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How Desalination Plants Are Trying to Overcome Environmental Concerns

Stakeholders are exploring different options to reduce the much-debated environmental impacts of desalination to make it a more attractive option for drought-hit regions.

Written by Padma Nagappan Published on Read time Approx. 8 minutes
The Carlsbad, Calif. desalination plant.AP/Lenny Ignelzi

As California labored under a severe drought for more than five years, industry and media debated the pros and cons of desalination coming to the rescue of the drought-stricken state. About a dozen or so desalination plants have been planned or proposed up and down the Golden State’s coast, with the 50 million gallon (189m liter) per day Carlsbad desalination plant opened in December 2015 and Santa Barbara’s smaller desalination facility set to open this spring.

The deluge of rain across the state and snow in the mountains over the last couple months have reduced the intensity of the drought, and most of the state is drought-free. California also faces overdrafted groundwater aquifers in many places, including the agricultural hub of the San Joaquin Valley. And with climate change predicted to ensure a future with more severe drought, the state’s water supply concerns will remain a primary focus for water managers.

How big a role desalination plays in future water supply decisions in California may depend on how well the industry deals with environmental concerns.

It takes about 2 gallons (7.6 liters) of seawater to produce 1 gallon of desalinated freshwater, and this process of separating freshwater from salt leads to highly concentrated brine that is then usually sent back into the ocean. This brine is toxic to bottom-dwelling marine life when it settles on the ocean floor, and can also cause hypoxia or oxygen deficiency in the ocean floor area.

The process of drawing in the seawater – the intake – also impacts marine life, with fish and crabs dying when they are trapped against the intake screen, referred to as impingement, and when smaller marine organisms like plankton and fish eggs become sucked into the intake screens and killed during the treatment process, referred to as entrainment.

Impingement and entrainment are two threats to marine life. One way to reduce this impact is to switch from surface intake to subsurface intake, which extracts seawater from beneath the sea floor or a beach, with the sand acting as a filter. As a Pacific Institute report on the marine impacts of desalination points out, this can also reduce the chemicals and energy used in the treatment process, thereby reducing operating costs.

But the desalination industry is vehemently opposed to it, since subsurface technology will add significantly to the cost of the project, sometimes making the project financially unviable. However, the State Water Resources Control Board put in place environmental regulations that require subsurface intake (or alternative technology) to mitigate marine life impacts for most projects.

A third major concern is that desalination is an energy hog. On average, it takes 15,000 kilowatt hours of power to treat 1 million gallons (3.8m liters) of sea water, which is roughly twice as much as recycling wastewater, according to a 2013 Pacific Institute report. This makes energy the biggest cost of a desalination plant’s operating costs, about 55 percent, and it also makes plant operators vulnerable to spikes in energy prices.

Solar to the Rescue?

Beach-goers walking on the sand near the San Onofre nuclear power plant in San Clemente, Calif. The nuclear plant is now closed but a nonprofit wants to turn the facility into a solar-powered desalination plant. (AP, Lenny Ignelzi)

Beach-goers walking on the sand near the San Onofre nuclear power plant in San Clemente, Calif. The nuclear plant is now closed but a nonprofit wants to turn the facility into a solar-powered desalination plant. (AP, Lenny Ignelzi)

When it comes to energy input and the associated greenhouse gas emissions, the stakeholders at SolRio think they have found a way around these environmental concerns. SolRio is a nonprofit that aims to function like a water users’ cooperative. It wants to tap solar energy at multiple power stations to supply a desalination plant that would not be built from scratch, but would actually adapt existing facilities at the San Onofre nuclear energy generating plant that is in the process of being decommissioned.

Is solar energy going to be feasible to power a desalination plant? And how can a nuclear plant become a desalination plant?

“If we do go ahead, it will be about 10 years or so before we build the solar plant, and solar costs are falling,” said Randy Carlson, a system design consultant and SolRio’s director of the board. “In Dubai, solar is delivered for less than 3 cents a kilowatt hour and makes a profit. The cost of power comes from capital cost, so the energy costs depend on the interest rates we pay. We have ways of leveraging our resources to get favorable interest rates.”

Carlson said with solar, the main issue would be the need for storage, to bank the excess power generated during the day and use it at night, and to move it across transmission lines during peak periods.

“By distributing the storage capacity at different places on the grid, we can move our energy through critical transmission lines only at times when that capacity is not being used,” he explained. “One of the difficulties with a project of this size is that some power lines are at full capacity, like during hot summer afternoons. If we have to move power at those times, the power lines have to be upgraded, which costs money, and there are environmental concerns.”

When it comes to other environmental issues, Carlson said entrainment can be handled by locating the filtering operation as far upstream as possible, but SolRio is still looking at feasible options. As for brine, it plans to tap the diluting system that exists at San Onofre to cool the generators. The system has lengthy discharge pipes that have nozzles at each end that disperse the cooling water into the ocean, which he said could be used to dilute and dispose of brine.

“This is a fundamentally different project,” he said. “We are not trying to build a desalination plant for a local population. We are trying to build a way to serve 10 percent of the Colorado River water users.

SolRio proposes to transport about 1 billion gallons of desalinated water a day from San Onofre, which is on the coast between Los Angeles and San Diego, to be used by the Metropolitan Water District of Southern California (MWD), which imports some of its water from the Colorado River and is a regional wholesaler of water to 26 member agencies that in turn supply water to 19 million people.

In comparison, the Carlsbad desalination plant that supplies parts of San Diego County with water and is the largest built in the U.S., has a capacity of 50 million gallons (189m liters) a day. To do this on such a large scale, SolRio faces technical challenges, among them the need to build a tunnel to Diamond Valley Lake, a major Southern California reservoir.

Asked if SolRio has gotten buy-in from the stakeholders it plans to draft into its co-op, Carlson said yes, it has had positive responses from the industry, but is not at liberty to reveal who they are yet.

“We’ve encountered no one who has said it can’t be done on the technical side. Nobody. The issues are entirely on the political side,” he said.

Industry Perspective on Desalination’s Hurdles

From the corporate perspective, IDE Americas, which is the U.S subsidiary of Israel-based IDE Technologies, thinks that desalination should be one of the solutions that California pursues, but not the only one.

IDE built the Carlsbad plant and is working on the Santa Barbara plant that is scheduled to come online in March or April.

Like other proponents of desalination, Gilad Cohen, CEO of IDE Americas, alluded to the control over supply that it offers, without depending on rain or the snowpack, and the advantage of guaranteed capacity and quality. He pointed out how conservation, while an essential step, does not reduce the price of water, since the customer could end up paying more. He also called for transparency in calculating the price for other sources of water, when comparing it with the price for desalinated water, which experts say costs more.

“Are we comparing apples to apples when we compare desalination with other sources? If you look at pumping water from the Sacramento River or any other point, you still have to pump it, bring it into a treatment station, and salinity needs to be reduced sometimes before it’s distributed into the system,” he pointed out. “Is desalination expensive? I’m not sure. I don’t think so. If we start putting the real numbers into calculations, not just presumed numbers, it would be interesting.”

Desalination costs versus imported water costs vary in different circumstances, but for the San Diego County Water Authority, its Water Purchase Agreement with Poseidon Water for desalinated water from the Carlsbad plant in 2017 is $2,125 to $2,368 per acre-foot, depending on the amount of water purchased. By comparison, treated water from the Metropolitan Water District is $979 an acre-foot, and Colorado River water via a transfer agreement is $1,106, although the price of imported water could become more expensive over time, but a long-term contract assuring rates for the desalinated water is in place.

Cohen said he expects to see low-energy, no-chemical sea water desalination systems that provide an environmentally friendly intake process. It has not been deployed in California so far, since it needs more permitting, but it has been in use in Australia.

Chemicals are used to clean scaling buildup in the membranes of the filtration system, but IDE has a system that constantly backwashes the membranes without taking the plant offline or using chemicals. When scaling builds up, it requires more energy to push water through the membranes, so keeping them clean reduces energy use.

IDE typically uses fewer high-pressure pumps that are bigger and more efficient in the treatment process, and this enables flexibility in increasing or decreasing capacity depending on peak electricity hours, he explained. This method works in Israel and in Carlsbad, where it also recovers 40 percent of the energy coming out of the brine in a recovery system.

Subsurface intake can mitigate marine life impacts, but it has to be economically feasible, otherwise it’s not a bulletproof solution, he pointed out. In Carlsbad, because the plant is co-located with the Encino power plant, it uses water from the power plant’s retake line, so it did not build a new intake, and the brine disposed is only about 10 to 20 percent more saline than ocean water, instead of being twice as saline, he said.

“The market needs to evaluate new solutions, and see if we can accelerate the adoption process for new solutions,” he said. “This needs to be weighed by the regulators, industry and consumers who need the water at the end of the day.”

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