Formatted Title
Formulation and Development of a Novel Dust-Free Carbon-Based Amendment for PFAS Immobilization in Soil
Background/Objectives
The widespread use of per- and poly fluoroalkyl substances (PFAS) in different industries, and aqueous film-forming foams (AFFF) in the last few decades has resulted in the spread and bioaccumulation of PFAS in the environment. The need for remediation of PFAS is growing due to more regulatory attention to this new class of contaminants with tightening soil and water quality standards. In situ immobilization of PFAS in soil by applying sorbents is often a preferred low-cost technique to reduce their mobility and leaching to groundwater. Powdered and granular activated carbon or mixed mode sorbents (mixed mineral/carbon) have been extensively used for PFAS immobilization in soil. Despite the efficacy of these sorbents for PFAS immobilization in soil, their dusty nature during handling and spreading in the field creates occupational health and community concerns. The creation of airborne dust also limits the application of any powdered materials as sorbents in the field.
Granulation of fine materials is one of the methods to eliminate dust formation during fine material transport, storage and filed application that has been extensively applied in the fertilizer and mining industries. One possibility is to granulate the powdered sorbent to facilitate safe transportation and economic use of the material. However, the granulation may decrease the surface area of the sorbent and affect its efficiency. Therefore, it is necessary to introduce a new preparation method that maintains the physical and chemical properties of the sorbents while not affecting the adsorption /immobilization efficiency of granulated sorbents.
Approach/Activities
A carbon-based amendment (containing powdered and granular activated carbon and clay) is extensively used for PFAS immobilization. The powdered amendment was either granulated in the laboratory using a high-shear granulator (Erich, Germany) or pelletized using a pellet press. The effect of binder type, rate and moisture during the granulation or pelletizing process was studied. The granulation and pelleting conditions were also optimized. The granules/pellets were tested for crushing strength as well as dispersibility in soil. The efficiency of the granules for PFAS immobilization was tested against the powdered materials using standard leaching tests such as LEAF 1314. An AFFF-contaminated soil was used in the leaching test. The concentrations of PFOS, PFHxS and PFOA were 2.8, 0.88 and 0.17 mg/kg in the contaminated soil, respectively. Concentrations of 28 PFAS in the leachates were determined using liquid chromatography-tandem mass spectrometry (LC-MS-MS).
Results/Lessons Learned
Binder type and rate had an important role in the strength of granules/pellets (e.g., crushing strength) and in reducing dust. Increasing the rate of binder enhanced the crushing strength of the granules or pellets and their dispersibility in soil. The optimized formulation contained 5% of a natural binder with a crushing strength of up to 12 kg force. The column leaching experiment on immobilized soil with powder or granular sorbents showed a significant decrease in PFAS leaching compared to untreated soil. Less than 0.3%, 0.6% and 0.6% of PFOS, PFHxS and PFOA leached from treated soil with granules after 15 pore volumes of leachates, respectively, and none of the short-chain PFAS (CF2≤ 5) were detectable in the leachates of immobilized soil. The percentages of leached PFOS, PFHxS and PFOA were less than 0.1, 0.2 and 1.3% from the immobilized soil with powdered sorbents, respectively. The data show that in situ remediation of PFAS-contaminated soils with these sorbents could be considered robust and durable with little risk of subsequent PFAS desorption.