COVER STORY

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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Illustrations by Eiko Ojala

Gone Fishing

Luke Plante, a twenty-eight-year-old Army captain dressed in jeans, a white T-shirt, and size 11½ steel-tipped work boots, opens the back of his white Ford Escape. He takes out a red Rubbermaid cooler and sets it down on the gravel under the glaring morning sun. “This’ll be quick,” he says.

He snaps on a pair of latex gloves, then picks up the cooler and carries it to the water’s edge.

The water is grayish-brown, fifteen feet deep. It sits in a narrow tank more than a hundred yards long. There are twelve of these tanks in a row. Divided by strips of cement walkway, they resemble individual swimming lanes. The air smells of ammonia, with an undercurrent of some grim, dank putrefaction.

Yet the water rushing into the complex from the city’s sewer pipes makes a soothing whisper, and there is a coolness to be drawn along the cement pathways, like the coolness near a pond on a hot day.

Plante has come to this wastewater-treatment facility in eastern Brooklyn (one of fourteen in New York City) as a graduate student in environmental engineering at Columbia. It’s his fourth visit this year.

In some tanks, the water churns. These tanks are being pumped full of air — a costly and energy-intensive process — to sustain the greedy bacteria that reside there. The bacteria’s dietary habits lower the nitrogen levels in the water before it gets released into the nearby creek. Nitrogen promotes the growth of algae, which suck up oxygen and block light, resulting in fish kills and dead zones.

But the water at which Plante stops is calm. No aeration in this tank. No oxygen, period. This water has what he needs.

Plante sets the cooler down on the cement and picks up a wooden pole with a plastic cup taped to one end. The water at his feet is murky, but if you look closely, you can see, floating here and there — and there, and there — cotton-ball-sized clumps of soggy brownish matter, tinged with red.

Guiding the pole, Plante dips the plastic cup into the water, adroitly scoops up some of the red stuff, and dumps it in the cooler. He does this five times. Then he closes the cooler, seals it with duct tape, wipes it down, and carries it back to the car.

It’s an hour’s drive to Morningside Heights. Plante parks the car, grabs the cooler, and walks across campus to the Mudd Building and the laboratory of Kartik Chandran, an associate professor of earth and environmental engineering at Columbia.

Now the real work begins.

The Gray and the Black

How much water do you think is reused in the United States?” says Kartik Chandran, seated in his office next door to his laboratory in Mudd.
 

Chandran has short, dark hair and wears rectangular glasses. At forty, he is one of the world’s top experts on recovering clean water and resources from sewage, and before he answers his own question he sets down some basics: wastewater is classified either as graywater (from sinks, tubs, washing machines) or blackwater (from toilets); domestic wastewater contains levels of nitrogen, carbon, and phosphorus — mainly from urine, feces, food, soap, and detergent — that can harm aquatic ecosystems; Americans use, on average, a hundred gallons of fresh water a day per person; a quarter of the US water supply comes from underground aquifers; a majority of aquifers are being drained faster than they are being refilled.

“The US reuses 7 percent of its water,” Chandran finally says. “Next question: how much water do you drink a day?”

Hmm. Let’s see: there’s wake-up coffee, mid-morning coffee, a glass of water with lunch — “Half a gallon?” says Chandran. “Let’s say half a gallon a day.”

Sounds reasonable.

“So,” says Chandran, “if we each drink half a gallon per day out of a hundred gallons used, we are drinking only one two-hundredth of what we consume. Yet we are treating all our incoming water to drinking-water quality. This makes no sense. Using potable water for everything — for irrigating crops, for flushing the toilet, for washing your car — takes more energy, more chemicals, more space. It’s needless.”

“This is not a conversation about water alone anymore. This is about water sustainability.”

Our outflow is similarly mismanaged, says Chandran: he rejects the notion of “waste” with regard to human effluvia. “It’s not wastewater, it’s used water,” he likes to say. And it’s valuable, too: “Used water has higher energy — it’s enriched compared to just H2O.”

There is gold in those streams, so to speak.

“In a healthy person, urine is near-sterile — it is mostly nutrients,” Chandran says. “Why do we need to treat it to near-drinkable levels and then use it for irrigation? Why not take it right to the fields? Since urine already contains nitrogen and phosphorus — the nitrogen is in the form of ammonia — this water could be directly used for irrigation. The nutrients are there in the form that plants need them. How do we currently get fertilizer? We spend horrendous amounts of energy converting dinitrogen gas into ammonia. Yet we have ammonia right here, and instead of using it, we use more energy to get rid of it.”

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