Scientific Study & Research: Chemistry & Chemical Engineering, Biotechnology, Food Industry, 2012
The studies on the biodegradation of lipids from olive oil mill wastewater with free and immobili... more The studies on the biodegradation of lipids from olive oil mill wastewater with free and immobilized Bacillus sp. cells indicated that the maximum specific rate of the process is reached at pH = 8. The use of immobilized cells allows to increasing the number of biodegradation process cycles, but reduces the rate of the process. In this case, the process rate depends on the biocatalysts size and cells concentration inside them. Thus, at bacterial cells concentration of 9 g d.w./100 mL biocatalyst, the apparent specific rate varied from 4.65 to 1.46×10-2 h-1 by increasing the biocatalyst particles diameter from 3 to 4.2 mm.The cumulated influences of the particles size and cells concentration have been included in a mathematical model for the apparent specific rate of lipids biodegradation. The model offers a good concordance with the experimental data, the average deviation being of +/- 7.38%.
Environmental Engineering and Management Journal, 2014
The distribution of mixing time for a split-cylinder gas-lift bioreactor has been investigated fo... more The distribution of mixing time for a split-cylinder gas-lift bioreactor has been investigated for simulated broths with apparent viscosities up to 26 cP. The results indicated important variation of mixing time on the height of riser or downcomer, as well as different behavior of dispersion flows in the two regions. Thus, the highest mixing efficiency for the ascending circulation has been recorded for the intermediary positions, placed above the sparger. Contrary, for the downcomer, the intermediary positions are associated with the lowest efficiency of mixing, due to the bubbles entrapping phenomenon. Moreover, at air superficial velocities over 1.05x10-3 m/s, the influence of air input rate on turbulence extent is continuously positive for the riser, while it became negative for the downcomer. By means of the experimental data and using MATLAB software, mathematical correlations for mixing time have been proposed for each circulation region, taking into consideration both the operational parameter and the distance from the bioreactor bottom. These equations offer a good concordance with the experiment, the average deviation being of 3.3 for the riser and 6.6% for the downcomer zone.
Environmental Engineering and Management Journal, 2012
Formic and acetic acids could be selectively removed from the mixture with succinic acid by facil... more Formic and acetic acids could be selectively removed from the mixture with succinic acid by facilitated pertraction with tri-noctylamine (TOA). The pertraction selectivity is positively influenced by increasing the pH-gradient between the feed and stripping phases and carrier concentration in liquid membrane up to 70 g/L, as well as by lowering the mixing intensity of the two aqueous phases, TOA concentration exhibiting the most important influence. The cumulated influences of the considered parameters have been included in a mathematical model describing the pertraction of these carboxylic acids by means of the selectivity factor. The proposed model offers a good concordance with the experimental values of selectivity factor, the average deviation being of 5.22%.
Environmental Engineering and Management Journal, 2011
The studies on the mixing efficiency of medium with apparent viscosity between 1 and 75 cP in a s... more The studies on the mixing efficiency of medium with apparent viscosity between 1 and 75 cP in a stirred bioreactor with a fixed basket bed of immobilized cells of S. cerevisiae indicated that the presence of basket leads to the significant intensification of medium circulation compared with a conventional stirred bioreactor. The mixing time recorded for the medium circulation in the outer region of basket was for about 7 to 72 times lower than that previously reached in the absence of the cylindrical bed of immobilized cells. The optimum position of the Rushton turbine on the stirrer shaft was found to be inside the cylindrical bed, at the superior extremity of the basket. This position offers the possibility to reach the lowest mixing time values and the most important attenuation of the negative influence of the apparent viscosity increase on the medium hydrodynamics. The mathematical correlation describing the influence of the main factors on the mixing time was established for the optimum position of turbine, and offers a good concordance with the experimental data (the average deviation was of ±6.85%).
Environmental Engineering and Management Journal, 2009
The study on the distribution of oxygen transfer rate in a stirred bioreactor for Propionibacteri... more The study on the distribution of oxygen transfer rate in a stirred bioreactor for Propionibacterium shermanii broths underlined the major influence of the presence and concentration of biomass on the interphasic transfer of oxygen. Owing to the bubbles surface blockage by the bacterial cells, the accumulation of biomass from 30.5 to 120.5 g/l d.w. led to the decreasing of k l a for about 1.3-2.4 times. Compared with the simulated broths without biomass having similar apparent viscosity, the oxygen transfer rate became for about 1.22-4.54 times lower in the bacterial broths. The intensification of aeration promoted the acceleration of oxygen transfer for about 1.2-1.9 times, due to the intensification of turbulence and of the extent of free interfacial area needed for the oxygen transfer, this influence being similar to that recorded for the mixing efficiency. Moreover, the increase of aeration rate led to the increase of oxygen transfer efficiency. Indifferent of the operating parameters of the bioreactor, k l a increased from the inferior region to the superior one, being nonuniformly distributed inside the broths.
Environmental Engineering and Management Journal, 2019
The present study represents an extension of ergosterol production by Saccharomyces cerevisiae fe... more The present study represents an extension of ergosterol production by Saccharomyces cerevisiae fermentation processes using oxygen-vector by establishing the influence of the analyzed main factors, such as aeration efficiency and hydrocarbon concentration. The study has been developed for batch and fed-batch fermentation systems and has been focused on the variation of ergosterol content inside the yeast cells during the fermentation cycle in correlation with hydrocarbon volumetric fraction, COV, glucose concentration, CG, and air superficial velocity, vS. Moreover, the variation of ergosterol content has been discussed in relation to the oxygen mass transfer coefficient, kLa. The experimental results obtained in both fermentation systems were quantified in two mathematical correlations describing the influences of the mentioned main parameters on ergosterol concentration, CE. These two equations have the general expression β γ δ E OV G S C α C C v =⋅ ⋅ ⋅ (α, β, γ, δ are coefficients and exponents), and offer a good agreement with the experiments, the average deviations being ±5.94% for batch fermentation and ±4.18% for fed-batchfermentation.
Environmental Engineering and Management Journal, 2010
This paper develops the previous studies on the transfer processes and biochemical reaction kinet... more This paper develops the previous studies on the transfer processes and biochemical reaction kinetics involved in the bioethanol production by immobilized S. cerevisiae cells using a bioreactor with mobile beds of biocatalysts. Although the immobilization of cells or enzymes offers a lot of advantages compared to the free ones, it induces the appearance of the internal diffusion of substrate or product, with negative effect on the overall biochemical process. In the investigated case, the influences of the substrate internal diffusion on physical and biochemical processes have been quantified by means of the Biot number, Thiele modulus and reduction factor λ. The biocatalyst particles size and volumetric fraction exhibit significant and different influences on these three parameters. The increase of particle diameter led to the increase of Bi number, to the decrease of Thiele modulus and to the decrease of factor λ, but the influence of biocatalysts concentration is favorable for all discussed parameters.
Environmental Engineering and Management Journal, 2015
The oxygen transfer into the fermentation broths could be improved in presence of oxygen-vectors,... more The oxygen transfer into the fermentation broths could be improved in presence of oxygen-vectors, without intensification of mixing or aeration. The experimental results for simulated, P. shermanii and S. cerevisiae broths indicated the significant increase of k L a, by adding n-dodecane, but the magnitude of this effect depends especially on the cells affinity for hydrocarbon droplets. Therefore, due to the higher affinity of yeasts cells for hydrocarbon droplets during their entire growth cycle, the increase of oxygen mass transfer rate was lower and the influence of specific power input was different than those recorded for simulated or bacterial broths. By means of the experimental data, mathematical correlations describing the influences of the main parameters on k L a have been proposed for each studied fermentation systems at different positions on the broths height, with an average deviations varying between ±6.72% and ±6.93%.
This paper is dedicated to the study on the external and internal mass transfers of glucose for s... more This paper is dedicated to the study on the external and internal mass transfers of glucose for succinic acid fermentation under substrate and product inhibitions using a bioreactor with stirred bed of immobilized Actinobacillus succinogenes cells. By means of the substrate mass balance for a single particle of biocatalysts, considering the kinetic model adapted for both inhibitory effects, specific mathematical models were developed for describing the profiles of the substrate concentration in the outer and inner regions of biocatalysts and for estimating the substrate mass flows in the liquid boundary layer surrounding the particle and inside the particle. The values of the mass flows were significantly influenced by the internal diffusion velocity and rate of the biochemical reaction of substrate consumption. These cumulated influences led to the appearance of a biological inactive region near the particle center, its magnitude varying from 0 to 5.3% of the overall volume of particles.
The oxygen mass transfer represents the most important parameter implied on the design and operat... more The oxygen mass transfer represents the most important parameter implied on the design and operation of mixing-sparging equipment of the bioreactors. It can be described and analyzed by means of mass transfer coefficient, k l a. The k l a values are affected by a lot of factors, such as geometrical and operational characteristics of the vessels, media composition, type, concentration and microorganisms morphology, biocatalysts properties. The aim of these experiments is to study the oxygen mass transfer rate through the mass transfer coefficient, for a stirred bioreactor and different fermentation broths, using a large domain of operating variables. For quantifying the effects of the considered factors (concentration and morphology of biomass, specific power input, superficial air velocity) on k l a for submerged and surface aeration, the experiments were carried out for non-respiring biomass suspensions of Propionibacterium shermanii, Saccharomyces cerevisiae and Penicillium chrysogenum, mycelial aggregates (pellets) and free mycelia morphological structures. By means of the experimental data and using MATLAB software, some mathematical correlations describing the influences of the considered factors on k l a have been proposed for each microbial culture. These equations offer a good agreement with the experiment, the maximum deviation being ±8.4% for submerged aeration, and ±9.1% for surface aeration, respectively.
The compartmental models using differential equations are basic models in epidemiology. The tempo... more The compartmental models using differential equations are basic models in epidemiology. The temporal evolution of spatial models for epidemic spreading is suitable for parallelization and GRID services are solutions for speeding the algorithms used in these models. We investigate several computational aspects of parallel algorithms used in cellular automata model and small world networks model. The four compartmental small world network model of disease propagation (SEIR) is parallelized. In the second application, ...
Scientific Study & Research: Chemistry & Chemical Engineering, Biotechnology, Food Industry, 2012
The studies on the biodegradation of lipids from olive oil mill wastewater with free and immobili... more The studies on the biodegradation of lipids from olive oil mill wastewater with free and immobilized Bacillus sp. cells indicated that the maximum specific rate of the process is reached at pH = 8. The use of immobilized cells allows to increasing the number of biodegradation process cycles, but reduces the rate of the process. In this case, the process rate depends on the biocatalysts size and cells concentration inside them. Thus, at bacterial cells concentration of 9 g d.w./100 mL biocatalyst, the apparent specific rate varied from 4.65 to 1.46×10-2 h-1 by increasing the biocatalyst particles diameter from 3 to 4.2 mm.The cumulated influences of the particles size and cells concentration have been included in a mathematical model for the apparent specific rate of lipids biodegradation. The model offers a good concordance with the experimental data, the average deviation being of +/- 7.38%.
Environmental Engineering and Management Journal, 2014
The distribution of mixing time for a split-cylinder gas-lift bioreactor has been investigated fo... more The distribution of mixing time for a split-cylinder gas-lift bioreactor has been investigated for simulated broths with apparent viscosities up to 26 cP. The results indicated important variation of mixing time on the height of riser or downcomer, as well as different behavior of dispersion flows in the two regions. Thus, the highest mixing efficiency for the ascending circulation has been recorded for the intermediary positions, placed above the sparger. Contrary, for the downcomer, the intermediary positions are associated with the lowest efficiency of mixing, due to the bubbles entrapping phenomenon. Moreover, at air superficial velocities over 1.05x10-3 m/s, the influence of air input rate on turbulence extent is continuously positive for the riser, while it became negative for the downcomer. By means of the experimental data and using MATLAB software, mathematical correlations for mixing time have been proposed for each circulation region, taking into consideration both the operational parameter and the distance from the bioreactor bottom. These equations offer a good concordance with the experiment, the average deviation being of 3.3 for the riser and 6.6% for the downcomer zone.
Environmental Engineering and Management Journal, 2012
Formic and acetic acids could be selectively removed from the mixture with succinic acid by facil... more Formic and acetic acids could be selectively removed from the mixture with succinic acid by facilitated pertraction with tri-noctylamine (TOA). The pertraction selectivity is positively influenced by increasing the pH-gradient between the feed and stripping phases and carrier concentration in liquid membrane up to 70 g/L, as well as by lowering the mixing intensity of the two aqueous phases, TOA concentration exhibiting the most important influence. The cumulated influences of the considered parameters have been included in a mathematical model describing the pertraction of these carboxylic acids by means of the selectivity factor. The proposed model offers a good concordance with the experimental values of selectivity factor, the average deviation being of 5.22%.
Environmental Engineering and Management Journal, 2011
The studies on the mixing efficiency of medium with apparent viscosity between 1 and 75 cP in a s... more The studies on the mixing efficiency of medium with apparent viscosity between 1 and 75 cP in a stirred bioreactor with a fixed basket bed of immobilized cells of S. cerevisiae indicated that the presence of basket leads to the significant intensification of medium circulation compared with a conventional stirred bioreactor. The mixing time recorded for the medium circulation in the outer region of basket was for about 7 to 72 times lower than that previously reached in the absence of the cylindrical bed of immobilized cells. The optimum position of the Rushton turbine on the stirrer shaft was found to be inside the cylindrical bed, at the superior extremity of the basket. This position offers the possibility to reach the lowest mixing time values and the most important attenuation of the negative influence of the apparent viscosity increase on the medium hydrodynamics. The mathematical correlation describing the influence of the main factors on the mixing time was established for the optimum position of turbine, and offers a good concordance with the experimental data (the average deviation was of ±6.85%).
Environmental Engineering and Management Journal, 2009
The study on the distribution of oxygen transfer rate in a stirred bioreactor for Propionibacteri... more The study on the distribution of oxygen transfer rate in a stirred bioreactor for Propionibacterium shermanii broths underlined the major influence of the presence and concentration of biomass on the interphasic transfer of oxygen. Owing to the bubbles surface blockage by the bacterial cells, the accumulation of biomass from 30.5 to 120.5 g/l d.w. led to the decreasing of k l a for about 1.3-2.4 times. Compared with the simulated broths without biomass having similar apparent viscosity, the oxygen transfer rate became for about 1.22-4.54 times lower in the bacterial broths. The intensification of aeration promoted the acceleration of oxygen transfer for about 1.2-1.9 times, due to the intensification of turbulence and of the extent of free interfacial area needed for the oxygen transfer, this influence being similar to that recorded for the mixing efficiency. Moreover, the increase of aeration rate led to the increase of oxygen transfer efficiency. Indifferent of the operating parameters of the bioreactor, k l a increased from the inferior region to the superior one, being nonuniformly distributed inside the broths.
Environmental Engineering and Management Journal, 2019
The present study represents an extension of ergosterol production by Saccharomyces cerevisiae fe... more The present study represents an extension of ergosterol production by Saccharomyces cerevisiae fermentation processes using oxygen-vector by establishing the influence of the analyzed main factors, such as aeration efficiency and hydrocarbon concentration. The study has been developed for batch and fed-batch fermentation systems and has been focused on the variation of ergosterol content inside the yeast cells during the fermentation cycle in correlation with hydrocarbon volumetric fraction, COV, glucose concentration, CG, and air superficial velocity, vS. Moreover, the variation of ergosterol content has been discussed in relation to the oxygen mass transfer coefficient, kLa. The experimental results obtained in both fermentation systems were quantified in two mathematical correlations describing the influences of the mentioned main parameters on ergosterol concentration, CE. These two equations have the general expression β γ δ E OV G S C α C C v =⋅ ⋅ ⋅ (α, β, γ, δ are coefficients and exponents), and offer a good agreement with the experiments, the average deviations being ±5.94% for batch fermentation and ±4.18% for fed-batchfermentation.
Environmental Engineering and Management Journal, 2010
This paper develops the previous studies on the transfer processes and biochemical reaction kinet... more This paper develops the previous studies on the transfer processes and biochemical reaction kinetics involved in the bioethanol production by immobilized S. cerevisiae cells using a bioreactor with mobile beds of biocatalysts. Although the immobilization of cells or enzymes offers a lot of advantages compared to the free ones, it induces the appearance of the internal diffusion of substrate or product, with negative effect on the overall biochemical process. In the investigated case, the influences of the substrate internal diffusion on physical and biochemical processes have been quantified by means of the Biot number, Thiele modulus and reduction factor λ. The biocatalyst particles size and volumetric fraction exhibit significant and different influences on these three parameters. The increase of particle diameter led to the increase of Bi number, to the decrease of Thiele modulus and to the decrease of factor λ, but the influence of biocatalysts concentration is favorable for all discussed parameters.
Environmental Engineering and Management Journal, 2015
The oxygen transfer into the fermentation broths could be improved in presence of oxygen-vectors,... more The oxygen transfer into the fermentation broths could be improved in presence of oxygen-vectors, without intensification of mixing or aeration. The experimental results for simulated, P. shermanii and S. cerevisiae broths indicated the significant increase of k L a, by adding n-dodecane, but the magnitude of this effect depends especially on the cells affinity for hydrocarbon droplets. Therefore, due to the higher affinity of yeasts cells for hydrocarbon droplets during their entire growth cycle, the increase of oxygen mass transfer rate was lower and the influence of specific power input was different than those recorded for simulated or bacterial broths. By means of the experimental data, mathematical correlations describing the influences of the main parameters on k L a have been proposed for each studied fermentation systems at different positions on the broths height, with an average deviations varying between ±6.72% and ±6.93%.
This paper is dedicated to the study on the external and internal mass transfers of glucose for s... more This paper is dedicated to the study on the external and internal mass transfers of glucose for succinic acid fermentation under substrate and product inhibitions using a bioreactor with stirred bed of immobilized Actinobacillus succinogenes cells. By means of the substrate mass balance for a single particle of biocatalysts, considering the kinetic model adapted for both inhibitory effects, specific mathematical models were developed for describing the profiles of the substrate concentration in the outer and inner regions of biocatalysts and for estimating the substrate mass flows in the liquid boundary layer surrounding the particle and inside the particle. The values of the mass flows were significantly influenced by the internal diffusion velocity and rate of the biochemical reaction of substrate consumption. These cumulated influences led to the appearance of a biological inactive region near the particle center, its magnitude varying from 0 to 5.3% of the overall volume of particles.
The oxygen mass transfer represents the most important parameter implied on the design and operat... more The oxygen mass transfer represents the most important parameter implied on the design and operation of mixing-sparging equipment of the bioreactors. It can be described and analyzed by means of mass transfer coefficient, k l a. The k l a values are affected by a lot of factors, such as geometrical and operational characteristics of the vessels, media composition, type, concentration and microorganisms morphology, biocatalysts properties. The aim of these experiments is to study the oxygen mass transfer rate through the mass transfer coefficient, for a stirred bioreactor and different fermentation broths, using a large domain of operating variables. For quantifying the effects of the considered factors (concentration and morphology of biomass, specific power input, superficial air velocity) on k l a for submerged and surface aeration, the experiments were carried out for non-respiring biomass suspensions of Propionibacterium shermanii, Saccharomyces cerevisiae and Penicillium chrysogenum, mycelial aggregates (pellets) and free mycelia morphological structures. By means of the experimental data and using MATLAB software, some mathematical correlations describing the influences of the considered factors on k l a have been proposed for each microbial culture. These equations offer a good agreement with the experiment, the maximum deviation being ±8.4% for submerged aeration, and ±9.1% for surface aeration, respectively.
The compartmental models using differential equations are basic models in epidemiology. The tempo... more The compartmental models using differential equations are basic models in epidemiology. The temporal evolution of spatial models for epidemic spreading is suitable for parallelization and GRID services are solutions for speeding the algorithms used in these models. We investigate several computational aspects of parallel algorithms used in cellular automata model and small world networks model. The four compartmental small world network model of disease propagation (SEIR) is parallelized. In the second application, ...
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Papers by Marius Turnea