In the present article, the experimental research of electrochemical cleaning of oil-contaminated soil is provided. The decrease of oil concentration in the soil from 1100 mg/kg down to 250 mg/kg at the current density in the range from 22 A/m2 to 174 A/m2 during 90 minutes is shown. It has been established that there is the limit amount of charge required for effective cleaning, which amounted to 0.96·107 coulombs per kilogram of oil. The electrodes placement variant for the proposed method realization in real conditions is described. It is shown that at a voltage between the electrodes about 18 V and the cleaning efficiency of 77% the energy consumption will be 173 MJ/kg of oil.
The electrochemical method of soil cleaning by passing small amperage has rather high efficiency for oil products, phenols, salts, heavy metals, and other chemicals pollution. Cleaning can be realized through a whole complex of physical, chemical and biological processes. The most important are the electrokinetic movement of the pollutant, the oxidation and evaporation of the components. The arrangement of anodes and cathodes that reduces the resistance between the electrodes by creating in the interelectrode space an electric field close to homogeneous is considered. This calculation allows to determine the number of electrodes, the amperage between them, the voltage depending on the properties of the soil, the area, the depth of contamination of the treated area, the geometric parameters of the electrodes and the required degree of cleaning.
The changes in the properties of contaminated soil during electrochemical cleaning is very important. The results of research of phytotoxicity of soil contaminated with oil and mineralized formation water after electrochemical treatment are presented in this paper. A biotesting methodic with Lepidium sativum L. allowed to do complex assessment of the hazardous properties of contaminated soil. Lepidium sativum L is one of the most useful test object because of its high responsiveness to the presence of pollutants and ability to quickly germination. The most presentative parameters of this methodic are the percentage of seed germination and the total length of seedlings (sum of underground and aboveground parts length). A statistical analysis of the experimental data was carried out too.
Electrochemical treatment of contaminated soils is an actual method for the remediation of industrial and urban areas. It represents a good alternative to methods of mechanical, thermal, chemical and biological treatment, and, if necessary, can be used with them. Passing electric current through the soil allows to reduce the concentration of such pollutants as oil and oil products at a considerable depth, to successfully reduce the content of dissolved mineral salts. In recent years a number of works of scientists around the world have been devoted to the study of such technologies. This article discusses the results of experimental studies conducted in the Russian Federation, Romania, Italy, the United States of America and some other countries. A review is given of various options for implementing the electrical treatment of soils contaminated with oil, diesel fuel and oil-containing waste using various types and sizes of electrochemical cells, as well as a variation in the sizes, shapes and materials of the electrodes used (cathodes and anodes). When modeling processes occurring in the soil and induced by electric current, the most significant monitoring parameters are the hydrogen index (soil acidity), amperage and voltage, soil resistance and electrical conductivity, redox potential, and the concentration of pollutants. When assessing the appropriateness of applying electric cleaning methods, the value of energy costs and the efficiency (degree) of cleaning the treated soil are of high importance, therefore, special attention is paid to their analysis. Also the results of author's research in this field are presented in this work. The results of cleaning model soils of various types are considered, mathematical calculations of some of the most important process parameters are given. A specific arrangement of electrodes in wells in vast areas of soil with various concentrations of pollutants is proposed, which allows achieving optimal cleaning results for all areas simultaneously using a single power source without additional energy and, accordingly, material costs.
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