There were years of wrangling and competing designs. All the same, a plan is moving forward. 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 salt afterward.
The simplest intake is essentially a straw in the ocean -— a design that risks trapping and killing sea life. One solution is to affix a grate to the end of such a pipe, but even then, tiny larvae and fish eggs can still be sucked in.
The idea is to run a slant well hundreds of feet out, passing beneath the dunes to a spot under the waves. From below feet of sand, and well insulated from any vulnerable sea life, Cal Am hopes to suck up a couple thousand gallons of water per minute. That requires immense pressure — on the order of a pressure-washer. One other still-tentative design element addresses the third challenge of the desalination process: all that salt has to go somewhere.
Only about half of the saltwater piped into a desal plant is made drinkable. If it's just dumped carelessly back into the ocean, it sinks, and can kill any marine life having the misfortune of dwelling on the seafloor below. It's a pipe that runs thousands of feet out to sea, with small holes spaced ten feet apart, so not too much brine would pour out in any one place. In recent years, desalination projects were considered in places like Marin County and Santa Cruz, only to end up sidelined amid skepticism.
She says, indeed, communities should first exhaust their other options. That question of what constitutes sustainable development underpins the debate around desal. The counter-argument I heard from Scott Maloni, vice president at Poseidon Water, is: what if there are no alternatives?
But a key authority, a regional water board, approved a permit for the project in April on condition that the company increase its commitment to rehabilitate the nearby 1,acre hectare Bolsa Chica wetlands reserve, an important bird habitat, and build an artificial reef.
TO , to provide additional mitigation at Bolsa Chica or elsewhere, said Tom Luster, a senior environmental scientist on the commission staff. The political appointees and locally elected officials from coastal districts on the commission could choose their own course. California's water wars date at least to the late 19th century. This latest chapter shows grassroots movements can at least delay plans, if not halt them.
A plant Poseidon has operated since down the coast in Carlsbad was approved locally before the state adopted regulations for desalination plants. It is the largest desalination plant in the United States. Steve Sheldon, the Orange County Water District's board president, in voted in favor of a provisional deal to buy 56, acre-feet of water per year from Poseidon for at least 30 years.
He said he weighed the environmental arguments, which he called "fair comments," but that based on the science presented to him found the impact on ocean life was "by and large de minimis. While current drought conditions are particularly dramatic, California has seen extremely dry years for most of this century.
Scientists say human-influenced climate change has exacerbated the situation. Membrane processes are unrivaled for treatment of brackish waters and seawater. They work particularly well for stand-alone "water only" situations. Mechanical vapor compression can be used to treat the brine reject from RO plants increasing system water recovery. An Asian manufacturer is participating in the first major project of this type in the Middle East.
RO is a type of membrane process that could be considered as "pressure driven," but there are several types of membranes that can be used with different results. The toughest application for membranes is to remove salt; seawater membranes are different from brackish membranes.
A less difficult pressure membrane application is the removal of other ion species which are not classically considered salt or small suspended particulates. An example of this is known as NF, which can be used to remove ions that are larger and have higher molecular weights than salts and also other materials such as viruses and bacteria.
Other types of membranes can be used to remove troublesome particulate matter, and these systems are known generically as membrane filtration. While this membrane reuse application has been widely utilized for wastewater and some brackish water desalination, it now is beginning to find use in higher salinity applications.
A new class of hybrid process utilizes NF as a pretreatment for thermal desalination processes allowing the distillation to occur at temperatures that previously would have led to the deposition of process-inhibiting mineral scale.
The desalination industry not only continues to grow but, more importantly, it moves from an obscure technical possibility to mainstream, accepted practice. There are many technical measures of the improved technology and economics of desalination, but nonscientific analyses also are possible.
Whether referred to by the industry terminology, desalination, or the more common usage of desalinization, the word is out: desalination is viable. People are beginning to get the message on a large scale via mass media.
Not a desalination conference goes by without more discussion about desalinated total water costs TWC and what is the best metric to compare TWC and overall economics. The scope of one project may differ greatly from another. There is great variation from locale to locale in the value of energy and the cost of capital.
Comparing water costs often is "apples and oranges. Trinidad, where the largest seawater desalination plant in the Americas recently was commissioned, considered desalination and traditional water sources. Many people in Trinidad feel their traditional source of water from the mountains to be adequate.
However, the cost of pipelines and the environmental impact of dams could not compete with desalination or the potential for drought. In the United States, water-rich central states provide water across multiple state borders to reach the arid southwest. Transportation of water in this manner requires a large capital investment and significant operating cost.
These arrangements are not drought proof, especially if the drought were to be "politically" created. The water rich regions currently providing water to the southwest are beginning to reconsider this practice as their water wealth dwindles. The political sensitivity of water transportation is more critical when national borders are crossed.
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