Permeable reactive barrier (PRB) is a technique for the remediation of contaminated sites.
The operating principle is based on the excavation of a trench downstream of the land to be recovered, which is filled with a reactive material (i.e. capable of degrading pollutants to non-toxic, or less toxic substances); this can be an adsorbent, filtering or biological material capable of degrading contamination. Groundwater movements lead polluted water to transit through the barrier, in which biological and oxidation-reduction reactions take place that lower the concentration of certain pollutants.

The purpose of this technique is to prevent the spread of contamination, released from the soil into the groundwater, to areas outside the remediation site.

The PRB prototype simulates the slow filtration flow of groundwater and the spillage of a solution containing petroleum hydrocarbons.
In this way, an artificial contamination plume is produced, which, thanks to the flow of the groundwater, crosses the reactive barrier.
The purpose of the prototype is to analyze the spread of contamination and the barrier’s ability to degrade the contaminant before it crosses it completely.

The prototype consists of a transparent polymethylmethacrylate tank, divided into communicating rooms, in which contaminated experimental soil was placed.
A bio-reactive permeable barrier was reproduced in the center of the tank, consisting of a diaphragm filled with a reactive material and SBP (Small Bioreactor Platforms®) capsules. The capsules were inoculated with microorganisms (Pseudomonas putida bacteria) isolated for their ability to deplete the organic contaminants of interest (TPHs and PAHs).

A combination of modified zeolite and inoculated SBP bio-capsules was tested in the prototype with positive results.
A synergetic effect was attributed to the adsorptive function of the zeolite and the bacterial biomass within the SBP bio-capsules: the zeolites lowered the hydrocarbon levels by physicochemical adsorption and the bio-capsules removed residual contamination by biodegradation.