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Abstract

Содержание

Introduction

At the moment, the state of the environment in the Donetsk region is in a state of acute ecological crisis. Donbass problems are the accumulation and annual formation of significant volumes of industrial and solid household waste. One of such wastes is sewage sludge from urban sewage treatment plants.

Sewage treatment plants (WTP) are used to protect natural water bodies from pollution by wastewater (CB) of household, industrial and mixed origin.

At the stages of mechanical and biological treatment of municipal wastewater a significant amount of solid waste is formed – wastewater sludge (WWS). This type of waste consists of coarse pollution retained by gratings, sediment from sand traps, sediment falling out in primary sedimentation tanks, waste activated sludge or biofilm from the structures of aerobic biochemical water purification (BHO) [1]. The solid fraction of the raw sludge consists of organic (up to 80 %) and mineral (up to 20 %) substances, and the spent activated sludge is represented by a complex of microorganisms after the BHO process. The greatest waste formation is accounted for by the crude sediment of the primary clarifiers (48,5 %) and spent activated sludge (47,5 %).

Another important problem of Donbass is the formation of significant volumes of industrial waste – rock dump of the coal mining industry (slagheap), causing significant damage to the natural environment.

For a long time, the natural environment of Donbass was subjected to significant anthropogenic stresses, which did not in the best way affect the ecological state of its main components. Thus, a total of 521 rock heaps were installed on the territory of the DPR (83 – burning, 292 – not burning, about 146 waste heaps data are not available). In the coal dumps of Donbass thousands of tons of rock have accumulated, which occupies vast territories. The area of land occupied by 444 rock heaps is 3385,54 hectares, of which – 760,7275 rock heaps under abandoned dumps, which could be used in economic activities [2].

Much of the rock heaps of Donbass are burning. Thereby have a negative impact on all components of the environment. Excessive gaseous substances, such as carbon oxides, sulfur dioxide, and hydrogen sulfide, are emitted into the atmosphere in large quantities. The weathering of finely dispersed coal-rock dust, leaching of sulphides, and as a result of pollution of the aquatic environment with sulphates and toxic components. Also, rock dump heaps reduce the area of land that may be suitable for industrial and residential construction.

1. Topic relevance

During the operation of sewage treatment plants and the coal industry, large amounts of WWS and waste rock are generated, which annually accumulate in waste disposal sites, occupy vast territories of fertile land and pose an environmental hazard due to pollution of the soil, atmospheric air, surface and groundwater. At the same time, household sewage sludge is characterized by a high content of elements and compounds (nitrogen, phosphorus, potassium, calcium, magnesium), which favorably affect the growth and development of plants. Therefore, WWS, treated appropriately, are often not inferior to traditional organic fertilizers.

The soil dump are characterized by a low content of nitrogen, phosphorus, organic carbon and elements vital for plants, which create additional difficulties for the gardening of waste dumps.

Therefore, the use of sewage sludge, which contain valuable nutrients for the biological recultivation of technologically disturbed lands, is relevant and allows to solve a number of important problems: reducing the load on the lithosphere, preserving fertile soils, clean groundwater and surface water.

2. Goal, objectives, object, subject of study, the planned scientific novelty

The purpose of the work is to study the possibility of using urban sewage sludge obtained from the wastewater treatment plant of The Company Water of Donbass for biological reclamation of waste dumps of coal mines.

To achieve this goal it is necessary to solve the following main tasks:
– to analyze the technological scheme of wastewater treatment and determine the stages of sewage sludge formation;
– to study the system of management of sewage sludge in the enterprise and consider their impact on the state of the environment;
– to analyze the main methods and technologies of processing, neutralization and disposal of sewage sludge;
– establish the advantages and disadvantages of using WWS as a fertilizer;
– describe the stages of biological remediation;
– present the methodology of the experiment;
– on the basis of the obtained results, make a conclusion about the effect of WWS on the vital activity of plants during the biological recultivation of rock heaps of coal mines.

The object of study – sewage sludge sewage treatment facilities of the city of Makeyevka and rock dump No 12 Inclined.

The subject of the study – analysis of the possibility of using sewage sludge for the biological recultivation of rock heaps of coal mines.

Planned scientific novelty: the use of WWS urban sewage treatment plants for the biological reclamation of waste dumps of coal mines in order to reduce the negative impact on all components of the environment.

3. Sewage sludge is a source of environmental hazard

An essential condition for the efficient operation of sewage treatment plants is the treatment and disposal of WWS from the territory of treatment facilities for the environmentally safe use or storage of sediments.

Sewage sludge – is a solid fraction of sewage consisting of organic (up to 80 %) and mineral (up to 20 %) substances separated in the process of sewage treatment using the method of sedimentation (wet sediment), and a complex of microorganisms that participated in biological treatment of sewage and removed from the process (excess activated sludge).

It is known that WWS contains substances that are valuable for plant development (nitrogen, phosphorus, potassium, trace elements, calcium, magnesium, treated accordingly, they can be used as fertilizer.

Despite the fact that sewage sludge is classified as low-hazardous waste (class IV), and in real conditions it is placed openly on sludge beds, dumps, they are a source of environmental pollution, create environmental, economic and social problems. Most of the conditions necessary for the normal operation of WWS storage sites are not met. There are no measures for the sorting and disposal of WWS [3].

The bulk of WWS is stored on sludge beds and dumps, landfills, creating technological problems in the process of sewage treatment. The conditions of their storage, as a rule, lead to environmental pollution as a result of release (distribution) of a number of chemical elements (organic substances, nitrogen and phosphorus compounds, sulfur, heavy metals and other elements) contained in this type of waste [4].

Over the past 15-25 years, most of the treatment facilities have expired long-term storage facilities for OSV storage facilities, and they are currently overcrowded and require new areas to accommodate precipitation, which is associated with financial payments for waste disposal and degradation of new areas under sludge sites and sludge ponds [4]. As a result, there is nowhere to dump the newly formed sediments, there is a danger of collapse of the embankment and the contents of the sites in the rivers.

Sewage sludge is a favorable bacteriological environment for the development of various parasitic agents (helminth eggs and larvae, intestinal protozoan cysts), and homeless animals and birds, being carriers of dangerous infections, create epidemiological adverse situations [5].

Mechanical and physical methods for treating sewage sludge used in sewage treatment plants, such as aerobic stabilization, sludge beds and sludge ponds are associated with significant economic costs, require a lot of labor and do not always provide environmental safety.

Therefore, the introduction of technologies for reuse of sewage sludge to reduce the volume of stored waste, reduce their negative impact on the state of the environment, comply with environmental standards for waste management and ensure environmental safety in the operation of the enterprise is an important task.

4. General characteristics of waste dumps as a source of environmental hazard

Mining activities are associated with the storage of large-tonnage wastes, which are mainly located in the form of waste dumps.

At present, the problem of ecological deformation of territories under the influence of anthropogenic factors is acquiring great importance.

An important environmental issue for the Donetsk region is the activity of mining enterprises directly related to the accumulation of a large amount of industrial waste in the form of waste dumps that have a negative impact on the atmosphere, soil, surface and underground water sources.

Dumps of coal mines are burning, dusting, eroding, radioactive and occupy large areas of fertile land. As a result of physical and chemical weathering, the rock is destroyed, turns into dust and, together with combustible gases and a burning center, is one of the main sources of air pollution and deterioration of the sanitary condition of cities.

Burning waste dumps are a source of emissions of a number of substances, namely carbon monoxide, nitrous oxide, sulfur dioxide and solid particles (in particular, coal dust), heavy metals. Combustion contributes to a significant change in the composition of atmospheric air and acid rain, as 4–5 tons of carbon monoxide and from 600 to 1100 kg of sulfur dioxide, as well as small amounts of hydrogen sulfide, nitrogen oxides and others burning products. The amount of pollutant emissions from the heaps is about 70 thousand tons per year.

Of particular danger is the possibility of radiation contamination of the area as a result of the displacement and the discovery of deeper layers of rock, which may have an increased background radiation. Donbass shale contain sulphide sulfur in the form of pyrite in fairly large quantities, and an increase in the level of radiation on waste dumps is caused by the fact that uranium is in coal containing sulphide sulfur [6].

In humid air, sulfurous anhydride, which is released from the heaps, forms sulfuric acid, which, together with the rains, falls to the ground.

Rainwater leaching and leaching processes lead to contamination of nearby territories with heavy metals and radionuclides.

The washed away rock is very toxic, since the oxidation of pyrite causes the freshly poured neutral rock of the heaps to become sulfuric acid with a pH of 3. Sulfuric acid, which is formed as a result of pyrite oxidation, dissolves various metals and migrates to adjacent territories.

It is possible to reduce the activity of wind and water erosion in the waste heaps by controlling the water permeability of the rock in relation to heavy rainfall and melt water, which largely depends on the presence of woody vegetation at dumps. By creating artificial plantations and contributing to the development of self-seeding woody vegetation, erosion processes on dumps can be completely stopped [7].

Thus, reclamation and landscaping of waste dumps gives many positive results, including: eliminating the negative impact of waste dumps on the environment, the possibility of using the dump territory for economic activities, the possibility of creating recreational zones.

Therefore, the relevance of landscaping is due to the fact that it provides: the creation of new productive areas of the land fund, the involvement in the economic circulation of unproductive and unproductive lands, the elimination of the negative impact of disturbed lands on the environment.

5. Analysis of the possibility of using sewage sludge for biological reclamation of coal mine rock dumps

One of the options for reducing the negative impact of dumps on the environment is their biological reclamation, which involves planting trees, shrubs and grass vegetation on the surface of the waste heaps.

Land reclamation can be understood as a set of activities aimed at restoring the biological productivity and economic value of disturbed lands, as well as improving environmental conditions.

In the conditions of modern Donbass, the most convenient way of reclamation is sowing grass at the foot of the dump and their further spread on the slopes.

As herbs for sowing, perennial herbs are used: Achillea millefolium, Artemisia absintium, Artemisia vulgaris, Berteroa incana, Eriheron canadensis, Lactuca serriola, Melilorus, Tanacetum vulgare and others [8].

Also, for planting on dumps use ornamental plants of different geographical origin:

Sorbus sibirica Hedl., Cotinus coggigria, Elaeagnus argentes Pursh., Swida alba, Thelycrania alba L., Syringa josikae Yacg., Acer tataricum [9].

Plants inhabiting the heaps should be resistant to extreme values of indicators (pH, the amount of toxic salts, the content of gypsum and carbonates, the amount of mobile aluminum, the content of humus).

The decisive role on the landscaping of the waste heap by grassy species is rendered by:
– conditions of waste dump: edaphic factors, temperature and amount of harmful gas emissions, dust;
– relief features of a heap;
– species diversity of the surrounding phytocenosis.

Their landing will lead to:
– restoration of a natural type of a technogenic zone of waste heaps;
– strengthening the slopes of the dump, reducing the negative impact of dumps on the environment;
– formation of soil cover, settling with new plant species.

One of the limiting factors for successful landscaping is the lack of biogenic elements (nitrogen, phosphorus, organic carbon and other elements) in the rock dumps. At the same time, domestic sewage sludge is characterized by a high content of elements and compounds, which have a favorable effect on the growth and development of plants [9].

At the moment, on the basis of GU Donetsk Botanical Garden we are conducting an experiment, which consists in preparing soil mixtures with different particle size distribution of the waste rock and different percentage ratio of the studied WWS (25 %, 50 %, 75 %), and the control soil mixture not containing WWS, further seeding of test-plants of herbaceous plants.

As a result of the experiment, it is planned to determine: the morphometric parameters of plants and the accumulation of toxicants (TM) by the vegetative organs, and the initial level of toxicants (TM) in soil mixtures will also be determined. In addition, it is also planned to determine seed germination. Germination of herbaceous plants occurs under certain conditions: the average air temperature is 22 °C, the average soil temperature is 24 °C, with periodic watering (once every 3 days) with ordinary settled water.

The results of this experiment will determine the feasibility of using WWS for landscaping the waste dumps of coal mines.

Conclusions

Thus, the question of the possibility of using sewage sludge for non-reclaimed waste dumps and their further landscaping will solve the problems associated with the disposal of these wastes occupying large areas of fertile land, restoring soil fertility of waste heaps, increasing the salivary fertilizer value of soil waste dumps, as well as reducing the negative impact of sewage sludge and waste dumps on all environmental components.

This masterʼs work is not completed yet. The term of final completion: June 2019. The full text of the work and materials on the topic can be obtained from the author or his head after this date.

References

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