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Earth, Wind And...Sea Water

Five years ago, local scientists found a way to transform brackish groundwater to potable water, using nothing but a windmill and a small research lab on Coconut Island, located off the coast of Oahu.

At 30 feet, the windmill is the tallest standing structure on Coconut Island. However, it represents one of the most energy- and cost-efficient methods of desalination. “Eighty percent of desalination costs is energy,” says Dr. Clark Liu, civil engineering professor at the University of Hawaii and the project’s principal investigator. “If we can find a cost-effective way to desalinate, then we wouldn’t have problems [with reusing water].” Today, the Coconut Isle project combines desalination studies with other research [i.e., to measure the water quality in tilapia fish tanks].

The world’s 12,500 desalination plants have a combined capacity of 6 billion gallons per day. Florida boasts the largest seawater desalination facility in the nation; it generates 25 million gallons per day and runs on electricity.

The wind-powered demonstration plant on Coconut Island is humble by global standards; it only spews up to 2,000 gallons of water per day. But Liu and his research team say the wind-powered plant is a prototype for tiny Pacific islands, where drinking water is scarce but wind and water are abundant.

The Water Cycle
What happens to water after it is flushed and drained? An engineered process transports the water to a treatment plant, where the water is disinfected. Then one of two things happens: the water either is discharged into the ocean, or it is reused for other (non-drinking) uses. On Oahu, the Honouliuli Water Recycling Facility produces roughly 12 million gallons of recycled, or reclaimed, water, per day.

It produces two types of water: RO (reverse osmosis) for industrial uses; and R1, for irrigation. The recycling facility, previously owned by USFilter Operating Services, was purchased three years ago by the Honolulu Board of Water Supply for $48 million.

“It is more expensive to use recycled water than to dump it into the ocean,” says Dr. Roger Babcock, associate professor of civil and environmental engineering at the University of Hawaii. “The transmission systems are the most expensive about the recycling process.”

However, using higher-quality water (such as drinking water) for irrigation and industrial needs is more expensive. It also is wasteful.

-CSC

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