Enhanced sorption and destruction of PFAS by biochar-enabled advanced reduction process

Realistic and field scale applications of biochar for water remediation: A literature review

Biochar has received increasing attention in recent years as a potentially cost-competitive adsorbent for removing various contaminants from surface water and groundwater. However, most published studies have been conducted in the laboratory on a bench scale. Laboratory conditions do not necessarily reflect the complex, heterogeneous, and dynamic field conditions of actual contaminated surface water and groundwater environments. There is a lack of comprehensive literature review regarding the performance of biochar for contaminant removal, especially under realistic field conditions and at field scale. Here, we evaluated 31 studies on realistic applications of biochar for water remediation by searching the keywords: pilot scale, field scale, and mesocosm scale combined with biochar and water remediation. Biochar was found to be incorporated into a variety of water remediation technologies for treating both inorganic and organic contaminants, such as nutrients, heavy metals, pesticides, and pharmaceuticals in polluted waters and wastewaters. Also, biochar showed the potential to be effective on a field scale or in realistic remediation technologies, although it is not always as effective as other sorbents, such as activated carbon (AC). This is partially because AC has better physicochemical characteristics such as higher surface area and more micropores. Effectiveness for contaminant removal varies according to the targeted contaminants, the type and dosage of biochar used, and the treatment technology incorporating biochar. Finally, knowledge gaps and future research areas are identified. For example, more field scale studies are needed to test the effectiveness of biochar as an adsorbent under realistic conditions to pinpoint specific characteristics suitable for target contaminants. Physicochemical characteristics of the biochar can also change over time during the treatment process due to weathering, which may negatively affect the treatment performance. The effects of scaling up production on biochar quality should therefore also be further investigated, as physicochemical characteristics can be affected by varying the synthesis conditions. Regeneration and disposal of spent biochar is another active research area to determine the overall treatment costs.

Electrochemical Characterization of Pyrogenic Carbons: Implications for Degradation of Groundwater Contaminants with Carbon-Based Amendments

Pyrogenic carbons (PCs) are important mediators of biogeochemical redox reactions and contribute to contaminant degradation in some remediation methods. Contaminant degradation by electron transfer from PC is influenced by its electron conductivity and storage capacity, and atom transfer reactions involving atomic hydrogen, but resolving their contributions is difficult. In this study, we developed a method to modify working electrodes with agarose-stabilized thin films of PCs and used them to characterize PC reactivity using 2,4,6-trinitrotoluene (TNT) as a model contaminant and several electrochemical methods. Chronoamperometry showed that TNT reduction rates increase with increasing PC temperature, and electrochemical impedance spectroscopy showed that this is because the heterogeneous electron transfer rate constants (k0) are inversely correlated to resistivity (Rp) of the PC films. As a result, PCs like biochars, which have higher charge transfer resistance (Rct), give lower TNT reduction rates, whereas lower Rct PCs like activated carbons give faster TNT reduction. Current from reduction of H2O/H+ to H2 (HER) was significant only for low Rp PC-films on Pt working electrodes. The reactive intermediates involved in HER react preferentially with quinonoid moieties on the PC, thereby competing with and limiting TNT reduction at low overpotentials ( Collapse

Key Words

• capacitance
• hydrogen evolution reaction
• pyrogenic carbon
• resistance
• rotating disk electrode
• thin film

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MESH Headings

• Carbon/chemistry
• Groundwater/chemistry
• Trinitrotoluene/chemistry
• Water Pollutants, Chemical/chemistry
• Electrochemical Techniques
• Oxidation-Reduction
• Charcoal/chemistry

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Affiliation(s)

Jeffrey M Hudson OHSU/PSU School of Public Health, Oregon Health & Science University, Portland, Oregon 97239, United States
Paul G Tratnyek OHSU/PSU School of Public Health, Oregon Health & Science University, Portland, Oregon 97239, United States

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Adsorption of perfluorooctanoic acid from aqueous matrices onto chitosan-modified magnetic biochar: Response surface methodology-based modeling, performance, and mechanism

Perfluorooctanoic acid (PFOA) removal has gained significant attention due to its environmental stability and potential toxicity. This study aims to synthesize a chitosan-modified magnetic biochar (CS_MBC) for efficient PFOA removal from aqueous solutions. Various CS loading ratios (0.25:1, 0.5:1, and 1:1) were explored to determine the optimal adsorbent, with preliminary experiments exhibiting superior performance of CS1_MBC. To explore the impact of various experimental conditions (pH, adsorbent dose, time, and initial PFOA concentrations) on PFOA removal and optimize these parameters, central composite design of response surface methodology was applied. Statistical analysis of variance was conducted to assess the model's adequacy, which demonstrated a strong correlation between experimental results and the model. The predicted optimal conditions for achieving maximum PFOA removal (∼94%) were pH 4, 120 mg/L dose, 60 min time, and 20 mg/L PFOA concentration. The kinetics and isotherm studies revealed that the pseudo-second-order (R2 = 0.9996) and Redlich-Peterson (R2 = 0.999) models better described PFOA adsorption, with Langmuir maximum adsorption capacity of ∼517 mg/g. Thermodynamic study confirmed the spontaneous, endothermic, and physisorptive nature of PFOA adsorption, with electrostatic and hydrophobic interactions and hydrogen bonding governing the process. Further, the fixed-bed column experiment was conducted to evaluate the effectiveness of CS1_MBC for practical applications, which demonstrated the maximum experimental adsorption capacity of 39.63 mg/g. The breakthrough data showed an excellent fit with both the Thomas and Yoon-Nelson models, with a high correlation coefficient (R2 = 0.99). Therefore, this research underscores the potential of CS_MBC as an efficient adsorbent for mitigating PFOA contamination in aqueous environments.