Mechanistic understanding of perfluorooctane sulfonate (PFOS) sorption by biochars

Samuel Krebsbach; Jianzhou He; Sushil Adhikari; Yaniv Olshansky; Farshad Feyzbar; Leonard C Davis; Tae-Sik Oh; Dengjun Wang

doi:10.1016/j.chemosphere.2023.138661

Mechanistic understanding of perfluorooctane sulfonate (PFOS) sorption by biochars

Chemosphere. 2023 Jul:330:138661. doi: 10.1016/j.chemosphere.2023.138661. Epub 2023 Apr 10.

Authors

Samuel Krebsbach¹, Jianzhou He¹, Sushil Adhikari², Yaniv Olshansky³, Farshad Feyzbar⁴, Leonard C Davis⁵, Tae-Sik Oh⁴, Dengjun Wang⁶

Affiliations

¹ School of Fisheries, Aquaculture and Aquatic Sciences, Auburn University, Auburn, AL 36849, USA.
² Biosystems Engineering Department, Auburn University, Auburn, AL 36849, USA.
³ Department of Crop, Soil, and Environmental Sciences, Auburn University, Auburn, AL 36849, USA.
⁴ Department of Chemical Engineering Auburn University, Auburn, AL, 36849, USA.
⁵ Department of Biological and Environmental Sciences, East Central University, Ada, OK, 74820, USA.
⁶ School of Fisheries, Aquaculture and Aquatic Sciences, Auburn University, Auburn, AL 36849, USA. Electronic address: dzw0065@auburn.edu.

PMID: 37044140
DOI: 10.1016/j.chemosphere.2023.138661

Abstract

Biochar has recently emerged as a cost-effective solution to combat per- and polyfluoroalkyl substances (PFAS) pollution in water, but mechanistic understanding of which physicochemical properties of biochars dictate PFAS sorptive removal from water remains elusive. Herein, 15 biochars were pyrolyzed from five feedstocks (corn, Douglas fir, eucalyptus, poplar, and switchgrass) at three pyrolysis temperatures (500, 700, and 900 °C) to investigate their removal efficiencies and mechanisms of perfluorooctane sulfonate (PFOS) from water. A commercial biochar was also included for comparison. Biochar physiochemical properties, including elemental composition, pH, specific surface area (SSA), pore structure, hydrophobicity, surface charge, surface functional groups, and crystalline structure were systematically characterized. Batch sorption data showed that the Douglas fir 900 biochar (Douglas fir and 900 are the feedstock type and pyrolysis temperature, respectively; this naming rule applies to other biochars), poplar 900 biochar, and commercial biochar can remove over 95% of PFOS from water. Structural equation model (SEM) was used to elucidate which biochar properties affect PFOS sorption. Interestingly, biochar pore diameter was identified as the most critical factor controlling PFOS removal, but pore diameter/pore volume ratio, SSA, pyrolysis temperature, hydrophobicity, and elemental composition all played variable roles. Hypothetically, biochars with small pore diameters and large pore volumes had a narrow yet deep pore structure that traps PFOS molecules inside once already sorbed, resulting in an enhanced PFOS sorption. Biochars with small pore diameter, low nitrogen content, and high pyrolysis temperature were also favorable for enhanced PFOS sorption. Our findings advance the knowledge of using biochars with optimized properties to remove PFOS and possibly other similar PFAS compounds from water.

Keywords: Biochar; Perfluorooctane sulfonate (PFOS); Physicochemical properties; Sorption; Structural equation model.

MeSH terms

Adsorption
Charcoal / chemistry
Fluorocarbons*
Populus*
Temperature

Substances

biochar
perfluorooctane
Charcoal
Fluorocarbons