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1.1.10 Remediation using alcohol – using methods from the crude oil industry as a model

Using methods from the crude oil industry as a model for protecting the environment? A research team from the Versuchseinrichtung zur Grundwasser- und Altlastensanierung (research facility for the remediation of groundwater and abandoned waste, VEGAS) at the University of Stuttgart has shown that this is indeed possible. Experts at the institute for water engineering (IWS) there and the institute for hydromechanics at the University of Karlsruhe (IfH) developed an alcohol-based form of remediation technology for treating contaminated aquifers. They concentrated primarily on contamination through hydrocarbons of varying density and medium to low solubility (LNAPL/DNAPL). Their work has resulted in a procedure that enables aquifers contaminated in this way to be cleaned “in situ” – i.e. in its existing location.

The crude oil industry first of all managed to use traditional pumping methods to extract around 40% of the accumulated crude oil from the discovered source. The main reasons for the low yield were the surface tension and the different viscosities and densities of water and oil. The specialists at the oil company then injected alcohol and tensides into the oil fields as solubilisers to test their effect. These substances reduced the surface tension and significantly increased pumping efficiency.

However, certain types of alcohol prevent the CHCs from moving freely. This put alcohol flushing back in the picture for use in in-situ groundwater remediation. This method is only economically viable though if alcohols can be found that enable a quick and controlled discharge of contaminants in dissolved form or as a free phase and that can be recovered and reused several times during remediation.

Alcohol flushing of aquifers contaminated with LNAPL

Alcohol flushing of aquifers contaminated with LNAPL
Alcohol flushing of aquifers contaminated with LNAPL

Large-scale tests

The BMBF-funded project entitled “Development of an advanced groundwater remediation technique for the removal of anthropogenic chlorinated hydrocarbons with high density (CHC) by alcohol injections” saw scientists from IfH and VEGAS testing whether alcohol flushing was suitable for remediation and investigating how to determine the relevant dimensions. The research focused on efficiency, stability of the cocktail (separability), production costs and above all hydraulic control. On the one hand, this means that a cocktail of alcohol with its specific physical properties must be transported in a targeted manner to the source of the contamination; on the other, that uncontrolled mobilisation of the contamination must be avoided. The IfH investigated what happens when alcohol cocktails are injected in a spatially targeted manner into a contaminated aquifer and whether the effects can remain under control. To clarify these questions, the experts from both institutes performed two large-scale tests among others in realistic conditions.

The researchers produced a mixture of hydrocarbons (BTEX) of low density (LNAPL) in a 6 x 3 x 4 metre tank so that the pollution lay in residual saturation – i.e. captured through capillary forces – beneath the surface of the water and as a floating phase. They then used a horizontal well to target injection of a mixture of alcohol and water (isopropanol and water at a ratio of 60:40) into the artificial aquifer. The alcohol permeated the contaminated region and dissolved the pollution, which could then be pumped out via two vertical wells. The result: almost 90% was removed.

Alcohol flushing of aquifers contaminated with LNAPL

Alcohol flushing of aquifers contaminated with LNAPL
Alcohol flushing of aquifers contaminated with LNAPL

In further tests, the scientists introduced a source of CHC contamination (TCE) to a heterogeneous artificial aquifer in a large tank (9 x 6 x 4.5 m). They used a groundwater circulation well to inject a cocktail of alcohol into the lower regions of the aquifer. At the same time, the same well was used to draw out the mixture of alcohol, water and pollution from the upper regions. Scientists managed again to remove over 90% of the contamination – in dissolved but also mobilised form. It must be emphasised that no uncontrolled downwards vertical displacement of the pollution took place.

The alcohol used was recycled in order to reduce costs and the amount of wastewater. The project team designed and built a wastewater treatment facility for this purpose.

Alcohol cocktails for tough cleanin

These successful tests meant that the researchers could now make more accurate statements on which alcohol cocktails are suitable for which types of remediation. For example, a cocktail of 2-propanol (54% volume), 1-hexanol and water (both 23% volume) is recommended for CHC contamination. This mixture enabled the soil material to be cleaned safely and efficiently in all tests. The required initial concentration of the mixture depends on the flow conditions and the heterogeneity of the soil. It must be noted that the higher the proportion of alcohol, the more expensive the remediation process. The lower the proportion, the greater the risk that the cocktail will separate.

Complex use cases

Finally, the project partners used the test data to produce mathematical equations for the dependency of the density, viscosity and surface tension on temperature and the mixture ratio. They are currently being used to expand the MUFTE-UG (Multiphase Flow, Transport and Energy Model – Unstructured Grid) numeric model at the department of hydromechanics and modelling of hydrosystem at IWS with a module that can simulate a complex multiphase/ multi-component flow.

Project website www.vegasinfo.de

Karlsruhe Institute of Technology (KIT)
Department of Civil Engineering, Geo and Environmental Sciences
Institute of Hydromechanics
Prof. Gerhard H. Jirka
76128 Karlsruhe, Germany
Tel.: +49(0)721/608-2200
Fax.: 0721/608-2202
Funding reference: 02WT0065

University of Stuttgart
Institut für Wasserbau (water engineering institute), VEGAS

Pfaffenwaldring 61
70550 Stuttgart, Germany
Tel.: +49(0)7 11/6 85-6 47 17
Fax: +49(0)7 11/6 85-6 70 20
E-mail: vegas@iws.uni-stuttgart.de
Funding reference: 02WT0064

VEGAS scientific manager
Dr. Jürgen Braun
Tel.: +49(0)7 11/6 85-6 70 18
E-mail: juergen.braun@iws.uni-stuttgart.de

VEGAS technical manager
Dr.-Ing. Hans-Peter Koschitzky
Tel.: +49(0)7 11/6 85-6 47 16
E-mail: hans-peter.koschitzky@iws.uni-stuttgart.de
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