helping people. Uh. So you know, it's it's a rewarding business to be and GEE is very committed to it. We're investing a lot and solving problems today and in the future and and uh, you know, I love talking about it and I'm really excited about where this can all go over the next Thank you so much. Thank you, Eric, and and uh, We're always glad to have people who advocate that sort of mindset to to really get people interested in science, technology, engineering. These are areas that are they're they're leading the way to the future of what our world is going to be. And uh, you know, if we have students out there listening, feel free to let us know. Tell us what you are interested in, let us know what what areas we should cover in our future podcasts. You can let us know by sending us an email that addresses tech Stuff at Discovery dot com, or drop us a line on Facebook or Twitter. You can find our handle at both of those locations. It's tech Stuff hs W and Chris and I will talk to you again really soon for more on this and thousands of other topics because it hostaff works dot com. See, guys, I told you we talked to you again really soon. That really soon is right. And now I'm just reminding you that we have our photo upload widget live on the site at www dot how stuffworks dot com. Slash upgrade your tech Toyota is giving us the chance to let you share your creativity. So send us those pictures of your modifications, your tech ideas, those gadgets that you've created, all those hacks. 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