How viable of a water solution can converting seawater to fresh water be? Ask Bob Yamada. He is the San Diego County Water Authority’s (SDCWA) water-resources director. According to Engineering News-Record, Yamada explained that water recently began flowing through a new $1 billion, 54-million-gallon-a-day desalination plant in Carlsbad, California. The plant has been running smoothly since it opened in December, and it is expected to provide 10 percent of the water supply to local residents as a part of SDCWA’s strategy to diversify the region’s water-supply portfolio.
The plant is the largest desalination plant in the western hemisphere which enhances the status of its builder and operator, Poseidon Water. The San Diego Union Tribune clarified the roles Poseidon and others play in distributing water. Specifically, Poseidon will sell the fresh water it produces to SDCWA, the region’s main provider. The authority will resell that water to retail districts that serve residents, schools and businesses.
For California, the Carlsbad plant represents the mainstreaming of seawater desalination in the golden state. Ocean desalination has long been used in nations such as Saudi Arabia, Australia and Israel, where the company that designed the Carlsbad plant, Israel Desalination Enterprises, is based. Israel’s extensive use of desalination to conquer a seemingly perpetual drought has become an internationally recognized success story. California may be poised to join the trend, because approximately 15 other desalination projects have been proposed for the state’s coastline, from the San Francisco Bay Area to Southern California.
Desalination does have some critical challenges to address. As KQED Science points out, there are three main environmental considerations when building a desalination plant: how seawater is brought in, how the drinkable water is separated out, and what happens to the remaining salt at the end of the process.
The simplest intake is basically a straw in the ocean in pipe form -– a design that risks trapping and killing sea life. One solution is to affix a grate to the end of such a pipe, but tiny larvae and fish eggs can still be sucked into the pipe.
Instead, regulators tend to prefer what’s known as a “subsurface intake.” At a beachside site on Monterey Bay, California American Water Company is currently working on a proof-of-concept for this approach. They’re using directional drilling, similar to the technology oil companies use to extract fossil fuels. The idea is to run a slant well hundreds of feet out, passing beneath the dunes to a spot under the waves. From below 200 feet of sand, and well insulated from any vulnerable sea life, California American hopes to suck up a couple thousand gallons of water per minute.
Once the seawater gets to the plant, it has to be pushed through membranes fine enough that salt cannot pass through them. This requires immense pressure analogous to that of a powerful pressure-washer as well as a lot of energy. An official at a smaller desalination facility shared it takes $25,000 of electricity per month to produce enough water for 1,200 homes. Therefore, the operation of any desalination plant will likely drive up energy costs.
Only about half of the saltwater piped into a desalination plant is converted to drinkable water. All the salt that is separated out ends up concentrated into a brine-like liquid that’s much denser than seawater. As a result, this liquid doesn’t easily mix back in to seawater. If this brine-like liquid is dumped carelessly back into the ocean, it sinks and can kill any marine life having the misfortune of dwelling on the seafloor.
Last May, the California State Water Resources Control Board enacted new regulations that require permit applicants for desalination facilities to consider and use the best available site design and technology to minimize impacts on wildlife. Given California’s water needs and the success so far of the Carlsbad plant, Poseidon is moving forward with its permit application to build a 50-million-gallon-a-day plant in Huntington Beach, California. So, it looks like desalination has potential staying power.
(Photo: Visit to IDE Hadera, Flickr)