Enhanced removal of copper from contaminated silt soil using bioelectrokinesis.

An initial electrokinetic experiment was performed using a characterised silt soil, spiked with 1000 mg/kg of Cu. The results showed that 92% of the Cu was mobilised and recovered in the cathode solution after 15 days treatment. The pH in the soil decreased from 7.5 to 2.1. Time course analyses of soil cores indicated the mobilisation of the metals present in the soil followed the order Ca>Mn>Cu while SO42-, Mg and Fe showed no relative mobility. Cu contaminated silt soil was further amended with 5% (w/w) elemental sulphur in order to stimulate the activity of Sulphur Oxidising Bacteria (SOBs). Soil kept at constant moisture (30%w/v) was acidified to pH 5.4 after 90 days incubation at room temperature (similar to 20 degrees C). Further acidification did not occur, as the presence of partially mobile Cu seemed to inhibit the SOB activity. The soil was packed into the electrokinetic reactor operated at the same current density used in the initial study (3.72 A/m(2)). The data showed that after a 10 day treatment period the pH of the soil profile was <3.0 and 80 % of the Cu was successfully removed. During the electrokinetic process SO42-, concentration across the soil profile significantly increased suggesting that the toxic inhibition of the Cu upon the SOBs was removed as the metal was recovered at the cathode. Ca, Mn, Mg and Fe showed the same order of mobility as reported in the initial run while sulphate accumulated as a band in the middle of the soil cell. Although the total Cu removal (86%) after 16 days treatment was similar to the initial run without SOBs, a cost assessment based on the power consumption revealed that this integrated process could potentially produce substantial energy savings in a full scare treatment system.