Granular Activated Carbon Regeneration after Poly- and Perfluoroalkyl Substances Removal

Abstract

PFAS are a group of persistent and harmful chemicals that are widely used in both industrial applications and consumer products. PFAS are commonly detected in the environment and pose health concerns. Adsorption by GAC is considered an effective treatment method for removing PFAS from water. After a certain period of operation, GAC requires high-temperature incineration as disposal method. Another sustainable treatment approach is GAC regeneration. Thermal regeneration at high temperatures has been confirmed experimentally feasible and applied in the industry. This thesis aims to further explore and optimize thermal regeneration and reactivation technologies for GAC adsorbed with PFAS, with a focus on reducing operational temperatures and energy consumption.

This study collected the spent GAC samples from a firefighting site in Korsør, Denmark, where they had been used for onsite water treatment. The spent GAC was subjected to thermal regeneration and reactivation at 500℃, 700℃, and 900℃. To evaluate the adsorption capacity of regenerated GAC, ¹⁴C-labeled PFOA was introduced into water samples, and liquid scintillation counting was employed to measure radioactivity in the water after different mixing time. Additionally, a separate batch of GAC pre-loaded with ¹⁴C-labeled PFOA was subjected to pyrolysis and combustion to analyze the degradation of PFOA during thermal regeneration. The experimental results indicate that thermal regeneration under nitrogen at 500℃, 700℃, and 900℃ can effectively restore the adsorption capacity of GAC. Subsequent reactivation under CO₂ atmosphere at higher temperatures further enhances the performance of the regenerated GAC, enabling removal of over 95% of the ¹⁴C-labeled PFOA from water samples. This experimental study demonstrates the feasibility of combining low-temperature regeneration and high-temperature reactivation for GAC reuse. Moreover, pyrolysis experiments of PFOA (absorbed on GAC) verify that thermal regeneration above 400℃ leads to complete degradation of PFOA into CO₂, as evidenced by the acidification and gas re-collection in NaOH trapping solutions. This supports the conclusion that thermal treatment contributes to PFAS permanent removal from the water.

Popular Abstract

Regeneration of Activated Carbon: A Cooler and Greener Way to Break down PFAS

PFAS refer to a big group of man-made chemicals. PFAS have excellent water-resistant and fire-resistant properties and are commonly used in everyday life, such as in raincoats, non-stick pans, cleaning agents, and firefighting foams. Since the 1950s, PFAS have been widely used all over the world. PFAS are difficult to degrade in the natural environment. Therefore, they are also known as ‘forever chemicals’. They enter the environment through industrial discharges, household waste, and other routes, and could persist for a long time. PFAS have been detected all over the world—even in glaciers. Research shows that PFAS can accumulate in creatures, leading to chronic diseases and threatening human health.

Water and food packaging are the main sources of human exposure to PFAS. Conventional water treatment methods, such as sedimentation, filtration and chemical treatment, are mainly designed to remove particles and harmful bacteria. These processes cannot effectively remove PFAS from water. Currently, one of the widely used methods is granular activated carbon (GAC). Activated carbon has a porous structure that allows it to adsorb pollutants from water, like a sponge soaking up water. But after a period of use, the GAC reaches its adsorption limit (just like sponge becomes saturated), and needs to be replaced with fresh carbon. This increases operational costs, and the used carbon (filled with pollutants) may cause a secondary environmental risk. Therefore, regeneration of GAC is recommended, which means removing PFAS from the carbon pores to restore its adsorption capacity (like squeezing the water out of the sponge). A common regeneration method is to burn off the contaminants from the GAC at high temperatures, but this approach is expensive and energy-consuming. This thermal treatment still has great potential for optimization and improvement.

This study focuses on improving the regeneration process by exploring thermal regeneration methods that require lower temperatures and less energy. In industrial applications, GAC is typically heated to over 1000℃ for thermal treatment. In this experiment, the feasibility of regenerating GAC from 500℃ to 900℃ is tested. The thermal treatment in this study includes two steps: regeneration and reactivation. Regeneration involves heating the material in nitrogen atmosphere, while reactivation works under CO₂ condition. The specific test method involves using regenerated GAC to re-adsorb PFAS—specifically PFOA, a common type of PFAS—and then measuring its adsorption capacity. The results show that thermal regeneration at 500℃, followed by reactivation at 900℃ can almost fully restore the adsorption ability of GAC. This study presents a more energy-efficient and cost-effective regeneration strategy, offering promising potential for future practical applications.

• author: Xu, Yiwei
• supervisor: Per Falås; Michael Cimbritz
• organization: Chemical Engineering (M.Sc.Eng.)
• course: VVAM01 20251
• year: 2025
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Water and Environmental Engineering, PFAS, GAC, Regeneration
• language: English
• id: 9197887
• date added to LUP: 2025-06-12 13:41:40
• date last changed: 2025-06-12 13:41:40