This project will investigate the fundamental mechanisms and processes involved in activated carbon (AC)- based treatment technology, an emerging in situ groundwater remediation approach for chlorinated solvents. The primary focus will be on characterizing and quantifying the dynamic interactions between adsorption and biodegradation, which are the core processes inherent to the technology, but have not been rigorously examined for assessing its long-term effectiveness for in situ groundwater remediation.

This research will be conducted at laboratory scale, using experimental systems that have been previously applied to study contaminant sorption and sorbent-based biofilms separately. Colloidal activated carbon, a representative type of AC that is commercially available and has been applied for in situ remediation of chlorinated solvents, will be tested, together with other well-characterized ACs to qualitatively and quantitatively interrogate the fundamental processes involved in the treatment facilitated by the AC amendments. This research will first establish baseline understanding of biofilm colonization and contaminant sorption/desorption behavior in active and abiotic batch systems, respectively, containing AC-impacted aquifer solids. The two systems will then be combined to quantitatively characterize the link and potential synergy between sorption and biodegradation. Finally, column tests will be conducted to evaluate how the dynamic sorption and biodegradation processes characterized in batch systems can impact long-term treatment effectiveness under flow-through conditions. A suite of solution chemistry, modeling, microscopy, and molecular biological tools will be applied in this project to obtain robust data.

AC-based treatment technology has attracted increasing interest due to its claimed long-term effectiveness, but independent evaluation is lacking. This work presents a quantitative and rigorous study focusing on the fundamental processes—combined sorption and biodegradation— involved in AC-based remediation technology to address the need for improved understanding of processes influencing the effectiveness of AC-based remedial technology. This research, although performed at laboratory scale, is designed to simulate the temporal and spatial variations of conditions during in situ treatment, providing scientific information of direct practical value. Additionally, this research will significantly advance the state of science and practice on biofilm-based remediation for in situ groundwater remediation. Overall, the outcome of the work is expected to greatly benefit researchers, practitioners, and Department of Defense site managers by:

• addressing critical concerns of the quantitative differentiation between sorption and degradation;
• identifying key environmental factors that influence the applicability of AC-based technology, and
• improving the ability to predict the long-term performance of AC-based technology in field applications.

(Anticipated Project Completion - 2024)