Modeling transport and retention of graphene oxide in porous media under subsurface condition

Author: Md Sazadul Hasan, Department of Civil and Environmental Engineering

Mentor: Dr. Mengistu Geza, Department of Civil and Environmental Engineering

The physical and chemical properties of porous media dominate the Graphene Oxide (GO) transport and retention behavior under a subsurface environment. A series of fixed-bed column studies were conducted using quartz sand, biochar (BC), and BC surface modified with nanoscale zero-valent iron (BC-nZVI) in three configurations as a function of ionic strength (IS). Colloid filtration theory (CFT) was employed to develop mathematical models based on the one-dimensional convection-dispersion equation along with blocking phenomenon using the experimental GO breakthrough curves (BTCs). Three blocking phenomenon such as no blocking, site-blocking (Langmuirian attachment), and depth-dependent (straining) blocking accounted for the retention coefficients to understand the GO transport and retention behavior. The inverse modeling approach was implemented to determine the attachment coefficient (K_a) and maximum solid-phase retention capacity (S_max) for all media. It was demonstrated that the model considering site-blocking can appropriately describe the measured GO BTCs (R² ~ 0.60-0.99) in BC and BC-nZVI. Higher K_a (0.62) in BC compared to BC-nZVI (0.35) at 10 mM IS verifies the influence of aggregation which agrees with the GO aggregation studies. In contrast, higher K_a (6.47) values were predicted in BC-nZVI at lower IS (0.1 mM), primarily due to the attachment of GO onto nZVI where nZVI in BC pores was also favorable for the straining process. Longer GO applications analyzed via forwarding simulations exhibited that 60 cm depth of BC and BC-nZVI can prevent a complete GO breakthrough up to 6.62 and 8.57 days, respectively, whereas sand required 0.074 days. This study revealed that surface-modified BC-nZVI could be an efficient filter media for environmental GO remediation. Moreover, CFT and the Lagnmuirian dynamics blocking appropriately describe the GO transport and retention processes in BC and BC-nZVI under subsurface environmental conditions.

Keywords: Transport modeling, Graphene oxide, Biochar, Colloid transport, nanoscale zero-valent iron modified biochar.