PERFORMANCE OF A MULTISTAGE FERMENTOR WITH CELL RECYCLE FOR CONTINUOUS ETHANOL PRODUCTION

The unsteady and steady-state performance of a multistage fermentor with cell recycle is investigated numerically for continuous production of ethanol. The tanks-in-series model is employed to describe the flow behaviour of culture in multiple tanks. In establishing mass balances, the cell volume fraction and the equilibrium partition coefficient for intracellular and extracellular ethanol concentrations are taken into account. Kinetic expressions are taken from the literature. Compared to a single tank fermentor with recycle, multi-staging and cell recycle are shown to bring high cell and product concentrations and low substrate concentration in the final tank during unsteady-state operation. Solutions to the steady state model are presented graphically, showing concentrations as a function of dilution rate for different numbers of tanks. Results are given for the maximum ethanol productivity as a function of the optimal dilution rate, with parameters of tank number, bleed ratio and recycle ratio. Also, the effects of the fractional tank volume and the saturation constant on the productivity and the substrate conversion are examined.     

Operating Conditions for High Production Rates of Ethanol in a Continuous Two‐Stage Fermenter with Cell Recycle

A continuous two‐stage fermenter with cell recycle at each stage is studied numerically for efficient production of ethanol. In this system, both filtrate and bleed from the first stage are provided to the second fermenter. Using a product‐inhibition kinetic model with different saturation constants, operating conditions giving the maximum ethanol productivity attainable at high substrate conversions are examined. For high substrate conversions close to complete consumption, the ethanol productivities predicted for this system are found to be higher than those for a single‐stage system and a previous two‐stage configuration at the same bleed ratios.     

Comparison of Lactic Acid Productivities at High Substrate Conversions in a Continuous Two-stage Fermenter With Cell Recycle Using Different Kinetic Models

The steady-state performance of a two-stage recycle fermenter with two different types (I and II) of configurations for staging was investigated numerically for the continuous production of lactic acid. In Type I the bleed broth withdrawn from the first stage is supplied to the second fermenter, and in Type II both filtrate and bleed broth from the first stage are introduced to the second stage. Using four different kinetic models taken from the literature, the effects of operating parameters on the overall lactic acid productivities and the overall substrate conversions are examined. At moderate conversions, productivities for Type I operation are found to be higher than those for Type II and for the single-stage system. In the case of high conversions close to complete consumption, Type II operation is more efficient than the Type I and single-stage systems. For 99% conversion and 40 kg m^-3 substrate feed concentration, productivities for Type II are predicted to be 14-74% higher compared to those for the single-stage system at the same bleed ratios.     

Comparison of Lactic Acid Productivities at High Substrate Conversions in a Continuous Two-stage Fermenter With Cell Recycle Using Different Kinetic Models

The steady-state performance of a two-stage recycle fermenter with two different types (I and II) of configurations for staging was investigated numerically for the continuous production of lactic acid. In Type I the bleed broth withdrawn from the first stage is supplied to the second fermenter, and in Type II both filtrate and bleed broth from the first stage are introduced to the second stage. Using four different kinetic models taken from the literature, the effects of operating parameters on the overall lactic acid productivities and the overall substrate conversions are examined. At moderate conversions, productivities for Type I operation are found to be higher than those for Type II and for the single-stage system. In the case of high conversions close to complete consumption, Type II operation is more efficient than the Type I and single-stage systems. For 99% conversion and 40 kg m^?3 substrate feed concentration, productivities for Type II are predicted to be 14–74% higher compared to those for the single-stage system at the same bleed ratios.     

Bifurcation analysis of two continuous membrane fermentor configurations for producing ethanol

A detailed bifurcation/chaotic investigation of a single continuous fermentor using an experimentally verified model was published earlier by the authors (Chem. Eng. Sci. 58 (2003) 1479); the present paper is an extension of the earlier one. It uses the same biokinetic model to investigate the effects of continuous ethanol removal using permselective membranes, cell recycle with varying cell separation efficiencies and recycle of unused sugars for two configurations of fermentors. The rich static/dynamic bifurcation and chaotic behavior of two different configurations are investigated. The aim is to gain deeper understanding of the complex static/dynamic characteristics of this system as a prelude to a detailed experimental investigation. The emphasis is on achieving higher sugar conversion, ethanol yield and productivity through the exploitation of these characteristics and optimal manipulation of operating and design parameters within the bifurcation/chaotic regions.     

Analysis of acetic acid productivity in a continuous two‐stage bioreactor with cell recycling

The performance of a two‐stage system with cell recycling and fresh feed at each stage is studied numerically for continuous acetic acid production. In this system, both filtrate and bleed broth from the first stage are supplied to the second fermenter. At high substrate conversions, this configuration is found to provide higher acetic acid productivities than either a previous configuration where only the first‐stage bleed broth is fed to the second stage or a single recycle chemostat at the same bleed ratios. Copyright © 2005 Society of Chemical Industry     

膜技术在连续发酵制乙醇中的应用研究

本文对膜技术在连续发酵制乙醇中的应用研究情况作了综述,重点介绍了膜循环发醇器(MRE)。对不同的膜过程、膜组件的形式、微生物种类的影响等作了比较,并简单介绍了循环发酵动力学模型的特征在 MRE 制乙醇中,发酵液中细胞浓度可高达100g(干重)/l,因此在较高稀释率下,基质转化率仍较高,生产率可比间歇发酵提高20倍以上,是非常有开发前途的发酵方法     

Optimization of two-stage continuous culture system for production of poly-β-hydroxybutyrate

The optimization of poly-β-hydroxybutyrate (PHB) fermentation process is essential to obtain a high PHB productivity. An optimization of two-stage continuous culture system by complex method for PHB production is presented. PHB production rate of the system obtained in the present study was chosen as the objective function. The PHB production rate of the system was higher than that of the phasewise optimization method which maximizes the growth rate of residual biomass in the first stage and the PHB production rate in the second stage. When the inlet glucose concentration in the first stage increased, PHB content and yield also increased. When the fermentor volume ratio (V2/V1) was 0.5, maximum PHB productivity in the second stage was 2.86 g/L’ h, which is highest compared with the reported value on PHB.     

Dynamic modelling,simulation and optimization of an extractive continuous alcoholic fermentation process

The conventional alcoholic fermentation is a typical inhibitory process, leading to low productivity and yield. The ethanol produced inhibits yeast cells, causing a reduction in the alcohol production rate and cell growth rate. In this work, modelling and simulation have shown that continuous extractive fermentation, coupling a fermenter with an extractive vacuum flash chamber, is technically possible. In this case, the ethanol is partially removed, increasing drastically the productivity. Additionally, temperature control can be performed without using heat exchangers. The optimization was carried out using the method of factorial design and response surface analysis, leading to the determination of the most relevant variables, which were: 1.2 h residence time, 0.4 flash recycle rate, 180 g dm⁻³ sugar concentration and 0.35 cell recycle rate. The results, using optimized variables, were 98% conversion and 23 g dm⁻³ h⁻¹ productivity, which represent a three times higher productivity than in a conventional continuous process. © 1999 Society of Chemical Industry     

乙醇连续发酵与膜超滤耦合过程研究

采用ＣＡ－Ｔｉ复合管式膜组件与发酵耦合操作，用啤酒酵母从葡萄糖连续发酵乙醇是一个从不稳态到稳态的过程。其稳态的最佳操作参数为：初始葡萄糖浓度１４０ｇ／Ｌ，稀释率０．３ｈ~（－１），轴出比０．６３８，相应的细胞浓度２×１０~９ｃｅｌｌ／ｍＬ，葡萄糖利用率９２％，生产率２２ｇ／（Ｌ·ｈ）。当细胞浓度增加到一定程度时，乙醇生产率和酵母比生长速率的增长减缓。反应器中细胞的浓度由稀释率和轴出比决定。     

Mixed-culture microbial protein from waste sulfite pulping liquor II: Its production on pilot-plant scale and use in animal feed

This paper describes a pilot plant system set up to produce a mixed-culture biomass having a very high content of protein (43%), for use in animal feed. Waste liquor from sulfite pulping was used as substrate. Conversion of carbohydrates in the said liquor to biomass was carried out in a 1200-liter, nonaseptic, aerated, continuous flow tank fermentor. Fermentation conducted at pH = 6.5 gave rise to better settling of microorganisms than at the other pH's studied. The air input was a very important factor affecting fermentor productivity. Under the operating conditions used, the results for carbohydrate conversion, BOD₅ reduction, biomass yield coefficient, and productivity were respectively, 90%, 85%, 0.53 kg/kg, and 3.67 kg/(m³d). With respect to the whole production system, operating and/or control problems were identified and useful technical data were collected in view of an eventual industrial implantation. The final product consisted of about the same varieties of microorganisms (yeasts, bacteria and microfungi) obtained in our previous work, Its nutritive qualities were not affected by the scale-up of fermentor, i.e., from the previous 400 liters to the present 1200 liters. Animal feeding experiments were conducted using 240 chickens fed 4 diets. At least 50% of the soybean protein in commercial diet could be replaced with the biomass protein, without creating a significant effect on growth performance, on the health status of animals examined ante-mortem and post-mortem, and on the organoleptic quality of chicken meat.     

Oxygen and methane enrichment — a comprison of module arrangements in gas permeation

In the separation of gaseous mixtures by gas permeation, it is in some cases impossible to achieve the desired product quality in a single stage and, therefore, several stages may be necessary. Multistage processes can be implemented by membrane modules arranged in the form of a cascade or by a membrane column design. On the basis of an economic analysis, this paper discusses different possible module arrangements for 2 cases, i.e. the enrichment of oxygen from air and the separation of methane from biogas. Present calculations indicate that, in the first case, two-stage cascades with or without recycle and, in the second case, one-stage cascade without recycle constitute the optimum module arrangements. However, depending on the selling price of the methane enriched gas, one- or two-stage cascades with recycle have to be considered. Finally, It was shown that, in the permeation of non-ideal gases, the Joule-Thomson effect has to be taken into account.     

Alcoholic Fermentation with Self‐Flocculating Yeast in a Tower Upflow Reactor

Ethanol production using self‐flocculating yeast in a batch tower upflow reactor system operating with a recirculation loop was examined. Ethanol productivity, yield, and residual sucrose concentration were evaluated experimentally according to a central composite design with initial cell and sucrose concentrations and recirculation flow rate as independent variables. Yeast cell concentration strongly influenced the reactor performance. Alcoholic fermentation was conducted using this strain and reactor configuration which allowed for high productivity and high sucrose conversion. The ethanol yield was comparable with industrial yields. A kinetic study of the fermentation process under optimized conditions was performed using the experimental data and considering inhibition by sucrose and ethanol.     

OPERATION OF A TWO-STAGE MEMBRANE SYSTEM FOR THE TREATMENT OF WASHWATER IN SPACECRAFT

A two-stage membrane-based system was developed and designed to recycle washwaters generated aboard spacrcraft. The first stage is a fouling-resistant tube-side-feed hollow-fiber ultrafiltration module; the second stage is a spiral-wound reverse-osmosis module. Throughout a 10-week test at the National Aeronautics and Space Administration's Johnson Space Center, the system consistently produced high-quality permeate, processing actual washwater to 95% recovery.     

Ethanol production by co-fermentation of hexose and pentose from food wastes using Saccharomyces coreanus and Pichia stipitis

To improve the conversion rate of a saccharification liquid from food wastes containing pentoses and hexoses into bioethanol, after selecting Saccharomyces coreanus and Pichia stipitis, the respective fermentation and co-fermentation properties were investigated. In the fermentation using S. coreanus, the result under anaerobic condition was better than under aerobic conditions. In the anaerobic fermentation, the concentration of the reducing sugar and glucose remaining after 24 hrs was 9.09 and 1.88 g/L, respectively, with 40.59 g/L of ethanol produced; the ethanol productivity was 1.69 g/L-h. Also, even with the fermentation using P. stipitis, the reducing sugars and glucose were rapidly reduced, with a marked production of ethanol, but the ethanol produced was lower than those under anaerobic and aerobic conditions with the use of S. coreanus. Therefore, for the production of a high concentration of bioethanol from food wastes, ethanol fermentation was induced using S. coreanus until the middle of the fermentation, with P. stipitis used during the latter stage of the fermentation, where the circumstance favored its use, and thus, the carbon source not converted by S. coreanus was later converted to ethanol. As a result, both ethanol production of 48.63 g/L and productivity of 2.03 g/L-h increased over those of the anaerobic fermentation using S. coreanus.     

Hydrogen separation from the H2/N2 mixture by using a single and multi-stage inorganic membrane

The separation characteristics of hydrogen from a gas mixture were investigated by using a single and two-stage inorganic membrane. Three palladium impregnated membranes were prepared by using the sol-gel, hydrolysis, and soaking-and-vapor deposition (SVD) techniques. A two-stage gas separation system without a recycling stream was constructed to see how much the hydrogen separation factor would be increased. Numerical simulation for the separation system was conducted to predict the separation behavior for the multi-stage separation system and to determine the optimal operating conditions at which the highest separation factor is obtained. Gas separation through each prepared membrane was achieved mainly by Knudsen diffusion. The real separation factor for the H₂/ N₂ mixture was increased with the pressure difference and temperature for a single stage, respectively. For the twostage separation system, there was a maximum point at which the highest separation factor was obtained and the real hydrogen separation factor for H₂/N₂ mixture was increased about 40 % compared with a single stage separation. The numerical simulation for the single and two-stage separation system was in a good agreement with the experimental results. By numerical simulation for the three-stage separation system, which has a recycle stream and three membranes that have the same permeability and hydrogen selectivity near to the Knudsen value, it is clear that the hydrogen separation factors for H₂/N₂ mixture are increased from 1.8 to 3.65 and hydrogen can be concentrated up to about 80 %. The separation factors increased with increasing recycle ratio. Optimal operating conditions exist at which the maximum real separation factor for the gas mixture can be obtained for three-stage gas separation and they can be predicted successfully by numerical simulation.     

Mathematical modelling and simulation of a recycle dialysis membrane reactor in a reversed micellar system

A mathematical framework was developed for the evaluation of a recycle dialysis membrane reactor (RDMR). The lipase-catalyzed hydrolysis of olive oil in an AOT-iso-octane reversed micellar system was employed as a model. Three specific operational strategies have been considered, namely batch, fed-batch, and fed-batch-bleed. Simulation shows the conversion of substrate to be strongly dependent on efficient use of the substrate, since the permeability coefficients of both substrate and product are quite similar. Sensitivity analyses were performed to assess the influences of various parameters (membrane area, substrate feed rate, solvent bleed rate and permeability) on the performance of the reactor in different modes of operation. The analyses presented are useful to assist the optimization of the operational strategy used for the RDMR system.     

Minimum end time policies for batchwise radical chain polymerization—II A two-stage process for styrene polymerization

For styrene polymerization, a two-stage process is considered. The first stage, initiated by initiator, is operated along the best isothermal policy for a predetermined number average molecular weight and monomer conversion at end of the stage as described in the previous paper. The second stage is operated at higher temperature level at which thermal initiation polymerization is significant. A mathematical model is proposed for describing the changes of conversion and number average molecular weight with time in the second stage based on the experimental data obtained. All parameters involved in the model are calculable using the kinetic constants of the initiator initiation system and the thermal initiation system. Experimental verification on the optimal temperature policies for the second stage shows promising. Further calculations indicate that the optimal two-stage process can be significantly better than the optimal process of initiator initiation or thermal initiation polymerization.     

Continuous ethanol fermentation in a closed‐circulating system using an immobilized cell coupled with PDMS membrane pervaporation

BACKGROUND: A closed‐circulating system for ethanol fermentation was constructed by coupling a cell‐immobilized bed fermentor with pervaporation using a composite PDMS membrane. A continuous fermentation experiment was carried out for about 250 h in the system at 28 °C. RESULTS: The cell density in the immobilized bed was up to 1.76 × 10¹⁰ cells g^?1 gel. The ethanol concentration in the broth was maintained at about 43 g L^?1. The glucose utilization and ethanol productivity were 23.26 g L^?1 h^?1 and 9.6 g L^?1 h^?1, respectively. The total flux and the ethanol flux through the membrane pervaporation unit varied in the range 300–690 g m^?2 h^?1 and 61–190 g m^?2 h^?1, respectively. The average ethanol concentration in the permeate was 23.1% (wt%). The carbon recovery efficiency was 86.8% (wt%), determined by calculating the carbon balance kinetics. The effect of ethanol concentration in the broth on the ethanol productivity was analyzed by modeling product formation kinetics of the system. CONCLUSIONS: Compared with the traditional free cell fermentation system and packed bed fermentation system, the closed‐circulating system has the promising features of higher glucose utilization and ethanol productivity, and cleaner production. Copyright © 2010 Society of Chemical Industry