Start‐up and recovery of a biogas‐reactor using a hierarchical neural network‐based control tool

Due to its intricate internal biological structure the process of anaerobic digestion is difficult to control. The aim of any applied process control is to maximize methane production and minimize the chemical oxygen demand of the effluent and surplus sludge production. Of special interest is the start‐up and adaptation phase of the bioreactor and the recovery of the biocoenose after a toxic event. It is shown that the anaerobic digestion of surplus sludge can be effectively modeled by means of a hierarchical system of neural networks and a prediction of biogas production and composition can be made several time‐steps in advance. Thus it was possible to optimally control the loading rate during the start‐up of a non‐adapted system and to recover an anaerobic reactor after a period of heavy organic overload. During the controlled period an optimal feeding profile that allowed a minimum loading rate of 6 kg COD m^?3 d^?1 to be maintained was found. Maximum loading rates higher than 12 kg COD m^?3 d^?1 were often reached without destabilizing the system. The control strategy resulted simultaneously in a high level of gas production of about 3 m³_biogas m^?3_reactor and a methane content in the biogas of about 70%. To visualize the effects of the control strategy on the reactor's operational space the data were processed using a data‐mining program based on Kohonen Self‐Organizing Maps. Copyright © 2003 Society of Chemical Industry     

IgM and IgG Immunoreactivity of SARS-CoV-2 Recombinant M Protein

Diagnostic evaluation of specific antibodies against the SARS-CoV-2 virus is mainly based on spike (S) and nucleocapsid (N) proteins. Despite the critical functions in virus infection and contribution to the pattern of immunodominance in COVID-19, exploitation of the most abundant membrane (M) protein in the SARS-CoV-2 serology tests is minimal. This study investigated the recombinant M protein’s immunoreactivity with the sera from COVID-19 convalescents. In silico designed protein was created from the outer N-terminal part (19 aa) and internal C-terminal tail (101–222 aa) of the M protein ({"type":"entrez-protein","attrs":{"text":"YP_009724393.1","term_id":"1796318601","term_text":"YP_009724393.1"}}YP_009724393.1) and was recombinantly produced and purified. The designed M protein (16,498.74 Da, pI 8.79) revealed both IgM and IgG reactivity with serum samples from COVID-19 convalescents in Western blot. In ELISA, more than 93% (28/30) of COVID-19 sera were positive for IgM detection, and more than 96% (29/30) were positive for specific IgG detection to M protein. Based on the capacity to provoke an immune response and its strong antigenic properties, as shown here, and the fact that it is also involved in the virion entry into host cells, the M protein of the SARS-CoV-2 virus as a good antigen has the potential in diagnostic purposes and vaccine design.     

Suppression of inherent ferromagnetism in Pr-doped CeO(2) nanocrystals

Ce(1-x)Pr(x)O(2-δ) (0 ≤x≤ 0.4) nanocrystals were synthesized by self-propagating method and thoroughly characterized using X-ray diffraction, Raman and X-ray photoelectron spectroscopy and magnetic measurements. Undoped CeO(2) nanocrystals exhibited intrinsic ferromagnetism at room temperature. Despite the increased concentration of oxygen vacancies in doped samples, our results showed that ferromagnetic ordering rapidly degrades with Pr doping. The suppression of ferromagnetism can be explained in terms of the different dopant valence state, the different nature of the vacancies formed in Pr-doped samples and their ability/disability to establish the ferromagnetic ordering.     

Biomonitoring of mercury in polluted coastal area using transplanted mussels

The Kastela Bay is heavily polluted with inorganic mercury originated from direct discharges from the chlor-alkali plant, which operated in the period from 1950 to 1990. Even though the plant was closed 15 years ago, elevated levels of total mercury are still evident in surface sediments of the bay. In order to assess the availability of remobilized mercury to marine organisms, cultured mussels (M. galloprovincialis) were transplanted from pristine area to Kastela Bay, in the period from September 2000 to March 2001. Mussel samples were collected for the analysis of THg and MeHg in whole soft tissue, gills and digestive gland. Surface sediments and suspended matter were collected for the analysis of THg. Digestive gland was the target organ for the accumulation of THg, while concentrations of MeHg were similar in all analyzed tissues. The percentage of MeHg in mussel tissues (4-27%) was characteristic for the areas contaminated with inorganic mercury. A significant negative correlation was observed between the THg concentration in the tissues and the percentage of MeHg. Concentrations of THg in mussel tissues, which were decreasing from the source of contamination in an anticlockwise direction towards the exit of the bay, were significantly positively correlated to THg content in sediment and suspended particles. Spatial distribution of mercury species (THg and MeHg) in different environmental compartments was in accordance with the prevailing circulation in the bay. Data obtained through 6 months of biomonitoring experiment indicated that digestive gland was more sensitive indicator of THg concentrations in the environment than the whole organism or gills. As for MeHg, all tissues were equally suitable as biomonitors of MeHg concentrations in the environment.     

Drying of Slurries in Fluidized Bed of Inert Particles

A fluid bed dryer with inert particles was used for drying of slurries. Experiments were performed in a cylindrical column 215 mm in diameter and 1200 mm in height with glass spheres as inert particles. Slurries of Zineb fungicide, copper hydroxide, calcium carbonate, and pure water were used as the feed material. The effects of operating conditions on dryer throughput and product quality were investigated. Main performance criteria, i.e., specific water evaporation rate, specific heat consumption, and specific air consumption, were quantified. Temperature profile along the bed was mapped, and nearly isothermal conditions were found due to thorough mixing of the particles. The material hold-up and residence time were determined. Simple heat and mass balances predict the dryer performance quite well.     

Amperometric assessment of glucose electrode behaviour in mixed solvents and determination of glucose in dairy products

An amperometric biosensor based on a ruthenium(III), nickel(II) and iron(II) hexacyanometallate (HCM)-modified graphite electrode and immobilized glucose oxidase has been used for the determination of glucose in water-miscible organic solvent/aqueous buffer mixtures. Although the specific activity of biochemically active molecule such as enzyme is reduced in organic environment, it was established that the presence of water soluble organic solvents such as methanol, ethanol and acetonitrile (φ = 10%) enhance the biosensor response. Hydrogen peroxide, produced by enzyme-catalysed reduction of glucose, was measured in phosphate buffer solution (pH = 6.86) at −50 mV against a reference Hg|Hg₂Cl₂|3 M KCl electrode to determine the concentration of glucose. The influence of the addition of different volume fractions (φ = 10–60%) of methanol, ethanol, acetone, acetonitrile and isopropanol on biosensor response was investigated. The obtained amperometric signals were fast, reproducible and linearly proportional to glucose concentrations in the range of 0.1–0.8 mM, with a squared correlation coefficient of 0.9994 for buffer solution. With the addition of ethanol (φ = 10% and 40%) the plateau on I/c curve was obtained for concentrations of glucose higher than 0.8 and 1.1 mM, respectively. The biosensor proved to be stable for several months. The recoveries of added glucose (0.200 and 0.300 mM) from aqueous solution and from solution with ethanol φ = 10% ranged from 96.0% to 108.0%. The biosensor was used for the determination of glucose in some food samples of dairy industry, and the results were consistent with those obtained with the commercially available glucose enzyme photometric kit.     

Thermal properties of 3-hydroxy fatty acids and their binary mixtures as phase change energy storage materials

In the present work, we describe the chemical synthesis of 3-HFAs as prominent derivatives of fatty acids and assess if they could be applied as phase change materials (PCM). In addition, 3-HFAs were obtained by depolymerization of a bacterial biopolymeric material, polyhydroxyalkanoate. Thermal properties of 3-hydoxyoctanoic, decanoic, and dodecanoic acids are reported for the first time. These materials showed the potential to be applied as PCM in temperature range from 33°C to 66°C. In order to expand the temperature range for application of 3-HFAs as PCM, eutectic mass ratios of three kinds of binary mixtures of 3-HFAs were calculated, and their properties were predicted using the Schröder-van Laar equation. Thermal properties of these mixtures were validated by differential scanning calorimetry (DSC) analysis. These results showed that eutectics considerably expanded the scope of applications of 3-HFAs as PCMs. 3-HFAs originating from biotechnologically obtained polyhydroxyalkanoates also showed potential to be applied in development of PCMs.