Bulgarian Chemical Communications, Volume 50, Special Issue-B, 2018

Pages 5-6
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Seventh International Conference
“Modern Trends in Science” - FMNS-2017
14 - 18.06.2017, Blagoevgrad, BULGARIA


Section: Chemistry


Impact of malt quality parameters on beer filtration optimization process
Original Research Article
Pages 9 – 14
T. Kamburi, L. Pinguli, L. Lici
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Filtration optimization process needs developing a strategy based on observations, empirical determinations, and continuous monitoring in order to ensure efficient filter operation. This objective will be reached by identifying critical malt parameters which will influence filtration efficiency. Yeast and components that came from malt dominate the filtration process. The biggest case of concern, since they are more difficult to remove than yeast, are thenon-microbial particles. Malt is also responsible for the major part of enzymes that impact on beer and wort filterability. Experiments were carried out in pilot and industrial scale. Proteins and polyphenols dominate the filtration process, but if we use filter-aids and centrifugation, carbohydrates will dominate the filtration characteristics. More important carbohydrates include: unmodified starch, dextrins, pentosans and β-glucans. Carbohydrates that have a significant impact on filtration were tested using enzymatic techniques for three different beers.


Computer modelling of the CB1 receptor by Molecular Operating Environment
Original Research Article
Pages 15 – 19
F. I. Sapundzhi, T. A. Dzimbova
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Thus far two classes of G-protein-coupled receptors (GPCRs) have been discovered and validated as the main therapeutic targets of this system: the cannabinoid receptor type 1 (CB1), which is most widely expressed in the brain and the cannabinoid receptor type 2 (CB2), predominantly found in the immune system. These receptors have been intensively studied for drug development and for their role in the signalling pathway. The computer modelling and homology modelling approaches can be used in the design and discovery of cannabinoid analogues, because the computational structure prediction methods provide a cost-effective alternative in the absence of experimental structures. This study aims to present an attempt to construct a homology model of the cannabinoid receptor using Molecular Operating Environment. The present investigation provides a consistent framework for further investigation of the ligand-receptor interactions.


Amino acid functionalized silica gel as a selective sorbent for enrichment of Pt (II)
Original Research Article
Pages 20 – 24
P. Petrova, M. Chochkova, I. Karadjova, I. Dakova, M. Karadjov
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In this study we report on the synthesis and applicability of 3 new sorbents based on silica gel impregnated with amino acids or with amino acid derivatives, namely L-cystine modified silica gel (SiO2-Cys-Cys), silica gel modified with L-cysteine amide of 4-aminoantypirine (SiO2–Cys) and silica gel modified with N-benzyloxycarbonyl-L-methionine (SiO2-Met) as an efficient sorbent for solid-phase extraction of Pt from hydrochloric acid solutions. Extraction efficiency and selectivity of the sorbents toward Pt(II)/Pt(IV) were studied by batch procedure. The influence of analytical parameters such as acidity of the sample solution, eluent type and volume, effects of foreign ions on the sorption/desorption behavior of Pt(II)/Pt(IV) were investigated. The results obtained demonstrate that SiO2-Cys and SiO2-Met showed high sorption activity toward Pt(II) while SiO2-Cys-Cys is not able to extract quantitatively neither Pt(II) nor Pt(IV). The experiments revealed that the new sorbents SiO2–Cys and SiO2-Met are highly selective toward Pt(II) extracted as Pt(Cl)42- complex while sorption of Pt(IV) is negligible at the same HCl concentration. Analytical procedure was developed for total Pt determination in cosmetic cream samples, based on solid-phase extraction using SiO2-Met as an effective sorbent combined with ICP-OES measurements. Under optimised conditions, the limit of quantification achieved for total Pt in cosmetic creams was 0.2 μg g-1, the RSD value varied between 6-16 % for Pt content between 0.2-1 μg g-1. The accuracy of the proposed method was confirmed by the added/found method and by comparative analysis using direct ICP-MS measurements.


Optimization of biogas production from lignocellulosic materials by different methods of substrate treatment
Original Research Article
Pages 25 – 28
I. Angelov, V. Beschkov
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Biogas is considered a possible alternative to the conventional fuels. It is produced by anaerobic digestion of different organic materials. Generally those materials include mostly manure and municipality waste. Our research focuses on the possibility to utilize new types of organic materials (e.g. ground coffee residue, coniferous vegetation) in combination with the traditional ones. We believe that adding new materials will enhance the process of biogas production and will contribute to higher range of waste treatment. The final product is biogas with higher methane content which makes it useful for heat and power generation. Therefore we focused on utilizing of coniferous material mixed with other organic materials in anaerobic digestion reactor.


Еlectrohydraulic ragging of metallurgical silicon
Original Research Article
Pages 29 – 31
B.R. Nussupbekov, A.K. Khassenov, D.Zh. Karabekova, М. Stoev, A.Zh. Beysenbek, B.I. Kazankap
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The article presents a crushing technology of metallurgical silicon. The proposed ore crushing method is based on the use of the energy of an impulse shock wave resulting from an electrical spark discharge in a liquid. Electro-hydraulic technology is one of the most acceptable in production environment because it provides intensive ragging and crushing of the test material.


Correlation between Cambisols soil characteristics and lead content in wild edible mushrooms (Cantharellus cibarius, Tricholoma equestre, Craterellus cornucopioides)
Original Research Article
Pages 32 – 37
L. Dospatliev, M. Ivanova, K. Gavazov
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The study was conducted on Cambisols soils and wild edible mushrooms from the Batak Mountain, Bulgaria. The total lead content in the soils was determined after their decomposition with HF, HClO4, and HNO3 acids. The mushroom samples were prepared by dry ashing and subsequent dissolution in 3 M HCl. All lead analyses were performed by inductively coupled plasma atomic emission spectroscopy (ICP-OES) at a wavelength of 220.353 nm. Certified reference materials (three soils and tobacco leaves) were also analysed for verification of the accuracy of Pb determination. A correlation/regression analysis was carried out to reveal possible associations between pH, humus content, and total lead content of the soils and the concentration of this element in the mushroom samples.


A cloud-point extraction-chromogenic system for copper(II) based on 1-(2-thiazolylazo)-2-naphthol
Original Research Article
Pages 38 – 43
T. S. Stefanova-Bahchevanska, R. S. Ahmedov, S. Zaruba, V. Andruch, V. B. Delchev, L. K. Dospatliev, K. B. Gavazov
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A cloud point extraction-chromogenic system, containing CuII, 1-(2-thiazolylazo)-2-naphthol (TAN), and Triton X-100 (TX) was investigated. The optimum conditions for CuII extraction and spectrophotometric determination were found: absorption maximum (565 nm), concentration of TAN (4  10–5 M), mass fraction of TX (2.5%), pH (6.0), and incubation time (65 min). The molar absorptivity, limit of detection, linear working range, and fraction extracted were 2.9  105 dm3 mol−1 cm−1, 2.2 ng cm−3, 7.2 – 380 ng cm−3 and 91%, respectively. The composition of the extracted complex is 1:2 (Cu:TAN). Its structure was optimized at the BLYP/aug-cc-pVDZ level of theory. The electron spectrum of the compound was simulated using Lorentzian band shape and compared with the experimental one.


Molecular docking experiments of cannabinoid receptor
Original Research Article
Pages 44 – 48
F. I. Sapundzhi, T. A. Dzimbova, N. S. Pencheva, P. B. Milanov
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The cannabinoid receptor is a part of the endocannabinoid signaling system. CB1 is a therapeutic drug target, and its structure and conformational changes after ligand binding are of great interest. The present study aimed to investigate the interaction between the crystal structure of the human cannabinoid (CB1) receptor (PDB id:5TGZ) and several known cannabinoid ligands in order to determine the structure-activity relationship by using molecular docking with software GOLD 5.2. Four scoring functions provided with GOLD 5.2 were used for molecular docking between the crystal structure of CB1 receptor and the cannabinoid ligands. The obtained results could be used further for in silico experiments of the cannabinoid receptor-ligand interactions.


Adamantane-1-carboxamides: synthesis and antimicrobial activity
Original Research Article
Pages 49 –54
B. Stoykova, M. Chochkova, G. Ivanova, I. Tsvetkova, H. Najdenski, M. Štícha, Ts. Milkova
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The rapid emergence of resistant bacteria highlights the urgent demand for new effective drugs. In view of the importance of adamantane skeleton in various antimicrobial drugs, herein the synthesis of N-adamantane-1-carboxamides of polyamine derivatives is described. The in vitro antibacterial activity of the new synthesized compounds against two Gram-positive (Staphylococcus aureus, Bacillus subtilis) and two Gram-negative (Escherichia coli, Pseudomonas aeruginosa) bacteria, as well as the antifungal activity against Candida albicans was assessed. The results revealed that amongst the new synthesized bisamides, N,N’-bis-adamantane-1-carboxamide of 1,6-diaminohexane was the most effective one and inhibited both Gram-negative and Gram- positive strains with MIC of 125 μg.ml-1. Moreover, the same amide showed the highest antifungal activity (MIC of 63 μg.ml-1) against Candida albicans.

  Section: Methodology in Education    

Didactic methods of teaching physics at "Fan S. Noli" University in Korca
Original Research Article
Pages 57 – 63
L. Kelo, M. Dede, S. Marko, E. Guliqani
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Didactics, once valued as the art of a teacher, is today an established science with properly defined laws, regulations and methods. Considering the actual needs of our schools, the studies concerning the scientific approach of the didactic methods of physics take central priority. The pedagogue at the “Fan S. Noli” University of Korca has put himself up to the selection of the most efficient forms and methods of conveying the concepts of physics to students with different backgrounds, who study the subject of physics for one semester. This article examines the factual aspects of applying just in time teaching method (Peer Instruction), using ConcepTest and solving strategy/scheme for problems, intertwined these with group studying method regarding the subject of physics (this includes lectures, seminars and lab work). The results derived, demonstrate an increased efficiency of the new teaching practices, compared to the traditional ones from two years ago. This is clearly manifested in the increased collaboration between students and teachers when discussing about the subject of physics. Finally, an increased conceptual scale is being evidenced, along with higher results/evaluations than two years ago.


The problem solving method and the research needed to transmit the new sets of knowledge in physics
Original Research Article
Pages 64 – 68
S. Marko, L. Kelo, E. Guliqani
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If the basic principle defining that “Science gets valued from organized knowledge” is properly respected, then the levels of a whole set of student work outcomes like motivation, interest, differentiated work and effectiveness regarding physics classwork, will increase significantly. From this point of view the results achieved by each student, cultivated during the learning process, will arise to a whole new degree. Cultivating the will to study natural sciences, especially physics, means organizing class work throughout independent student work, stimulating a sense of discovery for each student, not an inventorial one. The traditional type of lectures transmits only basic knowledge, without evaluating the real life situations. Also, it doesn’t take into consideration a full scale analysis of the elements presented by a specific model, as well as extracting the needed equations for calculating the quantitative aspect of physical phenomena and their place in the laws of physics. Averaging doesn’t count when evidencing knowledge. The use of interactive methods is supported by presenting a problematic or experimental case and its solution. The teacher, as a moderator, and the student, as an explorer, interact to discover the analysis of a specific problem, along with its ways of solving. This also includes hypothesis formulation, raising arguments and verifying them. Finally, a balanced report is created between the work of the student and that of a teacher. This report helps the student transform, from a simple listener, to an analyzer and determinant of the correct knowledge. The texts used in this branch of science should allow the use of such teaching methods. Such a method shapes consistent and connected knowledge to students by preparing the underlying foundation on which to develop in-depth studies in areas where physics has a priority role.


Non-formal education of physics including making devices for demonstration
Original Research Article
Pages 69 – 71
G. Malchev
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The article views non-formal education of physics as an opportunity for upgrading knowledge, acquiring new skills and improving the personal and social qualities of students during their high-school education. The article offers an alternative form of education in the course of which students make their own devices for demonstrating harmonic oscillation in the 9th grade. It summarizes the importance of non-formal education namely as a way of enlarging the scope of students’ intellectual properties and increasing their interest in science and engineering, which, in its turn, makes the learning process a desirable challenge.


Cognitive problems for developing students’ scientific literacy in their physics education
Original Research Article
Pages 72 – 74
R. I. Vassileva
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The paper deals with one of the most topical issues related to school education – how to form and develop key competencies in natural sciences? A variety of strategies for the realization of this goal are explored and a focus is placed on the opportunities to solve context-based real-life problems. The author suggests custom-designed problems which can
be used in physics education. They are in agreement with the requirements of the Program for International Student Assessment (PISA)..


The role of using educational tasks in teaching сhemistry
Original Research Article
Pages 75 – 78
V.P. Dimitrova, M. E. Shekerliyska
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One of the main purposes of modern education is building scientific literacy in students. Teaching сhemistry pro-vides a variety of opportunities for achieving this. An appropriate tool for acquiring literacy is the use of educational tasks. Research was conducted on implementation of such tasks in learning of chemical processes in the 10th grade. The results showed that systematic and purposeful application can lead to increased interest, development of skills for self-studying and building scientific competence.

  Section: Physics and Technical Sciences    

Study of residual radioactivity in fish and fishery products imported into Bulgaria from China, Vietnam, Japan and Norway
Original Research Article
Pages 81 – 84

L. Direkov
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In the last few years - 2012 - 2014, in Bulgaria, fish and fish products are massively imported from the regions of China, Vietnam, Japan and Norway. As we know in these areas, especially in the zone 61, which is adjacent to the nuclear power plant Fukushima, where there was a global nature disaster in 2011(7 degrees on the scale of INES), there was mass infection with radioactive substances of the Pacific water, plankton, algae and fish. Contamination of the Pacific water with radioactive substances. It was extremely dangerous in the initial period after the accident, but after this as well, mainly after 2015.


Study of residual stresses during electron beam welding of alloyed steels using neutron diffraction
Original Research Article
Pages 85 – 90
P.Petrov, D. Kaisheva, G. Bokuchava, I. Papushkin
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In this work the results from studies of residual stresses of plates of alloyed steel welded using electron beam welding technology (EBW) are presented. The chemical composition of the first and the second welded plate is respectively (wt %): 0.11% C; 0.27% Si; 1.35% Cr; 0,6% Mn; 3,25% Ni and 0.08% C; 1% Si; 2% Mn; 0.045% P; 0.03% S; 8-10.5%Ni; 18-20% Cr. EBW was carried out on the ESW300 / 15-60 welding units manufactured by Leybold-Heraeus at the Instituteof Electronics – BAS. The technological parameters of the EBW process were the following: accelerating voltage U = 60kV; beam current I = 50 mA, welding speed V = 0.5 cm/s; 1 cm/s; 2 cm/s, focusing lens-specimen distance D0 = 38 cm.The measurement of residual stresses was carried out at the Laboratory of Neutron Physics of the Joint Institute forNuclear Research - Dubna, Russia. The flow of neutrons obtained by pulsed fast reactor IBR-2 was used. The diffractionspectra were obtained on a Fourier stress diffractometer FSD, located on the channel №11a of the reactor. The temperaturefields in EBW of both of the alloyed steels were calculated.


Improved multisoliton compressor
Original Research Article
Pages 91 – 94
L.M. Ivanov
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A fiber optic laser pulse compressor, consisting of two fibers, one with positive and the other with negative dispersion of group velocities for the same wavelength, was investigated. This compressor combines the positive sides of the known fiber grating compressor and multisoliton compressor and can be viewed as modified and improved variant of the multisoliton compressor. A numerical model was made to examine the parameters of the proposed compressor and determine the conditions at which the highest compression degree is obtained. The optimal length of the additionally added fiber with positive dispersion which gives maximum compression was determined. A comparative analysis was made between the classic multisoliton compressor and the proposed scheme with improvements. The proposed method is suitable for pulse compression within the spectral range 1.3 − 1.5 μm, where fibers with positive as well as with negative dispersion can be produced using one and the same material.


Analysis of average power at simistor phase adjustment
Original Research Article
Pages 95– 98
V. Milovanski, G. Kalpachka
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The systems for phase adjustment of average power depend on the type of the load. The influence of an active load on the adjustment mode is considered in the paper. When different modes of operation are changing smoothly then the change in the familiar ways is inconvenient. A criterion for delivered average power (when the visual control is missing) is the indication of the measuring instruments that are plugged in the regulated electric circuit. The analysis, that is made and presented in the article, shows a highly nonlinear variation of the average regulated power at corresponding linear amendment of the parameters of the regulating element of the delay time. This leads to complicated settings in the operating mode. Through the made research of the process and the change in the control electric circuit is reached linearization of the delivered average power to the load.


Thermodynamic properties of helium – oxygen mixtures
Original Research Article
Pages 99 – 103
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The paper reports regression functions describing thermodynamic properties of helium-oxygen mixtures covering the pressure range p=0.1-1.8 MPa, temperature T=273.15-333K and helium molar fraction xHe=0.65-0.98. Regression equations that have been derived enable to determine specific heat, specific enthalpy, density, dynamic viscosity and thermal conductivity as the function of pressure, temperature and helium molar fraction in helium-oxygen (HELIOX) breathing mixtures.


Stress distribution in elastic isotropic semi-space with concentrated vertical force
Original Research Article
Pages 104 – 109
L. B. Petrova
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The distribution of stresses in elastic isotropic semi-space in horizontal and vertical direction under the effect of con-centrated vertical force is investigated. A transition to line influences for stresses and their determination to arbitrary load is performed. Analysis and comparison of the results obtained is made.


Force line influences in a single static undetermined beam
Original Research Article
Pages 110 – 114
L. B. Petrova
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General expressions for force line influences in a single static undetermined beam – bilateral fixed and beam fixed–joint pin are investigated. The ordinates of the line influences were obtained in an arbitrary section of the beam. The beam’s elements with constructed lines influences are used for finding line influences in static undetermined systems with application of the displacement method.


Optimization algorithms for finding the shortest paths
Original Research Article
Pages 115 – 120
F. I. Sapundzhi, M. S. Popstoilov
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Graph traveling problems are among the oldest problems of graph theory. The shortest path algorithms are intensively studied problems, which have a lot of applications such as: many problems of dynamic programming with discrete state and discrete time; network optimization problem-networks of roads and telecommunication networks, etc. At the present
time the graphs provide simple but often useful formal representation of biological networks capturing one-to-one relationships between biological units. The aim of the present work is to evaluate the Dijkstra’s algorithm, Floyd-Warshall algorithm, Bellman-Ford algorithm, and Dantzig’s algorithm in solving the shortest path problem, that can be applied to
very different biological systems and problems for biological system modelling. A brief overview of the different types of algorithms for finding the shortest paths is given. C# implementation of the considered algorithms are presented to show how works each of them. The results of evaluating the algorithms along with their time complexity are shown..


Sulfide and nitrate driven fuel cell. Chemical and biochemical denitrification
Original Research Article
Pages 123 – 129
S.Stefanov, E. Razkazova-Velkova,M.Martinov, Ts. Parvanova-Mancheva, V. Beschkov
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A fuel cell is constructed for simultaneous sulfide oxidation and nitrate reduction. The results for biological and chemical denitrification in the cathode compartment are compared. The influence of different concentrations of sulfides and nitrates on the electrical power output of the fuel cell is examined, as well as their simultaneous neutralization. The electrodes used in the anode compartment are graphite rods and pyrolyzed paddling. The biological reduction of the nitrates is carried out by Pseudomonas denitrificans which increases the rate of nitrate depletion compared to the chemical fuel cell.


Improved operational stability of a laccase-based electrode applicable in biofuel cells
Original Research Article
Pages 130 – 135
N.Dimcheva, E. Horozova
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To ensure high electrocatalytic activity and operational stability of immobilized laccase enzyme (isolated from the basidiomycetes Trametes pubescens), different immobilization protocols on various electrode materials (graphite, gold and glassy carbon) were studied. The physical methods of immobilization – physisorption or entrapment of the enzyme in a composite layer, did not yield bioelectrodes with long lasting activity, whilst the immobilization approach based on covalent attachment of the enzyme to the electrode surface was found to produce a bioelectrode with extended operational stability. The basic electrode material was found to play an important role in bioelectrode’s performance. The comparative studies carried out with two different electrode materials – polycrystalline gold and glassy carbon, modified with electrodeposited gold nanoparticles, with identically immobilized laccase on them showed much higher current density for the second type of enzyme electrode. An extended operational stability of ca. 3 weeks was achieved for the laccase immobilized on gold-nanoparticles modified glassy carbon electrode. The value of the open circuit voltage (over 450 mV vs. Ag/AgCl, 3M KCl at pH = 4.5) of the laccase based electrode suggests that it is a good candidate for cathode when engineering biofuel cells.


Copper recovery combined with wastewater treatment in a microbial fuel cell
Original Research Article
Pages 136 – 140
M. Y. Mitov, I. O. Bardarov, E. Y. Chorbadzhiyska, Y. V. Hubenova
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A novel type of microbial fuel cell (MFC), called metallurgical MFC, is an attractive alternative for metal recovery with simultaneous wastewater purification. Valuable metals can be recovered at the cathode by using electricity generated from microbial-assisted oxidation of organic matter at the anode. In this study, the possibility for copper recovery combined with wastewater treatment in double-chamber MFC was examined. CuSO4 solutions with different concentrations were used as a catholyte and synthetic wastewater inoculated with activated sludge from municipality WWTP-Blagoevgrad was applied as an anolyte. Current generation resulting in a decrease of copper ions concentration in the catholyte and deposition of copper on the cathode was documented. It was established that the use of more diluted Cu2+ solutions enhances the degree of copper recovery. The decreased COD in the anolyte at the end of experiments proves the concept for simultaneous copper recovery and wastewater treatment by means of MFC technology.


Photo-induced charge transfer between Lemna minor and anode of photosynthesizing plant fuel cell
Original Research Article
Pages 141 – 146
Y. Hubenova, G. Ivanov, E. Hubenova, M. Mitov
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The photosynthesizing plant fuel cells (PPFC) are bioelectrochemical devices, in which aquatic plants are grown as biocatalysts in fuel cell. Recently, it was proved that higher electrical current is generated by duckweed-PPFC during daytime. In this study a new experimental set-up is developed, so that the Lemna minor duckweeds grown in the PPFC can be irradiated with polarized monochromatic light with precise wavelength, 650 nm (red) and 450 nm (blue-violet), while the electrical current generated is monitored. The higher current values during photoperiod show that photo-induced charge transfer between duckweed and fuel cell anode takes place. The results from both chronopotentiometric and electrochemical impedance spectroscopy analyses reveal the contribution of duckweed` light absorbing photosystems (PS I and PS II) and ETC in the thylakoid membranes to a direct electron transfer to the anode.


Identification of bacterial community in a Sediment Microbial Fuel Cell
Original Research Article
Pages 147 – 153
S. Hristoskova, I. Bardarov, D. Yankov, S. Danova, Y. Hubenova, M. Mitov
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The aim of the present study was to investigate the bacterial community structure in a single-chamber sediment fuel cell (SMFC). The SMFC was prepared with sediment and water from Struma River and was functioned more than three years before analysis. Samples were taken from different places from cathode and anode compartments as well as from both electrodes. A protocol for microbes’ isolation and characterisation has been adapted, using classical microbiological methods and different selective media. The genomic DNA was isolated from pure microbial cultures, obtained from selected single colonies and cultivated twice for biomass accumulation. The obtained DNA samples were analyzed by 1% v/v agarose gel electrophoresis and the concentration and purity were checked. The DNA was used as a target in the PCR assay and following 16 rDNA sequencing analysis. The obtained sequences were analyzed with BLAST analyses, and species identification of the strains were performed .