Sewage Potential Limitless

terça-feira, 25 de março de 2014

Most people would rather not think twice about their waste, but Kartik Chandran spends hours a day considering the limitless potential of sewage. Chandran, an associate professor of earth and environmental engineering, studies how to improve wastewater treatment and extract energy from sewage.

His latest work involves converting the dangerous greenhouse gas methane, a byproduct of sewage treatment plants that is typically burned off or released into the atmosphere, into the reusable biofuel methanol. He does this by finding microbes that can be put into giant treatment tanks to render the substance harmless.

Right now sewage treatment plants use microbes that break down waste by oxidizing ammonia, a chemical in sewage that has uses in fertilizer and cleansers but is toxic to wildlife when released into the water stream. In a treatment plant, a combination of microbes turns ammonia into benign nitrogen gas; the process has been standard in wastewater treatment plants in the United States for the last century.

These bugs are equally useful for processing methane because they don’t have the ability to completely oxidize it. If methane is oxidized, it simply turns to carbon dioxide—another greenhouse gas—but if it’s only partially oxidized, it leaves methanol, which can then be recycled and sold.

“The plants are just blowing off methane, but we’re putting it right back into the tanks and converting it into methanol,” says Chandran. “The beauty of it is, the tanks we use are already in place.”

For now, Chandran is developing the process in his lab in Mudd but is working toward perfecting the technology so it can be incorporated at existing sewage treatment plants around the United States.

“Today, chemists are trying to create catalysts to convert methane to methanol, but it’s not a trivial problem,” he says. “On the other hand, these bugs do this conversion anyway, so I thought, ‘Why not use a process that happens in nature all the time?’” Chandran is the first to study implementing this conversion process on a large scale.

The work involves studying which strains of bugs are most effective and developing mathematical models to describe the process and better understand how the microbes work. In October, Chandran presented preliminary results of this project, which was funded by the $100,000 Paul L. Busch award from the Water Environment Research Foundation, to the largest conference of water quality experts in the world.

Chandran has a complementary project in Accra, Ghana, for which he won a $1.5 million Bill & Melinda Gates Foundation award, to develop technology to transform fecal sludge into biodiesel fuel and create an urban sanitation facility in the country’s capital. The goal of both projects is to understand how to convert a wastewater treatment plant using existing technology into a biorefinery that can also be a source of fuel.

Chandran’s other research involves implementing a more efficient type of sewage treatment with microbes that don’t require oxygen—a process called anaerobic ammonia oxidation, or anammox. This method of breaking down human waste takes 62 percent less oxygen (and thus less energy) and emits much lower amounts of the byproduct nitrous oxide than other processes.

Nitrous oxide is a more dangerous greenhouse gas than carbon dioxide as it traps heat at a rate 300 times as effectively as carbon dioxide, and the molecules can remain in the atmosphere for up to a century. With Chandran’s help, anammox will be introduced in plants within the next two years in New York City, Washington, D.C. and the Hampton Roads region in Virginia.

Chandran has always been interested in technology, taking apart transistors and other gadgets when he was growing up in New Delhi, India. His interest in waste conversion was piqued as an undergraduate studying chemical engineering at the Indian Institute of Technology.

“I was learning about how to build reactors and use technologies to synthesize chemicals, but I realized we should probably do something with all the pollutant streams we were creating,” he recalls. “My dream dissertation project was to develop technologies to address these pollutant streams.”

Chandran moved to the United States to get his Ph.D. at the University of Connecticut and was a research associate at Virginia Polytechnic Institute before arriving at Columbia in 2005. In the interim, he was involved in helping to redesign the wastewater treatment plants of New York City.

“My adviser at the University of Connecticut planted the seed of the nitrogen cycle, and it was a real eye-opener,” says Chandran. “And I’ve been doing this ever since.”

Source: Columbia University