Granular activated carbon (GAC) treatment is currently the most common approach to remove per- and polyfluoroalkyl substances (PFAS) from water, especially perfluorooctane sulfonic acid (PFOS) and perfluorooctanic acid (PFOA), due to the United States Environmental Protection Agency (USEPA) Health Advisory in May 2016. Recent studies have shown relatively short breakthrough times for certain PFAS when using GAC and there is a significant need to develop more cost-effective treatment solutions for the removal of a broad-range of PFAS (e.g., short-chain perfluoroalkyl acids [PFAAs] and precursors). As a result, a recent collaboration between Aqua-Aerobic Systems, Inc. (AASI) and the Colorado School of Mines evaluated the use of sub-micron powdered activated carbon (SPAC) in conjunction with ceramic microfiltration (CMF) to remove PFAS from various contaminated water sources during a laboratory study. These laboratory studies indicated that SPAC had a significantly higher sorption capacity (> 2,000 times) for certain PFAS compared to conventional GAC.
The overarching objective of this study is to field-demonstrate the effectiveness of SPAC-CMF for the removal of a broad-range of PFAS from contaminated groundwater at an impacted DoD site, understand the long-term performance of SPAC-CMF, and gather the necessary data to perform a detailed cost analysis. Specific project-based objectives will evaluate:
- The effectiveness of SPAC-CMF for the removal of a broad spectrum of PFAS;
- PFAS treatment performance under different conditions and in the presence of co-contaminants; and
- Cost and performance requirements related to SPAC dewatering efficiency and retentate management.
The technology is an integrated system using SPAC at high concentrations to accelerate adsorption of PFAS. The SPAC medium is maintained in a closed-loop system as treated water is separated using high-strength ceramic membranes in an innovative bleed and feed carbon conservation and recovery process. Two SPAC-CMF pilot systems will be deployed at the selected DoD site for demonstration testing over 3 – 9 months to prove performance and identify key design parameters. Eighteen PFAS will be evaluated as well as precursors and non-target analytes that includes greater than 1,000 PFAS. During the demonstration phase, the impact of system parameters (e.g., SPAC dose and detention time, membrane operation, waste minimization, and membrane restoration) on PFAS removal will be evaluated. The project team will also evaluate the influence of co-contaminants on SPAC-CMF PFAS removal performance using data generated through previous studies and this project. Experiments will determine exhausted SPAC concentration methods and characterize residual streams (i.e., retentate) requiring disposal.
The results from this demonstration will provide SPAC removal data for a broad-spectrum of PFAS and co-contaminants, information needed for a comprehensive cost analysis, and comparison of SPAC-CMF to a variety of PFAS treatment technologies. Most importantly, findings will be used to inform the DoD and the broader community on a novel and promising PFAS treatment technology and provide guidance regarding PFAS treatment selection.