Innovations in Clean Water Technology

welcome to the science for the public lecture series science for the public is an organization committed to bringing science information and issues to the general public visit our website for our program listings and blog you good evening I’m Yvonne staff for science for the public and tonight our subject is the shortage of drinking water in the world tonight we’re very honored to have as our guest one of the world’s foremost experts and innovators on this subject John Leonarda fit he’ll explain both the reasons for the rapidly dwindling water supply and the possible solutions to the problem dr. Leonardo is the Samuel Collins professor of mechanical engineering at the Massachusetts Institute of Technology he’s also the director for the Center for clean water and clean energy at MIT and King Fahd University of petroleum and minerals in Saudi Arabia he serves also as associate department head for education he’s an international expert on desalination and he’s received many awards and honors for his work in desalination as well as for other engineering accomplishments dr. Leonardo saved his PhD in fluid dynamics from the University of California San Diego in 1988 and in the same year he won the prestigious National Science Foundation’s presidential Young Investigator award and he joined the MIT Department of Mechanical Engineering this is probably a first in history in since that time he’s pioneered so many innovations and accumulated so many awards that we refer you to his MIT webpage or to our link to it on the science for the public web site to view a very long list but I would like to point out that a number of those awards are for his teaching skills a vitally important talent in an age of engineering dr. Leonardo serves in editorial capacities for numerous international journals and he’s bothered a couple of mechanical engineering textbooks as well I will stop praising dr and just let him talk now and to say that we are very very honored to have him with us tonight and we offer him a great thank you thank you to all of you for coming tonight to hear us and thank you to those who are watching the program after it’s been recorded I’m going to talk tonight about water supply and clean water and the use of desalination to create additional water supply the things I’ll cover are listed on this slide I’m going to say a bit about water supply and water scarcity we hear a lot about the scarcity of water in the world and I’ll try and say a bit about what that means I’m going to talk about what we want from water when we say water is clean water that we would drink and I’m going to talk about the differences between typical water supply and seawater why we don’t just drink seawater itself then I will talk about desalination systems how they work I will talk in most detail about something called reverse osmosis desalination so widely used method of desalinating sea water and I will say a bit about some other types of desalination systems and then finally I’ll talk a little bit about the energy required to desalinate water as compared to other kinds of energy supply that we work with so I want to say a few words about safe water supply and about the availability of water the UN has through its agencies published a number of statements in recent years and they’ve made a strong focus on water they point out that approximately 3.6 million people die each year as a result of water related diseases usually easily preventable diseases about one person in eight lacks access to an improved safe water supply and about half the people in the world do not have sanitation systems that are even as good as the ones the Romans had 2,000 years ago the folks shown in these pictures are I believe in Somalia and you can see that what they’re doing to obtain their water supply is filling

buckets from a source in one case from some taps and the figure on the left and the other case from a water truck that’s delivering water people fill these buckets they take them home and somebody in the household does this every day typically a child or a female member of the household who will devote perhaps hours per day to the process of getting water for the family many millions of people around the world do this all the time and it makes me reflect on the miracle that I’ve grown up with I have always had access to a water faucet in my house I can open it and I can be sure that what comes out is safe for me to drink so the situations are very different worldwide the water that’s available on earth is mostly salt water about 97% of the water in the world is in the oceans contain salts and I’ll show you a bit about what the salts are two and a half percent of the world’s water is in a fresh form but of that two and a half percent almost 70 percent is locked up in glaciers and ice caps in areas that we’re not going to get it is in a certain sense fossil water it’s been there a long time if it were removed it might not be replaced that quickly similarly we have about 30 percent of the world’s freshwater that’s locked up in large lakes for example the great lakes in the US and as you know the Great Lakes are left over from the last ice age they’ve been there a long time water flows in and water flows out but the great bulk of that water is again fossil water were we to drain those lakes completely it might be a long time before they were refilled so when we think about renewable sources of water we’re really looking at precipitation over land and rainfall over land and that amounts to our renewable resource for water and it’s less than one percent of the water in the world to give you some idea of what those water flows are and how much water we’re talking about this chart shows water in cubic kilometers per year so a kilometer by a kilometer by a kilometer of water about a hundred and twenty thousand cubic kilometers fall as precipitation over land each year and about seventy thousand of those are immediately or relatively quickly evaporated back into the atmosphere the remainder is either taken away as runoff in rivers and streams or it seeps into the ground and recharges groundwater and aquifer is below the ground of the part that goes into rivers and groundwater about twelve thousand cubic kilometres are accessible to us for a year and of that we are using roughly 5,000 of those cubic kilometres so we make great use of the available water supply the available fresh water supply already now that water supply is not uniformly distributed this is a chart from my colleague Rafael Ferrari and mi t–‘s earth science department and it shows the difference between evaporation and precipitation so in the areas that are yellow you have more evaporation from the surface than you have rainfall in the areas that are more toward the blue and red you have more rainfall than precipitation and as you look at this graph you’ll see that some of the areas in which you have relatively high rainfall say over here in Papua New Guinea these are areas that might be considered to be rain for us they’re very wet some of the areas where you have more evaporation than you see precipitation would include regions that we think of as being quite arid you have essentially a zero balance everything that comes as precipitation is evaporated in areas like the Sahara Desert and so there’s very little available supply in some of these regions so when we talk about water scarcity or water stress what we are thinking of is whether the amount of water that’s being withdrawn for human use is on the same order of nearly the same size as the difference between what falls is rain and of a parades if we use everything that falls his reign if we withdraw all of it we’ve taken all of the renewable supply from that area and immediately you can see there’s going to be a problem with either increasing the amount of water available or simply meeting the current needs so in this graph the areas that are in red are ones where most were perhaps even more than what’s falling in a given year is being withdrawn for human use you might say how can you withdraw more than Falls you might be pumping water out of the ground and lowering the level of a prefers underground and taking groundwater at a rate faster than its replenished which is happening in many places so you can

see that large parts of the world are facing water scarcity or water stress southern India much of the Gulf area Israel northern Africa parts of South America and big sections of the western United States as well where water is relatively short at the same time you can think about where people live this is a map that shows population density this is dated 1990 for the areas that are red or purple have the highest number of people per square mile of per square kilometer and you can see that many of the areas that have very high population density are also the areas where you’re seeing water stress in water scarcity there are a large number of people living there who rely on whatever water is available for their day-to-day use and their survival there are trends behind this then that are creating additional problems first we’ve recently come to a a world population beyond seven billion people and that number is rising steadily and as the number of people in the world Rises the amount of renewable water is not increasing in tandem it’s more or less fixed and so the additional people we add are going to have to have their water provided from the same renewable resource that everybody else is relying on already which means that there’s a lot of pressure on water supplies and that pressure grows as population Rises another interesting fact is that many of the areas of high population density are along the coast and we’ve recently passed the point where 50% of the world’s population now lives in cities as opposed to rural areas and many of these very large cities are coastal which is fortunate from the perspective of those interested in desalination because if you are living in a coastal city purifying seawater is a reasonable option to consider in looking for a source of water supply now the impacts of the very high demand on water in some of these regions can be quite suppressed on assuring these are some photographs from NASA and what they show is the aral sea in Central Asia you probably can’t read the small type here but the image on this side is the RLC is that appeared from space in 1989 the image here is the RLC as it appeared in 2003 and the image here is the RLC as it appeared in 2009 and so you can see that the demand for water in this case for agriculture has led to an enormous environmental impact and an enormous change of lifestyle for the fishermen who used to fish from this sea there were villages cities along the margin of this and people who made their livelihood fishing and if you dig around online you can find pictures of those ships sitting out here in the middle of dust and nothingness so the problem is really a very serious one when we start to run out of water and we start to tap into what is in this case essentially a fossil resource we use it up and then what another example of this kind of phenomena can be seen in the United States in California there is a very famous story about Owens Lake which is behind the Sierra Nevada mountains there’s a book you can read it’s called Cadillac desert by Mark Reisner I believe is the author which describes how that lake came to be pumped away the city of Los Angeles bought up water rights for that for the Owens Valley and diverted a lot of the water to supply water to the city of Los Angeles with the result that the lake which used to be in here is gone no longer being replenished by rainfall and runoff from the Sierras there was a similar situation with Mono Lake which is not far away this area was also being tapped for Southern California’s water supply at one point the water had been drained the water level in the lake had dropped so that these islands were actually connected to the shore by a land bridge as it happens these islands are big nesting sites for birds migratory birds they lay their eggs out here when the land bridge formed coyotes and other animals could get in and eat the eggs and eventually after many years of lawsuits the water withdrawals were checked in that region on the grounds of prevent protecting the endangered species living on the island and so now

the water level is back up the amount of water that’s withdrawn worldwide is enormous and it’s put to various purposes this figure shows the withdrawal of water in a given year this would be from about the year 2003 or so I believe the data set is and it shows that there were three thousand eight hundred billion cubic meters of water withdrawn that year much of that water was used the sector that’s in orange in the figure for agriculture and growing crops worldwide the red sector is what’s used domestically in households and the blue sector is what’s used industrially and in power production worldwide and these are some of the major categories of use to which withdrawn water is put in the US the distribution is a little different so these are data from 2005 showing that the US water withdrawals amounted to almost 600 billion cubic meters that year and 49 percent of that water was withdrawn for the purpose of cooling power plants the water has taken perhaps run through a condenser to help condensed steam and a power cycle and then the warm water might be put back into the river or lake from which it was withdrawn some of it may have been evaporated in a in a cooling tower which is an effective way to cool things off about 34 percent of the u.s. withdrawals were for agriculture and the other 17% were for various types of public supply and self supply this would include households it would include say manufacturing industries it would include mining or livestock things of that sort so this gives you a sense again of what withdraw water is withdrawn for and how it’s used the amounts of water people use differ on the world what I showed you for the u.s was a very different distribution than for the rest of the world much of the world withdraws water to grow crops in the US we’re using a lot more of it for industry or for power general let me say a little bit about then saline water and I’m going to think specifically about sea water all right first question is why don’t we drink seawater short answer doesn’t taste very good the longer answer is that the amount of salt and sea water is actually about three and a half times the equivalent amount of salt in human blood and so when sea water is in your gut the natural tendency is for water to diffuse out of your body into the sea water the process of osmosis that I’ll explain a couple more slides but the net result is the drinking seawater dehydrates you you’re gonna wind up thirstier than you started and you know so if you’re on a ship at sea you know you’re on a lifeboat at sea you start drinking the seawater you’re gonna get dried out fast than if you just didn’t drink it at all so that’s the primary reason not to drink seawater now seawater desalination is of interest in many countries and it turns out that it’s used very widely here in the US what I’m showing in this table are the world’s 10 largest desalinator –zz of water either seawater or groundwater that’s salty so called brackish water the largest desalination arabia they make 70% of all their water by desalinating sea water from the Gulf or from the Red Sea the United Arab Emirates is right behind them they’re also on that on the Arabian or Persian Gulf and the US comes in number 3 which you wouldn’t think if you weren’t aware of some of the plants that exist in the US we use a lot of water as I’ve already shown you and so the amount of water that we’re creating by desalination is relatively small out of our total consumption but relative to the entire world it’s quite large and you can see a number of other countries here some of them are in North Africa and the Gulf but Japan is on the list China is on the list and so is Australia and Australia has been very active in building desalination plants one of the important points to make about desalination of seawater you’re removing the salt so you make water you can drink you’re doing it by taking water out of the ocean putting the salts back in the oceans the amount of salt in the ocean doesn’t change and the water that you take out of the ocean eventually finds its way back to the ocean with wastewater however you’ve treated it and replaced it so in a sense the net amount of water and salt in the ocean is unchanged by

desalination you’ve got what is effectively a renewable process for making drinking water how to sea water it’s renewable with the exception that you use energy to desalinate water and the energy may be generated by a fossil fuel which would then be non-renewable even desalinate using renewable energy so much the better now I’m going to talk about a couple of different kinds of desalination I’m going to really just divide the assala nation to two types of processes one type is a membrane process where you pass water through a membrane and leave the salts behind reverse osmosis is the most widely used version of that and the second broad type is distillation when you boil water on your stove and condense the steam onto a pot lid the water on the pot lids essentially been desalinated if you’re boiling salt water on your stove and you condense the steam under the pot lid the water on the lid of the pot would be freshwater and that’s basically the idea behind a distillation process boil the water off leave the salts behind and collect the vapor there good ways to do that there bad ways to do that I’ll try and tell you a bit about that in terms of what’s done worldwide in 2008 there are about 14,000 large-scale desalination plants by next year that number is going to be around 15,000 they’re being built very rapidly the largest category is the one in red here this is reverse osmosis membrane based desalination the next largest category would be the yellow and this green band these are thermal processes known as multistage flash or multi-step multi-effect distillation and then there’s some other processes that are less widely used that I’m not going to discuss the amount of water desalinated worldwide is equivalent to about five percent of what’s used in household use not all desalinated water is used that way it’s equivalent to about half a percent of all the water that’s withdrawn for every purpose including agriculture and power plants okay this is this slide is my nod to everybody out there who is either an engineer or a person with a science background basically what it’s showing you is that to take seawater and to break it into some part that’s freshwater and some part that’s saltier water you have to do some type of work you got to add energy to the system you can do it using pumps for instance electrically driven pumps and as an engineer I would call that electrical work and so it’s possible to compute what’s the best I could possibly do it’s a thermodynamic calculation for those who like thermodynamics I love thermodynamics and I apologize to any former student who doesn’t also love thermodynamics come back and take another class we’ll get you to love it but you can show that the smallest amount of energy required to desalinate a cubic meter of seawater is around one kilowatt hour of electricity the best you could possibly do under the laws of thermodynamics in practice real systems because they have losses and inefficiencies take three to four times as much energy at best and so right now we’re able to desalinate water to something within about a factor three to four are the best we could possibly do that’s pretty good odds are we’ll be able to get within a factor of two over time if we look at examples from other types of systems maybe even better so there’s room for progress and the technology has moved way ahead in the last 20 years the amount of energy has gone down dramatically relative to what it was and say 1990 and the cost of the systems has gone way down cost is an important fact because if you’re supplying drinking water at the end of the day you do worry a lot about how much you have to pay for it in terms of desalinated water energy represents 30 to 40% of the cost operation and maintenance represents say another third and the investment you make to pay for capital represents another third debt service the interest you pay on the money you borrowed to build the plant if you like and that’s a way of thinking of it so when you think about lowering the cost of water you’re looking at reducing the amount of energy you’re looking at reducing the cost to the components and you’re looking at reducing the expenses for personnel and maintenance of the plant now I’ve mentioned reverse osmosis I’m going to explain to you roughly how it works there’s a thermodynamic process known as

osmosis and if I had a membrane such as I’ve shown here that water could go through but salt couldn’t go through and we know how to make those membranes if you put salt water here and fresh water here and they were at the same pressure and temperature the tendency would be for water to diffuse from the fresh water into the salt water that’s how the system would respond as it tried to as we’d say get toward equilibrium and so this is the normal process and it’s called osmosis if you were to look at what we do to desalinate water instead of keeping the salt water at the same pressure as the fresh water we raise the pressure on the saltwater side a lot and that causes the direction of the flow to reverse and that’s what we mean when we say reverse osmosis by pressurizing a salty water you can force the water to flow out of the salty side and into the fresh side and that’s how the systems are to work so this is a photograph which shows you Representative reverse osmosis desalination plant and I’ll explain a bit about what’s in here the first thing you see in the foreground this large black and silver object this is a pump and so the vertical of silver part is the pump and above it is a motor that drives the pump so electrical energy is compressing as pressurizing the water it’s pressurized to about 60 times atmospheric pressure in a typical reverse osmosis plant for seawater so the water’s at very high pressure then the seawater is taken into these cylindrical typically fiberglass vessels where the membranes are wound up in cylinders and the water is passed through the membranes on one side where it’s pressurised into a freshwater side at low pressure and that’s how you collect the freshwater in a reverse osmosis plant typical plant will have hundreds and hundreds of these vessels typically these plants require between say three to five kilowatt hours of electricity per cubic meter of water produced and that number keeps dropping the best available plants are a little bit under three kilowatt hours now the spiral-wound membranes look more or less such as the one shown here the membranes are inside this and they’re bound up by wrapping successive layers one over another the standard for many of these is twenty centimeters or eight inches in diameter by one meter in length and you’ll put maybe seven or eight of these things in a line inside a pressure vessel so here’s one of the pressure vessels I’ll bring in green the green is seawater it comes into a series of these cylinders the freshwater and blue flows out through a channel in the center and is collected for use and then the leftover seawater having had a lot of the fresh water taken out of it as much saltier typically about twice as salty as it went went in and the salty water is then discarded typically by injecting it back in the ocean this is a photograph of a typical plant another plant this is a smaller plant I bring this one up in part because it’s in the Commonwealth of Massachusetts it’s located in Swansea and the Swansea Water District along the Palmer River crossed from Fall River and this plant just came online recently it’s being used in Swansea to help augment the local water supply most of their water comes from groundwater and they’re not part of the MWRA system and by desalinating sea without Palmer River water I should say they are adding to the local supply now you might wonder about the brine it’s injected back into the ocean and that has to be done carefully because you don’t want to create a whole lot of salty water in a region where you’ve got a lot of marine life because slow moving things aren’t going to be able to swim out of the way if you pour it all that salty water along the ocean floor plants that grow there might be affected marine life that lives in a fixed position would have trouble with it so generally what’s done instead is to disperse the seawater you’ll take it out of the most active zones under water where there is not so much sensitive marine life and then you might have an array of nozzles spread out over many acres that disperses the water so that it mixes with other water and gets back to low salinity so this is a slide that I got from Gary crisp who designed a number of reverse osmosis plants in Australia and this is a photograph from a test they did off

Perth Australia where they’ve built now two large reverse osmosis desalination plants birth is a very dry region it’s also got very strict environmental regulations and so the builders of the plant were required to show that to sea with the brine they put back in the sea dispersed adequately they did numerical models with computers to simulate the fluid flow and then they did a test where they put purple dye into the that they were injecting back into the ocean and so this shows a diver next to one of the diffuser ports as the dyed water is coming back in I want to emphasize that the brine that comes from desalination is not normally purple they found very good agreement between the tests and the simulations they were very they were able to satisfy local authorities that they were in fact complying with environmental regulations and not producing damage Gary also pointed out that there is marine life growing right there on the diffusor port so at least for some forms of marine life it’s not a big problem now the cost of seawater over time from reverse osmosis plants is illustrated on this slide on the very far left-hand side you see a plant from 1991 that was built in santa barbara california and for that plant the cost of water was about a dollar and a half per cubic meter these would be prices generally leaving the plant as opposed to with delivery and other charges added on and you can see that over time the cost of water has dropped progressively so you have 1991 here here’s a plant built in cypress at Larnaca in 1999 here’s a plant in Tampa Florida and from 2000 the ashkelon plant in Israel which is the world’s largest reverse osmosis plant is over here and the plant and Singapore is here the state-of-the-art plants nowadays are producing water for on the order of 50 or 60 cents per cubic meter by reverse osmosis desalination so it’s a dramatic drop in pricing it’s still significantly more expensive than you might pay for water you’re just taking out of a lake with minimal treatment but if this is your source of water this is becoming much more competitive years ago using older thermal technologies other kinds of technology cost a desalinated water can be several dollars per cubic meter and some for some types of technologies it still is this is another slide for the engineers in the audience instead of using electrical energy you can use thermal energy so you bring in heat from a relatively high temperature typically steam not such a high temperature typically around 100 degrees Celsius the boiling point of water you keep it low so that you don’t create scale and the heat exchangers you can show that you know the best you’re ever going to do by such a system is about a hundred times less energy than it would take just to boil water on your stove and condense it and so the the best system would be a hundred times more efficient than what I described with the pot lid maybe even better real systems are still a good deal a good distance from the best you can do because thermal systems do have a lot of inefficiencies in them the way power is generated where heat is generated for these systems is typically by pulling steam at relatively low temperature out of a power plant and so the way that an engineer might look at the energy cost of that steam is to say okay I could use that steam to desalinate water or I could use it to make more electricity so how much electricity could I have made with that steam well it turns out that you could have made something in the order of say nine ten fourteen kilowatt hours of electricity per cubic meter of water which means that you’re using about the electrical equivalent of about three times as much energy as you would have used to do it with reverse osmosis so it’s less efficient than reverse osmosis in practice on the other hand these systems are robust and they can handle water that reverse osmosis may have some challenges with they’re very widely used these thermal systems let me see if I can step you through a drawing of one of these thermal desalination plants and again this is somewhat small type you bring in seawater at this end seawater is taken out of the ocean and it’s typically relatively cold cold water and so you can bring it in and use

it as a coolant in a condenser you can condense water vapor on the seawater and that vapor might then become the fresh product water the fresh water you’re trying to produce and you can do this over and over again every time you use the sea water in a condenser the energy from the steam is transferred to the seawater so the seawater gets a little warmer and with each stage through this system the seawater is warmer and warmer finally by the time you bring it out the far end the seawater might be up to 70 degrees Celsius something in that range a bit hotter than the water you’d get from your household water heater but not boiling you take the water over then finally to a heater where it’s heated by steam from a power plant you might bring it up to ninety or a hundred degrees C almost at the boiling point of water and then you’ll run it through a bunch of separate chambers each chambers got a slightly lower pressure than the one before us every time you run the seawater from high pressure to lower pressure you get something that we would call flashing some vapor is created because of the pressure change vapors created the temperature of the brine or the seawater goes down a little bit you take the vapor that’s created the steam that’s created and that’s what you were condensing before you do this over and over again a large plant might have twenty five stages of small pressure drops and eventually you might extract 40% of the water from the system you know you know in a reasonably sophisticated design I’m showing a very simple version of this and finally you’d have some warm seawater that you would dispose of the warm water would typically be put back in the ocean where I would flow it along the surface and disperse because it’s warm it doesn’t settle to the bar cold water tends to fall warm water tends to rise and as a result it doesn’t tend to get down to the plants and animals living on the ocean floor now I’ve mentioned steam over and over again for these thermal processes and power plants as well and the reality of thermal desalination systems is that they are almost always built at very large scales with power plants so this is a photograph of a combined electricity and water production plant from the Middle East here is the power production facility the turbines for the power generation and these units in the front they’re kind of small in this drawing but these units are the desalination units in this case multistage flash desalination systems similar to what I showed in the slide before and they’ve got a whole bunch of them a large plant like this can produce enough water for a city of several million people every day ones that I have seen in the Gulf produce on the order of 200 to 500 thousand cubic meters of water per day and supply cities with populations of two million or more the largest plants of this type are above 1 million cubic meters of water per day you can think of this as rivers of water it’s at that scale just enormous amounts of water being treated now one of the things I mentioned early on was that you have water scarcity in a number of parts of the world which also are places where you don’t have much precipitation these tend to be places that are very sunny they have a lot of solar energy and so on this figure I’m showing in color bands the amounts of solar energy available in different places these areas that are brown and sort of orange in beige are areas with a lot of sunshine at the highest end they have something like six kilowatt hours of energy falling on a square meters they have 3 feet by 3 feet area every day so there’s a lot of energy available to be collected in these places these also happen to be areas that have a lot of water stress or water scarcity and as a result people have often thought gee could I solve the water problem by using solar energy to desalinate to produce water and so there’s been a lot of interest in using solar energy as the energy source for producing fresh water in particular solar energy is renewable which means that if you could do desalination with solar energy you’d have a renewable source of water fully renewable I’ll show you some examples of how that’s been done or attempted the first picture on this slide is just the rain cycle as we know it sunshine falls on say the ocean warms the surface water the water evaporates into the sky the water that evaporates

is pure pure water vapor the salts are left in the ocean that condenses up in the atmosphere falls as rain and so we get humidification of air here dehumidification when the rain falls very simple way to approximate that process is to have a sheet of glass and to have a tray of salt water sunlight comes through the glass warms the water the water vapor comes up and condenses on the glass and the condensed water is collected at one end this is what’s known as a solar still and it’s simple to build basic survival stills for people you know say on boats or something might use more or less this principle and and so this technology has been used it’s been around for probably 150 years or more it’s not very efficient and so a thermal engineer like myself would look at this system and say gosh you’ve got the warm water looking directly at the surface where you want to condense you want the condenser to be cold you want the warm water to be warm you don’t want them exchanging heat with one another as they do here and so you start thinking of ways to redesign is how about if I separate the part the heats from the part where the vaporization happens from part where the condensation happens how about if I think about whether or not I can reabsorb the heat that’s released when the vapor condenses and use it to heat more water up and vaporize more water and so as a thermal engineer approaches a system like this he might break it up into pieces an example is this this box that I’m showing here we have dry air coming in heated by a solar collector comes into a humidifier where seawater is sprayed into a packing the warm air coming through here is then humidified as it travels through this system the warm humid air goes to a dehumidifier where it’s condensed water is condensed out creating the fresh waters product and so you can start looking at this I’m not going to go into the details of this except to say that my group at MIT has studied these systems very extensively and it turns out there are a lot of different ways to put these flows in and out of the humidifier and dehumidifier some of them work much better than others and we’ve managed to improve the performance of these systems by perhaps a factor of five relative to what was the benchmark in the literature when we started that research so there’s a lot happening in this type of technology as well another set of systems this is from my colleague professor Steve dubofsky also at MIT he’s interested in driving reverse osmosis systems using photovoltaic power and so what you see in the bottom picture is a system it’s on the roof of one of our buildings over at MIT in the background is the dome that you can see from the Charles River and here’s a solar panel and behind it are some containers that contain his reverse osmosis system so he’s using solar energy directly to desalinate water and the concept in his system is that you could make something like this you could put it on a skid or a pallet and you could load it into say a c-130 such as is shown in that picture above you could take systems like this to places where they’re needed perhaps Haiti after their you know disaster recently and you could deploy these and purify water on-site without having to have additional energy sources Steve’s group is not the only group to have looked at this technology but he and his students have been looking in particular at ways to control the system to use very careful kinds of sensing and computers that read the sensors and control the pressures and the rates the motors are running and other aspects of the system to optimize its energy consumption and to produce water very efficiently and they’ve made a lot of progress with that type of system another example of using solar energy to produce seawater can be found from a number of studies particularly this one was done that the DLR lab in Germany but it’s also been looked at extensively by researchers at plataforma so lara de almería in spain and other groups including groups in the u.s. at Sandia and other places concept here is to use solar energy to concentrate it with mirrors and to use the energy that you collect from the Sun to heat working fluid perhaps water or some other fluid high enough temperature that you can run an electrical power generation system effectively so they’ll then use sunlight to make electrical energy the electrical energy can then be used to drive a reverse osmosis system to make water furthermore the waste heat from a system

like this might also be used to desalinate water through a thermal process and so these and other researchers have looked at configurations that would allow you to do this in terms of large-scale cost-effective solar desalination these sorts of systems are the ones that look the best the concentrating solar power systems and there’s a lot of potential here to make water and energy from sunlight if you do it in this con generated way I want to say a little bit about the amounts of energy that are used to produce water by desalination I mentioned some numbers before and I want to compare those numbers to other things that we do to get water I’ll start just with a couple of the numbers near the top I’m talking about the amounts of electrical energy kilowatt hours per cubic meter that are required to do things so if you wanted to desalinate water using multistage flash like the co production plant that I showed you use something like 10 11 12 13 kilowatt hours per cubic meter if you had a state-of-the-art plant if you do it using reverse osmosis you might use three kilowatt hours per cubic meter so it’s better the best you’re ever gonna do from under the laws of thermodynamics is in the range of about one to two kilowatt hours per cubic meter you can’t need that so this is sort of where things are for desalination now if you compare that to say pumping water out of the ground to pump water up 50 meters from say 150 feet below the surface up to ground level takes about 0.25 quarter kilowatt hour per cubic meter so 1/4 as much as the best you can do with desalination to pump that same water a hundred and fifty kilometers over ground with no grade no up and down is about point six kilowatt hours per cubic meter to do conventional water treatment purification we might normally do point two to one kilowatt hours per cubic meter and these things can add up when you start going through the whole water distribution cycle waste water treatment at the end it’s a very last row here may be 0.45 kilowatt hours per cubic meter it’s all part of the life cycle of how we used water the biggest contributors to the amounts of energy used in domestic water are all found in and use when you get to a household or a commercial activity a hotel a hospital actory a lot of energy is expended to heat water and so if you’re using an electric water heater you want to raise it up to the typical temperature you’d use to take a shower you’re gonna use something like 70 kilowatt hours per cubic meter many many times which used desalinate or to transport or treat water so they’re very high impacts at end-use you don’t see those drag recover all use you don’t see those if all you’re doing is cooling water in a power plant it’s using water to cool a power plant but on the other hand the amounts of energy associated with other kinds of venues are enormous and that has to be kept in mind I’ll mention that if you wanted to recycle the water you want to take waste water and purify it to the point that it would be good for drinking water you would use something in the order of one to one-and-a-half kilowatt hours per cubic meter about like ideal sea water desalination maybe a bit less so water recycling is energy intensive but far less so than desalination and that’s important too to give you an idea of the scale of the water transfers that are used I’ve drawn a map of California I borrowed from the Wikimedia Commons a map of California here this is the state of California two of the large water projects serving Southern California bring water from either the Sacramento area down to Southern California or from the Colorado River over to Southern California this is the distance of almost 400 kilometers and the other is even longer coming from the north to the south the amount of energy used per cubic meter is 2.6 kilowatt hours of electricity it’s very high very comparable to desalination of seawater the amount used to take water from the Colorado River to Southern California it’s around 1.6 kilowatt hours again not so different than what it would take to just desalinate the water locally and there are consequences to these water transfers because you’re taking it out of the local environment I showed you Mono Lake previously I’ll mention the example of the Colorado River as well this is the Aysen of the Colorado River originating here in Colorado traveling through Utah down into Arizona along the california nevada borneo

arizona border and finally into the gulf of mexico excuse me the gulf of california on average the amount of water traveling in the vicinity of the Glen Canyon Dam is about 500 cubic meters per second 100-year average fairly large amount of water by the time you get down here to the northern international border near Yuma the average is about 56 cubic meters per second about 10 percent of the amount of water that was up here much of that water has been diverted in Southern California Phoenix other cities in the area some years by the time you get to the southern international border the average flow is zero the water has simply been extracted completely from the river this according to Wikipedia is a photograph of the Colorado River at the southern international border so the point is that by making the choice to transport the water from one place to another you have a very substantial environmental impact in addition to the energy cost and that has to be considered in making decisions about where you’re going to get water whether you might be salan eight or recycle locally as opposed to importing water from another place the last example of clean water technology that I’ll mention comes from Singapore in Singapore they have a very active program in recycling waste water and reusing it Singapore is essentially an island nation it’s adjacent to land only on the border with Malaysia and they get most of their water supply from Malaysia their contracts with Malaysia are going to run out in 2060 and they’re very concerned about obtaining water independence before that happens so they’re very active in desalination and water recycling both at present recycling waste water meets about 30 percent of Singapore’s demand thirty percent of it most of that water is used for non potable non drinking purposes it’s used in their factories where they make you know semiconductors and other things like that maybe 10% is reinjected into their main water reservoir and some of it is distributed to the public and these colorful bottles that the young lady and the photograph is holding they call it new water they give these away at public events with the hope of increasing public acceptance of the concept of water recycling their aim is to meet 50% of their demand with recycled water by 2060 so I’ve talked to a lot of people from a lot of different cultures about reclamation and recycling of water and there are substantial barriers I think in many people’s minds to using recycled water in some cases they’re very strong well I think in most cultures there’s strong cultural taboos against waste water and and you know it’s contact with people and so forth one of the things that’s important to note about this kind of recycled water when it’s been treated with these types of filtration and reverse osmosis UV ultraviolet disinfection this water is typically going to be cleaner than the water that you receive for many municipal supplies that are just taking surface or river water because it will have removed all of the synthetic organic compounds that are not removed by most standard municipal treatments and so potentially this water is actually cleaner than what people are getting from supplies they may consider to be more acceptable so to sum up I haven’t gone through all of the technology research at MIT on this topic I will say that I’m aware of more than 25 faculty members at MIT and hundreds of students who are doing research on clean water technology and water supply and there are many other institutions around the world that have similarly large scale efforts there’s some very substantial efforts in industry both here in the Commonwealth and elsewhere to develop new technologies and to make them cheaper more affordable more reliable to meet the challenge of growing water scarcity as the world’s population rises in terms of technical issues things that are really driving new technologies and desalination include advances in sensing and control and actuation our ability to detect water quality in real time and to control sensors to find leaks and water distribution networks as well novel materials things that we get through nanotechnology and nano engineering we’ve got people working on advanced membranes of all sorts technologies to prevent bacteria from growing in the membranes and the water systems we have

people who are using various types of nano engineering to make molecular scale filters these are things that can filter at the one to two nanometer level there’s a lot of work on solar energy that’s being directed this way particularly on the concentrating power the optimization of its use there’s a lot of work being done on system performance because at the end of the day water technology has to fit within a system context it’s not just a widget that works on your desk and take salt out of water it’s got to go with the rest of the distribution system and with all the things that come with being in a system setting and there’s also a lot of work in looking at water technology for sustainability and particularly in the developing world I have colleagues at MIT who are sending students to Africa to work with small villages on their local water supply issues attempting to design new techniques that can be deployed affordably and maintained by people there and so there’s there’s a lot of activity in addition the research on water around the world is highly collaborative across many countries water conferences are very international much of the research sponsorship that we see for water at MIT is coming from foreign governments foreign institutions large multinational companies that are trying to solve water problems not just in the US but worldwide perhaps in countries that have very acute shortages of water so I’ll close there and I thank you all for your time and attention it’s my pleasure to talk to you and if you have any questions shoot me an email it was sort of inevitable that I got into mechanical systems and engineering my father happened to be an engineer as well very famous one as well a very well-known engineer and and so the path kind of unfolded for me I knew from early on that I wanted to go on into academics and do this kind of work were you planning as a child to go into de salad issue no not at all not at all I mean originally I thought I might might do things that were more oriented toward energy and fluid mechanics and some related subjects so I got involved in desalination and really the last five years or so as it became apparent that the world had a growing problem with water and it turned out that many of the basic skills that I developed over the years were very naturally adapted to the development of desalination technology so you fell into it very very well right right and what about your work do you like the most what I liked the most in my work is when my students really get interested and excited about the things we’re studying either in a class or in research when they start to take off on their own they come up with their own ideas and you know they get fire in the belly about these concepts and and go on to have a career based on what they learned in school this is an age of engineering would you agree with that is that the case we live in an age of technology and science and you know today’s world I think engineering is is is in itself a liberal art and yeah you know the liberal arts are the things that set you free right they make it possible to live in the world as a productive citizen and knowing something about technology and how science and technical work as just as essential as being competent in reading and writing and knowing history and literature things well put is there anything about your work that is slightly frustrating or more than slightly from I think I think anybody who works and is in a workplace encounters frustrations from time to time yeah for me I guess the hardest thing is when we’re trying to do something as a group and there’s somebody who is not ready to be a team player and that can be very frustrating yes but in general you’ve had a brilliant career and you know I wish you all success in the future as well and we’re very very honored to have you with us thank you