Breakdown of Fuel Componets and Solvents in Groundwater and Contaminated Soil
E. ELGRESSY L.t.d has developed the EBR system (Electro-Bioremediation), the EK system (Electro-Kinetic) and E.F system (Electro-Fenton) for groundwater and soil remediation.
These systems are appropriate for in-situ treatment of a wide range of contaminants such as fuel compounds and chlorinated solvents.
Unsaturated zone and groundwater are commonly polluted by disintegration of underground storage vessels, pesticide residues, penetration of polluted water from higher layers, infiltration of waste from dumps or direct disposal of industrial spillage to the ground and groundwater. Accordingly, the most common contaminants are fuel compounds, solvents, pesticides, lead and other heavy metals.
E.ELGRESSY has developed a modern patent systems that treat contaminated groundwater and soil by means of electrolysis. This fact provide the technology with great advantages such as low cost (compare to other remediation technologies), low maintenance expenses, elimination of air pollution (as opposed to SVE systems), remote control and long-term rehabilitation skills.
History of electrochemical soil remediation methods
The effects of applying an electric potential to a soil were first tested during the 1930s. Casagrande (1948) was the pioneer who started to use the electro-osmotic effect for dewatering fine grained soils. He used that technique to stabilize earth masses where classical methods had failed.
Brush and Lewis (1973) proposed to extend the usefulness of the electro- kinetic phenomenon to being a tool in ground water pollution control in soils of low hydraulic permeability. In 1980 the movement of heavy metals in a soil in an applied electric field was first reported by Segall and others. In the liquid samples from the process they found various heavy metals. Even though this was just noted in the actual work, this finding given different researchers the idea of using an applied electric field for soil remediation.
In 1981s more teams started to develop electrochemical remediation methods.
The majority of the published research conducted in the late 1980s and early 1990s
Soils polluted with heavy metal pose a major risk to water quality and human health. Remediation of fine grained soils, polluted with heavy metals, is difficult or even impossible by traditional methods. However, E. ELGRESSY technologies are very effective in fine grained soils.
Electrochemical soil remediation methods are based on the transport processes that occur due to an electric current that passes through the soil medium.
The electric current passes through the micro pores, where resistance is low and heavy metals accumulate. Therefore, electrochemical methods are especially suitable for highly-porous fine grained soils.
Ionic-contaminated ground and groundwater are hard to recover because soil is a powerful ion exchange medium. Ions of heavy metals, such as cyanide and arsenic, are adsorbed to soil particles. Negatively charged soil particles causes an accumulation of positively charged cations on the surface, creating a diffuse electric double layer. Accordingly, flushing is inefficient in trying to desorb and mobilize these contaminants, and flushing with strong acids may destroy the basic soil structure. Electro-kinetic acidification is an alternative solution that uses physicochemical remediation techniques. Instead of flushing with acidic chemicals the EK system introduce a direct-current (DC) to the soil so that ions start to move in a specific direction, forcing the water molecules to move with them. Three electro-kinetic phenomena occur under the influence of an electric field:
1- Electrophoresis = the movement of charged particles through the soil media.
2- Electro osmosis = the movement of water from anode to cathode.
3- Electro migration = the movement of ionic species in pore water or groundwater.
Electrophoresis is the movement of particles under the influence of E field. The movement of these particles is similar to the movement of ions. In the pore fluid of clay soils, the particles participate in the transfer of electrical charges and influence the electrical conductivity and the electro osmotic flow. The minerals can polarize in two ways: The first is the permanent dipole moment, which results from the structure and depends on the atomic masses, and the second polarity is perpendicular to the first one and is a result of the external electrical field. It depends on the polarization capacity of the electrical double layer.
The mobility of particles depends on the combined action of these two moments, and varying between 1.10-10 and 3.10-9 m²/U.s .
Electro osmosis is the movement of pore water or groundwater under the influence of a DC field. With electro osmosis the direction of flow is from anode to cathode. In some cases one can also observe a flow from cathode to the anode. This phenomenon is known as electro endosmosis. Electro osmosis is influenced by the following factors;
the mobility of the ions and charged particles present in the pore fluid, including those ions and particles entering the pore fluid via ion exchange; the hydration of ions and charged particles present in the pore fluid; the electrical charge and direction of movement of ions particles, resulting in net water transport.
The average electro osmotic mobility is 5.10-9 m²/U.s, where U = drop in potential in Volts.
When inert electrodes are placed in water and a direct current is passed through them, changes occur at the anode and the cathode.
At the anode, electrons are stripped from the water molecules, oxygen is evolved, and protons (H+) are formed and travel through the electrolyte towards the cathode:
2H2O – 4e-à O2 + 4H+
At the same time, the cathode is donating electrons to water molecules that creating hydroxyl ions and liberating hydrogen gas:
4H2O + 4e- à 2H2 + 4OH-
The two reactions are in balance and there is no net change in the pH of the electrolyte. In a liquid electrolyte, so much mixing occurs that the local changes in pH around the anode and cathode are difficult to detect unless the electrodes are well separated. There is little or no mixing in soil, sludge, concrete and gels due to the fact that the remixing of the electrolyte is inhibited, the area around the anode becomes acidic and the area around the cathode becomes alkaline. This has a significant impact on the chemical process in soil.
Most soils are conductive because they contain dissolved ions, such as calcium, magnesium, sodium, potassium, bi carbonate, some soluble fatty acids, nitrate, phosphate and chloride ions. Soils that seem to be dry usually have moisture sufficient to provide a continuous path for these ions to move along. The direct current is carried by ions, so electro-migration will occur with any species that will form ions in aqueous environments.