Aktivnost enzima katalaze i sadržaj organskih kiselina kod Hajdučke trave (Achillea millefolium) sa sanirane deponije „Žitkovac“ Rudarsko metalurško hemijskog kombinata „Trepča“

In this comparative study, the activity of enzyme catalase and total content of organic acids were determined in undergroung and above-ground plant parts of medicinal plant Achillea millefolium from tailing pond “Žitkovac” of Mining and Metallurgical Chemical Company „Trepča“ and from uncontaminated area near city of Niš. Catalase activity was measured using the gasometric method and the values obtained for this activity were expressed as ml of O2. The content of organic acids in the plant material was detrmined by modified titration method in the presence of indicator. An increased catalase activity on tailing pond, in comparison with uncontaminated habitat, is a result of stress that is caused by chemical changes in the soil on tailing pond representing good metabolic ways of detoxification, which belongs to the mechanisms of defence and acquiring resistance. An increased content of organic acids in samples on tailing pond is an efficient mechanism reducing the heavy metal uptake, binding them to complexes and allowing the plant growth at high level of contamination.U ovom komparativnom istraživanju određeni su aktivnost enzima katalaze i ukupan sadržaj organskih kiselina u podzemnim i nadzemnim delovima lekovite biljke hajdučka trava (Achillea millefolium) sa sanirane deponije „Žitkovac“ Rudarsko Metalurško Hemijskog Kombinata „Trepča“ i nezagađenog područja okoline Niša. Aktivnost katalaze je izmerena korišćenjem gasometrijske metode i izražena u ml kiseonika. Sadržaj organskih kiselina u bilјnom materijalu određen je modifikovanom metodom titracije u prisustvu indikatora. Uvećanje aktivnosti enzima katalaze kod uzoraka na deponiji u poređenju sa nezagađenim staništem je rezultat stresa uzrokovan hemijskim promenama u zemljištu i predstavlja metabolički vid razgradnje štetnih jedinjenja, odnosno detoksikacije, koja spada u kvalitetne mehanizme sticanja otpornosti, kao odgovor na izmenjene uslove u životnoj sredini. Povećan sadržaj organskih kiselina u uzorcima sa deponije je efikasan mehanizam, koji smanjuje unos teških metala u bilјku vezujući se za njih u komplekse i omogućava rast biljke pri visokom nivou kontaminacije

Continuous biodisel productions: A review

Continuous biodiesel production on laboratory and industrial scale was analyzed, with focus on their advantages and disadvantages. Attention was paid to specific characteristics of industrial processes in order to point out the advanced technologies. The well-known base-catalyzed continuous biodiesel production processes are related to problems caused by the immiscibility of the reactants (alcohol and oil), application of relatively high operating temperature (usually the boiling temperature of alcohol or one near it) and obtained yield of methyl ester yields lower than desired. One way to overcome these problems is to employ special reactor design favoring the emulsion process and increasing the overall rate of biodiesel production process, even at room temperature and atmospheric pressure. The second way is to apply heterogeneous catalysts in continuous processes, which will probably be the optimal approach to economically justified and environmentally friendly biodiesel production

The gas holdup in a multiphase reciprocating plate column filled with carboxymethylcellulose solutions

Gas holdup was investigated in a gas-liquid and gas-liquid-solid reciprocating plate column (RPC) under various operation conditions. Aqueous carboxymethylcellulose (sodium salt, CMC) solutions were used as the liquid phase, the solid phase was spheres placed into interplate spaces, and the gas plase was air. The gas holdup in the RPC was influenced by: the vibration intensity, i.e., the power consumption, the superficial gas velocity, the solids content and the rheological properties of the liquid phase. The gas holdup increased with increasing vibration intensity and superficial gas velocity in both the two- and three-phase system. With increasing concentration of the CMC PP 50 solution (Newtonian fluid), the gas holdup decreased, because the coalescence of the bubbles was favored by the higher liquid viscosity. In the case of the CMC PP 200 solutions (non-Newtonian liquids), the gas holdup depends on the combined influence of the rheological properties of the liquid phase, the vibration intensity and the superficial gas velocity. The gas holdup in the three-phase systems was greater than that in the two-phase ones under the same operating conditions. Increasing the solids content has little influence on the gas holdup. The gas holdup was correlated with the power consumption (either the time-averaged or total power consuption) and the superficial gas velocity

The gas holdup in a multiphase reciprocating plate column filled with carboxymethylcellulose solutions

Gas holdup was investigated in a gas–liquid and gas–liquid-solid reciprocating plate column (RPC) under various operation conditions. Aqueous carboxymethylcellulose (sodium salt, CMC) solutions were used as the liquid phase, the solid phase was spheres placed into interplate spaces, and the gas plase was air. The gas holdup in the RPC was influenced by: the vibration intensity, i.e., the power consumption, the superficial gas velocity, the solids content and the rheological properties of the liquid phase. The gas holdup increased with increasing vibration intensity and superficial gas velocity in both the two- and three-phase system. With increasing concentration of the CMC PP 50 solution (Newtonian fluid), the gas holdup decreased, because the coalescence of the bubbles was favored by the higher liquid viscosity. In the case of the CMC PP 200 solutions (non-Newtonian liquids), the gas holdup depends on the combined influence of the rheological properties of the liquid phase, the vibration intensity and the superficial gas velocity. The gas holdup in the three-phase systems was greater than that in the two-phase ones under the same operating conditions. Increasing the solids content has little influence on the gas holdup. The gas holdup was correlated with the power consumption (either the time-averaged or total power consuption) and the superficial gas velocity

Calcium oxide as a promising heterogeneous catalyst for biodiesel production: Current state and perspectives

The present paper is an overview of the recent progress in the development of various CaO-based catalysts suitable for biodiesel production. The mechanism, kinetics and optimization of transesterification reaction over these catalysts are first considered. Then, the practical application of CaO-based catalysts is discussed with a special stress on leaching and reusability of these catalysts. Also, various continuous reactor systems currently in use for biodiesel production are appraised. In addition to it, purification of crude biodiesel and the ecological aspects of using CaO-based catalysts are considered. Finally, the potentials of CaO-based catalysts for heterogeneous catalysis for biodiesel production are emphasized to assess the future perspectives of their use. This review might help in selecting suitable CaO-based catalysts and the optimum reaction conditions for biodiesel production

Transesterification of used cooking sunflower oil catalyzed by hazelnut shell ash

Hazelnut shell ash was investigated as a new base catalyst for the transesterification of used cooking sunflower oil to biodiesel. To understand its catalytic properties, the prepared ash was characterized by EDX, XRD, TGA/DTA, Hg porosimetry, N-2 physisorption, FE-SEM, and basic strength measurements. The effects of the catalyst loading in the range of 1-5% of the oil weight and the methanol-to-oil molar ratio of 6:1-18:1 on the kinetics of the fatty acid methyl esters synthesis were established. Moreover, the leaching and reusability of the catalyst were assessed. The obtained results revealed that hazelnut shell ash was mostly composed of K, Ca, and Mg. The highest ester content (98%) was achieved at the catalyst loading of 5%, the methanol-to-oil molar ratio of 12:1, and the reaction time of 10 min. The contribution of homogeneous catalysis because of the catalyst leaching was confirmed but did not determine the overall reaction rate. The catalyst can be reused after the recalcination at 800 degrees C for 2 h achieving the high methyl esters content (>96%) in 30 min after three subsequent runs. The overall reaction followed the pseudo-first-order kinetics with respect to triacylglycerols. A linear relationship between the apparent reaction rate constant and the catalyst loading and the methanol-to-oil molar ratio was determined. The determined value of the reaction rate constant was 0.0576 dm(6)/(min.mol(2))

Validation of the Study Burnout Inventory and the Copenhagen Burnout Inventory for the use among medical students

ObjectivesThe aim of this study was to assess the validity and reliability of the Serbian versions of the Copenhagen Burnout Inventory (CBI) and the Study Burnout Inventory (SBI) among fifth-year medical students at 5 universities in Serbia.Material and MethodsThe study included 573 fifthyear medical students at 5 universities in Serbia. The research instrument consisted of SBI and CBI. The reliability of these instruments was assessed using an internal consistency measure (Cronbach’s α), an intra-class coefficient (ICC) and factor analysis.ResultsCronbach’s α for SBI was 0.83, including for exhaustion 0.73, for cynicism 0.70, and for inadequacy 0.48. The test-retest reliability (ICC) was 0.75. Cronbach’s α for personal burnout on CBI was 0.89, for the faculty-related burnout 0.86, and for the faculty-members-related burnout 0.92. Cronbach’s α for CBI was 0.93. The factor analysis for SBI showed 2 factors and for CBI 3 factors.ConclusionsThis study revealed that the Serbian versions of both SBI and CBI could be used for the assessment of burnout in this population

The ecological role of permanent ponds in Europe ::a review of dietary linkages to terrestrial ecosystems via emerging insects

Permanent ponds are valuable freshwater systems and biodiversity hotspots. They provide diverse ecosystem services (ES), including water quality improvement and supply, food provisioning and biodiversity support. This is despite being under significant pressure from multiple anthropogenic stressors and the impacts of ongoing global change. However, ponds are largely overlooked in management plans and legislation, and ecological research has focused on large freshwater ecosystems, such as rivers or lakes. Protection of ponds is often insufficient or indirectly provided via associated habitats such as wetlands. This phenomenon is likely exacerbated due to lacking a full-scale understanding of the importance of ponds. In this review, we provided a detailed overview of permanent ponds across Europe, including their usages and the biodiversity they support. By discussing the concepts of pondscape and metacommunity theory, we highlighted the importance of connectivity among and between ponds and identified fluxes of emerging insects as another ES of ponds. Those insects are rich in essential nutrients such as polyunsaturated fatty acids (PUFA), which are delivered through them to the terrestrial environment, however the extent and impact of this ES remains largely unexplored. Several potential stressors, especially related to ongoing global change, which influence pond diversity and integrity were discussed. To conclude this review, we provided our insights on future pond management. Adaptive measures, taking into account the pond system per se within the pondscape, were found to be the most promising to mitigate the loss of natural ponds and restore and conserve natural small water bodies as refuges and diversity hotspots in increasingly urbanized landscapes