Ecological Engineering and Environment Protection

ENVIRONMENTAL IMPACTS OF SUBSTATIONS: A SHORT REVIEW
Anđela Jevtić, Vladimir Stanković, Srđan Glišović, Evica Jovanović
Faculty of Occupational Safety in Niš, University of Niš, Serbia
Abstract. Transformers are key elements of the power system, without which the transmission of electricity over long distances would be impossible. Although transformers are required for the power system to function in a stable, efficient and reliable manner, their negative impact on the environment is obvious.
This paper will describe various aspects of that impact, including electromagnetic radiation, soil and water pollution, noise, fire risk, and visual disturbance to the environment. Transformers emit electromagnetic radiation as a result of the electromagnetic fields they generate while operating. This radiation can affect both the environment and human health. Furthermore, oil leaks from transformers can contaminate soil, groundwater, and surface water, increasing the risk of fires and explosions. Transformer noise can pose a significant problem in urban areas, industrial plants, and rural areas. Additionally, the appearance of substations can significantly affect the aesthetics of the environment. This impact is particularly pronounced in urban areas, tourist destinations, and natural areas. The environmental consequences of fire should not be ignored, as they include air, soil, and water pollution, destruction of vegetation, danger to animals, and the potential spread of fire to vegetation or buildings nearby. In addition to various aspects of the negative impact of substations on the environment, the paper also reviews the implementation of preventive measures that can significantly reduce these effects.
Keywords: transformers, environmental effects, risks, preventive measures.

doi.org/10.32006/eeep.2024.2.1218

COMPARING SECONDARY AND TERTIARY FILTERS FOR SUSPENDED SOLIDS AND BOD REMOVAL FROM URBAN WASTEWATER

Albena Vatralova
Climate, Atmosphere and Water Research Institute at the Bulgarian Academy of Sciences, Sofia, Bulgaria
Abstract: A comparison is made between results for removal of suspended solids (SS) and biodegradable carbon pollutants (in terms of BOD₅)from pilot-plant experiments in two types of downflow filters with different role and location in technological schemes for advanced treatment of urban wastewaters. The first type is a dual-media rapid gravity tertiary filter placed after a conventional wastewater treatment plant (WWTP) with primary sedimentation, activated sludge process and secondary sedimentation. The second type is a submerged biological aerated filter (BAF) in a two-stage system of fixed-film reactors for SS, BOD₅ and nitrogen removal in the secondary stage of an urban WWTP (after the primary clarifiers). The grounds for such a comparison are the similarities between the two devices in the: (a) construction, (b) media type and size; (c) influent SS load; (d) hydraulic load, (e) location among the other reactors in the relevant biotechnological schemes. The experimental results show that the BAF in the secondary stage achieves the same and better degree of purification in terms of SS and BOD₅ than the tertiary rapid gravity filter.
Keywords: advanced wastewater treatment, tertiary filters, submerged biological aerated filters (BAFs)

doi.org/10.32006/eeep.2024.2.1927
DECONTAMINATION OF SLUDGE THROUGH THE USE OF A STABILIZER ADAPT MADE BY "DEVNYA CEMENT" AD
Svetla Marinova¹, Elena Zlatareva¹, Nicholas Catidotes²
¹IPAZR „N. Pushkarov”, Bulgaria
²University of Nicosia, Cyprus
Abstract: The large amount of sludge that is generated in wastewater treatment plants /WWTP/ and the lack of drying fields to stabilize them necessitates the conduct of this study. The use of sludge in practice can be a source of biological contamination of soil, water and plants, including pathogenic microorganisms. Regardless of the developed normative documents, there are a number of problems in practice that limit the realization of sewage sludge. One of these problems is related to the disturbed microbiological parameters in most treatment plants. Sludge storage is used as the only way to eliminate pathogenic microorganisms. This method is not effective enough since it requires large areas for sludge storage. The purpose of the study was to determine the possibility of decontamination of sewage sludge using an ADAPT stabilizer for waste treatment produced by ‚Devnya Cement‘ AD. For the preparation of the cement clinker, mainly natural rock materials are used, which, after crushing and grinding, form a "raw material mixture" consisting of natural survins and industrial products containing the major minor oxides - CaO, Si0₂, Al₂O₃and Fe₂O₃. Fresh sludge from WWTP Varna was used, treated with 20, 25 and 35% of the stabilizer. The sludge was analyzed before and after treatment by agrochemicals and microbiological parameters. It was found that the most effective treatment was with 20% sludge dry stabilizer treatment for a period of 20 days. Treatment of the sludge with the stabilizer does not have a negative effect on their chemical and agrochemical characteristics.
Keywords: decontamination, sludge, stabilizer

doi.org/10.32006/eeep.2024.2.2835
COMPARING PROCESS PERFORMANCE OF BIOLOGICAL AERATED FILTERS IN DIFFERENT SCHEMES FOR ADVANCED WASTEWATER TREATMENT
Albena Vatralova
Climate, Atmosphere and Water Research Institute at the Bulgarian Academy of Sciences
Abstract: Experimental results are presented from the performance of downflow biological aerated filters (BAF) in two technological schemes for advanced treatment of primary settled municipal wastewaters. In the first scheme two BAF with granular (Column 1) and crushed (Column 2) expanded clay media operate in parallel for oxidation of organic carbon compounds and ammonium nitrogen (biological nitrification). In the second scheme, Column 1 operates as a submerged anoxic biofilm reactor, which serves for the reduction of oxidized nitrogen (denitrification) in the recirculated nitrified effluent from Column 2. BOD₅ and COD are not affected significantly from the changed purification scheme and the effect on these parameters is very high in both cases. In terms of inorganic nitrogen forms, the nitrification-denitrification system achieves more than twice the pollutant reduction compared to the nitrification-only scheme. At the same time, the increase in the total construction volume of the two-stage system would be less than twice due to the greater purification capacity of the anoxic reactor. This makes the two-stage scheme more economically efficient per unit volume of facilities.
Keywords: advanced wastewater treatment, biological aerated filters (BAF), nitrification, denitrification

doi.org/10.32006/eeep.2024.2.3650
RECENT RESULTS IN TWO-STAGE ANAEROBIC DIGESTION SYSTEMS CONTROL: A MINI REVIEW
Nicolai Christov¹, Haoping Wang², Ivan Simeonov³
¹Université de Lille, France
²Nanjing University of Science and Technology, Nanjing, China
³The Stephan Angeloff Institute of Microbiology, Bulgarian Academy of Sciences, Sofia, Bulgaria
Abstract. This paper briefly presents the research in the field of two-stage anaerobic digestion (TSAD) process control, realized in 2021-2023 by the joint research team of the Department of Biotechnology at The Stephan Angeloff Institute of Microbiology (SAIM), Bulgarian Academy of Sciences, the French-Chinese Laboratory on Automatic Control and Signal Processing (LaFCAS) at Nanjing University of Science and Technology, and the Research Center CRIStAL at University of Lille.
In 2021-2022 the joint research team developed an algorithm integrating extremum seeking control (ESC) with composed recursive model free controller (CRMFC) for output trajectory and disturbance compensation of the TSAD process. In 2022, an efficient Newton-based ESC for TSAD systems is proposed, in which Kalman filter is used to estimate the gradient and the Hessian of the system output equilibrium map. This makes possible to obtain more accurate gradient and Hessian estimates, and enables to speed up the convergence to the extremum. In 2022-2023, a performance guaranteed ultra-local model (ULM)-based predictive control (PG-ULMPC) is developed to address the trajectory tracking problem for TSAD processes in presence of input saturation. These recent results of the joint research team are briefly described in the present survey paper.
Keywords: two-stage anaerobic digestion, hydrogen, methane, extremum seeking control, Kalman filtering, time-delay estimation, ultra-local models, predictive control

doi.org/10.32006/eeep.2024.2.5157

SYNERGISM – KEY TO SUSTAINABLE AGRICULTURE
Alexander Sadovski
Abstract: The report presents a project to study the synergy between fertilization and irrigation of agricultural crops. The goal is to optimize agricultural production processes to achieve Sustainable Agriculture in climate change conditions. Multifactorial experiments with macronutrients nitrogen, phosphorus, potassium, silicon, and micronutrients zinc and boron are described. Crop rotation as the most important element of agricultural practice is explained and the stages and modules of Precision Agriculture are presented. Results from a simulation-modeled experiment are given.
Keywords: Ecological engineering, fertilization, irrigation, precision agriculture, sustainable agriculture, synergy

doi.org/10.32006/eeep.2024.2.5866
SIGNIFICANCE OF RELIEF ELEMENTS FOR THE SILVICULTURAL PROPERTIES OF BROWN FOREST SOILS (DYSTRIC-EUTRIC CAMBISOLS) IN THE PIRIN MOUNTAIN, BULGARIA

Simeon Bogdanov, Pavel Pavlov
University of Forestry, Department of Silviculture, Sofia, Bulgaria
Abstract. The article presents the results of a study on the role of the relief elements in the fertility of Brown Forest soils (Dystric-Eutric Cambisols) and its significance for the composition and productivity of forest stands. To investigate the forest vegetation properties of the soils, soil profiles were created at various altitudes, slopes, and expositions of the terrain. With increasing altitude, the intensity of organic matter transformation in the soil decreases. The influence of slope on soil fertility is reflected in a reduction of soil depth and a decrease in the soil organic matter and total nitrogen content. Differences in hydrothermal conditions depending on the terrain exposition led to the formation of brown forest soils with varying fertility.
Keywords: soils, fertility, relief, forest stands.

doi.org/10.32006/eeep.2024.2.6774
SPECIES COMPOSITION OF TREE VEGETATION IN THE CITY OF SOFIA
Mariam Bozhilova
Forest Research Institute, Bulgarian Academy of Sciences, Sofia, Bulgaria
Abstract. The article examines the diversity of tree species in part of Sofia, Bulgaria, spanning approximately 60 km². A total of 91 species from 53 genera and 25 families were identified. Dominating in the area is Fraxinus excelsior, which constitutes 494 individuals, representing 12.7% of the total number of trees. The genus Fraxinus is the most abundant, with five species accounting for 22.21% of all trees observed. Although these proportions marginally surpass the thresholds outlined by the 10/20/30% rule, they do not yet indicate significant concern. Nonetheless, the high prevalence of Fraxinus excelsior and its genus raises alarms about potential increased risks of disease and environmental stress. Other frequently encountered species include Prunus cerasifera, Quercus robur, Aesculus hippocastanum, Juglans regia, Fraxinus oxycarpa and Tilia cordata. Two invasive species were found in notable quantities: Robinia pseudoacacia (163 individuals) and Ailanthus altissima (88 individuals).
Keywords: Urban forest, tree species composition, Sofia

doi.org/10.32006/eeep.2024.2.7580
RESEARCH ON THE SHIELDING PROPERTIES OF THE INRNE-BAS CYCLOTRON BUNKER
Galina D. Dimitrova, Anguel Demerdjiev, Nikolay Goutev, Elena Geleva, Stefan G. Genchev, Verzhinia Variyska, Velislava Pavlova, Dimitar Tonev
Institute for Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences
Abstract: The purpose of the current work is the evaluation of the radiation fields induced by the beam losses in the cyclotron vacuum tank. For this purpose, we performed simulations with the Monte Carlo particle transport and interaction code FLUKA. Simplified models of the cyclotron and the source of primary particles are implemented. The proton beam is modelled as an isotropic point source positioned in the centre of the cyclotron vacuum tank. This study evaluates the distribution of radiation fields generated by the beam losses during cyclotron operation and after the end of an irradiation session. The effect of replacing parts of the shielding bunker walls with low activation concrete is also studied.
Keywords: TR-24 cyclotron, Radiation shielding, Beam losses, Monte Carlo simulations, FLUKA

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