Significant challenges remain in remediating low-permeability porous media (e.g. clays, silts) contaminated with organic contaminants. Current remediation technologies such as in-situ chemical oxidation (ISCO) are often ineffective, with treatment limited by very slow rates of groundwater advection and molecular diffusion. Previous studies indicated that electrokinetic transport (EK), as induced by electric field application, increased transport rates of charged solutes through low-permeability sediments. Research into utilising EK to deliver oxidants (EK-ISCO) was conducted by the University of Western Australia and Golder Associates as an ARC Linkage project. In laboratory tests, application of direct current resulted in permanganate transport within clay, however this stalled after some time. A specially-designed experimental apparatus showed that stalling could be mitigated by controlling the electrode reservoir pH, resulting in breakthrough of permanganate through the clay. Experiments assessing persulfate transport via EK-ISCO through dichloroethane contaminated peat found that transport was inhibited by natural oxidant demand. This was found to be a key factor for determining persulfate dosage. A numerical model was developed that simulates groundwater flow and multi-species reactive transport under both hydraulic and electric gradients. Modelling and experimental studies evaluated different strategies for field implementation. The technology is currently being trialled to deliver bioremediation agents and oxidants in North America and Europe.

Electrokinetic experiments were undertaken to transport permanganate (MnO4-) through a low permeability porous media. The experiments employed a one-dimensional apparatus in which MnO4- was electromigrated through a central porous media core. Two outer porous media cores separated the electrode reservoirs from the inner permanganate source and permanganate target reservoirs. By utilizing a pH-isolation technique, whereby electrolysis reactions occurring at electrodes were isolated, uniform and repeatable MnO4- electromigration was achieved. This result was compared with non-pH-isolated experiments (normal mode), which resulted in a stalled MnO4- electromigration front. The research also investigated potential stalling mechanisms, including voltage gradient nonlinearity through the central porous media core and the reduction of MnO4- to Mn2+. It was observed that the voltage gradient decreased as a result of MnO4- stalling; however, it was not considered a stalling mechanism. Results from Mn2+ analysis determined that the Mn2+ distribution for normal modde experiments extended partially beyond the extent of MnO4- electromigration; however, competing ions interfered with the analysis and definitive conclusions could not be made. pH-isolated experiments described in this research provide a simple method for implementing electrokinetic in situ chemical oxidation as a groundwater remediation technique where low permeability porous media exists. DOI: 10.1061/(ASCE)EE.1943-7870.0000660. (C) 2013 American Society of Civil Engineers.

A newly developed groundwater and electrokinetic (EK) flow and reactive transport numerical model was applied to simulate electrokinetic in situ chemical oxidation (EK-ISCO) remediation. Scenario simulations that considered the oxidation of a typical organic contaminant (tetrachloroethene) by permanganate were used to gain a better understanding of the key processes and parameters that control remediation efficiency. In a first step a sensitivity analysis was carried out to investigate a range of EK, hydraulic and engineering parameters on the performance of EK-ISCO. While all investigated parameters affected the remediation process to some extent, the duration and energy required for remediation were shown to be most dependent upon the applied voltage gradient, the natural oxidant demand and the concentration of the injected oxidant. Secondly, the efficacy of EK-induced oxidant transport was further examined for a heterogeneous aquifer system with random permeability fields. Oxidant migration under EK was slower in low-permeability media due to the increased oxidant consumption of competing reductants. Instead of injecting oxidant only at the cathode, locating injection wells between the electrodes greatly increased the contaminant degradation by decreasing the distance the amendment had to migrate before reaching the contaminant.

A new numerical model is presented that simulates groundwater flow and multi-species reactive transport under hydraulic and electrical gradients. Coupled into the existing, reactive transport model PHT3D, the model was verified against published analytical and experimental studies, and has applications in remediation cases where the geochemistry plays an important role.A promising method for remediation of low-permeability aquifers is the electrokinetic transport of amendments for in situ chemical oxidation. Numerical modelling showed that amendment injection resulted in the voltage gradient adjacent to the cathode decreasing below a linear gradient, producing a lower achievable concentration of the amendment in the medium. An analytical method is derived to estimate the achievable amendment concentration based on the inlet concentration. Even with low achievable concentrations, analysis showed that electrokinetic remediation is feasible due to its ability to deliver a significantly higher mass flux in low-permeability media than under a hydraulic gradient. (C) 2011 Elsevier Ltd. All rights reserved.

Numerical simulations were used to identify and evaluate optimum electrode configurations and approaches for electrokinetic in situ chemical oxidation (EK-ISCO) remediation of low-permeability sediments. A newly developed groundwater and EK flow and reactive transport numerical model was used to conduct two-dimensional scenario simulations of the coverage of an injected oxidant, permanganate, and the oxidation of a typical organic contaminant (tetrachloroethene, PCE). For linear configurations of vertical electrodes, the spacing of same-polarity electrodes is recommended to be about one-third to one-quarter of the anodecathode spacing. Greater coverage could also be achieved by locating additional oxidant injection wells at the divergence of the electric field in linear electrode configurations. Horizontal electrodes allowed greater contact between the injected permanganate and PCE and resulted in faster degradation of PCE compared to vertical electrodes. Pulsed oxidant injection, closer electrode spacing, and electric field reversal also resulted in faster EK-ISCO remediation.

A promising method for remediation of low-permeability aquifers is the electrokinetic transport of amendments for in-situ chemical oxidation. Laboratory results have shown the approach to be capable of migrating chemicals through low permeability clays at rates orders of magnitude greater than hydraulic advection or diffusion. Stalling or rapid dispersion of the treatment fluid fronts, however, was observed in most experiments. Stalling is attributed to the influence of low pH due to the migration of H+ generated through electrolysis at the anode. Numerical modelling showed that amendment injection resulted in the voltage gradient adjacent to the cathode decreasing below a linear gradient resulting in a higher voltage gradient with distance from the injection point, and therefore lower achievable concentrations of the amendment in the medium. Even with low achievable concentrations, analysis showed that electrokinetic remediation is feasible due to its ability to deliver a significantly higher mass flux in low permeability media than under a hydraulic gradient.

Research has been conducted to evaluate if electrophoresis could transport surface stabilized nanoscale zerovalent iron (nZVI) through fine grained sand with the intent of remediating a contaminant in situ. The experimental procedure involved determining the transport rates of polymer modified nZVI and hematite in fine grained sands under an applied electrical gradient under different physical and chemical conditions. Results indicated transport of polymer modified nZVI and hematite can be accomplished by electrophoresis, with rates found to be much higher than diffusion alone and comparable to those predicted by electrokinetic theory. This study indicates there is potential for this method to deliver polymer modified nZVI into contaminated zones within fine grained sands for the purpose of remediation.

An apparatus was designed, manufactured, and implemented to isolate pH during electrokinetic in situ chemical oxidation (EK-ISCO). H+ and OH- electromigration were used to determine the adequacy of the designed apparatus for pH isolation. A series of pH-isolation and normal-mode (no pH-isolation) experiments were undertaken and compared. It was found that pH isolation was achieved when the electrode reservoirs were separated by porous media combined with the purging of the electrode reservoir fluid. The electromigration retardation factor of H+ and OH- was calculated for the porous media using the observed pH breakthrough times. The retardation factor for H+ was also calculated by considering mass flux data. The retardation factors for H+ and OH- were found to be 28.3 and 95, respectively, when using the breakthrough time. The retardation factor for H+ was calculated to be 36.7 using the mass flux data. DOI: 10.1061/(ASCE)EE.1943-7870.0000385. (C) 2011 American Society of Civil Engineers.

This research was conducted to evaluate the combination of electromigration and potassium permanganate as a potential remediation method for low-permeability media (e.g., soil and sediment) contaminated with dissolved and sorbed organic contaminants. The experimental procedure was composed of two stages: determination of migration rates of permanganate through homogeneous cores and a primarily qualitative analysis of migration in more heterogeneous, two-dimensional scenarios. Results indicated that transport of permanganate through fine-grained porous media and clays can be undertaken using electromigration, and electromigration rates were found to be at least 400% faster than diffusion alone. In addition, the use of an applied electric field in a flushing scenario was shown to result in almost 100% sweep efficiency of a domain consisting of clay blocks interspersed in a glass bead medium. The results of the study show that there is potential for this method to be able to deliver permanganate and other potential remedial agents to treat contaminated zones within heterogeneous and low-permeability porous media through in situ chemical oxidation or other processes.

On the basis of a combination of laboratory microcosm experiments, column sorption experiments, and the current spatial distribution of groundwater concentrations, the origin of a mixed brominated ethene groundwater plume and its degradation pathway were hypothesized. The contaminant groundwater plume was detected downgradient of a former mineral processing facility, and consisted of tribromoethene (TriBE), cis-1,2-dibromoethene (c-DBE), trans-1,2-dibromoethene (t-DBE), and vinyl bromide (VB). The combined laboratory and field data provided strong evidence that the origin of the mixed brominated ethene plume was a result of dissolution of the dense non-aqueous-phase liquid 1,1,2,2-tetrabromoethane (TBA) atthe presumed source zone, which degraded rapidly (half-life of 0.2 days) to form TriBE in near stoichiometric amounts. TriBE then degraded (half-life of 96 days) to form c-DBE, t-DBE, and VB via a reductive debromination degradation pathway. Slow degradation of c-DBE (half-life >220 days), t-DBE (half-life 220 days), and VB (half-life >220 days) coupled with their low retardation coefficients (1.2, 1.2, and 1.0 respectively) resulted in the formation of an extensive mixed brominated ethene contaminant plume. Without this clearer understanding of the mechanism for TBA degradation, the origin of the mixed brominated ethene groundwater contamination could have been misinterpreted, and inappropriate and ineffective source zone and groundwater remediation techniques could be applied.