Adsorption cleaning of soils from heavy metals. Heavy metals are the most dangerous elements that can pollute the soil
The invention relates to the field Agriculture. The method for cleaning soils from heavy metals includes growing plants of phytomeliorants on contaminated soils with their subsequent removal. Safflower is used as a phytomeliorant plant. Safflower seeds are sown in contaminated soil at the rate of 20-22 kg/ha, mature plants are brought to the end of flowering phase and the beginning of dying off. lower leaves, after which the phytomeliorant is completely removed from the soil. Complete absorption of heavy metal ions is ensured. 3 tab.
The invention relates to agriculture and can be used in carrying out special measures to reduce the content of toxic concentrations of heavy metals in contaminated soil cenoses in order to restore or improve agrochemical indicators necessary to obtain environmentally friendly products.
Currently, domestic and foreign researchers are searching for hyperaccumulative plants, the properties of which make it possible to effectively extract heavy metals from contaminated soil.
Literature sources report that soil reclamation or cleaning it from pollution with the help of plants is a relatively new method (ten years old), ecological and progressive. It allows eliminating or limiting the transfer of heavy metals along the chain from humans to soils and groundwater without harming the environment.
In analogue works, the authors show that for the purpose of phytoremediation of polluted soils (purification with the help of plants), the following accumulative plants are used: broom, oil radish, amaranth, and even wild plants.
The closest analogue to the invention in terms of the totality of the main essential features is a method for cleaning soils from heavy metals by growing plants - phytomelirants on contaminated soils with their subsequent complete removal from the soil (see RU 2282508, CL A01B 79/02, 27.0.2006).
The disadvantages of analog work include the study of only one pollutant - cesium, the coefficient of biological accumulation of the pollutant for the crops used is not indicated, there is no clear concept of the harvesting period, since crops were used different groups technological requirements and developmental biology.
The objective of the invention is to improve the ecological state of natural and cultural biogeocenoses by reducing the content of toxic concentrations of heavy metals in the root layer of soils.
The technical result is a more complete absorption of heavy metal ions (lead, cadmium and copper) from the soil solution while creating an optimal coverage of the polluted area by safflower plants.
In essence, the task is achieved by the fact that safflower is cultivated on polluted soils, seeds are sown at the rate of 60-80 plants per m 2 (20-22 kg/ha), followed by bringing and complete removal of plants to the phase of the end of flowering and the beginning of the death of the lower leaves.
The proposed seeding rate provides full coverage of the root system of the plant in terms of the volume of contaminated soil. At a lower seeding rate, the coverage is not complete, and at a higher rate, the productivity of the aboveground mass decreases sharply and, as a result, the total removal of heavy metals by safflower plants.
Example of a specific implementation
The experiments were carried out on the territory of the wastewater treatment plant in Istra.
Plants were sown in spring by hand, followed by raking.
Soil samples were taken before sowing and immediately after harvesting safflower.
Harvesting was carried out by bringing the development of plants to the phase of the end of flowering and the beginning of the death of the lower leaves.
The results obtained in the course of the experiment in the field convincingly prove that safflower can be attributed to plants - hyperaccumulants of heavy metals.
It is interesting to note that, as a rule, when grown on contaminated soils, even in hyperaccumulants, the content of metals such as lead, cadmium and copper in plant samples does not exceed 1.2 in the above-ground part; 0.5-1 and 10-12 mg/kg dry weight, respectively (Table 1).
Based on the presented results and data on the content of heavy metals (mobile form) in the soil, the coefficient of biological accumulation (absorption) was calculated (Table 2).
As is known, if the coefficient of biological accumulation of toxicants in plants, even in terms of aboveground mass, is greater than one, then this species can be classified as hyperaccumulants; in the example under consideration, a high CBN TA was also achieved in the root part of the experimental plants.
An analysis of the bioproductivity of plants in the flowering phase did not reveal any manifestation of the toxic effect of contaminated soil on the growth and development of safflower - the average dry weight of the stems was 557 g, the roots - 143 g cm 2, respectively. Sowing seeds is carried out manually at the rate of 60-80 plants per 1 sq. m.
With thickened sowing, over 80 plants / m 2, a decrease in the productivity of the above-ground mass by an average of 16% was noted, the plants lagged behind in growth, the safflower root system had a smaller mass, apparently, when the crops are compacted, safflower plants manifest allelopathy - mutual inhibition of growth and development .
The results of testing safflower when used as a phytomeliorant convincingly prove high efficiency storage capacity of plants to reduce the content of heavy metals in the root layer of the soil.
The cleaning method includes the following activities:
Soil preparation for sowing;
Sowing phytomeliorant at the rate of 60-80 plants/m 2 (20-22 kg/ha), seeding depth 4-5 cm;
The development of safflower plants is brought to the phase of the end of flowering and the beginning of the death of the lower leaves, then they are completely removed from the contaminated soil.
The proposed method allows to significantly increase the efficiency of phytosanation, and when establishing copyright, it provides a basis for the development of specifications for various schemes for phytorehabilitation of contaminated areas.
Information sources
1. Baran S., Kzhyvy E. Phytoremediation of soils contaminated with lead and cadmium using broom / Influence of natural and anthropogenic factors on socioecosystems, 2003. No. 2. - P.39-44.
3. Zhadko S.V., Daineko N.M. Accumulation of heavy metals by tree species of the streets of Gomel. // Izv. Gomel. state university, 2003. No. 5. - P.77-80.
4. Kudryashova V.I. HM accumulation wild plants. - Saransk - 2003 - P.10, 18, 50, 78.
5. Rakotosson Voahirana. Les metaux lourds et la phytorenediation: l "etat de l" art. // Eau, ind., nuisances. 2003. No. 260. - C.45-48.
A method for cleaning soils from heavy metals by growing plants - phytomeliorants on contaminated soils with their subsequent removal, moreover, safflower is used as a plant - phytomeliorant, safflower seeds are sown in contaminated soil at a rate of 20-22 kg/ha, adult plants are brought to the flowering end phase and the beginning of the death of the lower leaves, after which the phytomeliorant is completely removed from the soil.
UDC 546.621.631
SOIL SOIL CLEANING FROM HEAVY METALS1
A.I. Vezentsev, M.A. Trubitsyn,
L.F. Goldovskaya-Piristaya, N.A. Volovicheva
Belgorod State University, 308015, Belgorod, st. Victory, 85
The results of studying the ability of clays in the Belgorod region to absorb Pb (II) and Cu (II) ions from water and buffer soil extracts are presented. During the experiment, the optimal ratio clay:soil was established, at which the removal of heavy metals from soil is most effective.
Key words: clay sorbents, soil, sorption activity, montmorillonite, heavy metals.
The industrial use of heavy metals is very diverse and widespread. That is why phytotoxicity and harmful accumulation in soils, as a rule, are observed near enterprises. Heavy metals accumulate in the upper humus horizons of the soil and are slowly removed during leaching, consumption by plants, and erosion. Humus and the alkaline environment of the soil contribute to the absorption of heavy metals. The toxicity of such heavy metals as copper, lead, zinc, cadmium, etc. for crops in natural conditions expressed as a decrease in the yield of commercial crops in the fields.
There are several methods for reclamation of soils contaminated with heavy metals and other pollutants:
Removal of the contaminated layer and its burial;
Inactivation or reduction of the toxic effect of pollutants using ion-exchange resins, organic substances that form chelate compounds;
Liming, application of organic fertilizers that absorb pollutants and reduce their entry into plants.
The introduction of mineral fertilizers (for example, phosphate, reduces the toxic effect of lead, copper, zinc, cadmium);
Growing Pollution Tolerant Crops.
Currently in world practice for ecological refining fertile soils mineral aluminosilicate adsorbents are increasingly used: various clays, zeolites, zeolite-containing rocks, etc., which are characterized by high absorption capacity, resistance to environmental influences and can serve as excellent carriers for fixing various compounds on the surface during their modification.
Materials and methods of research
this work is a continuation of earlier studies of clays of the Gubkinsky district of the Belgorod region, as potential sorbents for cleaning fertile soils from heavy metals.
1 The work was supported by the Russian Foundation for Basic Research, project No. 06-03-96318.
In this work, clays from the Kyiv suite of the Sergievsky deposit in the Gubkinsky district were used as sorbents, which differed in material composition and properties: K-7-05 (middle layer) and K-7-05 YuZ (lower layer). Soil samples K-8-05 and No. 129, taken on the territory of the Gubkinsko-Starooskolsky industrial region, were used as cleaning objects. Preliminary studies have shown that the clays of the Sergievsky deposit absorb copper and lead ions well from model aqueous solutions. Therefore, further studies were carried out with water and buffer extracts from the soil.
The aqueous extract was prepared according to the standard procedure. The essence of the method lies in the extraction of water-soluble salts from the soil with distilled water at a ratio of soil to water of 1: 5. The concentration of metal ions was determined by the photocolorimetric method on a KFK-3-01 instrument according to the appropriate methods for each metal.
The buffer extract from the soil was prepared according to the standard method of the Central Institute of Agrochemical Services for Agriculture (TsINAO) using an ammonium acetate buffer solution with a pH of 4.8. This extractant is accepted by the agrochemical service for the extraction of trace elements available to plants. The initial concentration of mobile forms of copper and lead available to plants in the buffer extract was determined by atomic absorption spectrometry.
Sorption of copper and lead ions was carried out at constant temperature(20 °C), under static conditions for 90 minutes. The ratio of sorbent: sorbate was: 1: 250; 1:50; 1:25; 1:8 and 1:5.
The discussion of the results
A study of the water extract, which was prepared for 4 hours, showed that the concentration of water-soluble copper compounds is insignificant and amounts to 0.0625 mg/kg (in terms of Cu2 ions). Water-soluble lead compounds were not detected.
The initial concentration of heavy metal ions in buffer extracts from soils was: for K-8-05 soil: Cu2+ 2.20 mg/kg, Pb2+ 1.20 mg/kg; for soil No. 129: Cu2+ 4.20 mg/kg, Pb2+ 8.30 mg/kg.
The results of determining the degree of purification of soil K-8-05 with clays K-7-05 (middle layer) and K-7-05 YuZ (lower layer) are presented in Table 1.
Table 1
The degree of purification of the buffer extract from the soil K-8-05, mass, %
Sorbent ratio: sorbate Clay K-7-05 (middle layer) Clay K-7-05 YuZ (lower layer)
Cu2+ Pb2+ Cu2+ Pb2+
1: 250 45,5 33,3 54,5 33,3
1: 50 70,5 45,8 68,2 58,3
1: 25 72,3 58,3 79,5 58,3
1: 8 86,4 75,0 87,3 83,3
1: 5 95,5 83,3 95,5 83,3
The results presented in Table 1 show that with an increase in the ratio of sorbent: sorbate from 1: 250 to 1: 5, the degree of purification of the buffer extract from copper ions with K-7-05 clay increases from 45.5 to 95.5%, and from lead ions - from 33.3 to 83.3%.
The degree of purification of the buffer extract with clay K-7-05 YuZ with the same increase in the ratio increased from 54.5 to 95.5% (for Cu2+) and from 33.3 to 83.3% (for Pb2+).
Note that the initial concentration of copper ions was higher than that of lead ions. Therefore, cleaning the buffer extract from copper ions with these clays is more effective than from lead ions.
table 2
The degree of purification of the buffer extract from soil No. 129 with K-7-05 clay (middle layer), wt. %
Ratio of sorbent: Cu2+ sorbate +
1: 250 39,3 66,7
Note: with clay K-7-05 YuZ, the experiment was not made, due to the lack of a sufficient amount of the sample.
The results presented in Table 2 show that the degree of purification of the buffer extract from soil No. 129 with clay K-7-05 with an increase in the ratio of sorbent: sorbate from 1: 250 to 1: 5 increases from 39.3 to 93.0% (for copper ions) and from 66.7 to 94.0% (for lead ions).
It should be noted that in this soil the initial concentration of copper ions was lower than that of lead ions. Therefore, we can assume that the efficiency of purification from copper ions of this soil is no worse than that of K-8-05 soils.
To clarify the mechanism of sorption of heavy metals, we assessed the composition and state of the ion-exchange complex of clayey rocks in the Belgorod region. It has been established that the cation-exchange capacity of the studied samples varies from 47.62 to 74.51 meq/100 g of clay.
Conducted comprehensive study acid-base properties of clays. Determination of active acidity confirmed that all clays have an alkaline character. At the same time, the pH of the salt extract of the same samples is in the range of 7.2-7.7, which indicates that these clays have a certain share of exchangeable acidity. Quantitatively, this value is 0.13-0.22 mmol-eq/100 g of clay and is due to the low content of sufficiently mobile exchangeable protons. The value of the sum of exchangeable bases fluctuates within a fairly wide range of 19.6 - 58.6 mmol-equiv / 100 g of clay. Taking into account the data obtained, a hypothesis was formulated that the sorption capacity of the studied clay samples with respect to heavy metals is largely determined by the processes of ion exchange.
From the work carried out, the following conclusions can be drawn.
With an increase in the ratio of sorbent: sorbate from 1: 250 to 1: 5, the degree of soil purification increases: from 40 to 95% (for copper ions) and from 33 to 94% (for lead ions) when using clay from the Sergievsky deposit (K-7- 05) as a sorbent.
The studied clays are a more effective sorbent for copper ions than for lead ions.
It has been established that the optimal ratio of clay: soil is 1: 5. With this ratio, the degree of soil purification is:
For copper ions, about 95% (wt.)
For lead ions, about 83% (wt.)
Bibliography
1. Bingham F.T., Costa M., Eichenberger E. Some questions of the toxicity of metal ions. - M.: Mir, 1993. - 368 p.
2. Galiulin R.V., Galiulina R.A. Phytoextraction of heavy metals from contaminated soils // Agrochemistry.- 2003.- №3. - S. 77 - 85.
3. Alekseev Yu.V., Lepkovich I.P. Cadmium and zinc in plants of meadow phytocenoses // Agrochemistry. - 2003. - No. 9. - P. 66 - 69.
4. Dayan U., Manusov N., Manusov E., Figovsky O. On lack of interdependency between the abiotic and antropeic factors/// International Scientific Journal for Alternative Energy and Ecology ISJAEE, 2006.-№ 3(35). - P. 34 - 40.
5. Vezentsev A.I., Goldovskaya L.F., Sidnina N.A., Dobrodomova E.V. Zelentsova E.S. Determination of the kinetic dependences of the sorption of copper and lead ions by the rocks of the Belgorod region. Nauchnye Vedomosti BelSU. Series Natural Sciences. - 2006. - No. 3 (30), issue 2. - P.85-88
6. Goldovskaya-Piristaya L.F., Vezentsev A.I., Sidnina N.A., Zelentsova E.S. Investigation of the total content and content of mobile forms of cadmium in the soils of the Gubkinsko-Starooskolsky industrial region. Nauchnye Vedomosti BelSU. Series "Natural Sciences". - 2006. - No. 3 (23), issue 4. - P.65-68.
7. Guidelines for the determination of heavy metals in agricultural soils and crop production.- M.: TsINAO, 1992.-61p.
8. State control of water quality. - M.: IPK. Publishing house of standards, 2001. - 690 p.
SORPTION PURIFICATION OF SOILS FROM HEAVY METALS A.I. Vesentsev, M.A. Troubitsin, L.F. Goldovskaya-Peristaya, N.A. Volovicheva
Belgorod State University, 85 Pobeda Str., Belgorod, 308015 [email protected] edu. en
Results of research of ability of clays of the Belgorod region to absorb ions Pb(II) and Cu(II) from water and buffer soil extracts are presented. During experiment of the optimum ratio clay: ground with most effective purification from heavy metals is established.
Key words: clay sorbents, soil, sorption activity, montmorillonite, heavy metals.
When soils and vegetation are contaminated with heavy metals, the following methods are used:
1) Limiting the entry of heavy metals into the soil. When planning the use of fertilizers, ameliorants, pesticides, sewage sludge, it is necessary to take into account the content of heavy metals in them and the buffer capacity of the soils used. Dose restriction due to environmental requirements, is an necessary condition ecologization of agriculture.
The entry of heavy metals into plants can be reduced by changing the nutrient regime, by creating competition for the entry of toxicants and fertilizer cations into the roots, and by the precipitation of heavy metals in the root in the form of sparingly soluble precipitates.
2) Removal of heavy metals beyond the root layer is achieved in the following ways:
Removal of contaminated soil layer;
Backfilling the contaminated layer with clean earth;
Growing crops that absorb HM and removing their plant mass from the field;
By flushing soils with water and water-soluble (usually organic) compounds that form water-soluble complex compounds with heavy metals, products from agricultural waste are used as organic ligands;
Washing the soils with a solution for leaching HMs from the upper horizons to a depth of 70–100 cm and then depositing them at this depth in the form of hardly soluble sediments (due to subsequent washing of the soils with reagents containing anions that form precipitation with heavy metals).
3) Binding of HMs in soil into low-dissociation compounds. Reducing the intake of heavy metals in plants can be achieved by their deposition in the soil in the form of precipitation of carbonates, phosphates, sulfides, hydroxides; with the formation of low-dissociating complex compounds with a large molecular weight. in the best way, providing a significant reduction in the content of heavy metals in plants, is the joint application of manure and lime. Most effective measures leading to decrease in the mobility of lead in soils, is claying (zeolite application) and joint application of lime and organic fertilizers. The use of a full range of chemical ameliorants (organic and mineral fertilizers, lime and organics) reduces the content of polyvalent metals in the soil by 10-20%.
4) Adaptive-landscape farming systems as a factor in optimizing the ecological situation in case of soil pollution with HMs.
Different kinds and crop varieties accumulate unequal amounts of HMs in plant products. This is due to the selectivity of the root systems of individual plants to them and the peculiarity of their metabolic processes. HMs accumulate to a greater extent in the roots, less in the vegetative mass and generative organs. At the same time, certain groups of cultures selectively accumulate certain toxicants. The selection of crops for growing on soils of a certain degree and nature of pollution is the simplest, cheapest and most effective way optimization of the use of contaminated soils.
Phytoremediation
Microorganisms are not able to remove heavy metals harmful to human health (arsenic, cadmium, copper, mercury, selenium, lead, as well as radioactive isotopes of strontium, cesium, uranium and other radionuclides from soil and water. Plants are able to extract from the environment and concentrate in their own tissues various elements.It is not difficult to collect and burn the plant mass, and the resulting ashes can either be buried or used as secondary raw materials.
The method of cleaning the environment with the help of plants was called phytoremediation- from the Greek "phyton" (plant) and the Latin "remedium" (restore).
Phytoremediation- a set of methods for purifying water, soil and atmospheric air using green plants.
Story
The first simple methods of wastewater treatment - irrigation fields and filtration fields - were based on the use of plants.
First Scientific research were carried out in the 50s in Israel, however, the active development of the methodology took place only in the 80s of the XX century.
The plant affects environment in a variety of ways, the main ones being:
rhizofiltration - roots absorb water and chemical elements necessary for the life of plants;
phytoextraction - the accumulation of dangerous contaminants in the body of a plant (for example, heavy metals);
Phytovolatilization - evaporation of water and volatile chemical elements (As, Se) by plant leaves;
phytotransformation:
1. phytostabilization - the transfer of chemical compounds into a less mobile and active form (reduces the risk of pollution spreading);
2. phytodegradation - degradation by plants and symbiotic microorganisms of the organic part of pollution;
Phytostimulation - stimulation of the development of symbiotic microorganisms involved in the cleaning process. Microorganisms play the main role in the degradation of pollution. The plant is a kind of biofilter, creating a habitat for them (providing oxygen access, loosening the soil. In this regard, the cleaning process also occurs outside the growing season (in the non-summer period) with somewhat reduced activity.
Short description
Pollutants are substances of anthropogenic origin that enter the environment in quantities exceeding the natural level of their intake.
Soil pollution is a type of anthropogenic degradation, in which the content of chemicals in soils subject to anthropogenic impact exceeds the natural regional background level. The excess of the content of certain chemicals in the human environment due to their intake from anthropogenic sources is an environmental hazard.
Attached files: 1 file
With the expansion of environmental monitoring of the state of soils, methods for determining the content of acid-soluble (1 N HCI, 1 N HNO3) HM compounds began to be widely used. Often they are given the name “conditional gross content of HMs.” The use of dilute solutions of mineral acids as reagents does not ensure complete decomposition of the sample, but allows the main part of the compounds of chemical elements of technogenic origin to be transferred to the solution.
The mobile forms of HM include elements and compounds of the soil solution and the solid phase of the soil, which are in a state of dynamic equilibrium with the chemical elements of the soil solution. To determine mobile HMs in soils, weakly saline solutions are used as an extractant, with an ionic strength close to the ionic strength of natural soil solutions: (0.01–0.05M CaCI 2, Ca(NO 3) 2, KNO 3). The content of potentially mobile compounds of controlled elements in soils is determined in an extract of 1 N. NH4CH3COO at different pH values. This extractant is also used with the addition of complexing agents (0.02–1.0 M EDTA).
For analysis, the upper layers of the soil (0–10 cm) are most often selected, sometimes the distribution of pollutants in the soil profile is analyzed. The upper horizons play the role of a geochemical barrier to the flow of substances coming from the atmosphere. Under the conditions of the leaching water regime, pollutants can penetrate deep into and accumulate in illuvial horizons, which also serve as geochemical barriers.
The sanitary and hygienic criterion of environmental quality is the maximum permissible concentration (MPC) of chemicals in environmental objects. MPC corresponds to the maximum content of a chemical in natural objects that does not cause a negative (direct or indirect) impact on human health (including long-term consequences).
The toxic effect of various chemicals on living organisms is characterized by a general sanitary indicator, which is often used as the LD-50 indicator (lethal dose), which shows the mass of the substance that entered the body of experimental animals (mice, rats) and caused the death of 50% of them. The unit of this indicator is mg of the substance/kg of the mass of the experimental animal. Direct contacts of a person with the soil are insignificant and occur indirectly through other components: soil - plant - person; soil - plant - animal - man; soil - air - man; soil - water - man. The determination of MPC in soils is reduced to the experimental determination of the ability of these substances to maintain the concentration of substances acceptable for living organisms in water, air, and plants in contact with the soil. That is why the MPC of chemicals for soils is set not only according to the general sanitary indicator, as is customary for others. natural environments, as well as three other indicators: translocation, migratory water and migratory air.
The translocation indicator is determined by the ability of soils to provide the content of chemicals on acceptable level in plants (radishes, lettuce, peas, beans, cabbage, etc. serve as test cultures).
Accordingly, migratory water and migratory air are determined by the ability of soils to ensure the content of these substances in water and air is not higher than the MPC. However, sanitary and hygienic standards for soil quality are not without drawbacks; the main one is that the conditions of the model experiment for determining the MPC and natural conditions are very different.
One of the steps in solving the problem of environmental regulation was an approach based on determining the permissible load on the soil, taking into account its buffer properties, which ensure the ability of the soil to limit the mobility of chemicals coming from outside, the ability to self-purify. Such approaches are being developed in Russia and other countries.
But it is very difficult to develop MPC for each type of soil. It is advisable to develop chemical standards for soil-geochemical associations, united by the commonality of the basic physical and chemical properties that determine their resistance to chemical pollution.
At the next stage, for a number of chemical elements, AECs (approximately permissible concentrations) of these elements were developed for soils that differ in the most important properties (acidity and granulometric composition). They were developed not on the basis of a standardized experimental method, but on a generalization of the available information on the relationship between the level of load on soils, the state of soils and adjacent environments.
Table 3
List of major soil polluting chemicals for which maximum allowable concentrations have been determined
Substances |
MAC in soil, mg/kg |
Hazard Class |
Manganese |
||
Formaldehyde |
||
Benz(a)pyrene |
||
Acetaldehyde |
||
4 Methods for cleaning soil from heavy metals
The ability to convert metals into a mobile form is the basis for soil purification methods by washing, extraction, chemical leaching, electrodialysis, and electrokinetic treatment. Metals are removed from the soil in the form of solutions, which are processed by ion exchange, reagent precipitation, evaporation, membrane separation, electrochemical precipitation, electrodialysis to obtain solid residues with a small volume, suitable for disposal in landfills, places of disposal of harmful substances.
When choosing a method for extracting metals, their amount in the soil, the composition and dispersion of the solid phase are taken into account. Metals that are in the exchange form are extracted by salt solutions associated with carbonates-solutions of acids, with oxides of iron and manganese-chemical reducing agents, with organic matter-solutions of complexing agents, in the form of sulfides-chemical oxidizing agents.
In biological methods for increasing the mobility of heavy metals, microorganisms and plants are used to extract them from the soil. The mobility of metals increases:
- as a result of biomineralization of organic substances containing metals.
- in the course of oxidative reactions occurring with the participation of microorganisms in the processes of bioleaching;
- as a result of changes in pH, Eh of the soil environment during the course of biological processes;
- in the formation of soluble metal complexes with organic substances synthesized and excreted by microorganisms and plant roots;
- in the bioreduction of metals by organic substances under anoxygenic conditions;
- as a result of the transfer of metals into a volatile form during methylation and transalkylation.
The fixation of heavy metals in soil reduces their availability for plants and migration through food chains.
One of the options for reducing the bioavailability of heavy metals is the introduction of sorbents into the soil.
From various sorbents of natural and artificial origin, zeolites, bentonites, red clay, ash, phosphates, peat, manure, compost, pond sludge, biomass of microorganisms on various carriers, waste wool, silk, waste containing tannin and fiber are used. General requirements for sorbents: pH 6.0-7.5, available and relatively cheap.
One technology, called the Bio Metal Sludge Reactor (BMSR), designed to treat soil, sludge, solid waste, uses the bacteria Ralstonia metallidurans. Bacteria solubilize metals with synthesized siderophores and adsorb metals on the cell surface with metal-induced outer membrane proteins, cell wall polysaccharides, and peptidoglycans. Bacteria are resistant to heavy metals. Metals are removed from the cell by antiport with protons, which leads to the accumulation of OH - ions in the periplasmic space, alkalization of the external environment and the formation of carbonates and bicarbonates. Metal ions exported from the cytoplasm form carbonates and bicarbonates in supersaturated concentrations on the cell surface and around the cell and crystallize on cell-bound metals that serve as crystallization centers. This results in a high metal to biomass ratio (0.5 to 5.0). Such bacteria remove metals from solution in the late phase of exponential growth or in the stationary phase of growth, which is convenient for the extraction of metals from contaminated soils by ex situ methods. Bacteria have special properties that cause a low settling rate of bacterial cells compared to organic and clay soil particles. This makes it possible to separate soil particles and cells with absorbed metal by the precipitation method. Bacteria with adsorbed metals, which are in the aqueous phase after separation, are easily removed from the latter by flotation or flocculation.
5 General information about Ralstonia metallidurans
Fig.1 Image of Ralstonia metallidurans
Cell structure and metabolism
R. metallidurans is a gram-negative, rod-shaped bacterium. Thus, they share the structural features of Gram-negative bacteria, such as peptidoglycan-containing cell walls, lamella-containing outer membranes, and periplasmic spaces.
R. metallidurans has the ability to use various substrates as a source of carbon. It can grow autotrophically using molecular hydrogen as an energy source and carbon dioxide as a source of carbon. In addition, in the presence of nitrate representatives, it can grow anaerobically. They do not grow on fructose and its optimum growth temperature is 30 C.
Ecology
Due to its ability to withstand the action of toxic metals, the use of this feature in the fields of biological restoration has been studied.
Pathology
It was found that R.metallidurans is not pathogenic for humans.
Application in biotechnology
R. metallidurans has been found to be able to produce enzymes that can be used to make fuel cells. These enzymes are able to oxidize hydrogen, which can eventually lead to electricity generation.
6 Technology for cleaning soil from heavy metals
When cleaning using BMSR technology, contaminated soil is introduced into a flow-type reactor with a stirrer, into which water and nutrients (acetate-5g/l, nitrogen-0.5g/l, phosphorus-0.05g/l) are supplied, bacteria are introduced ( in the amount of 10 8 cells/ml). The soil is pre-fractionated to remove large agglomerates, debris, etc. The particle size in the reactor should be no more than 2 mm. The pH is maintained at 7.2. The hydraulic residence time in the reactor is 10 to 20 hours.
During processing, contaminant metals are transferred from the soil particles to the bacterial walls. After treatment in the reactor, the sludge is deposited in a sump, into which water is added. In the presence of bacteria, soil particles have good sedimentation properties and settle in the sump within 1-2 hours. The metal-containing bacteria remain in suspension, which from the settler enters the settling tank (decanter). A flocculant is added to it, after which the biomass sludge can be dehydrated and dried. The content of metals in the biomass of bacteria is: Zn-8-25, Pb-3-5, Cd-0.16-0.25. This biomass can be incinerated by pyrometallurgical treatment to produce ash with a high metal content that can be recovered by leaching, or with subsequent storage of the ash in a landfill. The content of heavy metals in the cleaned soil is reduced by 5-10 times. Soil treated with bacteria at neutral pH using BMSR technology can be reused. Waste water contains very low concentrations of metals and can be recycled.
Calculation of the process of soil bioremediation from heavy metals.
Soil samples were taken from a 6 ha site at a depth of 9 cm (0.09 m). The lead content is 50 mg/kg.
1. Determination of the volume of contaminated soil.
V p \u003d S p × H
V p \u003d 6000 m 2 × 0.09 \u003d 540 m 3
2.Weight of contaminated soil.
R n = V n × d
R p \u003d 540 m 3 × 1.2 t / m 3 \u003d 648 t
3.Total weight of heavy metals.
1 kg of soil - 2.5 g HM
1 ton of soil - 2500 kg HM
640 t soil - x kg HM
x = 640 t × 2.5 t = 320 t
The IBU of microorganisms Ralstonia metallidurans is 8 m 3 /t HM.
x m 3 - 640 t
Set the amount of amophos.
For 1 t HM - 24 kg AMF
R AMP = 320 × 24 = 7680 kg AMP
Solubility of AMP = 18 kg/m 3 .
Water volume.
1 m 3 H 2 O - 18 kg AMP
x m 3 H 2 O -104.8 kg
V in \u003d 104.8 / 18 \u003d 5.82 t
7680 t + 5.82 t = 7686 t
Site selection
Soil harrowing
Transportation for remediation
Grinding up to 2 mm
bacteria
Loading into the bioreactor
Nutrients
settling
flocculant
decanter
Dehydration
pyrometallurgical processing
Storage at burial sites
Fig.2 Technological scheme of soil bioremediation from heavy metals.
BULLETIN OF THE RUSSIAN ACADEMY OF SCIENCES, 2008, volume 78, no. 3, p. 247-249
FROM THE RESEARCHER'S WORKBOOK
The article is devoted to the description of a simple and soil-sparing method of its purification from heavy metals - phytoextraction, which consists in sowing and growing for a certain period of time specially selected species of agricultural plants in contaminated areas to extract metals from the soil by the root system and accumulate them in aboveground biomass.
R. V. Galiulin, R. A. Galiulina
Heavy metals are a large group of chemical elements with an atomic mass of more than 50 c.u. They fall into the soil different ways: as part of gas and dust emissions, atmospheric precipitation, irrigation water, polluted by industrial effluents, etc. A person can get "his share" of heavy metals not only directly with inhaled air and soil dust, but also through food produced on contaminated agricultural land. Evil Influence heavy metals per person is that a number of their compounds are characterized by high toxicity and carcinogenicity. Emissions from metallurgical industries are especially dangerous, causing an increase in morbidity and mortality from malignant neoplasms, among which lung cancer occupies the first place. In this regard, the problem of cleaning soils from heavy metals becomes relevant for the territories of the so-called ecologically unfavorable regions, which include Chelyabinsk.
The authors work at the Institute for Fundamental Problems of Biology, Russian Academy of Sciences. GALIULIN Rauf Valievich - Doctor of Geography, Leading Researcher, Laboratory of Functional Ecology. GA-LIULINA Roza Adkhamovna - researcher at the same laboratory.
Binsk region. This region occupies one of the leading places in the country in terms of concentration industrial production. Pollution of the air basin and territories around ferrous metallurgy enterprises reaches tens of kilometers. According to space shooting, technogenic pollution of the lands of the region with heavy metals covers 29.5 thousand km2 at its total area 87.9 thousand km2.
Meanwhile, various methods are known for cleaning soils from heavy metals, among which phytoextraction is of particular interest. It consists in sowing and growing for a certain period of time on contaminated areas specially selected species of agricultural plants to extract heavy metals from the soil by the root system and accumulate them in above-ground biomass, which is subsequently utilized. At the same time, the coefficient of accumulation of metals in plants is increased due to the introduction of phytoextraction effectors into the soil. This technology is considered simple to implement, gentle on the soil, and cost-effective compared to mechanical and physico-chemical approaches. So, mechanical methods are associated with cutting off the most polluted surface layer and placing it in landfills (sequestration), or mixing it with less polluted deeper layers of soil by plantation plowing (dilution), or covering it with "imported" clean soil (earthing). Physico-chemical cleaning methods are based on washing the soil with special reagents to extract heavy metals from it (chemoextraction) or cleaning it by exposing the contaminated layer to direct electric current through electrodes (electrokinetic remediation).
Observations show that it is better to use specially selected types of agricultural plants for phytoextraction than wild hyperaccumulator plants.
GALIULINA, GALIULINA
species, such as bluish yarutka (Thlaspi caer-ulescens), wall beetroot (Alyssum murale), Galler's rezuha (Cardaminopsis halleri), etc. Although they accumulate dozens of times more metals than other plants, they are distinguished by a low growth rate and small aboveground biomass. Meanwhile, phytoextraction, like any other approach to soil cleanup, has a number of its own characteristics.
The content of heavy metals in the soil of the contaminated area should be acceptable for plants, that is, it should not cause pronounced phytotoxic symptoms in seedlings (discoloration, pigmentation and yellowing of leaves, growth retardation, etc.), which will characterize their tolerance to heavy metals and at the same time the ability to absorb the latter. root system and move to the above-ground biomass due to the flow created by the evaporation of water from the leaf surface of plants.
Plants used to clean the soil should be different high speed grow and produce large aboveground biomass, have a deep root system, high resistance to diseases and pests, be responsive to conventional farming practices, be easy to harvest, and unattractive to domestic and wild animals so as not to cause cases of heavy metal-laden aboveground biomass poisoning.
To increase the accumulation of heavy metals in plants, it is necessary to use the so-called phytoextraction effectors in the form of complexons from among polyaminopolyacetic acids, such as ethylenediaminetetraacetic acid (EDTA), dihydacid (D DD A), diethylenetriaminepentaacetic acid (DTPA), ethylene-bis(oxyethylentriamin)tetraacetic acid (ETTA), ethy(E DP A), cyclohexane-trans-1,2-diamintetraacetic (CDTA), etc. These substances are able to form strong water-soluble intracomplex compounds with many metals, increase the solubility, mobility of metals in the soil, and therefore , their absorption by the root system and accumulation in above-ground biomass. Usually, phytoextraction effectors in the form of aqueous solutions of their salts are introduced under plants in the phase of reaching their maximum aboveground biomass. This technique allows multiple sowing and cultivation of plants during one growing season, which means reducing the time for cleaning soils from heavy metals. It should also be noted that when introducing phytoextraction effectors into the soil, rainy days should be avoided to reduce the risk of groundwater contamination with heavy metals due to
an increase in their content in the soil solution and migration along the soil profile.
Cleaning the soil from heavy metals must be carried out until the relevant sanitary and hygienic standards are reached, that is, maximum permissible concentrations (MAC) or approximately permissible concentrations (AEC). At the same time, a period of 5-10 years is considered economically feasible for phytoextraction. The final stage of phytoextraction is the harvest, collection and utilization of aboveground plant biomass contaminated with heavy metals, since harvesting of the entire root biomass, initially saturated with heavy metals, is practically impossible. The above-ground plant biomass can later be used to extract non-ferrous metals from it by pre-drying, ashing and subsequent special processing.
The prospects of the above method of cleaning soils from heavy metals are evidenced by the results of a vegetative experiment with gray mustard, or sarepta (Brassica juncea), and leached chernozem from agricultural land in the vicinity of Chelyabinsk. This type mustard is widely used in the practice of cleaning soils from heavy metals. The experiment simulated the situation associated with the accumulation of copper and nickel for several years in the soil of a site located in the zone of influence of metallurgy and energy enterprises of Chelyabinsk. The choice of these metals for the experiment is not accidental, since copper and nickel, along with chromium, zinc, lead and cadmium, are among the main soil pollutants in the world. The soil was treated with aqueous solutions of copper and nickel salts in amounts of 100 mg/kg, then mustard seeds were sown and the growth and development of plants was observed for several weeks. When the mustard reached the maximum above-ground biomass, the most commonly used in practice phytoextraction effector EDTA was applied under the plants in the form aqueous solution its sodium salt in doses from 1 to 10 mmol/kg. A week later, the aboveground mustard biomass was cut, dried, and the content of copper and nickel in it was analyzed. As it turned out, with an increase in the dose of EDTA, the coefficients of accumulation of heavy metals, that is, the ratio of the content of metals in the plant and soil (soil cleaning potential) increased relative to the control (without the introduction of EDTA) for copper by 2.8-43.6 times, for nickel - 1.8-25.3 times ( Table 1).
Calculations carried out using the exponential dependence showed that the multiplicity of sowing and cultivation of mustard with the use of the phytoextraction effector significantly reduces the time for cleaning the soil from heavy pests.
BULLETIN OF THE RUSSIAN ACADEMY OF SCIENCES volume 78< 3 2008
SOIL CLEANING FROM HEAVY METALS WITH THE HELP OF PLANTS
Table 1. Values of accumulation coefficients of copper and nickel for mustard sizoy (ratio of metal content in plant and soil) depending on the doses of EDTA introduced into the soil
Cu and Ni, 100 mg/kg each 0.09 0.21
The same + EDTA, 1 mmol/kg 0.25 0.37
» , 5 mmol/kg 1.20 2.51
» , 10 mmol/kg 3.92 5.32
Accumulation factor
Table 2. Time to reach the initial background concentrations of copper (31.6 mg/kg) and nickel (63.5 mg/kg) in the soil with multiple sowing and cultivation of blue mustard during one growing season and the application of EDTA
single double option
Cu and Ni, 100 mg/kg each 14.9 22.5 7.4 11.3
The same + EDTA, 1 mmol/kg 7.4 8.8 3.7 4.4
» , 5 mmol/kg 6.6 7.9 3.3 3.9
» , 10 mmol/kg 5.8 6.9 2.9 3.4
In conclusion, I would like to note that the urgent task of today is the implementation of this method for the systematic return of scarce arable land to crop rotations after their cleaning with the help of plants in the territories of ecologically disadvantaged regions. Without a doubt, the large-scale implementation of phytoextraction, as well as any other method of soil purification, makes sense, provided that the massive technogenic pollution of land is severely
R. V. Galiulina, R. A. Galiulina - 2012
I. P. Balabina, N. P. Nevedrov, E. P. Protsenko, and A. V. Prusachenko - 2013
