Once we exhaust the world’s supply of fresh water, there isn’t any more. Or is there? For millennia all the fresh water we’ve needed has fallen from the skies and the hydrological cycle still functions as it always has: Evaporation purifies the water it extracts from the sea and condensation distributes the life-sustaining result around the planet. Having helped nourish terrestrial life, the water finds its way back to the sea and the cycle repeats.
The process purifies only a tiny fraction of the world’s water, less than 3%. But since 75% of the planet’s surface is covered by seawater, that has been more than enough — until recently.
Now agriculture, industry, energy production and sanitation consume vast quantities of the planet’s limited fresh water; pollution renders much of what’s left unfit for human consumption; and much of the rest is simply wasted. Already, nearly a billion people don’t have access to safe drinking water. With the global population heading towards nine billion, and climate change disrupting weather patterns and melting glaciers of pure water back into the sea, the situation is only likely to get worse.
Given that the amount of water on the earth has not changed for eons, a great deal of attention has been focused on conserving water — reducing what we need and what we waste to a bare minimum. Much has been accomplished and much more remains to be done. But it is far from clear that these efforts alone will suffice, and it seems increasingly likely that our demand for fresh water will soon surpass the capacity of the hydrological cycle.
Desalination Offers Hope
If that happens, the only feasible solution in the near future is desalination, the use of technology to purify seawater. “Desalination is the only hope to produce new water for future generations at affordable prices,” according to Leon Awerbuch, past president and currently a director of the International Desalination Association (IDA), as well as president of Leading Edge Technologies.
The Middle East has been using desalination for 40 years, but the industry did not expand much until relatively recently. Widespread interest in desalination, especially within the business community, started in the 1990s as scientists began improving the technology, and the demand for fresh water grew more intense. Speaking at the Initiative on Global Environmental Leadership (IGEL) Conference, “The Nexus of Energy, Food and Water,” Neil Hawkins, vice president of sustainability and environmental health and safety at Dow Chemical Company, noted that solving the issues of the nexus is “the greatest business opportunity in our generation.” The rapid growth of the desalination industry in recent years proves his point.
Thanks to the commercialization of those scientific breakthroughs, today more than 16,000 desalination plants are producing water in 150 countries, including in China, India, Australia, Chile and the U.S. Desalination is now considered a growth industry: “Desalination Seen Booming at 15% a Year as World Water Dries Up,” declared a recent Bloomberg headline.
Overcoming Energy Limitations
For much of its history, the desalination industry has been limited by its massive need for energy. The two desalination technologies that currently dominate the field are both energy-intensive. Reverse osmosis (RO) uses electricity to generate the high pressure needed to force seawater through semi-permeable membranes, while thermal distillation uses energy both to heat seawater and to drive the system’s pumps. This demand for energy has kept the cost of desalination too high for any but the richest, most water-starved regions of the world (Saudi Arabia has been — and is expected to remain — the largest producer and consumer of desalinated water in the world).
But growing business investment in R&D produced innovations that have greatly reduced the industry’s energy requirements. Awerbuch points to significant advances in both RO and thermal desalination. For RO technology, one of the most significant developments has been isobaric energy recovery devices (ERD). The technology exploits the fact that very little of the pressure used to force seawater through the RO membranes is consumed in the process. ERD is able to recover 98% of this energy and use it to power the intake process, virtually cutting in half the amount of energy needed to run RO plants. To put this in context, a plant equipped with ERD technology can now produce six gallons of clean water with the same amount of energy a 100-watt light bulb uses in just one hour.
Advances have also significantly reduced energy use in thermal distillation. Both multi-effect distillation (MED) and the newer, and more widely used, multi-stage flash distillation (MSF) process represent sophisticated versions of the most ancient approach to desalination: the evaporation and condensation of seawater (analogous to the natural hydrological cycle). These systems heat seawater and then run it through a series of process stages, which successively lower the atmospheric pressure. As the pressure drops, so does the boiling point of the seawater. Thus, at each stage additional water boils into steam, leaving salt behind. Thermal distillation plants are generally coupled with power plants. This dual-purpose approach further improves efficiency by using waste heat from the power plant to warm the seawater.
Efficiency in thermal distillation is measured in terms of gain output ratio (GOR), which in simple terms is the amount of clean water generated per volume of steam. The GOR has historically been about eight to one (one unit of steam has generated eight units of clean water). But Awerbuch says that some plants have already achieved a ratio of 15 to one and he foresees a 16 to one ratio in the near future
Combining reverse osmosis and thermal distillation in one hybrid plant increases energy efficiency still further. Thermal distillation produces distilled water, which exceeds drinking water standards. Since the RO water will be mixed with this ultra-pure distilled water, it can be of somewhat lower quality and still contribute to an end product that meets drinking water standards. As a result, the RO system can be run at lower pressure, saving energy and extending the life of the membrane. What’s more, heat from the thermal system is used to increase the temperature of the seawater in the RO part of the plant, further improving the efficiency of the membrane.
Membranes themselves have also been revolutionized. Over the past 25 years, improvements have increased the amount of salt extracted, extended the life of the membranes themselves and reduced costs. At the end of 2012, Dow Chemical announced a new membrane chemistry that reduces salt by 99.7% compared to traditional brackish water membranes, while also reducing energy consumption by 30%.
According to Tracy Young, global application development leader for Dow Water and Process Solutions, as the company expands its desalination business, it will be taking this new membrane chemistry beyond brackish water into other segments of the market, including seawater desalination and wastewater treatment. (There is no exact definition of brackish water, but the term generally means water that it is less salty than seawater to some degree, and therefore is less costly to de-salt).
Together, these and other breakthroughs have dramatically reduced the cost of desalination, bringing it within reach of many more countries. And innovation is continuing on several fronts, including the development of forward osmosis, a process that uses naturally occurring, unassisted osmotic pressure rather than reverse osmotic pressure, which has to be powered artificially.
A New Approach — Off-peak Pricing
In the Middle East, power consumption soars in the summer months. In parts of Saudi Arabia, for instance, peaks can go above 120 degrees Fahrenheit and air conditioning units run continually. But in winter, power use drops by 30%. One new idea, reports Awerbuch: Use idle, winter power capacity to produce more desalinated water than needed. The excess water would be stored in underground aquifers to be tapped in the summer, when power is much more expensive. Such desalination aquifer storage and recovery (DASR) produces more water at lower cost, and also increases the efficiency of the otherwise underutilized power plants.
The practice of storing water in aquifers for later use is widespread in the U.S. Just as the nation developed strategic underground reserves of petroleum years ago, many areas with dwindling water supplies are now resorting to a similar strategy for water. The Environmental Protection Agency (EPA) estimates that more than 1,000 aquifer storage and recovery (ASR) wells are currently operating or waiting to be used, mostly in dry regions of the country. Few areas outside the U.S. are storing significant amounts of water, but given the strategic importance of securing adequate supplies, more may turn to DASR in the future.
The Renewable Energy Card
Most of the world’s desalination plants still tap fossil fuels, which makes them unsustainable long term environmentally and economically, no matter how efficient their energy use.
In the Middle East and North Africa (MENA) region, the obvious choice is to convert the plants from oil to solar power, which potentially is unlimited. The region could generate enough solar energy to meet current world demand several times over, According to a 2012 report by the World Bank. Replacing fossil fuels would also significantly reduce carbon dioxide emissions, a chief contributor to climate change.
Of the various solar technologies available, says the World Bank report, “Concentrating solar power (CSP) is the best match because it is scalable to demand; can provide both peak and base load electricity; and with heat storage and oversized solar collectors, it can provide a firm power supply 24 hours a day.”
The conversion from fossil fuel to solar energy in the MENA region will take time. Current plants will not be decommissioned until 2041-2043, and it will take further research and development to make solar power costs manageable. In the meantime, Saudi Arabia has already developed a number of solar-powered desalination plants, and recently started up the first large-scale solar-powered seawater reverse osmosis (SWRO) plant in the world in Al-Khafji, near the Kuwait border.
Eight thousand miles away in Australia, the world’s driest inhabited continent, wind is far more plentiful than sunshine. But a lack of fresh water remains a significant problem. So with severe droughts already dominating recent history, and climate change threatening more to come, Australia now views desalination as a strategic necessity and has constructed plants throughout the country. None are powered by fossil fuels. Australia opted instead for wind power, building up more than enough capacity to power, indirectly, all of the country’s desalination plants.
Building a desalination plant is still a capital-intensive business that many countries cannot afford. Recognizing an opportunity, private entrepreneurs have developed an innovative business model. Independent water and power producers (IWPP) raise capital, and then build and run the plant themselves under a long-term agreement guaranteeing that the local government will buy the output over 20 to 30 years. Governments that cannot afford the upfront capital can often afford the regular payments over the life of the agreement.
An example of such a project in the U.S. is the Carlsbad desalination plant currently being built in southern California by Poseidon Resources. Poseidon brought the project to San Diego country, which sits at the end of the water delivery system in California, and therefore has “the greatest need, pays the most for its water and is most at risk in the event of a drought or shortage on the aqueduct,” says Peter MacLaggan, senior vice president of California project development for Poseidon. With much of its water coming from outside the region and subject to intense competition, San Diego County saw an advantage to working with Poseidon.
The county has agreed to pay a fixed price, indexed to inflation, for the water it uses, and to pay the cost of the energy consumed by the desalination plant, as long as that cost stays within a preset limit. If the plant exceeds that limit, Poseidon has to eat the additional cost (a strong incentive to maintain high efficiency).
At the beginning, the county will be paying about twice as much for the desalinated water as it does for the water it imports from traditional sources. Based on history, however, the price of imported water is likely to rise significantly. “Over the last 20 years, the imported water rate has gone up an average of 6.4% per year; over the last 10 years, it’s doubled,” says MacLaggan. So assuming that the price of imported water continues to rise as it has for the past 20 years, and that inflation remains at predicted levels, the price of desalinated water and imported water will be at parity by 2025. After that, San Diego County will save money on the desalinated water it buys from Poseidon.
All of the capital for the Carlsbad project is coming from private investors. Poseidon has raised $734 million in the bond market, offering investors an average return of 4.85%. The remaining $168 million is coming from equity investors, including Poseidon itself, who are expecting a return in the low teens over the 30-year life of the project. The higher return compensates the equity investors for the relatively greater risk they are assuming: Since their investment is subordinate to bondholders, equity investors are more likely to lose out if the project fails to realize its projected profit.
A desalination plant can increase the supply of drinking water without ever processing any seawater. It accomplishes this feat by using essentially the same technology to process brackish water (desalinating brackish water typically costs about one-quarter as much as desalinating seawater and uses much less energy).
The U.S. is one of the biggest producers of desalinated brackish water. The International Desalination Association ranks the U.S. as the world’s third-largest user of desalination. According to the Florida Water Resources Journal, Florida accounts for more than half of the country’s desalination, and 85% of the plants in the state process brackish water. In Texas, another major player in the U.S. market, none of the state’s 44 desalination plants treats seawater, according to The New York Times.
Typically, brackish water is drawn from underground aquifers, but with the growing use of fracking to produce natural gas, the oil and gas industry is a potentially huge customer of brackish-water desalination. The fracking process uses liquid under high pressure to fracture shale rock, and the water that emerges at the end of the process is very saline. Desalinating this brackish water could play an important role in limiting the environmental harm fracking can cause.
The major challenge in desalinating brackish water: what to do with the brine that is left over. In seawater plants, such as Carlsbad, the concentrated brine is generally diluted with more seawater, to make it safe for marine life, and then returned to the ocean. Since this is not possible inland, one option is to use the salt from the brine for a wide range of industrial purposes, including the production of hydrogen, chlorine and sodium hydroxide by means of electrolysis. China, the world’s leading producer of salt, makes extensive use of the brine from desalination plants.
Other challenges to the growth of desalination remain and are being addressed, including pollution caused by chemicals used in the process, thermal pollution from MED and MSF plants, and the potential of harming marine life. But with global corporations like Dow Chemical, BASF and GE looking for ways to solve these problems and continue driving down the costs of desalination; private enterprise partnering with governments worldwide; and the demand for water outpacing the naturally occurring supply, that 15% annual growth rate Bloomberg mentioned looks like a good bet.
Other challenges to the growth of desalination remain and are being addressed, including pollution caused by chemicals used in the process, thermal pollution from MED and MSF plants, and the potential of harming marine life. The bottom line is that the 15% annual growth rate that Bloomberg cited looks like a good bet. Within the current landscape, the demand for water is outpacing the naturally occurring supply, there is a push by global corporations (like Dow Chemical, BASF and GE) to improve on various environmental and cost issues, and private enterprise is increasing its stake. All bode well for the future of the industry.