In a warming world, freshwater production is moving deep beneath the sea

CARLSBAD, Calif. (AP) — A company about four miles off the coast of Southern California claims it can solve one of desalination’s biggest problems by taking the technology deep below the ocean’s surface.

OceanWell’s planned Water Farm 1 will use natural ocean pressure to power reverse osmosis (a process that forces seawater through membranes to filter salt and impurities) and produce up to 60 million gallons (about 225 million liters) of freshwater per day. Desalination is energy-intensive and production takes place at sites around the world. 500 and 850 million tonnes of carbon emissions per year – roughly approaching 880 million tons It is being propagated by the entire global aviation industry.

OceanWell claims its deep-sea approach, 1,300 feet (400 meters) below the water’s surface, will reduce energy use by nearly 40% compared to conventional facilities, while also tackling other major environmental problems that plague traditional desalination: highly concentrated brine can be discharged back into the ocean and used there. damaging seafloor habitats, including coral reefsand entry systems trap and kill At the base of the marine food web are fish larvae, plankton and other organisms.

“The world’s freshwater future will come from the oceans,” said Robert Bergstrom, CEO of OceanWell. “And we’re not going to ask the ocean to pay for it.”

This is an ambitious promise at a time when the world desperately needs alternatives. As climate change intensifies droughts, disrupts rainfall patterns and fuels wildfires, more regions are turning to the sea for drinking water. For many countries, particularly in the arid Middle East, parts of Africa, and Pacific island nations, desalination is not optional; There is not enough fresh water to meet demand. more than that 20,000 plants It now operates globally and the industry has been expanding at approximately 7% annually since 2010.

“With the increasing challenges of drought and climate change, desalination will become increasingly prevalent as a key technology on a global scale,” said Peiying Hong, professor of environmental science and engineering at King Abdullah University of Science and Technology in Saudi Arabia.

But scientists warn that the cumulative damage to coastal ecosystems – many of which are already under pressure from warming waters and pollution – could intensify as desalination scales up.

Search for solution

Some companies run their power plants with renewable energy, while others are developing more efficient membrane technology to reduce energy consumption. Some take the technology completely underwater. Norway-based Flocean and Netherlands-based Waterise have tested subsea desalination systems and are working toward commercial use. Beyond Southern California, OceanWell has signed a deal to test its system starting this year in Nice, France, another region facing intensifying drought and wildfires.

Currently, the technology is under development. A single prototype is operating at the Las Virgenes Reservoir, where the local water district has partnered with the company to diversify its water supply. If successful, the reverse osmosis chambers would eventually float above the seafloor in Santa Monica Bay and be anchored with a minimal concrete footprint, while an underwater pipeline would carry freshwater to shore. The system will use screens designed to keep out even microscopic plankton, producing a less concentrated brine discharge.

Gregory Pierce, director of the UCLA Water Resources Group, said deep-sea desalination looks promising from an environmental and technical standpoint, but the real test will be cost.

With new technologies, “it’s almost always much higher than you anticipated,” he said. “So I think the technology is either there or it will be gone.”

Las Virgenes Reservoir serves approximately 70,000 residents in western Los Angeles County. Almost all of the water comes from the northern Sierra Nevada and is pumped over about 400 miles (640 kilometers) of the Tehachapi Mountains; It’s a journey that requires a tremendous amount of energy. Due to years of low rainfall and snowpack in the Sierra, the reservoirs and communities it serves are suffering.

California’s desalination dilemma

The Carlsbad Desalination Plant, located about 100 miles (160 kilometers) down the coast, has become a focal point in the state’s debate over the environmental tradeoffs of desalination.

The facility became operational in 2015 as the largest seawater desalination plant in North America. Capable of producing up to 54 million gallons (204 million liters) of potable water per day, the plant provides approximately 10% of San Diego County’s water; This is enough for approximately 400,000 households.

Intensifying drought and wildfires in Southern California have exposed the region’s unstable water supplies. Agricultural expansion and population growth have depleted local groundwater reserves, making cities dependent on imported water. San Diego imports roughly 90% The bulk of its supply comes from the Colorado River and Northern California, resources increasingly strained by climate change. Desalination has been proposed as a solution: a local, drought-tolerant source of drinking water drawn from the Pacific Ocean.

But environmental groups have argued that the plant’s seawater intake and saltwater discharge pose risks to marine life, while high energy demands increase water bills and worsen climate change. Environmental organizations filed a lawsuit before the facility started operating. more than a dozen Legal challenges and regulatory disputes. Most were rejected, but some led to changes in the project’s design and permits.

“A tremendous amount of water is being sucked out, and marine life with it,” said Patrick McDonough, senior attorney for the San Diego Coast Guard who has participated in many legal cases related to the project. “We’re not just talking about fish, turtles, birds, but larvae and spores—entire ecosystems.”

A. 2009 Regional Water Quality Control Board order He estimated that the facility would trap about 4.5 kilograms of fish per day, and that these impacts would need to be offset by restoring wetlands elsewhere. Seventeen years later this restoration is still not completed. And 2019 research found that the facility’s brine discharge increased offshore salinity above permissible levels, but detected no significant biological changes; this was probably because the plant had already been heavily altered by decades of industrial activity of a neighboring power plant.

These effects are particularly severe in roughly California. 95% of coastal wetlands largely lost to development, the remaining lagoons remain vital habitats for fish and migratory birds.

“This is critical, and when we start dealing with unfortunately sparse coastal lagoons and wetlands, this can have huge impacts on the ocean,” McDonough said.

Michelle Peters, CEO of Channelside Water Resources, which owns the facility, said the facility uses large organism exclusion devices and one-millimeter screens to minimize marine life intake, but acknowledged some smaller species may still get through.

He said the plant dilutes the brine discharge with additional seawater before releasing it back into the ocean, and years of monitoring have shown no measurable impact on surrounding marine life.

The Carlsbad plant has significantly reduced energy consumption through efficiency improvements and is working under a plan to make the facility carbon neutral, Peters said.

Many experts say recycling and protecting water should come first; He notes that wastewater treatment generally uses much less energy than desalinating seawater and can significantly reduce impacts on marine life. Alongside the desalination partnership, Las Virgenes is running a wastewater reuse project.

“What we’re looking for is a water source we can rely on when Mother Nature can’t provide it,” said Pedersen of Las Virgenes. “Developing new local water resources is a really critical measure for greater drought and climate preparedness.”

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Follow Annika Hammerschlag on Instagram @ahammergram.

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