Microbes Clean Up Wastewater

A microbial cleanser of water pollution does its best work when surrounded by neither too many nor too few of its own kind—and when it has developed a taste for junk food.

This phenomenon, seen in an ARS laboratory, is stimulating new thinking about finding and harnessing nature's talent for detoxifying industrial wastewater—an approach called bioremediation.

Baqar R. Zaidi, associate professor of marine microbiology at the University of Puerto Rico, found the bacterium Pseudomonas putida surviving—but not flourishing—on nitrophenol wastes at a petrochemical plant in Guayanilla, Puerto Rico. The plant had been closed because of concern for the island's coastal waters environment.

Nitrophenols are generated by industries involved with dyes, explosives, leather, paper, and wood. In high concentrations, they can be toxic to plants, fish, and other life forms.

An industry/University of Puerto Rico consortium granted Zaidi support for further research. And ARS chemists Richard V. Greene and Syed H. Imam at the National Center for Agricultural Utilization Research (NCAUR) in Peoria, Illinois, shared their laboratory facilities and expertise on biodegradation.

Included in the research was a strain of Corynebacterium bacteria that Zaidi, while a postdoctoral researcher at Cornell University, had isolated from Cayuga Lake near Ithaca, New York.

By culturing each strain in a series of otherwise sterile liquid diets with increasingly large amounts of nitrophenols, Zaidi developed strains of each that could survive only if they had their needed dose of the toxic soup. But in a nonsterile environment more like the real world, only the P. putida—added in amounts not too large nor too small—reduced nitrophenol concentrations to levels regarded as nonpolluting.

"Until we did this research, we had thought that bioremediation on highly concentrated pollutants would also work at lower levels," says Imam.

That assumption could cause some good microbes to be overlooked.

And the finding may encourage more on-site bioremediation—before wastewater is released into the environment. The scientists envision sequential steps, with different microbes taking turns digesting toxic organic molecules.

The research was begun through NCAUR's Outreach Programs, in which ARS scientists are encouraged to develop collaboration with scientists at 1890 Land-Grant Institutions. -- By Ben Hardin, ARS.

Scientists mentioned in this story are at the USDA-ARS National Center for Agricultural Utilization Research, 1815 N. University St., Peoria, IL 61604; phone (309) 6816335, fax (309) 681-6689

"Microbes Clean Up Wastewater" was published in the July 1996 issue of Agricultural Research magazine.