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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Lall is also critical of what he sees as excessive energy use. He points to the biggest expense in the California system: the power needed to pump water from central California over the mountains and into Southern California.

“The energy use connected with that pipeline is even greater than that of building a desalination plant,” Lall says. (Desalination plants, which cost hundreds of millions of dollars to build, burn vast amounts of fossil fuels.) “In the California legislature, some people are pushing for a second pipeline. This requires three times the energy needed to treat wastewater to drinking-water standards. The smarter thing would be to take wastewater and super-treat it so you are back to H2O level.”

This is the nose-wrinkling idea that’s been branded in the media as “toilet to tap.”

Lall acknowledges that “for most people there is still an ick factor,” but necessity has a way of eroding psychological barriers: localities in California and Texas are already recycling blackwater for drinking, through further purification steps like UV-light exposure and the energy-hungry filtration method of reverse osmosis.

Closer to home, Lall, like Chandran, sees waste of a different color: green.

“I live in Manhattan, I have no lawn, and my water bill is $120 a month,” he says. “One-fourth for delivery, and three-quarters for cleaning the wastewater I generate. What do we do with the wastewater? We treat it and dump it into the Hudson. I’m paying three times the cost of my drinking water to dump it into the Hudson. Toilets, washing machines, showers: why are we treating it all to the same standard?”

Pipe Dreams

Last May, in East Bridgewater, Massachusetts, a two-foot-wide water main broke. The rupture of the decades-old pipe, as reported by the Boston Globe, affected seventy-five thousand people, “shuttering businesses, forcing the cancellation of surgeries at a hospital, and closing schools,” and leaving whole towns with little or no water.

This is not unusual. At any given moment in the US, pipes break, streets and highways are inundated, basements flood, roadways buckle, water-boiling advisories are issued, service is cut off, and life changes at its most basic level.

“In many locations, our water-delivery systems are reaching the end of their design lives,” says Michelle Ho. “In the US, 20 percent of water is lost through pipe leakage. We can look at that as a waste, but we can also look at it as an opportunity to totally overhaul how we deliver and manage water.”

Kartik Chandran dreams of such a makeover.

“If you separate the water, you’re super—treating not one hundred gallons per person per day, but maybe ten gallons.”

In the dream, Chandran sees pipes. Not one pipe, like the kind that brings treated, potable water to our homes and businesses, so that we wash our cars and soak our lawns with drinking water; nor like the lone sewer pipe that mixes graywater and blackwater together on its way to the wastewater-treatment facility, where the fluid must be treated to a single rigorous standard.

No: Chandran sees dual pipes.

“Two pipes in, two pipes out,” he says.

In: water for toilets, and water for everything else (drinking, cooking, washing).

Out: graywater and blackwater, to separate destinations.

“Graywater can be treated and used for non-potable purposes, like for cooling power plants,” Chandran says. “If you separate the water, you’re super-treating not one hundred gallons per person per day, but maybe ten gallons. So these massive plants can be one-tenth the size. Then, instead of using more energy to convert the carbon in the water into CO2 and then releasing it into the atmosphere — a stupid thing to do — you can produce energy from it and run the plant on that energy.

“Now,” says Chandran, “you can put these plants in buildings. In Mudd we have a plant where we’re recovering carbon in food waste for biodiesel. Now we can talk about nutrient recovery, and urban farming on campus: we can take food waste from our cafeteria, get energy out, get clean water out, get the nutrients, and grow crops for food.

“Come, let’s go outside — I will show you something.”

It’s a sunny summer day. Out on Pupin Plaza, behind the curved rear of Uris Hall, two green plots of land the size of motel kiddie pools are abuzz with herbage and nectar-fueled bees. There are shocks of green grass, yellow-buttoned daisies, blue cones of delphinium, stalks of metallic-green Swiss chard veined bright crimson, heirloom tomato plants chock-full of dangling pale-green fruit. Against a brick wall lean a shovel, a hoe, and a faded painted sign that says “Food Sustainability Project.”

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