Desalination: The techno-evolution still leads back to a simple solution.
There's no shortage of nail-biting statistics conveying the scale of our global water crisis. One in nine people on the planet lack access to clean drinking water. Meanwhile, three-quarters of illnesses in developing countries are tied to unsafe water sources. Our warming climate will only worsen the growing gap between people and the water we need to survive. Look at the Rongbuk glacier. Nestled in the Himalayas. Geotagged before and after images captured in 1921 and 2008 visually suggest this massive ice sheet has lost upwards of 90 metres of vertical ice, a sea-level raising retreat that could induce devastating floods or starve rural communities in India, Afghanistan, and Mongolia of agricultural water.
With 71 percent of Earth's surface covered in saltwater, humans have long looked to the sea as a seemingly limitless alternative to our finite groundwater supply. Converting saltwater into potable freshwater is already meeting water needs in arid areas. And the sector is growing. In 2017, the worldwide-contracted capacity of desalination grew to almost 100 million cubic metres daily ([m.sup.3]/d), up from 47 million [m.sup.3]/d in 2008. It's a market that analysts expect will be worth $33 billion by 2025.
Yet as we cut down forests for resources, transforming natural areas into farms and cities, a technology that has so far supplied water to supplement agriculture may soon be leaned on heavily to meet our worst H20-stressed regions' day-to-day water needs. And that's not without risk.
Desalination takes many forms, but every process aims to remove the sodium, magnesium, boric acid and other chemical ions, viruses and microorganisms residing in saltwater.
While Aristotle described a basic structure of transforming saltwater into freshwater as far back as the fourth century BC, it wasn't until 1869 that humans constructed a large-scale desalination plant, a steam-powered facility built by the British government at Aden in Yemen. It provisioned freshwater to Navy ships. Supplying ocean-going vessels with freshwater came to dominate any discussion of desalting seawater for a century.
That changed with high oil prices in the 1970s. This gave many Middle Eastern countries, flush with fossil fuel cash, a chance to expand their critical infrastructure, water plants among them.
We have two main ways to remove salt from water. We can push it through a salt-stopping filter; or pressurize it, boil it and cool the saltless vapour back into liquid. Known as thermal evaporation, this strategy for heating saltwater was long the only way to desalinate water. The process typically relied on waste heat from connected electricity generating stations to boil ocean water and was popular in places where oil and gas are cheap and abundant.
Thermal evaporation's desal dominance ended in the 1960s as membrane technology advanced. Reverse osmosis, a process that separates salt by forcing pressurized seawater through a semipermeable membrane, required substantially less energy than thermal plants to transform saltwater. Desalination was now detached from power generation. This breakthrough allowed desal plants to be located anywhere there is brackish water. The American Water Works Association notes that reverse osmosis has gotten so efficient and flexible in the past half-century that it's now the world's desal technology of choice, accounting for 56 percent of all desalinated water produced.
What form of desalination any country undertakes is determined by a range of factors from available energy supplies and technology access, to politics and local histories. Even the sea itself plays a role. Saltwater salinity ranges widely from brackish estuaries at 3,000 parts per million (ppm) to the shores of the United Arab Emirates at 50,000 ppm. The higher the concentration of salt, the more time and energy it needs to become drinkable.
Canada has little desalination at home. Yet the country excels at exporting desal technology abroad, including new methods for energy-efficient freshwater extraction from government and academic labs in Vancouver and Kingston.
Desalination has gained a foothold south of the border. More than two dozen desal plants operate in the United States, largely in Florida, Texas and California. Like other high-capacity desal plants in Singapore, Australia and Spain, these facilities provide both day-to-day domestic and agricultural water needs. With four million dollars in funding announced in August 2017 by the Reclamation Bureau to pilot more American desal projects, expect more US consumers to soon get their water from brackish sources.
Membrane technology is fast evolving in mobile ways. This has allowed a new generation of researchers to craft on-demand desalination plants, deployed to areas where potable water is scarce, or where existing sources have been compromised. This summer, a team of chemical and environmental engineers from the University of Arizona retrofitted an old school bus into a mobile desal plant, capable of providing ongoing water to the state's parched Navajo Nation. In September, two Dutch companies airlifted three portable reverse osmosis plants to the Caribbean island of Saint Martin, machines capable of desalinating 94,000 litres of ocean water daily. Hurricane Irma had left the island without safe water supplies for weeks.
In India, after gambling on rainwater for centuries to supply the country's water needs, science and technology minister Harsh Vardhan announced in June a "desalination mission" to guide water infrastructure development. With Himalayan glaciers in retreat and the value of their bottled water industry topping $3.3 billion in 2018, India has turned to Israeli technology to close their water gap.
Israel is a useful role model. No more than a decade ago, the country faced their worst drought in 900 years. Farmers in neighbouring Syria drilled wells 500 metres deep in a fruitless pursuit of dwindling groundwater supplies. Farmland productivity collapsed, scattering millions of climate refugees globally in search of food and water. To avoid a similar fate, Israel turned to desalination to ensure civic stability. Now home to the world's largest reverse osmosis facility with 50,000 active water-filtering membranes, desalination in Israel generates potable water for 1.5 million people, some 55 percent of the country's requirements. They now produce more than they need.
No region in the world is better-suited to generate water from desalination than the Middle East and North Africa, where renewable energy can and should play a starring role in desalination. The area's "solar energy potential is without parallel," The World Bank noted in a 2012 report, and could supply all 1,100 terawatt hours per day the region requires with power to spare.
Burning oil to make water is unsustainable. Saudi Arabia, the world's largest fossil fuel exporter, blows through 1.5 million barrels of crude oil each day in electricity-desal cogeneration plants. By 2040, that daily burn could top eight million barrels, releasing 400 million tonnes of greenhouse gases into the atmosphere. A switch to concentrated solar power (CSP), a process that collects solar energy from a wide field and concentrates it via mirrors to heat steam boilers, could revolutionize how solar power is employed to desalinate water. The Middle East and North Africa's total CSP potential is 462,000 terawatt hours of power annually, more than 20 times the energy used by everyone on Earth in a year. CSP technology is still young, yet demand will grow as the need for low-cost, low-carbon alternatives to water production around the world becomes acute.
Concentrated solar is just one way that technological advances are pushing desalination forward. New Mexico-based Sandia Labs has developed a method for using tidal power to pump seawater to shoreline desalination plants; all operating without the need for external energy. Sandia Labs piloted the project off the coasts of Oregon and Peru between 2011 and 2015, producing five million cubic feet of freshwater for Peruvian agriculture. Low-cost solar stills generating water via evaporation, largely fabricated with whatever black and clear plastic cases and tubing a community might have on hand, are gradually closing the safe water gap for coastal residents in the developing world. Last summer, a University of Connecticut chemist used graphene, a material stronger than steel and thinner than human hair, to remove salt from water using electrodes. And back in 2015, MIT researchers used electrically driven shockwaves to separate salt from freshwater without using filtration membranes at all.
But desalination is not without risk. Countries in the Middle East and North Africa could turn towards renewable energy to power desalination plants; but in such energy-rich environments, the push for desalinated water might easily lead to the quick-fix of burning oil instead, increasing GHG emissions.
It may also lead some countries to expand nuclear power in place of burning oil to create water. In August 2017, Saudi Arabia announced just that.
None of this addresses how to dispose of concentrated brine, the hazardous by-product of reverse osmosis. Often 2.5 times saltier than the water it once was, brine can contain disinfectants and other chemicals used in pretreatment. Piping this toxic waste into aquatic ecosystems damages water quality and weakens marine life. Few shellfish like mussels and crabs or reef-building coral can tolerate highly concentrated saltwater. In the US, almost 90 percent of waste brine is dumped into nearby surface waters, flushed into local sewers or injected into underground wells.
Others question whether energy will ever be cheap enough to make desalinated water less expensive for agricultural use than tapping finite groundwater. Creating water, even via reverse osmosis, often requires a lot of fuel. Society cannot make pure water from seawater for less than 1.06 kilowatts of electricity used per hour (kw/h)--that's the theoretical minimum energy necessary. In California, farmers working near an aqueduct can typically secure freshwater for four dollars per acre-foot. Yet with electricity costs at $0.15 per kilowatt hour, that same acre-foot of desalinated water would cost farmers $50 or more. Desalinated water "is affordable if you need water to drink and to take showers," said University of California-Berkeley physicist Robert Muller, "but not if you are using it for agriculture in a world market."
As game-changing an option as desalination can be, it's wise to search out other ways of closing the gap between the water we need and the water we have. Half-a-percent of global freshwater not locked in soils or ice caps is enough to sustain human life on Earth, but only if we use it wisely. In their report on desalination in the Middle East and North Africa, the World Bank argued that "increasing efficient water use should be the first line of action" in making people water secure. Municipal utilities and industry in the region lose 30 to 50 percent of the water they transport from inefficiencies and ancient pipes. Local farmers grow water-intensive wheat, while governments subsidize fossil fuels and drilling water wells. Cleaning up these expensive and wasteful inefficiencies, the World Bank notes, must be priority one.
Remember Israel's remarkable turnaround following 2008's disastrous drought? Desalination played a role, but so too did conservation. In 2015's Let There Be Water, author Seth M. Siegel writes that desalination has become one part of a comprehensive water management plan. Israel transitioned to drip irrigation of water-efficient crops; priced water appropriately to encourage conservation; and replaced leaky infrastructure to halt preventable losses. "Even with the easy surplus that desalination has brought," Siegel wrote, "Israel's water professionals have effectively pursued an 'all of the above' approach that consciously integrates all possible sources of water and all possible technologies for conservation."
As the world looks to desalination to meet its growing water needs, Israel's turn towards conservation offers valuable lessons. Creating more water is good; using what we have more efficiently is better.
Andrew Reeves is an environmental writer and a contributing editor for A\J. His specialty is water and his forthcoming book is on Asian carp in North America.
Land Art Generator Initiative holds an international, biennial open competition to demonstrate that "renewable energy can be beautiful." The goal is to accelerate the transition to post-carbon economy. Landartgenerator.org
Caption: Ring Garden, triple benefit details on next page.
Caption: The Ring Garden concept performs triple duty--and then some. It's a short-listed project submission of team Alexandru Predonu for the 2016 Land Art Generator Initiave competition. The system design includes a solar-powered pump that uses reverse osmosis to desalinate seawater. Of the freshwater harvest, 30 percent (60 million litres annually) is sent to the city supply, and the other 60 percent is used for the rotating aeroponics farm in the wheel--in a system that is notably more water and energy efficient than conventional cultivation. Discover how the public art piece uses the excess brine solution for more cultivation at ajlinks.ca/RingGarden.
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|Date:||Mar 22, 2018|
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