Electrokinetics

Electrokinetics (EK) uses a direct current (DC) voltage applied to the subsurface to migrate charged and dissolved non-charged ions through low permeability regions at rates orders of magnitude greater than can be achieved by flushing or hydraulic methods. EK can be applied to improve the effectiveness of ISCO for the remediation of contaminant mass that is stored in low permeability zones is the application of electrokinetics. Recently, one of our industrial partners has very been investigating the potential for using this technique to deliver oxidants into low permeability zones. The applied voltage also results in electroosmosis, which is the bulk migration of water from one electrode to the other due to the charged double layer present on many soils. Electroosmosis and electromigration can be used in conjunction to migrate treatment compounds in different directions within the subsurface.

Since NZVI and chemical oxidants such as permanganate have a net negative charge EK has been proposed to enhance their transport in the subsurface (Reynolds et al., 2008; Jones et al., 2010). Ideally permanganate and NZVI would be attracted to and migrate towards the anode, via EK, due to their net negative charges. The impact of EK enhanced migration will be most significant in fine grained soils with very low hydraulic conductivity (Kh). Since electrophoretic velocity is independent of soil media permeability, decreasing permeability does not affect the EK migration. This will potentially allow emplacement of NZVI and negatively charged oxidants in fine grained soils such as clays. Although EK holds significant promise to deliver either ISCO or NZVI it has not been rigorously tested in large scale laboratory experiments or at the field scale. In addition to scale-up issues, there are significant scientific and engineering issues to address associated with control of pH and oxygen and hydrogen build-up at the electrodes.

How does it work?