Investigation of Adsorption Kinetics for Per- and Poly-fluoroalkyl substances (PFAS) Adsorption onto Powder Activated Carbon (PAC) in the Competing Systems

Batch kinetic test was performed for nine per- and polyfluoroalkyl substances (PFASs). Pseudo-first-order (PFO) and pseudo-second-order (PSO) kinetic models as well as the intraparticle diffusion (ID) model were used to determine the rate constants representing K-1, K-2, and K-id, respectively. They were then compared to evaluate the effect of the carbon chain length and adsorption surface area (i.e., different powder activated carbon (PAC) concentrations) on the competing conditions of nine PFAS species. The lowest and average of coefficient of determination (R-2) was 0.965 and 0.992, and 0.692 and 0.898 and for nonlinear and linear PFO, respectively, implying that linear PFO included extraordinary sample point. K-1 increased by 3.6 times on average from 10 and to 100 mg/L of PAC. For nonlinear PFO, K-1 increased up to 5.9 times (from 1.63 to 9.64) and 8.3 times (from 1.11 to 9.24) with the increase of the carbon chain length and PAC concentration, respectively. PSO obtained a higher average coefficient of determination (R-2) of 0.996 than PFO of 0.992 determining PSO is more suitable than PFO. K-2 was more affected than K-1 by concentration of PAC based on linear and exponential quantitative correlations for K-1 and K-2, respectively, although the behavior of K-2 was a very similar to K-1 at all condition except for 100 mg/L of PAC. The value of K-id showed an opposite pattern to those of K-1 and K-2, in which the sum of K-id and C decreased from 3.67, 1.73, 0.816, and 19.2 to 15.1, 12.0, and 7.89 at 10, 30, 50, and 100 mg/L of PAC concentration, respectively, indicating that the effect of the film and intraparticle diffusions on the adsorption was not significant when there is higher interaction and enough surface area because, in this case, the process rapidly reaches equilibrium.

Automated summary

Batch kinetic tests were conducted on nine PFASs, and pseudo-first-order, pseudo-second-order, and intraparticle diffusion models were used to determine the rate constants. The effects of carbon chain length and adsorption surface area on the competing conditions were evaluated. The results showed that the linear model in the pseudo-first-order kinetic model included exceptional sample points, while the pseudo-second-order kinetic model was more suitable. In addition, the impact of intraparticle diffusion on adsorption was not significant.