EAGER: Deterioration of Stormwater Filter Media by Deicing Salts: X-ray Micro Computed Tomography (µCT)
This EAGER project is proposed to explore an innovative use of x-ray micro computed tomography (µCT) to investigate the effects of deicing salts on stormwater filter media (SFM). By allowing stormwater to infiltrate into the ground and entrapping the pollutants, SFM play a crucial role in preventing floods and protecting the environment. Prior studies have raised concerns about the deicing salts’ role in deterioration of SFM. SFM deterioration is not mechanistically understood so far because no studies have used experimental techniques that could visualize the pore structure. Current understanding is based on field and laboratory tests that focused on the chemical analysis of the effluent and/or SFM before and after salt application. Such traditional approaches have proved unsuccessful to observe and comprehend the micro-scale phenomena that occurs inside the SFM. Based on the results of this EAGER project, µCT can be utilized in further research to visualize the interior of SFM samples for quantifying the effects of deicing salts on the pore structure. This proposal is a good fit for EAGER, but not as a regular proposal, because x-ray µCT has not been used so far to understand the pore structure of SFM. The PI outlines a plan to conduct flow tests for application of NaCl as a deicing salt, and to compare the pre- and post-salt-application pore structures acquired in µCT.
This EAGER project will explore x-ray µCT and use the data in computer simulations for developing scientific understanding of SFM deterioration, a critical research need. Two hypotheses to be tested are:
(1) There is a statistical correlation between “flow rate” and “ratio of active porosity to total porosity”.
(2) Given the total amount of NaCl is similar, differences in SFM degradation (the ratio of “active porosity” to “total porosity”) will not be significantly different at three different NaCl concentrations.
The results of this research will address two scientific questions:
(1) How does the pore structure of a SFM change due to application of NaCl?
(2) Is there a relationship between the “ratio of active porosity to total porosity” and infiltration rate?
Success of this EAGER project will pave the way to use x-ray µCT in investigating other aspects of SFM deterioration, such as SFM with compost added, and effects of other deicing salts (calcium chloride, sodium acetate, calcium acetate). This EAGER project’s goal is to explore and test this radically different research approach for addressing the critical need to scientifically understand the deterioration of SFM. We propose to achieve this goal by using state-of-the-art of x-ray µCT, and a combination of discrete element method and lattice Boltzmann method (DEM-LBM) simulations. X-ray µCT has demonstrated success in other research fields, viz., medicine, biology, agriculture, geology, industrial, etc. The PI has successfully conducted a pilot study using µCT for visualization of SFMs’ pore structure. Same samples will be µCT scanned before and after salt application. The 3D image data will be used for constructing 3D pore structures of SFM. The 3D pore spaces will be used in morphological analysis and DEM-LBM simulations. Results (distribution of porosity, gradients, etc.) will help us in understanding the mechanism of SFM deterioration. The PI is committed to publish results in high-quality refereed journals for stimulating interest in the use of µCT for investigating transport phenomena in granular and/or porous media. This EAGER project will establish x-ray µCT as a suitable method for studying porous media, and will transform the scientific understanding of different porous media.