Hold the Salt
BY Simon Gonzalez
Locally worries about GenX and harmful contaminants in our drinking water have some people concerned about turning on the tap. Nationally about one-fourth of the country is in drought conditions at any given time. Internationally an estimated 780 million people lack access to clean water.
Water is necessary for life yet it seems a safe plentiful supply is an elusive and ongoing struggle.
Make that a plentiful potable supply. Take a walk out on any New Hanover County beach and look to the east. Water stretches as far as the eye can see. It’s not just here. About 71 percent of the Earth’s surface is covered by water. And about 96.5 percent of that water is contained in the oceans and seas. It’s an unlimited supply.
But when it comes to the ocean the ancient mariner’s lament in Samuel Taylor Coleridge’s famous poem rings true: “Water water everywhere/nor any drop to drink.”
That of course is the problem. All this water and humans can’t drink it. Not just because the taste makes it unpalatable. Salt water can literally kill us.
The National Ocean Service succinctly explains why.
“The salt content in seawater is much higher than what can be processed by the human body. Living cells do depend on sodium chloride (salt) to maintain the body’s chemical balances and reactions; however too much sodium can be deadly. Human kidneys can only make urine that is less salty than salt water. Therefore to get rid of all the excess salt taken in by drinking seawater you have to urinate more water than you drank. Eventually you die of dehydration even as you become thirstier.”
These days there can be harmful levels of bacteria and contaminants close to shore but the offshore seawater would still be safe to drink if we could somehow remove the salt from the water. That however is not easy.
“Salt and water really like to be together ” Justin Sonnett says. “It’s very difficult to pull them apart.”
Difficult but not impossible. Sonnett has done it. During his senior year as an engineering student at the University of North Carolina Charlotte the Wilmington native and Wrightsville Beach surfer was part of a team that developed a system that used wave power to desalinate (remove salt from) seawater.
“We tested the first prototype here at Wrightsville Beach ” Sonnett says. “We borrowed a buddy’s boat and dragged it out just past the inlet and let it rip. It worked. It didn’t work very well but it worked.”
Sonnett describes the prototype as a “crazy-looking design like a pontoon boat with a big frame on it supporting a heavy pendulum. The pendulum alone weighed about 1 100 pounds.”
The pontoon part would rock back and forth with the waves swinging the pendulum and driving pumps to suck in seawater. The salt was removed by reverse osmosis a process that pressurizes water and runs it through a membrane that filters out particles and dissolved salt.
After graduation Sonnett fellow project member Chris Matthews and Laura Smailes with the backing of Charlotte entrepreneur Fred Wagner formed a company called Eco H2O Innovations.
They worked out of Charlotte for two years in the research and development phase to improve on their original design and developed a buoy-shaped device “one-fourth the size of the first with 10 times the amount of water for less than half the cost ” Sonnett says. They named the buoy SAROS for Swell Actuated Reverse Osmosis System.
They moved to Wilmington to test out the second prototype opening an office on Judges Road. They got a permit to launch the buoy off Masonboro Island.
“The first time we put the buoy in the water was like the most amazing feeling ” Sonnett says. “This thing you’ve put all your heart and soul into your child. And it worked. The buoy we tested off Masonboro was basically a wave-powered pump. It would intake seawater through a strainer so we didn’t suck up fish or seaweed. It would take that water and pressurize it to about 150 PSI. It was designed to send that water back to shore to a desalination system that would be located on land but we couldn’t get the permits to run the hoses along the bottom and set up a structure on Masonboro Island. Most of the time the buoy was just sucking up water and spitting it back out to the ocean. When we were actually making water and testing the desalination component we would take our boat out and I would spend the night out there with the desalination system in the back of the boat. We had a hose running from the buoy to the anchored boat and made water that way.”
The prototype could produce about 300 gallons of fresh water a day in waves from 2 1/2�to 3 feet. Sonnett and Matthews were designing a commercial system that could make about 2 500 gallons a day.
The average American uses about 100 gallons a day so the wave-powered system never was intended to produce water on a massive scale or even to meet the needs of even a small town like Wrightsville Beach. Instead Sonnett and Matthews envisioned SAROS as a means to provide safe clean water to small impoverished communities on remote islands and coastal regions around the world.
“Desalination consumes so much energy and typically energy in regions that rely on desalination is prohibitively expensive ” Sonnett says. “Our thinking was if we can replace the expensive energy source by using the free wave energy that exists in the area where salt water is it would be a win-win. It would be environmentally friendly and less expensive.”
They had a system that worked and a strategy to deploy the technology but it all fell apart when they moved to the implementation phase. They were working with officials in Puerto Rico and Colombia to use SAROS in remote coastal villages but the cost of permitting and other expenses was insurmountable.
“The groundwork to set up these projects was far too expensive to justify the relatively small output of our systems ” Sonnett says. “If our buoy was spitting out oil that would be another story. But it was spitting out water which is a pretty low-value item even in places where water is scarce.”
The expense was also a major obstacle the first time efforts were made to remove salt from seawater at Wrightsville Beach.
The federal government built a facility in the town in 1964 to research freeze desalination. Ice made from seawater is salt-free but it is difficult to separate the ice from the brine. Like Sonnett’s wave-powered system it worked. The plant produced fresh water. But not in a cost-effective manner.
“The small ice crystal size developed in OSW [Office of Saline Water] pilot plants at Wrightsville Beach resulted in a high economic penalty to wash the crystal free of salt ” a U.S. Department of the Interior report states.
Cost remains a major factor in why desalination is not an option even as Wrightsville Beach wrestles with ongoing water-quality issues.
Public works director Bill Squires says the town gets its water from nine wells drawing on the Peedee aquifer an underground source about 170 feet below the surface.
The wells are subject to salt intrusion because of the proximity to the ocean.
“It’s good water ” Squires says. “But if you overdraw your wells you will bring in salt water. We have to monitor our wells. There’s a bubble of fresh water down there and if you suck it too hard you are going to get that intrusion. We see a lot of that in the summertime when we’re wide open running the wells all the time.”
Reverse osmosis would make salt intrusion moot but that’s not in the town’s plans. Even a small-scale plant would require upwards of $10 million.
“It’s extremely expensive and labor intensive and maintenance intensive ” says Tim Owens Wrightsville Beach town manager. “We have a small customer base and it’s hard to provide that service. Your rates would be astronomical. With 1 600 customers it’s not cost feasible for us.”
Still desalination just might be the wave of the future. The technology works whether on a small scale like Sonnett’s SAROS system or a large scale like the massive reverse osmosis plants in Israel and Saudi Arabia.
The desalination plant in Sorek Israel about 10 miles south of Tel Aviv was the largest in the world when it became operational in October 2013. It takes seawater from the Mediterranean and transforms it into enough drinking water for 1.5 million people. Desalination at Sorek and other plants accounts for 55 percent of the country’s domestic water supply.
The largest plant in the world is now located in Ras Al-Khair Saudi Arabia which became operational early in 2015. The arid country is the world’s largest producer of desalinated water with more than two dozen plants taking seawater from the Persian Gulf Red Sea and Arabian Sea to meet the needs of 60 percent of the population.
Wave of the Future?
Closer to home Dare County in the Outer Banks operates four reverse osmosis plants that desalinate brackish water from shallow ground sources and estuaries.
Those are not isolated examples. The International Desalination Association says about 300 million people worldwide get some freshwater from more than 17 000 desalination plants in 150 countries.
There are a couple of obstacles keeping more plants from being built.
One is extremely salty brine discharge left behind from the reverse osmosis process.
“Discharge is a really hot topic with desalination ” Sonnett says. “People have asked me if desalination became a big thing aren’t we going to raise the salinity of the ocean? And the answer technically is yes. But really the answer is no. If you are dumping a bunch of salt water where it’s stagnant and can’t wash away yeah it can accumulate significant amounts of salt and that can have negative impacts on the environment. If you put it in a place that’s offshore with lots of currents to sweep it away the ocean is so massive there is no way that if all the water in the world was generated from desalinity you would notice a difference.”
A hefty price tag remains the major deterrent.
“It’s so expensive because it requires so much energy ” says Sonnett who became a research and development engineer at Corning after shutting down SAROS in July 2017. “The only reason desalination exists is because that’s the only option some places. You don’t desalinate water for fun. If there’s water you can collect from rain or from a well in a ground you definitely do that first. As a last resort a lot of places turn to desalination.”
New Hanover County currently is not subject to water shortages. Most households get their water from the Cape Fear. While it must be treated for pollution it is plentiful. It would take unprecedented droughts for an extended period of time for the river to run dry. There’s no financial incentive to turn to the Atlantic and desalination.
So while desalination is increasingly a solution in parts of the world that have little alternatives a large-scale effort to take the seawater off the Southeast Carolina coast and turn it into freshwater is still sometime in the future.
“Nobody’s created that perfect cost-feasible solution yet ” Owens says.
Desalination at Wrightsville Beach
By Pat Bradford
As part of the Saline Water Act of 1952 and the Anderson-Aspinall Act of 1961 the U. S. Department of the Interior Office of Saline Water built at least six test facilities. The fifth a pilot plant for research development and demonstration was completed on Wrightsville Beach between U.S. highways 74 and 76 Salisbury Street and Causeway Drive in July 1964 by the Carrier Corp. at a cost of $948 000.
Municipal and state officials induced the federal government to pick Harbor Island by offering 25 acres of sandy marshland without charge.
In the early years at the facility contractors conducted experimental work under standardized conditions on seawater fresh water steam electricity compressed air fuel storage waste disposal and reinforced concrete foundations for erection of pilot equipment or plants.
Stewart Udall Secretary of the Interior is quoted in a report from 1961 in the Congressional Record – Senate: “This new approach to the economic conversion of saline water to fresh has only recently reached the pilot plant stage of development. A 15 000-gallon-per-day pilot plant using one type of freezing process is now operating on sea water at Wrightsville Beach N.C.”
Senate hearings from May 1965 state “Mechanical difficulties and some design problems are listed as having prevented successful operation and fresh water production.”
The 1970s saw budget cuts but the site remained open doing reverse osmosis in six pilot plant sites. Successful lobbying in the early 1980s saw the land conveyed back to the town with restrictions by the Department of the Interior when contractor test work at the plant completely stopped. It became the site of the town’s municipal complex police and fire ball fields park and historic square. (For more on the history of this facility see Wrightsville Beach Magazine August 2001.)
The saltwater intake for the Office of Saline Water test facility extended into Banks Channel on the south side of the Causeway Drive bridge. The intake now is used by the UNCW Aquaculture program behind the town hall facility.