Liquid Assets

As the California drought brings home the global problem of water scarcity, Columbia engineers are advancing a challenging idea: reusing our wastewater. Are we ready to go with the flow?

by Paul Hond Published Fall 2015
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Seen through Chandran’s goggles, municipal effluent is a sea of energy and nutrients waiting to be ingeniously tapped, an efficient way to lower energy costs, save resources, and reduce greenhouse emissions. The clean water that comes out at the end? That, Chandran says, is “the bonus.”

“This is not a conversation about water alone anymore,” he says. “This is about water sustainability. And one way to water sustainability is to stop talking about just water.”

Pumping Up the Volume

Two floors below Chandran’s lab, at the Columbia Water Center — a research consortium of scientists and engineers — they spend their days talking about water. Yet if you listen closely, you realize that they aren’t talking about water alone. They’re talking about water’s children: food, energy, climate, cities. They, too, speak the language of sustainability.

“Fresh water is a finite resource,” says Upmanu Lall, the Alan and Carol Silberstein Professor of Engineering and the Water Center’s director. As Lall explains, Earth’s hydrologic cycle is a constant exchange between the seas and the atmosphere: ocean water evaporates; the H2O molecules disperse in the air, drift, condense, and fall as precipitation; this water, should it fall over land, evaporates or is absorbed by plants (which return it through transpiration, a vapor from leaves) or locked in soil or caught in lakes, rivers, and reservoirs (surface water) or filtered through the soil to aquifers (groundwater). The rest returns to the ocean. Water isn’t gained or lost: it only changes form and location. The water in your teacup is the water Brontosaurus bathed in. We have what we have.

Now consider that 97 percent of Earth’s water is salt water. The rest is fresh water, of which more than two-thirds is frozen in ice sheets. The remainder — 1 percent of all the water on the planet — is surface water (those lakes and rivers), or groundwater. This is our water supply. Last year, the Water Center released a report showing that most aquifers in the US are being depleted, and a study this summer from the University of California at Irvine used data from satellites that indicate stress in twenty-one of the planet’s largest thirty-seven aquifers. When groundwater runs out, it can take years, even centuries, for it to be restored.

In the US, the trouble has been most conspicuous in California’s Central Valley, a major agricultural region.

“We’re pumping groundwater that, due to drought, isn’t being replenished,” says Michelle Ho, an engineer and Water Center postdoctoral research scientist. “In some cases, heavily pumped aquifers have collapsed — the ground caves in — and there’s no chance of water ever being stored there again.”

Ho, who grew up in bone-dry Australia, notes that around 70 percent of water that humans use goes to agriculture.

“Everything on your plate needs water,” she says. “Most people don’t realize how much water goes into making that nice steak.” (Answer: about 1,200 gallons for eight ounces of beef.) “Look in your fridge, look in your closet.” (Nine hundred gallons for a pair of jeans.) “We need to focus on crop management and find market-based solutions to help the agricultural sector use water wisely.”

“Most people don’t realize how much water goes into making that nice steak.”

Michael Puma ’99SIPA, a Water Center affiliate who studies the hydrologic cycle in relation to climate, ecosystems, and society, agrees. “In a democratic country with a market economy — farmers grow crops in response to the market — it’s much more difficult to start mandating what to grow or not grow,” says Puma, who teaches in the sustainability-management program at the School of Continuing Education. “You don’t want people who have never been out in the field to bring in the farmers and say, ‘Oh, great, you’re here. Now we’re going to tell you what to do.’ That’s not going to work. We need state-level efforts to improve management of scarce water resources, and to find ways to optimize water use through the selection of crops grown in a given state. But this has to be done together with the farmers.”

Puma also shares Ho’s concern about groundwater: from California to the Ogallala Aquifer beneath the US Great Plains, this indispensable element is being tapped to its ancient depths. The deeper you drill, the older the water.

“This water was deposited there thousands and thousands of years ago,” Puma says. “Farmers rely on that groundwater. But it’s not a resource that’s going to last.”

The Magical Microorganism

Inside Chandran’s lab, the lid comes off the Rubbermaid cooler.

The lab is filled with pitcher-sized bioreactors containing bacteria whose chemical-altering capabilities Chandran wants to understand. He and his students are working on ways not only to capture and reuse the nitrogen, carbon, and phosphorus in wastewater, but also to remove modern impurities like antibiotics and hormones (from factory farms) and pharmaceuticals (from your medicine cabinet). The bioreactors, built by students, hum and beep continuously, and have a homespun science-fair quality, basic yet sophisticated, their tubes suggestive of a high-tech bong. In one of them floats a substance of copper-red.

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