Evaluation of a vertical flat-plate photobioreactor for outdoor biomass production and carbon dioxide bio-fixation: effects of reactor dimensions, irradiation and cell concentration on the biomass productivity and irradiation utilization efficiency

Outdoor culture of the thermophilic cyanobacterium Synechocystis aquatilis SI-2 with a vertical flat-plate photobioreactor (VFPP) was studied during the period of January to August of 1999 in the northern region of Japan (Kamaishi, Iwate, 39 degrees N, 142 degrees E). The aim of this study was to investigate the CO2 fixation ability of the VFPP device under various irradiation conditions. An average biomass productivity of over 30 g m(-2) day(-1), which corresponds to a CO2 fixation rate of 50 g m(-2) day(-1), was achieved during this period with a 192-l scale culture. The effects on biomass productivity of the light path, height of the reactor, cell concentration and irradiation were also investigated. Variation of the optimal cell concentration to achieve the highest productivity for outdoor operation is discussed. A cell concentration of 1-2 g l(-1) was found to be most suitable for the irradiation range of 1-12 MJ m(-2) day(-1) under the experimental conditions used.     

Oxygen transfer rates in a mammalian cell culture bioreactor equipped with a cell-lift impeller

Measurements of k(L)a were carried out in 1. 5- and 5-L New Brunswick Scientific CelliGen(R) bioreactors. The measured k(L)a in water were identical for both vessel sizes operated in similar condition. The mass transfer rate increased with temperature, mixing speed, and aeration rate, with this last parameter being the most significant. Surface aeration alone gave k(L)a values of 0. 4 to 1. 6 h(-1). A 25% decrease in k(L)a was observed above an aeration rate of 1. 6 vvm. This was caused by the particular foam breaker of the CelliGen bioreactor. Measurements of k(L)a using a mammalian cell culture medium supplemented with 5% fetal calf serum (FCS) have confirmed the negative effect of the foam breaker on k(L)a The measured value in this medium was 1. 2 h(-1) for all aeration rates, more than 60% of which was attributed to surface aeration.     

Cultivation of microplantlets derived from the marine red alga Agardhiella subulata in a stirred tank photobioreactor

Macrophytic marine red algae are a diverse source of bioactive natural compounds. "Microplantlet" suspension cultures established from red algae are potential platforms for biosynthesis of these compounds, provided suitable bioreactor configurations for mass culture can be identified. The stirred tank bioreactor offers high rates of gas-liquid mass transfer, which may facilitate the delivery of the CO(2) in the aeration gas to the phototrophic microplantlet suspension culture. Therefore, the effects of impeller speed and CO(2) delivery on the long-term production of microplantlet biomass of the model red alga Agardhiella subulata was studied within a stirred tank photobioreactor equipped with a paddle blade impeller (D(i)/D(T) = 0.5). Nutrient medium replacement was required for sustained biomass production, and the biomass yield coefficient based on nitrate consumption was 1.08 +/- 0.09 g dry biomass per mmol N consumed. Biomass production went through two exponential phases of growth, followed by a CO(2) delivery limited growth phase. The CO(2)-limited growth phase was observed only if the specific growth rate in the second exponential phase of growth was at least 0.03 day(-)(1), the CO(2) delivery rate was less than 0.258 mmol CO(2) L(-)(1) culture h(-)(1), and the plantlet density was at least 10 g fresh mass L(-)(1). Increasing the aeration gas CO(2) partial pressure from 0.00035 to 0.0072 atm decreased the cultivation pH from 8.8 to 7.8, prolonged the second exponential phase of growth by increasing the CO(2) delivery rate, and also increased the photosynthetic oxygen evolution rate. Impeller speeds ranging from 60 to 250 rpm, which generated average shear rates of 2-10 s(-)(1), did not have a significant effect on biomass production rate. However, microplantlets cultivated in a stirred tank bioreactor ultimately assumed compact spherical shape, presumably to minimize exposure to hydrodynamic stress.     

Development and bioreactor cultivation of a novel semidifferentiated tissue suspension derived from the marine plant Acrosiphonia coalita

A semidifferentiated tissue culture consisting of linear filaments in liquid suspension was established from Acrosiphonia coalita, a cold-water green macroalga known to express pharmacologically active oxylipins deriving from lipoxygenase metabolism of linolenic acid. The tissue was vegatively propagated by blending the filaments down to 1 to 5 mm in length prior to subculture. The filamentous A. coalita tissue suspension was successfully cultivated in an illuminated, 3-L stirred-tank bioreactor at 12 degrees C, 0.46-vvm aeration rate, 250-rpm mixing speed, and incident illumination intensity of 77 muE m(-2)s(-1). The mean specific growth rate over the exponential phase was 0.185 day(-1) and a final cell density of 1083 mg dry cell weight (DCW) L(-1) was achieved within 15 days of cultivation from an initial cell density of 200 mg DCW L(-1). The addition of 3500 ppm CO(2) to the aeration gas provided a maximum CO(2) transfer rate of six times the maximum CO(2) consumption rate and stabilized the pH to 8.0 during the light phase of growth, but did not improve biomass productivity. (c) 1996 John Wiley & Sons, Inc.     

Lipid accumulation and CO2 utilization of Nannochloropsis oculata in response to CO2 aeration

In order to produce microalgal lipids that can be transformed to biodiesel fuel, effects of concentration of CO(2) aeration on the biomass production and lipid accumulation of Nannochloropsis oculata in a semicontinuous culture were investigated in this study. Lipid content of N. oculata cells at different growth phases was also explored. The results showed that the lipid accumulation from logarithmic phase to stationary phase of N. oculata NCTU-3 was significantly increased from 30.8% to 50.4%. In the microalgal cultures aerated with 2%, 5%, 10% and 15% CO(2), the maximal biomass and lipid productivity in the semicontinuous system were 0.480 and 0.142 g L(-1)d(-1) with 2% CO(2) aeration, respectively. Even the N. oculata NCTU-3 cultured in the semicontinuous system aerated with 15% CO(2), the biomass and lipid productivity could reach to 0.372 and 0.084 g L(-1)d(-1), respectively. In the comparison of productive efficiencies, the semicontinuous system was operated with two culture approaches over 12d. The biomass and lipid productivity of N. oculata NCTU-3 were 0.497 and 0.151 g L(-1)d(-1) in one-day replacement (half broth was replaced each day), and were 0.296 and 0.121 g L(-1)d(-1) in three-day replacement (three fifth broth was replaced every 3d), respectively. To optimize the condition for long-term biomass and lipid yield from N. oculata NCTU-3, this microalga was suggested to grow in the semicontinuous system aerated with 2% CO(2) and operated by one-day replacement.     

Carbon dioxide uptake efficiency by outdoor microalgal cultures in tubular airlift photobioreactors

The influence of solar irradiance and carbon dioxide molar fraction of injected CO(2)-air mixtures on the behavior of outdoor continuous cultures of the microalga Phaeodactylum tricornutum in tubular airlift photobioreactors was analyzed. Instantaneous solar irradiance, pH, dissolved oxygen, temperature, biomass concentration, and the mass flow rates of both the inlet and outlet oxygen and carbon with both the liquid and gas phases were measured. In addition, elemental analysis of the biomass and the cell-free culture medium was performed. The oxygen production rate and carbon dioxide consumption rate increased hyperbolically with the incident solar irradiance on the reactor surface. Carbon losses showed a negative correlation with the daily variation of the carbon dioxide consumption rate. The maximum CO(2) uptake efficiency was 63% of the CO(2) supplied when the CO(2) concentration in the gas supplied was 60% v/v. Carbon losses were >100% during the night, due to CO(2) production by respiration, and hyperbolically decreased to values of 10% to 20% in the midday hours. An increase in the carbon fixed in the biomass with the solar cycle was observed. A slight daily decrease of carbon content of the cell-free culture medium indicated the existence of carbon accumulation in the culture. A decrease in CO(2) molar fraction in the injected gas had a double benefit: first, the biomass productivity of the system was enhanced from 2.05 to 2.47 g L(-1) day(-1) by reduction of CO(2) inhibition and/or pH gradients; and second, the carbon losses during the daylight period were reduced by 60%. The fluid dynamics in the reactor also influenced the carbon losses: the higher the liquid flow rate the higher the carbon losses. By using a previous mass transfer model the experimental results were simulated and the usefulness of this method in the evaluation and scale-up of tubular photobioreactors was established.     

Optimization of oxygen mass transfer in a multiphase bioreactor with perfluorodecalin as a second liquid phase

Oxygenation is an important parameter involved in the design and operation of mixing-sparging bioreactors and it can be analyzed by means of the oxygen mass transfer coefficient (k(L)a). The operational conditions of a stirred, submerged aerated 2-L bioreactor have been optimized by studying the influence of a second liquid phase with higher oxygen affinity (perfluorodecalin or olive oil) in the k(L)a. Using k(L)a measurements, the influence of the following parameters on the oxygen transfer rate was evaluated: the volume of working medium, the type of impellers and their position, the organic phase concentration, the aqueous phase composition, and the concentration of inactive biomass. This study shows that the best experimental conditions were achieved with a perfluorodecalin volume fraction of 0.20, mixing using two Rushton turbines with six vertical blades and in the presence of YPD medium as the aqueous phase, with a k(L)a value of 64.6 h(-1). The addition of 20% of perfluorodecalin in these conditions provided a k(L)a enhancement of 25% when pure water was the aqueous phase and a 230% enhancement when YPD medium was used in comparison to their respective controls (no perfluorodecalin). Furthermore it is shown that the presence of olive oil as a second liquid phase is not beneficial to the oxygen transfer rate enhancement, leading to a decrease in the k(L)a values for all the concentrations studied. It was also observed that the magnitude of the enhancement of the k(L)a values by perfluorodecalin depends on the biomass concentration present.     

Reduction of CO2 by a high-density culture of Chlorella sp. in a semicontinuous photobioreactor

The microalga incorporated photobioreactor is a highly efficient biological system for converting CO2 into biomass. Using microalgal photobioreactor as CO2 mitigation system is a practical approach for elimination of waste gas from the CO2 emission. In this study, the marine microalga Chlorella sp. was cultured in a photobioreactor to assess biomass, lipid productivity and CO2 reduction. We also determined the effects of cell density and CO2 concentration on the growth of Chlorella sp. During an 8-day interval cultures in the semicontinuous cultivation, the specific growth rate and biomass of Chlorella sp. cultures in the conditions aerated 2-15% CO2 were 0.58-0.66 d(-1) and 0.76-0.87 gL(-1), respectively. At CO2 concentrations of 2%, 5%, 10% and 15%, the rate of CO2 reduction was 0.261, 0.316, 0.466 and 0.573 gh(-1), and efficiency of CO2 removal was 58%, 27%, 20% and 16%, respectively. The efficiency of CO2 removal was similar in the single photobioreactor and in the six-parallel photobioreactor. However, CO2 reduction, production of biomass, and production of lipid were six times greater in the six-parallel photobioreactor than those in the single photobioreactor. In conclusion, inhibition of microalgal growth cultured in the system with high CO2 (10-15%) aeration could be overcome via a high-density culture of microalgal inoculum that was adapted to 2% CO2. Moreover, biological reduction of CO2 in the established system could be parallely increased using the photobioreactor consisting of multiple units.     

Oxygen and carbon dioxide mass transfer and the aerobic, autotrophic cultivation of moderate and extreme thermophiles: a case study related to the microbial desulfurization of coal

Mass transfers of O(2), CO(2), and water vapor are among the key processes in the aerobic, autotrophic cultivation of moderate and extreme thermophiles. The dynamics and kinetics of these processes are, in addition to the obvious microbial kinetics, of crucial importance for the industrial desulfurization of high-pyritic coal by such thermophiles. To evaluate the role of the temperature on the gas mass transfer, k(L)a measurements have been used to supplement the existing published data. Oxygen mass transfer from gas (air) to liquid (5 mM H(2)SO(4) in water) phase as a function of the temperature has been studied in a laboratory-scale fermentor. At 15, 30, 45, and 70 degrees C, (k(L)a)(o) values (for oxygen) were determined under three different energy input conditions by the dynamic gassing in/out method. The (k(L)a)(o) was shown to increase under these conditions with increasing temperature, and straight lines were obtained when the logarithm of (k(L)a)(o) was plotted against the temperature. By multiplying the equilibrium concentration of O(2) in water with (k(L)a)(o) maximal, O(2) transfer capacities were calculated. It appeared that in finite of a decreased solubility of O(2) at elevated temperature in mechanically mixed fermentors the calculated transfer capacities showed only minor changes for the range between 15 and 70 degrees C. However, in an air-mixed fermentor the transfer capacity of O(2) decreased slowly but steadily.Carbon dioxide mass transfer was predicted by calculations on the basis of the data for oxygen transfer. The maximal CO(2) transfer capacity, calculated as the product of the equilibrium CO(2) concentration times (k(L)a)(c), decreased slowly as the temperature increased over the range 15-70 degrees C under all three energy input conditions. Subsequent process design calculations showed that for aerobic, autotrophic cultures, CO(2) limitation is more likely to occur than O(2) limitation.     

Effect of oxygen transfer on glycerol biosynthesis by an osmophilic yeast Candida magnoliae I(2)B

The influence of oxygen on glycerol production by an osmophilic yeast, Candida magnoliae I(2)B, was studied in a bioreactor. Oxygen transfer rates (OTRs) and volumetric oxygen transfer coefficients (k(L)a) were determined at different aeration and agitation rates. Cell growth as well as glycerol production was strongly affected by oxygen supply. Improvement in OTRs resulted in increased cell growth and glycerol yield. However, at high OTRs, there was a reduction in glucose uptake rate, indicating Pasteur Effect, and glycerol accumulation was also reduced at k(L)a of 253 h(-1). The availability of oxygen per unit of cell mass was found to be the most important factor that controlled cell growth, glucose uptake, and glycerol yield. The overall productivity and yield of glycerol could be related with k(L)a. The biosynthesis of glycerol was found to both growth- and non-growth-associated, although glycerol was mainly produced in post-exponential phase.     

产油微藻自养培养条件调控

作为新兴生物燃料的生物柴油近年来发展迅速,以微藻为代表的第二代生物能源是解决能源危机的长远之计,但如何提高其产量仍是研究的热点问题。以提高产油自养微藻生物量和油脂含量为目的,在气升式光反应器中运用均匀设计实验方法进行了条件优化试验。分别得出了氮原子浓度、通气速率、二氧化碳体积浓度和光照强度4个因素对小球藻C2生物量积累和油脂含量影响的显著回归方程和反应器优化培养条件。以生物量为指标的优化培养条件是:氮原子浓度0.178 g/L,通气速率5 L/min,二氧化碳体积浓度3%(V/V),光照强度6000 lx。该优化条件下,生物量为2.11 g/L,即生产速率为0.352 g/(L.d),比测试实验中检测到的最高生物量[1.88 g/L,即生产速率为0.313 g/(L.d)]提高了12.2%;以油脂含量为指标的优化培养条件是:进气速率0.400 L/min,二氧化碳体积浓度1.94%(V/V),得到油脂含量为22.4%,比测试实验中检测到的最高油脂量(20.7%)提高7.7%。     

Photolithotrophic cultivation of Laminaria saccharina gametophyte cells in a stirred-tank bioreactor

Filamentous cell cultures derived from female gametophytes of the temperate brown macroalga Laminaria saccharina were photolithotrophically cultivated in artificial seawater medium within an illuminated 1.3-L stirred-tank bioreactor at 13 degrees C using CO(2) in air as the carbon source. A Monod model adequately described light-saturated growth. The apparent half-saturation constant (K(o)) was 23 muE/m(2)-s, and maximum specific growth rate was 0.15 day(-1). At a constant inoculation cell density of 50 mg DCW/L, biomass productivity after 26 days of cultivation increased from 630 mg DCW/L at 18 muE/m(2)-s to 890 mg DCW/L at 228 muE/m(2)-s. At 98 muE/m(2)-s, 1.1 vvm aeration rate, and 250 rpm impeller speed, the CO(2) transfer rates (CO(2) TRs) and CO(2) consumption rates (r(co(2) )) were determined over the cultivation period. At peak CO(2) demand, the maximum CO(2) TR was 0.19 mmol CO(2)/L-h, but r(co(2) ) was only 0.15 mmol CO(2)/L-h, implying that the culture was not CO(2) transport limited. This is the first reported bioreactor cultivation study of cell cultures derived from a macrophytic marine alga. (c) 1995 John Wiley & Sons, Inc.     

Oxygen uptake and citric acid production by Candida lipolytica Y 1095

The rates of oxygen uptake and oxygen transfer during cell growth and citric acid production by Candida lipolytica Y 1095 were determined. The maximum cell growth rate, 1.43 g cell/L . h, and volumetric oxygen uptake rate, 343 mg O(2)/L . h, occurred approximately 21 to 22 h after inoculation. At the time of maximum oxygen uptake, the biomass concentration was 1.3% w/v and the specific oxygen uptake rate was slightly greater than 26 mg O(2)/g cell . h. The specific oxygen uptake rate decreased to approximately 3 mg O(2)/g cell . h by the end of the growth phase.During citric acid production, as the concentration of dissolved oxygen was increased from 20% to 80% saturation, the specific oxygen uptake and specific citric acid productivity (mg citric acid/g cell . h) increased by 160% and 71%, respectively, at a biomass concentration of 3% w/v. At a biomass concentration of 5% w/v, the specific oxygen uptake and specific citric acid productivity increased by 230% and 82%, respectively, over the same range of dissolved oxygen concentrations.The effect of dissolved oxygen on citric acid yields and productivities was also determined. Citric acid yields appeared to be independent of dissolved oxygen concentration during the initial production phase; however, volumetric productivity (g citric acid/L . h) increased sharply with an increase in dissolved oxygen. During the second or subsequent production phase, citric acid yields increased by approximately 50%, but productivities decreased by roughly the same percentage due to a loss of cell viability under prolonged nitrogen-deficient conditions. (c) 1994 John Wiley & Sons, Inc.     

Oxygen transfer in animal cell culture medium

Both k(L)a and k(L) measurements were carried out by an unsteady state technique at impeller speeds ranging from 1.6 to 5.8 s(-1) in a mechanically agitated animal cell culture vessel of working volume 1.5 L. Checks were made that the time constant of the oxygen electrode was negligible compared to the time for aeration and that the oxygen electrode reading was not a function of agitator speed in the range employed. The k(L) values by surface aeration of (1.18-3.54) x 10(-5) m/s and k(L)a values by sparged aeration of (2.8-8.5) x 10(-4) s(-1) were found. The former are in reasonable agreement with published experimental values and the latter in accord with values estimated from published correlations based on agitator power input and aeration rate. The fluids used were water, basal medium, and basal medium supplemented with 5% (v/v) foetal calf serum; for each of these, k(L) and k(L)a values were similar. However, the addition of silicone antifoam (6 PPM) reduced the k(L)a value by ca. 50%.     

Strategies for improved dCO2 removal in large-scale fed-batch cultures

Carbon dioxide buildup in large-scale reactors can be detrimental to cell growth and productivity. In case of protein X, a therapeutic glycoprotein, when cultures were scaled up from bench scale to the pilot plant, there was a 40% loss of specific productivity. The dissolved CO(2) (dCO(2)) level was 179 +/- 9 mmHg at the pilot plant scale and 68 +/- 13 mmHg at bench scale. The authors proposed a comprehensive approach to maintain dCO(2) levels between 40 and 120 mmHg throughout the 14-day fed-batch process. A cell-free experiment was used to investigate the impact of the following parameters on dCO(2) removal: (1) sparge rate, (2) agitator speed, (3) bubble size, (4) bicarbonate concentration, (5) impeller position, and (6) aeration rate at the headspace of bioreactor. dCO(2) was measured using a fiber optic based probe. dCO(2) removal rate was a strong function of sparge rate and a weak function of agitator speed. Bubble size was modulated by the presence or absence of a sparge stone (10 microm pore size, 1 cm pipe i.d.). Open pipe provided 3- to 4-fold better dCO(2) removal for the same mass transfer coefficient (k(L)a) value. A mathematical model and a bench-scale experiment indicated that the benefit of a lower level of sodium bicarbonate in the culture medium was transient for batch and fed-batch cultures. Thus, this strategy was not used at pilot scale. Decreasing top impeller position improved k(L)a of dCO(2) by 2-fold. Changing headspace aeration rate from 0.02 to 0.04 vvm had no impact on dCO(2) removal. Two pilot runs were conducted using (A) open pipe and (B) antifoam in the presence of sparge stone, both in conjunction with lower impeller position. The presence of antifoam may interfere in product purification; however, demonstration of antifoam removal can be difficult. Open pipe allowed an alternative to using antifoam, as foam level with open pipe was significantly less. Both strategies successfully reduced dCO(2) level by 2.5-fold (179 +/- 9 vs 72 +/- 9 mmHg). Titer at day 10 of culture improved by 1.5-fold. Specific productivity improved by 41%. Historically, cultures were harvested around day 9-11 because of the high amount of foam; both strategies allowed the cultures to be extended up to day 14, resulting in 2-fold higher titer compared to that of the historical control without compromising protein quality.     

Controlled biomass formation and kinetics of toluene degradation in a bioscrubber and in a reactor with a periodically moved trickle-bed

The kinetics of degradation of toluene from a model waste gas and of biomass formation were examined in a bioscrubber operated under different nutrient limitations with a mixed culture. The applicability of the kinetics of continuous cultivation of the mixed culture was examined for a special trickle-bed reactor with a periodically moved filter bed. The efficiency of toluene elimination of the bioscrubber was 50 to 57% and depended on the toluene mass transfer as evident from a constant productivity of 0.026 g dry cell weight/L . h over the dilution rate. Under potassium limitation the biomass productivity was reduced by 60% to 0.011 g dry cell weight/L . h at a dilution rate of 0.013/h. Conversely, at low dilution rates the specific toluene degradation rates increased. Excess biomass in a trickle-bed reactor causes reduction of interfacial area and mass transfer, and increase in pressure drop. To avoid these disadvantages, the trickle-bed was moved periodically and biomass was removed with outflowing medium. The concentration of steady state biomass fixed on polyamide beads decreased hyperbolically with the dilution rate. Also, the efficiency of toluene degradation decreased from 72 to 56% with increasing dilution rate while the productivity increased. Potassium limitation generally caused a reduction in biomass, productivity, and yield while the specific degradation increased with dilution rate. This allowed the application of the principles of the chemostat to the trickle-bed reactor described here, for toluene degradation from waste gases. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 686-692, 1997.     

Modeling and optimization of poly(3hydroxybutyrate-co-3hydroxyvalerate) production from cane molasses by Azohydromonas lata MTCC 2311 in a stirred-tank reactor: effect of agitation and aeration regimes

The effects of agitation and aeration rates on copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [P(3HB-co-3HV)] production by Azohydromonas lata MTCC 2311 using cane molasses supplemented with propionic acid in a bioreactor were investigated. The experiments were conducted in a three-level factorial design by varying the impeller (150-500 rev min(-1)) and aeration (0.5-1.5 vvm) rates. Further, the data were fitted to mathematical models [quadratic polynomial equation and artificial neural network (ANN)] and process variables were optimized by genetic algorithm-coupled models. ANN and hybrid ANN-GA were found superior for modeling and optimization of process variables, respectively. The maximum copolymer concentration of 7.45 g l(-1) with 21.50 mol% of 3HV was predicted at process variables: agitation speed, 287 rev min(-1); and aeration rate, 0.85 vvm, which upon validation gave 7.20 g l(-1) of P(3HB-co-3HV) with 21 mol% of 3HV with the prediction error (%) of 3.38 and 2.32, respectively. Agitation speed established a relative high importance of 72.19% than of aeration rate (27.80%) for copolymer accumulation. The volumetric gas-liquid mass transfer coefficient (k (L) a) was strongly affected by agitation and aeration rates. The highest P(3HB-co-3HV) productivity of 0.163 g l(-1) h(-1) was achieved at 0.17 s(-1) of k (L) a value. During the early phase of copolymer production process, 3HB monomers were accumulated, which were shifted to 3HV units (9-21%) during the cultivation period of 24-42 h. The enhancement of 7.5 and 34% were reported for P(3HB-co-3HV) production and 3HV content, respectively, by hybrid ANN-GA paradigm, which revealed the significant utilization of cane molasses for improved copolymer production.     

Improved poly-ε-lysine biosynthesis using Streptomyces noursei NRRL 5126 by controlling dissolved oxygen during fermentation

The growth kinetics of Streptomyces noursei NRRL 5126 was investigated under different aeration and agitation combinations in a 5.0 l stirred tank fermenter. Poly-epsilon-lysine biosynthesis, cell mass formation, and glycerol utilization rates were affected markedly by both aeration and agitation. An agitation speed of 300 rpm and aeration rate at 2.0 vvm supported better yields of 1,622.81 mg/l with highest specific productivity of 15 mg/l.h. Fermentation kinetics performed under different aeration and agitation conditions showed poly- epsilon-lysine fermentation to be a growth-associated production. A constant DO at 40% in the growth phase and 20% in the production phase increased the poly-epsilon-lysine yield as well as cell mass to their maximum values of 1,992.35 mg/l and 20.73 g/l, respectively. The oxygen transfer rate (OTR), oxygen utilization rate (OUR), and specific oxygen uptake rates (qO2) in the fermentation broth increased in the growth phase and remained unchanged in the stationary phase.     

Hydrodynamic and mass transfer characteristics of three-phase gaslift bioreactor systems.

This review focuses on the hydrodynamic and mass transfer characteristics of various three-phase, gaslift fluidized bioreactors. The factors affecting the mixing and volumetric mass transfer coefficient (k(L)a), such as liquid properties, solid particle properties, liquid circulation velocity, superficial gas velocity, bioreactor geometry, are reviewed and discussed. Measurement methods, modeling and empirical correlations are reviewed and compared. To the authors' knowledge, there is no 'generalized' correlation to calculate the volumetric mass transfer coefficient, instead, only 'type-specific' correlations are available in the literature. This is due to the difficulty in modeling the gaslift bioreactor, caused by the variation in geometry, fluid dynamics, and phase interactions. The most important design parameters reported in the literature are: gas hold-up, liquid circulation velocity, 'true' superficial gas velocity, mixing, shear rate, aeration rate and volumetric mass transfer coefficient, k(L)a.     

High cell density cultivation of Pseudomonas oleovorans: growth and production of poly (3-hydroxyalkanoates) in two-liquid phase batch and fed-batch systems

Pseudomonas oleovorans is able to accumulate poly(3-hydroxyalkanoates) (PHAs) under conditions of excess n-alkanes, which serve as sole energy and carbon source, and limitation of an essential nutrient such as ammonium. In this study we aimed at an efficient production of these PHAs by growing P. oleovorans to high cell densities in fed-batch cultures.To examine the efficiency of our reactor system, P. oleovorans was first grown in batch cultures using n-octane as growth substrate and ammonia water for pH regulation to prevent ammonium limiting conditions. When cell growth ceased due to oxygen limiting conditions, a maximum cell density of 27 g .L(-1) dry weight was obtained. When the growth temperature was decreased from the optimal temperature of 30 degrees -18 degrees C, cell growth continued to a final cell density of 35 g . L(-1) due to a lower oxygen demand of the cells at this lower incubation temperature.To quantify mass transfer rates in our reactor system, the volumetric oxygen transfer coefficient (k(L)a) was determined during growth of P. oleovorans on n-octane. Since the stirrer speed and airflow were increased during growth of the organism, the k(L)a also increased, reaching a constant value of 0.49 s(-1) at maximum airflow and stirrer speed of 2 L . min(-1) and 2500 rpm, respectively. This k(L)a value suggests that oxygen transfer is very efficient in our stirred tank reactor.Using these conditions of high oxygen transfer rates, PHA production by P. oleovorans in fed-batch cultures was studied. The cells were first grown batchwise to a density of 6 g . L(-1), after which a nutrient feed, consisting of (NH(4))(2)SO(4) and MgSO(4), was started. The limiting nutrient ammonium was added at a constant rate of 0.23 g NH(4) (+) per hour, and when after 38 h the feed was stopped, a biomass concentration of 37.1 g . L(-1) was obtained. The Cellular PHA content was 33% (w/w), which is equal to a final PHA yield of 12.1 g . L(-1) and an overall PHA productivity of 0.25 g PHA produced per liter medium per hour. (c) 1993 John Wiley & Sons, Inc.