Improvements to TCE Microcosm Protocols for Biostimulation in Bedrock Aquifers



In this study, a factorial-designed experiment of biostimulated trichloroethene (TCE) dechlorination in fractured bedrock aquifers using microcosms evaluated several potential biostimulants (i.e., nutrients, vitamins, and sterile groundwater). Substantial cost savings and resource efficiency can be provided by this approach because: factorial designs require relatively few microcosms per factor; the interpretation of the observations can proceed largely by common sense, simple arithmetic, and computer graphics; the observations can indicate promising directions for further experimentation and causative relationships; and designs can be suitably augmented when a more in-depth exploration is needed.

TCE degradation was evaluated using three methods of data analysis: (1) analysis of covariance (ANCOVA) between biotic and abiotic treatment trend-line slopes; (2) calculation of biodegradation half-life; and (3) effects screening by model fitting. Microcosm preparation with crushed rock in groundwater was found to more closely match the previously observed field rates than the preparation with only groundwater. Injection of nutrient and vitamin mixtures was made into microcosms that were previously aged to obtain consistent conditions, and the TCE concentration measured after incubating for 45 days. Comparison of results indicated that the nutrient mixture slows or inhibits the degradation of TCE compared to the sterile groundwater; however, the vitamin mixture offsets and nearly compensates for the inhibitory effect of the nutrient mixture. It is recommended that this factorial experiment be augmented with additional studies of individual or groups of compounds from the vitamin mixture using this methodology to isolate and identify the specific factor or interaction responsible for the inhibitory compensation. © 2013 Wiley Periodicals, Inc.