Researchers at Lawrence Berkeley Labs discuss their work on groundwater recharge, brackish desalination, and seawater desalinization
As droughts intensify and the snowpacks diminish, California will need creative solutions to provide enhanced water supplies for urban use and agriculture. Scientists at Lawrence Berkeley National Laboratories are working on addressing these problems, focusing on groundwater recharge, low-cost desalination, and energy efficient purification.
Like other national labs, Lawrence Berkeley National Laboratory exists to tackle the biggest, hardest scientific challenges; however, Lawrence Berkeley is different in that they are the only national lab that is wholly managed by the University of California and is 100% dedicated to open research. The lab represents a $1 billion per year federal investment that benefits the entire University of California system with more than 4000 California scientists use these facilities each year, including researchers from every UC campus.
At a forum at the UC Center in Sacramento earlier this year, researchers from the Lawrence Berkeley National Laboratories discussed their research on groundwater recharge, brackish desalination, and seawater desalination.
Dr. Peter Fiske is the Director of Water Energy Resilience Research Institute at the laboratory, which brings together researchers from multiple disciplines to tackle the biggest challenges in water. He began by noting that the Lawrence Berkeley National Laboratory possess some of the premier research capabilities for tackling challenging problems, such as water. About 30% of research is conducted in collaboration with other sponsors besides the Department of Energy, some of those being California agencies.
“The particular reason we are coming to you today is that water research at Lawrence Berkeley Lab is growing, and so we think it’s very timely to tell you about some of the emerging trends we’re seeing in water technology and why it might be important for water’s future,” Dr. Fiske said, noting that today’s presentation will feature three of their scientists who will discuss their research as well as some of the scientific trends they are seeing that could indicate pathways for new sources of water for California. “We want to let you know that we intend to be partners with Sacramento to create a sustainable water future for California.”
Dr. Fiske explained that the Department of Energy focuses on water because water is intimately related with the production of energy, from the use of water for oil and gas production to the use of water for refining fossil fuels. In California, water is used directly to generate power with hydropower, as well as the power plants that need water to use water in the cooling process to regulate their temperatures.
“At the Department of Energy, there is a realization that energy is a critical part of the water story as well,” he said. “From the time we use electricity to pull water out of the ground in our water wells, to the energy we use to treat drinking water all the way to the energy associated with wastewater treatment, water and energy are inextricably linked. And that’s why the Department of Energy realizes this is a coupled problem.”
California has long recognized that water and energy are a coupled problem, and Dr. Fiske noted that the recent drought provided an interesting opportunity to realize just how inextricably linked water and energy were. During the drought, the citizens of California responded admirably to the call for water conservation, achieving about 25% reduction in water use. A team of researchers at UC Davis looked at the amount of money being spent through a wide variety of different energy conservation programs, covering all aspects from building energy conservation to clean vehicle conservation.
“If you total up all of the money that California spends on those energy conservation programs, how much money and energy do we save, simply by conserving water?,” said Dr. Fiske. “When they tallied it up, it was shocking. The amount of energy saved simply with the water conservation in California was equal to all the other conservation measures we do as citizens in California combined. So that really was a revelation that in California, water is energy and energy is water.”
A comprehensive R&D group has been organized at Lawrence Berkeley National Laboratory called the Water Energy Resilience Research Institute (or WERRI), which is organized around four basic themes: Generating new water sources such as improving water treatment technologies to make it more energy and carbon efficient, and developing water treatment processes to treat water that cannot be economically treated presently; Storing water for future use, with groundwater being the principal area of storage for California; Predicative climate modeling to determine where the distribution of water in the future as well as the where the risks will be; and how to influence and optimize the demand for water systems and how to create programs that align the energy and water efficiency with the needs of citizens.
“A lot of people don’t realize that California is the most hydrologically engineered place on earth,” Dr. Fiske said. “We have built more infrastructure to move water around than any other place, and frankly, that investment our parents and our grandparents and our great grandparents made is one of the reasons why we are the fifth largest economy in the world. All of that infrastructure and more infrastructure will be needed in the future, but the 20th century approach of technology, while it certainly will be an important part of our future, those technologies alone will not get us to a sustainable California future. We need to think about new technologies and new ways of creating water supply.”
“Water is not scarce in California,” he continued. “We have double the average rainfall of Australia and Israel. But it is uncertain, and with climate change, we will only be seeing greater uncertainty on where the water will be and when it is available. And frankly that uncertainty is what is a real threat to our economy and to the well-being of California citizens. We think science can be used to reduce that uncertainty and to provide assurance and resilience to our water supply in the future. In fact, the irony is that many of the places in California where we have the greatest water stress also have abundant renewable resources. They are sunny and they are dry.”
“We would like you all to think about the coupled problems we have in California today between water production, housing, and agriculture. Imagine if we could combine those problems and create new housing in new communities with new supplies of water that were sustainable, utilizing renewable resources both from the sky and from the ground. That’s the sort of optimism we think is worthy of California and that’s the sort of work we do at Lawrence Berkeley National Laboratory.”
Mr. Fiske was then followed by presentations from three researchers with different scientific backgrounds and different areas of research:
Dr. Chinmayee Subban next discussed how emerging low-cost high efficiency desalination technologies can take groundwater that presently is not usable and clean it to the point where it could be used for agriculture.
Dr. Dan Miller then wrapped it up with a discussion on the emerging trends in ocean desalination.
DR. PETER NICO: Aquifer Recharge: Saving rain for a sunny day
About 96% of all liquid freshwater on the planet is groundwater, and it’s an exceedingly important part of the hydrologic cycle. “Groundwater is critical to our life, our agricultural life and our urban life in California and in much of the world,” he said. “But its current use is unsustainable – to the tune that we overdraft 1 to 2 MAF every year, meaning we take out more than naturally goes back in. This is a picture of Science Magazine looking at the droughts and mapping out the loss of groundwater over that time, entitled ‘the drought we can’t see.’ We overdraft more when we’re in a drought.”
In 2014, California passed the Sustainable Groundwater Management Act, which means that groundwater management needs to change. Dr. Nico said that science can help improve management strategies, so he will discuss some of the science solutions that researchers at the laboratory have been working on to help with groundwater issues.
California’s water life is uncertain. Dr. Nico presented a graph depicting four years of flow for the American River, pointing out that there are two or three big years and then one really small year, and even within the wet years, there are just a handful of storms. “We get half of our water in 5 to 15 days per year, so it’s very sporadic and very uncertain and we want to couple that to a groundwater system that we can manage over decades, one that can bring us through a decade-long drought.”
One of the tools that researchers at the Lawrence Berkeley National Laboratory have been working on is using agricultural land to infiltrate water; however, one of the challenges is determining where there is suitable subsurface for infiltrating water, as not all land is suitable for infiltrating water into the aquifers.
Researchers have been repurposing technologies to help see the underlying geology to assess the suitable lands for recharge. One example of a project they are working on is spreading out water on an almond orchard in the winter. The picture on the right hand side of the slide is an almond orchard in January of 2017; the trees are dormant and it was pouring down rain.
“We used the technology we have to run a series of electrodes down the center of that orchard to look at what the ground looks like underneath, because we want to know where the sandy areas area and where the clay-ey areas are,” said Dr. Nico. “If you take a groundwater suitability map for infiltrating water, this all looks good, but if you look at the colored map of the ground underneath … The red areas are very sandy, the blue areas are much more clay-ey, and that’s going to make a big difference when the water starts to infiltrate.”
In January, while it was raining, the farmer applies 6 inches of water to dormant trees in the rain because that’s when the water was available, and researchers watched where that water went.
“We start with a blank at the beginning of the experiment, and we look where things are turning blue,” said Dr. Nico. “Where things are turning blue is where the water is going. We can see the top gets very uniformly wet, because we spread it out all over, but once you get below that surface, the water doesn’t go uniformly down; it goes to a handful of those very sandy places. That’s the water that went down quickly, that’s where most of it went down.”
This is important information for predicting which part of the orchard is most suitable for infiltrating water, and if you have to fallow land, deciding which land to fallow and which land to use for infiltration. It’s also important to know how much water can be applied without hurting the trees because how fast the water infiltrates is important. “All of that more detailed understanding of the subsurface relates to how this land can be used for that kind of process, and that’s what we’re trying to help with,” Dr. Nico said.
Researchers have also been studying subsidence which, in simple terms, refers to the sinking of land due to withdrawal of water from the underlying aquifer. Subsidence has been a problem historically and continues to occur. Subsidence is now monitored from space by satellites bouncing laser beams off of the ground.
Dr. Nico presented a map showing subsidence in the Central Valley from 2014 to 2015, noting that the areas in blue around Tulare and Visalia are where 12 to 16 inches of subsidence occurred due to groundwater pumping in the area; the black lines on the map are natural gas pipelines which can be damaged by subsidence. Researchers are using subsurface modeling and prediction capabilities to predict risk and stress on natural gas pipelines from subsidence in an effort to try to understand how that water result is coupling with the energy infrastructure.
With satellites flying over California and collecting data every week or so, the subsidence can be monitored in very fine time resolution.
On a more positive side, the ground goes down but it also comes back up somewhat in wet years. The graph on the slide shows the subsidence at a single point in the Tulare Irrigation District over two and a half years; the blue bars are the winter season; the white spaces are the summer season.
“You can see it drops down about 6-7 meters,” said Dr. Nico. “During the summer months, it drops fast. In the winter of 2015-2016, it slows down because nobody’s pumping and because it’s raining. Back to the summer, it drops fast again, but then in 2016-2017 we get a huge amount of rain, and not only does it flatten out, but it actually starts to come back a little bit. Ideally you wouldn’t like the ground to move back and forth at all frankly, if you’re a bridge or a pipeline, but we can still use this to try to understand how much water is coming in and coming out.”
The ground movement can be used to create a map of the entire Tulare Irrigation District, shown in the left corner of the slide. Each pixel on the map is colored red or blue, representing whether the ground went up and down.
“You can see the amount of recharge that there was, and we can integrate that over the entire Tulare Irrigation District and we can say that that wet winter recharged 175,000 acre-feet of water,” he said.
The researchers contacted the head of the Tulare Irrigation District, and told them what they had estimated for recharge, an as it turns out, the District had estimated recharge at 173,000 acre-feet. “We’re in the right area for this and we can do this by satellite in real time, up and down all the time to help keep track of where the water is coming and going from,” he said.
Lastly, there is the issue of preserving the water quality while managing groundwater, which is a big challenge. The map shows wells in California that have arsenic above the 10 ppm level. Dr. Nico noted that this is not contamination because somebody spilled something on the ground; the arsenic is naturally-occurring and coming out of the sediments.
He presented a slide showing where the arsenic is coming out into the water, noting that the arsenic is coming out into the water in the same places where the groundwater is subsiding more; this is because as the ground collapses, the layers that have the high arsenic water in them are being squeezed, causing the arsenic to come out into the rest of the water supply.
“That’s just one example of a process we need to understand in order to manage correctly because whether it’s arsenic or chromium or uranium or boron or a lot of these things we can worry about, these are natural contaminants, so the source doesn’t matter,” he said. “There’s nobody to sue or blame or go after. They didn’t dump it on the ground. The source is there; what matters is the mechanism that takes them from the rock, from the sediment and out into the water. And more importantly, how those fundamental geochemical soil mechanisms interact with the management strategies we employ.”
“We want to be ahead of this, so we want to have management strategies that are smart so that we don’t get things into solution,” he continued. “The chemical insight that we can bring to these processes about pressure, about oxygen changes that lead to solubility of certain things, and about what kind of dissolved minerals there are that cause arsenic release or uptake by the sediment – understanding these mechanisms and using our insight and models to predict how they change under different kinds of groundwater management practices is what we’re trying to do to keep the water as clean as we can keep it.”
Dr. Nico then concluded by noting that so much of the land in California is underlain by groundwater. The boxes on the diagram show the relative concentrations of groundwater as compared to snowpack and the amount of reservoir storage; it’s been estimated that there’s as much as 850 million acre-feet in the state’s aquifers, which far exceeds the snowpack and surface water amounts. “We can’t pump it all out for the reasons I’ve just described, but if we could just learn to manage well, smartly, this top box, we can account for a lot of the problems we’re concerned about in terms of dams and loss of snowpack.”
DR. CHINMAYEE SUBBAN: Low-cost desalination of brackish groundwater: Turning the brown valley green
She began by presenting a picture she took from Route 33 near Shafter, California. “To me, it’s a very good example of what engineering and technology can do,” she said. “California’s been described as the most hydrologically altered landmass on the planet … there’s a clear mismatch between where it rains and where we grow our food, and the ability to grow food in these arid parts of California has been made possible because of engineering infrastructure projects.”
She noted that it is because of the State Water Project (and the Central Valley Project) that has made California the top supplier of nation’s fruits, vegetables, and nuts; one-third of all vegetables and two-thirds of all fruits and nuts consumed in the US are produced in California. California’s land area is about 100 million acres, 43 million acres of which is used for ag. Of that, just 9 millions of acres is used for irrigated agriculture, but it is that 9 million acres that is responsible for 62% of all economic output from agriculture in California and so the state has really deemed it prime, unique, and statewide important land, she said.
However, in recent years, some of the land had to be fallowed with the 2015 drought causing about 540,000 acres to go fallow and resulting in $3 billion in losses, as well as about 21,000 lost jobs. In 2016, 770,000 acres had to be fallowed.
One of the options for finding water supplies for agriculture is to look at brackish groundwater, which is currently an untapped resource, she said, explaining that freshwater is defined as anything that has half a gram of salt of less per liter or water; seawater is about 35 grams of salt per liter of water, and brackish water has a lower salinity window, about half to ten grams of salt per liter.
There are a lot of naturally occurring brackish aquifers that have been found, but there are also new sources of brackish water generated as a result of human activity. One example is groundwater contamination from fertilizer use in agriculture-heavy areas such as the Central Valley; another example is seawater intrusion into groundwater in coastal aquifers.
“There is an abundant amount of brackish water but the problem is we can’t use it for irrigation as is, because almost all the plants are very sensitive to salt,” said Dr. Subban. “So in order to use these sources of water that exist and are available, we need to treat it and get rid of the salt.”
At a high level, the brackish desalination process involves passing brackish water through a technological process to separate the water and salts, which will yield a freshwater stream suitable for irrigation and a second stream which is a waste brine with the salt concentrated in it. A desirable technology would be very energy efficient, have a high freshwater recovery, be inexpensive, easy to operate and maintain, and modular so it can be used at different site scales.
So for low salinity brackish water, the ideal approach is to look at charged based salt separation. Dr. Subban explained that when salt is dissolved in water, it splits into sodium ions that are positively charged and chloride ions that are negatively charged. If a voltage is applied, the positively charged sodium ions will be attracted to and stick to the negatively charged plate, and the negatively charged ions will be attracted to and want to stick to the positively charged plate, and the result is salt-free water.
This technology is attractive for low salinity water sources, but the problem is that the materials are too expensive and not robust, and sometimes can’t select for specific ions. So to address this, researchers at the Berkeley Lab have developed low cost electrodes by utilizing industrial-scaled inexpensive polymer materials and composites that work very well. These materials have been tested in a prototype unit to make sure they can reproducibly remove salt. Currently, researchers are evaluating the scientific and engineering challenges in terms of limitations and opportunities for this technology, specifically looking at how the technology performs when the water quality changes, how it can be operated to be the be most energy efficient, and how it can be scaled up and down.
But not all brackish water is made equal, Dr. Subban pointed out. “You can have two sources that are equally salty but the salt contribution can be from very different kinds of salts, so knowing what’s in the brackish water could give you some new opportunities and abilities to treat it differently,” she said. “So for example, if you have a source of water where you want to selectively remove only the ions that are harmful for humans and plants, but leave all the other salts behind that are completely benign and safe, then that would save a lot of energy because you’re not removing all of the salt.”
By designing the right materials, the harmful substances can be removed, and the substances that are not harmful can be left behind, and this has clear applications in the state of California.
“For example, in the Central Valley, the use of fertilizers has contaminated the groundwater with nitrates, and high nitrates are not safe to drink, and often the most affected by these are communities that are rural, low income communities,” Dr. Sabban said. “So if we can make materials that can selectively remove the nitrate but keep everything else in that is safe to drink, then that would be a very effective way of treating these water sources and making them viable for drinking.”
The second example is boron, which is a micronutrient for plants, but when it is present in excess, it becomes a problem. “There are sources in the Central Valley that are currently not used because of high boron, but everything else is fine with the water source,” Dr. Sabban said. “So if we can selectively remove the boron, then there’s more water that is available.”
These are the opportunities that researchers are exploring, but in order to do it in an effective way, they must communicate with people that are going to use it. So lab researchers have been engaged regularly with growers in the Central Valley, Coastal California, and Southern California to understand their constraints, the challenges they face, and how this technology would be applied. They also partner regularly with the UC Extension Agents in collaborating on projects, because they are in the field and are experts on agriculture, and obtaining the real-world view is important to do, she said.
Researchers also consider the energy impacts for the state. California has a lot of excess solar agency, so is there a way desalination technologies which require energy can offset some of the excess solar, and can demand response be accommodated? These are some ideas that researchers at the lab are working on. Taking a technology or any new idea and implementing it requires a highly interdisciplinary team of people working together, so at Berkeley Lab, there area a variety of different project experts from policy to technology to economics working on projects together, she said.
“With that, I want to leave you with a very positive note,” said Dr. Subban. “California has been a leader and we’ve done it before. When Californians originally agreed to build the State Water Project in the 1950s, people thought we were crazy.”
“But today, a lot of California’s economic strength has been attributed to the State Water Project. And I think we can do it again. What we need to do is have sustained investment in water-related technology and engineering to sustain California’s productivity and economic growth.”
DR. DAN MILLER: Energy-efficient desalination membranes for a sustainable future
He began by noting that desalination as a means to secure a reliable source of potable fresh water from the ocean came into the national consciousness in the middle of the 20th century when President Kennedy recognized that the water shortages that we would experience with a growing population not only created technological hurdles, but also social and geopolitical issues as well. President Kennedy famously said, ‘Anyone who can solve the problems of water will be worthy of two Nobel Prizes: One of peace and one for science.’
The Department of Interior established the Office of Saline Water in 1955, and for 17 years, a broad portfolio of different technologies were funded to develop desalination technologies, including one of the very first saline conversion plant which was located in San Diego. At the time, two researchers at UCLA, Loeb and Sourirajan, were working on cellulose acetate membranes that were capable of separating salt from water. They found that these cellulose acetate membranes would allow water to pass through while rejecting salt and not allowing it to pass through. They struggled for many years with funding from the state of California with membranes that were too thick and didn’t allow enough freshwater to go through.
In 1963, just one year after President Kennedy’s famous quote, Loeb and Sourirajan had a breakthrough: They discovered a way to cast these cellulose acetate membranes into asymmetric structure. Dr. Miller explained that the cellulose acetate membrane they developed had a very large pore structure at the bottom, much like a sponge, but as you move up through the membrane, the pores get smaller and smaller; at the very top, there is a very thin, essentially non-porous skin layer of cellulose acetate at the top. This thin layer at the top allowed a lot of water molecules to go through, but was still sufficient to block the passage of salt ions. Loeb and Sourirajan continued to work on these membranes throughout the 1960s and the technique perfected in the late 1960s by researchers in San Diego. This forms the basis of all of the commercial desalination membranes that are in use today.
Modern desalination membranes reject 99.7% of the salt that comes into contact with them, which means for every 1,000 molecules of salt that are fed to the membrane, only three molecules will go through.
If a semipermeable membrane is placed between two chambers, one with freshwater on the left side and one containing salt solution on the right side, the membrane will allow water to go through but will block the salt, and the water will tend to move from the freshwater side into the salt solution to try to dilute the salt. That movement will create a pressure as the fluid on the right hand side as the salt solution rises, and eventually will reach a point where the pressure is great enough to prevent any further water from flowing through the membrane.
In reverse osmosis, a pressure is exerted in the salt solution that is greater than the osmotic pressure which squeezes the water backwards through the membrane, thus the name, reverse osmosis.
In practice, a typical reverse osmosis process takes the seawater coming in, puts it through a high-pressure pump that increases the pressure of the seawater; this is where most of the energy is consumed in reverse osmosis. The high-pressure water then goes into a membrane module, the water comes into contact with the membrane, the membrane lets the water can go through and the salt is rejected into a brine.
Current reverse osmosis membranes are manufactured in flat sheets by the mile; the long sheets of membranes are then cut up and folded into envelopes and they are wound into spiral wound modules. This allows a tremendous membrane area to be packaged into a relatively small module volume. A typical membrane module contains approximately 500 square meters of membrane per cubic meter of module – roughly a football field of membrane.
Membrane modules are manufactured in a huge variety of different sizes, from very large, industrial modules that are used in municipal treatment down to very small modules that can be used under your kitchen sink.
Although reverse osmosis is very often described as a power-hungry process, Dr. Miller said that reverse osmosis is actually remarkably efficient. The minimum energy required to separate salt from water, assuming no loss of energy of any kind, is just over 1 KW per cubic meter of freshwater that’s produced.
“In the 1970s when reverse osmosis first came onto the marketplace, it was in fact extremely power hungry with over 15 kilowatt hours to make a cubic meter of water,” he said. “But as time has progressed, the power consumption of reverse osmosis has come down dramatically, and modern reverse osmosis systems consume only around 2 kilowatt hours per cubic meter of freshwater that’s produced.”
Because of the compact nature of the modules and the relative efficiency of reverse osmosis processes, desalination world-wide is now a very large scale process, with 90 million cubic meters per day of desalinated water being produced – about 6 times the amount of oil per day that is produced. This desalination happens in over 18,000 desalination plants in 150 countries and it supplies drinking water for 300 million people around the world. The United States is the second largest desalinator in the world, just behind Saudi Arabia.
The Carlsbad Seawater Desalination Plant was completed in December of 2015. The plant produces around 190,000 cubic meters of freshwater a day with 14,000 reverse osmosis modules that have about 576,000 square meters of total membrane area – or about 100 football fields worth of membrane. The Carlsbad plant produces enough water for about 7% of San Diego’s consumption – about 300,000 people.
“It may seem like a small number, but the key here is that that water is reliable,” said Dr. Miller. “That water is not prone to drought or groundwater shortages. We can always produce this water. As large as this plant is, thought, it is dwarfed in comparison to some of the other seawater reverse osmosis plants in the world. Plants in Israel, India, and China are several times larger than the Carlsbad plant.”
However, Dr. Miller said that despite the promise of desalination, challenges remain. One of the key problems is that many reverse osmosis membranes do not adequately reject many toxic compounds, such as organic micropollutants such as boron and arsenic. The typical arsenic rejection of a state of the art reverse osmosis desalination membrane is about 70 to 80%, which is far below the 99.7% salt rejection that those exact same membranes exhibit. In order to remove the arsenic, they would have to have some kind of auxiliary purification technology to remove the arsenic separately, or run the water through the reverse osmosis process twice, which would then use twice the amount of energy to produce the same amount of water.
Arsenic is a huge problem in California, especially if reverse osmosis is used to purify water for agriculture, so developing reverse osmosis membranes that more effectively reject toxic compounds like arsenic would significantly improve water quality and reduce energy consumption, Dr. Miller said.
Fouling, or clogging of the surface of the membranes is another challenge, especially in seawater desalination. For example, the Carlsbad Desalination Plant takes in the seawater from a lagoon just outside of the city, which contains substances such as organic matter, particulates, microorganisms and minerals; these substances sucked up into the plant and clog the surface of the membrane. Fouling reduces the membrane productivity because the membrane is clogged and not as much pure water can go through it, so more pressure is needed for the freshwater to go through the membrane, increasing the energy requirement substantially.
One of the solutions Dr. Miller and other researchers are looking at is engineering the surface of the membrane so that it is less prone to fouling.
“These foulants can get trapped on the surface of the membrane or they can become entrained within pore structure of the membrane, and when that happens, the amount of energy that’s required to purify a given volume of water goes up as this fouling occurs,” he said. “What we’ve been working on is developing coatings for the surface of the membranes. These coating repel the adhesion of foulants on the surface of the membrane, and that allows the membrane to operate at a much lower energy to produce the same volume of purified water. So reducing the fouling adhesion to the membrane can substantially decrease the energy consumption in the desalination process.”
So in conclusion, Dr. Miller said, “Loeb and Sourirajan are science heroes. They never won a Nobel Prize, much less two as would have been suggested by Kennedy. But their invention is at the center of one of the greatest technological achievements of the 20th century which supplies water for millions of people around the world.”
“So what do we need to do? We need to stand on the shoulders of these giants and look forward. We want to improve the membrane rejection of toxic compounds like arsenic; we want to reduce the susceptibility of membranes to fouling and in so doing, we can help California meet the challenges of minimizing the cost and environmental footprint of desalinated water and also to reliably provide high quality desalinated water for a number of different applications, including municipal, agricultural, and industrial use.”