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ARS Home » Pacific West Area » Riverside, California » Agricultural Water Efficiency and Salinity Research Unit » Research » Publications at this Location » Publication #433917
Research Project: Water Management for Crop Production in Arid and Semi-Arid Regions and the Safe Use of Alternative Water Resources

Location: Agricultural Water Efficiency and Salinity Research Unit

Title: Enhancing adsorption of short-chain PFAS in water using metal-modified biochar: Insights from Fe, Mn, and Zn

Author
item HU, JIAHUI - University Of California, Riverside
item MORENO, ALLIE - University Of California, Riverside
item Schmidt, Michael
item Ashworth, Daniel

Submitted to: American Chemical Society National Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 6/9/2026
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Per- and polyfluoroalkyl substances (PFAS) are persistent and ubiquitous environmental contaminants that pose long-term risks to ecosystem and human health. Biochar amendment has emerged as a promising strategy for PFAS adsorption from water; however, the effective removal of short-chain PFAS remains challenging due to their high mobility and low hydrophobicity. Metal modification offers an attractive approach to introduce positively charged sites for enhancing electrostatic interactions with anionic PFAS. Nevertheless, a trade-off exists, as metal loading can both enhance adsorption via surface charge and hinder it through pore blockage. In addition, the chain length–dependent response of PFAS to metal modification remains insufficiently understood. In this study, we synthesized nano metal-modified pinewood biochar (PBC) incorporating Fe, Mn, and Zn with varying metal loadings (0–50%) to elucidate the mechanisms governing PFAS adsorption as a function of metal morphology and electronegativity. Among the tested materials, Mn-modified biochar exhibited superior performance for short-chain PFAS, including PFPeA, PFHxA, PFHpA, and PFBS, while showing limited effectiveness for ultra-short-chain compounds (e.g., TFA, PFPrA, and PFBA). This selectivity is attributed to the formation of nanoscale Mn domains that generate pore structures favorable for PFAS with 4–6 CF2 units, but are less accessible to shorter-chain analogues. Using PFPeA as a representative compound, adsorption isotherm results demonstrated the following trend: Mn > Fe > Zn, with an optimal Mn loading of 12.92% (denoted as 5Mn-PBC). The representative material (5Mn-PBC) was further evaluated to investigate competitive adsorption and environmental effects. In PFAS mixtures, the distribution coefficients (Kd) of PFPeA, PFHxA, PFHpA, and PFBS decreased relative to single-solute systems, indicating competitive interactions. Adsorption of PFAS with 6 or less CF2 units decreased with increasing pH (3–11), whereas longer-chain PFAS (e.g., PFOA, PFNA, PFOS) showed minimal pH dependence. The presence of calcium and magnesium enhanced adsorption, particularly for PFPeA and PFHxA, while common anions (sulfate and nitrate at 3 mmol/L) exhibited negligible interference. Dissolved organic matter, including humic acid, fulvic acid, citric acid, and biosolid-derived organic matter (30 mg/L C), consistently suppressed adsorption, with fulvic acid showing the strongest inhibition. Overall, this study reveals that PFAS with intermediate chain lengths (4–6 CF2 units) are most responsive to metal-modified biochar and environmental factors. These findings provide mechanistic insights and a practical strategy for designing engineered biochars to enhance PFAS removal in water treatment systems.