Dry dock to wet tap: Old ships become floating desalination plants

by David Kreamer
Thursday, January 5, 2012

Last year’s hurricane season was not kind to Haiti. First, tropical storms Fay, Gustav and Hanna hit the Caribbean nation; then Hurricane Ike pummeled the island, flooding much of the country, wrecking roads and bridges and leaving Haitians desperate for food, water and other basics. To help the battered country, the United States sent hundreds of metric tons of supplies and hygiene kits aboard the aircraft carrier USS Kearsarge. The Navy deployed helicopters, landing craft and personnel to help local residents. And they brought in thousands of gallons of freshwater.

The USS Kearsarge handled the challenges of a short-term humanitarian crisis well. It has even been called an “ideal platform to support urgent humanitarian relief missions” by some officials. Its capabilities are limited, however. It does not have the large amounts of power and water needed to provide relief for longer periods. But with some modifications, the aircraft carrier, as well as a host of other naval ships, could be retrofitted to supply large amounts of water and power for protracted periods of time. This has benefits far beyond humanitarian missions: Such ships could also be used to provide water in everyday situations to locations that lack freshwater.

If a natural disaster, infrastructure failure or terrorist attack occurs, ships equipped to produce and distribute significant amounts of water could alleviate human suffering by moving to areas of sudden need. Alternatively, these ships could anchor off the coast of major cities with consistently high demand such as Los Angeles, Calif., or near regions of severe drought that desperately need water such as Australia, Cyprus or the Middle East. These mobile vessels could provide needed resources with minimal environmental damage.

Many factors are converging to make this a realistic possibility. Desalination is becoming more efficient and less expensive. And producing large quantities of potable water — and the power to produce that freshwater — at sea is becoming increasingly environmentally friendly. For example, ships can tap a variety of alternative energies that are low-carbon emission, “green” technologies. Generating freshwater and power in coastal areas may also free up resources for inland use as well.

Mobile shipboard desalination may also make the world a safer place. As the human population continues to rapidly expand, some researchers predict that future wars and human conflict will increasingly arise because of diminishing natural resources. An increased availability of water could act as a politically stabilizing force in the world, reducing conflicts over competition for resources. Shipboard mobile desalination is an idea whose time has come, and is about to make port.

A Crucial Need

The need for water — and the power needed to generate freshwater — in coastal areas is tremendous and will continue to grow. The United Nations estimates that more than half the human population lives within 200 kilometers of a coastline, and eight of the world’s 10 largest cities are coastal. In the future, coastal regions will grow faster than any other part of the globe: According to one estimate by Columbia University’s Center for Climate Systems Research, the number of people living within 100 kilometers of coastlines will increase by about 35 percent between 1995 and 2025 alone. And with more people comes a greater demand for water.

By 2015, the five countries bordering the Persian Gulf in the Middle East alone are projected to double their water demand to 5 billion gallons per day. Providing that additional amount of water will likely cost $20 billion for desalination, according to the Gulf Times. Inland population pressures also impact coastal areas by diminishing shared water resources in river and aquifer systems. In cases where coastal cities use large amounts of freshwater, any upstream use can limit coastal supplies. But water delivered to coastal areas, such as that supplied by mobile desalination and power vessels, could additionally help both coastal and inland areas by adding extra resources.

Already Happening

Many countries experiencing drought have already proposed or designed some form of mobile desalination. Australia’s Queensland government, for example, is proposing to install mobile desalination barges on the Brisbane River to ensure water supplies as a possible response to an ongoing record drought. Then-Acting Premier Paul Lucas noted in 2008 that two barges would cost $550 million and deliver more than 38 million gallons of water per day, which, in his words, would be “extra water for more than a million people a day.”

Cyprus has also experienced intense drought, and in 2007, 27 percent of the country’s water supplies came from desalination plants. Cyprus has a land-based, mobile desalination plant in the southern coastal town of Limassol, which generates 5.3 million gallons of desalinated water per day. The government considers this a temporary solution until the completion of a permanent desalination facility. In January, the Cyprus Ministry of Agriculture announced plans to build a floating desalination plant near Limassol as well.

Other proposals, conceptual models, intellectual property claims and patents are also going forward to make shipboard mobile desalination and power generation a reality. Water Standard, a Houston-based company, has designed and is preparing to convert existing ships into environmentally responsible, seawater desalination vessels that can deliver between approximately 5 million and 50 million gallons of freshwater per day. Alion Science and Technology in McLean, Va., together with the U.S. Naval Surface Warfare Center, Carderock Division in Maryland, has designed and built a full-scale desalination plant prototype, scaled to fit on an aircraft carrier that can generate more than 300,000 gallons of potable water per day.

There are other conceptual designs, proposals and prototypes as well. One operating prototype, commissioned by India’s National Institute of Ocean Technology in April 2007, is a barge-mounted desalination plant successfully stationed off the coast of Chennai in southern India. This vessel can produce 264,000 gallons of freshwater per day using Low Temperature Thermal Desalination, a form of flash evaporation that converts warm surface seawater to vapor under low pressures, and then condenses it to potable water using cold seawater drawn from a depth of 450 meters.

Some conceptual designs and proposals also incorporate renewable power production, everything from wind and solar energy to wave and tidal energy (see sidebar, p. 49).

Retrofitting Mothballed Military Ships

Building new ships to host mobile desalination and power plants is not necessary. Armed forces worldwide are home to whole fleets of aging or “mothballed” ships that could be transformed into desalination and power-generating vessels. Allocating money to refurbish these ships, or designing new ships, for this purpose is in line with the U.S. military’s mission to actively engage in humanitarian work and address the root causes of conflict.

The fact that the world’s armed forces have not yet developed efficient “peaceships” that can produce large amounts of water and power is not due to a lack of resources. The U.S. military has several hundred vessels that are retired from active duty or are nearing the end of their planned use. These retired and stored U.S. ships include the Navy’s Reserve Fleet (Naval Inactive Fleet or “Mothball Fleet”), which are mostly retired warships that are retained in case they are needed for future national defense or in a national emergency, and the National Defense Reserve Fleet, which is primarily merchant ships and is part of the Department of Transportation’s Maritime Administration.

The funding required for maintaining, upgrading, decommissioning and storing ships is sizable, but this money could be used to retrofit vessels for desalination and power production. Even a decade ago, the average historical inactivation cost for an aircraft carrier and supporting ships found in a typical carrier battle group could be approximately $1.5 million to more than $6 million for each vessel. Inactivation costs for amphibious warfare ships required to constitute an Amphibious Ready Group could be $1.5 million to more than $ 2.1 million per ship. The annual, five-year average storage maintenance costs in that same time period could be $500,000 to more than $1 million for each vessel in a carrier battle group and $400,000 to more than $525,000 for each vessel in an Amphibious Ready Group.

Decommissioning a nuclear-powered ship is even more expensive. The defueling of the eight nuclear engines of the USS Enterprise aircraft carrier, for example, is estimated to eventually cost the U.S. government hundreds of millions of dollars. Although decommissioning and storage maintenance is expensive, continued operation of warships is also costly. In the fiscal year 2006 budget request, the Pentagon proposed decommissioning the non-nuclear USS John F. Kennedy, the third-oldest aircraft carrier in the fleet, which was not scheduled for retirement until 2018. The Navy estimated early retirement would save about $1.2 billion and the ship was decommissioned in 2007.

But the current mothballing of our ships isn’t just expensive, it’s also dangerous. Without proper maintenance, many ships quickly fall to a state beyond any future use. If funding for maintenance is denied, only minimal fire and flood protection is provided and deterioration is rapid. Some ships end up in an “artificial reef donation program” and are sunk at sea as part of military bombing and torpedo practice, others are sold for scrap metal, and a few become floating museums. Many ships are stored so long that corrosion becomes a problem; ships have leaked petroleum products, asbestos and flaking paint chips containing lead, zinc, barium, copper and other possibly dangerous metals into the sea.

Retrofitting these vessels as desalination stations before mothballing them prevents ships from degrading into environmental hazards. And if typical refurbishing costs could be applied to transforming portions of naval fleets into peaceships during normal maintenance and upgrades, it could also save the most money.

Desalination’s bum rap

Desalination is the process of producing freshwater by removing salt from saltwater. But despite its benefits, desalination operations — whether on mobile ships or at traditional, land-based plants — are not without their critics. First, desalination costs a lot. Exact prices are hard to set, due to varying factors — the source of the water, how far the water must travel, the quality of the water — but typical costs are higher than those of more traditional water resources. Desalination also uses a lot of electricity. And ship-based desalination plants would have to produce all their own power. How exactly they could produce that power is a matter of debate.

The two most widely used desalination processes are membrane separation-reverse osmosis and thermal separation-multistage flash distillation. Together, these two processes comprise 90 percent of the desalination market. The membrane separation-reverse osmosis process typically uses either pressure or an electrical current to push salt­water or salt ions through semi-permeable membranes, filtering out the salt. The thermal separation process uses heat to separate out the salts. In the past, energy costs alone accounted for up to half the cost of the produced water.

Environmental concerns also abound. One concern is the discharge of saline and heated water into offshore environments. Desalination creates an extremely salty fraction in addition to potable water. Because desalination plants are typically located in coastal areas, many critics worry that discharging this saline fraction into sensitive coastal areas may irreparably damage some of the world’s most diverse marine ecosystems.

Desalinated water also tends to be high in boron, which causes human health problems. Reverse osmosis desalination has difficulty removing boron from seawater, and such desalinated water typically contains boron concentrations that exceed World Health Organization guidelines, a problem that has slowed down the permitting of U.S. desalination plants.

At first glance, these adverse aspects of desalination are daunting. In spite of these challenges, however, many of the traditional arguments against desalination are rapidly diminishing. Recent advances in reverse osmosis membranes are bringing down desalination costs, which now stand at about $0.002 to $0.003 per gallon of potable water produced. By contrast, average city water in the United States costs about $0.0007 to $0.0057 per gallon. New membranes that reduce operational costs are also more efficient at removing boron and are being developed to withstand chlorination. Mobile shipboard desalination plants in particular are more environmentally friendly than land-based plants because they do not have to release saline and/or thermal plumes into fragile coastal areas. At sea, brines and elevated temperature water can be diluted, cooled and released more safely into the deep ocean. Mobile desalination plants also have the added benefit of being able to sail away from approaching hurricanes, unlike their land-locked counterparts.

Mobile shipboard desalination plants can also eliminate the problem of producing large amounts of greenhouse gases. These ships could rely on a variety of low-carbon energy alternatives and emerging technologies, from wind to nuclear power.

Challenges Ahead

If mobile desalination vessels are to become a reality, many design considerations must be addressed. Some of these challenges include ship balance, water intake design, water and power delivery considerations, and water quality safeguards.

Ballast and vessel stability has been a concern with ships throughout history. At sea, large vessels balance and distribute weight carefully, and sometimes have double hulls and store fuel between them, constantly readjusting balance. Water is typically denser than many liquids, such as petroleum products, that are currently transported by tanker vessels. Therefore, one of the considerations in generating large amounts of heavy, potable water at sea is stable storage.

One important measure of a ship’s propensity for capsizing is its metacentric height, which is a measure of its stability. If aircraft carriers were to be retrofitted for water and power generation, for example, planning and designing for balance would be particularly important. A Nimitz-class carrier has a relatively high center of gravity, whereas the planned new Gerald R. Ford-class carrier has a lower center of gravity and is more stable because of a more aft location of the above-deck navigation bridge and “island” (the raised platform on the deck). Clearly, some military vessels would be more versatile, balanced and appropriate for the multipurpose uses of a desalination and power generation ship than others.

Another consideration is the intake design for inflowing seawater to a shipboard desalination plant. Sustaining a slow velocity of inflow to the system is necessary to reduce sea life from being entrained into or colliding with the system. The U.S. Environmental Protection Agency has established regulatory controls for intake screens, and proper water intakes can include a number of options that both discourage sea life from approaching the intake and block sea life from entering it. Unlike coastal desalination plants, ocean-going vessels can have a shorter intake pipe length, thus reducing pipe and power requirements, and can draw water from great depth, which is often of higher quality than coastal water.

There’s also the issue of getting the water from the ship to land. Many of the planned shipboard desalination projects propose ship-to-shore pipelines for distribution of potable water. Although this is likely the least expensive alternative for getting water to shore, and excellent for moored vessels, other forms of distribution might be required in times of emergency.

The ability initially to allocate small, manageable quantities of water to victims of catastrophic events would necessitate action similar to that rendered by the USS Kearsarge in Haiti in response to Hurricane Ike. Specifically, helicopters and landing craft would need to be ready to supply water to many groups of isolated people and animals, and containers would need to be available to hold the water. In a major disaster, it would be necessary to quickly construct larger, land-based storage and distribution units to provide continuing aid in the long run. Large, transportable bladders and storage tanks, strategically positioned, would allow groups of people and animals to gather for sustained assistance.

Lastly, water quality maintenance during desalination and storage is an important consideration. Retired petroleum tanker ships have been considered for conversion to desalination vessels, and this could possibly be accomplished safely with systematic cleaning and resurfacing of the inside of tanks and bulkheads. It should be noted, however, that petroleum products contain hundreds of compounds, many recalcitrant to desorption from ship tank surfaces. So it is possible that the refurbishment of the inside of petroleum tanker ships might meet with some resistance from the public. The International Bottled Water Association states in its “Bottled Water Code of Practice” that “tankers that have been previously used to haul non-food commodities such as toxic materials, petroleum products or other harmful substances shall not be used to haul drinking water for human consumption.” Thus, to avoid problems with petroleum products, some entrepreneurs have looked to ships that have transported vegetable oil or retired juice tankers for conversion to mobile desalination plants.

The future of an environmentally friendly freshwater supply from the oceans is intriguing. Developing desalination vessels could help forestall resource crises and prepare countries for meaningful responses to sudden disasters. A fleet of peaceships sailing on the world’s oceans and delivering freshwater could raise the image of industrialized nations in the eyes of the rest of the world, reduce the potential for conflict, and support traditional humanitarian values.

© 2008-2021. All rights reserved. Any copying, redistribution or retransmission of any of the contents of this service without the expressed written permission of the American Geosciences Institute is expressly prohibited. Click here for all copyright requests.