Showing papers in "Bioprocess Engineering in 1995"

Production of xylitol from raw wood hydrolysates by Debaryomyces hansenii NRRL Y-7426

Abstract: Xylose solutions were obtained from the hemicellulosic fraction of Eucalyptus globulus by means of sulphuric acid treatments performed under selected operational conditions. The hydrolysates were neutralized, supplemented with nutrients, sterilized and utilised as fermentation media for xylitol production using the yeast Debaryomyces hansenii NRRL Y-7426. Preliminary experiments allowed the adaptation of the strain to the culture media. Further fermentation trials were performed with adapted cells according to an incomplete, factorial design of experiments. Empirical models describing the bioconversion were derived from the experimental results. The effects of three operational variables (nutrient concentration, initial pH and shaking speed) on both xylose consumption and xylitol production rates were described by significant mathematical equations. Additional aspects in relation to the process were also discussed.

Modeling of heat and mass transfer for solid state fermentation process in tray bioreactor

Abstract: A mathematical model is developed to simulate oxygen consumption, heat generation and cell growth in solid state fermentation (SSF). The fungal growth on the solid substrate particles results in the increase of the cell film thickness around the particles. The model incorporates this increase in the biofilm size which leads to decrease in the porosity of the substrate bed and diffusivity of oxygen in the bed. The model also takes into account the effect of steric hindrance limitations in SSF. The growth of cells around single particle and resulting expansion of biofilm around the particle is analyzed for simplified zero and first order oxygen consumption kinetics. Under conditions of zero order kinetics, the model predicts upper limit on cell density. The model simulations for packed bed of solid particles in tray bioreactor show distinct limitations on growth due to simultaneous heat and mass transport phenomena accompanying solid state fermentation process. The extent of limitation due to heat and/or mass transport phenomena is analyzed during different stages of fermentation. It is expected that the model will lead to better understanding of the transport processes in SSF, and therefore, will assist in optimal design of bioreactors for SSF.

Production of monoglycerides by glycerolysis of olive oil with immobilized lipases: effect of the water activity

Abstract: The production of monoglycerides by glycerolysis of olive oil catalyzed by lipases from Candida rugosa, Chromobacterium viscosum and Rhizopus sp. immobilized in a hydrophylic polyurethane foam was investigated. The effect of the amount of aqueous phase used for foam polymerization on the competing reactions of glycerolysis and hydrolysis was studied. The highest monoglyceride production was achieved with the C. rugosa lipase which was thus selected for subsequent studies.

Storage stabilization of enzyme activity by poly(ethyleneimine)

Abstract: The effect of mixing penicillin acylase with poly(ethyleneimine) is discussed. The properties of the polymer-enzyme system were evaluated for a wide range of enzyme concentrations (0.3–45.5 mg/cm3) and poly(ethyleneimine) concentrations (0.0001–10% wt). It was shown that addition of poly(ethyleneimine) to crude enzyme preparation caused precipitation of ballast protein and stabilization of the enzyme fraction remaining in the supernatant. The soluble fraction had stable activity for 21 days storage at 37 °C while the native enzyme lost about 80% of its initial activity. Additionally, it was ascertained that the polymer very slightly affected the properties of penicillin acylase in the PEI-enzyme preparations. Finally, possible ways of using the polymer-enzyme preparations in a membrane reactor are suggested.

The effects of cells on oxygen transfer in bioreactors

Abstract: Cells may affect oxygen transfer rates by three mechanisms: respiration of cells accumulated at the gas/liquid interface, physical presence of cells as solid particles, and modification of the medium by cells. These effects were studied experimentally in bubble-aerated bioreactors using baker's yeast at different cell concentrations, agitation speeds, aeration rates, and specific oxygen uptake rates. The overall effect of cells was to enhance oxygen transfer rates. The physical presence of cells as solid particles was found to retard oxygen transfer, presumably due to the lower oxygen permeability in the cell layer accumulated near the bubble surfaces. Cell respiration and medium modification, on the other hand, enhanced oxygen transfer rates. The retardation by nonrespiring cells and the enhancement due to cell respiration were found stronger at higher agitation speeds and lower aeration rates employed. This was attributed to the higher interfacial cell accumulation associated with the smaller bubbles produced under these conditions in the systems studied.

Classification system for immobilization techniques

Abstract: Biotechnological processes call for an overall process optimization. One of the major possibilities of optimizing biotechnological processes lies in immobilization technologies, which may increase productivities and product concentrations. This paper gives a systematic approach to the various immobilization techniques reported in literature. The most important levels of influence on overall process performance are considered within a classification system by three criteria: Substrates and products flow pattern criterion, catalyst criterion and apparatus criterion. Some important immobilization systems are discussed, and the classification system is applied to these examples.

Hydrodynamic performance of a three-phase airlift bioreactor with an enlarged degassing zone

Abstract: The hydrodynamics of biotechnological processes is complex. So far, few studies were made with bioreactors of the airlift type with an enlarged degassing zone.

Liming impact on granules activity of the multiplate anaerobic reactor (MPAR) treating whey permeate

Abstract: A 19.2 l multiplate anaerobic reactor (MPAR) was used to assess the impact of lime (Ca(OH)2) on the anaerobic treatment of whey permeate effluents. The amount of Ca(OH)2 required to maintain the pH of the whey permeate around 5 ranged between 3.0 and 4.5 kg/m3, which corresponded to concentration varying between 1.62 and 2.43 kg/m3. Soluble chemical oxygen demand (COD) removal efficiency exceeded 92% with a methane production rate of 6.7 m3/m3.d. at an organic loading rate (OLR) as high as 20 kg COD/m3.d. Extended operation of the MPAR resulted in the accumulation of significant amounts of calcium precipitates in the sludge bed which reached after three months of operation 0.19, 0.25 and 0.33 kg Ca2+ per kg of suspended solid (SS) in the lower, the middle and the upper compartment of the MPAR, respectively. The volatile suspended solids to suspended solids ratio (VSS/SS) decreased from 0.83 in inoculum to 0.37, 0.22 and 0.08 in the lower, the middle and the upper compartment of the MPAR, respectively. As a result, the soluble COD reduction and the methane production rate decreased to 31% and to 2.3 m3/m3.d. respectively, at OLR of 20 kg COD/m3.d.

Biofilm thickness effect on the diffusion limitation in the bioprocess reaction: Biofloc critical diameter significance

Abstract: A convenient physical model for biomass involves consideration of individual cells as “active” centers dispersed through a continuous region in which transport takes place by molecular diffusion. This paper investigates for steady state conditions the variation of apparent kinetic constant (K ) of bacteria in relation to biofloc diameter with solid and/or liquid-phase diffusion. When the biochemical reactions are limited only by liquid-phase diffusion, theK increases whenD increases. With solid-phase diffusion limitation only, theK increases linearly with the diameterD of the floc. When both solid and liquid-phase diffusion limitations are considered, the apparentK m is affected by liquid-phase diffusion limitation with very smallD and by solid-phase diffusion limitation with higherD. The critical diameterD c can be assumed to be theD at which solid-phase diffusion limitation becomes more significant than liquid-phase diffusion limitation.

Applications of modelling for bioprocess design and control in industrial production

Abstract: The on-line measurement of the relevant parameters and the control conception for three production processes for fine chemicals by fermentation and biotransformation at the 15 m3 scale were developed. The models describe the bioprocesses which successfully result in fully automated manufacturing steps. Modelling also proved to be a valuable tool for a better insight into biochemical fundamentals of the processes. Moreover, proper use of data logging, modelling and process control was important for quality, since two processes were controlled on-line and quality relevant deviations were registered early. Finally, combining modelling with simulation, we could drastically reduce both development time and cost.

Comparative study of anaerobic digestion of olive mill wastewater (OMW) and OMW previously fermented with Aspergillus terreus

Abstract: A comparative kinetic study was carried out on the anaerobic digestion of olive mill wastewater (OMW) and OMW that was previously fermented with Aspergillus terreus. Two completely-mixed bioreactors were used for the study. The results obtained were evaluated using the Chen-Hashimoto methane production model to obtain values for the maximum specific growth rate (μmax) and kinetic constant (K) of the process for each case studied. The kinetic parameters were found to be influenced by the pretreatment carried out, and were 4.5 and 3.8 times higher for pretreated OMW than that obtained in the anaerobic digestion of untreated OMW. This was significant at 95 % confidence level. This behaviour is believed to be due to the lower levels of phenolic compounds and biotoxicity present in the pretreated OMW, as compared to untreated OMW, resulting in an improved process performance and stability. Finally, the experimental values of methane production were reproduced with deviations equal to or less than 10% in every case.

The effects of fermentation conditions on yeast cell debris particle size distribution during high pressure homogenisation

Abstract: Experiments were performed to characterize the particle size distribution of bakers' yeast cells during high pressure homogenisation. Results were obtained for mechanically agitated batch and continuously grown cultures under a range of operating conditions. It was found that the dependency of cell debris size distribution on the number of passes through the homogeniser and the homogeniser pressure was independent of the cell properties and culture conditions, but for a fixed pressure and number of passes the extent of disruption was strongly affected by the operating conditions in the fermenter. The entire cell debris size distributions were successfully simulated using the mean and variance of the distributions and a previously published model equation which related these parameters to the operating pressure and number of passes through the homogeniser.

Hydrodynamic behaviour of animal cell microcarrier suspensions in split-cylinder airlift bioreactors

Abstract: Hydrodynamic characteristics of suspensions of microcarriers used for culturing anchorage dependent animal cells are reported in split-cylinder internal-loop airlift bioreactors. Cell culture media are simulated using salt solutions that duplicate the ionic strengths of typical media. Effects of solids loading (0–30 kg·m−3), microcarrier particle size (150–300×10−6 m diameter) and density (1030–1050 kg·m−3) on gas induced circulation of the slurry, mixing time, gas holdup and gas velocity requirements to attain complete suspension of solids are discussed for two reactors with aspect ratios of 7.6 and 14.5, but equal riser-to-downcomer cross-sectional area ratios of 1.0, aerated at low air flow rates (0–8×10−6 m3·s−1) through a sintered glass sparger with 110×10−6 m diameter pores. The study covers the ranges of solids concentrations, types, densities, particle sizes and aeration rates that are of relevance in animal cell culture applications.

Study of the liquid circulation velocity in external-loop airlift bioreactors

Abstract: Liquid circulation velocity was studied in externalloop air-lift bioreactors of laboratory and pilot scale, respectively for different gas input rates, downcomer-to-riser cross-sectional area ratio, A D/AR and liquid phase apparent viscosities. It was found that, up to a gas superficial velocity in the riser v SGR ≈ 0.04 m/s the dependency of v SLR on v SGR is in the following form: v SLR = a v SGR b , with the exponent b being 0.40. Over this value of v SGR, only a small increase in liquid superficial velocity, v SLR is produced by an increase in v SGR. A D/AR ratio affects the liquid superficial velocity due to the resistance in flow and overall friction. For non-Newtonian viscous liquids, the circulation liquid velocity in the riser section of the pilot external-loop airlift bioreactor is shown to be dependent mainly on the downcomer-to-riser cross-sectional area ratio, A D/AR, the effective (apparent) liquid viscosity, η eff and the superficial gas velocity, v SGR. The equation proposed by Popovic and Robinson [11] was fitted well, with an error of ± 20%.

Feasibility of using water-immiscible organic solvents in biological waste-gas treatment.

Abstract: In order to conclude about the feasibility of using water-immiscible organic solvents in biological waste-gas treatment, a theoretical study was done in which different types of organic-solvent-containing systems are compared with systems where the pollutant is transferred directly to the water phase. For each system the total equipment volume needed to remove 99% of a pollutant from a waste-gas stream is calculated. Three different pollutants with a different solubility in water are considered: Hexane (mgw=71), dichloromethane (mgw=0.1) and acetone (mgw=0.0016), withmgw the partition coefficient (kg/m3 gas/kg/m3 water) of the pollutant between the gas and the water phase. From the results it is concluded that the use of organic solvents is only advantageous in case the specific area for mass transfer between solvent and water is large enough to compensate for the additional transport resistance introduced by the solvent, and secondly if the solvent shows a sufficiently high affinity for the pollutants.

Ultrafiltration of fermented broths and solvent extraction of antibiotics

Abstract: Experiments of ultrafiltration with diafiltration were performed on fermented broths of benzylpenicillin and clavulanic acid produced at pilot scale at CIPAN, SA to achieve solid/liquid separation, antibiotic recovery and soluble protein retention. This study was done using a laboratorial/pilot scale ultrafiltration facility from Paterson Candy International Ltd. whose modules have a tubular configuration. PVDF membranes with a molecular weight cut-off of 100 000 (FP10) and 200 000 (FP200) were assessed. Comparison between solvent extraction of benzylpenicillin and clavulanic acid from filtered broth and ultrafiltered broth was also done. It was concluded that ultrafiltration with diafiltration of fermented broths of antibiotics using the FP10 membrane is a valid alternative to the use of rotary vacuum filters, flocculants and filter aid, deserving a further study to establish the best operating conditions. An economic appraisal also seems to be of paramount importance.

Two mathematical models for the development of a single microbial pellet

Abstract: Starting from the results of a morphologically detailed description of pellet development, a mathematical model is presented which is expected to yield equivalent results with substantially less computing expenditure. The simplification of the original model (part I of the paper) resulted in an about 60–100fold reduction of the demands for computing capacity. This was achieved by averaging the mycelial morphology within radial layers. Quantities such as cell volume density and substrate consumption rates were taken to be constant within a layer. The description by means of partial differential equations was intentionally omitted except for the mass-transfer into the pellet. The results of the layer model show a far-reaching equivalence to the detailed single-hypha-model. Data from image processing investigations and microprobe measurements of oxygen and glucose in Penicillium chrysogenum pellets correspond to the simulation results. The model appears suitable for further process-simulations with larger ensemble of pellets.

Anaerobic digestion of palm oil mill effluent and condensation water waste: an overall kinetic model for methane production and substrate utilization

Abstract: The process of anaerobic digestion is viewed as a series of reactions which can be described kinetically both in terms of substrate utilization and methane production It is considered that the rate limiting factor in the digestion of complex wastewaters is hydrolysis and this cannot be adequately described using a Monod equation In contrast readily assimilable wastewaters conform well to this approach A generalized equation has thus been derived, based on both the Monod and Contois equations, which serves extreme cases The model was verified experimentally using continuous feed anaerobic digesters treating palm oil mill effluent (POME) and condensation water from a thermal concentration process POME represents a complex substrate comprising of unhydrolyzed materials whereas the condensation water is predominantly short chain volatile fatty acids Substrate removal and methane production in both cases could be predicted accurately using the generalized equation presented

Effect of carbon sources on the synthesis of pectinase by Aspergilli

Abstract: The synthesis of pectinase is investigated using six species of Aspergillus, with five media differing either in their carbon sources or level of carbon source(s). Five of the six species used, synthesized appreciable amounts of pectinase in the media containing sugars. Pectinase synthesis was highest for A. niger, NCIM 548, with all the sugar containing media. A. foetidus, NCIM 510, was the only one among the organisms studied, that responded well to the medium containing pectin in the absence of additional sugars supplied in the medium.

Biodegradation of phenol by arthrobacter and modelling of the kinetics

Abstract: The toxic effects of phenol, a common constituent of many industrial effluents, necessitates treatment of the polluted streams. Biodegradation is a popular technique and enjoys many advantages. The degradation of phenol with Arthrobacter species is studied in batch cultures and it is observed that the substrate is inhibiting. The fit of various models, including the model proposed earlier by us [17], to the experimental data is studied. The model is used to fit available data in literature, which unfortunately is very sparse. In all the cases the present model fits the data best.

Description and evaluation of reciprocating plate bioreactors

Abstract: The environment in which live microorganisms has a major impact on their productivity. One important factor is the mechanical mixing that is used to promote good heat and mass transfer in bioreactors. In this paper, the performance of reciprocating plate bioreactors is first evaluated for their ability to produce high oxygen transfer coefficients. Pure water and a glycerol water (50∶50 wt%) solution are used for this evaluation. Then, the performance of reciprocating plate bioreactors for the production of an exocellular polysaccharide (pullulan) by yeast Aureobasidium pullulans is analyzed in terms of quantity and quality of the polysaccharide. Results clearly show that a more efficient substrate utilisation is achieved with reciprocating plate bioreactors.

Immobilization of urease on gelatin — poly (HEMA) copolymer preparation and characterization

Abstract: Urease was immobilized onto gelatin-poly (HEMA) copolymer by covalent linkage. Maximum amount of urease was immobilized onto the support at a pH of 8.5. The optimal pH of the immobilized urease was similar to that of free urease; the optimal temperature showed an increase of 10 °C over the free enzyme. The stability of the immobilized urease for a range of pH, temperature and shelf life was greater than the corresponding values for the free enzyme. The same result was obtained for km also.

Design and simulation of a fuzzy controller for fed-batch yeast fermentation

Abstract: In baker's yeast fermentation, the process is non-linear and the response of the system to changes in glucose feeding has a very long delay time. Therefore, a conventional system can not give satisfactory results. In this paper, a fuzzy controller designed to control a fed-batch fermenter is presented. The fuzzy controller uses Respiratory Quotient (RQ) as a controller input and produces glucose feeding rate as control variable. The controller has been tested on a simulated fed-batch fermenter. The results show that the maximum yeast production is possible by keeping the specific growth rate (μ) and the glucose concentration (Cs) at preset values (μCand Cs,c) and minimizing the ethanol production.

Alcoholic fermentation under oenological conditions: use of a combination of data analysis and neural networks to predict sluggish and stuck fermentations

Abstract: The possibility of predicting sluggish fermentations under oenological conditions was investigated by studying 117 musts of different French grape varieties using an automatic device for fermentation monitoring. The objective was to detect sluggish or stuck fermentations at the halfway point of fermentation. Seventy nine percent of fermentations were correctly predicted by combining data analysis and neural networks.

Two mathematical models for the development of a single microbial pellet: Part I: Detailed morphological model based on the description of individual hyphae

Abstract: A mathematical model for pellet development of filamentous microorganisms is presented, which simulates in detail location and growth of single hyphal elements. The basic model for growth, septation and branching of discrete hyphae is adopted from Yang et al. (2, 23]. Exact solutions to the intracellular mass-balance equations of a growth-limiting key component is given for two types of either branched or unbranched cellular compartments. Furthermore, the growth model was extended in regard to the external mass-balance equations of limiting substrates (oxygen, glucose) under the assumption that the substrates can enter the denser regions of the pellet only diffusively. Penetration of the substrates into the more porous outer regions of the pellet occurs more easily due to microeddies in the surrounding fluid. Chipping of hyphae from the pellet surface by shear forces was included in the model as well. The application of shear forces leads to a marked smoothing of the simulated pellet surface. The development of pellets from spore germination up to late stages with cell-lysis due to shortage of substrates in the pellet centre can be described. The effects of various model parameters are discussed

Oxygen transfer measurements during yeast fermentations in a pilot scale airlift fermenter

Abstract: Measurements of oxygen transfer were made during cultivation of the yeast Saccharomyces cerevisiae in a 90–250 litre working volume concentric tube airlift fermenter. Results demonstrated that the rate of oxygen transfer varies with position in the fermenter, being higher in the riser and top-section than in the downcomer and lowest near the base of the fermenter. The time for liquid circulation was generally smaller than the time constant for oxygen transfer (1/kLa) indicating that the rate of oxygen transfer was slow compared to the rate of liquid movement. Measured dissolved oxygen concentrations therefore did not represent the equilibrium arising from the balance between the rates of oxygen transfer and oxygen depletion. Hence measuredkLa values were not representative of local oxygen transfer conditions but instead were indicators of the rate of mass transfer the liquid flow had encountered prior to reaching the point of measurement. Generally the individual rates of oxygen transfer in the vessel were found to increase with increasing vessel height.

Some kinetic aspects and modelling of biotransformation of D-glucose to keto-D-gluconates

Abstract: The bacterial oxidation of D-glucose to D-gluconic and keto-D-gluconic acids has been studied. Different approaches to pH-control have been checked. It is demonstrated, that the microbial growth is independent on pH-control. However, the rate of keto-gluconate production is too sensitive to the strategy of pH-maintenance and particularly to the neutralizing agent. The general opinion for the essential importance of addition of calcium ions for keto-gluconate formation is confirmed. The interpretation of the obtained experimental data by means of a simple mathematical model shows that the apparent lag-phase in keto-gluconate production is probably due to the necessity of accumulation of biomass as a biocatalyst and gluconic acids as a substrate.

Sorption of heavy metals by four basidiomycetous fungi

Abstract: Biosorptions of Pb2+, Cr6+, Cd2+ and Ni2+ were investigated, with special emphasis on the first one, using live and dead fungal mycelia. Of the four fungi, namely Polyporus ostreiformis, Volvariella volvacea, Pleurotus sajor-caju and Phanerochaete chrysosporium, the last one was found to be most effective in Pb2+ removal. Total biosorption was effected in 6 days up to the Pb2+ concentration of 6 mg/l, with a specific uptake of 1.33 mg Pb2+/g dry cell mass. The removal of other three metals varied between 28.8–73.3% from a medium containing 4 mg/l of each of the metals.

Glycerolysis of olive oil : batch operational stability of Candida rugosa lipase immobilized in hydrophilic polyurethane foams

Abstract: The operational stability of the Candida rugosa lipase immobilized in a hydrophilic polyurethane foam was evaluated in consecutive batches for the glycerolysis of olive oil in n-hexane, aimed at the production of monoglycerides. Glycerol controlled the glycerolysis in the system under study, since it is both a substrate and a powerful water binder that reduces the water activity of the reaction medium and of the microenvironment. Two sets of experiments were carried out under different glycerol/triglyceride ratios. After 345 hours of consecutive 23 hours batches no lipase inactivation was observed.

Mass transfer and liquid mixing in an airlift reactor with a net draft tube

Abstract: Mass transfer and liquid mixing in an airlift reactor with a net draft tube were experimentally investigated. Four different column diameters were considered. The mass transfer was measured using the volumetric gas-liquid mass transfer coefficient which was determined by the dynamic method. The mass transfer coefficients in the airlift reactors with different column diameters were not always higher than those in the bubble columns. The liquid mixing was measured using mixing time which was determined by a pulse technique. Under the same superficial gas velocity, the mixing times of the airlift reactors with a net draft tube were always less than those of the bubble columns.