Most Active Stories
Valley Public Radio Staff
Fri September 13, 2013
US Cities Quench Growing Thirst with Saltwater
IRA FLATOW, HOST:
This is SCIENCE FRIDAY, I'm Ira Flatow. I don't have to tell you that the southwest is in the midst of a record drought, some 14 years in the making, which means the water supply for many Western states - California, Arizona, Utah, Nevada - is drying up. Last month the Bureau of Reclamation announced they're cutting the flow of water into Lake Mead, which has already lost 100 feet of water since the drought began.
That white bathtub ring around a reservoir, it just keeps getting bigger. So what to do? Well, California, one of the states that depends on the Colorado River's water, is already looking to the sea. Just north of San Diego, the largest desalination plant in the country is being built and when it's done it will be capable of pumping out 50 million gallons of fresh water a day.
Israel, one of the pioneers of turning deserts green with innovative water use, is building the largest desalination plant in the world. But is desalination worth its salt, so to speak? Is it sustainable from an energy and environmental standpoint? And how does the cost compare to water sucked from a reservoir or underground? What are the engineering challenges to bringing a desalination plant online?
That's what we'll be talking about. Our number, 1-800-989-8255. Desalination is happening around the country. We're going to talk about that with my guests. Mike Hightower is a distinguished member of the technical staff at Sandia National Laboratories in Albuquerque, New Mexico. Welcome to SCIENCE FRIDAY, Dr. Hightower.
MIKE HIGHTOWER: Thank you, Ira.
FLATOW: You're welcome. Amy Zander is professor and director of engineering and management at Clarkson University in Potsdam, New York. Welcome to SCIENCE FRIDAY, Dr. Zander.
AMY ZANDER: Glad to be here.
FLATOW: Mike Hightower, is desalination cheap enough to take off today, compared with other ways of getting water?
HIGHTOWER: Well, in the past desalination has been relatively expensive when compared to developing fresh water resources. But as you mentioned, as those fresh water resources become more and more scarce, the cost to develop those and import water from 10, 20, 50 miles away is getting to be more and more energy intensive.
At the same time, desalination, the costs have been high, but over the last several decades those costs are - have come down significantly and in some parts of the country we're actually seeing that the utilization of local brackish groundwater, for example, is more cost effective to develop than trying to go out and look for fresh water 50 or 100 miles away. So we're seeing a large increase in desalination plants in the United States and worldwide because if you do have a resource of impaired water, non-traditional water, brackish water, or sea water that's close by, in many cases that's becoming more cost effective than trying to develop new fresh-water resources.
FLATOW: Where would I find some major desalination plants around the country?
HIGHTOWER: In the United States, you're going to see a large number of desalination plants in places like Florida, the Gulf Coast, the Atlantic Coast, North and South Carolina. Currently the largest desalination plant in the United States is in El Paso, Texas. It is the largest inland desalination plant in the world. It pumps and treats as much as 30 million gallons a day.
So you're seeing new desalination plants on the coastal regions and in inland regions in the desert Southwest. There's also desalination plants in Scottsdale and in other cities around the country.
FLATOW: Amy Zander, you were the chair of a national academy's report on desalination a few years back. Is it ready for prime time? There have got to be downsides to every technology.
ZANDER: I think it's absolutely ready in a technological standpoint. The energy use of, especially reverse osmosis desalination, is now only twice the theoretical minimum energy to get salt of out water. So we're really asymptotically(ph) approaching the theoretical possibility. And so the technology is absolutely there, mature and available.
What we need to worry about is perhaps the other sides, the economic, social, environmental, political sides of placing a desalination plant in some areas.
FLATOW: Are there environmental concerns?
ZANDER: There are approachable environmental concerns, absolutely. Ocean desal, getting water from brackish near shore ocean, seems to be very doable. I mean they've done it in Tampa on a very large scale and using resources that they had available, so we can't just walk into any area, any ocean spot and say we can put a desal plant here.
There needs to be interest in how we're going to get the water to the plant and what we're going to do with the concentrate from the plant, and those have environmental implications.
FLATOW: Mike, do you agree?
HIGHTOWER: Yes, I do. But we're seeing places like - Australia recently has just built about seven desal plants in coastal regions and have been able to site those plants and handle the concentrate management concerns in an environmentally friendly manner. We're seeing in some of the inland desalination plants - for example, in El Paso, the ability to take the concentrate and do deep-well injection so that it's not environmental concerned, but I agree with Dr. Zander that the issue around concentrate management is probably one of the biggest environmental issues that we have to deal with with desalination.
FLATOW: Tell me about that. What is in there that is so much of an environmental problem?
HIGHTOWER: Well, it's really not anything that is what we did call truly hazardous. It's essentially, as you do desalination, you treat the water to take the salts out of some of the resource. And when you do that, what you do is you essentially create fresh water and the leftover salt then goes into what we call the concentrate.
So if you start off with water that's, let's just, for an example, 2,000 parts per million of total dissolved solids or salts, if you desalinate that, now that becomes 10,000 parts per million, so it's increasing the salt concentration by a factor of five. So that 10,000 parts per million TDS is pretty brackish, quite salty, and you need to address how you can handle that, because water at that concentration, you really can't do land disposal.
You can't put it on land. It will salinize the soil, so you have to figure out a way to handle the salts associated with that. Some people are looking at technologies to try to economically recover those salts and use them for things like building materials and insulation tiles, et cetera. So there are ways that people are looking at trying to handle that high concentration of salt such that it doesn't become an environmental hazard.
But that's still somewhat expensive today.
FLATOW: Amy Zander, would you agree there's a problem yet to be solved there?
ZANDER: I totally agree and I believe it's on a very, very case-by-case basis. You know, even ocean water isn't the same everywhere across the Earth. It can change in salinity from location to location quite a bit, and brackish water in the inland parts of the United States changes quite a bit, so you really need to find not only a sustainably - a source water of brackish water that you can sustainably take water out of.
You don't want to be mining the water. You can only take the water at the rate at which it can be recharged. And you also have to find a place to dispose of the concentrate, often deep-well injection, but that needs an aquifer that can take in the large quantity of this, because like Mike was saying, about five - only about 20 percent of the water becomes product water, in some cases 20 to 60.
The rest is the concentrate and we need an aquifer of the appropriate salinity and porosity to be able to accept that much concentrate. So it's very case specific.
FLATOW: So at this time it's easier than to place a desal plant on the ocean because you're not worried about - it's easier to discharge into the ocean and not be as environmentally damaging?
HIGHTOWER: In general.
ZANDER: I think that's true. I think that - yeah. Go ahead, Mike.
HIGHTOWER: Go ahead Amy.
ZANDER: In general I believe that's true because we have the technologies available for carefully removing the water from the ocean. We can reduce the velocity at which we take it from the oceans so that we can reduce impingement or entrainment of microorganisms or large organisms on the screens or in the water
And same with the concentrate disposal. It can be blended with another water and sent out and dispersed with diffusers. And so technologies do exist to environmentally, safely dispose of the concentrate.
FLATOW: Well, you know, it seems that as the Earth gets older and the population grows, and you're looking for, using more resources, people say all the time that water is going to become a very, very valuable resource, and the price of buying, selling water or using water is going to go up. It seems that you have a potential here for keeping that price down or allowing other things to rise just so that you can use the water and extract it out of the seawater or brackish water, that this will become valuable enough to do it.
ZANDER: That's right. When you look at the cost now of desal - San Diego did a study looking at ways to find water, take the Colorado River, more Colorado River water that can't take more water from the Central Valley. Their groundwater systems are done. So they looked at the costs of doing things, and the cost of desal for them, ocean desal for them was about the same as the cost of wastewater reclamation, taking the water back from domestic wastewater. And you can imagine the yuck factor that goes along with wastewater reclamation. And so, all of a sudden, you know, the cost for desal when you have no other choice becomes something that you're willing to face.
FLATOW: Mm-hmm. Is there another way of saving water, or, you know, we always say that the low-hanging fruit is conservation when we we're talking about energy. Is water conservation still a low-hanging fruit, that if we just conserved water, we might not be running out of fresh water so quickly?
ZANDER: In that case, for example, El Paso, the biggest inland desal plant, they, before they made that decision, they really exhausted every conservation method they did. They rearranged the price structure for water. They were able to provide conservation devices and reduced the demand in El Paso by 40 percent.
ZANDER: But that was that. You know, then what do you do?
FLATOW: Yeah. How come we don't hear very much about desalination plants being put up? You know, we hear...
HIGHTOWER: In my opinion, a lot of the cities just take the look that they're going to look at the resources that they have and allocate them as most appropriate. And I think in many cities, as Amy mentioned, they essentially try, or implement desalination - especially in inland areas - probably as one of their last resorts. They tried water conservation, and we've seen across the West, for example, water conservation has reduced water consumption by anywhere, 40 to 50 percent in most large cities.
Then they also look at wastewater reuse - what we call purple pipe - indirect reuse, using it for irrigation of lawns and golf courses and green spaces. That's well-known to be done across the Western U.S. And then, as they look at the next level resources that they need, that's when they start to look at desal. So, a lot of cities have a portfolio that has a small desal plant, but it's not the large plants that we see in places like Australia and Israel.
HIGHTOWER: And I think what we're seeing is that Australia, Israel, some of the Mideast countries, are probably 10 to 15 years ahead of us in the need for the utilization of desalination technologies. So I think what you're going to see, Ira, is in the next decade, that desalination plants and desalination will be on quite a few minds and in the resource development in a number of cities not only in the Western U.S., but in the Eastern U.S. in the Southeast.
FLATOW: This is SCIENCE FRIDAY, from NPR.
Are there any engineering challenges? You mentioned before that we've gotten desalinations to be done so efficiently, there were almost at the limit - I think, Amy, you were saying before - of what needs to be done. That sounds amazing. There's no engineering breakthroughs that need to happen?
ZANDER: Well, there can be. We can make a 5 percent - we can make it 5 percent more efficient, or bring the cost down by roughly 5, 6, 7 percent. And when you're thinking about this cost, that's still a breakthrough.
ZANDER: But there's not going to be a step change. There's not going - we're not going to cut the cost or the energy in half. That - it's not on the horizon. So better membranes, better cleaning technologies, better pretreatment. Sure, there's engineering progress that can be made, but it's not going to change the overall picture by a step.
FLATOW: Mike Hightower, are private industries creating their own desalination plants at all, if they need to make something and use a lot of water, a product?
HIGHTOWER: Yes. You're seeing a number of companies that are utilizing desalination and water reuse within their own industrial processes, their own industrial plants. Many power plants currently are - have some level of desalination or reverse osmosis for feed water, for power plants, feed water for power processes in chemical plants. And we're seeing that those industries are beginning to accelerate and increase their utilization of these technologies.
FLATOW: And I guess if...
HIGHTOWER: We're also seeing...
FLATOW: ...it's tasty enough to drink, you could make a soft drink out of it, or something.
HIGHTOWER: Well, if you really look at most of the water groups that you can use today, most of them are treated with reverse osmosis from a safety and water quality standpoint. So the drinking water that you get from the Dasanis and other bottled water groups oftentimes are treated with the same technologies that we're talking about using for your municipal system.
FLATOW: Wow. It sounds quite interesting, and I think I certainly learned a lot. I didn't realize the extent that desalination is going on around the country, and how successful it has been in many places.
I want to thank you both for taking time to be with us today. Mike...
ZANDER: Thank you.
HIGHTOWER: Thank you.
FLATOW: You're welcome. Mike Hightower, distinguished member of the technical staff at Sandia National Laboratories in Albuquerque. Amy Zander, professor and director of engineering and management at Clarkson University in Potsdam, New York.
We're going to take a break. After the break, another installment of food failures. You know when things go wrong when you're cooking? Well, this installment is the science of cooking gone wrong. We're going to - well, I'm just going to give you a little hint of what we're talking about: cooking chemistry.
Stay with us. We'll be right back after this break. Transcript provided by NPR, Copyright NPR.