Vol 11, No 4 (2017)

A new semiempirical method for the mathematical description of the space–time concentration profiles of contaminants in soil during its electrokinetic remediation is proposed. The method is based on approximating the experimental data on the spatiotemporal behavior of the concentration, C = C(D_a, t). The experimental and theoretical C = C(D_a, t) dependences reported in the literature and obtained in our studies were approximated by seventh order polynomials. For example, the space–time concentration profiles of chlorinated hydrocarbon contaminants in unsaturated soils, such as tetrachloroethylene, trichloroethylene and carbon tetrachloride, have been successfully described by a polynomial function with determination coefficients of R² = 0.9941, 0.9988, and 0.9972, respectively. A pilot test setup for studying the electrokinetic remediation of soils contaminated with mercury compounds, with ten sampling sections and replaceable cartridges with ionites, was designed and built. This setup allowed measuring the space–time concentration profile of mercury in soil samples during electrokinetic remediation. This profile obtained was approximated by a seventh order polynomials with a determination coefficient of R² = 0.9929. It is shown that the polynomial approximation of the space–time concentration profiles of contaminants in soil describes the experimental C = C(D_a, t) dependences no worse (sometimes better) than the Poisson–Nernst–Planck model for ionic flow.

The properties of gas-generating soils (GGS) in the process of biofermentation under anaerobic and aerobic conditions are studied. The degradation of organic matter (OM) in a soil under natural occurrence conditions (without free access of air oxygen) at temperatures from 10 to 12°C is demonstrated to proceed at a specific reaction rate of k = 0.096 year⁻¹. The main phase of gas generation (biogas formation) is shown to take 15 years, with the content of methane in the biogas being 60−80 vol %. It has been established that, under the conditions of forced aeration of the GGS array, the specific reaction rate of OM degradation increases 10-fold, to 0.9673 year⁻¹, with a nearly complete decomposition of OM taking 1.5−2.0 years. A prerequisite for achieving of the predicted result is the maintenance of the environment humidity at a level not lower than 50%. Application of an alternative method, a thermal treatment of GGS increases the degree of OM decomposition to 59% within 4 h at 200°C and to 75% within 2 h at 300°C. In this case, residual organic substances are carbonized in the course of thermal treatment, transforming into a material resistant to microbiological decomposition. In fact, after heating at 200−300°C, GGS becomes inert from the gas-geochemical point of view.

The forms of existence, pathways of migration, and mechanisms of transformation of polychlorinated organic compounds (POCs) and polyaromatic hydrocarbons (PAHs) in the aqueous medium are analyzed. For 2,4,5-trichlorophenol, as an example, a free-radical mechanism of the formation of polychlorinated dibenzofurans and dibenzodioxins during the direct photolysis of POCs has been established. For benzo[a]pyrene, as an example, the role of OH radicals in the oxidation of PAHs sorbed on organomineral sorbents by singlet oxygen has been revealed. The role of monosulfide complexes of Fe(II) and 1: 1 monothiolate complexes of Cu(I) in the formation of a quasi-reducing state of the natural aquatic environment, toxic for aerobic organisms with intensive water exchange, has been elucidated, a state in which copper ions become biologically inaccessible.

Physical experiments and mathematical modeling are used to study the kinetics of the reactions of carbon dioxide and water with potassium superoxide accompanied by oxygen release at various values of the temperature and humidity of the breathing gas mixture. The kinetics of the chemisorption is demonstrated to be limited by the rate of air regeneration in an airtight habitable facility. Experimental and analytical approaches are applied to determine the kinetic coefficients of the chemical reactions using the experimental data and a mathematical model of chemisorption kinetics. To perform the above chemical reactions, an original-design chemisorption reactor was developed, which contains plates with potassium superoxide nanocrystalline fixed on the fibers and pore surface of a fibrous polymer matrix. A mathematical model of chemical air regeneration is developed to calculate the guaranteed values of the parameters of the reactor and the protective effect time of the chemisorbent during which, at a given load, the reactor provides the appropriate concentrations of oxygen and carbon dioxide in the breathing gas mixture in an airtight habitable.

The chemistry and technology of new versatile multipurpose catalytic systems developed and studied by the authors for the purposes of heterogeneous catalysis are reviewed. A theoretical background for a successful search for these new catalytic systems is based on an unconventional approach with emphasis on an essential role of branched-chain reaction mechanisms of heterogeneous catalysis previously developed by the authoring team. The catalytic systems under study are based on silica (aluminoborosilicate) glass-fiber amorphous matrices doped with various metals and manufactured as articles with various types of woven structure. The specific features of these glass-fiber woven catalytic systems, such as their structure, phase state of the matrix, manufacture and activation methods, design of catalytic reactors in which they operate, as well as production technologies and operation methods, make a compelling case to regard them as a new separate class of catalysts. As compared to conventional catalytic materials, these new catalysts are highly efficient in neutralizing industrial gas emissions, in contact stages of the production of nitric acid and sulfuric acid, in various reactions of catalytic hydrocarbon processing, in water purification from nitrate and nitrite contaminants, in catalytic heat generation, etc.

A formula for a mathematical description of the relationship between the breakthrough curve C(t)/C₀ for the dynamic sorption purification of water and the space–time concentration profile of contaminant q(x, t) in the fixed sorbent bed is derived. The derivation is based on the simplifying assumption that the dependence of the adsorbate concentration profile q(x, t) on the longitudinal coordinate x of the bed is described by the logistic function q(x, t) = a/{1 + exp{–k(t)[x–b(t)]}}, in which a is a constant and the time-dependent parameters k(t) and b(t) are expanded into the power series k(t) = k₀ + k₁t + k₂t² and b(t) = b₀ + b₁t + b₂t² + b₃t³ + b₄t⁴ with the expansion coefficients b₀, b₁, b₂, b₃, b₄, k₀, k₁, and k₂, so that C(t)/C₀ = 1–(S/(C₀v))F(t, b₀, b₁, b₂, b₃, b₄, k₀, k₁, k₂), where C(t) is the breakthrough concentration of contaminant in the water effluent from at the fixed bed, C₀ is the concentration of the contaminant in the water influent into the fixed bed, S is the cross-sectional area of the bed, v is the water flow rate, and F is a definite analytic function dependent on the profile q(x, t). The coefficients b₀, b₁, b₂, b₃, b₄, k₀, k₁, and k₂ are determined by fitting the theoretical breakthrough curve to the experimental one. With the help of this approach, space–time profiles for dynamic water purification from lead, nitrate, and perchlorate ions are calculated. It is shown that the adsorbed contaminant ions are redistributed between different parts of the fixed bed in the course of the adsorption process.

The mechanisms of redox processes occurring in natural water with participation of molecular oxygen and the product of its reduction hydrogen peroxide as a carrier of reactive oxidative equivalents and hydrosulfide as a carrier of reducing equivalents in the formation of a toxic quasi-reducing state of the natural water medium were analyzed. The conditions for the formation of the toxic superoxidation state of the aqueous medium as a result of intensification of free-radical processes involving OH radicals and microcolloidal mixed-valence manganese(III, IV) particles were characterized.

A procedure involving specific lux biosensors has been applied to rapid detection of environmental ammonium perchlorate (AP) under both laboratory and field conditions. The procedure is based on evaluating the influence of AP on the level of bioluminescence of lux biosensors. Two lux biosensors—Escherichia coli MG1655 katG::kan (pKatG-lux) and E. coli MG1655 (pSoxS-lux)—have been employed in testing the ability of AP to cause an oxidative stress associated with the appearance of hydrogen peroxide and superoxide anion radicals in the cell. The lux biosensors designed contain hybrid plasmids with appropriate regulatory DNA regions transcriptionally fused with the bacterial luciferase lux genes as reporter genes. AP at concentrations of 5–50 mmol/L exerts an effect on the induction of luminescence of the lux biosensors with the P_katG and P_soxS promoters. The intensity of the bioluminescence of the cells that contain the pKatG-lux and pSoxS-lux plasmids and have been treated with AP is 5–10 higher than the intensity of the bioluminescence of the untreated cells. Therefore, AP induces an oxidative stress in the bacterial cells through the formation of reactive oxygen species, namely, hydrogen peroxide and the superoxide anion radical. The high sensitivity and specificity of the lux biosensors makes them usable in AP detection in the environment.

This paper reports on our study of the pH effect of solutions on the average hydrodynamic diameter (d_av) of the particles of the disperse phase and the electrokinetic potential (ζ) of the particles of low-soluble iron subgroup metals compounds using Fe(II, III), Ni(II), and Co(II) compounds as an example. The pH effect of solutions on the efficiency of the electroflotation extraction of metal ions from aqueous solutions containing these ions in individual form or in mixture was studied. The efficiency of the electroflotation extraction of the low-soluble compounds of iron subgroup metals is directly related to the particle size and electrokinetic potential of the particles, which depend on рН. The maximum degree of particle extraction α reached 97–99% at рН values characterized by the maximum hydrodynamic diameter of particles (over 20 μm for Fe(II) and Co(II) compounds and over 50 μm for Fe(III) and Ni(II) compounds) at ζ potentials of up to–10 mV for systems approximated to real wastewater. In the case of the extraction of the disperse phase of the Fe(III)–Ni(II)–Co(II) multicomponent system, the synergic effect was observed: the coextraction of metals was more complete and effective, which may be due to suppressed negative charge. In the range of рН 10–11, the degree of extraction of the Fe(III) disperse phase did not exceed 74%; in the ternary system, it reached 94%.

The reaction of dispersed aluminum with water under the exposure of an A-IX-2 aluminum-containing explosive compound to hydrocavitation has been discussed. A kinetic model of the process has been developed; the chemical reaction rate constant has been determined under experimental conditions. It has been shown that the reaction occurs in an autocatalytic mode and can lead to the complete conversion of aluminum to aluminum hydroxide. A method to stabilize dispersed aluminum during the hydrocavitational extraction of a conversion explosive by using a phosphate buffer has been developed. Experiments have shown that the phosphate buffer has a stabilizing effect and leads to an improvement of the characteristics of the resulting industrial explosive composition.

The oxidation of nitrocellulose (NC) containing 13.38% nitrogen has been investigated. The oxidation process under the action of hard UV radiation and ozone has been conducted for 27 h. As result, the nitrogen content of NC has decreased by less than 4.0%. For oxidation using Desulfovibrio (D.) desulfuricans sulfate-reducing bacteria, NC has been incubated with these bacteria for 65 days. This processing has reduced the nitrogen content of NC by 1.66–2.8%. D. desulfuricans incubation with NC pretreated with UV light + ozone has decreased the nitrogen content of the sample by at most 2.75% (compared to the baseline). UV + ozone pretreatment enables subsequent NC oxidation by D. desulfuricans: the resulting samples are richer in low-molecular-weight fractions and nitrate and nitro groups, and they reach their maximum extent of oxidation within 16 h of incubation with the bacteria, whereas the untreated samples oxidize to the maximum extent in 38 h. It is likely that the UV + ozone treatment cleaves carbon–carbon bonds in the polymer chain and lowers the degree of polymerization of individual chains, thereby facilitating the penetration of bacteria into the bulk polymer globules and the bacterial oxidation of ester bonds.

A series of environmentally safe bioactive chelators based on racemic aspartic and glutamic acids have been obtained. In addition, an optically active L-isomer of N-(carboxymethyl) aspartic acid (L-CMA) was synthesized, and its acid-base characteristics were determined by pH-titration analysis. The detected high activity of the nitrogen atom of L-CMA (pK₄ = 10.42) is apparently due to the betainic structure of this compound in solution and formation of a cycle with an intramolecular hydrogen bond between the nitrogen atom of the protonated amino group and the oxygen atom of the water molecule included in this cycle. This hypothesis is confirmed by IR spectral analysis of the L-isomers of the parent acids.