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A novel aerobic cometabolic process has been developed for the passive treatment of groundwater plumes containing chlorinated aliphatic hydrocarbons (CAHs) and 1,4-dioxane. The process involves the co-encapsulation of Slow-Release-Compound (SRC) inside a gellan gum hydrogel along with the pure culture of bacteria that cometablizes the groundwater contaminants. Our studies have focused on Rhodococcus rhodochrous ATCC 21198 which cometablically transforms 1,4-dioxane (1,4-D) and diverse mixtures of CAHs, including 1,2-cis-dichlorethene (cis-DCE), 1,1,1-trichoroethene (1,1,1 TCA), and 1,1-dichloroethene (1,1-DCE) when grown on 1-butanol and 2-butanol. 1-butanol and 2-butanol are slowly released by the SRCs. We have also observed that short chain alkane monoxygenase (SCAM) responsible for the cometabolism of the Contaminants of Concern (COCs) is induced after growth on these specific alcohols. The gellan gum beads that co-encapsulate strain ATCC 21198 and SRCs reduce concentrations of COC mixtures several orders of magnitude, to concentrations of less than 1 µg/L, which may be required to meet regulatory standards. Strain ATCC 21198 is able to grow on a broad range of primary and secondary alcohols. SCAM activity was observed after growth on 2-butanol and after 1-butanol grown cells were exposed to 1,4-D. In batch tests with strain ATCC 21198 and the SRC co-encapsulated in gellan-gum beads, the continuous cometabolic transformation of a mixture of 1,1,1-TCA, cis-DCE, and 1,4-D was achieved for over 300 days, with the rates of cometabolism correlated with the rates of alcohol release, CO2 production and oxygen consumption. Continuous flow experiments were conducted with columns packed with the gellan gum beads co-encapsulated with strain ATCC 21198 and SRCs. The columns have been operating for over nine months and have treated 400 to 500 pore volumes (PVs) of injected solution. Effective treatment of a mixture of 1,1,1-TCA, cis-DCE, and 1,4-D was achieved with over 99 percent removal of all three contaminants added, each at an influent concentration of 250 µg/L. In the later stages of the test (240 PVs), cis-DCE was replaced by 1,1-DCE (100 µg/L). Extremely high removal efficiencies of 1,1-DCE were observed (> 99.5%), while maintaining 1,4-D and 1,1,1-TCA transformation, even after the influent 1,1-DCE concentration was increased to 250 µg/L. These results support creating permeable reactive barriers for the in-situ passive cometabolic treatment of complex mixtures of COCs, using this co-encapsulation treatment technology.

This project presenter is available for live video chat on Sept. 1, 2020 from 1:00 - 2:45 p.m. PDT.