From the New York Times:

New wastewater treatment technology: bacteria that eat odors

One of the least pleasant odors is from hydrogen sulfide gas at sewage treatment plants. The wastewater-treatment industry spends millions of dollars annually to control foul smells with chemical scrubbers.

But scrubbers, which use caustic chemicals to absorb the gas as it passes through exhaust stacks, are costly to operate and, because they use hazardous compounds, have environmental problems of their own. As a result, some companies and researchers have developed biofilters, which use live bacteria to consume the hydrogen sulfide.

Now, Dr. David Gabriel and Dr. Marc A. Deshusses of the University of California at Riverside have developed a biofilter that can be installed in an existing chemical scrubber. The filter, which uses bacteria of the genus Thiobacillus, is relatively inexpensive to install and operate, and it is environmentally more benign than the one it replaces.

The device is called a biotrickling filter, because the bacteria grow on an inert medium (in this case, open-cell polyurethane foam) and are fed by a spray of nutrient-rich water (in this case, sewer water itself, eliminating the need for another source of nutrients). As the smelly air passes through the scrubber stack, the bacteria convert the sulfide to sulfate, which is washed back into the sewage stream.

The researchers, who described their device in The Proceedings of the National Academy of Sciences, say it can effectively remove hydrogen sulfide even from large, relatively fast-moving airstreams.