Sewage research makes space for rocket science

July 29, 2010, 12:31 a.m.

Anyone who thinks that sewage treatment isn’t rocket science may have to think again.

University researchers have created a new method of treating wastewater that they say would have a positive environmental impact and drastically lower the cost of the expensive and inefficient process. With the support of a Woods Institute Environmental Venture Projects grant, researchers Craig Criddle and Brian Cantwell led the venture.

Criddle is a civil and environmental engineering professor and an expert in wastewater management; Cantwell is an aeronautics and astronautics professor with interests ranging from fluid mechanics to propulsion. While these fields seem to hold little in common, the researchers brought new meaning to the word “interdisciplinary” by applying rocket technology to sewage treatment, aiming to make the process energy-neutral and emissions-free.

“If the energy savings we envision work out, then anyone designing a new wastewater plant will have to seriously consider our approach,” Criddle said. “In this case, the impact could be enormous.”

The method uses anaerobic bacteria to convert sewage into two greenhouse gases, nitrous oxide and methane gas. Aerobic bacteria require oxygen through a process called “aeration,” in which air is pumped into wastewater sludge, enabling the bacteria to colonize and decompose the waste. By using anaerobic, or oxygen-independent, bacteria, however, the amount of air that must be pumped decreases along with costs.

The resultant nitrous oxide and methane complete the cyclic process, as methane powers the treatment plant while the nitrous oxide fuels a rocket thruster. Intact, the nitrous oxide is harmful, but after fueling the thruster, it is converted into harmless nitrogen and oxygen gas.

Ultimately, these gases are released into the atmosphere, replenishing the nitrogen supply that human activity has depleted in processes such as the manufacture of agricultural fertilizer.

While the concept for this process has generated significant buzz, the researchers haven’t yet determined the technology required for its execution.

“The application to nitrogenous waste treatment could turn out to be the most important result of our research,” Cantwell said. “But there is still much to learn about the underlying physics of the decomposition process.”

“I expect there will still be space applications we have not envisioned yet,” Criddle said.

— Uttara Sivaram

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