Wastewater treatment and aeronautics do not tend to go hand in hand, but two Stanford professors and an innovative graduate student are using rocket technology to make wastewater treatment systems more sustainable.

In a nutshell, the idea is to use bacteria to convert nitrous oxide, a byproduct of wastewater treatment plants normally viewed as an unwanted greenhouse gas, into air (pure nitrogen and oxygen gas), in the process producing both heat energy and methane that can be used as fuel.

The ultimate goal is to use these conversion processes to power the entire treatment plant, making it not only sustainable, but also emissions-free.

It may not sound glamorous, but treatment plants currently use significant amounts of energy. In fact, the local wastewater treatment plant is the one of the largest electricity consumers in Palo Alto, according to aeronautics and astronautics Prof. Brian Cantwell.

“If there is a way to derive [methane] from this kind of biological source, you’re carbon-neutral because you’re not bringing it out of the ground,” he said. “We think, using this approach, a wastewater plant could produce enough energy so it could be energy self-sufficient.”

Cantwell works on this venture with civil and environmental engineering Prof. Craig Criddle and fourth-year doctoral student Yaniv Scherson.

The idea began in 2008, when Scherson was seeking a topic for his doctoral thesis. Having used nitrous oxide as fuel for rockets, Scherson began looking at other ways to use the gas.

“Nitrous oxide is also a greenhouse gas 310 times more powerful than carbon oxide,” he said. “Since I had an efficient way to get rid of a greenhouse gas…I thought this could be a great source of clean energy and removal of a greenhouse gas. I started to look for ‘free’ sources on nitrous oxide, [and] my search led me to Professor Criddle.”

Criddle, an expert on wastewater treatment, then helped Scherson to develop the project.

There are two steps to the proposed process. The key step is to use methane gas to power the plant and convert nitrous oxide into energy and clean air. In order to do this, plants need to first increase the amount of methane and nitrous oxide being produced.

Cantwell explained that this idea is innovative because wastewater researchers have conventionally focused their attention on minimizing, not maximizing, nitrous oxide production.

“People who work in the field of wastewater don’t think of the energy,” Cantwell said. “And propulsion researchers and wastewater researchers rarely cross paths. In many ways, we would have still been wandering in the desert looking for an application of our thruster technology if we hadn’t come across the wastewater researchers.”

Cantwell explained that maximizing nitrous oxide would surprisingly save treatment plants a lot of money.

Currently, plants use oxygen-hungry processes to minimize nitrous oxide production, and the process of pumping oxygen into the wastewater is both costly and energy-consuming. However, the bacteria-driven process they propose requires much lower oxygen levels than conventional practices.

For now, Scherson, Criddle and Cantwell are still researching ways to maximize the amount of nitrous oxide produced at treatment plants. Cantwell predicts that research will continue for a couple of years before they can seek out a municipal treatment plant and create a pilot program.

But a number of facilities have already expressed interest in partnering with Stanford for a pilot program, which could lead to larger-scale projects, Cantwell said.

Scherson’s enthusiasm for the project’s potential is unbounded.

“This treatment process could be implemented at a city scale like San Jose, a high rise building in Manhattan or a small village in the developing world,” he said. “ I envision every water treatment facility in the U.S. and many world-wide retrofitting their water treatment plants from the energy pigs that they are today to efficient, low-cost, possible no energy cost treatment facilities.”