With drought becoming a normal feature of life in California, finding reliable ways to increase freshwater resources has become imperative. One promising solution may be desalination — the process of removing salt and other minerals from seawater or brackish groundwater to make potable water — which could potentially provide improved resiliency and create new sources of potable water within California’s diminishing supplies.
However, high costs and environmental impacts have so far limited the role desalination plays in the state’s water portfolio. But is there a larger role for desalination in California? At a webinar held in February 2023, the California Council on Science and Technology brought together four experts to explore the potential and the challenges of expanding desalination in California.
Desalination is, of course, not new to California; the first commercially viable reverse osmosis membrane was invented and patented by UCLA in 1960, and the first modern desalination plant was built over three decades ago on Catalina Island. Seawater desalination already contributes to local water supplies for some coastal communities, such as San Diego and Santa Barbara. Further inland, brackish groundwater, high in salts and other dissolved solids, is desalinated to serve communities in the Inland Empire.
However, desalination’s contribution to California’s water supply remains small: Seawater desalination only accounts for about 1% of California’s water supply; brackish desalination even less.
So why all the discussion about desalination? Dr. David Sedlak, Director of the UC Berkeley Water Center, said desalination could be a lifeline if you don’t have other water sources. “Where we see the importance of desalination for California’s water portfolio is in the places where they have either junior water rights, where there are no other good sources of water that haven’t already been exploited, where conservation has already been implemented, or where there are limited opportunities for water recycling. So there’s a real desire among these communities to have desalination as one of the tools in their arsenal for consideration.”
The high cost of desalinated water
However, the cost of desalinated water per acre-foot is often higher than most other water supply options. And these costs can vary widely between desal plants as costs are dependent on site-specific factors, such as the availability of land, conveyance from the desal facility to end users, and the contracting mechanism.
In most cases, desalination is a marginal water supply that would provide somewhere between five and 10% of a municipalities water source, so the costs should be amortized over the full water supply portfolio and looked at relative to the other available sources, said Dr. Meagan Mauter, the Research Director for the National Alliance for Water Innovation (NAWI) and an associate professor at Stanford University in the Stanford Doerr School of Sustainability.
Desal is getting more expensive in California, not less expensive; this is mostly due to permitting costs rather than energy costs, Dr. Mauter said. She foresees the costs will be reduced when small-scale plants are modular in their technology and uniformly deployed; these modular systems could then be brought in and put to work for a whole host of different water supply systems. Eliminating a lot of the design costs and the economies of scale in manufacturing and deployment will help drop some of those costs, she said.
Dr. Reza Lakeh, Associate Professor at Cal Poly Pomona, pointed out that the transition to renewable energy is an opportunity for desal plants. California aims to run the grid fully on renewable energy by 2045, which will impose a significant demand on energy storage technologies because of the intermittent nature of renewables in the power grid.
“This has a huge potential that can be tied into water desalination because we can consume the energy at the times that is not needed by other sectors to generate water,” he said.
Dr. Mauter agreed and noted that many facilities sign contracts with electricity providers to ensure grid stability by curtailing plant operations when power supplies are constrained – and deriving substantial revenue yearly, usually equivalent to 1-2 months of the plant’s total energy costs.
“We’re not designing for that right now in our desalination plants,” she said. “There’s an enormous opportunity to build flexibility into these desalination plant designs, potentially allowing them to flex their operation … if not daily, then several times a week. The value-add to the grid, especially in displacing the need for things like battery storage, is tremendous. And I think there’s an opportunity in the research arena to better articulate what that value is, and then also better design plants and standardize the design of plants that really allows for high intermittency operation.”
However, Dr. David Sedlak pointed out that the true value of seawater desalination and brackish water desalination is its reliability; during periods of extended drought, that water becomes much more valuable. Also, desalinated water can be used to blend with other water with slightly elevated concentrations of constituents to bring it to acceptable drinking water quality.
“So there are opportunities when you have desalination for increased drought resilience, and also using that extremely clean water to improve the overall water quality in a larger water system,” he said. “Here in California, many of our existing water systems need that low salinity water to improve their quality, aesthetics, and overall composition.”
Disposing of the brine
Discharging brine to coastal waters can cause the saltier brine to sink to the seafloor without mixing with the ocean waters, creating a salty zone that can impact marine life in that area. New diffuser technologies have been developed that mix the brine with ocean water as it is discharged, said Dr. Sunny Jiang, a professor of Civil Environmental Engineering at UC Irvine. Diffusers lower the salinity and environmental impacts dramatically.
However, Dr. Lakeh noted that the use of diffusers has been subject to many debates and discussions in academia. “There are papers that support this method of disposal, but there are others that show concerns, so there is no clear indication,” he said.
Disposing of brine is much harder for inland facilities, a challenge that has hindered the growth of brackish desalination. Southern California solved this problem by building a brine line from the Inland Empire to the coast, and the Livermore Valley has a pipeline that takes its sewage effluent to San Francisco Bay for discharge. Brine lines have also been considered for other areas.
However, Dr. Eric Hoek, a professor at UCLA and the faculty director of UCLA Sustainable LA Grand Challenge, noted that the brine lines in Southern California are either fully or almost fully allocated, so there’s not a lot of room for additional brine sources.
“I saw a map recently of what Southern California looked like when those pipelines were installed,” he said. “The population was a fraction of what it is now. Then, it was mostly dirt and undeveloped land that the pipes were laid through. But now there are neighborhoods and business districts and industry all surrounding them. And so to do that again would be unbelievably expensive. But in other places, there may be opportunities.”
“That brine has the potential to become feed streams and other industrial processes,” said Dr. Mauter. “It has the potential to help us source specific elements that we may be interested in. But, broadly, we need to look at place-based solutions for brine management that account for existing disposal pathways, subsurface geology, and existing markets that a concentrate might feed into.”
Dr. Lakeh pointed out that the real opportunity lies in the development of zero-liquid discharge technologies. “The development of technologies that desalinate the water to almost solids, or zero liquid discharge technologies, they can extract more water, and at the end, the reject of that process is a solid that can be repurposed in different applications, such as energy storage or construction,” he said.
Dr. Hoek noted that in the Middle East, they are already exploring the idea of productizing the brine for something which can be selectively removed from the brine of a much higher value, like magnesium or a bromide for industrial applications or even selling a clean sodium chloride brine for the production of chlorine and caustic soda.
“In many cases, the money from selling those products that you harvest from the brine can pay for the whole water treatment operation and with profit on top,” he said. “So some of the future direction is going to involve what some people refer to as valorizing what is traditionally viewed as a waste; squeezing as much clean, fresh water out as we can, and trying to extract value from high-value constituents that may exist in that concentrated brine stream.”
The potential for small-scale modular designs for smaller communities
Researchers have been developing modular systems that could be a potential solution for those reliant on wells at risk of running dry during droughts or those with water contamination problems, such as nitrate or arsenic.
Dr. Sedlak acknowledged that modular systems present challenges, such as making them operate autonomously, ensuring the maintenance is simple, and the system is not rejecting large quantities of water.
“Right now, you could deploy a small-scale desalination system that relies upon reverse osmosis or another technology to a household well or cluster of homes or a small community; they just happen to be relatively expensive,” said Dr. Sedlak. “By focusing on the best ways of using sensors, changing the materials used in membranes, and working on pretreatment, we think that there’s a path to lowering that cost and making it the go-to option when we think about protecting communities from threats of water contamination and also being able to access brackish water resources.”
“The water contamination issues in these small communities are not exclusively issues with total dissolved solids,” said Dr. Mauter. “There can be issues with nitrates or with arsenic. So the National Alliance for Water Innovation (NAWI) is piloting technologies designed to be small-scale systems that serve communities and may or may not be membrane-based. So you’re not generating the same degree of concentrate that needs to be managed in those inland communities, but are focusing on separating the ions of concern and doing so through either sorbent or electrochemical based processes.”
Streamlining the permitting process
Governor Newsom’s water supply strategy directs state agencies to consider avenues for streamlining coastal desalination permitting processes. Panelists agreed that developing modular systems could potentially speed up the permitting process.
However, Dr. Sedlak said getting it right with these early desalination projects is important. “I don’t work directly in the permitting process for ocean desal plants. But as an observer from the outside, it feels to me a lot like the early days of potable water recycling, where every single project is quite different from one another and undergoes a lot of scrutiny; those take a long time, there are differences of opinions, and it does delay the process.”
He suggested that an independent science panel might be able to provide advice on the technical issues complicating permitting because it does seem like every project is a Ph.D. dissertation. Once the state has permitted half a dozen projects, the permitting process will likely go much faster.
“Want it or don’t want it, desalination is going to come because you’re going run out of water,” said Dr. Jiang. “So California should seriously consider streamlining the permitting process.”
“I would just encourage us to think about desalination more broadly than just seawater desalination,” said Dr. Mauter. “There are a lot of impacted water supplies that are not available to us for consumption or productive agricultural or industrial use because of specific contaminants of concern or because of some specific ions that are at concentrations that don’t really allow for their use. So we need to think about desalination as serving a broad set of non-traditional waters. And we need to think about those non traditional waters as that will help provide California with a resilient water supply portfolio.”
“One of my observations from my time working on potable water reuse is that new technologies often undergo a process of ‘legitimization,’ where the public has to decide whether they think it’s the right thing to do,” Dr. Sedlak said. “Having lived through the legitimization of potable water reuse, I understand the importance of academic researchers, professional scientists, utilities, and regulators coming together to conduct research needed to support decisions about investments in future water infrastructure.”
Dr. Sedlak said the state needs to take the issue of legitimization more seriously by listening to the critics, doing the science, and building regulation in a way that addresses those issues. “We have potable water reuse, which is going gangbusters in the state. And on the other end, we have nuclear power, which is shutting down at a time when the state might have been well served by having it, and those can be traced to a lack of good stewardship by the legitimization process. And so we’re at a critical point for desalination. And if we get it right, this could be something in our portfolio going into the future.”