Electro-bioremediation at the prototype scale: what it should be learned for the scale-up

A large scale electro-bioremediation test is carried out in a prototype composed by an electrokinetic soil remediation reactor with soil-treatment capacity of 32 m3. Soil polluted with a mixture of Oxyfluorfen and 2,4-Dichlorophenoxyacetic acid undergoes a combined treatment in which the electrochemically assisted remediation produced by six electrodes placed in a hexagonal alternating configuration is aimed to be enhanced with the addition of concentrated activated sludge in a central position of the prototype. Results demonstrate that this technology can remove pollutants down to a very low concentration although, as compared to a previous study, its performance does not differ significantly of that followed in a process in which bioremediation was not included. In both studies, volatilization was found to be the key mechanisms to explain the removal of both herbicides. After a treatment period slightly over month, only 7.10% of the 2,4-D and 9.22% of the oxyfluorfen remained in soil and these values are very similar to those obtained by applying a non biological electrokinetic remediation fence process in which 10.10% of the 2,4-D and 13.03% of the oxyfluorfen remained in the soil after the treatment. Results pointed out that it is very difficult to optimize simultaneously electrokinetic and biological processes because most of the processes caused by the electric field affect negatively to the microorganisms viability. Results also pointed out the significance of the sampling procedure to characterize an electro-bioremediation process at full scale