Plenty of Drops to Drink : Environment: With skyrocketing prices for fresh water, the old idea of removing salt from seawater has resurfaced. And it works.
When Southern California Edison and a condominium developer were planning their $3-million project to turn seawater into drinking water on Catalina Island, the technology they chose came straight off the rack.
Increasingly efficient and time-tested methods of removing salt from water have made desalination reliable in more and more situations. All that has kept the decades-old industry from flowering has been the relatively cheap supply of bulk water from more traditional sources.
But today, with higher water prices in the offing, desalination may be coming of age, particularly as it overcomes its image as an exotic technology best suited to Saudi Arabia’s deserts.
“When you talk about desalination, people still get the picture of plants worked by people wearing turbans,” says Neil A. Berlant, managing partner of Water Research Associates, a Los Angeles investment and consulting firm. “That myth has been hard to shatter.”
More than 750 desalination facilities now operate in the United States, second only to the Middle East. Annual sales of U.S. desalination equipment run $300 million, some 30% of the world market.
The largest systems provide as much as 7 million gallons of water a day, enough for the needs of entire cities in the Middle East, Florida, the Caribbean and the Soviet Union. Smaller plants routinely desalinate water aboard surface and submarine naval vessels, on offshore oil platforms, at such facilities as the Diablo Canyon nuclear power plant, at Japan’s New Osaka International Airport, on water-poor Malta, at chemical plants in the Virgin Islands, at numerous isolated tourist hotels around the world, even in the humble water-vending machines outside supermarkets.
Over the years, interest has been steady overseas. In the United States, research efforts launched during the Kennedy Administration died when funds dried up during the Vietnam War. Technological improvement, which might have made desalination more competitive with then-cheap water, never came.
“I went to Oak Ridge to head what amounted to a $100-million research program in today’s dollars,” recalls R. Philip Hammond, a consulting engineer to the Metropolitan Water District who specialized in desalination and nuclear energy at Los Alamos Scientific Laboratory and Oak Ridge National Laboratory for more than 25 years.
“I had a hundred engineers working for me,” says Hammond, “and we developed a lot of technology that has never appeared in the marketplace. . . . That’s why I’m convinced that we can get the costs down.”
The fledgling American industry, particularly in systems for the largest desalination plants, moved out of the country to exploit lower labor costs and be near active markets.
Most U.S. desalination projects so far have been installed where water was needed at any price, as on Catalina Island.
Hamilton Cove Associates had plans for a 330-unit condominium development. The project was approved by the California Coastal Commission and the City of Avalon in 1979 on the condition that Hamilton Cove would provide its own source of water for all construction beyond 165 units. Edison could supply water for no more than half the planned condos.
The developer first considered drilling more wells in Catalina’s hills or building basins to catch more rainwater. But these could have cost more than installing a desalination plant.
Hamilton Cove then discovered that economies of scale made the plant cost-effective only if it produced twice the condo project’s water needs. The developer suggested a joint project to Edison. Hamilton Cove would build the plant, gaining enough new water to finish its condominiums. Edison would own and run the plant and would be able to build up its drought reserves and satisfy a longstanding list of water-starved customers.
Edison was skeptical at first.
“One of our driving concerns,” says Keith LeFever, district manager for Edison’s utility operations on the island, “was that we could produce water using the economics of the existing rate structure.”
Water isn’t cheap on the island even now. Edison retails its water at a rate set by the state Public Utilities Commission that is roughly five times current rates on the Southern California mainland, an average $8 per 1000 gallons. Edison changed its mind when its studies showed that, under full production, the plant would produce desalinated seawater for about $5 per 1000 gallons.
Edison was also impressed with the maturity of current technology.
“There aren’t many public utility systems that are injecting potable water from the sea into their freshwater systems,” admits LeFever, “but I think that’s likely to change.” When the plant opens next September, it will increase the island’s water supply by 29%. Part of that will be used for long-stalled developments, big and small, on the island.
“We’ve got a hundred people on a list,” says LeFever, “waiting for us to tell them we have water available for their construction--ranging from extra bedrooms, remodels of residences, all the way to 20- and 30-unit hotels.”
On a much larger scale, water shortages could soon slow development on the mainland.
The Metropolitan Water District, wholesaler to such water districts as L.A.’s Dept. of Water & Power, warns that Southern California has already begun to lose much of the Colorado River water on which it has traditionally depended as the water is diverted to the new Central Arizona Project.
“Metropolitan is going to have to find a billion gallons a day somewhere over the next quarter century,” says Philip Hammond. “And our (demand) will increase also.”
Bulk water prices have begun to rise. As one measure, MWD estimates that its operating budget will have to double in the next 20 years.
With that in mind, MWD is looking at desalination plants of immense capacity, at least 10 times greater than any ever built, which could be economically competitive by the end of the 1990s.
“We’re talking about large systems, 100 million gallons a day at a minimum,” says Gary Snyder, assistant chief engineer and desalting expert at MWD. Typical systems in the Middle East are in the 5- to 7-million-gallon range.
Two basic concepts lie behind most desalination systems, distillation and membrane purification. Distillation is the equivalent of a sophisticated teakettle, vaporizing the water, leaving salt and other chemicals behind, then cooling the vapor back to liquid state. Distillation systems are usually used to desalinate large volumes of seawater.
Membrane techniques, primarily one called reverse osmosis, are more often used for smaller seawater systems and for demineralizing less salty brackish water. In these systems, water is forced through semipermeable membranes that separate salt--and in some applications, other minerals, bacteria and even viruses--from the water. The Catalina Island project will employ reverse osmosis, as do most facilities in Florida, which has the highest concentration of desalination plants in the United States.
Reverse osmosis has also been used extensively in Orange County, notably at Water Factory 21--as in “21st-Century technology”--of the Orange County Water District. For 16 years, this plant has been treating waste water from a nearby sewage plant and injecting the clean water along a nine-mile area of coastline, to form a freshwater barrier against seawater intrusion. Underground cracks formed over millions of years would otherwise allow seawater to seep in and contaminate the Santa Ana water basin.
The Orange County Water District currently pays $230 an acre-foot for water that it brings into the area. Water Factory 21 produces its water for $250. (An acre-foot is the amount that would cover one acre to a depth of one foot.)
“While it doesn’t make pure economic sense yet to build a plant like Water Factory 21,” says William R. Mills, Jr., general manager of the district, “we believe that in time, as the cost of imported water increases, that the cost of water production at Water Factory 21 will remain relatively stable.” Mills predicts that in five years the district will have 10 reverse osmosis plants in operation. And he sees membrane technology becoming cheaper as the technology improves.
“The trend in the industry,” Mills says, “is that the membranes are becoming more sophisticated, and so the pressure needed to move water through them is less.” Less pressure means lower energy fees, the major operating cost of desalination.
In 1974, Mills says, the standard was 600 pounds per square inch. His district just replaced their membranes with models that need only 200 to 250 psi.
“Sometime in the future it will drop to 100 pounds,” says Mills, “So it will become much more economical as time goes on.”
THE BASIC TECHNOLOGY
* Distillation--Usually used to desalinate large volumes of seawater. Systems work basically like tea kettles, turning water to vapor, leaving contaminants behind, then re-liquefying the steam. One variation uses a series of these, each at lower pressure. The steam formed at the first is used to heat the next in line, which needs less energy to boil because of the decreased pressure. And so on. These systems can be extremely efficient.
* Reverse osmosis--This uses pumps, not heat, to force water through semipermeable membranes to separate salt and other contaminants. It is one of the most promising, growing technologies for smaller desalination projects as well as a wide variety of specialized needs, including treatment for other chemicals, bacteria and viruses.
* Electrodialysis--This membrane technique uses electrical current to “pull” contaminants away from the water.
* Ion exchange--Water is run through chemicals called “resins,” which exchange ions not wanted in the water with benign ions. It is competitive only for water with low levels of contaminants.
* Freeze desalination--Water and salt can be separated while freezing, but it is a troublesome process. Only a few plants using this technology still operate.
