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Objective To explore the enhanced separation behavior of ferulic acid in organic solution by nanofiltration. Methods In the experiment, molecular weight cut-off (MWCO) of nanofiltration membrane, ethanol concentration, and solution pH were selected as influencing factors to find the sensitive region of ethanol concentration and pH on the retention rate of ferulic acid with Box-Behnken central composite experiment design. And then, the separation rule of ferulic acid with organic solution was analyzed, the correlation between mass transfer coefficient and concentration of organic solvent was fitted with the changed organic solution by nanofiltration mass transfer mathematical model. Results Experiments indicated that the enhanced separation behavior appeared and the mass transfer coefficient decreased as the ethanol concentration increased from 20% to 40% with MWCO 450 and pH 8.0. Under the same condition, the enhanced separation behavior happened as the solvent was changed into methanol and acetonitrile, and the enhanced effect was positively correlated with the concentration of the three common organic solvents, the effect rule was ethanol ≈ methanol > acetonitrile material. Conclusion The enhanced separation effect of nanofiltration was related to the type and concentration of organic solvent. And taking ferulic acid as an example, the mechanism of nanofiltration separation in the environment of organic solution was studied, and the results provided references for nanofiltration concentrate for heat-sensitive traditional Chinese medicine of phenolic acid in organic solution.
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Based on the molecular sieving and solution-diffusion effect in nanofiltration separation, the correlation between initial concentration and mass transfer coefficient of three typical phenolic acids from Salvia miltiorrhiza was fitted to analyze the relationship among mass transfer coefficient, molecular weight and concentration. The experiment showed a linear relationship between operation pressure and membrane flux. Meanwhile, the membrane flux was gradually decayed with the increase of solute concentration. On the basis of the molecular sieving and solution-diffusion effect, the mass transfer coefficient and initial concentration of three phenolic acids showed a power function relationship, and the regression coefficients were all greater than 0.9. The mass transfer coefficient and molecular weight of three phenolic acids were negatively correlated with each other, and the order from high to low is protocatechualdehyde >rosmarinic acid> salvianolic acid B. The separation mechanism of nanofiltration for phenolic acids was further clarified through the analysis of the correlation of molecular weight and nanofiltration mass transfer coefficient. The findings provide references for nanofiltration separation, especially for traditional Chinese medicine with phenolic acids.
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Objective To explore the correlation of molecular state of caffeic acid from Perilla frutescens and its nanofiltration mass transfer process. Methods The pH value of solution was changed and the free-dissociation ratio was adjusted with caffeic acid as an index, the rejection and membrane flux of the corresponding initial concentration and operating pressure in different existence conditions were collected. Based on the solution-diffusion effect and charge effect in nanofiltration separation, the linear equations between the rejection and mass transfer coefficient was constructed, the correlation between mass transfer coefficient and initial concentration was established, the mathematical models which based on the operating pressure and initial concentration to predict the rejection of caffeic acid was developed and used to verify its applicability by aqueous extract of P. frutescens. Results Experiments indicated that there was a linear relationship between operation pressure and membrane flux. Besides, mass transfer coefficient and initial concentration of caffeic acid were positively correlated with each other by solution-diffusion effect and charge effect. The mass transfer coefficient of dissociated caffeic acid was less than those of free state and free-dissociation. Moreover, on the basis of power function relationship between mass transfer coefficient and initial concentration, the results showed that the predicted rejections of caffeic acid from P. frutescens water extract using mathematical model approximate well to real ones. Conclusion The mass transfer coefficient of caffeic acid is associated with existential state and initial concentration. The predicted model of nanofiltration separation has a preferable applicability to caffeic acid and provides references for nanofiltration separation, especially for heat-sensitive traditional Chinese medicine.
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Objective To investigate radioactivity levels in the main agriculture products around a uranium mine in Northern Guangxi.Methods The agriculture products and soil samples were collected and analyzed by using HPGe gamma ray spectrometer.Results The specific activity of 226Ra in radish (including leaf),radish leaves and radish,collected in one place,were 45.0,66.7 and 32.3 Bq/kg,respectively.Those of 226Ra and 23SU in the radish soil collected in the same place were 19 672 and 85 917 Bq/kg,respectively.The transfer coefficients of soil-to-radish and soil-to-leaves were 1.61 × 10-3 and 3.40 × 10-3,consistent with those reported in relevant literature.Radioactivity levels in agricultural products in another survey was in consistence with those in the national survey for food products.Radioactivity levels in soil elsewhere near the radish site was consistent with the results of the national soil radioactivive background survey.Conclusions The soil in this place has been contaminated by the nearby uranium mine.It is important to investigate this place further and take the necessary measures.
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OBJECTIVE: To study preliminarily the cadmium absorption and accumulation in Ligusticum Wallichii to provide a scientific basis for solving the problem of cadmium excess. METHODS: The aboveground and underground parts of Ligusticum Wallichii in different growth periods and the rhizosphere soil were collected from Aoping Town, Pengzhou City and Yongshou Town, Meishan City. The cadmium content was determined, and the enrichment coefficient and transfer coefficient were calculated. RESULTS: The average cadmium content in the underground part was 77.21% higher than that in the aboveground part. The cadmium enrichment coefficients and cadmium transfer coefficients of different parts were both greater than 0.5, and the enrichment coefficient of the underground part was 64.75% higher than the aboveground part. CONCLUSION: Ligusticum Wallichii has a certain capacity to absorb and transfer cadmium, and most cadmium is enriched in the medicinal roots.
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Aims: To evaluate the effect of volumetric oxygen transfer coefficient on the production of xylitol by Debaryomyces nepalensis and to enhance the yield and productivity of xylitol by fed-batch fermentation using xylose as substrate. Place and Duration of Study: All experiments were performed at the Applied and Industrial Microbiology Laboratory, Indian Institute of Technology Madras, from March 2013 to May 2014. Methodology: Batch cultivations were carried out in a 7.5 L fermentor under various oxygen transfer coefficients in the range 12 to 39.6 h-1 in order to understand the effect of oxygen on xylitol production. Fed-batch studies were performed in 2.5 L bioreactor with a working volume of 1 L. The cultures were initially grown as batch cultures. Feed containing xylose and nitrogen source was added to the medium intermittently. Samples were periodically collected at regular intervals of time and the concentrations of xylose, xylitol and glycerol were determined by HPLC. Results: Maximal xylitol yield (0.64 g/g) and productivity (0.43 g/L·h) were obtained at kLa 13.68 h-1. The effect of pH was also studied at this kLa. A pH value of 6.0 was found to be favorable for xylitol accumulation. Fed-batch fermentation involving feeding of xylose and nitrogen source was used for xylitol production by D. nepalensis. Within the fed-batch phase, the yield of xylitol was 0.83 g/g and the productivity was increased to 0.83 g/L.h with a final product concentration of 90 g/L. Conclusion: Higher kLa favors biomass production whereas product formation was favored at lower kLa. Fed-batch process resulted in enhancement of final product concentration by 73%.
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En el cultivo de microorganismos aerobios se ha observado que los biorreactores convencionales conducen a inconvenientes asociados a la limitación de oxígeno. Para dar solución a esta problemática se diseñó, construyó y evaluó un prototipo de biorreactor con aireador externo. Este sistema permitió incrementar la velocidad de transferencia del oxígeno desde la fase gaseosa a la fase líquida, superando la limitación de oxígeno. Sin embargo, esta nueva configuración carece de modelos empíricos o teóricos para predecir la transferencia de oxígeno a través del cálculo del coeficiente global de transferencia de oxígeno (KLa). En ese sentido, en este trabajo se propuso el uso de análisis dimensional (Teorema Pi de Buckingham), como herramienta para evaluar el efecto sobre el KLa de las diferentes variables involucradas en el proceso, como las de operación, las propiedades de los fluidos y dimensiones geométricas. Luego de desarrollar el análisis propuesto, se encontró una correlación de 0.89 entre los valores generados por el modelo y los datos experimentales disponibles. Se encontró que las variables con mayor incidencia sobre el coeficiente KLa son el flujo de medio de cultivo que circula por el aireador externo denominado flujo de recirculación, la presión en el aireador externo y la velocidad de agitación.
In aerobic microorganism culture, it has been observed that conventional bioreactors lead to disadvantages associated with oxygen limitation. To solve this problem it was designed, built and tested a bioreactor prototype with external aerator. This system allowed increasing the speed of oxygen transfer from gas phase to liquid phase, overcoming the limitation of oxygen. However, this new configuration doesn't have theoretical or empirical models to predict the oxygen transfer by calculating the global volumetric coefficient of transfer of oxygen (KLa).In that way, this paper proposed the use of dimensional analysis (Buckingham's Pi Theorem), as a tool to evaluate the effect of various operating variables, fluid properties and geometrical dimensions involved in the process over KLa. After developing the proposed analysis, we found a correlation of 0.89 between the values generated by the model and the available experimental data. It was found that the main variables which affect the coefficient KLa are: the medium flow flowing through the external aerator called recirculation flow, the pressure in the external aerator, and the stirring speed.