FED-BATCH SIMULTANEOUS SACCHARIFICATION AND FERMENTATION OF MICROWAVE/ACID/ALKALI/H2O2 PRETREATED RICE STRAW FOR PRODUCTION OF ETHANOL

The batch simultaneous saccharification and fermentation (SSF) of microwave/acid/alkali/H₂O₂ pretreated rice straw to ethanol was optimized using cellulase from Trichoderma reesei and Saccharomyces cerevisiae YC-097 cells prior to the fed-batch SSF studies. The batch SSF optima were 10% w/v substrate, 40°C, 15 mg cellulase/g substrate, initial pH 5.3, and 72 hours. Under the optimum conditions the ethanol concentration and its yield were 29.1 g/L and 61.3% respectively. Based on the optimal batch SSF, the fed-batch SSF was investigated and its operation parameters were optimized. Under its optimal conditions the ethanol concentration reached 57.3 g/L, while its productivity and yield were only slightly less than those in the batch SSF. This suggests that fed-batch SSF is a potential operation mode for effective ethanol production from microwave/acid/alkali/H₂O₂ pretreated rice straw.     

High-Performance Production of Biosurfactant Rhamnolipid with Nitrogen Feeding

Nitrate is one of the most important factors for fermentative production of rhamnolipid, while it has not yet been conclusively demonstrated that nitrogen limitation or abundance is beneficial for improvement of rhamnolipid production. This study clarified that high concentration of NaNO₃ is conducive for high-performance production of rhamnolipid. An optimum rhamnolipid yield was achieved by 43.3 g L⁻¹ with an initial concentration of NaNO₃ equal to 10 g L⁻¹ during the regular fed-batch fermentation process by Pseudomonas aeruginosa ATCC 9027. Additionally, this rhamnolipid production was further improved to 61.2 g L⁻¹, which was two folds higher than that value obtained during batch fermentation, when the NaNO₃ concentration was maintained about 5 g L⁻¹. Furthermore, specific volume productivity of rhamnolipid was improved by over 30% in the presence of NaNO₃ at concentration ranging from 5 to 6 g L⁻¹ during sequential fed-batch fermentation, resulting a high value of 0.4 and 0.59 g L⁻¹ h⁻¹ within one batch of sequential fed-batch fermentation for a period of 17 days by P. aeruginosa ATCC 9027 and PAO1, respectively. It seems that sustaining high-concentration NaNO₃ during fed-batch fermentation is advantageous for high-performance production of rhamnolipid.     

Optimal culture condition for the production of phenyalanine ammonia lyase from <Emphasis Type="Italic">E. coli</Emphasis>

The effects of culturing conditions on phenylalanine ammonia lyase production by a recombinant E. coli strain were investigated by using a controlled fed-batch fermentation system. In a 5 L fermentor, the optimal composition of the batch medium was 2% glucose, 1% yeast extract, 0.7% K₂HPO₄, 0.8% KH₂PO₄, 0.5% (NH₄)₂SO₄, 0.1% MgSO₄·7H₂O. The optimal feed glucose solution was 50%. Glucose concentration and pH of the culture broth were maintained at about 2.0 g/L and 7.0 during the fed-batch phase, respectively. Following 24-h cultivation, 0.2 mmol/L isopropyl-β-D-thiogalactopyranoside (IPTG) was added and temperature was shifted from 37°C to 42°C to induce pal gene expression. Under optimal conditions, a high productivity of 300 U/g could be achieved after 48 h culture, and a cell density of OD₆₀₀ about 82 was obtained at 52 h culture at 500 r/m stirrer speed and 1 vvm, respectively.     

FED-BATCH SIMULTANEOUS SACCHARIFICATION AND FERMENTATION OF MICROWAVE/ACID/ALKALI/H2O2 PRETREATED RICE STRAW FOR PRODUCTION OF ETHANOL

The batch simultaneous saccharification and fermentation (SSF) of microwave/acid/alkali/H₂O₂ pretreated rice straw to ethanol was optimized using cellulase from Trichoderma reesei and Saccharomyces cerevisiae YC-097 cells prior to the fed-batch SSF studies. The batch SSF optima were 10% w/v substrate, 40°C, 15 mg cellulase/g substrate, initial pH 5.3, and 72 hours. Under the optimum conditions the ethanol concentration and its yield were 29.1 g/L and 61.3% respectively. Based on the optimal batch SSF, the fed-batch SSF was investigated and its operation parameters were optimized. Under its optimal conditions the ethanol concentration reached 57.3 g/L, while its productivity and yield were only slightly less than those in the batch SSF. This suggests that fed-batch SSF is a potential operation mode for effective ethanol production from microwave/acid/alkali/H₂O₂ pretreated rice straw.     

重组大肠杆菌分批-补料高密度发酵生产类人胶原蛋白的动力学

The kinetics of batch and fed-batch cultures of recombinant Escherichia coli producing human-like collagen was investigated. In the batch culture, a kinetic model of a simple growth-association system was concluded without consideration of cell endogeneous metabolism. The cell lag time, the maximum specific growth rate and Yx/s were determined as 1.75h, 0.65h^-1 and 0.51g·g^-1, respectively. In the fed-batch culture, different specific growth rates were set at （0.15, 0.2, 0.25h^-1） by the method of pseudo-exponential feeding, and the expressions for the specific rate of substrate consumption, the growth kinetics and the product formation kinetics of each phase were obtained. The result shows that the concentrations of cell and product can reach 77.5g·L^-1 and 10.2g·L^-1 respectively. The modal predictions are in good agreement with the experimental data.     

Production of Hexanoic Acid by Free and Immobilised Cells of Megasphaera elsdenii: Influence of in-situ Product Removal Using Ion Exchange Resin

The objective of this work was to improve the production of hexanoic acid by the anaerobic rumen bacterium, Megasphaera elsdenii, using product removal and immobilised cell approaches. Hexanoic acid, the major product of glucose metabolism by M. elsdenii strain ATCC25940, was produced at concentrations of 2–3 g dm⁻³ in stirred batch cultures. With pH controlled manually at 7, maximum concentrations of hexanoic acid increased to 6–8 g dm⁻³ with yields (g product per g glucose used) of approximately 30%. When an anion exchange resin, Amberlite IRA 400, was added during early stages of culture to minimise product inhibition, growth was not impaired and cell lysis, which was commonly seen during the stationary phase in control fermentations, was prevented. The presence of resin in pH-controlled, stirred batch fermentations increased the rate of glucose consumption and doubled hexanoic acid productivity: the equivalent of 11 g dm⁻³ of hexanoic acid was made with an estimated yield of up to 39%. Cells were immobilised successfully in κ-carrageenan and, when cell densities in inocula were sufficiently high, rates of glucose consumption and product formation were similar to free cells. Including resin in cultures of immobilised cells had effects similar to those above. Using a fed-batch mode with immobilised cells cultured in the presence of resin further increased final concentrations of hexanoic acid (up to 19 g dm⁻³) but yields were lower (20–30%) and productivity did not increase. These results show that production of volatile fatty acids can be improved significantly by product stripping onto an anion exchange resin. © 1997 SCI.     

Improvement of fermentative production of exopolysaccharides from Aureobasidium pullulans under various conditions

The optimization of exopolysaccharide (EPS) production was investigated in the polymorphic fungal strain of Aureobasidium pullulans (KCTC 6081) with varying pH, nutrients concentration, and mixing parameters in batch fermentation condition. The maximum production of EPS (～7.5 g/L) was observed at pH 4, while optimum nutrient concentration of carbon (sucrose), nitrogen (NaNO₃), phosphorous (K₂HPO₄), and ascorbic acid was 50 g/L, 5 g/L, 1 g/L and 2 g/L, respectively. Interestingly, EPS productivity under non pH controlled fermentation conditions was 0.12 g/L/h with 400 rpm mixing, while under a controlled pH of 4, the EPS productivity was 0.21 g/L/h with 600 rpm, respectively. The fed-batch fermentation increased the EPS productivity up to 0.345 g/L/h with changing mixing conditions from 200 to 600 rpm and reached 47 g/L with 88% pullulan. Thus, pH and mixing were the key parameters for enhancing EPS production from A. pullulans. It is expected that these optimized parameters can be well used for enhanced industrial production of pullulan.     

Formation and reduction of nitric oxide in fixed-bed combustion of straw

Mechanisms of nitric oxide (NO) formation and reduction in fixed-bed combustion of straw have been modeled mathematically and verified experimentally. The model for the straw combustion and nitrogen chemistry consists of sub-models for evaporation, pyrolysis, tar and char combustion, nitrogen conversion, and energy and mass conservation. Twenty chemical reactions are included, of which 12 belong to the fuel nitrogen reaction network. Volatile nitrogen is assumed to be NO, NH₃, HCN and HNCO, and char nitrogen is converted to NO during char oxidation. The model predictions are in qualitative agreement with the measurements during the ignition phase, i.e. when the combustion front passes through the un-burnt fuel. The yield of NO can be reduced considerably by using a low primary air flow due to the longer gas residence in the fixed-bed, while the NO exhaust concentration is insensitive to the bed temperature. The NO exhaust concentration initially reaches a maximum and then decreases towards a stable value after the straw bed is ignited. Variations of NO, NH₃, HCN, and HNCO concentrations in the ignition flame front indicate that a large quantity of NO can be reduced in the thin flame front zone. The developed model is further validated by separate experiments in which NO or NH₃ was added at the middle through tubes or at the bottom of the bed with the primary air flow. Both the simulations and measurements showed that the variation of the NO exhaust concentration is small as compared with the injected NO or NH₃ concentration. According to the simulations and experiments, it is proposed that flue gas recirculation may be a very effective method of reducing NO emissions from flue gas in the fixed-bed combustion of straw. Calculations indicated that about 20% of the flue gas may be recirculated without significantly affecting the combustion behavior.     

Kinetics and reaction engineering of penicillin G hydrolysis

A general diffusion reaction model for immobilised biocatalysis has been developed. The model has been used to study the deacylation of penicillin G to 6-aminopenicillanic acid using two commercially available immobilised Penicillin acylases. The values of D_e/R² for the enzyme pellets have been estimated using data on uptake of 6-aminopenicillanic acid and phenylacetic acid by the enzyme pellets. The kinetic parameters of the model were individually estimated from a suitably designed set of experiments. The values of the Thiele modulus from the kinetic parameters so calculated have been found to be in the range 1·67 to 9·8 for the two enzymes studied, implying that diffusional effects cannot be ignored. The effect of such diffusional limitations on the overall rates and hence on the utilisation of the intrinsic kinetic ability of the enzyme has been demonstrated. This paper also reports on the implementation of the fed-batch strategy for this system. The proposed strategy, which involves maintaining the substrate concentration at the optimum value for a large part of the conversion, results in higher product concentrations than in batch operation, thereby reducing downstream procesing costs. The productivity was also shown to be considerably higher than for batch operation. Further, the ease of implementation of this mode of operation has been demonstrated.     

Production of poly‐3‐hydroxybutyrate by Cupriavidus necator from corn syrup: statistical modeling and optimization of biomass yield and volumetric productivity

BACKGROUND: The paper reports an investigation into the possibility of producing poly‐3‐hydroxybutyrate (P(3HB)) polyester using corn syrup, a relatively low cost by‐product from the starch industries. The concentrations of medium components, corn syrup, dipotassium hydrogen phosphate (K₂HPO₄), sodium dihydrogen phosphate (NaH₂PO₄) and ammonium sulfate [(NH₄)₂SO₄] were optimized using design of experiments (DOE). RESULTS: Response surface methodology (RSM) under central composite face design (CCFD) was used to obtain the optimum values of medium components and responses in terms of biomass yield and volumetric P(3HB) productivity. The highest P(3HB) productivity and biomass yield obtained were 0.224 g L^?1 h^?1 and 0.57 g g^?1, respectively. A limited‐nitrogen concentration had a higher volumetric P(3HB) productivity (0.170 g L^?1 h^?1) than that of the excess nitrogen batch experiment (0.0675 g L^?1 h^?1). The optimum corn syrup:N:P ratio of 50:0.078:1 was based on numerical optimization of the desirability function between biomass yield and volumetric P(3HB) productivity by Cupriavidus necator DSMZ 545. CONCLUSION: The results obtained in this study demonstrated that P(3HB) could be efficiently produced to a high concentration with high productivity by applying nitrogen limitation in a defined medium, indicating this agricultural by‐product to be a suitable nutrient source in further studies to develop biomaterials through biotechnology. Copyright © 2010 Society of Chemical Industry     

Performance evaluation of batch and unsteady state fed‐batch reactor operations for the production of a marine microbial surfactant

BACKGROUND: Biosurfactants are microbially derived surface‐active and amphipathic molecules produced by various microorganisms. These versatile biomolecules can find potential applications in food, cosmetics, petroleum recovery and biopharmaceutical industries. However, their commercial use is impeded by low yields and productivities in fermentation processes. Thus, an attempt was made to enhance product yield and process productivity by designing a fed‐batch mode reactor strategy. RESULTS: Biosurfactant (BS) production by a marine bacterium was performed in batch and fed‐batch modes of reactor operation in a 3.7 L fermenter. BS concentration of 4.61 ± 0.07 g L^?1 was achieved in batch mode after 22 h with minimum power input of 33.87 × 10³ W, resulting in maximum mixing efficiency. The volumetric oxygen flow rate (K_La) of the marine culture was about 0.08 s^?1. BS production was growth‐associated, as evident from fitting growth kinetics data into the Luedeking‐Piret model. An unsteady state fed batch (USFB) strategy was employed to enhance BS production. Glucose feeding was done at different flow rates ranging from 3.7 mL min^?1 (USFB‐I) to 10 mL min^?1 (USFB‐II). USFB‐I strategy resulted in a maximum biosurfactant yield of 6.2 g l^?1 with an increment of 35% of batch data. The kinetic parameters of USFB‐I were better than those from batch and USFB‐II. CONCLUSION: Comparative performance evaluation of batch and semi‐continuous reactor operations was accomplished. USFB‐I operation improved biosurfactant production by about 35% over batch mode. USFB‐I strategy was more kinetically favorable than batch and USFB‐II. © 2012 Society of Chemical Industry     

Continuous perfusion culture of encapsulated hybridoma cells

BACKGROUND: The production of Monoclonal antibodies (mAbs) is often performed in batch or fed‐batch operations where low cell densities and low volumetric productivities are achieved. The main bottleneck of both processes is the short operating time with productive cells at maximum cell concentration. RESULTS: The process studied in this work is based on a fluidized‐bed bioreactor culture of encapsulated KB26.5 cells in a liquid core of calcium alginate microcapsules as a culture strategy to produce IgG₃. First, DMEM medium was modified in order to protect the microcapsules from degradation, and later, the optimal operating conditions were set. Under these conditions encapsulated KB26.5 cells reached cell densities of 1.05 × 10⁸cells mL^?1 or 9.8 × 10⁶ cells mL^?1 (referred to the inner capsule volume or total bioreactor volume, respectively), and a mAb volumetric productivity of 2.75 µg mL^?1 h^?1. CONCLUSIONS: The productivity of encapsulated KB26.5 cells in perfusion culture was enhanced significantly in comparison with batch and fed‐batch processes. Continuous operation of the perfusion culture for periods longer than 35 days, represented a volumetric productivity about five‐fold higher than conventional operations. However, the fluidized‐bed also showed limitations such as low cell viability at high cell densities due to the mass transfer limitations of large molecules inside the microcapsules. Copyright © 2011 Society of Chemical Industry     

Plasma-assisted ammonia decomposition over Fe–Ni alloy catalysts for CO x-Free hydrogen

On-site ammonia (NH₃) decomposition is considered as a potential path to supply CO _x-free hydrogen for fuel cell vehicles. In this article, monometallic catalysts (Fe, Co, Ni, and Mo) and bimetallic catalysts (Fe–Co, Mo–Co, Fe–Ni, and Mo–Ni) were prepared and tested in plasma-catalytic NH₃ decomposition, where 6Fe–4Ni catalyst exhibited the highest activity and synergistic capability with plasma. At 500°C, NH₃ were completely decomposed (>99.9% NH₃ conversion); the rate of H₂ production and the energy consumption of H₂ production reached 0.96 mol g⁻¹ h⁻¹ and 0.050 kW h (mol g⁻¹)⁻¹, respectively. The 200 h continuous operation results indicate an excellent durability of 6Fe–4Ni catalyst. The catalysts characterization and plasma diagnosis results indicate that NH₃ was pre-activated by plasma into excited-state species (NH₃, ˙NH₂, and ˙NH), and the 6Fe–4Ni catalyst exhibited the highest capability to adsorb excited NH₃, ˙NH₂, and ˙NH species, which could be the main reason why 6Fe–4Ni catalyst exhibited the highest activity. © 2018 American Institute of Chemical Engineers AIChE J, 65: 691–701, 2019     

Enhanced Production of Podophyllotoxin by Fed‐batch Cultivation of Podophyllum hexandrum

Podophyllum hexandrum (Indian May Apple) was successfully cultivated in a 3 L stirred tank bioreactor under low shear conditions in batch and fed‐batch modes of operation. A statistically optimized culture medium was used for the batch cultivation of Podophyllum hexandrum. Under optimum culture conditions of P. hexandrum, the batch culture showed a growth‐associated product formation with a maximum biomass of 21.4 g/L dry cell weight (DCW) basis and a podophyllotoxin production of 13.8 mg/L in 26 d. A mathematical model was developed to design the nutrient feeding strategies for a fed‐batch cultivation to prolong the productive log phase of cultivation. The fed‐batch cultivation was able to enhance the biomass and podophyllotoxin accumulation to 48 g/L (DCW basis) and 43.2 mg/L, respectively, in 60 d. The volumetric productivity of podophyllotoxin in fed‐batch cultivation was found to be 0.72 mg/(L. d) as opposed to 0.53 mg/(L. d) in batch cultivation under optimized culture conditions.     

Experimental simulation of large-scale bioreaetor environments using a Monte Carlo method

Cells grown in production-scale stirred bioreactors experience fluctuating concentrations due to local variations in supply and consumption of oxygen and nutrients. A new method for studying the effects of fluctuations in local conditions on growth and productivity of cells was developed using a Monte Carlo approach to simulate circulation within a fermenter. A small fermenter was driven through cycles of aeration and feeding, with the time of each cycle controlled by a Monte Carlo method to give a log-normal distribution. Experiments with Monte Carlo supply of air to batch and fed-batch cultures of Saccharomyces cerevisiae showed that the method gave reproducible results which were different from both periodic cycling and continuous supply. When substrate was provided to a fed-batch culture of S. cerevisiae according to the Monte Carlo method, the yields of biomass were higher than experiments with continuous feeding or periodic feeding.     

A novel strategy on the high-cell-density cultivation of Candida utilis for the enhanced production of glutathione

Efficient glutathione production by high-cell-density cultivation of Candida utilis was investigated. A series of batch glutathione fermentations were carried out and the optimal initial glucose concentration was found to be about 26 g/L. Then, fed-batch fermentation under diverse feeding strategies was used to enhance glutathione production with a total glucose concentration of 150 g/L. Constant glucose feeding strategy cannot meet the requirement of cells at the late period of feeding, while exponential glucose feeding strategy cannot satisfy the needs of cells at the beginning of feeding. Based on the results above, a polynomial glucose feeding strategy was developed to provide enough glucose for cells along with the cultivation, under which both the cell and glutathione productivity were satisfactorily improved. Furthermore, fed-batch fermentation under this strategy with a total glucose concentration of 200 g/L was successfully performed, the dry cell weight and glutathione concentration reached 91.2 g/L and 825 mg/L, respectively.     

High density culture of Coptis japonica cells increases berberine production

A high density culture method was devised to improve the yield of berberine from highly productive cells of Coptis japonica. By adjusting aeration and stirring, Coptis cells were cultured at densities of up to 75 g dm^?3 (dry weight) in a culture tank fitted with a hollow-paddle type stirrer. Whereas a maximum density of 30 g dm^?3 of C. japonica cells could be used in ordinary batch culture, 48 g dm^?3 could be used in a fed-batch culture in which the amounts of the nutrients in the medium were made proportional to the density of the inoculum. Moreover, in fed-batch culture done with modified medium, the composition of which had been determined from the amounts of components incorporated in cells grown at the usual density for ordinary batch culture, the cell yield was improved to 55 g dm^?3 and the berberine yield to 3.5 g dm^?3.     

Strain isolation and optimization of process parameters for bioconversion of glycerol to lactic acid

BACKGROUND: The crude glycerol from biodiesel production represents an abundant and inexpensive source which can be used as raw material for lactic acid production. The first aim of this investigation was to select a strain suitable for producing lactic acid from glycerol with a high concentration and productivity. The second aim was to obtain the optimum fermentation conditions, as a basis for large‐scale lactate production in the future. RESULTS: Eight bacterial strains, which could aerobically convert glycerol to lactic acid, were screened from soil samples. One of the strains, AC‐521, which synthesized lactic acid with a higher concentration, was identified based on its 16S rDNA sequences and physiological characteristics. These results indicated that this strain was a member of Escherichia coli. The optimal fermentation conditions for Escherichia coli AC‐521 were 42 °C, pH 6.5, 0.85 min^?1 (K_La). CONCLUSION: Escherichia coli AC‐521 suitable for producing lactic acid from glycerol with high concentration and productivity was identified. After 88 h of fed‐batch fermentation, both the lactic acid concentration and glycerol consumption reached maximum, giving 85.8 g L^?1 of lactic acid with a productivity of 0.97 g L^?1 h^?1 and a yield of 0.9 mol mol^?1 glycerol. Copyright © 2009 Society of Chemical Industry     

Selection and isolation of glucose-tolerant amylolytic Aspergillus by cyclic fed batch culture process

A simple cyclic fed batch culture system was developed for selection and subsequent isolation of glucose-tolerant Aspergillus niger strain. A culture medium which contained 1.2 g dm⁻³ of glucose was inoculated with a non-glucose-tolerant A. niger (K_i =20.25 g dm⁻³). A culture medium of higher glucose concentration (100 g dm⁻³ and 200 g dm⁻³) was fed at a rate equal to the rate of HN₄⁺ consumption by means of a pH control system. The maximum and minimum liquid levels in the fed batch culture vessel were determined by two liquid level detectors which activated and deactivated a harvest pump. The novelty of the selection system is that the frequency and pressure of selection increase gradually but continuously, and they are determined by the intrinsic potential of the culture. The process was fully automatic. An Aspergillus mutant which had a glucose inhibition constant of 3200 g dm⁻³ was isolated after six generations. The process should be particularly useful for screening filamentous microorganisms growing on novel substrates or tolerating inhibitors.     

Spectroscopic Evidence for a Nitrite Intermediate in the Catalytic Reduction of NOx with Ammonia on Fe/MFI

The mechanism of selective catalytic reduction (SCR) of NO_x with NH₃ over Fe/MFI was studied using in situ FTIR spectroscopy. Exposing Fe/MFI first to NH₃ then to flowing NO + O₂ or using the reversed sequence, invariably leads to the formation of ammonium nitrite, NH₄NO₂. In situ FTIR results in flowing NO + NH₃ + O₂ at different temperatures show that NH₃ is strongly adsorbed and reacts with impinging NO_x. The intensity of the NH₄NO₂ bands initially increases with temperature, but passes through a maximum at 120 °C because the nitrite decomposes to N₂ + H₂O. The mechanistic model rationalizes that the consumption ratio of NO and NH₃ is close to unity and that the effect of water vapor depends on the reaction temperature. At high temperature H_2O enhances the rate because it is needed to form NH₄NO₂. At low temperature, when adsorbed H₂O is abundant it lowers the rate because it competes with NO_x for adsorption sites.