This thesis studies the effects of certain organic compounds upon the bacterial deposition of ferric hydroxide from ferric ammonium citrate.

Bioavailability denotes the ‘degree of interaction of chemicals with living organisms’. High bioavailability is generally needed for efficient biodegradation of environmental contaminants. Therefore, technologies to promote contaminant availability should foster bacterial transport and/or control interactions of chemicals with environmental matrices. Direct current (DC) electric fields and their electrokinetic phenomena (electro-migration, electroosmosis, and electrophoresis) have the potential to promote contaminant bioavailability by both mobilizing bacteria and contaminants. This thesis hence tested electrokinetic factors affecting bacterial transport and deposition and the interactions of contaminants with geo-sorbents, respectively. Studying electrokinetic effects on bacterial transport, we found that DC fields significantly changed bacterial deposition during transport in percolated laboratory columns. By calculating the bacteria collector interaction force FDLVO, the electroosmotic shear force FEOF, the electrophoretic drag force FEP, and the hydraulic shear force FHF, we developed an approach that interlinked the net forces Fnet on a bacterium to observed deposition efficiencies. The driving factor of electrokinetic effects was found to be the relative strength of |FEOF| and |FEP|. If |FEOF| > |FEP|, increased bacterial deposition efficiency and if |FEOF| < |FEP| decreased bacterial deposition efficiency was predicted. Investigating electrokinetic effects on bacterial deposition on planar surfaces using quartz crystal microbalance with dissipation (QCM-D) we confirmed our model by using different bacteria at varying ionic strengths of the electrolyte and of the DC electric applied, respectively. Our model can be used to predict DC field effects on bacterial deposition. Investigating the electrokinetic effects on the sorption/desorption of the model polycyclic aromatic hydrocarbon contaminant phenanthrene (PHE) we found that DC fields changed the rates and extents of PHE sorption and desorption in all geo-sorbents. Matrices of varying sorption strengths were tested. In strongly sorbing carbonaceous sorbents, the electroosmotic flow (EOF) increased the rates of PHE sorption and reduced PHE desorption while in more weakly sorbing matrices, EOF significantly reduced PHE sorption and increased its desorption. By interlinking the Gibbs free energy change of sorption (ΔGº) and the EOF velocity, an approach was developed to estimate electrokinetic effects on the sorption and desorption of PHE. The results of this thesis propose that electrokinetic phenomena have significant impact on both freely dissolved contaminant concentrations and bacterial deposition in porous media. They hence have high effect on contaminant bioavailability. Using conceptual approaches interlinking the electrokinetic forces with ΔGº and bacteria-matrix interactions energies (GDLVO), respectively, we were able to estimate electrokinetic effects on bacterial deposition and contaminant release. Our data thus give rise to future technical applications to control the bioavailability in natural and manmade ecosystems.