Enhanced remediation of groundwater contaminated with light non-aqueous phase liquids (LNAPLs)

Abstract

Cosolvent flooding is one of the most promising technologies for the removal of entrapped non aqueous phase liquids (NAPLs) from the groundwater. The purpose of this study is to evaluate the enhanced solubilization and mobilization of toluene and benzene using two chemical agents: ethanol an alcohol and hydroxypropyl-beta-cyclodextrin (HPCD) a modified sugar. Specifcally, the focus of the first part of the study is on investigating the recovery mechanisms encountered when ethanol solutions are used to flush a NAPL mass consisting of a single compound (toluene or benzene) or a mixture (toluene and benzene together). To achieve this objective, laboratory scale batch and column experiments were conducted. The batch experiments were conducted to assess the multiphase behaviour of the water/NAPL/ethanol system, namely the solubility and interfacial tension of the multiphase system. Upward flow experiments were then performed to evaluate the pure and multi-component NAPL recovery efficiencies. Results from these experiments show that for a 50% ethanol content by volume in the flushing solution, mobility is the dominant recovery mechanism for NAPL toluene, benzene and NAPL mixtures consisting of benzene and toluene. Moreover, while the mobility and dissolution processes are generally considered to be independent of each other, the flushing experiments conducted in this experiment show that the mobilization increases the mixing of the NAPL with the flushing solution which in turn increases the mass transfer rate leading to enhanced solubilization of the NAPL.