Effect of de-icing salts on the remobilization of retained pollutants on filter materials for treating traffic area runoff
The aim of this research project was the scientific description and determination of the remobilization behavior of heavy metals previously retained on filter materials by various de-icing salts. These filter materials are used in decentralized treatment systems for traffic area runoff. Until now, a test specification is missing in the approval process of the German Centre of Competence for Construction (Deutsches Institut für Bautechnik) that can be used to completely investigate the remobilization behavior. Therefore, no decentralized treatment plant for road runoff is currently available, for which the filter stability considering all relevant de-icing salts is proven.
To elucidate the effect of de-icing salts, an experimental setup was built on a laboratory scale at the Chair of Urban Water Systems Engineering. First, six selected filter materials were loaded in column experiments with the five heavy metals copper, zinc, cadmium, lead, and nickel with defined concentrations on the basis of real traffic area runoff water concentrations. After preloading, different de-icing salt experiments were carried out with pure sodium chloride, with a defined mixture of sodium chloride and calcium chloride, and with a defined mixture of sodium chloride and magnesium chloride, wherein each remobilization test is preceded by a new loading experiment.
Advanced analyses such as particle size distribution, pore volume, pore size distribution, content of heavy metals, specific surface areas, and surface properties, were used to identify different removal mechanisms and to determine the behavior of the filter materials under application of de-icing salts in realistic conditions. Concerning the de-icing salt experiments, the behavior of each filter material, each heavy metal, and each de-icing salt was very heterogeneous regarding the risk and the amount of remobilization.