InterPore2025

Optimizing Operational Parameters for PFAS Permeable Reactive Barrier Emplacement

21 May 2025, 15:05

1h 30m

Poster Presentation (MS18) Innovative Methods for Characterization, Monitoring, and Remediation of Contaminated Soils and Aquifers Poster

Speaker

mj ahmadi (School of Engineering, Brown University. 184 Hope St. Providence, RI 02912, USA)

Description

Perfluoroalkyl and poly-fluoroalkyl substances (PFASs), as constituents of many industrial products, pose significant risks to groundwater quality and ecosystem health due to their persistence in the environment and their association with various health issues. Permeable reactive barriers (PRBs) can offer a cost-effective and energy-efficient in situ solution for PFAS groundwater plume remediation by passively retaining and/or breaking down contaminants when installed across the flow path. Polymer-stabilized activated carbon (S-PAC) nanoparticles (NPs, which can be injected directly into a contaminated formation, are among the most effective and economical barrier materials for PFAS retention.
Here, a radial mathematical model for S-PAC field emplacement is presented and employed to explore operational factors that can affect barrier performance in the field for effective sorption of two representative PFAS, perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), both of which have a maximum concentration limit (MCL) of 4 ppt. Wurtsmith Air Force Base (Michigan, U.S.) is used as a representative case study for barrier installation. The model is based on modified filtration theory (MFT) and demonstrated to reproduce the observed behavior of S-PAC delivery in packed column bench-scale experiments. Column-fitted parameters are employed to investigate the sensitivity of barrier retention behavior to NP attachment parameters and operation injection parameters. Here, a pseudo-first-order kinetic model, based on a Freundlich isotherm, is implemented to model sorption. The target of the optimization process is to maximize the longevity of the barrier, defined by the time required for concentration breakthrough at a level that exceeds the MCL; while the total operation time, the total injected mass of NPs, and the well-spacing are fixed to ensure the greatest possible longevity of the barrier within the same cost. The retention of NPs within a range of attachment rates (katt) and maximum attachment capacities (Smax) were modeled to find the best set of pumping rates and injection concentrations that leads to the greatest barrier longevity for different sorption rates.
Simulation results indicate that high katt and low Smax generally lead to significant nanoparticle retention for multiple injection strategies. However, for low katt and high Smax, the retention profile depends more on the operational parameters (such as pumping rate and injection concentration). For these cases, a push-pull strategy is proposed to achieve a barrier with greater longevity. The proposed push-pull strategy is particularly effective in non-ideal situations where katt is low, offering a significant advantage over the conventional push scenario. This research highlights the importance of choosing the proper operational parameters to design a long-lasting PRB for treating PFAS-contaminated groundwater.