Combined ultrasound and electrokinetic treatment of organic contaminants: chemical and analytical approach

Introduction

Decontamination of soils through the removal of the organic contaminants becomes more and more urgent problem in present world. Various kinds of chemical pollutants have recently been detected in the environment, and this has created large social problems. Sediment contamination in estuarine and coastal regions is widespread in the whole world. Hydrophobic organic compounds such as polycyclic aromatic hydrocarbons (PAH) and polychlorinated biphenyls (PCB) are of particular concern because of their long life span and toxicity. Sediment serves as a contaminant reservoir for aquatic organisms that can accumulate toxic compounds like PCBs that are then passed up the food chain.

Contamination can be solved by the use of different techniques, like thermal or biological treatment of soils, pumping of solutions containing agents capable of extracting the toxic contaminants from the soil. However, usually those conventional techniques require high costs and remediation time. In addition, those remedial options may cause habitat alteration, and require large-scale material handling and long-term management. Therefore, in-situ stabilization methods that do not involve sediment relocation or capping are attractive.

Electrokinetic remediation technique has attracted an increased interest among the scientific community all around the world. This technique is based on the application of low-level direct current, which is used to solubilise and mobilize contaminants via electro-migration, electro-osmotic and electrophoresis phenomena. In addition it is economically feasible and the time scale of remediation can be reduced applying different enhancement methods. Sonochemistry is one of the novel approaches to enhance the reactions and processes by increasing a speed and output of reactions, more efficient use of energy, performance improvement of phase transfer catalysis, activation of metals and solids as well as increase in reactivity of reagents or catalysts.

The electrokinetic treatment process efficiency highly depends on the electro-osmotic phenomenon, which is mainly controlled by electrokinetic potential so called zeta-potential. It is well documented in the literature that usually soil or sediments surface is negatively charged having low zeta potential. In order to raise the efficiency of the contaminants removal there it is necessary to raise the zeta potential.

Aim of the research

To apply electrokinetic method to remove organic contaminants from low permeability clayey soils.

Materials and Methods

Laboratory scale experiments will be conducted in specially designed electrokinetic cells with the possibility to conduct batch scale experiments and in situ trials.

Set up of the experiments

Laboratory scale electrokinetic experiments will be conducted in cylindrical glass cell. The distance between electrodes will be 70 cm, diameter of the glass cell 30 cm, the length of sludge chamber 50 cm, the length of cathodic and anodic (with modification for electromigration experiments) will be 10 cm each. The contaminated medium will be separated from cathodic or anodic chambers by either fiber glass filter paper (0.45mm, Advantec GS25 Japan) or cation as well as anion membrane (Ionics Inc, the USA). The electrodes used for the experiments will be platinized titanium or titanium bars 7 cm length and 1 cm width. The pH, amount of heavy metals in the effluent and the amount of water, electric current, different potential gradient and other important parameters will be constantly monitored throughout the tests.