Events

Sediment and groundwater from a contaminated site were used to test a previously developed co-encapsulation technique of pure culture and slow release substrate to transform a mixture of 1,4-dioxane (1,4-D) and chlorinated solvents. Rhodococcus rhodochrous strain 21198 (21198) was co-encapsulated with tetra-sec-butyl orthosilicate (T2BOS), which hydrolyses to release 2-butanol. Batch studies in microcosms and a continuous flow column experiment were conducted with groundwater and aquifer material obtained from a Space Launch Complex at Cape Canaveral Air Force Station in Florida where a plume of 1,4-D had been located. Characterization of the site groundwater found low concentrations of chlorinated solvents 1,1-dichloroethene (1,1-DCE), 1,2-cis-dichloroethene (cis-DCE), and 1,1,1-trichloroethane (1,1,1-TCA) were detected as well as methane and pentane. In aerobic microcosms native microorganisms were unable to transform 1,4-D in over 250 days and neither isobutane nor 2-butanol utilizers were stimulated. A continuous uptake of oxygen suggests an intact native microbial population without advantageous cometabolic ability. This and subsequent experiments have shown the aquifer solids have a high abiotic oxygen demand. Under anaerobic conditions methanogenesis occurred once initial dissolved oxygen was consumed, after 220 days transformation of 1,4-D had not been observed.

When bioaugmented into microcosms with isobutane present as a primary substrate, suspended 21198 was able to cometabolize 1,4-D to 60 ppb, a 75% reduction in mass. The cells appeared to be limited in their cometabolic activity by a lack of nutrients, with an addition of a nutrient solution more complete transformation occurred. Macrobeads made of 21198 co-encapsulated with T2BOS in gellan gum were bioaugmented into equivalent microcosms at a biomass loading of 1:5 and 2:5 as compared to suspended cell experiments. These treatments cometabolized 1,4-D to 48% and 73% of the initial concentration, respectively. 21198 appeared to remain alive withing the gel beads after cometabolism had stalled as indicated by an elevated oxygen demand compared to controls and visually by the distinct orange color of the culture. Attempts to adjust microcosm conditions to induce cells to resume cometabolic activity are underway including pH adjustments, nutrient additions, and increased shaking for more uniform oxygen saturation. A continuous flow column experiment packed with site sediment and 20% by volume of 21198 and T2BOS beads mixed throughout is underway. Site groundwater with an addition of 30 mg/L hydrogen peroxide is flowing through the column with a residence time of 24 hours. Initial results suggest transformation of cis-DCE, evident by the presence of cis-DCE epoxide, the product of cometabolic oxidation of cis-DCE, in the column effluent.  

This project presenter is available for live video chat on Sept. 1, 2020 from 10:15 a.m. - 12:00 p.m. PDT.