To evaluate the factors influencing the electrokinetic transport and deposition of fluorene-degrading bacteria (Sphingomonas spec.) in a laboratory model aquifer (packed with glass beads) exposed to a direct current electric field typically used in electro-bioremediation measures.
Electro-bioremediation is a hybrid technology of bioremediation and electrokinetics for the treatment of soil contaminated with hydrophobic organic compounds. Electrokinetics has the potential to enhance the contact probability of the bacteria and their hydrophobic organic compounds substrates by transporting bacteria to contaminant sources or vice versa.
Bacterial transport in porous media is the result of either electrophoretic movement of negatively charged bacteria to the anode and/or bacterial migration with the electro-osmotic water flow to the cathode.
Total numbers of adherent and suspended cells were quantified and analysed at distinct distances from the injection point (0 cm), and at 4.5, 9, and 15 cm towards both electrodes.
More information on setup: Wick LY, Manic PA, Watliou P, Harms H (2004) Elctrokinetic transport of PAH-degrading bacteria in model aquifers and soil, Environ Sci Technol 38:4596-4602
|Chamber||two electrode chambers (2 x 7 x 3.5 cm) at the ends, a lid-covered model aquifer chamber (35.5 x 4 x 3.5 cm) in between and a bypass channel below the aquifer chamber having hydraulic contact with both electrode chambers to exclude advective hydraulic water flow through the aquifer chamber; chambers filled with buffer; aquifer chamber packed with glass beads|
|Sham exposure||A sham exposure was conducted.|
|Additional info||1 ml of bacterial inoculum was slowly injected during 1 min at half of the bed depth at equal distance from the two electrodes in the centre of the aquifer chamber.|
In presence of DC the cells were predominantly mobilised by electro-osmosis to the cathode with a velocity of 0.6 cm/h, whereas a minor fraction was mobilised to the anode by electrophoresis. Different electrokinetic behaviour of individual cells could be solely attributed to intra-population heterogeneity of the cell surface charge. In the absence of DC by contrast, a Gaussian-type distribution of bacteria around the point of injection was found.
DC had no influence on the deposition efficiency, as the glass beads in presence and absence of an electric field retained quasi-equal fractions of the cells. Propidium iodide staining and flow cytometry analysis indicated the absence of negative influences of DC on the cell wall integrity of electrokinetically mobilised cells and thus point at unchanged physiological fitness of electrokinetically mobilised bacteria.
Given the right conditions and organisms, electrokinetic dispersion could be used to distribute specialised bacteria in hotspots of contamination, e.g. in aquifer sediments.