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Institute of Hydraulic Engineering

Research: VEGAS - Research Facility for Subsurface Remediation

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Feasibility Study of Co-Solvent Flushing for a DNAPL-Remediation of a Dump Site
Project manager:Dr.-Ing. Hans-Peter Koschitzky, AD
Research assistants:Dipl.-Ing.(FH) Oliver Trötschler
Dr. rer.nat. Karolin Weber, M.Sc.
Duration:1.9.2003 - 31.3.2004
Funding:Solvay (S.A.), Brüssel
Comments:

This project is part of the research area:
In-Situ Remediation Technologies

Publications: Link

Abstract:

The feasibility of an in-situ contaminant phase extraction of highly-chlorinated hydrocarbons below the dump site of production residues using co-solvent flooding (ternary solvent-mixtures) was investigated under contract of an international chemical company.

Both cyclohexane and diethyl ether were selected as co-solvents because of their high partitioning capacity into the contaminant mixture and their ability to transform the contaminant mixture (DNAPL) into a single-phase LNAPL. Additionally, the selected co-solvents were able to dissolve the precipitated tar oil phase. The water-miscible solvents were acetone and 2-propanol.

Four different ternary phase diagrams (TPD) for the solvent-co-solvent-water system were determined in order to define the optimal co-solvent flushing (CSF)-mixture.

No significant differences were observed between the selected CSF-cocktails for a composition of 90/10 %v/v. Therefore, after considering the costs and safety and ecological aspects, the solvent 2-propanol and the co-solvent cyclohexane were selected. Solids and/or highly viscous tar oil precipitated during the determination of the ETPDs.

The hydraulic control of the remediation process may be compromised by a clogging of the aquifer during CSF.

The cost of the chemicals and the recycling of the CSF-cocktail were estimated after the recycling process was designed. Due to the physical and chemical properties of the chemicals, a thermal recycling of the CSF-cocktail by vacuum evaporation was proposed. The costs for the recycling process and the overall costs for the CSF-cocktail needed for the removal of the contaminants were estimated based on the results of previous research work. The costs are roughly estimated to be 800 - 900 €/m³ treated soil for the chemicals and the recycling of the CSF-cocktail.

A more accurate cost estimate must be based on further lab experiments to determine the mass fluxes, the effectiveness and the functionality of the process.