Veronika Lehotová, Monika Petruláková and Ľubomír Valík
New analytical techniques, the GreenLight™ system for rapid enumeration of total viable counts (TVC) were used to estimate the numbers of bacteria inoculated in different levels in broth nutrient media. The new detection methodology was compared with agar plating EN ISO 4833:2003 method showing excellent correlation. The following coefficients of determination R2 = 0.985 and 0.999 were calculated for aerobic Pseudomonas aeruginosa and facultative anaerobic E. coli, respectively. After calibration, the system based on the principle of quenching of luminescence intensity and lifetime of an oxygen-sensitive dye by sample O2 consumed during microbial growth enables to determine the number of microorganisms within less than 24 hours. The higher microbial load the shorter time for determination of viable count is needed. In case of simple food matrix for example, the results can be reached even within one shift of production.
Thermal inactivation of immobilized glucose isomerase in a concentrated glucose solution was investigated in the batch mode and temperature range of 83–95 °C, which is substantially higher than the temperature used in the industrial production of high-fructose corn syrup. Simultaneous evaluation of all inactivation data showed that first-order kinetics with the Arrhenius temperature dependence of the rate constant provided a good approximation of the biocatalyst stability under the investigated conditions. The model parameters were then used to predict the operational temperature for this biocatalyst in the production of high-fructose corn syrup based on the set operational life-time of the biocatalyst. The simulation predicted a window of operational temperature of 60–65 °C, which corresponds very well with the industrial applications of this biocatalyst. This observation demonstrates that the multi-temperature method of enzyme inactivation can provide a good estimate of biocatalyst process stability and is thus a useful tool in the development of biocatalytic processes.
Thermal inactivation of a commercial β-galactosidase from Aspergillus oryzae in a 300 g/L lactose solution was studied in the temperature range of 65–75 °C. Lactose exhibited a stabilisation effect when similar inactivation rates as those in lactose solution were observed in a lactose-free solution at temperatures lower by 5°C. Inactivation process in the lactose solution was biphasic. A kinetic model based on the Lumry-Eyring mechanism was proposed and successfully verified. Estimated activation energy values were very different. Rather high activation energy values of the forward reactions were responsible for both the significant change of rate constants and the rate-controlling reaction with temperature. For these two reasons, an increase of the operational lifetime of the enzyme from 7 days at 60 °C to 580 days at 55 °C was predicted.
In this study, mixed phase ZnO-TiO2 nanocomposite consisting of hexagonal ZnO and anatase/rutile TiO2 has been synthesized via sol-gel process.The physical and photochemical properties of samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (UV-vis DRS), photoluminscience spectra (PL) and and photocurrent action spectra techniques. In the case of minerlization of rhodamine B (RhB) and malachite green (MG) dyes, the coupled ZnO-TiO2 nanocomposite with the suitable band structure and the lowest photoluminescence intensity showed the best photodecolorization activity. Synergistic effects between the two oxides for photocatalytic decomposition of RhB and MG are proposed to elucidate the decolorization mechanism. The lifetime of electrons and holes was prolonged in the ZnO-anatase/rutile multiple-component system, which can enhance the light harvest and the ability of generating photo-induced electron-hole pairs of active sites, and the favorable electron-transfer properties in the coupled ZnO-TiO2 nanocomposite. Therefore, the as-prepared ZnO-TiO2 nanocomposite showed an excellent efficiency towards the removal of aqueous organic dyes and it is of certain significance for environmental photocatalysis.
I.V. Tudose, M. Suchea, K. Siderakis, E. Thalassinakis and E. Koudoumas
: Pollution of high voltage (HV) insulators is a phenomenon with a considerable impact to the performance of transmission and distribution electrical networks. The use of composite materials and especially Silicone Rubber proved to be an efficient improvement, capable of suppressing the problem and diminishing the flashover probability. As a result ceramic insulators in transmission lines are replaced by insulators with composite housing, either HTV Silicone Rubber or LSR. In the case of HV substations however, the replacement of insulators is rather difficult, due to the complexity of the equipment and the corresponding financial cost. In this case the application of RTV Silicone Rubber is an equivalent alternative. The ceramic insulators are covered with a 0.5 mm RTV SIR coating which provides the advantages of composite insulators on a ceramic substrate. After installation the possible material lifetime, which is determined by the service conditions and the material formulation, is of primary concern. In Crete, a large scale application exists and coatings that exceed a service period of 10 years are still in operation. The present study focuses on the structural and morphological characterization of field collected composite insulators of various ages so that the degradation degree can be correlated with their service.
Uchechi Bliss Onyedikachi, Chuka Donatus Belonwu and Mattew Owhonda Wegwu
This study investigated the potential health risk due to dietary exposure to Polycyclic Aromatic Hydrocarbons (PAHs) for the populace living around selected industrial areas in the south eastern states of Nigeria. The concentrations of PAHs were measured in edible food crops using Gas Chromatography - Flame Ionization Detection (GC-FID). The mean concentration of PAHs in food crops collected ranged from < 0.01 to 2.64 ± 0.02, 5.27 ± 0.04, 0.96 ± 0.02, 8.94 ± 0.01 and 1.95 ± 0.06 in mg/kg for Osisioma, Ishiagu, Irete, Akwuuru, and Ngwo respectively. PAHs distributions in food samples analyzed in this study showed vegetables to be significant higher (p ≤ 0.05) in the order vegetables > fruits > nuts > tubers. Total PAHs (ΣPAHs) concentrations in most crop samples had highest values 14.49, 36.29, 4.59, 23.36 and 21.8 mg/kg for Chyrysophyllum albidum, Telferia occidentalis, Vernonia amygdalina, Talinum triangulare and Elaies guinnensis for Osisioma, Akwuuru, Irete, Ishiagu and Ngwo respectively. The low molecular weight-PAHS/high molecular weight-PAHS were < 1 with values 0.76, 0.18, 0.28, 0.91 and 0.12 for Osisioma, Irete, Akwuuru, Ishiagu and Ngwo respectively. 58.3% and 71.7% of ΣB(a)P and ΣPAHs in food samples in the study areas exceeded the permissible limits set by DPR and EU. The estimated daily intake of PAHs via the ingestion of food crops were within the tolerable range. The carcinogenic risk values for the food crops were within the predicted permissible lifetime risks of carcinogen (10−6-10−4) for adults and children in Osisioma, Akwuuru, Ishiagu and Enugu respectively. Therefore, this study suggests that the populace around industrialized areas in South Eastern Nigeria, may be at risk due to PAHs exposure through food consumption.
Uchechi Bliss Onyedikachi, Donatus Chuka Belonwu and Mattew Owhonda Wegwu
In view of ensuring healthy agricultural foods for human consumption, this study assessed the human health risk implicated in selected heavy metals in some commonly consumed vegetables, tubers, nuts and fruits grown around the quarry sites at Ishiagu, Ebonyi State, Nigeria. Samples from agriculture area of Umudike, Abia State, Nigeria, constituted the control. The concentration of Mn, Zn, Fe, Cu, Cd, and Pb, were determined using atomic absorption spectrometry. The potential non-carcinogenic health risk for consumers which included Estimated Daily Intake (EDI) and Target Hazard Quotients (THQ) for Pb, Fe, Mn, Zn, Cd and Cu while carcinogenic health risk using Cancer Slope Factors (CSF) was established for Cd and Pb. Relative abundance of heavy metals across the locations and all samples was in the order Fe > Mn > Zn > Pb > Cu > Cd. There was statistical significant effect of quarrying activities on the concentration of the heavy metals (Fe, Mn, Zn, Pb, Cu, Cd) at p < 0.05 level. Based on the observed bioconcentration factors, cassava showed more hyperaccumulation potential compared to other samples. Pumpkin and bitter leaf also could be used in remediation owing to their high bioaccumulation index for Pb and Zn. THQ obtained for Mn and Pb were >1 indicating that the residents at the quarry site may be exposed to potential non-carcinogenic health risk due to Mn and Pb intoxication. With respect to US EPA prescriptions, average carcinogenic risk values obtained for Pb and Cd in this study indicated a lifetime (70 years) probability of contracting cancer suggesting that they be placed for further consideration as chemicals of concern with respect to the assessed locals.
In comparison to other energy producing techniques, photovoltaics (PV) is one of the most promising options: no emission of any matter into the environment during operation; extremely long operation period (estimated average: 25 years), minimum maintenance, robust technique, aesthetic aspects. The use of photovoltaics is rapidly increasing, and the respective market is developing accordingly. Although PV manufacturing equipment is now excluded from the scope of RoHS, according to the Kyoto Protocol and the EU Directives WEEE and RoHS the use of hazardous substances in electric/electronic devices has to be reduced stepwise to approximately zero level. Furthermore, a total recycling of nearly all materials involved is aimed. Thus, major attention is directed to avoidance of environmental pollution through combustion or landfill, to regain valuable material, to promote the development and use of renewable energy sources. As the lifetime of PV cells themselves is much longer than that of PV modules and the manufacturing process of cells requires much energy consumption, the reuse of base material of the cells is economically justified. The aim of this work was to develop and evaluate existing methods of PV cells and modules recycling. The article discusses the main outcomes and analyses the significance of recycling in relation to the environmental profile of the production and total life cycle of photovoltaic cells and modules
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