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.     

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.     

Fuzzy Optimization of Extractive Fermentation Processes Including Cell Recycle for Lactic Acid Production

In this study, a bioprocess optimization problem was considered for a multiple‐stage extractive fermentation, including cell recycling, to produce lactic acid. The aim of the optimization problem is to obtain the maximum overall productivity, conversion and yield simultaneously, so that the optimization problem is formulated as a multi‐objective optimization procedure. The fuzzy goal attainment method was introduced to the multi‐objective optimization problem in order to obtain a trade‐off solution. The approach was also employed to determine the optimal design for two simplified continuous fermentation processes. From the computational results, the overall productivity for the fermentation processes including cell recycling, enabled a higher dilution rate so that the overall productivity was ca. thirteen‐fold higher than that of the continuous fermentation process without cell recycling.     

Trade-off optimal design of a biocompatible solvent for an extractive fermentation process

In this study, crisp and flexible optimization approaches are, respectively, introduced to design an optimal biocompatible solvent for an extractive fermentation process. The optimal design problem is formulated as a mixed-integer nonlinear programming model in which performance requirements of the compounds are reflected in the objective and the constraints. In general, the requirements for the objective and constraints are not rigid; consequently, the flexible or fuzzy optimization approach is applied to soften the rigid requirement for maximization of the extraction efficiency and to consider the mass flow rate and biocompatibility of solvent as the softened inequality constraints to the solvent design problem. Having elicited the membership function for the objective function and the constraint, the optimal solvent design problem can be formulated as a flexible goal attainment problem. Mixed-integer hybrid differential evolution is applied to solve the problem in order to find a satisfactory design.     

Optimal biocompatible solvent design for a two-stage extractive fermentation process with cell recycling

In this study, crisp and fuzzy multiple-goal optimization approaches are respectively introduced to design an optimal biocompatible solvent to a two-stage extractive fermentation with cell recycling for ethanol production. When designing a biocompatible solvent for the extractive fermentation process, many issues, such as extractive efficiency, conversion, amount of solvent utilized and so on, have to be considered. An interactive multiple-goal design procedure is introduced to determine a trade-off result in order to satisfy such contradicted goals. Both approaches could be iterated to solve the interactive multiple-goal design problem in order to yield a trade-off result. However, the crisp optimization design is a tedious task that requires the designer to provide various pairs of the upper bounds for the design problem to obtain the corresponding solution. The fuzzy optimization approach is able to be trade-off several goals simultaneously and to yield the overall satisfactory grade for the product/process design problem.     

基于MKPLS和SQP方法的间歇过程迭代优化控制

采用多向核偏最小二乘（MKPLS）方法建立间歇过程的模型并进行操作条件的优化。由于存在模型失配和未知扰动，基于MKPLS模型的最优控制轨迹在实际对象上往往难以实现最优的产品质量指标。本文利用间歇过程批次间的重复特性与序贯二次规划（SQP）优化算法中迭代计算的相似特点，提出了一种基于MKPLS模型的批次间优化调整策略，使得经过逐步优化调整得到的控制轨迹作用于实际对象时，可以得到更优的质量指标。该方法的有效性在苯乙烯聚合反应器和乙醇流加发酵过程的仿真对象上得到了验证。     

Performance analysis and fuzzy optimization of a two-stage fermentation process with cell recycling including an extractor for lactic acid production

In this study, we consider a two-stage fermenter with cell recycling including an extractor to produce lactic acid. When the extractor was omitted, the proposed process was simplified to two special processes. Under the same operating conditions, we compared the overall lactic acid productivity and glucose conversion for the three processes. The proposed fermentation process was more efficient than the other processes. To simultaneously obtain the maximum productivity and conversion, the problem is formulated as a fuzzy multiobjective optimization problem. The fuzzy decision is introduced to convert the multiobjective fuzzy optimization problem into the fuzzy goal attainment problem. Hybrid differential evolution is applied to solve the fuzzy goal attainment problem to obtain a global Pareto solution.     

Studies on optimal control approach in a fed-batch fermentation

Fed-batch operation of fermentation processes has been receiving a great deal of interest as it offers the possibility to control a substrate concentration at a desired condition. However, control of a fed-batch fermentation reactor has been known to be a difficult task due to its highly nonlinear and complicated behavior. This work addresses an optimization-based control strategy for a fed-batch bioreactor where an ethanol fermentation process is chosen as a case study. The optimal control problem is formulated to determine the optimal feeding rate policy giving the highest product yield. The resulting optimization problem is solved by using an efficient sequential approach with a piecewise constant control parameterization. Due to the limitation of the sequential approach to cope with inequality path constraints, comparative studies of the methods for handling such constraints are carried out. Furthermore, the impact of time interval and switching time on the solution of the optimal control is investigated.     

高底物浓度纤维乙醇同步糖化发酵工艺的比较

引言日益加剧的能源危机和环境污染,正迫使人们寻求新的可再生替代能源。纤维乙醇作为一种重要的生物质替代能源,经过近40多年的发展,已经具备了实现工业化生产的潜力。为了进一步降低纤     

Strategies for Optimizing Feed Rate of Fed-Batch Yeast Fermentation by Fuzzy-Neural Network

In this paper,a novel fuzzy neural network model,in which an adjustable fuzzy sub-space was designed by uniform design,has been established and used in fed-batch yeast fermentationas an example.A brand-new optimization sub-network with special structure has been built andgenetic algorithm,guaranteeing the optimization in overall space,is introduced for the feed rateoptimization.On the basis of the model network,the optimal substrate concentration and theoptimal amount of fed-batch at different periods have been studied,aided with the optimizationnetwork and the genetic algorithm separately.The above results can be used as a basis for theestablishment of a fuzzy neural network controller.     

Simultaneous saccharification and fermentation of wheat bran flour into ethanol using coculture of amylotic Aspergillus niger and thermotolerant Kluyveromyces marxianus

Studies on simultaneous saccharification and fermentation (SSF) of wheat bran flour, a grain milling residue as the substrate using coculture method were carried out with strains of starch digesting Aspergillus niger and nonstarch digesting and sugar fermenting Kluyveromyces marxianus in batch fermentation. Experiments based on central composite design (CCD) were conducted to maximize the glucose yield and to study the effects of substrate concentration, pH, temperature, and enzyme concentration on percentage conversion of wheat bran flour starch to glucose by treatment with fungal α-amylase and the above parameters were optimized using response surface methodology (RSM). The optimum values of substrate concentration, pH, temperature, and enzyme concentration were found to be 200 g/L, 5.5, 65°C and 7.5 IU, respectively, in the starch saccharification step. The effects of pH, temperature and substrate concentration on ethanol concentration, biomass and reducing sugar concentration were also investigated. The optimum temperature and pH were found to be 30°C and 5.5, respectively. The wheat bran flour solution equivalent to 6% (w/V) initial starch concentration gave the highest ethanol concentration of 23.1 g/L after 48 h of fermentation at optimum conditions of pH and temperature. The growth kinetics was modeled using Monod model and Logistic model and product formation kinetics using Leudeking-Piret model. Simultaneous saccharificiation and fermentation of liquefied wheat bran starch to bioethanol was studied using coculture of amylolytic fungus A. niger and nonamylolytic sugar fermenting K. marxianus.     

Biomass production by a thermotolerant yeast: Hansenula polymorpha

Biomass production at high temperature by Hansenula polymorpha as part of a lignocellulosic utilizing process was studied. Compromise growth conditions (45°C and pH = 4.8) with an eventual saccharification step were established. The effects of stirring rate and initial glucose concentration on biomass yield coefficient, volumetric productivity and maximal cell density were determined. Process optimization led to a fed-batch fermentation process: high yield (0.63 g dry cell g^?1 glucose), volumetric productivity (1.3 g dry cell dm^?3 h^?1) and cell concentration (60 g dry cell dm^?3) were obtained. At these conditions, significant arabitol excretion (18 g dm^?3) as a unique by-product associated with cell mass production was obtained, making more interesting a high temperature operating process.     

Simultaneous saccharification and fermentation of wheat bran flour into ethanol using coculture of amylotic Aspergillus niger and thermotolerant Kluyveromyces marxianus

Studies on simultaneous saccharification and fermentation (SSF) of wheat bran flour, a grain milling residue as the substrate using coculture method were carried out with strains of starch digesting Aspergillus niger and nonstarch digesting and sugar fermenting Kluyveromyces marxianus in batch fermentation. Experiments based on central composite design (CCD) were conducted to maximize the glucose yield and to study the effects of substrate concentration, pH, temperature, and enzyme concentration on percentage conversion of wheat bran flour starch to glucose by treatment with fungal α-amylase and the above parameters were optimized using response surface methodology (RSM). The optimum values of substrate concentration, pH, temperature, and enzyme concentration were found to be 200 g/L, 5.5, 65°C and 7.5 IU, respectively, in the starch saccharification step. The effects of pH, temperature and substrate concentration on ethanol concentration, biomass and reducing sugar concentration were also investigated. The optimum temperature and pH were found to be 30°C and 5.5, respectively. The wheat bran flour solution equivalent to 6% (w/V) initial starch concentration gave the highest ethanol concentration of 23.1 g/L after 48 h of fermentation at optimum conditions of pH and temperature. The growth kinetics was modeled using Monod model and Logistic model and product formation kinetics using Leudeking-Piret model. Simultaneous saccharificiation and fermentation of liquefied wheat bran starch to bioethanol was studied using coculture of amylolytic fungus A. niger and nonamylolytic sugar fermenting K. marxianus.     

Evaluation of process conditions in the performance of yeast on alcoholic fermentation

This work studied the resistance of Saccharomyces cerevisiae Y904 to ethanol on an alcoholic fermentation process operated in fed-batch. The effect of temperature, inoculum size and substrate concentration on fermentation yield, productivity and residual sugars concentration was studied by a central composite design (CCD). Based on the CCD study, it was determined the optimum values of 240, 35?g/L, and 26°C for total reducing sugars, inoculum concentration and temperature, respectively. This set of conditions experimentally enabled a productivity of 6.0?g/L?h, a yield of 93% and an alcohol content of 113.6?g/L, after 10?h of fermentation. When yeast cells were adapted at 4°C, the inoculum pH adjusted to 2.5 and sugarcane broth used as substrate, a 94% yield and a 10.1?g/L.?h productivity were achieved.     

Simultaneous saccharification and fermentation of sludge‐containing cassava mash for batch and repeated batch production of bioethanol by Saccharomyces cerevisiae CHFY0321

BACKGROUND: The aim of this study was to examine the repeated batch production of bioethanol from sludge‐containing cassava mash as starchy substrate by flocculating yeast to improve volumetric bioethanol productivity and to simplify the process of a pre‐culture system. RESULTS: For the repeated batch production of bioethanol using cassava mash, the optimal recycling volume ratio was found to be 5%. The repeated batch fermentation was completed within 36 h, while the batch fermentation was completed after 42 h. Volumetric productivity, final ethanol concentration, and ethanol yield were attained to 2.15 g L^?1 h^?1, 83.64 g L^?1, and 85.15%, respectively. Although cell accumulation in the repeated batch process is difficult due to the cassava mash, the repeated batch process using Saccharomyces cerevisiae CHFY0321 could exhibited 10‐fold higher initial viable cell number (1.7 × 10⁷ CFU mL^?1) than that of the batch process. CONCLUSION: The liquefied cassava powder was directly used for the repeated batch process without removal of sludge. Repeated batch bioethanol production by simultaneous saccharification and fermentation using self‐flocculating yeast could reduce process costs and accelerate commercial applications. This result was probably due in part to the effect of the initial viable cell density. Copyright © 2008 Society of Chemical Industry     

Study of simultaneous saccharification and fermentation for steam exploded wheat straw to ethanol

Although simultaneous saccharification and fermentation (SSF) has been investigated extensively, the optimum condition for SSF of wheat straw has not yet been determined. Dilute sulfuric acid impregnated and steam explosion pretreated wheat straw was used as a substrate for the production of ethanol by SSF through orthogonal experiment design in this study. Cellulase mixture (Celluclast 1.5 l and ?-glucosidase Novozym 188) were adopted in combination with the yeast Saccharomyces cerevisiae AS2.1. The effects of reaction temperature, substrate concentration, initial fermentation liquid pH value and enzyme loading were evaluated and the SSF conditions were optimized. The ranking, from high to low, of influential extent of the SSF affecting factors to ethanol concentration and yield was substrate concentration, enzyme loading, initial fermentation liquid pH value and reaction temperature, respectively. The optimal SSF conditions were: reaction temperature, 35°C; substrate concentration, 100 g·L^-1; initial fermentation liquid pH, 5.0; enzyme loading, 30 FPU·g^-1. Under these conditions, the ethanol concentration increased with reaction time, and after 72 h, ethanol was obtained in 65.8% yield with a concentration of 22.7 g·L^-1.     

Pretreatment of barley husk for bioethanol production

This paper reports on the optimization of steam pretreatment of barley husk for high pentose and hexose recovery in the subsequent enzymatic hydrolysis step, as well as high ethanol yield, following simultaneous saccharification and fermentation. The parameters optimized in the steam pretreatment step were residence time (5–15 min), temperature (190–215 °C), and concentration of the acid catalyst (0 or 0.5% H₂SO₄). A microwave oven was employed for screening of the optimal conditions to obtain the highest sugar yield following combined pretreatment and enzymatic hydrolysis. The final optimization of the pretreatment prior to enzymatic hydrolysis was performed on a larger scale, in a steam pretreatment unit. Simultaneous saccharification and fermentation was carried out following steam pretreatment on 5 and 10% dry matter steam‐pretreated slurries. Fermentability tests were performed to determine the effect of by‐products (ie furfural and 5‐hydroxymethyl furfural) in the bioconversion of glucose to ethanol by baker's yeast. The maximum glucose yield, 88% of the theoretical, was obtained following steam pretreatment with 0.5% H₂SO₄ at 200 °C for 10 min. Under these conditions, a sugar to ethanol conversion of 81% was attained in simultaneous saccharification and fermentation. Copyright © 2004 Society of Chemical Industry     

Evaluation of Optimization Metrics for Continuous Fermentation of Plasmid DNA

An evaluation of cumulative productivity metrics for optimizing the continuous fermentation of plasmid DNA (pDNA) is carried out in this work. DNA plasmids provide a good illustrative example for comparison because of the plasmid instability issues associated with their production. However, the analysis presented in this work can also be applied to other intracellular bioproduct continuous fermentation systems. The productivity metrics considered are cumulative product mass per time, profit, and cost objective functions. These metrics are used to determine the optimal continuous fermentation run time at a given dilution rate, during the dynamic period associated with switching from batch to continuous fermentation. The results of this study indicate that different optimum continuous fermentation run times are predicted based upon the choice of the continuous fermentation operating conditions and optimization metric. In particular, the dilution rate must be larger than the inverse of a characteristic time, that is a function of the initial batch operating and plasmid stability times before continuous operation becomes optimal. Provided that this condition is met, different optimal continuous operation run times are obtained depending on the cumulative productivity metric, or operating objective, that is employed.     

Mathematical modeling and optimization of plasmid-harboring and chromosome-integrated recombinant yeast culture processes

For the enhanced secretion of foreign proteins, the mathematical modeling for overall recombinant yeast culture considering protein secretion dynamics is important because we can understand and predict the behavior of biosynthesis and secretion of foreign protein and can develop control strategies for feeding with these model equations. In this research, the mathematical modeling and simulation considering protein secretion dynamics for recombinant yeast cultures that contain multicopy plasmids or chromosomally integrated genes were performed for optimization of foreign glucoamylase production. The optimal feeding policy for maximizing glucoamylase production was suggested in fed-batch culture. By introducing this optimal feeding policy, final glucoamylase activity and productivity of fedbatch culture were significantly increased compared with those of batch culture in both recombinant yeasts.