Why you should care
Amid skepticism, Yaniv Scherson remains hopeful that his revolutionary method will make wastewater treatment sustainable and clean up oceans and lakes.
Growing up along the sun-drenched Orange County coastline, Yaniv Scherson’s respect for the ocean ran deep. “Climate change” and “pollution” weren’t just buzzwords. “It was very in my face,” he said. While surfing, kayaking and scuba diving, he often sighted garbage and oil slicks from motorboats fouling the ocean surface. Today, the 29-year-old rocket scientist-turned-environmental engineer is piloting a revolutionary, sustainable method for keeping his beloved waters clean – by turning poop into power.
Nitrogen and carbon in wastewater can seed massive algae blooms that suffocate aquatic life. In most treatment plants, bacteria convert the carbon into methane, which is then burned to generate power. Other bacteria break down waste ammonia into nitrogen gas, which goes unused in current treatment processes.
In order for innovation to happen… you gotta go for that small chance of success.
— Yaniv Scherson
Scherson, a postdoctoral researcher at Stanford, has designed the first-ever process that converts nitrogen into renewable energy in the form of nitrous oxide, which is typically viewed as a toxic greenhouse gas. Known as Coupled Aerobic-anoxic Nitrous Decomposition Operation, or CANDO, the system captures the nitrous oxide and uses it to fuel a wastewater treatment plant’s electrical generators. Scherson outlined CANDO in the journal of the Royal Society of Chemistry in January 2013 and will launch a year-long pilot at a plant in Antioch, California this month. CANDO could significantly lower the energy input and halve the expense of conventional nitrogen removal in wastewater treatment processes, which are the biggest energy consumers in many cities. Meanwhile, it would keep nitrogen from cycling back into waterways, helping prevent algae overgrowths.
Scherson knows that such a new technology has an inevitably high risk of failing. But “in order for innovation to happen… you gotta go for that small chance of success,” he said. “If this works, it could be a game changer.”
Inspired by his parents’ immigrant idealism, Scherson is used to starting from scratch. His father, originally from Chile, was a professor whose job took Scherson and his mother to San Francisco, New Jersey, and Irvine, California. When his parents divorced, Scherson and his mother struggled to stay afloat in upscale Irvine before moving to her native Mexico, where he helped her get back on her feet. He returned to Irvine three years later.
He found peace in the ocean and his garage, tuning up his 1971 surfer-style Volkswagen bus. “I was always interested in how things worked,” said Scherson, who double-majored in mechanical engineering and materials science at UC Berkeley.
The professor’s jaw dropped. “I had no idea this equation even existed,” he said.
He went on to Stanford’s engineering Ph.D. program, where he designed rocket technology for small satellites and renewable power applications. In his doctoral thesis, he searched for a renewable source of nitrous oxide gas, a highly powerful fuel used in rockets and racecars.
Then he read about how bacteria in wastewater could make nitrous oxide, and something clicked. Maybe treatment plants could burn nitrous oxide to make the combustion engines for their electric generators produce more power. But was there a way to extract nitrous oxide from wastewater?
Scherson contacted Craig Criddle, a professor of environmental engineering at Stanford. When they met in Criddle’s office, Scherson explained his idea and wrote the chemical equation for converting nitrogen into nitrous oxide on the whiteboard: nitrous oxide –> nitrogen + oxygen + energy.
The professor’s jaw dropped. “I had no idea this equation even existed,” he said. Although the rocket industry had long viewed nitrous oxide as an energy source, environmental researchers had condemned it as a greenhouse gas.
Criddle diagrammed the nitrogen cycle for the engineering student, who hadn’t cracked open a biology textbook since high school. Bacteria in wastewater can convert ammonia into nitrogen, he explained, but there are many intermediate forms in between — including nitrous oxide. ”Why not select for bacteria that were at the nitrous oxide step and capture the gas they produced?” Scherson thought.
It sounded simple enough. But first, Scherson had to train in environmental engineering. “I had to go back and learn what a cell was,” he said. What’s more, no one had ever tried using bacteria to make nitrous oxide let alone maximize its long-term production.
Scherson had essentially thrown a wrench into the nitrogen cycle. While the bacteria had stored enough food to survive, they had barely enough air to breathe, making them shift to stress mode. So when he reintroduced nitrite, they didn’t convert it all the way to nitrogen. Instead, they stopped halfway, producing nitrous oxide instead.
For twelve months Scherson painstakingly tweaked each parameter before settling on a process that supplies the bacteria in wastewater sludge with a high pulse of acetate and nitrite, which are like food and air for bacteria. The nitrous oxide levels rose, but were nowhere near enough to offer a viable energy source. So he tried alternating between giving them either acetate or nitrite each day. And then — “euphoria!” He saw a whopping 440% increase in the amount of nitrite the bacteria converted to nitrous oxide.
But it’s “still early days,” and researchers are hesitant to embrace CANDO. Some worry that the energy needed to run the process will ultimately outweigh the energy it produces, while others doubt whether it will offer a significant advantage over conventional nitrogen treatment processes. Plus, the bacteria used in CANDO take time to grow and isolate. Identifying and maintaining the conditions that allow them to thrive and churn out high volumes of nitrous oxide can also be tricky outside of a controlled, scaled-down lab environment.
Even if I fail, people will start thinking of nitrogen not as waste but as an energy resource and change the paradigm.
— Yaniv Scherson
“It’s delicate from the process standpoint… how to control biological processes very precisely,” said Tzahi Cath, assistant professor of environmental science and engineering at the Colorado School of Mines. “In wastewater, you have a lot of different types of bacteria, and you want to shift the equilibrium to specific microorgansims that will do what you want.”
Meanwhile, Scherson maintains his usual sunny outlook. “Even if I fail, people will start thinking of nitrogen not as waste but as an energy resource and change the paradigm,” he said. “The more we can find ways to align environmental and economic interests, the more likely we are to protect the environment.”