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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Though it has been around for billions of years, the red stuff is a newcomer to the reservoir of human knowledge, and is the answer to one of the great mysteries in the history of sewage treatment. Typically in the nitrogen-removal process, bacteria in aerated tanks consume nitrogen (in the form of ammonium), convert it to nitrite, then to nitrate, and lastly to nitrogen gas, which then bubbles from the tanks and diffuses harmlessly in the air. (Nitrogen makes up 79 percent of the earth’s atmosphere and more than 60 percent of all ocean gases.) But in some baffling instances, ammonium has appeared to be converted directly to nitrogen gas, without any of those energy-sucking intervening steps — a sort of alchemy with no known biological basis. It wasn’t until the early 1990s that researchers at Delft University of Technology in the Netherlands finally identified the process by which certain aquatic bacteria turn ammonium straight to nitrogen gas — without the need for pumped-in air.

Scientists named the process “anaerobic ammonia oxidation,” which was abbreviated and trademarked as the Seussian-sounding “anammox.” Anammox bacteria, like the ones from Plante’s cooler, are recognizable by their redness, which comes from their peculiar enzymes.

Chandran is a leader in anammox research. Before he came to Columbia in 2005, he worked in an engineering firm responsible for redesigning New York’s water-treatment systems to go from just carbon removal to nitrogen removal as well. Now his lab is part of an Environmental Protection Agency center focusing on sustainable nutrient management, and Chandran receives anammox bacteria and other bacteria from water utilities all over the world. He and his group take the samples and interrogate their biology: Are the bacteria doing what they’re supposed to be doing? What sort of bacteria are there, and how many? What are the concentrations? Are they the best bacteria for the job? How can they be made better?

“We are developing anammox processes that consume anywhere from 25 to 60 percent less energy and eliminate nearly all CO2 emissions,” says Chandran. “We are removing nitrogen at a far lower carbon footprint, while also generating nutrients and energy.”

Chandran doesn’t limit himself to the liquid side of waste. He has also pioneered a biochemical method to convert the methane from fecal sludge into methanol (methanol is used in wastewater-treatment plants to convert nitrite and nitrate into nitrogen gas). “The way we do things now is, we take organic matter, produce methane from it, and flare the methane we don’t use,” Chandran says. “Then we spend a hundred million dollars per year purchasing methanol. So my group has connected methanol into the process. No flaring, no buying methanol. We can produce the methanol internally.” For this, Chandran won the 2010 Paul L. Busch Award, a $100,000 research grant from the Water Environment Research Foundation.

“Kartik has a unique approach to bioengineering,” says Liron Friedman, a PhD candidate at the Water Research Center of Tel Aviv University who works in Chandran’s lab as part of his doctoral program. “He doesn’t look at bacteria according to species. He looks at function. He wants to see what they do. What are the functional abilities of the community? That’s what I’m doing: looking at bacteria as groups that can do something for the water. I’m manipulating the bacteria, using more nutrients, less nutrients, and different oxygen sources, seeing how that affects the community. I’m looking for groups that can take compound A and turn it into compound B. How many are there? How efficient are they? How fast? I’m an engineer: I want it better, faster, more efficient.”

At Columbia, Friedman is experimenting with a system he worked on in Israel, an arid country that recycles 80 percent of its water. The main Israeli process uses sand as a bioactive filter: water passes through the bacteria-rich sand for about a year before going straight into an aquifer. The chief machinery is gravity. “It takes less energy, and no special membranes or tubes or chemicals,” says Friedman. “Just pump the water out, and that’s it. This water is very high-quality, and it’s used for irrigation.”

Friedman is simulating this field process in Chandran’s lab, working on a controlled sand-based system that turns wastewater-treatment-plant effluent into water that can be safely reused.

“Look, this is the future,” Friedman says. “Water scarcity is here, and it’s already the first resource that’s in severe shortage in the world. Right now, there’s enough oil, enough coal, enough aluminum, enough natural gas — but there’s not enough fresh water in the world to supply everyone.”

Flush with Possibilities

Upmanu Lall once worked as a hydrologist in Utah, and he has intimate knowledge of the water ways of the West.


Take flood irrigation, still common in California. “Flood irrigation is low-efficiency,” Lall says. “Think of the backyard garden: typically, people use a sprinkler. The water goes into the ground, into the root zone, and is used by the plant. In flood irrigation you have a lot of water just sitting on the surface. Fifteen to 20 percent will evaporate under action of wind and radiation, and it’s lost. It’s gone. It had no productive capacity. Sprinklers can significantly increase efficiency. Drip irrigation is even better, but only for specific crops like grapes and walnuts.”

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