Brown coal in reactive walls Reactive walls are often the only economically viable means of cleaning or containing large-scale ground water impurities. The cleaning walls are sunk into the ground and filled with reactive materials through which the polluted ground water flows. The harmful substances are removed from the water as a result of their interaction with the reactive filling. The use of this type of wall has already achieved positive results worldwide. Iron and activated carbon are currently the preferred filling materials in reactive walls. While the use of activated carbon entails relatively high costs, iron walls are only suitable for selected halogenated bonds. Suitability proven in practice In cooperation with research facilities, microbiologically populated brown coal was successfully used to clean contaminated ground water (e. g. at the former chemical works in Bitterfeld). The cleaning performance and extended usage period demonstrate that brown coal possesses the potential required to clean contaminated ground water and is particularly suitable for use in reactive walls.