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Povzetek: The presence of plastics in the environment is currently one of the most pressing global environmental problems. Microorganisms start to form biofilms on plastic surfaces when they first come in contact with the biosphere; however, these interactions and processes are little understood, especially in freshwaters. This study aimed to better understand the colonization process of microorganisms from activated sludge on plastic materials exhibiting different surface characteristics. We inoculated synthetic fabric (PET), water bottles (PET), and plastic bags for packing vegetables and fruits (HDPE) with microorganisms from activated sludge. Mixtures of plastics and activated sludge, as well as the control, were incubated at 22-24°C in Bushnell Haas (BH) liquid medium and shaken at 120 rpm for two months. The mixtures were sub-sampled weekly and seeded into fresh BH medium with test plastic materials to avoid feeding microorganisms on dead biomass. The colonization was followed by measuring optical density (OD600) of liquid medium, by measurements of isotopic composition of carbon (δ13C) in untreated and treated plastic materials and, with in-specting the plastics surface with scanning electron microscopy (SEM). Overall, the study confirmed differences between colonizing microorganisms on different plastic material when comparing SEM micrographs of materials from the flasks inoculated with activated sludge. The texture of the HDPE bag changed during the experiment in both, control and inoculated flasks, but it is not clear whether the observed changes were due to abiotic or biotic factors. We concluded that microorganisms from activated sludge are capable of colonizing both PET and HDPE materials, and biofilm formation is most probably influenced by the chemical composition of plastics and their surface characteristics.
Ključne besede: biofilm, plastics, SEM, isotopic composition of carbon, co-cultivation, UV sterilization
Objavljeno v DiRROS: 31.07.2024; Ogledov: 90; Prenosov: 79
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Povzetek: The photosymbiosis with host-specific dinoflagellates is a widespread relationship in marine organisms. Despite the evidenced biodiversity of this kind of mutualism, most research focuses on the study of scleractinian corals, and there is a lack of knowledge about other symbiotic cnidarians such as jellyfishes. The Mediterranean jellyfish Cotylorhiza tuberculata (Rhizostomae, Scyphozoa) harbors an endosymbiotic dinoflagellate of the family Symbiodiniaceae. In this study, we examine the algae distribution within the host body as well as, the pigment content and cell density of the symbiont. Furthermore, the size, morphology and fluorescence of cultured symbionts were studied under light microscopy, Imaging Flow Cytometry (IFC), and Scanning Electron Microscopy (SEM). The C:N composition and optical properties of the medusa tissue were measured to evaluate their role in the symbiosis. The medusae body was divided into two different sections to investigate the distribution of symbionts in hospite: oral arms (OA) and umbrella (UM). C:N composition of C. tuberculata was and symbiont density was significantly higher in the OA section. Mean chlorophyll a concentration of the algae was 1.33 (± 0.83) pg Chl a cell–1. The study of the pigment composition by HPLC (High Performance Liquid Chromatography), revealed the presence of 13 different pigments, being the most representative chlorophyll a, chlorophyll c2, and peridinin typical pigments of Symbiodiniaceae. Cell diameter of algae freshly isolated from the host was 8.71 ± 0.97 μm and cell growth rate was 0.52 (± 0.09) 106 cell ml–1 d–1. The presence of vegetative coccoid cells, doublet and motile mastigotes were revealed within the Symbiodiniaceae cultures. A calcifying matrix typical of Symbiodiniaceae and formed in partner with bacteria, was also observed most cultures. The umbrella tissue of the medusa absorbed at ultraviolet radiation (UVR) region, suggesting that medusae tissue protects photosymbionts from the negative effect of the high energetic UVR and attenuates the light intensity reaching algae inside the host. The presence of a dense Symbiodiniaceae population and the protection to UVR and elevated environmental irradiance provided by medusae tissue, maintain symbionts in optimal light conditions for photosynthesis and may be a reason added to explain the population success of Cotylorhiza tuberculata.
Ključne besede: HPLC, SEM microscopy, absorbance, photosymbiosis
Objavljeno v DiRROS: 16.07.2024; Ogledov: 116; Prenosov: 108
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Povzetek: This study presents a comprehensive investigation of the formation, composition and behaviour of oxide layers during the high-temperature oxidation of four different steel alloys (16Mo3, 13Cr, T24 and P91) at a uniform temperature of 650 °C. The study is aimed at assessing the oxidation damage due to short-term overheating. The research combines CALPHAD (CALculation of PHAse Diagrams) calculations, thermogravimetric analysis (TGA) and advanced microscopy techniques, in- cluding scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD), to elucidate the complex mechanisms controlling oxidation kinetics and oxide layer development. CALPHAD calculations were used to determine the thermodynamically stable phases for each steel type at 650 ◦C and different oxygen activities. The results showed different phase compositions, highlighting the importance of the chromium content in steel for the formation of oxide layers. The different oxidation kinetics and oxide layer compositions are presented and associated with the increased risk of material degradation due to overheating. These results have significant implications for industrial applications, mainly the susceptibility to oxidation of low-alloyed steels like 16Mo3 and 13 Cr and contribute to a deeper understanding of oxidation processes in steels.
Ključne besede: high-temperature oxidation, thermogravimetric analysis, kinetics, CALPHAD, boiler steels, SEM, EBSD
Objavljeno v DiRROS: 26.01.2024; Ogledov: 430; Prenosov: 190
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Povzetek: The aim of the paper is to research the influence of foaming and stabilization agents in the alkali activation process of waste green ceramics for future low cost up-cycling into lightweight porous thermal insulating material. Green waste ceramics, which is used in the present article, is a green body residue (non-successful intermediate-product) in the synthesis of technical ceramics for fuses. This residue was alkali activated with Na-water glass and NaOH in theoretically determined ratio based on data from X-ray fluorescence (XRF) and X-ray powder diffraction (XRD) that was set to maximise mechanical properties and to avoid efflorescence. Prepared mixtures were compared to alkali activated material prepared in theoretically less favourable ratios, and tested on the strength and density. Selected mixtures were further foamed with different foaming agents, that are Na-perborate (s), H2O2 (l), and Al (s), and supported by a stabilization agent, i.e., Na-dodecyl sulphate. The goal of the presented work was to prepare alkali activated foam based on green ceramics with density below 1 kg/l and compressive strength above 1 MPa.
Ključne besede: alkali activation, foaming, SEM, XRF, XRD, mechanical strength
Objavljeno v DiRROS: 14.09.2023; Ogledov: 450; Prenosov: 233
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Povzetek: Alkali-activated composites of lightweight aggregates (LWAs, with beneficial insulating properties) and alkali-activated foams (AAFs, higher added value products due to their production from waste materials at well below 100 ◦C) allow for the expectation of superior properties if a chemical bonding reaction or mechanical interlocking occurs during production. However, the interfaces between LWAs and an AAF have not been studied in detail so far. Chemical reactions are possible if the LWA contains an amorphous phase which can react with the alkaline activators of the AAF, increase the bonding, and thus, also their mechanical strengths. These, in turn, allow for an improvement of the thermal insulation properties as they enable a further density reduction by incorporating low density aggregates. This work features a first-detailed analyses of the interfaces between the LWAs’ expanded polystyrene, perlite, expanded clay and expanded glass, and the alkali-activated foam matrices produced using industrial slags and fly ash. Some are additionally reinforced by fibers. The goal of these materials is to replace cement by alkali-activated waste as it significantly lowers the environmental impact of the produced building components.
Ključne besede: alkali activated materials/geopolymers, light weight aggregates, SEM
Objavljeno v DiRROS: 20.06.2023; Ogledov: 578; Prenosov: 263
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