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

Summary:

Dr. Michael Pleass and his colleagues designed low-cost desalination devices that use wave power. The inexpensive, easily installed systems can provide a viable, sustainable source of fresh water in arid coastal areas.

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.

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.

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.

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.

Similar Projects:

Botswana Solar-powered desalination; solution review pending

Documentation:

Documented in Program I of "One Second Before Sunrise"

Submitted by:

Information Date: 1989-03-17
Information Source: personal contact, Design News

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