Sirvi Autor "Klavins, M." järgi
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Kirje Algae processing for energy production: development of waste pyrolysis technology : [Retracted](Estonian University of Life Sciences, 2021) Bisters, V.; Kalviss, J.; Burlakovs, J.; Klavins, M.Kirje A comparative study of the properties of industrially produced humic substances(2020) Klavins, M.; Upska, K.; Viksna, A.; Bertins, M.; Ansone-Bertina, L.; Krumins, J.Humic substances (HSs) are produced industrially in large quantities from low rank coal, weathered coal, peat, also from soils, composts and other sources. Considering that the applications of industrially produced HSs also include food, pharmaceutical applications and environmental technologies, it is important to evaluate their composition and quality and to identify their sources. The aim of the present study is to compare the properties of industrially produced HS samples. HSs were characterised using spectroscopic and other methods. For the identification of origin of HSs, different methods can be used, such as elemental analysis and ratios of light stable isotopes. The results of the study indicate that many industrially produced HSs are of poor quality (low concentration of basic substance, admixture of undesirable substances, pollutants, no quality indications). In this situation, rigorous quality control should be implemented, providing detailed characteristics of the product. The composition of materials suggested for agricultural applications has not been analysed much. Most of the studied materials were designated as HAs, followed by fulvic acids (FAs) and HSs. However, an analysis of the humic matter types indicates that the majority of substances offered on the market are in fact mixtures of HAs and FAs; so, it would be more appropriate to designate them as HSs or their salts. This study identifies the main quality problems of industrially produced humic substances: 1) lack of strict quality indicators, 2) absence of indication of source materials/origins of HSs.Kirje Physical-chemical properties and possible applications of clay minerals and humic acid composite materials(2019) Jemeljanova, M.; Ozola, R.; Klavins, M.Pollution caused by pharmaceuticals has become an increasingly serious issue, therefore innovative and cost – effective methods of pharmaceutical’s removal must be studied. Clay – humic acid composite materials can be considered as prospective and low cost sorbents for contaminants. The aim of this study is to develop clay mineral and humic acid composite materials and to characterise their possible applications. For this research, three types of clay minerals (montmorillonite, kaolinite and bentonite) were modified with three types of humic substances: technical humic acid from lignite, humic substances extracted from raised bog peat and technical K humate from lignite. The sorption was characterised according to the chosen clay mineral and humic acid type and concentration. The obtained material was characterised by Fourier Transform Infrared spectroscopy and Scanning Electron microscopy. The composite materials were tested for sorption of pharmaceuticals (chloropromazine hydrochloride). The obtained results characterise clay mineral and humic acid composite materials’ possible applications as sorbents for removal of pharmacologically active substances.Kirje Properties of soil and peat humic substances from Latvia(2019) Klavins, M.; Purmalis, O.; Grandovska, S.; Klavina, L.The acidity, elemental, functional and spectral (UV, fluorescence, IR spectra) characteristics of humic substances isolated from soils of different origin and peat in Latvia are described and compared with values common for humic substances of different origin, to evaluate the character of processes during humification. Substantial dependence of properties of humic substances on the humification conditions are found.Kirje Role of humic substances in agriculture and variability of their content in freshwater lake sapropel(2019) Stankevica, K.; Vincevica-Gaile, Z.; Klavins, M.The term ‘humic substances’ (HS) refers to a general category of naturally occurring, biogenic, heterogeneous organic substances. They create the most widespread natural organic matter found in sediments, soils and waters. Organic carbon in soil (up to 70%) and peat (up to 90%) usually occurs in the form of HS. HS influence the formation process of fossil fuels, as well as they are involved in the plant nutrition process, have an influence on availability and toxicity of metallic and other elements. Furthermore, HS play a significant role in the global carbon geochemical cycle. Properties and application efficiency of humus depend on the source of HS. Freshwater sapropel is a huge reservoir of HS with superior biological activity, although their total content is lower than in peat. The aim of this paper, firstly, was to present the information about the options of HS in agriculture and their main effects on plant growth. Secondly, determination and characterization of HS content in freshwater lake sapropel was performed as sapropel nowadays becomes a popular natural organic-mineral fertilizer and soil conditioner. Sapropel samples were derived from Lake Pilvelis, Lake Pilcines, Lake Vevers, Lake Liducis and Lake Padelis situated in Eastern Latvia. Investigation of HS content in sapropel is significant for the Baltic States and Northern Europe due to wide distribution and availability of sapropel in freshwater bodies. That promotes a search for new ways of extraction methods and bioeconomically effective utilization of this natural resource, obtainable in economically significant amounts, with high opportunities of its use especially in agriculture. Contemporary agriculture strongly desiderates in new products of high effectivity enhancing soil and crop productivity and quality hand in hand with sustainable development and careful attitude to the nature and surrounding environment, thus, one of the ways how it can be achieved is understanding how, where and how much HS preparations can be applied.Kirje Sapropel processing approaches towards high added-value products(2018) Obuka, V.; Boroduskis, M.; Ramata-Stunda, A.; Klavins, L.; Klavins, M.Sapropel is an organic sediment from fresh water bodies that is widely distributed in the northern regions of the w orld. The distribution and unique properties of sapropel make it an important natural resource that can be used in agriculture , horticulture, forestry and farming directly as obtained. The aim of this study was to investigat e the extraction possibilities of sapropel and potential applications of its extracts. Humic substances constitute an important ingredient of sapropel, and they can be extracted by mild alkaline extraction. Humic substances from peaty sapropel have signifi cant differences in composition and properties, thus demonstrating the impact of precursor biological materials on the properties of humic substances formed in the humification process .Kirje Surface wax composition of wild and cultivated Northern berries(2019) Klavins, L.; Kviesis, J.; Klavins, M.Surface wax of plants is the outer layer, which protects the plant from dehydration, extreme temperatures, UV radiation and changes in the environment, as well as attacks from moulds and bacteria. Studies of berry surface wax are of importance to understand metabolism character (factors affecting wax layer composition in different berry species) as well as to increase the shelf life of berries and increase the microbial resistance. The aim of this study was analysis of surface wax composition of commercially grown 8 blueberry (Vaccinium corymbosum) varieties, wild bilberry (Vaccinium myrtillus L.) and bog bilberry (Vaccinium uliginosum L.). More than 80 different compounds were identified and quantified belonging to 9 groups of compounds, namely, alkanes, phytosterols, alcohols, fatty acids, phenolic acids, ketones, aldehydes, esters and tocopherols. Significant differences were found between blueberry (Vaccinium corymbosum) and bog bilberry (Vaccinium uliginosum L.) surface wax composition. Amongst studied berries differences were found in concentrations of triterpenes (up to 62% in blueberries), and fatty acids (up to 26% in bilberries) identifying species related differences influencing associated functional properties of berry wax (antimicrobial activity, stress caused by environmental changes). Blueberry variety ‘Polaris’ had the highest amount of ursolic acid (9.30 g 100 g -1 ), alpha-amyrin (11.07 g 100 g -1 ) and lupeol (10.2 g 100 g -1 ). Research on berry surface wax composition could help reduce loss of commercially produced berries due to environmental impacts or microbial attacks, prolonging shelf life and overall quality of fruits and vegetables post-harvest.Kirje What happens to peat during bog fires? Thermal transformation processes of peat organic matter(2020) Ozols, V.; Silamikele, I.; Kalnina, L.; Porshnov, D.; Arbidans, L.; Krumins, J.; Klavins, M.Bog fires are a serious natural phenomena. Major increase in the number of fires has happened during the last decades due to bog transformation into agricultural lands, accidents and human activities. During bog fires the peat is exposed to high temperatures due to which chemical transformation and even mineralisation of peat can occur. The aim of the study was to analyse the impacts of the bog fires on the bog as an ecosystem, advance the understanding and knowledge of fire impact on peat and humic matter properties and application possibilities. As the material for the study peat samples from burnt sites and thermally treated peat were used. To reveal peat transformation during bog fires, thermogravimetric analysis of peat samples were done, where amounts of bitumens, humic acids and mineral matter were estimated. During bog fires thermal modification of peat properties takes place, resulting in full mineralisation of peat and release of mineral substances. Bog fires lead to development of peat char, bitumens and significant changes in structure and properties of peat humic acids. However, from perspective of application of peat as a substrate and from perspective of impacts on the bog ecosystems, the effects are negligible.