Browsing by Author "Boer, Cjestmir Volkert de"

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Open Access
Transport of nano sized zero valent iron colloids during injection into the subsurface
(2012) Boer, Cjestmir Volkert de; Helmig, Rainer (Prof. Dr.-Ing.)
One of the recent In-Situ groundwater remediation techniques under development uses reactive zero valent iron (ZVI) to turn highly toxic chlorinated hydrocarbons (CHCs) into harmless compounds. CHCs are non miscible and characterized by a low solubility which determines their slow dissolution (over decades or centuries) into groundwater, forming plumes that can target drinking water wells, rivers and lakes. Injection of nano sized zero valent iron (nZVI) suspension into the subsurface could target the contaminants directly in the source zone. The high reactivity of nZVI together with the injection into the source fastens the depletion of the contaminant and interrupts the plume generation. The presented work focused on the transport of nZVI during the injection. To make quantitative descriptions of transport possible, an effective detection technique was developed. Exact concentrations of nZVI inside the porous medium was measured through changes in susceptibility detected with electromagnetic induction sensors. Mobility tests with different suspension concentrations were performed in a 1-D horizontally orientated two meter long column. Continuous concentration measurements were performed over the whole length of the column. In a near field scale container experiment a confined aquifer with a radial flow field over a radius of almost two meters was simulated. Different injection rates and pumping techniques were tested inside this experimental set up. A discretization method to represent all effects of a radial flow field using sets of columns was developed. The method could be verified successfully by comparing the concentration profiles to the results obtained from the container experiments. A mathematical model, developed by starting from the classic colloid filtration theory and by considering the transport of primary colloids and aggregates separately, was able to be fitted on the 1-D results. After implementation in a numerical solver, the model was furthermore capable of providing a very good fit on the results of the radial geometry tests while using exclusively the fitted parameters obtained from the 1-D tests. Throughout the work a better understanding of the transport of nZVI during the injection was developed. It was demonstrated that transport of nZVI without modification was possible over a distance of two meters in both 1-D and radial geometry flow fields. An extrapolation of the work for field application was furthermore described. By applying the methods developed in this work the necessary suspension concentration, the volume of suspension and the injection rate could be determined in advance. The presented work showed promising results and could be a sound scientific basis for further investigations and case studies on nZVI based remediation.