Nonequilibrium transport of polyacrylamides correlated with pore-water velocity
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Transport behavior of polyacrylamides (PAMs) in chernozem was investigated through the static equilibrium sorption experiment, column tests and modeling studies. In flow-through column studies, nonequilibrium sorption behavior of PAMs was described by a nonequilibrium mass transfer model combined with a Langmuir sorption model. Langmuir sorption isotherm parameters were obtained from the static sorption experiment and dispersion coefficients and pore velocities were obtained from breakthrough curves (BTCs) of Br-. Comparing with the traditional nonequilibrium mass transfer model with a linear isotherm, the developed nonlinear model predicts asymmetric sorption and desorption behavior. More importantly, we identified a strong linear relationship between the estimated first-order mass transfer rate coefficient and the pore velocity, which relates the empirical parameter mass transfer rate coefficients to the measurable system parameter of pore velocity. Our results suggest that mass transfer may limit the subsurface transport of PAMs and the lumped mass transfer rate coefficients are linearly correlated with flow velocities. The results also indicate that this one-site Langmuir sorption model may be applied to other contaminants’ transport during which the Langmuir mass transfer exists.