Dual-stage nanofiltration method is 30% more efficient than standard methods
While some cities near Long Beach, Calif. are protesting an emergency water allocation plan approved this week, officials of that city recently announced progress on a desalination project that could give the city an alternative to state water resources, the Press Telegram reported.
The Long Beach Water Department has developed a new method of turning seawater into drinking water that has been found to be about 30% more energy efficient than standard methods, water officials said.
Researchers spent more than six months of testing the new dual-stage nanofiltration system at the city's National Seawater Desalination Research and Development Project in southeast Long Beach, Water Department spokesman Ryan Alsop said. The method is an alternative to the reverse osmosis technology used most often by desalination plants, he said.
Traditional desalination methods extract salt by pushing seawater through a membrane at high pressure, while the city's method uses a second filter and less water pressure.
"We've demonstrated that the technology we've invented here is more energy efficient," Alsop said. "At the end of the day, what we're trying to do is demonstrate a more cost-effective, a more environmentally responsible way to desalinate seawater."
At least in the Water Department's prototype project, the 30% reduction in energy use resulted in lowering the cost of desalination by more than $120 per acre-ft of water, Alsop said.
Typically, desalination costs about $1,100 to $1,500 per acre-ft, he said.
Even though imported water and groundwater are still much cheaper, costing Long Beach $500 to $600 per acre-ft and $250 to $300 per acre-ft respectively, Alsop said, diminishing water supplies may force desalination to become a major source of water for Long Beach.
"Seawater desalination is more than double than what it costs for an equal amount of imported water," Alsop said. "Is it the future? Absolutely it's the future. But it must be done in a way that makes economic sense and is environmentally sound."
Alsop said about half of the funding for the 10-year, $20 million research project comes from the U.S. Department of the Interior, while Water Department funds and state grants make up the remainder, the paper reported.
Another aspect of the project being researched is a method for returning excess salts from the seawater to the ocean. The Under Ocean Floor Intake and Discharge Demonstration System being built near Bluff Park, the first of its kind in the U.S., uses the ocean floor as a natural filtration system, according to the paper.
Alsop said the project still must undergo more research to determine whether it ought to be used in a full-scale plant, a decision that is expected by 2012 or 2013.