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Bacteria Eat Human Sewage, Produce Rocket Fuel

Brian Handwerk
for National Geographic News
November 9, 2005
 
The high cost of treating human wastewater may one day tank thanks to a bacterium that eats ammonia and produces rocket fuel.

Standard water treatment plants use oxygen-hungry bacteria to break down human waste. To feed the microbes, plants must aerate sewage sludge with costly, power-hogging equipment.

But Brocadia anammoxidans, or anammox bacteria, survive without oxygen, producing energy from nitrite and ammonia, which is found naturally in human waste.

"Conventional [bacteria] treatments do a good job, so the big benefit is doing this much more efficiently and cheaply," said Marc Strous, a microbiologist at the University of Nijmegen in the Netherlands.

Strous says savings could be enormous, up to 90 percent versus standard sewage treatment plants. A prototype facility in Rotterdam is already earning praise.

Rocket Fuel

Scientists first discovered anammox bacteria in yeast and later in the open ocean in the late 1990s.

The unusual microbes consume ammonia, producing hydrazine—better known as rocket fuel—in the process. The ability still puzzles scientists.

"They are the only organism on Earth that produces hydrazine, so until their discovery, [hydrazine] was thought to be a man-made substance," Strous said.

The bacteria safely store the toxic fuel in an organelle, or specialized cell structure, similar to mitochondria, a type of biological power plant found in human cells.

The anammox organelle binds hydrazine with a fatty-acid membrane that could itself have intriguing scientific applications, including the design of optoelectronic equipment.

But don't expect the bacteria to supply NASA with rocket fuel to launch a spacecraft.

"It costs [the bacteria] a lot of energy, and they get return on their investment by consuming it again," Strous explained. "They are dependent on it, so it can't be removed."

Prototype Plant

Instead, researchers are harnessing the bacteria for more down-to-Earth applications, such as sewage treatment.

Strous says it took two or three years to scale up the anammox process from the lab to a waste treatment facility.

The prototype plant in Rotterdam is performing at a high level, he says, and others will soon follow. "The next one is already starting up much more quickly," Strous said.

The researcher, who advises sewage treatment projects in the Netherlands, notes that conventional sewage treatment facilities can be easily retrofitted to use the anammox reaction.

The low operating costs might allow such systems to provide much needed waste water treatment in regions where adequate facilities are lacking or nonexistent.

More sewage treatment plants could benefit human health. They could also reduce global amounts of ammonia from untreated waste.

Excessive ammonia can wreak havoc with freshwater ecosystems by reacting with oxygen, tying up the gas, which many species need for respiration.

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