Pullulan fermentation using a prototype rotational reciprocating plate impeller.

A rotational reciprocating plate impeller prototype, designed to improve the mixing homogeneity of viscous non-Newtonian fermentation broth, has been tested in pullulan fermentations. With this new impeller, the operating levels of several factors were investigated to improve pullulan production with Aureobasidium pullulans ATCC 42023 in a 22-L bioreactor using experimental designs. Because both high molecular weight (MW) and high concentration of pullulan were desired; the exopolysaccharide (EPS) concentration and the broth viscosity were used as optimization objective functions to be maximized. A 6-run uniform design was used to investigate five factors. Under the best operating conditions among the six runs, 29.0 g L(-1) EPS was produced at 102 h. This condition was used as the starting point for further investigation on the two statistically significant factors, the pH and the agitation speed. An 8-run 3-level custom design that investigates up to second-order effects was used in the second stage. An optimal zone of operating conditions for large quantity of high MW pullulan production was identified. A concentration of 23.3 g L(-1) EPS was produced at 78 h. This is equivalent to an EPS productivity of 0.30 g L(-1) h(-1). The corresponding apparent viscosity of the broth was 0.38 Pa s at the shear rate of 10 s(-1).

Separation of n-Butanol from Aqueous Solutions via Pervaporation Using PDMS/ZIF-8 Mixed-Matrix Membranes of Different Particle Sizes.

The use of mixed matrix membranes (MMMs) to facilitate the production of biofuels has attracted significant research interest in the field of renewable energy. In this study, the pervaporation separation of butanol from aqueous solutions was studied using a series of MMMs, including zeolitic imidazolate frameworks (ZIF-8)-polydimethylsiloxane (PDMS) and zinc oxide-PDMS mixed matrix membranes. Although several studies have reported that mixed matrix membranes incorporating ZIF-8 nanoparticles showed improved pervaporation performances attributed to their intrinsic microporosity and high specific surface area, an in-depth study on the role of ZIF-8 nanoparticle size in MMMs has not yet been reported. In this study, different average sizes of ZIF-8 nanoparticles (30, 65, and 80 nm) were synthesized, and the effects of particle size and particle loading content on the performance of butanol separation using MMMs were investigated. Furthermore, zinc oxide nanoparticles, as non-porous fillers with the same metalcore as ZIF-8 but with a very different geometric shape, were used to illustrate the importance of the particle geometry on the membrane performance. Results showed that small-sized ZIF-8 nanoparticles have better permeability and selectivity than medium and large-size ZIF-8 MMMs. While the permeation flux increased continuously with an increase in the loading of nanoparticles, the selectivity reached a maximum for MMM with 8 wt% smaller-size ZIF-8 nanoparticle loading. The flux and butanol selectivity increased by 350% and 6%, respectively, in comparison to those of neat PDMS membranes prepared in this study.

Pareto domain: an invaluable source of process information.

Due to the highly competitive market and increasingly stringent environmental regulations, it is paramount to operate chemical processes at their optimal point. In a typical process, there are usually many process variables (decision variables) that need to be selected in order to achieve a set of optimal objectives for which the process will be considered to operate optimally. Because some of the objectives are often contradictory, Multi-objective optimization (MOO) can be used to find a suitable trade-off among all objectives that will satisfy the decision maker. The first step is to circumscribe a well-defined Pareto domain, corresponding to the portion of the solution domain comprised of a large number of non-dominated solutions. The second step is to rank all Pareto-optimal solutions based on some preferences of an expert of the process, this step being performed using visualization tools and/or a ranking algorithm. The last step is to implement the best solution to operate the process optimally. In this paper, after reviewing the main methods to solve MOO problems and to select the best Pareto-optimal solution, four simple MOO problems will be solved to clearly demonstrate the wealth of information on a given process that can be obtained from the MOO instead of a single aggregate objective. The four optimization case studies are the design of a PI controller, an SO2 to SO3 reactor, a distillation column and an acrolein reactor. Results of these optimization case studies show the benefit of generating and using the Pareto domain to gain a deeper understanding of the underlying relationships between the various process variables and performance objectives.

Monte Carlo Simulations for the Estimation of the Effective Permeability of Mixed-Matrix Membranes.

Recent years have seen the explosive development of mixed-matrix membranes (MMMs) for a myriad of applications. In gas separation, it is desired to concurrently enhance the permeability, selectivity and physicochemical properties of the membrane. To help achieving these objectives, experimental characterization and predictive models can be used synergistically. In this investigation, a Monte Carlo (MC) algorithm is proposed to rapidly and accurately estimate the relative permeability of ideal MMMs over a wide range of conditions. The difference in diffusivity coefficients between the polymer matrix and the filler particle is used to adjust the random progression of the migrating species inside each phase. The solubility coefficients of both phases at the polymer−filler interface are used to control the migration of molecules from one phase to the other in a way to achieve progressively phase equilibrium at the interface. Results for various MMMs were compared with the results obtained with the finite difference method under identical conditions, where the results from the finite difference method are used in this investigation as the benchmark method to test the accuracy of the Monte Carlo algorithm. Results were found to be very accurate (in general, <1% error) over a wide range of polymer and filler characteristics. The MC algorithm is simple and swift to implement and provides an accurate estimation of the relative permeability of ideal MMMs. The MC method can easily be extended to investigate more readily non-ideal MMMs with particle agglomeration, interfacial void, polymer-chain rigidification and/or pore blockage, and MMMs with any filler geometry.

Modelling the Molecular Permeation through Mixed-Matrix Membranes Incorporating Tubular Fillers.

Membrane-based processes are considered a promising separation method for many chemical and environmental applications such as pervaporation and gas separation. Numerous polymeric membranes have been used for these processes due to their good transport properties, ease of fabrication, and relatively low fabrication cost per unit membrane area. However, these types of membranes are suffering from the trade-off between permeability and selectivity. Mixed-matrix membranes, comprising a filler phase embedded into a polymer matrix, have emerged in an attempt to partly overcome some of the limitations of conventional polymer and inorganic membranes. Among them, membranes incorporating tubular fillers are new nanomaterials having the potential to transcend Robeson's upper bound. Aligning nanotubes in the host polymer matrix in the permeation direction could lead to a significant improvement in membrane permeability. However, although much effort has been devoted to experimentally evaluating nanotube mixed-matrix membranes, their modelling is mostly based on early theories for mass transport in composite membranes. In this study, the effective permeability of mixed-matrix membranes with tubular fillers was estimated from the steady-state concentration profile within the membrane, calculated by solving the Fick diffusion equation numerically. Using this approach, the effects of various structural parameters, including the tubular filler volume fraction, orientation, length-to-diameter aspect ratio, and permeability ratio were assessed. Enhanced relative permeability was obtained with vertically aligned nanotubes. The relative permeability increased with the filler-polymer permeability ratio, filler volume fraction, and the length-to-diameter aspect ratio. For water-butanol separation, mixed-matrix membranes using polydimethylsiloxane with nanotubes did not lead to performance enhancement in terms of permeability and selectivity. The results were then compared with analytical prediction models such as the Maxwell, Hamilton-Crosser and Kang-Jones-Nair (KJN) models. Overall, this work presents a useful tool for understanding and designing mixed-matrix membranes with tubular fillers.

Gas Permeation Model of Mixed-Matrix Membranes with Embedded Impermeable Cuboid Nanoparticles.

In the packaging industry, the barrier property of packaging materials is of paramount importance. The enhancement of barrier properties of materials can be achieved by adding impermeable nanoparticles into thin polymeric films, known as mixed-matrix membranes (MMMs). Three-dimensional numerical simulations were performed to study the barrier property of these MMMs and to estimate the effective membrane gas permeability. Results show that horizontally-aligned thin cuboid nanoparticles offer far superior barrier properties than spherical nanoparticles for an identical solid volume fraction. Maxwell's model predicts very well the relative permeability of spherical and cubic nanoparticles over a wide range of the solid volume fraction. However, Maxwell's model shows an increasingly poor prediction of the relative permeability of MMM as the aspect ratio of cuboid nanoparticles tends to zero or infinity. An artificial neural network (ANN) model was developed successfully to predict the relative permeability of MMMs as a function of the relative thickness and the relative projected area of the embedded nanoparticles. However, since an ANN model does not provide an explicit form of the relation of the relative permeability with the physical characteristics of the MMM, a new model based on multivariable regression analysis is introduced to represent the relative permeability in a MMM with impermeable cuboid nanoparticles. The new model possesses a simple explicit form and can predict, very well, the relative permeability over an extensive range of the solid volume fraction and aspect ratio, compared with many existing models.

Separation of Organic Compounds from ABE Model Solutions via Pervaporation Using Activated Carbon/PDMS Mixed Matrix Membranes.

The pervaporation separation of organic compounds from acetone-butanol-ethanol (ABE) fermentation model solutions was studied using activated carbon (AC) nanoparticle-poly (dimethylsiloxane) (PDMS) mixed matrix membranes (MMM). The effects of the operating conditions and nanoparticle loading content on the membrane performance have been investigated. While the separation factor increased continuously, with an increase in the concentration of nanoparticles, the total flux reached a maximum in the MMM with 8 wt % nanoparticle loading in PDMS. Both the separation factor for ABE and the total permeation flux more than doubled for the MMM in comparison to those of neat PDMS membranes prepared in this study.

Morphological characterization and viability assessment of Trichoderma reesei by image analysis.

The production of cellulase from the filamentous fungus Trichoderma reesei is a critical step in the industrial process leading to cellulose ethanol. As a result of the lack of quantitative analysis tools, the intimate relationship that exists between the morphological and physiological states of the microorganism, the shear field in the bioreactor, and the process performance is not yet fully understood. A semiautomatic image analysis protocol was developed to characterize the mycelium morphology and to estimate its percentage viability during the fermentation process based on four morphological types (unbranched, branched, entangled, and clumped microorganisms). Pictures taken under bright field microscopy combined with images of fluorescein diacetate stained fungi were used to assess the morphological parameters and the percentage viability of microorganisms simultaneously. The method was tested during the course of fed-batch fermentation in a reciprocating plate bioreactor. The use of the image analysis protocol was found to be successful in quantifying the variations in the morphology and the viability of T. reesei throughout the fermentation.

Evaluation of oxygen mass transfer in Aspergillus niger fermentation using data reconciliation.

Fermentation experiments using Aspergillus niger result in a very viscous broth due to the growth of filamentous microorganism. For viscous fermentation processes, it is difficult to estimate with confidence the volumetric oxygen mass transfer coefficient (K(L)a), which can be used for scale-up or design of bioreactors. In the present study, four methods based on dynamic and stationary approaches were used to measure K(L)a throughout the fermentation. Data reconciliation was used to obtain a more reliable and consistent K(L)a. The K(L)a value obtained by a data reconciliation technique was found to be more reliable since it takes into consideration both the reliability of all measured variables and the accuracy of all mass balance equations.

High-titer adenovirus vector production in 293S cell perfusion culture.

Human 293S cells culture for recombinant adenovirus production is traditionally carried out in batch at a maximum of 6 x 10(5) cells/mL. A previous report demonstrated that fed-batch, applied to the adenovirus/293S cells system, improves the volumetric production of viral proteins by increasing the cell density at which cells can be infected, up to 2 x 10(6) cells/mL, without reducing the per-cell yield of product. To increase this cell density limit, the adenovirus production was performed in a perfusion system where the cells were separated by means of a tangential flow filtration device. 293S cell growth to 14 x 10(6) cells/mL was achieved in 10 days, at a medium renewal rate of 1 volume of medium per reactor volume and day (VVD). For adenovirus production, three 293S cell cultures were perfused at 1 VVD in parallel and infected at an average density of 8 x 10(6) cells/mL. One of the cultures was set at 37 degrees C and the two others at 35 degrees C. After a rapid initial cell loss, the average cell density stabilized at 5.75 x 10(6) cells/mL, 12 h postinfection, which was 8 times higher than the cell density in the batch control. This allowed the production of 3.2 x 10(9) infectious viral particles/mL (IVP/mL) at 37 degrees C and 7.8 x 10(9) IVP/mL at 35 degrees C, this last result being 5.5 times higher than the control. To our knowledge, this nonconcentrated titer is the highest value that has ever been published for adenovirus vector production. These observations lead to the conclusion that perfusion is an efficient tool to maintain, at high cell density, a specific production rate level sufficient to increase significantly the adenovirus volumetric production. Furthermore, it shows that perfusion at 35 degrees C can improve viral titer by 2.4-fold compared to 37 degrees C, in accordance with a previous study on adenovirus batch production.

Application of image analysis in the fungal fermentation of Trichoderma reesei RUT-C30.

Trichoderma reesei was grown in a stirred-tank bioreactor (STB) and a reciprocating plate bioreactor (RPB) at four different agitation speeds. A semiautomatic image analysis protocol that was developed to characterize the mycelium morphology during the fermentation process based on four morphological types (unbranched, branched, entangled, and clumped microorganisms) was applied to study the effect of agitation on the morphology of T. reesei. It was shown via statistical validation that broth samples used for image analysis represented the whole population of the fungi in the bioreactor. High shear was found to be damaging to T. reesei grown in the STB. The gentler shear produced in the RPB was not detrimental to the microorganism even at higher agitation speed. Better productivity was obtained for T. reesei grown in the STB and the highest productivity, 0.121 IU/mL h, was obtained at 400 rpm. The morphological parameter, the hyphal growth unit, was found to be correlated to the productivity. Understanding the effect of agitation on the morphology and productivity of T. reesei could lead to the design of better bioreactors and the selection of operating conditions of bioreactors to optimize the production of cellulase.

Design of a novel Couette flow bioreactor to study the growth of fungal microorganism.

Cultivations using Trichoderma reesei Rut C-30 were performed in a 5-l Couette flow bioreactor (CFB) which was designed and built to perform experiments in batch and continuous modes. Process parameters such as dissolved oxygen, pH and temperature were measured and controlled without disturbing the shear profile inside the bioreactor. Effect of shear on the growth, protein production and morphology was studied by performing runs at 100, 200, 300 and 400 rpm. At higher shear rates, lower protein production rate and activity, and higher rate of fragmentation were observed. Also, the cell thickness decreased with increasing speed, going from 8.3 microm for the experiment at 100 rpm to 4.3 microm at 400 rpm. The effect of substrate, lactose (an inducer) or glucose, was investigated by switching the feed medium during the two runs performed at 300 and 400 rpm. The novel design of the CFB used in the present study includes a large volume that allows growing larger size microorganisms (e.g. fungi) and permits larger sampling volumes without affecting the cultivation. It also has the ability to carry out experiments for long periods of time, both in batch and continuous modes.

Blood glucose monitor: an alternative off-line method to measure glucose concentration during fermentations with Trichoderma reesei.

Two home, blood-glucose monitoring meters, OneTouch Ultra and Ascensia Contour, were used to determine the glucose concentration during fermentations of Trichoderma reesei in both flasks and bioreactors. The results, when compared to those given by the 3,5-dinitrosalicylic acid reducing sugar assay, HPLC and YSI 2700 SELECT Biochemistry analyzer, showed that the glucose meters are a quick, reliable and economical alternative method for frequent glucose concentration measurement during fermentation. For T. reesei fermentations, the OneTouch meter was the more suitable.