In Situ Microcosm Studies

Site managers have frequently turned to laboratory microcosms or small pilot studies to evaluate bioremediation. However, duplication of in situ conditions in the laboratory is difficult and the results often do not correlate to the field. Pilot studies are performed in the field but are often prohibitively expensive as an investigative tool. Bio-Trap studies serve as cost-effective, in situ microcosms providing microbial, chemical, and geochemical evidence to screen remedial alternatives and evaluate biodegradation as a treatment mechanism.The figure to the right shows the configuration of a typical Bio-Trap in situ microcosm study. An Assembly consisting of 2 to 3 Units is deployed in a monitoring well for 30–60 days and recovered for analysis. Each unit corresponds to a treatment approach (Control-MNA, Treatment A, and Treatment B). Baffles are used to physically isolate each unit to eliminate vertical transport or “cross-talk” and establish each unit as an individual in situ microcosm. As will be discussed in more detail below, each unit contains passive diffusion samplers to determine contaminant of concern (COC) concentrations and geochemical parameters. Each unit also contains a MICRO sampler or Bio-Trap for characterization of the microbial community. Depending on the study design, units may also contain an Amendment Supplier corresponding to the type of treatment being investigated.

Results

Although in depth interpretation of results will be different for each study, the general approach involves comparison of chemical, geochemical, and microbiological data between units to quantitatively evaluate treatment options. Often the first question to be addressed is whether Treatment A or Treatment B significantly enhanced biodegradation relative to that observed under monitored natural attenuation (MNA) conditions. The purpose of the Control-MNA Unit is to provide the baseline for this comparison. Lower contaminant concentrations and increased daughter product formation in the Treatment Unit COC samplers would provide the first line of evidence that the treatments would be effective. Comparison of the geochemical parameters would be used to determine whether the treatments promoted redox conditions conducive to the desired biodegradation process. Finally, CENSUS analysis of the MICRO samplers would be used to determine whether the treatments stimulated growth of organisms capable of biodegradation of the contaminants of concern. The same comparisons would then be used to evaluate Treatment A versus Treatment B. Overall, a typical Bio-Trap in situ microcosm study will provide three lines of complementary evidence to:

  • assess the feasibility of MNA,
  • evaluate enhanced bioremediation as a treatment approach,
  • and even screen enhanced bioremediation options

allowing site managers to more effectively direct corrective actions. For more specific information about how Bio-Trap in situ microcosm studies can be used at your site, please contact info@microbe.com.

ISM-button