M/F Hybrid Plasma/Activated Carbon Process for PFAS Removal in Water: Remediation and Toxicity

Job Description

Thesis Subject

Per- and polyfluoroalkyl substances (PFAS), detected in surface water, groundwater, and drinking water, have become a major public health concern. Due to the chemical stability of C–F bonds, PFAS are extremely resistant to degradation and accumulate in the environment, sometimes reaching very high local concentrations. It is therefore essential to develop new removal processes that are more effective than conventional methods (adsorption, reverse osmosis…).
Atmospheric pressure non-thermal plasma (NTP) for PFAS removal has been studied by several research groups [1–4]. It is used as an Advanced Oxidation Process (AOP), enabling the generation of O₃ as well as short-lived species with high oxidation potential (HO•, ¹O₂, O₂⁻) and nitrogen species (NO₂⁻, NO₃⁻…) without adding external chemicals. However, plasma processes alone remain insufficient in terms of PFAS removal and mineralization. They lead to the formation of fluorinated species with shorter carbon chains, which may be more toxic than the parent molecule.
An innovative approach consists in coupling non-thermal plasma with catalysts or porous carbon materials such as activated carbons (AC). These hybrid processes have shown high removal and mineralization efficiencies for pharmaceutical molecules and herbicides [5,6].
Since 2020, a collaboration between GREMI (plasma process expertise) ICMN (carbon materials expertise) allowed to study the coupling of iron-grafted activated carbons (AC-Fe) with non-thermal plasmas [6]. Previous work on herbicide treatment demonstrated that this coupling improves herbicide degradation, reduces by products, and significantly mineralizes organic carbon, with no adsorption in iron grafted AC. AC Fe thus behaves as a pseudo catalyst for reactive species. These innovative findings led to investigating NTP/AC coupling for the treatment of PFAS, and particularly a target molecule, PFOA (C₇F₁₅COOH). Results showed that the hybrid NTP/AC Fe system can enhance PFOA removal and decrease Total Organic Carbon (TOC) in solution.
Generally, even under strong mineralization conditions (near-complete degradation of organics), toxic organic compounds may persist, limiting the development of treatment processes. Few studies in the literature consider toxicological effects of by products generated during pollutant treatment in water, and even fewer focus on PFAS [7,8].
Preliminary toxicity studies on solutions before/after treatment were therefore carried out by CBM (biology expertise) in collaboration with GREMI and ICMN for PFOA-containing solutions. After developing the biological assays, preliminary results were obtained on solutions treated with NTP alone, NTP/AC, and NTP/AC Fe. Results showed an increase in cell proliferation alongside an increase in cell death. Additional studies are required to better understand these findings and to dissect the molecular mechanisms and cellular signaling pathways involved. Depending on coupling conditions and treatment durations, toxicity peaks were observed, likely corresponding to the production of toxic compounds.
This preliminary study on PFOA helped identify several challenges that this PhD aims to overcome. The approach proposed here will guide the implementation of the plasma process coupled with different functionalized activated carbons and the selection of operating conditions in relation to toxicity results.

Objectives of the PhD
• To study treatment efficiency on several PFAS (different functional groups and chain lengths) in natural water matrices and PFAS mixtures in order to propose a universal and safe PFAS treatment process,
• To evaluate different functionalized or non functionalized AC materials coupled with NTP, determine the role of AC depending on its textural and surface chemistry properties, optimize iron-grafting processes, and monitor the evolution of AC texture and porosity after treatment as a function of treatment cycles,
• To identify the role of active species generated by the plasma (differentiating the roles of oxygen and nitrogen species, ROS, RNS, and solvated electrons),
• To evaluate toxicity before/after treatment on different cell lines and characterize cellular responses more thoroughly to better understand mechanisms of toxicity using a relevant and exploratory approach in this field and under these experimental conditions.
Expected outcomes include a better understanding of the phenomena involved in these discharges, determining the role and impact of functionalized adsorbent materials within the process, and optimizing process coupling in terms of conversion rates, energy efficiency, and mineralization. Toxicological studies will validate the process and demonstrate the effectiveness and safety of this hybrid remediation approach.

Your Work Environment

The PhD student will work within the three laboratories involved in the project: GREMI, ICMN and CBM. The laboratories are located within 2 km of each other, making daily movement between them easy.
The student will functionalize and characterize carbon materials at ICMN and implement them in plasma reactors for PFAS treatment at GREMI. The effect of treatment on carbon material properties (porous, chemical, morphological) and their lifetime will be studied at ICMN (with Dr B. Cagnon).
At GREMI (with Dr O. Aubry and Dr H. Rabat), the student will perform electrical and optical characterizations of discharges and chemical analyses of treated solutions depending on operating parameters (type of PFAS, AC properties, gas flow rates and composition…).
Toxicity studies will be carried out at CBM (Dr B. Vallée) on different cell lines before and after treatment. Biological studies may run in parallel with work at GREMI and ICMN. Depending on toxicological findings, additional experiments will be performed to understand molecular and cellular mechanisms.
Close collaboration with personnel from all three laboratories is essential. The student must therefore be able to communicate effectively, understand collaborative needs, and share results.

The teams at GREMI, ICMN, and CBM possess the expertise necessary to guide the PhD student toward achieving the project's objectives. The partners already have strong collaborations on related topics, ensuring optimal working conditions and project success.
GREMI has recognized expertise in designing and implementing cold plasmas interacting with liquids, discharge diagnostics (emission spectroscopy, fast imaging), electrical measurements (voltage, current, power), and solution chemical diagnostics (TOC analyzer, µHPLC, µHPLC MS…).
ICMN has strong expertise in carbon based adsorbent materials and characterization of porosity (N₂ isotherms at 77 K, TGA MS), surface chemistry (FTIR, XPS) and morphology (Raman, TEM) of AC before and after treatment. These analyses help study AC lifetime and determine its role in the hybrid NTP/AC process.
CBM has strong expertise in deciphering molecular mechanisms involved in physiological and pathological processes, with numerous available cell lines and tools (viability, cell death, signaling activation, morphology, cytoskeleton dynamics, migration, invasion…).

Compensation and benefits

Compensation

2300 € gross monthly

Annual leave and RTT

44 jours

Remote Working practice and compensation

Pratique et indemnisation du TT

Transport

Prise en charge à 75% du coût et forfait mobilité durable jusqu’à 300€

About the offer

About the CNRS

The CNRS is a major player in fundamental research on a global scale. The CNRS is the only French organization active in all scientific fields. Its unique position as a multi-specialist allows it to bring together different disciplines to address the most important challenges of the contemporary world, in connection with the actors of change.

CNRS

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