Micro-emulsions for the in situ-remediation of DNAPL-contaminated sites< Back

Soil extraction with microemulsions represents a new and promising technique to clean-up aquifers contaminated with dense non-aqueous-phase-liquids (DNAPL), e.g. tetrachloroethene. After extracting the DNAPLs, the amount of microemulsion constituents remaining adsorbed onto soil particles is minimized by water flushing. The residual microemulsion components and DNAPL pollutants are to be eliminated by biodegradation. Engineered in-situ bioremediation techniques or/and intrinsic biodegradation processes are considered for this final treatment period. The objective of our investigations is to develop reliable post-extraction biotreatment strategies.

Microemulsions are optically isotropic dispersions of two non-miscible liquids, that are stabilized by at least one amphiphilic component. The main components of the microemulsion are: (i) rape oil methyl ester (RME), (ii) the anionic surfactant AOT [bis(2-ethylhexyl)-sulfosuccinate], (iii) the non-ionic surfactant Uniperol EL [ethoxylated castor oil].
Biodegradation tests are performed in mineral media and under in-situ conditions at the chloroethene contaminated Eppelheim site. In the laboratory, biological O2-consumption is used as on-line parameter to assess microbial turnover and to calculate degradation degrees. Anaerobic degradation tests are performed in the presence of the electron acceptors nitrate, Fe(III), sulfate, and carbonate.

According to the experiments done so far, aerobic as well as anaerobic processes can be applied to eliminate microemulsion residues after DNAPL extraction. In particular the good anaerobic biodegradability of RME is promising with respect to a stimulation of reductive dechlorination of the residual DNAPL contaminants. Our further studies focus on the development of a biotreatment concept integrating aerobic and anaerobic periods in the most economical way.