Hydration-assisted sorption of a probe organic compound at different Peat hydration levels: the link solvation model

Sorption isotherms of phenol on Pahokee Peat as model natural organic matter(NOM) have been measured at different partial NOM hydrations (water activities). Sorption at a given phenol solution concentration is substantially smaller in the lower water activity systems than in higher water activity systems, reaching a sorption maximum at an intermediate water activity. Such cooperative phenol uptake at interim water activities as a result of NOM hydration (hydration-assisted sorption) is predicted by the link solvation model (LSM), whereby water enhances the disruption of the noncovalently cross-linked NOM structure, creating new sorption sites. The LSM is herein extended to account for the observed direct relationship between isotherm linearity and water activity. The extended LSM provides an excellent description of phenol sorption isotherm data at nine different NOM hydration levels with a single set of three unique parameters. The successful fit of the LSM supports the conceptual model of creation of new sorption sites for sorbate molecules in the hydrated organic matter sorbent, accompanied by competition for those new sites by water molecules at high water activities.