Zeitschriften und Ausgaben

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Volumen 13 (2020): Heft 1 (April 2020)

Volumen 12 (2019): Heft 2 (October 2019)

Volumen 12 (2019): Heft 1 (April 2019)

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Volumen 11 (2018): Heft 1 (April 2018)

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Volumen 10 (2017): Heft 1 (April 2017)

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Volumen 7 (2014): Heft 1 (April 2014)

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Volumen 5 (2012): Heft 1 (April 2012)

Zeitschriftendaten
Format
Zeitschrift
eISSN
1339-3065
Erstveröffentlichung
10 Dec 2012
Erscheinungsweise
2 Hefte pro Jahr
Sprachen
Englisch

Suche

Volumen 12 (2019): Heft 1 (April 2019)

Zeitschriftendaten
Format
Zeitschrift
eISSN
1339-3065
Erstveröffentlichung
10 Dec 2012
Erscheinungsweise
2 Hefte pro Jahr
Sprachen
Englisch

Suche

21 Artikel
Uneingeschränkter Zugang

Remediation potential of bacterial mixed cultures for polychlorinated biphenyls (PCBs) biodegradation

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 1 - 7

Zusammenfassung

Abstract

Remediation of polychlorinated biphenyls (PCBs) in minimal mineral water media in the presence of bacterial mixed cultures consisting of several individual strains is proposed. Starting from the fact that the properties and features of bacterial strains in mixed cultures can be supplemented and compensated, two-, three- and seven-membered mixed cultures (MC) were performed. The strains used for the construction of the MC were isolated from the waste canal of a former PCB producer. The highest biodegradation of 70 % of the sum of seven defined PCB congeners was achieved by two-membered MC containing the strains Rhodococcus sp. and Stenotrophomonas maltophilia added in the biomass ratio of 1 : 3 and 3 : 1. PCB biodegradation by a seven-membered MC was lower (58 %) but provided several benefits over the less-membered mixed cultures or the individual strains: similarity to naturally occurring microflora, easier preparation of the inocula, certain and repeatable results. Periodical reinoculation of the water media resulted to PCB biodegradation increase to 65 %. Seven-membered MC was applied to the historically PCB contaminated sediment as well, where a 59 % degradation of the sum of seven PCB congeners was determined.

Schlüsselwörter

  • bacteria
  • biodegradation
  • bioremediation
  • mixed cultures
  • PCBs
Uneingeschränkter Zugang

Electrolytic colouring of anodized aluminium on tin basis

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 8 - 13

Zusammenfassung

Abstract

The aim of the study was to find parameters of electrolytic colouring on tin basis to form uniform black coatings on anodized aluminium. A two steps electrolytic process consisting of aluminium anodization in a sulphuric acid electrolyte and colouring in tin acidic electrolyte was used. Among parameters influencing the colouring process, AC colouring voltage, composition of the counter electrode and agitation of the colouring electrolyte were studied. Spectrocolorimetry was applied to analyse the quality of the colouring. Thickness of the coloured and sealed anodized specimens was also evaluated. Optimal parameters for uniform colouring of anodized specimens were found. Unfortunately, colouring electrolyte on tin basis is susceptible to oxidation which negatively influences the colouring.

Schlüsselwörter

  • aluminium
  • anodic oxidation
  • tin based electrolytic colouring
  • hydrothermal sealing
  • system
Uneingeschränkter Zugang

Reactivity of calcium carbonate prepared from flue gas desulfurization gypsum

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 14 - 21

Zusammenfassung

Abstract

Reactivity of various calcium carbonate samples for flue gas desulfurization was tested. Two groups of CaCO3 samples were considered; natural limestone containing calcite phase dominantly and samples prepared by the conversion of gypsum with ammonium and carbon dioxide (precipitated CaCO3) containing different amounts of calcite, aragonite and vaterite.

Reactivity of precipitated calcium carbonate depends primarily on the particle size, similarly as in case of industrial samples. The initial reaction rate was comparable with the industrial limestones for samples with the average particle size lower than 15 μm. However, the conversion of laboratory samples was significantly higher after 5 min of the reaction.

Phase composition of the precipitated calcium carbonate has a minor but noticeable impact on the reactivity. The presence of vaterite slightly increased the reactivity, which is in accordance with its lower compact structure in comparison with calcite and aragonite. Unexpected effect of the increased content of aragonite, which is the most compact phase in comparison with calcite and vaterite, was observed. If calcium carbonate contains up to approximately 30 % of aragonite the reactivity increases, which can be explained by the SEM pictures showing agglomerate composition with relatively high specific surface. At higher contents of aragonite, the reactivity decreases. All the obtained results proved the suitability of precipitated CaCO3 prepared from flue gas desulfurization gypsum to be recycled in the flue gas desulfurization process.

Schlüsselwörter

  • flue gas desulfurization
  • CaCO reactivity
  • aragonite
  • calcite
  • vaterite
Uneingeschränkter Zugang

Electrical conductivity of low-temperature sodium-potassium cryolite melts

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 22 - 26

Zusammenfassung

Abstract

Electrical conductivity of NaF-KF-AlF3 melts with different ratios of sodium fluoride and potassium fluoride was measured using a pyrolytic boron nitride tube-type cell with constant distance of electrodes. Molar cryolite ratios MR = (n(NaF) + n(KF))/n(AlF3) varied from 1.5 to 1.2 (with a step 0.1) in the temperature range of (675—900) °C. AC-techniques with a sine wave signal with small amplitude in the high frequency range were applied. Electrolyte resistance was obtained from nonlinear regression analysis according to equivalent circuit. Concentration and temperature dependency of electrical conductivity was described and defined. Experimental data were compared with literary sources and regression equations.

Schlüsselwörter

  • electrical conductivity
  • aluminium electrowinning
  • low-temperature electrolytes
Uneingeschränkter Zugang

Plasma treatment of gelatin photography

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 27 - 33

Zusammenfassung

Abstract

Plasma pre-treatment represents the key enabler technology for microfine cleaning, surface activation and plasma coating of almost all types of materials — from plastics, metals and glasses to textiles, composites and photographs. More and more conventional industrial treatment methods are being replaced by plasma technology in order to make processes more effective and environmentally friendly. This study is oriented on the characterization of a photographic image on two types of photographic paper (glossy and matt photographic paper with a barite layer), and monitoring the effects induced by the Atmospheric Discharge with Runaway Electrons (ADRE) plasma in air atmosphere on the photographic image layers. To evaluate their long-term stability before/after plasma treatment, degradation of black and white gelatin photographic components upon accelerated light aging using Q-SUN was investigated and the photoinduced changes were recorded by FTIR spectroscopy, densitometry and colorimetry. The results obtained demonstrated that the plasma discharge had no significant destructive effect on the photographic image as only negligible changes in the structure of the gelatin were detected due to plasma processing. Consequently, it can be concluded that low-temperature ADRE plasma in air atmosphere has the potential for successful applications in microbial decontamination and purification of damaged gelatin photographs.

Schlüsselwörter

  • ADRE plasma
  • colorimetry
  • densitometry
  • FTIR spectroscopy
  • gelatin photography
Uneingeschränkter Zugang

Sewage sludge as a source of triclosan-resistant bacteria

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 34 - 40

Zusammenfassung

Abstract

Subinhibitory concentrations of antibiotics and biocides in wastewaters and sewage sludge have a great impact on the development of antibiotic resistance and its spread among bacteria. The aim of this work was to determine the occurrence of coliform bacteria and enterococci resistant to biocide triclosan in samples of sewage sludge. Subsequently, isolated strains of coliform bacteria were identified and characterized in terms of their antibiotic susceptibility and ability to form a biofilm. Occurrence of the studied bacteria was monitored in three samples of stabilized sludge from three different wastewater treatment plants (Vrakuňa, Petržalka, and Senec). The number of triclosan-resistant coliforms was the highest in the sludge sample from the wastewater treatment plant in Senec and the lowest in the sludge sample from the wastewater treatment plant in Petržalka. Triclosan-resistant Enterococcus spp. were not found in any sample of stabilized sludge. Most isolates were identified as Citrobacter freundii and Serratia spp. Triclosan-resistant isolates showed also resistance to antibiotics and the majority of them were strong biofilm producers.

Schlüsselwörter

  • antibiotic resistance
  • biofilm
  • coliform bacteria
  • stabilized sludge
  • triclosan
  • wastewater treatment plant
Uneingeschränkter Zugang

Prevalence of Staphylococcus aureus and antibiotic resistant Staphylococcus aureus in public transport in Bratislava, Slovakia

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 41 - 45

Zusammenfassung

Abstract

There is evidence that the transmission of Staphylococcus aureus and methicillin-resistant S. aureus between the community and environmental surfaces still exists. Even the means of this transmission remain uncertain, the public transport system may serve as a potential source of different bacteria, and the contact with contaminated public surfaces may increase the risk for bacterial diseases emergence. This study aimed to investigate S. aureus contamination on Bratislava’s public transport vehicles. Forty samples of hand-touched surfaces were collected during December 2015 and March 2017 by using surface sampling method. S. aureus was detected in all analysed swabs. Simultaneously, antibiotic resistance of S. aureus from swabs was evaluated. Of 40 samples, only 23 % did not contain S. aureus resistant to some of 10 analysed antibiotics. On the other hand, the severe prevalence of highly resistant S. aureus to penicillin, methicillin, ampicillin, and cefoxitin was confirmed. 15 % of isolates displayed resistance to at least three antimicrobial classes. The amount of S. aureus was not significantly influenced by the lines or by the analysed surface (grabs rails or on-board stop buttons). However, there was a statistically significant effect of year period, both between samples from December and March and between samples from the same month but different year. The study confirmed the widespread occurrence of resistant S. aureus in public transport vehicles in Bratislava, Slovakia.

Schlüsselwörter

  • antibiotic resistance
  • Bratislava
  • environmental contamination
  • public transport
Uneingeschränkter Zugang

Trichoderma atroviride: an isolate from forest environment with secondary metabolites with high antimicrobial potential

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 46 - 55

Zusammenfassung

Abstract

This work was focused on the characterization of novel isolate of Trichoderma atroviride O1, found in the forest around the village of Zázrivá (the Northern Slovakia, region Orava). The isolate was identified by sequencing its internal transcribed spacer (ITS) region of rDNA. T. atroviride O1 stimulated the development of lateral roots of model plant Lepidium sativum. Simultaneously, the isolate has proved its high mycoparasitic potential as it displayed the ability to attack colonies of phytopathogenic fungi (Alternaria alternata, Fusarium culmorum, Botrytis cinerea). This isolate produced secondary metabolites, which were isolated and tested for the antimicrobial activity against gram-positive bacteria Staphylococcus epidermidis and Staphylococcus aureus. The growth of these bacteria was suppressed to 10 % and 40 %, respectively. The suppression of the growth of two Candida species was also strong (10 % growth). However, growth parameters of three phytopathogenic fungi (Alternaria alternata, Botrytis cinerea and Fusarium culmorum) were less affected (75 % growth in comparison with the control). Attempts were made to characterize secondary metabolites isolated from T. atroviride O1. Known peptaibols, 20—21 amino acid long, but also shorter peptides, were detected by MALDI-TOF mass spectrometry. Thus, this study demonstrates the plant growth promotion, strong mycoparasitic potential and antimicrobial activity of the isolate T. atroviride O1, which could be in part ascribed to the production of secondary metabolites. This isolate does have a potential in the biocontrol in eco-farming. Further study, particularly, the identification of produced secondary metabolites, is needed.

Schlüsselwörter

  • antimicrobial activity
  • mycoparasitism
  • plant-growth promotion
  • secondary metabolites
Uneingeschränkter Zugang

Synthesis, crystal structure, infrared spectrum, and thermal properties of [Ni(1,10-phenanthroline)3](fumarate)·9H2O complex with hydrogen bonded supramolecular layers involving fumarate anions

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 56 - 62

Zusammenfassung

Abstract

From the aqueous-ethanolic system Ni(OH)2—H2fumphen (H2fum = fumaric acid, phen = 1,10-phenanthroline), novel complex [Ni(phen)3](fum)·9H2O (1) was isolated and characterized by chemical analyses and FT-IR spectroscopy. Results of single crystal X-ray structure analysis have shown that the ionic crystal structure of 1 is built of [Ni(phen)3]2+ complex cations, fumarate dianions and nine crystallographically independent water molecules of crystallization. The Ni(II) atom exhibits hexa-coordination by three phen ligands with mean Ni-N bond length of 2.090 Å. Water molecules form hydrophilic supramolecular layers with fumarate dianions via extended network of O—H···O type hydrogen bonds with O···O distances from the range of 2.676(2)—2. 916(2) Å; hydrophobic complex cations are embedded between these layers. Thermal study of 1 has shown that endothermic dehydration in the temperature range of 95—195 °C takes at least two steps of the process.

Graphical Abstract

Crystal structure of [Ni(phen)3]fum·9H2O (phen = 1,10-phenanthroline; H2fum = fumaric acid) which is built of supramolecular layers formed by hydrogen bonded water solvate molecules and fum dianions and between the supramolecular layers embedded [Ni(phen)3]2+ complex cations is described here.

Schlüsselwörter

  • Nickel(II)
  • fumarato ligand
  • crystal structure
  • hydrogen bond
  • thermal analysis
Uneingeschränkter Zugang

Magnetic composites based on NR and strontium ferrite

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 63 - 69

Zusammenfassung

Abstract

Two types of composites based on natural rubber (NR) and strontium ferrite were tested in this study. Composites of the first type were prepared by incorporation of strontium ferrite in the concentration range ranging from 0 to 100 phr (parts per hundred rubber) into pure NR based rubber matrix, while with those of the second type, strontium ferrite was dosed in the same concentration level into NR based rubber batch with constant amount of carbon black — 25 phr. For rubber matrices cross-linking, a standard sulfur based curing system was used. This work is focused on the effect of magnetic filler content on physico-mechanical, magnetic and thermo-physical properties of composite materials. Subsequently, the cross-link density and the structure of the formed sulfidic cross-links were examined. The results showed that the cross-link density of both types of composites increased with the increasing content of magnetic filler, while the structure of the sulfidic cross-links was almost not influenced by the amount of strontium ferrite. Tensile strength of rubber composites with pure rubber matrix was slightly improved by the incorporation of ferrite, while in case of composites based on a carbon black batch, the incorporation of magnetic filler resulted in the decrease of this characteristic. The presence of magnetic filler in both types of composites leads to a significant increase of the remanent magnetic induction.

Schlüsselwörter

  • rubber composite
  • magnetic filler
  • cross-link density
  • tensile strength
  • remanent magnetic induction
Uneingeschränkter Zugang

On local aromaticity of selected model aza-[n]circulenes (n = 6, 7, 8 and 9): Density functional theoretical study

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 70 - 81

Zusammenfassung

Abstract

A computational study using density functional theory is reported for selected model aza[n]circulenes (n = 6, 7, 8 and 9) and their derivatives consisting of pyrrole and benzene units. Local aromaticity of central rings was discussed and analyzed using theoretical structural indices. Depending on their molecular structures, energies of the highest occupied and lowest unoccupied molecular orbitals change from –5.23 eV to –4.08 eV and from –1.97 eV to –0.41 eV, respectively. Based on B3LYP calculated optimal geometries, electronic structure of molecules and their charge transport properties resulted in the suggestion of three planar molecules containing three or four pyrrole units as potential candidates for p-type semiconductors. Hole drift mobilities for ideal stacked dimers of these potential semiconductors were calculated and they range from 0.94 cm2·V−1·s−1 to 7.33 cm2·V−1·s−1.

Schlüsselwörter

  • aromaticity index
  • HOMED
  • hole mobility
  • molecular orbitals
  • reorganization energy
Uneingeschränkter Zugang

Application of photochromic pigment in mass dyed polypropylene fibres intended for intelligent textiles

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 82 - 90

Zusammenfassung

Abstract

At the present time, characterised by worsening environmental conditions, the protection of human organism against irreversible damage is necessary. Protective clothing on base of smart textiles represents the future in human clothing. In this article, the effect of photochromic pigments on spinnability, drawability and properties of pigmented polypropylene (PP) fibres is presented.

Mechanical properties (tenacity and elongation at break, Young’s modulus), thermo-mechanical properties and the factor of average orientation of fibres were evaluated and discussed. The obtained results indicate a possibility of fibres preparation with photochromic pigments.

Schlüsselwörter

  • polypropylene
  • smart polymers
  • mechanical properties
  • thermal properties
  • photochromic materials
Uneingeschränkter Zugang

Substrate inhibition and pH effect on denitritation with granular biomass

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 91 - 96

Zusammenfassung

Abstract

Undissociated HNO2 (up to 2 mg dm−3) was confirmed as substrate inhibitor for granular biomass from a denitritation upflow sludge bed reactor used for biological removal of nitrite. On the contrary, total nitrite nitrogen (N-NO2 up to 500 mg dm−3) and methanol (COD up to 2000 mg dm−3) were not proven to be inhibitors. pH also affected the denitritation efficiency (optimal pH was 5.9). Reduction of HNO2 concentration in the reactor by effluent recycling is recommended.

Schlüsselwörter

  • denitritation
  • granulated biomass
  • methanol
  • pH
  • substrate inhibition
  • undissociated HNO
Uneingeschränkter Zugang

Bis(3-methylsalicylato)bis(picolinamide)copper(II) complex — preparation, spectral properties and supposed structure

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 97 - 102

Zusammenfassung

Abstract

Blue methylsalicylatocopper(II) complex with picolinamide Cu(3-Mesal)2(pnia)2 has been prepared and characterized by elemental analysis and spectral methods. Based on the infrared spectra, monodentate coordination of 3-methylsalicylate anion has been assumed and the coordination variability of the anion has been shown. By determination and refinement of the unit cell from powder diffraction data, the existence of a monomeric Cu(II) complex can be anticipated. EPR spectrum of the complex is in good agreement with these results. The g-factors fulfil the relation g|| > g > 2.0023, which is consistent with the dx2 – y2 ground electronic state and indicates coordination sphere of distorted tetragonal symmetry {CuN2O2O2´} for the central copper(II) ions.

Schlüsselwörter

  • picolinamide
  • powder diffraction analysis
  • copper(II) complex
  • spectral properties
  • EPR spectroscopy
Uneingeschränkter Zugang

Recombinant human erythropoietin separation using a cation-exchange multimodal adsorbent

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 103 - 107

Zusammenfassung

Abstract

This work deals with the capture of human recombinant erythropoietin (rhEPO) from a mixture of proteins in a concentrated postcultivation supernatant. Cation-exchange multimodal adsorbent Capto MMC ImpRes was selected as potential chromatographic separation material. Its equilibrium properties were investigated in batch adsorption experiments. The effect of pH in the range of 5.5—7.5 and NaCl concentration in the range of 0—300 mM on the adsorption of rhEPO and contaminant proteins was examined. Optimal conditions found in these equilibrium experiments were applied to rhEPO adsorption in a chromatographic column. Several experiments were carried out at different elution conditions to optimize the rhEPO yield and selectivity.

Schlüsselwörter

  • erythropoietin
  • multimodal adsorbent
  • selectivity
  • elution chromatography
Uneingeschränkter Zugang

Thermodynamics of primary antioxidant action of flavonols in polar solvents

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 108 - 118

Zusammenfassung

Abstract

Very recently, a report on the antioxidant activity of flavonoids has appeared, where authors concluded that Hydrogen Atom Transfer mechanism represents the thermodynamically preferred mechanism in polar media (https://doi.org/10.1016/j.foodres.2018.11.018). Unfortunately, serious errors in the theoretical part of the paper led to incorrect conclusions. For six flavonols (galangin, kaempferol, quercetin, morin, myricetin, and fisetin), reaction enthalpies related to three mechanisms of the primary antioxidant action were computed. Based on the obtained results, the role of intramolecular hydrogen bonds (IHB) in the thermodynamics of the antioxidant effect is presented. Calculations and the role of solvation enthalpies of proton and electron in the determination of thermodynamically preferred mechanism is also briefly explained and discussed. The obtained results are in accordance with published works considering the Sequential Proton-Loss Electron-Transfer thermodynamically preferred reaction pathway.

Schlüsselwörter

  • phenolic antioxidant
  • intramolecular hydrogen bond
  • DFT calculation
  • sequential proton-loss electron-transfer
  • solvent effect
Uneingeschränkter Zugang

Influence of hydrotalcite preparation conditions on its physico-chemical properties

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 119 - 126

Zusammenfassung

Abstract

The aim of the research was to prepare and characterize hydrotalcite synthesized under different preparation conditions. The most common hydrotalcite preparation is the co-precipiaton method. The preparation process strongly influences the catalytic properties of hydrotalcite; therefore, optimal conditions have to be determined. During the study, seven samples of the catalyst were prepared in the pH range from 8 to 12 and the synthesis temperature range from 25 to 55 °C. Based on several catalyst properties, optimal synthesis pH 10 was found. Ideal temperature of the preparation was determined to be 35 °C, but the temperature does not have a significant effect on the catalyst properties.

Schlüsselwörter

  • hydrotalcite
  • preparation conditions
  • co-precipitation
  • catalyst
Uneingeschränkter Zugang

Analysis of C3 fraction splitting system performance by mathematical modeling in MATLAB environment

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 127 - 135

Zusammenfassung

Abstract

Propane-propylene mixture splitting by industrial conventional rectification incorporating a heat pump for energy intensity decrease was modeled in the Matlab environment. The constructed model was verified by comparing its results with operational data of a real C3 fraction splitting unit. As documented, increased product quality can be obtained at zero additional costs due to specific features of the system design. Process capacity and product purity limitations have to be considered in future C3 fraction production increase plans. Further compressor and its driving unit design features have to be incorporated in the calculation model to reliably assess the C3 fraction processing costs and provide a reliable tool for process operation optimization.

Schlüsselwörter

  • C3 fraction
  • industrial heat pump
  • mathematical modeling
  • product purity
Uneingeschränkter Zugang

Agile manoeuvres using model predictive control

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 136 - 141

Zusammenfassung

Abstract

This paper shows how model predictive control (MPC) can be used to perform agile manoeuvres in a pendulum-on-a-cart system, which is an abstraction of many mechanical systems commonly used in the industry, such as cranes. Specifically, the problem of moving a cart on which a pendulum is mounted using a free joint is rapidly moved from one position to another one while mitigating the swings of the pendulum. To achieve this goal, an optimization-based MPC strategy is employed that selects the control moves while minimizing the chosen cost function and, simultaneously, enforcing constraint satisfaction. As the controlled system is nonlinear, two options are considered. The first one solves the nonlinear MPC problem in an approximate fashion using the so-called random shooting approach. The second method is based on the first one approximating the nonlinear system by a linear one, followed by applying convex MPC techniques. The performance of both strategies was compared by means of real-time experiments.

Schlüsselwörter

  • nonlinear model predictive control
  • convex model predictive control
  • random shooting
  • linearization
Uneingeschränkter Zugang

An active indirect solar system for food products drying

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 142 - 149

Zusammenfassung

Abstract

An energy independent active indirect solar drying system for the study of food products drying at specific climate conditions was developed and tested. As a model material, sliced tomato was selected because of its short shelf live, high humidity and potential to be a high value dried product. Indirect solar dryer enabled complete protection of the dried material against sunlight, birds, insects, rain and dust during the drying process. The solar dryer system design includes a rectangular section (1000 × 600 × 400) mm chamber and a flat solar collector (1500 × 600 × 100) mm with the surface area of 0.9 m2. Air flow was induced by a fan installed at the inlet of the collector and powered by a photovoltaic solar panel and a battery system. Temperature and humidity of air were monitored at the collector inlet, collector outlet and the drying chamber outlet. The key element of the collector is a 10.5 m long rectangular section aluminum pipe (55 × 35) mm coated with an absorption layer. The maximum dryer capacity is around 3 kg of wet material (sliced tomato) per batch. Average air temperature increase in the collector was measured to be 30 °C during the winter season. Air relative humidity decreased from 21 % to 15 % after passing through the collector. The moisture of tomato slices decreased from the initial value of 92 % down to 22 % during the time of the experiment (30 h). Quality of tomatoes dried using the designed solar dryer differed significantly in color as well as in texture from those dried by the commonly used methods, like an open sun drying system. Equilibrium moisture content of the product was reached after 30 h in December when the maximum outside temperature was 17.6 °C. The tomato mass decreased from 333 g to 33.15 g; the mass loss being approximately 90 %. The heated air temperature and humidity at the dryer inlet and outlet were influenced by the change of the ambient temperature and humidity during the day. Variation of the drying rate with the change of the ambient temperature and humidity was observed. During summer, when the sun radiation increases, the drying time for sliced tomato with 9 mm thickness decreased from 25 h to 15 h. The sample thickness also has an impact on the drying process. When the sample thickness increased from 9 mm to 12 mm, the drying time increased from 15 h to 20 h of active device time.

Schlüsselwörter

  • Active indirect solar dryer
  • renewable energy
  • drying
  • upland condition
  • sliced tomatoes
Uneingeschränkter Zugang

Use of zeolites for macronutrients removal from wastewater

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 150 - 161

Zusammenfassung

Abstract

Natural or synthetic zeolites have unique physical, chemical and structural properties that predetermine their use in many processes, including wastewater treatment. This study presents the results of our preliminary research in the field of nitrogen and phosphorus removal using adsorption and adsorptive ozonation with natural and modified zeolites. Iron-modified zeolite was the most efficient for the removal of ammonium nitrogen by adsorption. Phosphorus removal efficiency using adsorption was relatively low and natural zeolite was not suitable for the phosphorus removal at all. Ozone had no significant impact on the removal efficiency. Regeneration of loaded zeolites with ozone has also been studied. This method was partly efficient but it needs be further examined.

Schlüsselwörter

  • adsorption
  • nitrogen and phosphorus removal
  • wastewater treatment
  • zeolites
21 Artikel
Uneingeschränkter Zugang

Remediation potential of bacterial mixed cultures for polychlorinated biphenyls (PCBs) biodegradation

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 1 - 7

Zusammenfassung

Abstract

Remediation of polychlorinated biphenyls (PCBs) in minimal mineral water media in the presence of bacterial mixed cultures consisting of several individual strains is proposed. Starting from the fact that the properties and features of bacterial strains in mixed cultures can be supplemented and compensated, two-, three- and seven-membered mixed cultures (MC) were performed. The strains used for the construction of the MC were isolated from the waste canal of a former PCB producer. The highest biodegradation of 70 % of the sum of seven defined PCB congeners was achieved by two-membered MC containing the strains Rhodococcus sp. and Stenotrophomonas maltophilia added in the biomass ratio of 1 : 3 and 3 : 1. PCB biodegradation by a seven-membered MC was lower (58 %) but provided several benefits over the less-membered mixed cultures or the individual strains: similarity to naturally occurring microflora, easier preparation of the inocula, certain and repeatable results. Periodical reinoculation of the water media resulted to PCB biodegradation increase to 65 %. Seven-membered MC was applied to the historically PCB contaminated sediment as well, where a 59 % degradation of the sum of seven PCB congeners was determined.

Schlüsselwörter

  • bacteria
  • biodegradation
  • bioremediation
  • mixed cultures
  • PCBs
Uneingeschränkter Zugang

Electrolytic colouring of anodized aluminium on tin basis

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 8 - 13

Zusammenfassung

Abstract

The aim of the study was to find parameters of electrolytic colouring on tin basis to form uniform black coatings on anodized aluminium. A two steps electrolytic process consisting of aluminium anodization in a sulphuric acid electrolyte and colouring in tin acidic electrolyte was used. Among parameters influencing the colouring process, AC colouring voltage, composition of the counter electrode and agitation of the colouring electrolyte were studied. Spectrocolorimetry was applied to analyse the quality of the colouring. Thickness of the coloured and sealed anodized specimens was also evaluated. Optimal parameters for uniform colouring of anodized specimens were found. Unfortunately, colouring electrolyte on tin basis is susceptible to oxidation which negatively influences the colouring.

Schlüsselwörter

  • aluminium
  • anodic oxidation
  • tin based electrolytic colouring
  • hydrothermal sealing
  • system
Uneingeschränkter Zugang

Reactivity of calcium carbonate prepared from flue gas desulfurization gypsum

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 14 - 21

Zusammenfassung

Abstract

Reactivity of various calcium carbonate samples for flue gas desulfurization was tested. Two groups of CaCO3 samples were considered; natural limestone containing calcite phase dominantly and samples prepared by the conversion of gypsum with ammonium and carbon dioxide (precipitated CaCO3) containing different amounts of calcite, aragonite and vaterite.

Reactivity of precipitated calcium carbonate depends primarily on the particle size, similarly as in case of industrial samples. The initial reaction rate was comparable with the industrial limestones for samples with the average particle size lower than 15 μm. However, the conversion of laboratory samples was significantly higher after 5 min of the reaction.

Phase composition of the precipitated calcium carbonate has a minor but noticeable impact on the reactivity. The presence of vaterite slightly increased the reactivity, which is in accordance with its lower compact structure in comparison with calcite and aragonite. Unexpected effect of the increased content of aragonite, which is the most compact phase in comparison with calcite and vaterite, was observed. If calcium carbonate contains up to approximately 30 % of aragonite the reactivity increases, which can be explained by the SEM pictures showing agglomerate composition with relatively high specific surface. At higher contents of aragonite, the reactivity decreases. All the obtained results proved the suitability of precipitated CaCO3 prepared from flue gas desulfurization gypsum to be recycled in the flue gas desulfurization process.

Schlüsselwörter

  • flue gas desulfurization
  • CaCO reactivity
  • aragonite
  • calcite
  • vaterite
Uneingeschränkter Zugang

Electrical conductivity of low-temperature sodium-potassium cryolite melts

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 22 - 26

Zusammenfassung

Abstract

Electrical conductivity of NaF-KF-AlF3 melts with different ratios of sodium fluoride and potassium fluoride was measured using a pyrolytic boron nitride tube-type cell with constant distance of electrodes. Molar cryolite ratios MR = (n(NaF) + n(KF))/n(AlF3) varied from 1.5 to 1.2 (with a step 0.1) in the temperature range of (675—900) °C. AC-techniques with a sine wave signal with small amplitude in the high frequency range were applied. Electrolyte resistance was obtained from nonlinear regression analysis according to equivalent circuit. Concentration and temperature dependency of electrical conductivity was described and defined. Experimental data were compared with literary sources and regression equations.

Schlüsselwörter

  • electrical conductivity
  • aluminium electrowinning
  • low-temperature electrolytes
Uneingeschränkter Zugang

Plasma treatment of gelatin photography

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 27 - 33

Zusammenfassung

Abstract

Plasma pre-treatment represents the key enabler technology for microfine cleaning, surface activation and plasma coating of almost all types of materials — from plastics, metals and glasses to textiles, composites and photographs. More and more conventional industrial treatment methods are being replaced by plasma technology in order to make processes more effective and environmentally friendly. This study is oriented on the characterization of a photographic image on two types of photographic paper (glossy and matt photographic paper with a barite layer), and monitoring the effects induced by the Atmospheric Discharge with Runaway Electrons (ADRE) plasma in air atmosphere on the photographic image layers. To evaluate their long-term stability before/after plasma treatment, degradation of black and white gelatin photographic components upon accelerated light aging using Q-SUN was investigated and the photoinduced changes were recorded by FTIR spectroscopy, densitometry and colorimetry. The results obtained demonstrated that the plasma discharge had no significant destructive effect on the photographic image as only negligible changes in the structure of the gelatin were detected due to plasma processing. Consequently, it can be concluded that low-temperature ADRE plasma in air atmosphere has the potential for successful applications in microbial decontamination and purification of damaged gelatin photographs.

Schlüsselwörter

  • ADRE plasma
  • colorimetry
  • densitometry
  • FTIR spectroscopy
  • gelatin photography
Uneingeschränkter Zugang

Sewage sludge as a source of triclosan-resistant bacteria

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 34 - 40

Zusammenfassung

Abstract

Subinhibitory concentrations of antibiotics and biocides in wastewaters and sewage sludge have a great impact on the development of antibiotic resistance and its spread among bacteria. The aim of this work was to determine the occurrence of coliform bacteria and enterococci resistant to biocide triclosan in samples of sewage sludge. Subsequently, isolated strains of coliform bacteria were identified and characterized in terms of their antibiotic susceptibility and ability to form a biofilm. Occurrence of the studied bacteria was monitored in three samples of stabilized sludge from three different wastewater treatment plants (Vrakuňa, Petržalka, and Senec). The number of triclosan-resistant coliforms was the highest in the sludge sample from the wastewater treatment plant in Senec and the lowest in the sludge sample from the wastewater treatment plant in Petržalka. Triclosan-resistant Enterococcus spp. were not found in any sample of stabilized sludge. Most isolates were identified as Citrobacter freundii and Serratia spp. Triclosan-resistant isolates showed also resistance to antibiotics and the majority of them were strong biofilm producers.

Schlüsselwörter

  • antibiotic resistance
  • biofilm
  • coliform bacteria
  • stabilized sludge
  • triclosan
  • wastewater treatment plant
Uneingeschränkter Zugang

Prevalence of Staphylococcus aureus and antibiotic resistant Staphylococcus aureus in public transport in Bratislava, Slovakia

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 41 - 45

Zusammenfassung

Abstract

There is evidence that the transmission of Staphylococcus aureus and methicillin-resistant S. aureus between the community and environmental surfaces still exists. Even the means of this transmission remain uncertain, the public transport system may serve as a potential source of different bacteria, and the contact with contaminated public surfaces may increase the risk for bacterial diseases emergence. This study aimed to investigate S. aureus contamination on Bratislava’s public transport vehicles. Forty samples of hand-touched surfaces were collected during December 2015 and March 2017 by using surface sampling method. S. aureus was detected in all analysed swabs. Simultaneously, antibiotic resistance of S. aureus from swabs was evaluated. Of 40 samples, only 23 % did not contain S. aureus resistant to some of 10 analysed antibiotics. On the other hand, the severe prevalence of highly resistant S. aureus to penicillin, methicillin, ampicillin, and cefoxitin was confirmed. 15 % of isolates displayed resistance to at least three antimicrobial classes. The amount of S. aureus was not significantly influenced by the lines or by the analysed surface (grabs rails or on-board stop buttons). However, there was a statistically significant effect of year period, both between samples from December and March and between samples from the same month but different year. The study confirmed the widespread occurrence of resistant S. aureus in public transport vehicles in Bratislava, Slovakia.

Schlüsselwörter

  • antibiotic resistance
  • Bratislava
  • environmental contamination
  • public transport
Uneingeschränkter Zugang

Trichoderma atroviride: an isolate from forest environment with secondary metabolites with high antimicrobial potential

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 46 - 55

Zusammenfassung

Abstract

This work was focused on the characterization of novel isolate of Trichoderma atroviride O1, found in the forest around the village of Zázrivá (the Northern Slovakia, region Orava). The isolate was identified by sequencing its internal transcribed spacer (ITS) region of rDNA. T. atroviride O1 stimulated the development of lateral roots of model plant Lepidium sativum. Simultaneously, the isolate has proved its high mycoparasitic potential as it displayed the ability to attack colonies of phytopathogenic fungi (Alternaria alternata, Fusarium culmorum, Botrytis cinerea). This isolate produced secondary metabolites, which were isolated and tested for the antimicrobial activity against gram-positive bacteria Staphylococcus epidermidis and Staphylococcus aureus. The growth of these bacteria was suppressed to 10 % and 40 %, respectively. The suppression of the growth of two Candida species was also strong (10 % growth). However, growth parameters of three phytopathogenic fungi (Alternaria alternata, Botrytis cinerea and Fusarium culmorum) were less affected (75 % growth in comparison with the control). Attempts were made to characterize secondary metabolites isolated from T. atroviride O1. Known peptaibols, 20—21 amino acid long, but also shorter peptides, were detected by MALDI-TOF mass spectrometry. Thus, this study demonstrates the plant growth promotion, strong mycoparasitic potential and antimicrobial activity of the isolate T. atroviride O1, which could be in part ascribed to the production of secondary metabolites. This isolate does have a potential in the biocontrol in eco-farming. Further study, particularly, the identification of produced secondary metabolites, is needed.

Schlüsselwörter

  • antimicrobial activity
  • mycoparasitism
  • plant-growth promotion
  • secondary metabolites
Uneingeschränkter Zugang

Synthesis, crystal structure, infrared spectrum, and thermal properties of [Ni(1,10-phenanthroline)3](fumarate)·9H2O complex with hydrogen bonded supramolecular layers involving fumarate anions

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 56 - 62

Zusammenfassung

Abstract

From the aqueous-ethanolic system Ni(OH)2—H2fumphen (H2fum = fumaric acid, phen = 1,10-phenanthroline), novel complex [Ni(phen)3](fum)·9H2O (1) was isolated and characterized by chemical analyses and FT-IR spectroscopy. Results of single crystal X-ray structure analysis have shown that the ionic crystal structure of 1 is built of [Ni(phen)3]2+ complex cations, fumarate dianions and nine crystallographically independent water molecules of crystallization. The Ni(II) atom exhibits hexa-coordination by three phen ligands with mean Ni-N bond length of 2.090 Å. Water molecules form hydrophilic supramolecular layers with fumarate dianions via extended network of O—H···O type hydrogen bonds with O···O distances from the range of 2.676(2)—2. 916(2) Å; hydrophobic complex cations are embedded between these layers. Thermal study of 1 has shown that endothermic dehydration in the temperature range of 95—195 °C takes at least two steps of the process.

Graphical Abstract

Crystal structure of [Ni(phen)3]fum·9H2O (phen = 1,10-phenanthroline; H2fum = fumaric acid) which is built of supramolecular layers formed by hydrogen bonded water solvate molecules and fum dianions and between the supramolecular layers embedded [Ni(phen)3]2+ complex cations is described here.

Schlüsselwörter

  • Nickel(II)
  • fumarato ligand
  • crystal structure
  • hydrogen bond
  • thermal analysis
Uneingeschränkter Zugang

Magnetic composites based on NR and strontium ferrite

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 63 - 69

Zusammenfassung

Abstract

Two types of composites based on natural rubber (NR) and strontium ferrite were tested in this study. Composites of the first type were prepared by incorporation of strontium ferrite in the concentration range ranging from 0 to 100 phr (parts per hundred rubber) into pure NR based rubber matrix, while with those of the second type, strontium ferrite was dosed in the same concentration level into NR based rubber batch with constant amount of carbon black — 25 phr. For rubber matrices cross-linking, a standard sulfur based curing system was used. This work is focused on the effect of magnetic filler content on physico-mechanical, magnetic and thermo-physical properties of composite materials. Subsequently, the cross-link density and the structure of the formed sulfidic cross-links were examined. The results showed that the cross-link density of both types of composites increased with the increasing content of magnetic filler, while the structure of the sulfidic cross-links was almost not influenced by the amount of strontium ferrite. Tensile strength of rubber composites with pure rubber matrix was slightly improved by the incorporation of ferrite, while in case of composites based on a carbon black batch, the incorporation of magnetic filler resulted in the decrease of this characteristic. The presence of magnetic filler in both types of composites leads to a significant increase of the remanent magnetic induction.

Schlüsselwörter

  • rubber composite
  • magnetic filler
  • cross-link density
  • tensile strength
  • remanent magnetic induction
Uneingeschränkter Zugang

On local aromaticity of selected model aza-[n]circulenes (n = 6, 7, 8 and 9): Density functional theoretical study

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 70 - 81

Zusammenfassung

Abstract

A computational study using density functional theory is reported for selected model aza[n]circulenes (n = 6, 7, 8 and 9) and their derivatives consisting of pyrrole and benzene units. Local aromaticity of central rings was discussed and analyzed using theoretical structural indices. Depending on their molecular structures, energies of the highest occupied and lowest unoccupied molecular orbitals change from –5.23 eV to –4.08 eV and from –1.97 eV to –0.41 eV, respectively. Based on B3LYP calculated optimal geometries, electronic structure of molecules and their charge transport properties resulted in the suggestion of three planar molecules containing three or four pyrrole units as potential candidates for p-type semiconductors. Hole drift mobilities for ideal stacked dimers of these potential semiconductors were calculated and they range from 0.94 cm2·V−1·s−1 to 7.33 cm2·V−1·s−1.

Schlüsselwörter

  • aromaticity index
  • HOMED
  • hole mobility
  • molecular orbitals
  • reorganization energy
Uneingeschränkter Zugang

Application of photochromic pigment in mass dyed polypropylene fibres intended for intelligent textiles

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 82 - 90

Zusammenfassung

Abstract

At the present time, characterised by worsening environmental conditions, the protection of human organism against irreversible damage is necessary. Protective clothing on base of smart textiles represents the future in human clothing. In this article, the effect of photochromic pigments on spinnability, drawability and properties of pigmented polypropylene (PP) fibres is presented.

Mechanical properties (tenacity and elongation at break, Young’s modulus), thermo-mechanical properties and the factor of average orientation of fibres were evaluated and discussed. The obtained results indicate a possibility of fibres preparation with photochromic pigments.

Schlüsselwörter

  • polypropylene
  • smart polymers
  • mechanical properties
  • thermal properties
  • photochromic materials
Uneingeschränkter Zugang

Substrate inhibition and pH effect on denitritation with granular biomass

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 91 - 96

Zusammenfassung

Abstract

Undissociated HNO2 (up to 2 mg dm−3) was confirmed as substrate inhibitor for granular biomass from a denitritation upflow sludge bed reactor used for biological removal of nitrite. On the contrary, total nitrite nitrogen (N-NO2 up to 500 mg dm−3) and methanol (COD up to 2000 mg dm−3) were not proven to be inhibitors. pH also affected the denitritation efficiency (optimal pH was 5.9). Reduction of HNO2 concentration in the reactor by effluent recycling is recommended.

Schlüsselwörter

  • denitritation
  • granulated biomass
  • methanol
  • pH
  • substrate inhibition
  • undissociated HNO
Uneingeschränkter Zugang

Bis(3-methylsalicylato)bis(picolinamide)copper(II) complex — preparation, spectral properties and supposed structure

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 97 - 102

Zusammenfassung

Abstract

Blue methylsalicylatocopper(II) complex with picolinamide Cu(3-Mesal)2(pnia)2 has been prepared and characterized by elemental analysis and spectral methods. Based on the infrared spectra, monodentate coordination of 3-methylsalicylate anion has been assumed and the coordination variability of the anion has been shown. By determination and refinement of the unit cell from powder diffraction data, the existence of a monomeric Cu(II) complex can be anticipated. EPR spectrum of the complex is in good agreement with these results. The g-factors fulfil the relation g|| > g > 2.0023, which is consistent with the dx2 – y2 ground electronic state and indicates coordination sphere of distorted tetragonal symmetry {CuN2O2O2´} for the central copper(II) ions.

Schlüsselwörter

  • picolinamide
  • powder diffraction analysis
  • copper(II) complex
  • spectral properties
  • EPR spectroscopy
Uneingeschränkter Zugang

Recombinant human erythropoietin separation using a cation-exchange multimodal adsorbent

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 103 - 107

Zusammenfassung

Abstract

This work deals with the capture of human recombinant erythropoietin (rhEPO) from a mixture of proteins in a concentrated postcultivation supernatant. Cation-exchange multimodal adsorbent Capto MMC ImpRes was selected as potential chromatographic separation material. Its equilibrium properties were investigated in batch adsorption experiments. The effect of pH in the range of 5.5—7.5 and NaCl concentration in the range of 0—300 mM on the adsorption of rhEPO and contaminant proteins was examined. Optimal conditions found in these equilibrium experiments were applied to rhEPO adsorption in a chromatographic column. Several experiments were carried out at different elution conditions to optimize the rhEPO yield and selectivity.

Schlüsselwörter

  • erythropoietin
  • multimodal adsorbent
  • selectivity
  • elution chromatography
Uneingeschränkter Zugang

Thermodynamics of primary antioxidant action of flavonols in polar solvents

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 108 - 118

Zusammenfassung

Abstract

Very recently, a report on the antioxidant activity of flavonoids has appeared, where authors concluded that Hydrogen Atom Transfer mechanism represents the thermodynamically preferred mechanism in polar media (https://doi.org/10.1016/j.foodres.2018.11.018). Unfortunately, serious errors in the theoretical part of the paper led to incorrect conclusions. For six flavonols (galangin, kaempferol, quercetin, morin, myricetin, and fisetin), reaction enthalpies related to three mechanisms of the primary antioxidant action were computed. Based on the obtained results, the role of intramolecular hydrogen bonds (IHB) in the thermodynamics of the antioxidant effect is presented. Calculations and the role of solvation enthalpies of proton and electron in the determination of thermodynamically preferred mechanism is also briefly explained and discussed. The obtained results are in accordance with published works considering the Sequential Proton-Loss Electron-Transfer thermodynamically preferred reaction pathway.

Schlüsselwörter

  • phenolic antioxidant
  • intramolecular hydrogen bond
  • DFT calculation
  • sequential proton-loss electron-transfer
  • solvent effect
Uneingeschränkter Zugang

Influence of hydrotalcite preparation conditions on its physico-chemical properties

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 119 - 126

Zusammenfassung

Abstract

The aim of the research was to prepare and characterize hydrotalcite synthesized under different preparation conditions. The most common hydrotalcite preparation is the co-precipiaton method. The preparation process strongly influences the catalytic properties of hydrotalcite; therefore, optimal conditions have to be determined. During the study, seven samples of the catalyst were prepared in the pH range from 8 to 12 and the synthesis temperature range from 25 to 55 °C. Based on several catalyst properties, optimal synthesis pH 10 was found. Ideal temperature of the preparation was determined to be 35 °C, but the temperature does not have a significant effect on the catalyst properties.

Schlüsselwörter

  • hydrotalcite
  • preparation conditions
  • co-precipitation
  • catalyst
Uneingeschränkter Zugang

Analysis of C3 fraction splitting system performance by mathematical modeling in MATLAB environment

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 127 - 135

Zusammenfassung

Abstract

Propane-propylene mixture splitting by industrial conventional rectification incorporating a heat pump for energy intensity decrease was modeled in the Matlab environment. The constructed model was verified by comparing its results with operational data of a real C3 fraction splitting unit. As documented, increased product quality can be obtained at zero additional costs due to specific features of the system design. Process capacity and product purity limitations have to be considered in future C3 fraction production increase plans. Further compressor and its driving unit design features have to be incorporated in the calculation model to reliably assess the C3 fraction processing costs and provide a reliable tool for process operation optimization.

Schlüsselwörter

  • C3 fraction
  • industrial heat pump
  • mathematical modeling
  • product purity
Uneingeschränkter Zugang

Agile manoeuvres using model predictive control

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 136 - 141

Zusammenfassung

Abstract

This paper shows how model predictive control (MPC) can be used to perform agile manoeuvres in a pendulum-on-a-cart system, which is an abstraction of many mechanical systems commonly used in the industry, such as cranes. Specifically, the problem of moving a cart on which a pendulum is mounted using a free joint is rapidly moved from one position to another one while mitigating the swings of the pendulum. To achieve this goal, an optimization-based MPC strategy is employed that selects the control moves while minimizing the chosen cost function and, simultaneously, enforcing constraint satisfaction. As the controlled system is nonlinear, two options are considered. The first one solves the nonlinear MPC problem in an approximate fashion using the so-called random shooting approach. The second method is based on the first one approximating the nonlinear system by a linear one, followed by applying convex MPC techniques. The performance of both strategies was compared by means of real-time experiments.

Schlüsselwörter

  • nonlinear model predictive control
  • convex model predictive control
  • random shooting
  • linearization
Uneingeschränkter Zugang

An active indirect solar system for food products drying

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 142 - 149

Zusammenfassung

Abstract

An energy independent active indirect solar drying system for the study of food products drying at specific climate conditions was developed and tested. As a model material, sliced tomato was selected because of its short shelf live, high humidity and potential to be a high value dried product. Indirect solar dryer enabled complete protection of the dried material against sunlight, birds, insects, rain and dust during the drying process. The solar dryer system design includes a rectangular section (1000 × 600 × 400) mm chamber and a flat solar collector (1500 × 600 × 100) mm with the surface area of 0.9 m2. Air flow was induced by a fan installed at the inlet of the collector and powered by a photovoltaic solar panel and a battery system. Temperature and humidity of air were monitored at the collector inlet, collector outlet and the drying chamber outlet. The key element of the collector is a 10.5 m long rectangular section aluminum pipe (55 × 35) mm coated with an absorption layer. The maximum dryer capacity is around 3 kg of wet material (sliced tomato) per batch. Average air temperature increase in the collector was measured to be 30 °C during the winter season. Air relative humidity decreased from 21 % to 15 % after passing through the collector. The moisture of tomato slices decreased from the initial value of 92 % down to 22 % during the time of the experiment (30 h). Quality of tomatoes dried using the designed solar dryer differed significantly in color as well as in texture from those dried by the commonly used methods, like an open sun drying system. Equilibrium moisture content of the product was reached after 30 h in December when the maximum outside temperature was 17.6 °C. The tomato mass decreased from 333 g to 33.15 g; the mass loss being approximately 90 %. The heated air temperature and humidity at the dryer inlet and outlet were influenced by the change of the ambient temperature and humidity during the day. Variation of the drying rate with the change of the ambient temperature and humidity was observed. During summer, when the sun radiation increases, the drying time for sliced tomato with 9 mm thickness decreased from 25 h to 15 h. The sample thickness also has an impact on the drying process. When the sample thickness increased from 9 mm to 12 mm, the drying time increased from 15 h to 20 h of active device time.

Schlüsselwörter

  • Active indirect solar dryer
  • renewable energy
  • drying
  • upland condition
  • sliced tomatoes
Uneingeschränkter Zugang

Use of zeolites for macronutrients removal from wastewater

Online veröffentlicht: 09 Jul 2019
Seitenbereich: 150 - 161

Zusammenfassung

Abstract

Natural or synthetic zeolites have unique physical, chemical and structural properties that predetermine their use in many processes, including wastewater treatment. This study presents the results of our preliminary research in the field of nitrogen and phosphorus removal using adsorption and adsorptive ozonation with natural and modified zeolites. Iron-modified zeolite was the most efficient for the removal of ammonium nitrogen by adsorption. Phosphorus removal efficiency using adsorption was relatively low and natural zeolite was not suitable for the phosphorus removal at all. Ozone had no significant impact on the removal efficiency. Regeneration of loaded zeolites with ozone has also been studied. This method was partly efficient but it needs be further examined.

Schlüsselwörter

  • adsorption
  • nitrogen and phosphorus removal
  • wastewater treatment
  • zeolites

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