Refractory Organic Substances in Capillary Fringes: Dynamics, Gradients and Reactions

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The capillary fringe is a highly active zone for chemical and biochemical transformation. Due to the broad abundance of synthetic organic micro-pollutants it is a basic question with high ecological significance how these substances behave in the unsaturated and saturated zone, and how these substances are biodegradable. The possible transformation of the pollutants and the integration of their metabolites into the biogeogenic organic matrix (bound residues) is fundamental but not well understood. It can be expected that the fringe zone with its bioactivity will be highly active for degradation and transformation of substances. The main objective of this project is to study mass transfer and biological transformation of organic compounds across the capillary fringe. Relevant processes and the main parameters influencing the reactions will be quantified. By this, studies in a 2D-tank (horizontal and vertical flow), column (vertical flow) and batch (diffusion) experiments will be performed. Mass transfer of the compounds of interest (phenol, salicylic acid, benzene sulfonic acid, X-ray contrast media and atrazine) will be measured as a function of horizontal flow velocity of the water, water table fluctuation amplitude and frequency, variable infiltration flux, composition of the aqueous phase (high and low ionic strength, NOM concentration) and the bioactivity of the fringe zone.