Partitioning of hydrophobic organic compounds to hydroxypropyl-β-cyclodextrin:: Experimental studies and model predictions for surfactant-enhanced remediation applications

Partitioning studies of hydrophobic organic compounds (HOCs) to hydroxypropyl-beta-cyclodextrin (HPCO) and one-dimensional transport simulations were conducted to evaluate the feasibility of using HPCD to remove sorbed HOCs in surfactant-enhanced remediation (SER) applications. HOC partitioning to HPCO was very fast, with over 95% of the complexation occurring within 10 min. Some influence of solution chemistry and HOC concentration on HOC- HPCD complex formation coefficients was observed; in general, the magnitude of the effects was similar to that observed previously for a nonionic surfactant (Tween 80) but much less than that for an anionic surfactant (sodium dodecyl sulfate, SDS). HPCO sorption on kaolinilte as quantified by both a fluorescence technique and total organic carbon measurements was negligible, indicating no significant affinity of HPCO for the solid phase. Although the HOC solubilization capability of HPCD was lower than that of conventional surfactants such as SOS and Tween 80, transport simulations showed that HPCO can be effective in removing sorbed HOCs from a model subsurface environment, primarily because of its negligible sorption to the solid phase (i.e., all HPCD added facilitates HOC elution). However, in contrast with SDS and Tween 80, HPCD becomes relatively less effective for HOC partitioning with increasing HOC size and hydrophobicity. Therefore, comparisons between HPCD and conventional surfactants for enhanced remediation applications must consider the specific HOC(s) present and the potential for surfactant material losses to the solid phase as well as other generally recognized considerations such as material costs and potential toxicological effects.