Water issues prompt new look at desalination
Popular in the 1960s and ’70s, desalination technology stagnated for the next decade. Now, dwindling water supplies are forcing cities and counties to take another look.
“Water, water, everywhere, but not a drop to drink,” cried the Ancient Mariner. Indeed, more than 95 percent of the world’s water is sea or brackish water, unsuitable for drinking. The amount of fresh water on the planet essentially has not changed in millions of years, but the number of users has, and in some places that has put a tremendous strain on water resources.
Ron Linsky of the National Water Research Institute in California says the country needs to improve the reliability of its supply and suggests that water could be on the commodities market in the next century. “We may ultimately face rationing or importing,” he says.
There are a number of ways to forestall this, however. One of those ways – desalination – is already being used across the country to stretch water supplies, clean up polluted water and provide protection for aquifers. The technique is ancient, dating back to the 4th century B.C. when, according to the National Water Supply Improvement Association, Greek sailors used simple evaporation to desalinate seawater.
The technology, however, is far more modern. Desalination – separating saline water into fresh water and water containing the concentrated salts – is accomplished in two main ways: through distillation or use of membranes.
Nearly 60 percent of the world’s desalted water is produced via the first method by heating salty water to produce water vapor that is then condensed to form fresh water.
The second process uses membranes to separate the salts from the water. In reverse osmosis (RO) facilities, water is forced through bundles of membranes under pressure, leaving behind impurities. In electrodialysis reversal (EDR) plants, an electrical current transfers ions through membranes, resulting in desalted water and concentrates.
Worldwide, desalting plants have the capacity to produce 3.5 billion gallons of water a day, nearly enough to provide 15 gallons a day for every American. Some nations, such as Saudi Arabia and Malta, desalt ocean water to produce fresh water for public and industrial consumption. In the United States, most desalting plants treat brackish water, a process that costs one-third to one-fourth as much as the treat involved in desalting ocean water.
The product water is used for direct supply, reserves or groundwater recharge. According to the American Desalting Association (ADA), other uses include irrigation, wastewater treatment and water purification. Hospitals, resorts, manufacturing plants, oil rigs and pleasure boats also employ desalination technology. During the Persian Gulf War, the Army had mobile desalination units that could produce 3,000 gallons per hour of potable water from brackish pools.
In a 1988 report, the Congressional Office of Technology Assessment suggested desalination could find application in treating contaminated groundwater, be it runoff from mines, agriculture, landfills or storage tanks. Of desalting in general, the report noted, “Desalination should be included as a viable option in any evaluation of water-supply alternatives.”
STRETCHING CALIFORNIA’S WATER
In Southern California, which in large part owes its growth to water drawn from the northern part of the state and from the Colorado River, water supply has long been an issue. The Orange County Water District, with some 2 million people in its service area, has an ambitious goal – 90 percent independence from external water supplies by 2010.
One means of reaching that objective is running secondary effluent from municipal and industrial sources through its Water Factory 21.
That RO plant, built about 20 years ago, produces 15 mgd for injection into the basin where it serves as a hydraulic barrier to salt water intrusion. It also becomes mixed with the groundwater and reused. Reportedly, Water Factory 21 already produces 17 percent of the water supplies of Fountain Valley and Huntington Beach. The product water of the plant surpasses water quality standards and is no longer required to be blended with deep-well water.
New desalters in Irvine and Tustin have specific purposes. The former will treat water contaminated with high levels of organics and with the solvent trichloroethylene, the resulting product water going to irrigation.
The latter facility, due to begin operation this fall, is designed to remove nitrates.
In Riverside, Calif., local groundwater did not meet drinking standards due to high concentrations of nitrates from decades of farm runoff. Additionally, the polluted water was escaping into tributaries on the Santa Ana River, which contributed to Orange County’s water supply problems.
To combat those problems and help bring the area’s water resources back to a useful condition, the Santa Ana Watershed Project Authority (SAWPA) opened a desalination plant in 1990 in the Riverside Area. The $13 million Arlington desalter uses RO on brackish water to produce 6 mgd.
Another slightly larger plant is planned for a nearby basin.
In Los Angeles, the Metropolitan Water District (MWD) has constructed a 2,000 gpd pilot plant to demonstrate the viability of vertical-tube evaporation technology and collocation of a desalination facility with a rehabilitated power plant. The plant would provide sea water intakes, out-falls and low-cost steam. Testing began in September, according to MWD Engineer David Dean.
If the technology and collocation prove out, he says, the goal by 2010 is a 50 mgd to 100 mgd distillation plant using ocean water.
The San Diego County Water Authority (SDCWA) serves an area that depends on imported water for 90 percent of its needs. Those sources are becoming more unreliable because of legal issues, environmental concerns and drought. To reduce that dependence, the authority and the city are launching a project that would put reclaimed wastewater through an RO plant and transport it to a 90,000-acre-foot reservoir where it would be blended with imported water and runoff, go though conventional treatment and become available for potable reuse. Scheduled to begin operation by 2001, the project is the first in California providing potable reuse via surface reservoir. Adding the RO element, says SDCWA Water Resources Supervisor Ken Weinberg, provides a level of treatment that ensures protection of public health because it will remove bacteria and protozoa as well as salts.
The estimated cost of the plant, which will be owned and operated by the city and should provide 20 mgd of potable water and another 10 mgd for irrigation, is $68 million with another $40 million to $50 million for the pipeline to the reservoir. Still, the total is comparable to the cost of importing the water the area needs, Weinberg says.
On the other side of the country, Florida, like California, claims a burgeoning population and, while far from arid, has few rivers and large areas of brackish water.
It boasts far more desalination plants than any other state; ranging from 40,000-gallon facilities at resorts and mobile home parks to a 9.5 mgd plant in Dunedin, a 14 mgd plant in Cape Coral and a 12 mgd facility in Fort Myers.
In fact, one of the country’s first RO plants for ocean water was built in Key West in 1980. It operated for 18 months, went on standby status and is now mothballed, according to Arlen Higley of the Florida Keys Aqueduct Authority. Key West pumps its water from Dade County via a 36-inch-diameter, 130-mile-long pipe, and the RO plant is strictly for use as an emergency backup in case of damage to that pipeline, which is attached to the Keys’ many bridges. (The plant did run for one week after Hurricane Andrew disrupted water supplies.)
Higley says the plant is too expensive to run on a daily basis, costing $4 per 1,000 gallons. Water can be pumped south, he says, for $1.50 per 1,000 gallons.
“In an emergency, we bite the bullet,” Higley says. “You can live without electricity, but you can’t live without water.”
The plant, comprised of six “trains” or modules that can run individually or in combination, is designed to produce 3 mgd of treated water from saltwater wells. Brine, with its collected salts, is pumped back into the sea.
DISPOSAL OF BY-PRODUCTS
In fact, disposal of by-products is beginning to eclipse cost as the No. 1 desalination issue in Florida and elsewhere. Little Jupiter, Fla., played David to the U.S. Environmental Protection Agency’s (EPA) Goliath in battling discharge regulations that were threatening its RO plant.
In the late ’80s, Jupiter realized that its fresh water supply was all but used up. It began planning for the installation of a desalination plant, which went on line in 1990.
Then, the shrimp died.
EPA regulations require toxicity testing before desalination plant concentrates can be discharged into any receiving waters. The tests involve tiny shrimp that are subjected to concentrates resulting from the process. If more than 50 percent of the shrimp die, EPA gets nervous.
In Jupiter’s case, the the tests indicated unacceptable toxicity levels. The town, however, did not believe that its discharge was the culprit. Still, the state pressured the facility to construct deep-injection wells for discharge of its concentrate (at a cost of up to $6 million).
“The town just said ‘no’,” says John Potts, a Florida environmental consultant and first vice-president of the ADA. “Of the 120 or so desalination plants in the state, Jupiter was the first one to be told that its discharge was toxic, so the town started conducting its own tests.”
Jupiter discovered that a factor called major ion toxicity was responsible for the shrimp deaths. In essence, the major salts in the concentrate – sodium, calcium, chloride, potassium – were present in different ratios than they would be in seawater.
That, the town found, caused the toxic reaction.
Unfortunately, Potts says, the regulations were written before anyone knew about major ion toxicity and, therefore, do not recognize it as a factor. Still, in a show of good sportsmanship, the state Department of Environmental Protection agrees that the phenomenon exists and has not shut down the Jupiter plant.
That is good news for the Southwest Florida Management District, which is considering building a $50 million desalination facility in the Tampa area that is expected to improve supplies, reduce damage to wetlands (from overpumping the current wellfields), provide high-quality and cost-effective water and possible hasten permitting through collocation with an existing power plant. The facility would draw water from the gulf and use RO technology.
That plant, like others, has elicited a mixed reaction, Potts says. “I have been surprised to have been contacted by representatives of environmental groups supporting the plant,” he says. “They view it as more desireable than importing water from other areas of the state and depleting those areas. They see it as the lesser of two evils.”
Still, desalting concentrates are classified by the U.S. Environmental Protection Agency as an industrial waste, Potts says.
That means that disposal is subject to stringent regulations, and that, he says, inhibits application of the technology. Consequently, ADA has been pushing to change the EPA designation.
The designation of desalination discharges spawns most of the opposition to the plants. “Most of it is due to the fact that the discharge is classified as industrial waste,” Potts says. He calls the designation “the most serious hindrance to the technology,” arguing that unless the concentrate can be disposed of, the technology cannot be used.
“The regulations,” he says, “are out of date and inappropriately being applied.”
Despite the disposal problems, though, desalination’s appeal extends beyond California and Florida. For example:
* The Mount Pleasant Waterworks and Sewage Commission in South Carolina operates three desalting plants with a combined capacity of 6.8 mgd. On line for three years now, the facilities treat brackish water from deep wells. The well water, says Water Superintendent Melvin Bennett, has a poor taste, which is the main reason the RO plants were installed.
* On North Carolina’s Outer Banks, Dare County installed an RO plant in 1989 in Kill Devil Hills to provide additional water for the summer when thousands of tourists increase the local population, putting extra demand on water resources. The facility, with a capacity of 3 mgd, taps brackish deep-well water.
* In 1993, Washington, Iowa, began operating an EDR plant to remove radium, a suspected carcinogen, from its drinking water, which originates in deep wells. Three EDR units with a combined capacity of 1.2 mgd perform that task.
* The Greater Texoma Utility Authority in Texas installed an EDR plant to acquire a new supplementary water source from a highly mineralized lake. The 4.5-mgd plant began operating in 1993.
Politically, desalination does not enjoy the favor it once did. In the 1950s and ’60s, the federal government funded considerable research and development through its Office of Saline Water, and much of the advancement in RO and other technologies derived from those efforts. Support diminished in the 1970s and disappeared altogether in the ’80s.
However, in recent congressional action, Sen. Paul Simon (D-Ill.) has introduced legislation providing for modest sums to “reinvigorate” U.S. desalination research. The ADA endorses the measures, according to organization Treasurer Glenn McPherson, but the current Congress is not in a spending frame of mind.
It also is in an anti-regulatory mood, and legislation such as the Clean Water Act is under scrutiny.
In the unlikely event that water quality standards are actually strengthened, desalination could be a major beneficiary, says Bill Katz of Boston-based Ionics, a membrane manufacturer. Still, he admits that population growth, and its attendant demand on water supplies, remains the real force driving desalination.
And, as technology advances, costs are lowered. For instance, one Minnesota firm recently reported development of a membrane that requires less energy for reverse osmosis. Additionally, advocates of desalination point out that it often compares favorably with the cost of developing other new sources of water like reservoirs, dams and aqueducts.
Robinson Township, Pa., got a quick – and costly – lesson in the importance of backflow prevention when a mixture of chemicals used to kill termites ended up in its water supply.
Backflow, the reversal of the flow of water and undesirable substances from any source – used water, industrial fluids, gases, etc. – can be prevented. But nearly every backflow prevention program in the country focuses primarily on commercial and industrial sites.
The Safe Drinking Water Act (SDWA), however, is making municipal water utilities increasingly aware of their responsibility to their customers. Unfortunately, budgets are shrinking, even as government regulation and operating costs increase.
Small water utilities – (Time magazine estimates that 83 percent of the nation’s systems serve fewer than 3,000 customers but that, combined, they serve 20 million Americans) have been the hardest hit.
Still, small utilities are not the exception. “Meeting expected federal requirements will cost the nation’s water suppliers more than $14 billion, the EPA estimates,” according to a 1991 article in U.S. News & World Report. Some of that $14 billion is wrapped up in the complex array of backflow prevention devices used at commercial sites, as well as the extensive labor involved in cutting the devices into a city’s water supply pipelines.
Installation is costly enough, but periodic testing requirements cause labor costs to skyrocket. Additionally, in making backflow prevention a residential issue, the SDWA has made installation and testing the responsibility of local water utilities.
Technology, however, is helping. One innovation, a residential water meter supplied to Schlumberger Water Division, Tallassee, Ala., is helping Pompano Beach, Fla., get control of its costs. The meters are fitted with backflow prevention devices within the standard 7 1/2-inch lay length. One series of meters incorporates double check regulators, and the second series integrates dual check valves within one standard meter body.
Both eliminate the need for resetters, as well as dual check and meter combinations by replacing them with an integral backflow/meter unit, making it easier for water utilities to implement aggressive backflow prevention programs economically. Both also accept encoders that serve as the basis for all the company’s automatic meter reading system solutions.
Lincoln Bates is an Atlanta-based freelance writer.