Novel repeated batch operation for flash fermentation system: Experimental data and mathematical modelling

A novel repeated batch operation mode was proposed for ethanol fermentation, where the fermenter beer was periodically exchanged between the fermenter with biomass recycle and the distillation unit, to promote the selective removal of ethanol. Using the mathematical model developed, as based on the experimental results, the optimal operation of the proposed method was shown to attain high performance, with a productivity of about 12 g dm⁻³ h⁻¹ and a product concentration of 400 g dm⁻³.     

Batch and Continuous Production of Lactic Acid from Beet Molasses by Lactobacillus delbrueckii IFO 3202

Process variables were optimized for the production of lactic acid from pretreated beet molasses by Lactobacillus delbrueckii IFO 3202 for batch and continuous fermentations. In the batch fermentation, maximum yields (95·4% conversion, 77·1% effective) and maximum lactic acid volumetric productivity (4·83 g dm⁻³ h⁻¹) was achieved at 45°C, pH 6·0, 78·2 g dm⁻³ sugar concentration with 10 g dm⁻³ yeast extract. Various cheaper nitrogen sources were replaced with yeast extract on equal nitrogen bases in batch fermentation. Of all the nitrogen sources tested, yeast extract yielded the highest and malt sprouts yielded the second highest level of lactic acid. In the continuous fermentation, maximum lactic acid (4·15%) was obtained at a dilution rate of 0·1 h⁻¹. Maximum volumetric lactic acid productivity (11·20 g dm⁻³ h⁻¹) occurred at D = 0·5 h⁻¹ dilution rate. © 1997 SCI.     

Cell recycle and broth reuse fermentation with cross-flow filtration and ion-exchange resin

A novel integrated fermentation system in which cross-flow filtration was coupled to an anion-exchange resin column was developed to achieve biomass recycle and broth reuse for lactic acid fermentation. An anion-exchange resin column was employed to recover lactic acid from the spent broth. The effluent was diluted with fresh medium, supplemented with glucose and nutrients. Spent broth was reused for three consecutive biomass recycle fermentations with no significant decrease in fermentation performance. The fermentation system enabled simultaneously high productivity of lactic acid (average value 7·75 g dm⁻³ h⁻¹ and total amount of lactic acid produced 85·21 g dm⁻³ after 11 h fermentation), high productivity of cells (average value 2·00 g dm⁻³ h⁻¹) and efficient utilization of medium (about 75% of the spent broth was reutilized). The system described may be applied to other organic fermentations subject to end-product inhibition.     

Effect of zeolite addition on ethanol production from glucose by Saccharomyces bayanus

Zeolite NaY at 5 g dm⁻³ concentration, was selected to improve the production of ethanol fermentation by Saccharomyces bayanus from high glucose concentration media. The highest ethanol productivity (3·07 g dm⁻³ h⁻¹) was obtained from a 220 g dm⁻³ initial glucose concentration, while the highest ethanol concentration (130 g dm⁻³) was obtained from a 350 g dm⁻³ glucose medium. The zeolite is believed to have acted as a pH regulator, maintaining the pH value around 3·7–3·8. Under these conditions cellular viability was preserved and metabolic activity was maintained. Thus all the glucose was consumed, and high ethanol productivity and concentration were obtained. Therefore, the addition of zeolite improved ethanol production from high concentrations of glucose by Saccharomyces bayanus. © 1998 Society of Chemical Industry     

Production of lactic acid from beet molasses by calcium alginate immobilized Lactobacillus delbrueckii IFO 3202

Lactic acid was produced from pretreated beet molasses by the homofermentative organism Lactobacillus delbrueckii subsp delbrueckii IFO 3202 entrapped in calcium alginate gel using batch, repeated batch and continuous fermentation systems. In batch fermentation studies successful results were obtained with 2.0–2.4 mm diameter beads prepared from 2% sodium alginate solution. The highest effective yield (82.0%) and conversion yield (90.0%) were obtained from substrate concentrations of 52.1 and 78.2 g dm⁻³ respectively. The gel beads produced lactic acid for 14 consecutive batch fermentations without marked activity loss and deformation. In the continuous fermentation, the highest lactic acid (4.22%) was obtained at a dilution rate of 0.1 h⁻¹ while the highest productivity (13.92 g dm⁻³ h⁻¹) was obtained at a dilution rate of 0.4 h⁻¹. © 1999 Society of Chemical Industry     

Effect of extraction and enzymatic esterification of ethanol on glucose consumption by two Saccharomyces cerevisiae strains: a comparative study

Extractive alcoholic fermentations of high glucose concentrations (300 and 400 g dm^?3) using a flocculent (saké) and a non‐flocculent (DER24) Saccharomyces cerevisiae strain were compared. The introduction of a Rhizomucor miehei lipase, in the extractive fermentations of 300 g dm^?3 of glucose, increased the ethanol extraction due to its esterification with oleic acid, allowing complete glucose consumption at an organic solvent/fermentation medium phase ratio of 1. In these conditions, an increase of ethanol yield was observed. Total glucose consumption was also obtained in enzymatic extractive fermentations of 400 g dm^?3 of glucose, but only when oleic acid was added at the exponential growth phase. From the comparison of the extractive fermentation performances obtained using the two yeast strains it was observed that the flocculent strain led to a lower glucose metabolisation rate. This behaviour was related to the highest diffusional limitations that occur in the presence of flocs. The developed processes showed that the association of alcoholic fermentation with enzymatic extraction led to the reduction of inhibitory effects as well as to the simultaneous production of fatty esters which are compounds with several commercial applications. © 2001 Society of Chemical Industry     

Wood blocks as a carrier for Saccharomyces Cerevisiae used in the production of ethanol and fructose

Saccharomyces cerevisiae ATCC 39859 was immobilized onto small cubes of wood in order to produce very enriched fructose syrup from synthetic glucose-fructose mixtures, through the selective fermentation of glucose. The kinetics of growth and ethanol production rates were studied. Several tests to assess the influence of substrate and product concentration on the production rates were carried out and appropriate rate equations were proposed as a design basis for continuous immobilized reactors. The ethanol production rate and cell growth rate were found to be inhibited linearly by both substrate and product concentrations. A maximum ethanol productivity of 21.9 g 1⁻¹ h⁻¹ was attained from a feed containing 10% (by weight) glucose and 10% (by weight) fructose. The ethanol concentration was 29.6 g 1⁻¹, the glucose conversion was 78% and a fructose yield of 99% was obtained. This resulted in a final fructose:glucose ratio of 2.7. At lower ethanol productivity levels the fructose:glucose ratio increased, as did the ethanol concentration in the effluent. The ethanol productivities obtained in this study were 33%–132% higher than those obtained in a previous study using the same system, under similar conditions, with the cells immobilized in alginate beads.     

Continuous ethanol production from carob pod extract by immobilized Saccharomyces cerevisiae in a packed-bed reactor

The continuous production of ethanol from carob pod extract by immobilized Saccharomyces cerevisiae in a packed-bed reactor has been investigated. At a substrate concentration of 150 g dm^?3, maximum ethanol productivity of 16 g dm^?3 h^?1 was obtained at D = 0·4 h^?1 with 62·3% of theoretical yield and 83·6% sugars′ utilization. At a dilution rate of 0·1 h^?1, optimal ethanol productivity was achieved in the pH range 3·5–5·5, temperature range 30–35·C and initial sugar concentration of 200 g dm^?3. Maximum ethanol productivity of 24·5 g dm^?3 h^?1 was obtained at D = 0·5 h^?1 with 58·8% of theoretical yield and 85% sugars′ utilization when non-sterilized carob pod extract containing 200 g dm^?3 total sugars was used as feed material. The bioreactor system was operated at a constant dilution rate of 0·5 h^?1 for 30 days without loss of the original immobilized yeast activity. In this case, the average ethanol productivity, ethanol yield (% of theoretical) and sugars′ utilization were 25 g dm^?3 h^?1, 58·8% and 85·5%, respectively.     

Improved Ethanol Production by Saccharomyces cerevisiae with EDTA,Ferrocyanide and Zeolite X Addition to Sugar Beet Molasses

The influence of ethylenediaminetetra acetic acid (EDTA), potassium ferrocyanide and zeolite X on ethanol production from sugar beet molasses by Saccharomyces cerevisiae was studied. For all of the three substances used, the effect was more pronounced when added to the fermentation medium rather than to the growth medium; 1·9 mmol dm⁻³ potassium ferrocyanide caused an increase in the final ethanol concentration of about 16·4% and 47·5% with respect to control culture on addition to growth and fermentation media respectively. The greatest stimulation in product yield was obtained with zeolite X introduced during the fermentation stage; 8·0 g dm⁻³ zeolite X increased ethanol concentration by 53·3%. © 1997 SCI.     

Continuous production of thrombomodulin from a Pichia pastoris fermentation

A rotary membrane separation system was used in a continuous fermentation of Pichia pastoris with cell recycling to obtain high cell concentration and high thrombomodulin production. The dilution rates of this continuous fermentation were between 0·25 and 0·35 dm³ day⁻¹, and the production process was maintained for 10 days. Since cells were recycled and only part of liquid broth was taken from the system, a very high cell concentration level (248 g dm⁻³) was obtained. The peak protein expression level was at 72 h after methanol induction, was 300 mg dm⁻³ (3·6 × 10⁵ activity unit cm⁻³) and the total harvested supernatant was three times the working volume.     

Production and extractive biocatalysis of ethanol using microencapsulated yeast cells and lipase system

An extractive biocatalytic process for in situ ethanol recovery from fermentation broths of high glucose concentration (200 and 400 g dm^?3) was developed. In this system, ethanol was recovered by liquid-liquid extraction and enzymatic reaction. Oleic acid was used as extractant, allowing the esterification of ethanol catalysed by a lipase from Mucor miehei. The distribution coefficient of ethanol between the aqueous and the organic phases was improved tenfold by esterification. The better performance of the extractive fermentations of ethanol was obtained when co-immobilized Saccharomyces bayanus cells and a lipase from Mucor miehei in microemulsions of phosphatidylcholine were used. These results emphasize the important role of the surfactant in the protection of biocatalysts against organic phase toxicity.     

Maximizing the production of acetone—butanol in an alginate bead fluidized bed reactor using clostridium acetobutylicum

Low volumetric solvent productivities are one of the characteristics of an acetone-butanol fermentation by C. acetobutylicum. A calcium alginate immobilized continuous culture was used in a novel gas-sparged reactor to strip the solvents from the aqueous phase and reduce their toxicity. A dilution rate of 0.07 h^?1 was found to give maximum solvent productivity at 0.58 g dm^?3 h^?1, although at 0.12 h^?1 the productivity was slightly lower. In order to increase glucose uptake by the culture, feed glucose concentrations were increased over time to attempt to acclimatize the culture. This resulted in a productivity as high as 0.72 g dm^?3 h^?1 although this production rate was found to be unstable.     

Technological and kinetic aspects of sublethal acid toxicity in microbial gum production

Chemostat culture of Xanthomonas campestris were obtained at a dilution rate of 0·05 h⁻¹ and the normal feed then supplemented with 0·58 and 1·74 mmol dm⁻³ isobutyric acid (IBA). Data revealed that the organism responded to sublethal acid stress by overproducing xanthan. The acid additions led to transient zones in the continuous cultivation profiles. By adding feed containing 1·74 mmol dm⁻³ IBA, volumetric growth rate immediately decreased from 0·059 to 0·026 g dm⁻³ h⁻¹ whereas the specific xanthan formation rate increased from 0·23 g g⁻¹ biomass h⁻¹ to a maximum 0·65 g g⁻¹ biomass h⁻¹ (with 1·0 mmol dm⁻³ IBA addition), before decreasing as the concentration of acid attained that of the feed. By monitoring the outlet CO₂ in parallel with biomass and polysaccharide levels in the IBA fermentation a 10% diversion of the total carbon flux from biomass synthesis to xanthan biosynthesis was detected. A consistent pattern of variation in activity was detected in enzymes of intermediary metabolism, suggesting an action at the regulatory level. Enhanced activities of carbon catabolism and xanthan anabolic reactions (phosphomannose isomerase) were observed in the presence of the acid. Batch experiments carried out in the pres-ence of IBA gave results which correlated with the undissociated acid form con-centration. An undissociated acid fraction of 6·5×10⁻³ mmol dm⁻³ was calculated in a set of flasks under the same conditions and a statistically vali-dated 12% increase in xanthan production was found. The maximum activation was determined to be below 1·1×10⁻² mmol dm⁻³ when a 58% specific xanthan production rate increase occurred in parallel with a 35% decrease in biomass concentration.     

Continuous ethanol fermentation using immobilized yeast in a fluidized bed reactor

Continuous ethanol fermentation of glucose using fluidized bed technology was studied. Saccharomyces cerevisiae were immobilized and retained on porous microcarriers. Over two-thirds of the total reactor yeast cell mass was immobilized. Ethanol productivity was examined as dilution rate was varied, keeping all other experimental parameters constant. Ethanol yield remained high at an average of 0.36 g ethanol g^?1 glucose (71% of theoretical yield) as the dilution rate was increased stepwise from 0.04 h^?1 to 0.14 h^?1. At a dilution rate of 0.15 h^?1, the ethanol yield steeply declined to 0.22 g ethanol g^?1 glucose (44% of theoretical yield). The low maximum percentage of theoretical yield is primarily due to an extended mean cell residence time, and possibly due to the inhibitory effect of a high dissolved carbon dioxide concentration, enhanced by the probable intermittent levels of low pH in the reactor. Constant ethanol production was possible at a high glucose loading rate of 840 g dm^?3 day^?1 (attained at a dilution rate of 0.14 h^?1). Although the highest average ethanol concentration (97.14 g dm^?3) occurred at the initial dilution rate of 0.04 h^?1, the peak average ethanol production rate (2.87 g (g yeast)^?1 day^?1) was reached at a greater dilution rate of 0.11 ^h-1. Thus, the optimal dilution rate was determined to be between 0.11 h^?1 and 0.14 h^?1. Ethanol inhibition on yeast cells was absent in the reactor at average bulk-liquid ethanol concentrations as high as 97.14 g dm^?3. In addition, zero-order kinetics on ethanol production and glucose utilization was evident.     

Sago starch saccharification and simultaneous ethanol fermentation by amyloglucosidase and Zymomonas mobilis

Simultaneous saccharification and ethanol fermentation (SSF) of sago starch was studied using amyloglucosidase (AMG) and Zymomonas mobilis. The optimal concentration of AMG and operating temperature for the SSF process were found to be 0.5% (v/w) and 35°C, respectively. Under these conditions with 150 g dm^?3 sago starch as a substrate, the final ethanol concentration obtained was 69.2 g dm^?3 and ethanol yield, Y_P/S, 0.50 g g^?1 (97% of theoretical yield). Sago starch in the concentration range of 100–200 g dm^?3 was efficiently converted into ethanol. When compared to a two-step process involving separate saccharification and fermentation stages, the SSF reduced the total process time by half.     

Microbial oxidation of naphthalene to cis-1,2-dihydroxy-1,2-dihydronaphthalene in a membrane bioreactor

A microbial dihydroxylation process for the production of cis-1,2-dihydroxy-1,2-dihydronaphthalene from naphthalene is reported. The oxidation reaction was initially studied in a stirred tank reactor using resting cells of a Pseudomonas fluorescens mutant, grown on glucose as carbon source and acetyl salicylate as inducer of the naphthalene dioxygenase enzymatic system. In these conditions the productivity of the system was limited by the efficiency of the oxygenation and by a reversible product inhibition phenomenon. In order to overcome the inhibitory effect of the 1,2-dihydrodiol accumulation, the biotransformations were carried out in a stirred reactor equipped with a membrane ultrafiltration device. In this way, the cells and the insoluble naphthalene were retained and recycled into the vessel, while the soluble diol was continuously removed through the membrane permeate. The diol was recovered by selective adsorption on a column packed with an adsorbent resin, allowing the rapid and direct recycle of the reaction medium back to the enzymatic reactor. This system afforded a final yield three-fold higher than that of the batch process, exhibiting a bioconversion rate of 1·3 g h⁻¹ dm⁻³ for more than 16 h of continuous working.     

同步闪蒸汽提发酵制乙醇

为提高乙醇生产发酵强度,提出了同步汽提闪蒸乙醇发酵新过程。该过程集合了闪蒸发酵和汽提发酵的优点,在发酵的同时能更有效地在位分离乙醇,从而提高发酵强度。通过与普通发酵、闪蒸发酵、汽提发酵等过程进行间歇实验比较,同步闪蒸汽提发酵过程具有发酵强度高的优势;而且,采用耐高温酵母高温发酵、提高通气量、闪蒸罐的进料流速可进一步提高其发酵强度。该过程简单、高效,具有工业应用的潜力。     

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     

Effect of Carrier Matrix on Fermentative Production of Ethanol by Surface Immobilised Yeast Cells

The production of ethanol for potable preparations is well established and the traditional methods used therein are changing. More important, however, has been the advent of fuel alcohol, first in Brazil, but now with ever-increasing possibilities of being adopted in North America and Europe. Production of alcohol by fermentation has therefore come to stay, and it is essential to discover ways of improving the productivities of such fermentations. The effect of organic (cellulose and corn stover) and inorganic matrices (silica gel, porous silica, Celite and derivatised Celite) on the performance of ethanol fermentation by Saccharomyces bayanus was tested. The hydrophilicity degree of the support seems to play an important role in the ability of reaching high ethanol concentrations in the fermentation of 300 g dm^?3 of glucose. Cells immobilised on carriers with low hydrophilicity degree, namely Celite, lead to better results (residual glucose: 56 g dm^?3; ethanol: 111 g dm^?3) than their free counterparts (residual glucose: 136 g dm^?3; ethanol: 71 g dm^?3). Celite was selected for further cell immobilisation studies, including time of adsorption, whole cell concentration, initial glucose concentration and time of addition of the support to the fermentation medium. The latter has revealed to be a very important factor, improving the performance of ethanol fermentation by reducing the fermentation time. Previous immobilisation seems to have no effect when compared with the simple addition of Celite to the inoculated medium and the eficiency of Celite did not increase when the concentration of glucose was enhanced.     

Effect of temperature on fermentation kinetics of waste sulphite liquor by Saccharomyces cerevisiae

The optimum operating temperatures for the maximum production of ethanol and the maximum utilization of substrate in batch fermentations of a waste sulphite liquor (WSL) as well as a synthetic medium using Saccharomyces cerevisiae were determined. The fastest consumption of substrate resulting in the shortest fermentation times of 13 h and 45 h was achieved at 35°C and 30°C for the synthetic medium and the WSL, respectively. The concentrations of ethanol in the two media were also maximum under these conditions: 11.6g dm^?3 and 9.4 g dm^?3 for the synthetic medium and the WSL, respectively. The productivities of biomass and ethanol increased with the increase of temperature and reached maximum values of 0.89 g dm^?3 h^?1 and 0.21 g dm^?3 h^?1 in the synthetic medium and the WSL, respectively. The inhibiting agents in the waste sulphite liquor affected the metabolic rates of microbial activities and prolonged the overall fermentation time while decreasing the productivities of biomass and ethanol. From analysis of the fermentation kinetics a mathematical model based on the Monod model was developed to describe the cellular growth and ethanol production. The model included inhibition terms for ethanol and the inhibiting agents in the waste liquor. The temperature dependence of the model parameters followed the Arrhenius law for temperatures between 15°C and 35°C. The activation energies (E) and the frequency constants (A) of these parameters were also determined.