Torrents of fresh water — from the ocean deep?
September 3rd, 2009, 6:00 am · 20 Comments · posted by Pat Brennan, science, environment editor
A pair of Tustin entrepreneurs is now testing a deep-sea device they say could radically change the way salt is separated from seawater – vastly reducing the cost by using far less energy than present-day systems.
The desalination device, called Demwax, would rely on the intense pressures found hundreds of feet deep to push seawater through a collection of filters, then pump purified drinking-water to the surface.
“Underwater desalination is using the natural pressure in a body of water to drive the desalination process,” said Michael S. Motherway, president of DXV Water Technologies.
For now, however, the company is starting small. Motherway and the inventor of the device, chief executive officer Diem X. Vuong, recently installed a suitcase-sized version at the bottom of the San Joaquin Reservoir in Newport Beach.
The device will purify the treated wastewater in the reservoir to test the maintenance requirements of the system, although the water it yields will not be put into the county’s water supply.
Most of today’s desalination systems, like the one proposed for Huntington Beach by Poseidon Resources, rely on coastal intake pipes that pull in seawater, often destroying the eggs and larvae of marine creatures in the process.
And the plants consume enormous quantities of electricity. The energy is needed to push the seawater through banks of tightly wound, reverse-osmosis filters, squeezing it through microscopic holes to screen out salts, bacteria, viruses and other impurities.
For both those reasons, seawater desalination often meets with strenuous objections from environmental activists.
The DXV device does the same job, minus the heavy electrical load, Motherway says.
The weight of the seawater above means that down deep, the ocean exerts a crushing force.
At a depth of about 850 feet, Motherway envisions erecting a series of specially designed filters, and using that crushing force to take the place of electrical power.
The arrays, looking something like accordion files, would be tethered across acres of ocean floor, though engineers would have to be careful to ensure the bottom was sandy and barren to avoid interference with sea life.
A ”snorkel” would make contact with the lower-pressure air at the surface, allowing the system to use the difference in pressure to help draw water through the filters below.
Because the water would be drawn weakly over a huge area, rather than strongly from a small area, they say the arrays would present no danger to eggs, larvae or other marine life, and would not boost leftover brine to high levels — two effects of traditional desalination systems that bother environmental activists.
“We’re trying to be environmentally friendly,” Vuong said.
Vuong and Motherway estimate that a full-scale deep-sea plant would cost roughly the same as the coastal facility proposed by Poseidon — about $350 million — and cover about the same amount of area.
Such a plant is perhaps 10 to 15 years away, Vuong said, though a working demonstration version could come much sooner, depending on how successful the company is at attracting private investors.
“I think we’re going to have a pilot plant in the ocean within a year,” Motherway said. “We’re getting funding to do that.”
In the meantime, small versions of the system could be used to purify fresh water in lakes or reservoirs; in fact, DXV hopes to interest the Irvine Ranch Water District or other agencies in trying out the device.
“We want to show not only that it’s a good idea, but that it actually works,” Vuong said.
Though it is hosting the company’s test of the device, the Irvine Ranch Water District is not planning any specific projects that would use it, said Paul Jones, general manager at the Irvine Ranch Water District.
Much depends on the cost of scaling up such a project, and of long-term operation and maintenance.
“Advancements in membrane technology are always very interesting to us in the water industry, especially if it lowers costs,” he said.
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Everybody thinks the ocean is going to be the way humans get fresh water when they use up the real thing. But what happens when giant algae blooms pollute all of the worlds oceans rendering all ocean water unusable? Those algae bloom are here now and only getting bigger and bigger as humans continue to destroy their environment.
Great THEORY, far from a news story.
10 to 15 yrs. out?
I thought algore said we only got 6.5 yrs. left before the planet is scorched from man made g/w.
This is a fantastic development for a huge problem we have worldwide, which is a shortage of clean drinking water. How wonderful that these people are bringing to market a device that is environmentally friendly, cost effective over time, and will save lives. Here is hoping that DXV Water Technologies will be able to be as successful in overcoming the political battles that are sure to lie ahead in implementation of this technology.
Does not sound any more environmentally-friendly than a standard desalination plant. To produce 50 MGD, they have to place these elements across 12 ACRES of land under the ocean floor. I would call that DISRUPTIVE to the natural environment. I wish Mr. DXV good luck in overcoming the obstacles in getting this kind of project permitted. The current process of getting a project approved is unwieldy, time-consuming and exorbitantly expensive.
Disruptive? Have you ever been thirsty? Wait until violence/wars start breaking out over water resources, that will be DISRUPTIVE to the natural environment!
Water diva,
Do you have any idea how big the ocean is? It covers nearly 75 % of the earths surface. Utilizing 12 acres of land under the ocean to prevent the depletion of fresh water on land is a hell of an improvement. In fact i would venture to say that it would be nearly impossible to build enough of these things.
The problem with you environmental “diva’s” is that nothing ever makes you happy. Except perhaps the thought that the world is going to hell and your complaining is going to save it.
At least Matt has the good sense to realize that the inhabitants of the 25 % of the earth which isnt covered in water (that leaves a lot of good 12 acre plots under the sea available for use) are violent, and thirsty. In your lifetime the population will have gone from 6 to 12 billion people. Since god has not seen fit to create any new lakes in the last few thousand years, i guess its up to us.
Don’t be an idiot, 12 acres is nothing, Its not even a big enough piece of land to raise a horse on, hell i wouldn’t even subject a dog to living on less than 50.
Yours truly,
Reality Check
How far out into the ocean do you have to go to get 850 feet down? How much energy does it take to pump the purified water back to the coast? What infrastructure is needed to get it to the drinking water distribution system? When is the last time the Coastal Commission permitted ANY new infrastructure project off of the California coast?
Let’s not let this theoretical pipe dream get in the way of desalination that is ready to go today. The Poseidon project in Huntington Beach uses existing infrastructure so it has no additional environmental impact.
Don’t let the perfect be the enemy of the good. We can’t wait 15 years to see if maybe this system will work (and another 15 years to get the permits necessary to build it). Let’s start desalination now and if this is as good as advertised, we can do this too.
Let’s face it… we need all the clean drinking water we can get!
Why do we need all this water? Why does every house need a 250 A breaker. Why is meat included with every menu item? When did it become acceptable to travel 40 miles a day round trip?
It is these technology breakthroughs that keep us from the brink of collapse as more people live increasingly consumptive lives. Poseidon is a step backwards using established technology requiring incredible amounts of horsepower. I would accept the challenge of Demwax, in that the alternative in case of flop, would be simply be more water conservation (responsible water use in a desert?).
“Poseidon project has no additional environmental imact”?!?!!? That’s intersting…so ALL that electricity that Poseidon needs to run those plants just shows up?? No emmissions from generating electricity eh, please show me – I need to see that….
Or you can use the approach from Ocean Motion Intl…that’s pure water from a clean, non-carbon system. I’d like to see this company get some of the publicity and support that these other “approaches” are seeing.
Maybe, someday when others realize that good money is being wasted and no real output is seen.
California, we need water. We can feed and save the smelt and then our farmers farm again!! Let’s take a look at all solutions and choose the best one’s (yes, plural! There are several viable, renewable and clean solutions out there!!)
Thanks for reading.
Several years ago I recognized the fact that the pressure differential between water at a great depth and atmospheric pressure could be a means of desalinating sea water. However it is clear that the energy needed to bring the fresh water to the surface would be about equal to the energy required to to maintain the pressure differentia in a conventional plant. The pressure in the submerged vessel containing the fresh water is equal to atmospheric pressure. The fresh water head that must be overcome to raise the fresh water to land level equals the pressure differential across the submerged filter. This would require a submerged pump. The added complexity of servicing the filters and the pump make it unlikely that this scheme would be practical.
Sidney,
Your concerns are not correct. I have consulted with this company and can tell you…
With the DEMWAX, only the product water is pumped to surface whereas onshore plants pressurize feedwater (2 to 3 times more water), which requires significantly much more energy.
Furthermore, the pressure required for this system is near osmotic pressure. Onshore systems are about 2X osmotic pressure. The reason is somewhat technical, but has to do with recovery rates. Again, significantly more energy is required for the onshore system.
Finally, submersible pumps are well established as a technology. They have widespread use as every land well has one. They have long duty cycles with little maintenance. Also, the water hitting this pump is behind RO membranes and a whole lot cleaner than well water, reducing the impact on the pump.
Dan,
Your first point is valid. This alternative would reduce the cost of pressurization of the water, since the quantity pumped will be approximately half. Your second point can be true for either the submerged system or the above-water system, so it isn’t relevant to the decision as to which is best. In either system, you can trade off pressure differential for area of membrane surface. Your third comment (about pumps) is true, but doesn’t consider the problem of maintenance of the membranes. The membranes foul and need to be serviced. There will be difficulties (and costs) in maintaining the submerged system that are not present in an accessible, above-ground system. I wish them well, but, as was said above, don’t let the perfect get in the way of the good.
Addressing“Gollini” below – can’t submit reply below his entry…
Great comments GoIllini, but I must address a couple things.
Regarding recovery rate: as you state, recovery rates can be the same onshore and off. You are right that an onshore plant can go to a 1% recovery to lower the osmotic pressure just like the DEMWAX system. However, the energy required will be far from the same as with the DEMWAX system. When an onshore plant goes to very low recovery, they must pump a whole lot of feedwater, even if it is at lower pressure. And because the best energy recovery devices are only about 91% efficient, that level of pumping will entail a substantial amount of extra energy (and costly energy recovery devices). The DEMWAX does not pump the feedwater at all so the ‘optimal’ recovery approaches zero. You will not find a shore based system that make any sense at that level of recovery.
As for the fouling, that is something that needs to be proven and is in testing. However, water at those ocean depths (and off the floor) is extremely clean. I think the maintenance economics will surprise people when they get their data in the ocean.
Well water is generally pretty clean when it gets to the well pump assuming the screens and gravel pack are intact. The RO water, while undoubtably very clean, will also be very corrosive. Possibly requiring very expensive pump and pipe materials to be used.
The truth is: The Government does not want this because they want the people to rely on them. The Gov is using the “Enviromental Advocates” to help their agenda! The entreprenuers are the people who make this a better country! As you saw in the OC Reg recently there is one California Rep thats against it. Sound familiar Oil of our coast but enviromental nut cases preventing it.
I HOPE IT WORKS!! I WILL HELP out with the drought!
No Brine and lower energy – no brainer!
Relax, folks.
There’s this pesky thing called conservation of energy standing in the way. You’re either going to pump to this great feed pressure, or pump the same amount of pressure on the filtered water to get it back up to sea level. A “snorkel” is going to change this basic concept.
Cute though. Where does OCR find this stuff?
Scott:
The membrane configuration allows the process to be done at far less pressure (i.e. Depth) than is required for onshore.
Also, the DEMWAX is only pressurizing the product water which is significantly less energy than a traditional onshore plant which pressurizes the feedwater. This is a huge energy saver. Read the white paper on their website.
This is an interesting idea. Here’s something that will work right now.
Achieving Water Security by Becoming Water Self-sufficient
Water, water everywhere and all we want to drink, shower in, swim in, grow food with, etc.
A Jim Bell Commentary
Many experts are projecting doom and gloom, scenarios of decreasing water supplies and increasing cost, yet the San Diego/Tijuana Region can easily become renewable water self-sufficient and even become a net water exporter.
Even if we assume the worst case scenario of zero precipitation and the complete cutoff of all imported water, the San Diego/Tijuana Region could completely replace all the freshwater it currently uses by installing PV panels over 4.3% of its roofs and parking lots. In 2015, 4.3% of our region’s roofs and parking lots will be about 9 sq. miles, or as shown in the graphic, 4.5 sq. miles on each side of the border.
The above statement is based on the following assumptions:
1. A yearly average of 5-hr. of sunlight per day,
2. 1,000 sq. feet of roof and parking lot per capita,
3. An average potable water consumption level of 180 gallons per capita per day,
4. A 2015 regional population of 6 million people,
5. That 70 gallons of freshwater can be extracted from seawater per kWh of electricity consumed through reverse osmosis (RO)
6. PV (photovoltaic) panels 15% efficient at converting sunlight into electricity, (Commercially available panels are already pushing efficiencies of 20% or better.
The electricity produced by this system would be used to power large scale reverse osmosis (RO) pumps to convert seawater into freshwater. The pumps push seawater through filters that let freshwater through while excluding salt, other minerals and contaminants in general.
The issue of sucking marine life into reverse osmosis system can be solved if seawater to be processed into freshwater is extracted from wells close to the ocean above high tide instead of direct ocean extraction. Since seawater coming into such wells would be sand filtered, marine organisms will be eliminated from the process.
Similarly, since “waste water” from the RO process will be twice as salty as seawater, it will have to be diluted by mixing it with seawater, also extracted from the near ocean wells, until the water to be returned to the ocean is no more than 20% saltier than seawater. Once diluted, its release into the ocean would be defused as an additional precaution against negative ecological consequences. Other sand filtering technologies have also been proposed.
Mining RO waste water for salt and other minerals opens up other local business and employment opportunities for the region and could potentially eliminate the need to return RO wastewater to the ocean at all.
The size of the “worst case scenario” RO system discussed above could be cut in half, if recycled sewage water was filtered and disinfected, then used for irrigation. Using graywater at home would also be a plus for efficient water use. This is because half of the potable water currently used in our region is used for irrigating landscaping and crops.
Water-use efficiency improvements could reduce the role of renewable-energy-powered RO as well.
Combining water recycling and efficient water use with better rainwater runoff collection and storage systems, our region would only need to install 15% efficient PV panels on 2% of its roofs and parking lots to provide equal or superior water use services in the future, compared with what we have today. Plus, if we want more freshwater, we can cover more roofs and parking lots with PV panels to power expanded RO capacity and create all the freshwater we want.
Additionally, all this can be funded through a water purchase agreement model that will pay for itself by redirecting the dollars we now export to pay for imported water into hiring local businesses and workers to make our region renewable water self-sufficient, with renewable energy powered RO being our back-up for water if all else fails.