New groundwater purification process

Scientists at USC discover a way to remove gasoline and other toxic wastes

niversity of Southern California researchers have developed a biological treatment process to remove gasoline and other toxic wastes from the groundwater that millions of Americans rely on for their drinking water.
"Groundwater can no longer be considered an inherently pristine source of drinking water," says environmental engineer Mike Pirbazari, Ph.D., leader of the USC research team. "Spills and leaks from underground storage tanks and pipelines are releasing substantial quantities of potentially dangerous substances from fuels and other chemicals into the water table. As large populations are dependent on groundwater resources for potable water supply, degradation in quality of subsurface water reserves has serious public health implications."

Bountiful bugs

Dr. Pirbazari and his students at the USC School of Engineering's Water Quality Research Laboratories are dealing with this environmental threat by feeding the gasoline and other toxic wastes to special bacteria.
Instead of transferring dangerous contaminants from one part of the environment to another (as other remediation techniques do), USC's new "hybrid MFBAPC process" combines two well-known techniques to actually destroy them.
The contaminated water first enters a "reactor" of biologically active powder carbon,where a special culture of toxin-eating bacteria breaks down the wastes and converts them to harmless substances. In addition to capturing cancer-causing benzene, ethylbenzene, toluene and xylenes - collectively known as BTEX contaminants - and allowing the reactor's toxin-eating bacteria to break them down, the carbon in the reactor catches and holds particles and impurities that would otherwise clog the filter through which the partially purified water then passes.
A cross-flow membrane filter, made of a special synthetic fiber, then removes bacteria, viruses and other suspended impurities - producing an output stream of high-quality water.
To keep the reactor working at top efficiency, the membrane filter retains the beneficial bacteria and the toxic-chemical-destroying compounds they produce.
"Together, the two techniques work far more efficiently than either technique would work by itself," Pirbazari says. "To combine the two techniques and make them work effectively, we had to do a lot of research on what causes membrane filters to clog and the best way to avoid such clogging."

Full-scale demo

So far, the hybrid technology has been demonstrated on the "mini-pilot" scale; Pirbazari hopes to demonstrate it soon in a full-pilot installation.
Two of the remediation techniques most widely used are spraying contaminated water into the air to evaporate the toxic components, and absorbing groundwater contaminants with granular activated carbon. But those techniques simply transfer the contaminants from the water to the air or from the water to a toxic dump site.
"Hybrid biological treatment technologies are a desirable alternative because they actually destroy the contaminants," Pirbazari says. "They might even be less expensive."
Pirbazari is a professor and associate chair of civil engineering at the USC School of Engineering and associate director of the school's Environmental Engineering Program. Graduate students working with Pirbazari included N. Badriyha, Mark D. Williams and Varadarajan Ravindran. The research was partially supported by USC's Zumberge Research Innovation Fund.
Results of the USC study on the MF-BAPC process and its use for the treatment of gasoline-contaminated water were presented at the annual meeting of the American Institute of Chemical Engineers, held Nov. 13-18 in San Francisco. Further developments will be presented at the American Water Works Association's Conference on Membrane Technology in Reno, Nev., next August.