Francisco Barajas Rodriguez
Dr. Barajas is an environmental engineer and laboratory manager at AECOM, and has been conducting treatability studies on the remediation of PFAS, 1,4-dioxane, chlorinated solvents, heavy metals, and industrial wastewater treatment. Most of his studies involve mechanisms based on biological and physico-chemical processes such as reductive dechlorination, aerobic cometabolism, chemical oxidation/reduction, electrochemical oxidation, adsorption, and solidification/stabilization. His research experience includes aerobic metabolism and cometabolism of 1,4-dioxane. Dr. Barajas holds a doctorate degree in Environmental Engineering from Clemson University and a Bachelor’s degree in Chemical Engineering from Universidad de Sonora, Mexico.
Batch and Column Studies on PFAS Removal from Landfill Leachate Using Adsorptive Media for a Permeable Barrier Application
Leachate groundwater at an industrial landfill has been impacted with PFAS for decades. A permeable barrier already installed at the site contains a select fill composed of soil and wood chips to remove other organic contaminants. A previous bench-scale treatability study demonstrated the superior performance of a mixture of soil containing 5% biochar when compared to the old select fill or to soil alone. Media such as biochar, peat moss, and a modified bentonite may be more cost-effective than granular activated carbon (GAC) or resins for in situ remediation purposes. This study aimed to demonstrate and evaluate the removal of PFAS from groundwater by different amendments, as well as to evaluate the longevity of the old select fill. The treatability study was conducted in two parts with focus on the removal of perfluorooctanoic acid (PFOA) and perfluorooctanoic sulfonic acid (PFOS), although other PFAS and total organic carbon were also quantified. Part 1 involved batch experiments to screen for adsorption capacity by biochar, peat moss, a modified bentonite, and GAC. Biochar and GAC were selected for the next experiment based on the batch results. To mimic field conditions closer, Part 2 consisted of a column experiment to determine the breakthrough of PFAS in the following sandy media compositions: 1) 10% biochar; 2) 20% biochar; 3) 10% GAC Type 1; 4) 20% GAC Type 1; 4) 10% GAC Type 2; and 6) Old select fill from landfill. Results from the first batch experiment from Part 1 indicated that peat moss had the lowest adsorption capacity, while adsorption of PFAS by the rest of the amendments was highly effective since equilibrium concentrations were below detection limit. Preliminary results from Part 2 indicate breakthrough of PFAS after only four pore volumes of water moved through the column; this suggests that the removal capacity of the old select fill is partially depleted. Retention of short-chain PFAS was poor in the old media as well. In contrast, both the biochar and the GAC amended columns have not shown any sign of breakthrough after 100 days of column operation, even for short-chain PFAS. Data collection from the column’s effluent is still ongoing. So far, these results demonstrate that biochar is a competitive adsorptive amendment relative to GAC. In addition, comparing these new results to the previous column study shows that increasing the content of biochar from 5% to 10% has an exponential improving effect on PFAS retention. These results also provide insight on the longevity of a potential new permeable barrier in which biochar or GAC can be used as an amendment.