Integrated Field, Laboratory, and Modeling Studies to Determine the Effects of Linked Microbial and Physical Spatial Heterogeneity on Engineered Vadose Zone Bioremediation

Brockman, Fred ; Selker, John

Pacific Northwest National Laboratory (U.S.)

关键词: Microorganisms;    Carbon Tetrachloride;    Oxygen;    Chloroform;    Organic Compounds;   

DOI  :  10.2172/833637
RP-ID  :  EMSP-70165
RP-ID  :  FG07-99ER62887
RP-ID  :  833637

美国|英语

来源: UNT Digital Library

【 摘 要 】

While numerous techniques exist for remediation of contaminant plumes in groundwater or near the soil surface, remediation methods in the deep vadose zone are less established due to complex transport dynamics and sparse microbial populations. Yet pollution in the vadose zone poses a serious threat to the groundwater resources lying deeper in the sediment. While the contaminant may be slowly degraded by native microbial communities; microbial degradation rates rarely keep pace with the spread of the pollutant. Hydrologic and microbiological properties of the zone, and their interactions, are fundamentally different from the saturated zone: the vadose zone has an additional phase (air), higher levels of oxygen, and contaminant transport and water movement is predominantly perpendicular to geologic strata and occurs in water films. In addition, microbial populations in the vadose zone are sparse and spatially discontinuous, especially in arid climates. At the Department of Energy's Hanford site in Richland, WA, numerous recalcitrant organic compounds were disposed of in the vadose zone, and now are continual sources of groundwater pollution. Among the most problematic of these is a plume of carbon tetrachloride (CT), a common solvent, the majority of which still resides in the vadose zone despite the presence of microbes that can degrade it and its byproduct chloroform. Gaseous nutrients can in principle be used to stimulate the native degrading population and has shown some promise in isolated field cases. However, there is a lack of knowledge on how physical and hydrologic features of the vadose zone control the spatial distribution of microbes, and the extent that microbes can colonize the vadose zone in response to nutrient delivery during bioremediation. The overall objective of the project was to increase knowledge of the feasibility of engineered bioremediation in the deep vadose zone, particularly at arid western sites where microbial populations and activities are low. Specific objectives were to: (1) Conduct laboratory studies of how physical and hydrologic features of the vadose zone control the spatial distribution of microbial growth and the ability of microorganisms to colonize microbially sparse or ''empty'' regions of the vadose zone. (2) Characterize microbiological properties of a carbon tetrachloride-contaminated deep vadose zone site at the DOE Hanford Site. (3) Evaluate the potential for gas phase feeding of carbon, nitrogen, and phosphorus to deep vadose zone microbial communities. (4) Use field and laboratory data generated from the project to parameterize an unsaturated zone transport model with microbial growth, colonization, and biotransformation kinetics and conduct reactive transport simulations.Pacific Northwest National Lab (PNNL) and Oregon State University (OSU) jointly addressed objectives 1, 3, and 4. PNNL addressed objective 2. For objective 4, laboratory data was simulated during the project; field data was not used in modeling and simulation due to the late initiation of the field study and the small number (n=24) of samples studied.