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McCarty mixes chemistry, biology, engineering for environment
STANFORD -- Environmental engineer Perry McCarty's research team was stumped.
The researchers had been feeding methane to bacteria to speed up the bacteria in breaking down the solvent trichloroethylene into harmless minerals. At a certain point, however, the organisms slowed down.
"It turned out they were being killed off by a spontaneously produced intermediate product." McCarty said. "We found the idea for what was happening in the medical literature.
"The organisms were dying for the same reason trichloroethylene is bad for us. We have enzymes in our liver that break down compounds the same way enzymes in microorganisms break them down in water; but there are certain compounds that can form in the process and start attacking us."
McCarty's knack for borrowing ideas from and working with biochemists, microbiologists, organic chemists and other specialists outside his civil engineering field has allowed his group to contribute major breakthroughs to the basic understanding of aquatic ecology and microbial biology.
Colleagues say his breadth is astonishing and a major reason for the success of the environmental engineering and science program he helped start at Stanford in 1961.
"These problems are so complex that you need a team of people with different expertise," McCarty said. "In our group, an organic chemist will come up with a question, a microbiologist will help answer it, and an engineer will attempt to apply the results.
McCarty's contributions form the basis for modern environmental engineering biotechnology and were acknowledged May 1 by his being named a 1992 Tyler laureate. He will share the $150,000 Tyler Prize for Environmental Achievement, the premier international prize for environmental science and leadership, with Robert M. White, former head of the National Oceanic and Atmospheric Administration.
White, who is currently president of the National Academy of Engineering, was honored for his contribution to the world's basic understandings of global environmental processes embracing oceans, the atmosphere and biosphere. The prize, administered by the University of Southern California, is given by Mrs. Alice C. Tyler. Recipients are selected by an executive committee, based on nominations that can be submitted by anyone but must be supported by the winners' scientific peers.
McCarty's career began with a search for a better understanding of wastewater treatment technology in the 1950s.
"As a graduate student in civil engineering at M.I.T., I was trying to understand the biological treatment process better so we could make generalizations that could be applied to specific industrial waste streams," McCarty said during a recent interview in his campus office.
Biological treatment of wastewater at the time was based on trial and error. In much the same way winemakers know they need yeast to ferment fruit, civil engineers knew they needed bacteria to break down unsavory components of municipal wastewater before discharging it into surface waters.
Others had tried to isolate the bacteria involved in the biological transformations, but they soon discovered that multiple microorganisms, each doing its own small part, were required to break down even the simplest compounds.
Microbiologists, however, understood enzyme kinetics - the mechanism by which enzymes acted upon and changed compounds - and knew that microorganisms were really collections of enzymes.
Armed with that approach, McCarty decided to assume that what was true for simple organisms on simple compounds could also be applied to multiple organisms on multiple compounds, such as industrial waste streams.
"I looked at the complex ecological system overall and said there are niches in it, and some organism will fill each one," he said. "We don't have to know which ones are which. Whatever one can get the most energy out of a particular niche will dominate that niche, because it will grow faster than the others. If we assume the process that works most efficiently is what is going to happen, then we can calculate the thermodynamics and kinetics overall."
He took his theory to the lab and tested it. It worked - not precisely, but well enough so that he could devise principles by which one could analyze a waste stream and make initial estimates of the size of a treatment system necessary to handle it.
The theory was of interest beyond his own field because it changed the concept of the rates at which biological processes take place. His estimates of the maximum yield and growth rates in microbial systems were applied by others to a wide variety of processes, including iron and manganese oxidation, nitrate and sulfate reduction, nitrogen fixation and methane fermentation, processes used widely in treatment of wastes around the world.
In 1962, McCarty came to Stanford, where he and his students have developed several biological treatment reactor methodologies.
He and his colleagues again surprised science in 1976 when his research team discovered that man-made chemicals thought to be non-biodegradable were actually disappearing in groundwater environments. Their discovery of a natural biological process known as co-metabolism preceded by several years the discovery that these same chlorinated solvents had contaminated groundwater all over the country.
McCarty's career then turned decidedly underground. He now directs a research center for the Environmental Protection Agency, based at Stanford and Oregon State University, that is researching ways of cleaning up and minimizing groundwater pollution.
"We've been able to provide a basic understanding of the natural chemical and biological processes and of the great difficulty in getting some of the materials out, " he said. It's difficult because "they lie so deeply beneath the Earth's surface, they adsorb strongly to soils or they are lodged in places that are difficult to reach by any means. I think this has helped industry understand the costs of cleanup are far greater than the costs of prevention."
The center is currently developing a two-step biological treatment process for a contaminated aquifer in St. Joseph, Mich., and is consulting with the Department of Energy on a massive cleanup project at its Savannah River facility.
The group's discovery last year of the reactions that kill the beneficial bacteria during trichloroethylene treatment was not good news for those in a hurry to use co-metabolism to treat groundwater, he said. It means that more methane must be added to the underground environment to break down trichloroethylene, or alternative treatment regimes must be found. The process is still attractive, however, for such compounds as vinyl chloride, which is a major concern at St. Joseph.
"In co-metabolism, we have to feed existing organisms what we call primary substrates, like methane, so that they can grow in number," he said. "The microorganisms transform a compound with enzymes that were designed for other purposes without benefitting from the transformation we want them to make.
"Eventually, one of our hopes is that we can find organisms or enzymes that can use these materials for their own energy and growth, and directly benefit from the transformation."
The insights that the Stanford team has provided so far are largely attributable to the diversity of its environmental engineering and science program, McCarty believes. One of the top-rated programs in the country, its faculty include a microbiologist, a chemist, a chemical engineer, an electrical engineer, an environmental science major and two civil engineers. They also work closely with faculty in the schools of earth sciences and medicine, and with water resources faculty in the civil engineering department.
"One of the reasons I came to Stanford is that people flow easily between departments without feeling there are barriers to doing so," he said. "These interactions have proved vital to our success."
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