Polymer Coatings Affect Transport and Remobilization of Colloidal Activated Carbon in Saturated Sand Columns: Implications for In Situ Groundwater Remediation

Electrochemical reduction for chlorinated hydrocarbons contaminated groundwater remediation: Mechanisms, challenges, and perspectives

Electrochemical reduction technology is a promising method for addressing the persistent contamination of groundwater by chlorinated hydrocarbons. Current research shows that electrochemical reductive dechlorination primarily relies on direct electron transfer (DET) and active hydrogen (H⁎) mediated indirect electron transfer processes, thereby achieving efficient dechlorination and detoxification. This paper explores the influence of the molecular charge structure of chlorinated hydrocarbons, including chlorolefin, chloroalkanes, chlorinated aromatic hydrocarbons, and chloro-carboxylic acid, on reductive dechlorination from the perspective of molecular electrostatic potential and local electron affinity. It reveals the affinity characteristics of chlorinated hydrocarbon pollutants, the active dechlorination sites, and the roles of substituent groups. It also comprehensively discusses the current progress on electrochemical reductive dechlorination using metal, carbon-based, and 3D electrode catalysts, with an emphasis on the design and optimization of electrode materials and the impact of catalyst microstructure regulation on dechlorination performance. It delves into the current application status of coupling electrochemical reduction technology with biodegradation and electrochemical circulating well technology for the remediation of groundwater contaminated by chlorinated hydrocarbons. The paper discusses practical application challenges such as electron transfer, electrode corrosion, water chemistry environment, and aquifer heterogeneity. Finally, considerations are presented from the perspectives of environmental impact and sustainable application, along with a summary and analysis of potential future research directions and technological prospects.

Review on the sources, distribution and treatment of per- and polyfluoroalkyl substances in global groundwater

Per- and polyfluoroalkyl substances (PFAS) have garnered increasing global attention due to their widespread occurrence in groundwater and the potential health risks to humans. This review aimed to clarify the occurrence and treatment of PFAS in groundwater by summarizing literature published in the Web of Science Core Collection from January 2000 to April 2024. Information on 461 reported PFAS-contaminated groundwater sites was compiled, revealing key characteristics of pollution sources and concentrations. The data indicated that firefighting training activities were a major source of PFAS groundwater contamination, accounting for 41 % of cases, followed by other fluorinated industrial activities, landfill leachate, and wastewater leakage. Non-point sources, such as atmospheric deposition, contributed to a lesser extent. The concentrations distribution of 25 PFAS showed a chain-length dependency, with short-chain PFAS generally exhibiting higher concentrations than long-chain PFAS. Additionally, the review systematically examined the application of separation methods and destructive methods at both laboratory and pilot/field-scales for PFAS-contaminated groundwater. Resins were favored for ex-situ treatment, whereas colloidal activated carbon (CAC) was more commonly used for in-situ treatment. In-situ direct injection of CAC was considered a highly promising approach for remediating PFAS source zones and plumes, offering advantages such as minimal surface disruption, high adsorption capacity and long-term effectiveness. Finally, the research focus and development trends in categories and treatment methods for PFAS in groundwater were noted. Overall, this review identified research gaps in the occurrence and treatment of PFAS in groundwater, and suggested further optimization of CAC-based methods to address the challenges of PFAS-contaminated groundwater.

Groundwater solutes influence the adsorption of short-chain perfluoroalkyl acids (PFAA) to colloidal activated carbon and impact performance for in situ groundwater remediation

Subsurface injection of colloidal activated carbon (CAC) is an in situ remediation strategy for perfluoroalkyl acids (PFAA), but the influence of groundwater solutes on longevity is uncertain, particularly for short-chain PFAA. We quantify the impact of inorganic anions, dissolved organic matter (DOM), and stabilizing polymer on PFAA adsorption to a commercial CAC. Surface characterization supported PFAA chain-length dependent adsorption results and mechanisms are provided. Inorganic anions decreased adsorption for short-chain PFAA (<7 perfluorinated carbons) due to competitive effects, while long-chain PFAA (≥ 7 perfluorinated carbons) were less impacted. DOM decreased adsorption of all PFAA in a chain-length dependent manner. High DOM concentrations (10 mg/L, ∼5 mg OC/L) decreased PFOA adsorption by a factor of 2, PFPeA by one order of magnitude, and completely hindered PFBA adsorption. High MW DOM has less impact on short-chain PFAA than low MW DOM, possibly due to differences in the ability to access CAC micropores. Low DOM concentrations (1 mg/L, ∼0.5 mg OC/L) did not impact adsorption. CMC (90 kDa average MW) had negligible impact on PFAA adsorption likely due to minimal CAC surface coverage. Longevity modeling demonstrated that groundwater solutes limit the capacity for PFAA in a CAC barrier, particularly for short-chain PFAA.