In Situ Test System for Evaluating Microbial Community Structure and Metabolic Activity Under Natural and Engineered Conditions

Evaluating intrinsic and engineered microbial processes without introducing sampling and laboratory induced artifacts can be accomplished by deploying into groundwater or wetland sediments a system of diffusion samplers, diffusible nutrient sources, and a matrix that can be colonized by indigenous bacteria. The assembled system is a cassette that may be suspended in a standard 2-inch or larger monitoring well or configured to be pushed directly into wetland sediments for the analysis of groundwater and sediment pore water, respectively. The system has been used to evaluate the natural attenuation and engineered bioremediation of chlorinated solvents, chlorobenzene, xylenes, toluene, the explosive RDX, and cyanide. Cassettes have been deployed in groundwater and wetland sediments.

Three to four cassettes may be deployed in a monitoring well with a 10-foot well screen. A typical configuration uses three cassettes to provide an untreated or natural attenuation condition, a biostimulated treatment where various nutrients are added using a diffusible source, and a biostimulated and bioaugmented treatment where both nutrients and certain microbes with specific biodegradation capacity are provided. For bioaugmentation treatments, the microbial growth matrix is inoculated with the bioaugmentation culture which forms a biofilm on the matrix prior to its deployment. When multiple treatments are deployed in the same well, elastomer baffles are installed between each treatment to minimize cross-contamination from diffusion or ambient groundwater flow within the well.

Results include microbial population analysis or the detection of specific bacteria, groundwater contaminants and their degradation products, groundwater geochemical parameters such as nitrate, sulfate, pH, chloride, ammonia, phosphate, volatile fatty acids, and total organic carbon. The results have provided evidence about the intrinsic biodegradation of groundwater and pore water contaminants and the benefits and design considerations for engineered bioremediation solutions. Examples of test configurations and results from groundwater and sediment pore water applications will demonstrate system applications.