DCVC DTOR 2024: Industry is turning to uncon­ven­tional water sources for fresh water and critical minerals

Thanks to population growth, conven­tional water sources — lakes, rivers, reservoirs, and aquifers — are being used up faster than they can be restored by the natural water cycle. At the same time, due to changing precip­i­ta­tion patterns, many locations on Earth are receiving far less water than they need, and others far more. So not only is the era of cheap, abundant water over, but we must now account for — and find ways to compensate for — global warming’s impact on the water cycle. 

That will certainly mean conserving existing water resources and using them more efficiently. But it will also mean aggres­sively harnessing uncon­ven­tional water resources, such as seawater, industrial and municipal water, polluted water, and the atmosphere itself. ​“We use the term ​‘uncon­ven­tional’ to describe currently untapped water resources,” says Earl Jones, an operating partner at DCVC. ​“It’s a nice way of saying ​‘dirty, expensive, and hard to access.’ When problems are expensive and hard, and the value of solving them is large, innovators get to work.”

One uncon­ven­tional source of water is the air. Earth’s atmosphere holds about 13,000 cubic kilometers of water, or 13 quadrillion liters. If we could extract H₂O from the atmosphere on demand, inex­pen­sively, we’d have an essentially inex­haustible source of freshwater. 

The purposeful extraction of water from air is called atmospheric water harvesting. Technically, it’s simple: we do it all the time with home dehu­mid­i­fiers. But these devices use so much energy that they’re orders of magnitude more expensive than other approaches to water generation, such as seawater desali­na­tion. There’s another approach to atmospheric water harvesting that may hold more promise: sorption systems that use novel materials, such as salt-impregnated polymers, zeolites, or metal-organics frameworks to suck water out of the air. DCVC is supporting the development of a compu­ta­tion­ally designed light-switchable polymer that could funda­men­tally alter the energy require­ments for sorption systems. An example of a light-switchable polymer is the photochromic layer in transition eyeglasses. When exposed to sunlight, the polymer changes color, giving the tint; indoors, the lenses revert to being clear. A DCVC-backed incubation will use a similar technology for water harvesting. ​“When the light is on, water is captured, and when the light is off, the water is released,” Jones says. ​“If we can bring this incubation to market and grab a lot of water cost-effectively, it has the potential to be world-changing.”

Another way to improve the economics of accessing uncon­ven­tional water sources is to extract impurities or cont­a­m­i­nants that may themselves be valuable. Seawater, for example, represents a nearly inex­haustible supply of magnesium — a special metal that has structural properties similar to steel and aluminum, but is 75 percent lighter than steel and 33 percent lighter than aluminum. If we had access to larger, cheaper supplies of magnesium, we could build lightweight magnesium vehicles that could travel much farther on a single tank of fuel or a single battery charge. 

Today, nearly all magnesium comes from mined ores such as dolomite and magnesite, 70 percent of which are mined and refined in China. And the refining method used to isolate magnesium, known as the Pidgeon process, is incredibly dirty, using more than 18 metric tons of coal and emitting 28 tons of CO2 for every ton of magnesium produced. Clearly, we need a cleaner source of magnesium, and a DCVC-backed company, Tidal Metals, is turning to the oceans, which contain 1.3 kilograms of magnesium chloride for every metric ton of seawater.

Tidal, headed by three physicists from MIT, Princeton, and the University of Wisconsin, has patented a technology that can econom­i­cally process seawater to extract anhydrous magnesium chloride, which can then be separated into chlorine and magnesium metal using traditional elec­trol­ysis. By eliminating the need for mined ores and dirty, energy-intensive thermal refining, Tidal Metals will deliver ​“green magnesium” for industries like auto manu­fac­turing without a green-premium price.

In last year’s Deep Tech Oppor­tu­ni­ties Report we profiled ZwitterCo, another DCVC-backed company using new materials to rethink water treatment. The company started out selling a non-fouling membrane designed to recapture high-value biological materials from the wastewater at facilities like dairies and phar­ma­ceu­tical fermen­ta­tion plants. Now it’s being pulled into an even bigger market, with a reverse osmosis membrane for brackish water, developed at its new R&D center in Woburn, Mass.

Brackish water contains dissolved solids like sodium chloride but isn’t quite as salty as seawater. Facilities such as power plants and wastewater treatment plants use trillions of gallons of it each year, and to help keep it clean they generally use reverse osmosis. In RO, pressure is applied on one side of a selective membrane, forcing the smaller molecules of the solvent (water, in this case) through the membrane while retaining the larger molecules of solute (salts and other solids) on the pressurized side. The problem is that most brackish waters contain biological cont­a­m­i­nants that quickly clog RO membranes, meaning it takes more pressure and more energy to push the H2O molecules through. The electrical properties of ZwitterCo’s zwit­te­ri­onic membranes make them immune to this fouling, which minimizes downtime, since the filters don’t have to be cleaned as frequently. 

If the U.S. intends to extend water, power, and mineral resources, rebuild its industrial base, and repatriate more of the manu­fac­turing supply chain from other countries, we don’t need to build more polluting factories or dig new mines. To a large extent, we simply need to get smarter about finding the needed resources in unexpected places. And we think that’s one mission where venture-backed deep-tech innovation can help.