Reactive wall

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A reactive wall (English: Permeable Reactive Barrier) is a construction in the ground through which contaminated groundwater flows and is cleaned. In most cases it has a thickness of 0.3 m to 2 m and extends up to 35 m into the ground. The width of the construction depends on the width of the pollutant-bearing groundwater flow. The groundwater flow can be influenced by additional construction measures, such as the construction of underground seals.

The active material of the wall is selected depending on the pollutant. For example, to remove volatile chlorinated hydrocarbons (LCKW) from the groundwater, elemental iron is introduced in the form of granules or as a sponge iron for dechlorination and thus to break down the pollutant. An alternative is the use of activated carbon , whereby the pollutant is spatially bound.

The most common alternatives to the reactive wall are excavating the ground or pumping out the groundwater with an above-ground cleaning system ( Pump and Treat ).

Reactive processes

There are a variety of ways that permeable reactive membranes can be used to remediate groundwater. The two main processes are immobilization (also known as sequestration) and transformation.

Immobilization

The impurity can be immobilized by sorption on the barrier materials or by precipitation from the dissolved state. Organic compounds tend to sorb due to the hydrophobic expulsion from the surrounding water. However, metals tend to sorb through electrostatic attraction or surface complexation reactions. Sorption and precipitation are potentially reversible and, therefore, may require removal of the reactive medium and collected products in order to proceed with remediation.

transformation

During the transformation, the impurity is picked up and converted into a less harmful or non-toxic form. One of the main advantages of transformation is that the reactive medium does not necessarily need to be removed (unless the reactive medium needs to be replaced due to decreased effectiveness or clogging occurs). The transformation takes place most often in the form of an irreversible redox reaction . The medium can directly deliver electrons for reduction or stimulate microorganisms to facilitate electron transfer.

Web links

Individual evidence

  1. ↑ a b Michelle M. Scherer, Sascha Richter, Richard L. Valentine & Pedro JJ Alvarez: Chemistry and Microbiology of Permeable Reactive Barriers for In Situ Groundwater Clean up. In: Critical Reviews in Environmental Science and Technology. 30, 2000, p. 363, doi : 10.1080 / 10643380091184219 .