Pore Blockage Effects on Atrazine Adsorption in a Powdered Activated Carbon/Membrane System. II: Model Verification and Application

The bisolute model developed in Part I of this study to describe the effect of pore blockage on trace organic compound adsorption was verified and then used to study the roles of various design and operating variables on process performance efficiency. Continuous flow experiments were conducted with atrazine and a pore-blocking macroelectrolyte, poly(styrene sulfonate) $\left(\mathrm{PSS}-1.8k\right)$ using two powdered activated carbons (PACs) in a bench-scale PAC/microfiltration (MF) system. The model was calibrated with one set of experimental data, and verified with additional data obtained at different operating conditions for both PACs. PAC B, which has a large mesopore surface area and volume, was found to be less affected by pore blockage at a given $\mathrm{PSS}-1.8k$ surface loading compared to PAC A, which has relatively small mesopore surface area and volume. However, it was also shown that when PAC B was fully loaded with $\mathrm{PSS}-1.8k$, the pore blockage effect on the rate of atrazine diffusion was even greater than that for PAC A due to the higher $\mathrm{PSS}-1.8k$ adsorption capacity of PAC B. Model simulations were conducted to investigate the effects of reactor hydraulic retention time, membrane cleaning interval, influent $\mathrm{PSS}-1.8k$ concentration, PAC dosage, PAC dosing scenario, and the quality of membrane cleaning water on system performance. Optimal PAC/MF system operating conditions were also determined based on model simulations. The study results showed the effects that different concentrations and adsorbent loadings with pore blocking compounds, such as the pore blocking fractions of natural organic matter, can have, and the importance of mesopores in mitigating the detrimental effect of pore blockage.