The Delbuoy, a low-cost, low maintenance, wave-powered desalination unit

Location:

Puerto Rico, other locations in Caribbean

Problem Overview:

Lack of fresh water in arid coastal areas

Fresh water sustains human life in a variety of ways. We need to drink it every day to replenish what we lose through perspiration and excretion. With few exceptions – salt-water fish, for example – all of the foods we consume, whether plant or animal, need abundant fresh water to grow. Not least, many of the things that provide beauty in our environment – trees, shrubs, lawns – need their own fresh water supply.

For people whose homes are situated where there is no fresh water supply, finding water and getting it to where it is needed ius a daily challenge. In the industrialized countries, pipelines and aqueducts move water hundreds of miles to the places it will be consumed. In developing countries, people may walk a dozen miles to bring back a bucket of fresh water to their villages. Even then, they face the risks of contracting water-borne diseases. Many dangerous and deadly diseases are carried by insects, worms, and bacteria that thrive in unclean water. Other diseases, such as chronic childhood diarrhea, which by causing dehydration is one of the main causes of infant and child mortality worldwide, are considerably less dangerous where fresh water is abundant.

In the wealthier countries of the world, one way to increase the supply of fresh water is to build a desalination plant, which will remove the salt from seawater. The basic technique is simple: the salt water must pass through a filter in order to become fresh. But this simple process requires a great deal of energy. To get fresh water from the sea in sufficient quantities you need to be able to provide and pay for the fossil fuels or other energy sources, such as nuclear power, that the desalination plant requires. These costs are quite high, particularly when added to the costs of building, staffing and maintaining the plant. Since burning fossil fuels and producing nuclear energy present, beyond their financial burdens, risks to human health and the environment, building a conventional desalination plant becomes an even more difficult decision.

In the developing countries, the costs of building and running a desalination plant are prohibitive. These are the same countries whose citizens bear the highest burden from water-borne diseases, and where the supply of fresh water for irrigation is most needed to help alleviate hunger. Even in wealthier lands, in areas where the population density is low and where revenues from taxes are not substantial enough, a conventional desalination plant is too expensive.

In all countries of the world, there are coastal areas that are effectively uninhabitable because of the lack of fresh water; making such areas inhabitable would relieve overpopulation and shortages of agricultural land worldwide. A method of desalination that is less expensive and easier to maintain can not only help avert disease and provide water for drinking and irrigation in the world’s poorer countries, but it can benefit the wealthier nations as well.

Update:

An Update of November 11, 2004, from:

Douglas C. Hicks, PhD
Department Chairperson
Engineering Technologies Department
Delaware Technical & Community College
Owens Campus--Georgetown, DE 19947
302-855-5914 Tel. 302-858-5458 Fax.
dhicks@college.dtcc.edu

The Delbuoy technology was developed by my graduate advisor, Dr. Charles M. Pleass and me during the late 1970's through the 1980's. The work resulted in numerous patents, several technical articles and a set of successful sea trials off the southwest coast of Puerto Rico.

We were making great progress towards commercialization of the technology. In the late 1980’s, the whole installation and operation was filmed by HORIZON International first in a co-production with WestDeutscherundfunk (WDR) German TV that was broadcast in Germany, then with additional filming for a version for the English-speaking audience, broadcast on PBS in the US and round the world, generating substantial interest.

During the time I was actively involved working on the technology we were able to operate prototype systems capable of producing potable water for periods of up to several months. The equipment operated as expected but required regular maintenance. The test site in St. Croix was intended to be the location where we could finalize the design and maintenance methodologies.

Our progress suffered a major set-back soon thereafter, due to five major reasons:

The first was due to mismanagement by the company that licensed the technology from the University of Delaware.

The second was the loss of all of the equipment and infrastructure that was put in place to begin full commercialization of the Delbuoy in St. Croix when hurricane Hugo devastated the island. When we lost everything in St. Croix (what didn't blow away was drowned, what didn't drown got stolen) the commercialization efforts stopped. I started my own company soon thereafter.

The third is that I undertook a parallel path by starting my own company to commercialize a patented motor powered, composite and polymeric high pressure seawater pump used for desalination that I developed towards the end of my work on Delbuoy.

Fourth, with the licensure of the pump technology I commercialized to a large multi-national corporation, I reduced my involvement somewhat in company and became Department Chairperson for the Engineering Technology program at a technical college.

The last is that my partner in the Delbuoy work, Dr. Pleass passed away.

The Delbuoy technology has not been worked on actively since the late 1980's.

I have considered getting involved in wave powered desalination work again but after all I learned during the 15 years of Research and Development (R & D) I put into the Delbuoy along with what I now know about successfully commercializing technology I decided to wait until I knew the time was right.

To successfully commercialize any wave energy conversion system requires a combination of factors, among them, either lack of viable alternatives or high energy costs for conventional power.

In addition:

Sufficient investment capital over a 2-3 year period to cover the cost of mass production (CNC machining, injection molding, composite forming), deployment, maintenance, testing, and monitoring of a large quantity of production units.
A management team that has the combination of vision and a realistic understanding of what it takes to work in the marine environment in what may be remote locations.
A mechanism to ensure long-term maintenance of the equipment in a remote region, for example, training of local people to install and maintain the systems.
The potential for a reasonable return on investment which can be difficult to predict.

Several of the areas that need to be addressed are:

How much water can be produced per day?

Approximately 300 - 500 gallons per day could be produced in a trade winds wave regime. The wave regime required to achieve this quantity of water is based on our work done in the Caribbean. The system could be scaled-up for slightly longer period waves

What is the cost of the system, including maintenance and life span?

The system cost is fairly easy to predict; it's the maintenance and life span issues that are yet to be determined for a production scale system and are what will really determine the cost effectiveness of wave energy conversion.

What are the strengths and weaknesses of the system?

Everything man has put to sea has been designed to minimize its extraction of incident wave energy and equipment is still lost regularly. By definition wave energy extraction requires that the system "takes it on the chin" with the incident waves. With wave forces and energy increasing with wave height squared it is difficult to design a cost effective system with the needed factor of safety. For example, working regularly in 3 - 4 foot high waves and withstanding the impact of 15 - 20 foot storm waves containing 25 times the energy requires that the system be heavily over-built. The Norwegians had a system they built that was washed off solid rock in less than a year!

The approach we used with Delbuoy was to allow large waves to flow over top the system and to put the expensive components below the surface where wave forces are lower. We sited the units in relatively shallow water (60 - 70 feet) to limit the maximum wave heights, and included a sacrificial link that would separate from the rest of the system part in the event that wave forces exceeded a predetermined upper limit (the buoy would be retrieved/replaced after the storm and the expensive components would fall to the sea floor for later recovery).

What is the quality of the product water (salinity, TDS, pH)?

With the existing membrane technology drinking water quality is attained.

What are the effects of fouling, and what measures are taken to mitigate fouling?

This is a problem area but materials and designs are available that could effectively prevent fouling and provide for reliable and cost effective maintenance.

Would the system be able to cope with phytoplankton blooms, red tide etc?

Pre-refiltration is best done using existing sediment as a slow sand filter; this does limit system locations but does not do so prohibitively.

What is the optimal temperature range?

This is not an issue.

Is the system being used commercially, and to what extent?

No.

I think wave energy is appropriate in specific applications and is certainly more realistic at the scale embodied by the Delbuoy, that is with multiple units deployed in an array rather than a single large capital intensive system.

Successful commercialization requires the combination of capital and appropriate management to move forward.

Background:

By vocation, Michael Pleass is a professor of chemistry, but by avocation he is a sailor. He has sailed around the world. On his voyages, surrounded by vast quantities of salt water, he has often been struck by how little fresh water is available at his ports of call. He has had to pay up to fifty dollars for a barrel of fresh water at some ports. Even more compelling to him has been the disease and hunger he has seen in various lands, and how the shortage of fresh water fostered those problems. He decided that he wanted to do something about the challenge of providing fresh water.

In the 1970’s, the United States faced an "energy crisis", a sharp rise in prices for oil which, although it had mainly political roots, forced people to confront the fact that the earth’s supply of fossil fuels such as oil and coal was finite. It was clear that conservation measures were needed to help stretch the supply, but it was also apparent that the world’s growing population and the spread of industry and technology meant that demand would continue to go up. One place that people turned was toward energy sources that would not run out. Solar energy and wind energy received, and continue to receive, the most attention.

Desalination unit preparation on dock by Dr. Douglas Hicks

When Michael Pleass began to try to find an inexpensive and simple method for desalinating water, his attention was drawn to a third kind of renewable energy, one that had received less focus than solar and wind. The ports and coastal communities where he had seen the hardships caused by a lack of fresh water had access to the potential energy of the sea’s waves, whose up and down motion created a powerful force that might be harnessed at low cost and in infinite quantities. He joined a number of scientists around the world who were making progress in the effort to exploit this energy source.

With many years of experimenting and testing, Pleass and his colleagues were able to develop a simple and inexpensive device that would use wave energy to desalinate sea water. They called the device a Delbuoy. "Del-" refers to the University of Delaware, where Pleass is a professor, and "buoy" refers to a buoy that rests on the water’s surface. When the waves lift and then lower the buoy, a piston connected to the bottom of the buoy drives a pump at the sea’s floor. The pressure created by the piston is strong enough to drive the sea water through a reverse osmosis filter, which removes salt and impurities from the water, and then to send the fresh water through a pipe to the shoreline, where it is tapped and used by people. Local divers with simple tools can install the devices in just ten minutes. The units cost little initially and can be maintained by trained local individuals. Best efficiencies are attained when the pump is deployed at depths of at least ten meters, and in the trade winds region from 30 degrees South to 30 degreesNorth latitude.

Lowering desalination unit, Delbuoy, into water from boat. Michael Pleass on left and Puerto Rican fisherman on right

Desalination unit being checked by inventor, Michael Pleass. Photo from film by Stan Waterman, underwater camerperson for One Second Before Sunrise I

The importance of the Delbuoy lies in its ability to provide fresh water at low cost and with simple technology. In the past, desalination has been an option available only in wealthier nations, and usually then only near large concentrations of people. The Delbuoy is inexpensive to purchase, and it uses a free and unlimited source of energy. It can be maintained with a simple set of household tools be anyone who has undergone just a few hours of training. It promises to give coastal communities, particularly in developing countries, access to abundant fresh water for drinking and irrigation, and that promises to improve the health and well-being of the people who live in those communities.