Volatile organic compounds (VOCs) and other associated organic solvents are commonly found across the United States in many contaminated sites. Common remediation efforts include pump and treat, natural attenuation, and in-situ bioremediation. Permeable reactive barriers (PRBs), which take advantage of the natural flow of groundwater in aquifers, treat groundwater by reacting with VOCs and other contaminants while the plume passes through the underground barrier.
One type of bioremediation is cometabolism, where a microbe uses enzymes to consume a compound which, fortuitously, can break down other compounds, such as the carcinogen 1,4 Dioxane. Cometabolism can be an effective method for decontaminating groundwater but typically requires the addition of a growth substrate to stimulate microbial activity. By co-encapsulating a slow-release growth compound (SRC) with specific microbes in a hydrogel gellan gum bead, a cometabolism delivery method is achieved. Co-encapsulated beads are then suitable for use in a PRB where the required SRC continuously stimulates microbial life necessary to decontaminate groundwater.
This project aims to combine co-encapsulation technology with PRB design in a larger-scale physical aquifer model. An approximately 1m long 100L reactor was packed with sand and divided horizontally by an impermeable clay layer. 3 bead housing columns were placed sequentially in the middle of the top portion of the reactor. One of these columns was filled with co-encapsulated gellan gum beads containing Rhodococcus rhodochrous ATCC 21198 and tetrabutylorthosilicate (TBOS) as an SRC. Additionally, a flow directing funnel was placed at the front of the columns to direct water flow into the packed bead column to function as a “funnel and gate” PRB design. Inlet feed syringe pumps provide a constant synthetic groundwater flow of 2 ml/min and an additional syringe pump is available for contaminant injection. The objectives of the project include determining the contaminant fate and transport throughout the system and understanding the effect of the PRB design on groundwater flow. The data will be used for modeling the effectiveness of the PRB design and further implementation.
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