Master of Engineering Science
Civil and Environmental Engineering
Gerhard, Jason I.
Per- and polyfluoroalkyl substances (PFAS) are a group of anthropogenic contaminants that are growing increasing concern due to their associated negative health affects. The properties of PFAS result in their persistence and stability which present challenges for remediation. Activated carbon is currently the most widely used method for PFAS treatment since carbon microparticle injection can be used for in-situ treatment; however, this method does not result in PFAS destruction. Thermal treatment is a promising post-treatment method that can be used with activated carbon as long as sufficient PFAS-destroying temperatures are achieved (> 900°C). A promising in-situ thermal treatment technology is Self-Sustaining Treatment for Active Remediation (STAR) which uses smouldering combustion to destroy organic contaminants embedded within a porous matrix. This study investigates carbon injection to support STAR for the treatment of PFAS. Four solutions were used (i) 17% colloidal activated carbon (CAC) (ii) 23% CAC (iii) 17% powdered activated carbon (PAC) and (iv) 23% PAC. Smouldering temperatures greater than required PFAS destruction temperature were reached for all carbons if 50 g carbon/kg sand was achieved for both injection and soil-mixing delivery methods. Moreover, emulsified vegetable oil (EVO) was demonstrated to be a successful secondary surrogate fuel to further enhance smouldering temperatures when supplied at a quantity less than or equal to carbon microparticles. These findings present the necessary intermediate laboratory work to evaluate methods that will achieve PFAS treatment through STAR when applied in the field.
Summary for Lay Audience
PFAS are a group of human-made chemicals that have been used since the 1950s for consumer products. These products include non-stick cookware, waterproof jackets, stain-resistant furniture, and waterproof cosmetics. One of the main sources of PFAS is fire fighting foam used to put out large and fast-spreading fires. PFAS has entered the environment from manufacturing companies releasing waste or firefighting foam being sprayed onto the ground. PFAS has been a growing concern in recent years because it is difficult to treat. The properties that make them desirable for use in commercial products cause them to persist in the environment and resist breakdown. This results in PFAS accumulating over time, making them more dangerous for both the environment and humans. PFAS is linked to many adverse health effects and cancers, which puts the need for proper treatment of PFAS as a priority.
Activated carbon has been successful at treating PFAS. This method works by carbon adsorbing the PFAS, which does not eliminate it. If this is used in the environment, the PFAS will be stuck in place and not destroyed through carbon injection into the ground. STAR is a heat-based technology that can be used both below and above the ground, which has successfully treated other contaminants while not requiring a large amount of energy. PFAS can be treated by burning it at temperatures above 900°C, which STAR can do. This research explored the use of carbon injection to support STAR to reach temperatures that will destroy PFAS. Carbon injection is necessary as this application will allow STAR to be used below the ground, and the carbon will be able to target the PFAS and provide a source of fuel to reach these high temperatures. Results showed that temperatures greater than 900°C could be achieved with various injectable carbon solutions supporting STAR. These methods can be used to treat PFAS when contaminating the environment underground.
Wilton, Gillian, "Carbon Injection to Support In-Situ Smouldering Remediation" (2022). Electronic Thesis and Dissertation Repository. 8452.