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 tensionAn interfacial surface is the contact zone between two phases, e.g. between water and air or between oil and water. Surface tension causes the surface of a liquid to behave like an elastic film. and the different viscositiesViscosity is the resistance of a liquid to flow. It is defined by the frictional resistance offered by a liquid against deformation. 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 phaseThe individual parts in a mixture of different substances (e.g. a liquid with a solid) are known as -> phases. The “free phase” is the part of a liquid (or gas liquid or gaseous phase) that is not bound (sorbed) to the solid parts of the mixture (solid phase) via bonding forces. and that can be recovered and reused several times during remediation.

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 aquiferIn the field of hydrogeology, an aquifer (from the Latin words aqua = water, and ferre = to bear or carry) is an underground layer carrying groundwater. Aquifers are also referred to as water-bearing strata. Different types of aquifer are distinguished depending on the individual rock type (and thus the rock’s porosity). 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 (BTEXAromatic hydrocarbons (benzene, toluene, ethyl benzene, xylene)) of low density (LNAPLMost hydrocarbons (i.e. non-chlorinated compounds, See: DNAPL) are lighter than water and form phases that float on its surface (e.g. on groundwater). Organic liquids with densities less than 1 g/cm3 are known as light non-aqueous phase liquids (LNAPL). The most important LNAPL compounds are fuels (gasoline, kerosene, diesel), with heating oil EL being another example. The ->BTEX compounds are of particular relevance in this regard.) 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.

In further tests, the scientists introduced a source of CHCCollective name for organic compounds containing at least one chlorine atom bound directly to a carbon atom. CHCs are contained in many products and are used as base materials in the chemical industry, as solvents and as pesticides. As a result of their wide-spread use and high stability, CHCs are now ubiquitous in the environment. 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, viscosityViscosity is the resistance of a liquid to flow. It is defined by the frictional resistance offered by a liquid against deformation. and surface tensionAn interfacial surface is the contact zone between two phases, e.g. between water and air or between oil and water. Surface tension causes the surface of a liquid to behave like an elastic film. 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

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1.1.11 Heat as an accelerator

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1.1.09 VEGAS research facility