New groundwater purification process
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
Scientists at USC discover a way to remove gasoline and other toxic
"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."
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
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."
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
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.