The Consortium focuses on three in situ bioremediation processes: cometabolic bioventing (for treatment in the vadose zone), intrinsic bioremediation (for treatment of the bulk of a plume), and accelerated anaerobic biodegradation (for treatment of more concentrated areas of a plume). These technologies are environmentally friendly; they cause minimal disturbance to the site as they require few surface structures. They can be less costly than conventional pumping and treating. The Consortium initiated Phase I field tests of the three processes at Dover Air Force Base (AFB) in Dover, Delaware, in early 1995. Planning is underway to conduct Phase II field studies for each of the processes.
Laboratory studies have shown that aerobic degradation of trichloroethylene (TCE) in soils occurs only in the presence of a cometabolite, such as toluene, propane, or methane. Cometabolic bioventing uses a technique, similar to methods currently used in bioventing technology, to efficiently deliver oxygen and a cometabolite to the vadose zone in order to remediate TCE. This technology appears to have great promise. The objective of the RTDF cometabolic bioventing study is to develop a cost-effective process that promotes the cometabolic bioremediation of TCE and other chlorinated solvents.
Intrinsic Bioremediation I
ntrinsic bioremediation, or natural attenuation, of chlorinated solvents in ground water can occur at sites where indigenous microbial populations are present that can degrade these chemicals. Certain microorganisms are capable of detoxifying chlorinated methanes, ethanes, ethylenes, and many other compounds by reductive dehalogenation or by oxidation. These processes can result in complete biodegradation to innocuous end products. The objective of the natural attenuation research effort is to quantitatively determine where, at what rate, and under what conditions intrinsic bioremediation occurs.
Accelerated Anaerobic Biodegradation
Complete in situ anaerobic
dechlorination requires that the necessary microorganisms are present. The
dechlorination is typically limited by the availability of food and nutrients
for microbial growth. The purpose of the accelerated anaerobic degradation
study is to (1) understand the microorganisms involved, (2) identify the
nutritional requirements, (3) determine how to effectively deliver the
nutrients, and (4) determine how to effectively deliver microorganisms to the
aquifer, when needed. Other study objectives include determining which electron
donors and acceptors best support anaerobic bioremediation; optimizing the
chlorocarbon destruction rate; determining what factors control the degradation
kinetics; and gathering cost and performance data in order to facilitate the
use of this technology at other sites.