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Impact of Particle Size on Activated Carbon Kinetics and Cap Modelling –

Application of Study Data to a Great Lakes Legacy Act (GLLA) Site Model Using CapSim 

Presenter: Moses A. Ajemigbitse Ph.D. AquaBlok Ltd.

           Co-Authors: Michael Healey, Jeff Roberts SiREM - Danny Reible Texas Tech University – Roy Clackum Cabot Corporation - John Collins & John Hull | AquaBlok Ltd.

Summary Abstract:

Activated carbon (AC) continues to play an important role in remediating sediments contaminated by hydrophobic organic compounds (HOC). Designs for in situ remediation often utilize AC-HOC aqueous equilibrium isotherms in predictive cap design models to determine ‘time to breakthrough’ or ‘life’ for performance benchmarking of various types and/or physical forms (powder or granular) of activated carbon amendments. However, a question remains related to the applicability of equilibrium behavior as an appropriate model for field-scale conditions within a transient, dynamic, kinetic-driven environment, such as in areas with high groundwater influx/flow rates. This situation is confounded by the fact that the equilibrium behavior of granular activated carbons (GAC) is commonly determined by pulverizing the GAC to the particle size of powder activated carbons (PAC), i.e. <325 mesh. This introduces a particle size bias to the expected behavior of GAC as compared to PAC. The objective of the work presented is to evaluate the effect of activated carbon particle size on removal kinetics of environmentally relevant HOCs, i.e., polyaromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) and the impact of kinetics on an active cap model of a GLLA site using actual test data and CapSim modeling. The results support the idea that particle size has a significant impact on activated carbon adsorption, especially where higher flux rates may be present. As a result, it is critical to understand the site-specific characteristics and ensure that data exists that can assist with appropriate material selection at a specific site. Smaller particle size may also significantly impact total adsorption capacity as well, particularly for larger molecular size contaminants such as PCBs. In this case, remedies utilizing PAC would require a much lower quantity of carbon than GAC to achieve a similar remediation result.