Afprøvning af ny elektrokemisk metode til oprensning af olieforurenet jord og grundvand

English Summary

Background for the technology project

The present technology project has been prepared on the basis of field experiences obtained with a new electrochemical in-situ technology for remediation of soil and groundwater contaminated with petroleum hydrocarbons. The technology is based on application of a direct current to the soil matrix.

"Geooxidation"

The technology was introduced in Denmark in 1996 under the name "Geooxidation". During the period 1996-2000, a number of in-situ remediation projects were carried out at sites contaminated with petroleum hydrocarbons. Most of the projects were carried out as test projects by Oliebranchens Miljøpulje.

The technology report uses one of the field projects carried out by Oliebranchens Miljøpulje as its starting point. An extensive monitoring program including soil and groundwater related chemical parameters, funded by the "Programme for Technology Development" under the Danish EPA, was carried out at this site concurrently with the remediation effort. The extensive monitoring program was carried out in order to determine the influence of the technology in reducing gasoline content in the soil matrix, as well as gasoline and MTBE contents in the groundwater. Also the monitoring program was carried out in order to facilitate a better description of the technology, and evaluate the possible risks associated with the application of direct current for in-situ remediation. The field project was carried out during the period August 21, 1998, through March 31, 2000.

General experiences

In order to strengthen the report’s conclusions regarding the general applicability of the technology, available data from the other field projects applying the technology, carried out by Oliebranchens Miljøpulje, were collected and evaluated. This part of the project was funded by the "Programme for Technology Development" under the Danish EPA.

Expectations for the technology

The contractors providing the electrochemical technology, introduced the technology as cost-effective for remediation of petroleum hydrocarbon contamination in low permeable soils, and with expected clean-up times of 3 to 12 months.

Knowledge level

The present understanding of the degree to which the electrical field induces or enhances chemical and/or biological processes responsible for removal of organic contaminants is insufficient. Hence, an adequate theoretical description and documentation based on laboratory tests, and carried out under controlled conditions, is required in order to document the conditions required for possible enhanced contaminant removal by the electrochemical method.

Corrosion risk

Field experiences have shown that the applied direct current electrical field entails a considerable risk of corrosion damages. Hence, mapping of all installations in and around the imposed electrical field should precede the application of direct current for in-situ site remediation, in order to assess the need for corrosion protection of exposed installations.

Groundwater chemistry

The monitoring results for a number of soil and groundwater related chemical parameters did not reveal notable changes in the soil and groundwater chemistry during site remediation. Hence, it is concluded that well known electrochemical phenomena, such as changes in pH, relating to hydrolysis of water molecules, ion transport, electro-osmosis etc. have occurred only to a minor degree due to the continuous supply of groundwater, and the low-intensity electrical field applied at the project location.

The results from the extensive field project and the general results obtained at all of the field projects carried out in Denmark, show that the technology expectations have not been met. Hence, at this point in time, all remediation efforts based on the technology, and mentioned in the present report, have been terminated, and none of the sites have been able to meet site closure criteria by use of the electrochemical technology alone.

The remediation efforts have been carried out at gasoline and diesel polluted sites in different soil types and under varying redox conditions. It was not documented that these conditions influence the remediation efficiency.

Need for further documentation

It is concluded, that a thorough documentation of the technology, based on laboratory experiments under controlled conditions, should be obtained before further field application of the technology in its present form. Laboratory results should document whether electrochemically induced reactions can remove petroleum hydrocarbons in soil, and if so, under which conditions.

Electrokinetic methods

The electrochemical technology, as presented in this project, has not been designed for utilization of electrokinetic transport processes induced by direct current application to the soil matrix. Electrokinetically based technologies, for remediation of soil polluted with petroleum hydrocarbons, are under continuous development, and there is still a large development potential for such technologies.