A critical review of biochar for the remediation of PFAS-contaminated soil and water

Boosting sewage sludge safety with nano-biochar for polycyclic aromatic hydrocarbons immobilization and ecotoxicity reduction

Polycyclic aromatic hydrocarbons (PAHs) are common pollutants in sewage sludge (SSL), posing environmental and health risks. Stabilizing these contaminants is crucial for improving the ecological safety and reuse potential of SSL. This study investigated the effectiveness of nano-biochars (n-BC) and bulk biochars (b-BC) derived from willow (WL) and rice husk (RH) in reducing freely dissolved (Cfree) PAHs in SSL and mitigating its ecotoxicity. RH-derived biochars demonstrated superior performance, achieving 1.5- to 4.7-fold greater reductions in Cfree PAH content compared to WL-derived variants. Notably, n-BC proved more effective than b-BC, with n-BC-RH and n-BC-WL showing up 1.2- to 2.0-fold greater reductions, respectively. The optimal BC's dose range was 2.5-5 %, with diminishing returns observed at higher concentrations (10 %). The n-BC treatment also showed enhanced toxicity reduction, improving Aliivibrio fischeri luminescence and Lepidium sativum root growth by up to 109 % and 369 % compared to b-BC. Analysis revealed that inorganic minerals (present in ash) in both BC types played a key role in PAH immobilization. These results highlight n-BC's potential as an innovative solution for sustainable SSL management. This research addresses a critical gap in sludge management by proposing practical, scalable, and sustainable solutions for PAH contamination.

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.

Effect of coexisting Cd(Ⅱ) and As(V) on anionic PFASs sorption in soils: Models and mechanisms

An in-depth understanding of the sorption behaviors of per- and polyfluoroalkyl substances (PFASs) in soil is essential to assess their environmental risks accurately. Due to chemical industry production and waste treatment, co-contamination soil of heavy metals (HMs)-PFASs has become a public concern worldwide. This study investigated soil sorption behaviors of PFASs including perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS), and perfluorohexanesulfonic acid (PFHxS). A multiple linear regression (MLR) model was developed to predict the sorption of PFOS in soil. Validation results demonstrated that this model could effectively predict the distribution coefficients (Kd) of PFOS based on soil organic carbon (OC), silt, clay, and free Fe/Al-oxide contents, exhibiting a strong predictive ability (r2 = 0.942, p < 0.001). In six soils, HMs (Cd2+ and As5+) influence three anionic PFASs sorption primarily by altering the electrostatic and hydrophobic interactions between soil components and PFASs. The Kd values of PFOS tend to rise with increasing Cd2+ concentration but decline with increasing As5+ concentration. In contrast, HMs have a relatively minor influence on the sorption of PFOA and PFHxS. Moreover, a nonlinear model was constructed for the first time to quantify the impact of HMs on PFASs sorption. The model achieves exceptional prediction accuracy when applied to both experimental data from this study and literature data. A comprehensive understanding of PFASs sorption behavior in soil under conditions of coexisting HMs is of great significance for formulating targeted degradation and mitigation strategies for co-contaminated sites.

Insights into poly-and perfluoroalkyl substances (PFAS) removal in treatment wetlands: Emphasizing the roles of wetland plants and microorganisms

Poly- and perfluoroalkyl substances (PFAS) are widespread emerging contaminants in aquatic environments, raising serious concerns due to their persistence and potential toxicity to both human health and ecosystems. Treatment wetlands (TWs) provide a sustainable, low-carbon solution for PFAS removal by harnessing the combined actions of substrates, plants, and microorganisms. This review evaluates the effectiveness of TWs in PFAS treatment, emphasizing their role as a post-treatment option for conventional wastewater treatment plants. Mass balance analysis reveals that substrate adsorption was the primary pathway for PFAS removal from TWs, while plant uptake and subsequent harvesting treatments, as well as microbial degradation, contribute substantially to long-term PFAS removal. Comparisons of bioaccumulation factor (BCF) and translocation factors (TF) between wetland and terrestrial plants demonstrate that wetland plants are particularly effective at adsorbing long-chain PFAS and transferring them from roots to aboveground tissues. The diverse environmental conditions within TWs support varied microbial communities, facilitating the evolution of PFAS-degrading microorganisms. Wetland microorganisms demonstrate the capacity to break down PFAS through processes such as head group transformations (e.g., decarboxylation, desulfonation) and defluorination (e.g., elimination, reductive defluorination, hydrolysis, dealkylation). This review emphasizes the crucial role of wetland plants and microorganisms in the sustainable removal of PFAS in TWs, providing insights for the ecological remediation of PFAS-contaminated wastewater.