H043-01
Biologically-Mediated Back Diffusion of Chlorinated Ethenes in Heterogeneous Porous Media due to Dehalococcoides mccartyi Activity

Tuesday, 8 December 2020: 07:02
Virtual
Natalie L Capiro1, Jason P. Hnatko2,3, Lurong Yang2,4, Kurt D Pennell5 and Linda M Abriola2, (1)Auburn University, Civil and Environmental Engineering, Auburn, AL, United States, (2)Tufts University, Civil and Environmental Engineering, Medford, MA, United States, (3)Environmental Resources Management, Boston, MA, United States, (4)Massachusetts Institute of Technology, Cambridge, MA, United States, (5)Brown University, School of Engineering, Providence, MA, United States
Recorded Presentation
Abstract:
Bioenhanced dissolution of non-aqueous phase liquids, leading to enhancements of up to 14-fold over abiotic dissolution alone, has been well-documented; however, less attention has been directed towards biologically-mediated diffusion from low-permeability media. In this study, the effects of microbial reductive dechlorination on trichloroethene (TCE) back diffusion from low permeability media were examined in a heterogeneous aquifer cell. The aquifer cell was packed with 20-30 mesh Ottawa sand (2.6 × 10-10 m2) as the background medium, with emplaced lenses of lower permeability (1.0×10-12-1.2×10-11 m2) and higher organic carbon (OC) content (<0.1-2%), and underlain by a layer of clay (6.4 × 10-14 m2). The system was initially contaminated by flushing with 0.5mM TCE. The influent concentration was then sequentially decreased to 0.01mM to mimic to the effect of upgradient source zone remediation. Total chlorinated ethene removal by hydraulic flushing was then compared between the abiotic control and a biotic system that was bioaugmented with KB-1® SIREM (Guelph, ON). A modified version of a three-dimensional multi-species modular transport model (MT3DMS), incorporating information on physical heterogeneity, diffusion and (de)sorption, was used to generate predictions of back diffusion and calculate bioenhanced TCE release from lower-permeability lenses, which was 6-53% greater than that of the abiotic control. While physical and chemical heterogeneities did not influence the distribution of the Dehalococcoides mccartyi (Dhc) 16S rRNA genes, the analysis of reductive dehalogenase (RDase) genes (vcrA, bvcA, and tceA) revealed that growth of specific strains was impacted. Cells harboring the vcrA gene (TCE to ethene) comprised 85% of the RDase genes within the background matrix but were less prevalent (50%) within low-permeability zones. In contrast, cells harboring the bvcA gene (dichloroethene isomers to ethene) comprised only 2% of the total RDase genes within the background media, but up to 44% in proximity to the clay layer and high OC lenses. These results highlight the importance of monitoring changes in the relative abundance of Dhc strains and considering the contribution of microbial processes to back diffusion during bioremediation assessments in heterogeneous aquifer formations.
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