Permeable reactive barrier

A permeable reactive barrier (PRB), also referred to as a permeable reactive treatment zone (PRTZ), is a developing technology that has been recognized as being a cost-effective technology for in situ (at the site) groundwater remediation. PRBs are barriers which allow some—but not all—materials to pass through. One definition for PRBs is an in situ treatment zone that passively captures a plume of contaminants and removes or breaks down the contaminants, releasing uncontaminated water. The primary removal methods include: (1) sorption and precipitation, (2) chemical reaction, and (3) reactions involving biological mechanisms.

The first field-scale application of PRBs in groundwater remediation was done in Base Borden, Ontario by Robert Gillham and Stephanie O'Hannesin of the University of Waterloo. The design, typical of many PRBs, consisted of a treatment zone formed by excavating an area isolated by sheet piles, refilling the hole with a mixture of granular iron and sand, and removing the sheet pile to leave an in situ, permeable, iron-bearing treatment zone. The contaminants, chlorinated ethylenes (PCE and TCE), were removed, leaving, for the most part, fully dechlorinated groundwater (little vinyl chloride was observed).

The success of the field test at Base Borden eventually led to commercialization of this technology. Since then, a great deal of interest has developed in the groundwater remediation community over the prospects of new treatment strategies (especially PRBs based on contaminant reduction by granular iron and other zero valent metals (ZVMs)). There have now been many feasibility studies, pilot tests, demonstration projects, and full-scale applications performed by numerous groups.

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

Immobilization of the contaminant may occur through sorption to the barrier materials or precipitation from the dissolved state. Organic compounds tend to be undergo sorption due to hydrophobic expulsion from the surrounding water. Metals, however, tend to sorb through electrostatic attraction or surface complexation reactions. Sorption and precipitation are potentially reversible and may thus require removal of the reactive medium and gathered products in order to continue with remediation.

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