The “Permeable Reactive Barrier” (Multibarrier) technology is an in situ system in which a trench is made perpendicular to the groundwater flow. This trench is filled with a coarse material and induced to treat the pollutants in the passing groundwater. The coarse material can consist of several kinds of materials that induce physical, chemical and biological removal or immobilization of the present pollutants. Examples are e.g. iron fillings to induce reductive dechlorination of VOCLs (reactive barrier) or it can be suitable for the development of a biofilm able to degrade organic compounds like BTEX (Benzene, toluene, ethylbenzene, xylene) or mineral oil (biobarrier). In the latter case, substrates or electron acceptors are infiltrated into the barrier material to stimulate bacterial activity. Finally, the coarse material can be an adsorbing material (for example compost) to remove heavy metals or some other compounds.
Mostly, reactive walls and biobarriers are designed to abate specific pollutants. However, in many cases polluted groundwater contains a mixture of both organic and inorganic contaminants. The abatement of such pollutant mixtures is not possible with a simple barrier based on removal of the pollutants by either physico-chemical or biological way. However, such pollutant mixtures might be treated using a combination of both systems. Such a Multifunctional Permeable Barrier (MULTIBARRIER) concept is based on the combination of a chemical reduction system to dechlorinate the AOX compounds and a biological system to further degrade the organic skeleton of the dechlorinated pollutants and other non-chlorinated pollutants. Furthermore, it can be combined with adsorbing materials such as carbon to remove traces of pesticides and other pollutants (like PCBs). Such an approach requests the efficient synergistic interaction and compatibility of the microbial and physico-chemical key-components of the system, i.e., the biofilm community and the coarse material which can function both as the biofilm support and as reactive material. The MULTIBARRIER-concept was developed in the 5th Framework programme under the contract number QLK3-CT-2000-00163 and proven to be successful.