Browsing by Author "Valchev I."
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Item Adsorption of Ag+ ions on hydrolyzed lignocellulosic materials based on willow, paulownia, wheat straw and maize stalks(2016-05-01) Vassileva P.; Radoykova T.; Detcheva A.; Avramova I.; Aleksieva K.; Nenkova S.; Valchev I.; Mehandjiev D.In the present work, the adsorption of Ag+ ions on hydrolyzed plant biomass (willow, paulownia, wheat straw and maize stalks) was investigated. Chemical analyses were performed to establish the composition of the obtained materials. Adsorption mechanism, adsorption sites and specific surface areas of these materials were examined by BET analysis, IR spectroscopy, XPS and EPR. The effects of contact time, acidity of initial solutions and Ag+ ion concentrations were followed. Pseudo-first-order, pseudo-second-order and intra-particle diffusion models were used to analyze kinetic data. In all cases, the adsorption was significantly affected by the pH value. Different types of adsorption isotherms of Ag+ ions (either Langmuir or Freundlich) were registered depending on the adsorbing material. The adsorption mechanism is complex, and the process passes through different stages as clustering of Ag+ ions and formation of elemental Ag. The maximal adsorption capacities varied from 2.05 to 6.07 mg g−1. The obtained results revealed that the examined waste lignocellulosic materials are promising adsorbents for Ag+ ions.Item Black liquor lignin products, isolation and characterization(2013-11-05) Radoykova T.; Nenkova S.; Valchev I.By extraction with toluene and ethyl acetate monomeric lignin compounds: 2-methoxyphenol, 2,6-dimethoxyphenol, 4-hydroxy-3-methoxybenzaldehyde, 4-hydroxy-3,5-dimethoxybenzaldehyde, 1-(4-hydroxy-3-methoxyphenyl) ethanone, 1-(4-hydroxy-3,5-dimethoxyphenyl) ethanone, etc. were isolated from black liquor and sulfate lignin, and identified through GC/MS analysis. The identified low-molecular mass lignin compounds do not contain organic bonded sulphur. The sulfate lignin, separated from black liquor after acidification with acid was subjected to an alkaline treatment (4 h; 180oC; 5 % NaOH; lignin/NaOH ratio -1:8).Item Cloacal bursa morphology in turkey broilers challenged with aflatoxin b1 alone or co-administered with mycotox ng(2020-01-01) Grozeva N.; Valchev I.; Lazarov L.; Hristov T.; Kanakov D.; Dimitrov K.; Binev R.Aflatoxins are toxic metabolites of moulds from the genus Aspergillus (Aspergillus flavus and Aspergillus parasiticus being the main producers). The aim of the present investigation was to evaluate the toxic effects of aflatoxin B1 on bursa of Fabricius morphology. Also, the possibility for prevention of toxic effects of AFB1 by feed supplementation of a mycosorbent (Mycotox NB) was studied. Experiments were carried out with sixty 7-day-old female turkey broilers (meat TM strain) divided into one control and five treatment groups (n=10). Groups were as followed: Group I – control (fed standard feed according to the species and age of birds); Group II – experimental, whose feed was supplemented with 0.5 g/kg Mycotox NG, Group III– experimental, whose feed contained 0.2 mg/kg aflatoxin B1, Group IV – experimental, whose feed contained 0.4 mg/kg aflatoxin B1, Group V – experimental, supplemented with 0.2 mg/kg aflatoxin B1 and 0.5 g/kg Mycotox NG and Group VI – experimental, supplemented with 0.4 mg/kg aflatoxin B1 and 0.5 g/kg Mycotox NG. The duration of the experiments was 42 days. The changes in bursal morphology in control and treated groups were followed out after the end of the study. In birds from experimental groups ІІI and IV, atrophy and degenerative changes have occurred in the bursa of Fabricius: reduction of lymphoid cell-populations in lymphoid follicles along with dystrophy. Feed supplementation with the tested toxin binder (Groups V and VI) resulted in partial neutralisation of deleterious effects of AFB1 on severity of histological lesions: interfollicular oedema, considerably lower lymphoid follicle rarefaction.Item Effect of aflatoxin B1 alone or co-administered with mycotox ng on the renal function and morphology of Turkey broilers(2019-01-01) Valchev I.; Grozeva N.; Kanakov D.; Hristov T.; Lazarov L.; Dimitrov K.; Binev R.The changes in relative weight of kidneys, blood plasma uric acid, urea, creatinine, calcium and inorganic phosphate, and the morphology of kidneys were investigated in turkey broilers with experimentally induced aflatoxicosis B1 (AFB1) treated or not with a mycosorbent (Mycotox NB). Experiments were carried out with 60 7-day-old female turkey broilers (meat TM strain) divided into one control and five treatment groups (n=10): Group I – control (0 mg/kg AFB1 not supplemented with Mycotox NG); Group II (0.5 g/kg Mycotox NG), Group III (0.2 mg/kg AFB1), Group IV (0.4 mg/kg AFB1), Group V (0.2 mg/kg AFB1 and 0.5 g/kg Mycotox NG) and Group VI (0.4 mg/kg AFB1 and 0.5 g/kg Mycotox NG). The changes in blood parameters were assayed on day 21 and 42. Blood analysis in groups III and IV on day 21 showed increased urea and creatinine concentrations and reduction in blood uric acid, calcium and inorganic phosphate. These changes tended to become more pronounced on day 42. The relative weight of kidneys was increased in groups III and IV after the end of the experiment. Morphological alterations of renal parenchyma in Groups I and II were not present. In birds from group III, desquamation of epithelial cells from the basement membrane, dilated glomerular subcapsular space and round-cell proliferation were noted. In Group V, these changes were far more severe and comprised granular and fatty dystrophy, karyolysis and plasmolysis, necrobiotic to necrotic processes, haemorrhages, congestion. The supplementation of the feed of groups V and VI with the tested toxin binder reduced the severity of reduction of kidneys’ relative weight, magnitude of changes in blood parameters, and the frequency and severity of histological lesions.Item Effect of Hot-Pressing Temperature on the Properties of Eco-Friendly Fiberboard Panels Bonded with Hydrolysis Lignin and Phenol–Formaldehyde Resin(2024-04-01) Valchev I.; Savov V.; Yordanov I.; Petrin S.; Antov P.Lignin is the natural binder in wood and lignocellulosic plants and is regarded as the main natural and renewable source of phenolic compounds. Its incorporation in the composition of fiberboards will enhance both the environmental performance of the panels and the complex use of natural resources. In recent years, the increased valorization of hydrolysis lignin in value-added applications, including adhesives for bonding fiberboard panels, has gained significant research interest. Markedly, a major drawback is the retention of lignin in the pulp until the hot-pressing process. This problem could be overcome by using a small content of phenol–formaldehyde (PF) resin in the adhesive mixture as an auxiliary binder. The aim of this research work was to investigate and evaluate the effect of the hot-pressing temperature, varied from 150 °C to 200 °C, in a modified hot-press cycle on the main physical and mechanical properties of fiberboard panels bonded with unmodified technical hydrolysis lignin (THL) as the main binder and PF resin as an auxiliary one. It was found that panels with very good mechanical properties can be fabricated even at a hot-pressing temperature of 160 °C, while to provide the panels with satisfactory waterproof properties, it is necessary to have a hot-pressing temperature of at least 190 °C.Item Effect of the Adhesive System on the Properties of Fiberboard Panels Bonded with Hydrolysis Lignin and Phenol-Formaldehyde Resin(2022-05-01) Savov V.; Valchev I.; Antov P.; Yordanov I.; Popski Z.This study aimed to propose an alternative technological solution for manufacturing fiberboard panels using a modified hot-pressing regime and hydrolysis lignin as the main binder. The main novelty of the research is the optimized adhesive system composed of unmodified hydrolysis lignin and reduced phenol–formaldehyde (PF) resin content. The fiberboard panels were fabricated in the laboratory with a very low PF resin content, varying from 1% to 3.6%, and hydrolysis lignin addition levels varying from 7% to 10.8% (based on the dry wood fibers). A specific two-stage hot-pressing regime, including initial low pressure of 1.2 MPa and subsequent high pressure of 4 MPa, was applied. The effect of binder content and PF resin content in the adhesive system on the main properties of fiberboards (water absorption, thickness swelling, bending strength, modulus of elasticity, and internal bond strength) was investigated, and appropriate optimization was performed to define the optimal content of PF resin and hydrolysis lignin for complying with European standards. It was concluded that the proposed technology is suitable for manufacturing fiberboard panels fulfilling the strictest EN standard. Markedly, it was shown that for the production of this type of panels, the minimum total content of binders should be 10.6%, and the PF resin content should be at least 14% of the adhesive system.Item Effects of aflatoxin B1 alone or co-administered with mycotox NG on performance and humoral immunity of Turkey broilers(2017-01-01) Valchev I.; Marutsova V.; Zarkov I.; Ganchev A.; Nikolov Y.The contamination of poultry feeds with aflatoxins is a global problem responsible for considerable losses to poultry industry. The aim of the present investigation was to evaluate the effects of aflatoxin B1 and Mycotox NG, applied either independently or together, on performance, relative weights of visceral organs and antibody titres against Newcastle disease in turkey broilers. Experiments of 42-day duration were carried out with sixty 7-day-old female turkey broilers (meat TM strain) divided into one control and five treatment groups (n=10): Group І - control (fed standard feed according to the species and age of birds); Group II - experimental, whose feed was supplemented with 0.5 g/kg Mycotox NG, Group II - experimental, whose feed contained 0.2 mg/kg aflatoxin B1, Group IV - experimental, whose feed contained 0.4 mg/kg aflatoxin B1, Group V - experimental, supplemented with 0.2 mg/kg aflatoxin B1 and 0.5 g/kg Mycotox NG and Group VI - experimental, supplemented with 0.4 mg/kg aflatoxin B1 and 0.5 g/kg Mycotox NG. In Groups III and IV, production traits (live body weight, daily weight gain, feed intake) as well as antibody titres were reduced along with increased feed conversion and relative weights of liver, kidneys, heart, pancreas, proventriculus and gizzard. At the same time, relative weights of the spleen, thymus and bursa of Fabricius were statistically significantly lower. The supplementation of the feed of Groups V and VI with 0.5 g/kg Mycotox NG reduced and prevented some of deleterious effects of AFB1 on production traits, antibody titres and relative weights of visceral organs.Item EVALUATION OF MYCOTOXIN BINDER SUPPLEMENTATION ON PRODUCTION PARAMETERS AND ORGAN WEIGHTS IN TOULOUSE GEESE WITH EXPERIMENTAL AFLATOXICOSIS(2022-03-01) Valchev I.; Stoyanchev K.; Marutsova V.; Kanakov D.; Lazarov L.; Hristov T.S.; Binev R.The present study was undertaken to evaluate the beneficial effects of a mycotoxin binder (Mycotox NG 0.05%) in 40 day-old Toulouse geese from both sexes with experimental aflatoxicosis. The birds were reared from day one to 42 days of age on deep litter system and divided into four groups. Nor-mal feed free of aflatoxin (AFB1), was given to the control (Group 1). The feed of Group 2 was supplemented with 0.5 g/kg Mycotox NG, aflatoxin (0.5 mg/kg feed) was supplemented to the feed of Group 3 and Mycotox NG (0.05%) + 0.5 mg/kg AFB1 – to the feed of Group 4. Production parameters (body weight gain, feed intake, feed conversion) and relative organ weights were recorded. The results showed that the total feed intake, final live weight of Mycotox NG + AFB1 treated birds (Group 4) at 6 weeks of age were significantly increased (P<0.01) as compared to birds treated only with AFB1 (Group 3). The total feed conversion ratio of the group given AFB1 only (Group 3) at 6 weeks of age was significantly increased (P<0.01) compared to controls while in Mycotox Ng + AFB1 treated birds (Group-4) it was significantly increased (P<0.01) by post treatment week 1 vs controls, but not as compared to birds treated with AFB1 alone. There was a significant increase in relative weights of liver, kidneys, spleen, heart, pancreas, proventriculus and gizzard in birds fed only afla-toxin (Group 3). The co-administration of Mycotox NG (0.5 g/kg feed) with AFB1 (Group 4) reduced the relative weights of thymus and bursa of Fabricius. The study concluded that dietary supplementa-tion of Mycotox NG could partially neutralise aflatoxicity in geese.Item Investigations on liver function in mulards with experimentally induced aflatoxicosis(2014-01-01) Groseva N.; Valchev I.; Binev R.; Kanakov D.; Hristov T.; Lazarov L.; Uzunova K.; Nikolov Y.Ducklings are among the most sensitive avian species to the toxic effects of aflatoxin .,B1 (AFB1). In this experiment, the toxic effects of AFB1 on liver morphology, blood plasma aspartate amino-transferase (AST), alanine amino-transferase (ALT), alkaline phosphatase (ALP), lactate dehydrogenase (LDH), γ-glutamyltransferase (γ-GT), albumin, blood glucose, and plasma total protein (TP) were established in mulard ducks. The experiment was carried out with four groups of 20 10-day-old ducklings each. Each group included three subgroups with 10 birds. The groups were as followed: group - control (which received standard feed according to the species and age), group - experimental, which received compound feed with 0.5 mg/kg AFB1, group I receiving compound feed supplemented with 0.8 mg/kg AFB1 and group IV . compound feed supplemented with 0.5 mg/kg AFB1 and 2g/kg Mycotox NG. The experiment lasted for 42 days. Macroscopically, livers were enlarged, rounded, with yellowish colour and a frail consistency in group and I. Histopathologically, a various extent of dystrophy was detected depending on the dose of ingested toxin. The supplementation of compound feed with the mycosorbent Mycotox NG improved deviations in blood biochemical parameters and substantially reduced the severity and prevalence of histological lesions.Item Numerical methods for monitoring and evaluating the biofouling state and effects on vessels’ hull and propeller performance: A review(2022-05-01) Valchev I.; Coraddu A.; Kalikatzarakis M.; Geertsma R.; Oneto L.Monitoring and evaluating the biofouling state and its effects on the vessel's hull and propeller performance is a crucial problem that attracts the attention of both academy and industry. Effective and reliable tools to address this would allow a timely cleaning procedure able to trade off costs, efficiency, and environmental impacts. In this paper, the authors carry out a critical review, accompanied with summary tables, of the biofouling problem with a particular focus on the shipping industry and the state-of-the-art techniques for monitoring and evaluating the biofouling state and its effects on the vessel's hull and propeller performance. In particular, different techniques are grouped according to the three main families of numerical models that have been designed and exploited in the literature: Physical Models (i.e., models relying on the mechanistic knowledge of the phenomena), Data-Driven Models (i.e., models relying on historical data about the phenomena together with Artificial Intelligence), and Hybrid Models (i.e., a hybridisation between Physical and Data-Driven Models). A conclusion from the performed review, open problems, and future direction of this field of research is detailed at the end of the review.Item Optimization of the hot-pressing regime in the production of eco-friendly fibreboards bonded with hydrolysis lignin(2022-11-26) Valchev I.; Yordanov Y.; Savov V.; Antov P.This research was aimed at studying the potential of using residual lignin from acid hydrolysis as a binder in manufacturing eco-friendly, dry-process fibreboards. For that purpose, a modification of the adhesive system and hot-pressing regime was conducted. The adhesive system applied was composed of 2 % phenol-formaldehyde (PF) resin and 10 % hydrolysis lignin (based on the dry fibres). The PF resin does not only act as a binder but generally contributes to the even distribution and good retention of the main binder – hydrolysis lignin. A specific hot-pressing cycle was used. In the first stage, the pressure was 1.0 MPa, followed by an increased pressure of 4.0 MPa, and subsequent cooling. The purpose of the initial lower pressure was softening the lignin and reduction of the material moisture content. The effect of the second stage of hot-pressing on the properties of eco-friendly fibreboards was investigated. It was determined that the fibreboards produced with 2 % PF resin and 10 % hydrolysis lignin have similar physical and mechanical properties to those of the control panels, produced with 10 % PF resin at a standard hot-pressing cycle. The findings of this work demonstrate that residual hydrolysis lignin can be effectively utilized as a binder in the production of eco-friendly, dry-process fibreboards with acceptable physical and mechanical properties.Item Producing bleached microcrystalline cellulose by two-stage dilute acid hydrolysis(2020-01-01) Valchev I.; Yavorov N.; Todorova D.This study investigates the process of producing microcrystalline cellulose (MCC) through two-stage acid hydrolysis with intermediate washing and removal of dissolved sugars. The temperature–time dependence shows fast xylose extraction in the initial phase of the process, while the glucose increases slowly and permanently over the period. After the second stage of hydrolysis, a cleaning effect and an increase in pulp brightness is observed. This method allows obtaining MCC, with high brightness and properties appropriate for usage in the pharmaceutical, cosmetics and food industries, as well as in the chemical industry, from paper grade pulp, which contains large amounts of hemicelluloses.Item The genomic history of southeastern Europe(2018-03-08) Mathieson I.; Alpaslan-Roodenberg S.; Posth C.; Szécsényi-Nagy A.; Rohland N.; Mallick S.; Olalde I.; Broomandkhoshbacht N.; Candilio F.; Cheronet O.; Fernandes D.; Ferry M.; Gamarra B.; Fortes G.G.; Haak W.; Harney E.; Jones E.; Keating D.; Krause-Kyora B.; Kucukkalipci I.; Michel M.; Mittnik A.; Nägele K.; Novak M.; Oppenheimer J.; Patterson N.; Pfrengle S.; Sirak K.; Stewardson K.; Vai S.; Alexandrov S.; Alt K.W.; Andreescu R.; Antonović D.; Ash A.; Atanassova N.; Bacvarov K.; Gusztáv M.B.; Bocherens H.; Bolus M.; Boroneanţ A.; Boyadzhiev Y.; Budnik A.; Burmaz J.; Chohadzhiev S.; Conard N.J.; Cottiaux R.; Čuka M.; Cupillard C.; Drucker D.G.; Elenski N.; Francken M.; Galabova B.; Ganetsovski G.; Gély B.; Hajdu T.; Handzhyiska V.; Harvati K.; Higham T.; Iliev S.; Janković I.; Karavanić I.; Kennett D.J.; Komšo D.; Kozak A.; Labuda D.; Lari M.; Lazar C.; Leppek M.; Leshtakov K.; Vetro D.L.; Los D.; Lozanov I.; Malina M.; Martini F.; McSweeney K.; Meller H.; Mentušić M.; Mirea P.; Moiseyev V.; Petrova V.; Douglas Price T.; Simalcsik A.; Sineo L.; Šlaus M.; Slavchev V.; Stanev P.; Starović A.; Szeniczey T.; Talamo S.; Teschler-Nicola M.; Thevenet C.; Valchev I.; Valentin F.; Vasilyev S.; Veljanovska F.; Venelinova S.; Veselovskaya E.; Viola B.; Virag C.; Zaninović J.; Zaüner S.; Stockhammer P.W.; Catalano G.; Krauß R.; Caramelli D.; Zariną G.; Gaydarska B.; Lillie M.; Nikitin A.G.; Potekhina I.; Papathanasiou A.; Borić D.; Bonsall C.; Krause J.; Pinhasi R.; Reich D.Farming was first introduced to Europe in the mid-seventh millennium bc, and was associated with migrants from Anatolia who settled in the southeast before spreading throughout Europe. Here, to understand the dynamics of this process, we analysed genome-wide ancient DNA data from 225 individuals who lived in southeastern Europe and surrounding regions between 12000 and 500 bc. We document a west-east cline of ancestry in indigenous hunter-gatherers and, in eastern Europe, the early stages in the formation of Bronze Age steppe ancestry. We show that the first farmers of northern and western Europe dispersed through southeastern Europe with limited hunter-gatherer admixture, but that some early groups in the southeast mixed extensively with hunter-gatherers without the sex-biased admixture that prevailed later in the north and west. We also show that southeastern Europe continued to be a nexus between east and west after the arrival of farmers, with intermittent genetic contact with steppe populations occurring up to 2,000 years earlier than the migrations from the steppe that ultimately replaced much of the population of northern Europe.Item Utilization Perspectives of Lignin Biochar from Industrial Biomass Residue(2023-06-01) Naydenova I.; Radoykova T.; Petrova T.; Sandov O.; Valchev I.The present study aimed at utilizing technically hydrolyzed lignin (THL), industrial biomass residue, derived in high-temperature diluted sulfuric acid hydrolysis of softwood and hardwood chips to sugars. The THL was carbonized in a horizontal tube furnace at atmospheric pressure, in inert atmosphere and at three different temperatures (500, 600, and 700 °C). Biochar chemical composition was investigated along with its HHV, thermal stability (thermogravimetric analysis), and textural properties. Surface area and pore volume were measured with nitrogen physisorption analysis often named upon Brunauer–Emmett–Teller (BET). Increasing the carbonization temperature reduced volatile organic compounds (40 ÷ 96 wt. %), increased fixed carbon (2.11 to 3.68 times the wt. % of fixed carbon in THL), ash, and C-content. Moreover, H and O were reduced, while N- and S-content were below the detection limit. This suggested biochar application as solid biofuel. The biochar Fourier-transform infrared (FTIR) spectra revealed that the functional groups were gradually lost, thus forming materials having merely polycyclic aromatic structures and high condensation rate. The biochar obtained at 600 and 700 °C proved having properties typical for microporous adsorbents, suitable for selective adsorption purposes. Based on the latest observations, another biochar application was proposed—as a catalyst.