Studies On Electrokinetic Remediaiton Of Persistent Toxic Substance Contaminated Soils/Sediments

Persistent toxic substances (PTS), such as persistent organic pollutants (POPs) and heavy metals, migrate with atmospherical settling, raining and surface run off, deposit in soils and sediment and lead to soil and sediment pollution. It is therefore necessary to remediate the polluted sites. However, most remediation technologies are suitable to permeable soils. Electrikinetic (EK), which utilizes electric field to drive the movement of pollutants in soils, has shown great potential in the remediation of clayed soils.This study reviewed the literatures on EK remediation and point out the problems involved in the process. The efficiency and mechanism of EK remediation of soils contaminated with POPs such as polychlorinated aromatic hydrocarbons are still unknowm. The electric energy consumption of EK remediation is relatively high, which restricted the extensive practical application. It is possible to integrate the EK movement of organic pollutants in soils and the in situ electrochemical degradation in aqueous solutions.Therefore, this paper first investigated the EK movement of hexachlorobenzene (HCB), a typical polychlorinated aromatic hydrocarbon, in soils. In order to reduce electric consumption in EK process, a novel galvanic cell EK process was developed. The electrochemical degradation of toxic organic pollutants was studied to provide useful information on the integration of EK migration and in situ electrochemical degradation. The main conclusions are drawn as follows:(1) The potential of single surfactants to enhance the desorption of HCB from soil was obtained as Tween 80 > sodium dodecyl benzene sulfonic (SDBS) > myristyl pyridinium bromide (MPB). All the surfactants were largely adsorbed on soil and the sorption followed MPB > Tween 80 > SDBS. The desorption of HCB increased significantly and linearly with the increase of the aqueous micelle concentrations of surfactants. Optimal combination of surfactants could reduce the sorption loss of surfactants.(2) With the increase of buffering capacity of anodic purging solution (0?0.05 mmol/L), electroosmotic flow (EOF) fisrt increased and then decreased. EOF decreased with the increase of ionic strength. Addition of Tween 80 orβ-CD to anodic purging solution could highly attribute to the movement of HCB. Althoughβ-CD led to less desorption of HCB from soil than Tween 80, the migration of HCB withβ-CD was more significant than that with Tween 80. The mechanism of HCB movement involved the desorption of HCB from soil to pore solution and the subsequent migration with electroosmotic flow. The EK movement of less chlorinated benzenes was significant and the efficiency increased with the increase of their aqueous solubility.(3) It is feasible to drive the electromigration of heavy metals in soil by a galvanic cell constructed with iron and carbon. The migration of copper in soil increased with the drop of soil pH. The series of multiple galvanic cells could expand the treatment area, but the migration of cadmium of each cell in the series was lower than that in separated cell. Copper in sediment could be also removed by the galvanic cell and the removal efficiency increased with the increase of electrolyte in sediment or the decrease of electrolyte in supernatant water.(4) The EK movement of nitrophenol in soil driven by the galvanic cell was insignificant. Nitrophenol in soil could diffuse into electrode compartments. Nitrophenol in sediment diffused into supernatant water and was then removed by carbon adsorption, iron reduction, volatilization and natural degradation. The reduction of nitrophenol on iron stick was clear and could be enhanced when a carbon stick was connected. The reduction of nitrophenol in both cases rose with the drop of aqueous pH.(5) In the EK remediation of organic compound polluted soils, it is possible to integrate the EK movement of organic compounds from soils to compartments and the electrochemical degradation of the compound in the compartments via conditioning the EK parameters. This integration may avoid post-treatment or reduce the post-treatment difficulty, inhibit the evolution of H2 and O2, and decrease the change of soil characteristics.