Continuous ethanol fermentation of concentrated sugar solutions coupled with membrane distillation using a PTFE module

Continuous ethanol fermentation of concentrated glucose and molasses solutions was coupled with membrane distillation using a PTFE ethanol stripping module. Experimental results indicated that the PTFE module can remove a high concentration of ethanol from the fermentation broth and thus maintain a low ethanol concentration in the broth, thereby alleviating the problem of product inhibition. Accordingly, the product yield and the specific ethanol production rate increased. During the continuous fermentation runs, long-time operation using the PTFE module was found to be possible (i.e. 430 h using the glucose medium and 695 h using the molasses medium) and no significant change in the ethanol separation performance of the PTFE module was observed. Although cell flocculation became undetectable when a concentrated molasses medium containing 316 g/l sugar solution was used, the ethanol separation performance of the ethanol stripper was not adversely affected by the presence of the free cells. This suggests that clogging of the membrane pores by cells or other particulates is not a major problem when using the PTFE module in continuous ethanol fermentation.     

Extractive acetonobutylic fermentation by coupling ultrafiltration and distillation

An extractive acetonobutylic fermentation process is developed by integrating bioproduction, Ultrafiltration, and distillation, providing simultaneous retention of biomass, selective removal of inhibitors from the permeate, as well as separation and purification of acetone-butanol-ethanol solvents. Successive batch fermentations were performed with normal pressure distillation (98 degrees C), which permitted prolonging and enhancing (by a factor of 3) solvent production, with very few volume exchanges of medium (average dilution rate ws 0.002 h(-1)), and recovering on-line concentrated solvents. Different operating conditions were also tested in order to study the presence of extracellular autolytic enzymes as inhibition factors: It was shown that, (1) extracellular autolytic activity remains low during the larger part of fermentations, even without enzyme-inactivating thermotreatment in the distillation boiler, and (2) high-temperature distillation causes deleterious effects to the culture medium for long duration treatments. Progressive improvements of the process were achieved, first, by managing continuous runs, providing a minimum renewal of the culture medium and, mainly, by decreasing temperature and pressure of distilation. Solvent productivity then reached 2.6 g/L h for a 0.036 h(-1) average dilution rate, corresponding to a feed concentration of 156 g/L glucose actually consumed.     

Extractive acidogenic fermentation by a supported liquid membrane

An on-line extractive fermentation system using a supported liquid membrane, recently termed pertractive fermentation, was investigated in order to overcome end-product inhibition and to enhance the productivity of microbial acidogenesis. It was observed that the pH of the fermentation broth was the key parameter for the successful operation of this pertractive fermentation system. At pH 4.8, 300 ml of broth and 80 sq·cm of extracting area, microbial activity in the system was prolonged and the productivity was enhanced about 5 fold compared to conventional acidogenic fermentation without extraction.     

Extractive lactic acid fermentation using ion-exchange resin

Lactic acid fermentation is an end-product-inhibited reaction. The restriction imposed by lactic acid on its fermentation can be avoided by extractive fermentation techniques. Studies were performed by attaching an ion-exchange resin packed column with a 2-L fermentor for separation of lactic acid. The fermentation, in a conventional batch mode, resulted in a lactic acid yield of 0.828 g . g(-1) and a lactic acid productivity of 0.313 g . L(-1) . h(-1). However, these could be further enhanced to 0.929 g . g(-1) and 1.665 g . L(-1) . h(-1) by extractive fermentation techniques. The effect of temperature on extractive fermentation was remarkable and has been included in this work.     

Continuous ethanol fermentation using immobilized yeast cells

Growing cells of Saccharomyces cerevisiae immobilized in calcium alginate gel beads were employed in fluidizedbed reactors for continuous ethanol fermentation from cane molasses and other sugar sources. Some improvements were made in order to avoid microbial contamination and keep cell viability for stable long run operations. Notably, entrapment of sterol and unsaturated fatty acid into immobilized gel beads enhanced ethanol productivity more than 50 g ethanol/L gel h and prolonged life stability for more than one-half year. Cell concentration in the carrier was estimated over 250 g dry cell/L gel. A pilot plant with a total column volume of 4 kL was constructed and has been operated since 1982. As a result, it was confirmed that 8-10%(v/v)ethanol-containing broth was continuously produced from nonsterilized diluted cane molasses for over one-half year. The productivity of ethanol was calculated as 0.6 kL ethanol/kL reactor volume day with a 95% conversion yield versus the maximum theoretical yield for the case of 8.5% (v/v) ethanol broth.     

Improved selectivity of microbial biosensor using membrane coating. Application to the analysis of ethanol during fermentation

A ferricyanide mediated microbial biosensor for ethanol detection was prepared by surface modification of a glassy carbon electrode. The selectivity of the whole Gluconobacter oxydans cell biosensor for ethanol determination was greatly enhanced by the size exclusion effect of a cellulose acetate (CA) membrane. The use of a CA membrane increased the ethanol to glucose sensitivity ratio by a factor of 58.2 and even the ethanol to glycerol sensitivity ratio by a factor of 7.5 compared with the use of a dialysis membrane. The biosensor provides rapid and sensitive detection of ethanol with a limit of detection of 0.85 microM (S/N=3). The selectivity of the biosensor toward alcohols was better compared to previously published enzyme biosensors based on alcohol oxidase or alcohol dehydrogenases. The biosensor was successfully used in an off-line monitoring of ethanol during batch fermentation by immobilized Saccharomyces cerevisiae cells with an initial glucose concentration of 200 g l(-1).     

Tower fermentation using Zymomonas mobilis for ethanol production

Summary Flocculation was induced in a pure strain of the bacteria Zymomonas mobilis. When fermenting glucose to ethanol, cell densities of up to 40g/l were achieved and sustained in a 0.92 litre tower fermenter with dilution rates of up to 2.3 hr^-1. A maximum productivity of 100g EtOH/l/hr with 98% conversion of the 105g/l glucose feed was achieved. The limitation to performance with increase in throughput arose from incomplete fermentation of the feed glucose, rather than washout of the flocculated bacteria.     

Extractive fermentation for lactic acid production

Lactic acid extractive fermentation was demonstrated using Alamine 336 in oleyl alcohol at acidic pH. The use of an efficient extraction system was possible through employment of the cell immobilization procedure. Process modeling was performed to relate the various process parameters such as flow rate, concentration, and pH. In experiments with 15% Alamine 336/oleyl alcohol, the bioreactor operation resulted in a higher productivity (12 g/L gel h) compared to that of a control fermentation (7 g/L gel h). Strategies for optimizing the extractive fermentation process were proposed considering both productivity and product recovery.     

Optimization of two-stage continuous ethanol fermentation using flocculating yeast

Summary Two-stage two-stream continuous ethanol fermentation using flocculating yeast was studied to produce high ethanol concentration from blackstrap cane-molasses. Optimizing pH, RQ, cell concentration, and medium molasses concentration of the first stage to give a good cell yield without a significant decrease in ethanol yield, the final ethanol concentration of as high as 92.0–93.5 g/l at an overall dilution rate of 0.10 l/h was obtained. This process could work stably as long as 3 weeks without any decreases in the efficiency.     

Recovery of ethanol from fermentation broths using selective sorption-desorption

Industrialized nations face a critical problem in replacing the sources of liquid fuels that traditionally have been supplied by petroleum. One solution that has gained increasing support in this country is the use of ethanol produced by fermentation of renewable biomass as an extender in, or supplement to, gasoline for transportation fuel. Distillation, the present method of separating ethanol from the fermentation broth, is an energy-intensive one and frequently uses more energy than is available from the ethanol recovered. There are many investigations under way to find alternative, less energy-intensive techniques for the ethanol-water separation. The separations method described in this article involves the use of solid materials to preferentially remove ethanol from fermentation broths. Subsequent stripping of the ethanol from the sorbent with a dry gas reduces dramatically the energy required for the separation. Three solid sorbents have been investigated experimentally. Their sorption/desorption characteristics are described, and their incorporation in an ethanol recovery process is evaluated. Three sorbents were investigated: two commercially available divinylbenzene crosslinked polystyrene resins in bead form (one with a nominal surface area of 300 m(2)/g, the other with 750 m(2)/g) and an experimental proprietary molecular sieve with hydrophobic properties. Equilibrium adsorption isotherms for two of the sorbents were obtained at ambient temperature (21 degrees C) for ethanol-water solutions containing up to 12 wt. % ethanol. In addition, 40 degrees C isotherms were obtained for the polystyrene sorbents. Although different, the equilibrium isotherms for the sorbents indicated that ethanol could be preferentially sorbed from a dilute solution. Column breakthrough curves indicated very favorable kinetics. Desorption of the ethanol was readily effected with warm (60-80 degrees C), dry nitrogen.     

Extractive fermentation of clavulanic acid by Streptomyces DAUFPE 3060 using aqueous two-phase system

The influence of four variables, specifically PEG molar mass (400, 1,000, and 8,000 g/mol), concentrations of PEG and phosphate salts (15, 20, and 25% for both), and agitation intensity (110, 150, and 200 rpm), on clavulanic acid (CA) extraction by extractive fermentation with PEG/phosphate salts aqueous two-phase system was investigated in shaken flasks using a 2(4-1) -fractional factorial design. After selection of the two most significant variables (agitation intensity and PEG molar mass), an optimization study conducted according to a 2(2) -central composite design revealed that 25% PEG 8,000 g/mol and phosphate salts at 240 rpm (run 6) were the best conditions for the extractive fermentation, leading to the best results in terms of partition coefficient (k = 8.2), yield of CA in the PEG-rich phase (η(T) = 93%) and productivity (P = 5.3 mg/Lh). As a first attempt to make a scale-up of these results, the effectiveness of the extractive fermentation was then checked in a bench-scale bioreactor under conditions as close as possible to the optimum ones determined in flasks. The highest CA concentration obtained in the PEG-rich phase (691 mg/L) was 30% higher than in flasks, thus demonstrating the potential of such a new process, integrating the production and extraction steps, as a promising, low-cost tool to obtain high yields of this and similar products.     

Extractive recovery of products from fermentation broths

Considerations of partition coefficients, selectivity, biocompatibility, and waste generation are important in selection of appropriate solvents to be used for extractive recovery of products from fermentation broths. Several selection criteria can be used based upon the nature of different species present in the broth. These criteria, along with examples of specific case studies, were presented. These serve not only in screening of useful solvents, but also in pointing to the specific modes of operation of recovery-coupled bioprocesses.     

纤维素乙醇发酵液中复杂组分对乙醇渗透汽化传质过程的影响

考察了木质纤维素乙醇发酵液中各组分对乙醇透过聚二甲基硅氧烷(PDMS)-silicalite-1渗透汽化膜传质性能的影响。结果表明:酵母细胞、玉米秸秆残渣和发酵用无机盐可增加乙醇通过膜的通量和选择性;而葡萄糖和甘油的存在会对乙醇的透膜传质产生负面影响;木质纤维素水解后的产物如糠醛和羟基丙酮,表现出对膜分离乙醇轻微的抑制作用。本文建立了渗透汽化优先透醇与纤维素乙醇发酵集成过程,批次发酵20 h后乙醇产率从最初的12.95下降到10.22 g/(L·h),60 h后乙醇产率下降为0,葡萄糖消耗速率与乙醇消耗产率呈同样趋势;连续发酵过程中,乙醇产率较稳定地维持在13.30 g/(L·h)。实验证明,集成过程可及时地将产物乙醇分离出去,能够有效地消除产物抑制,提高乙醇生产速率和葡萄糖转化率。     

Vacuum fermentation for ethanol production using strains of Zymomonas mobilis

Summary Using strains of Z.mobilis, a vacuum fermentation system has been evaluated. The system was designed with the fermentor at atmospheric pressure and an external vacuum vessel (50 mm Hg). Sequential operation of the vacuum vessel was under microprocessor control. The use of Z.mobilis together with the two-stage design of the vacuum system has been found to overcome the problems of oxygen addition and the possibility of contamination reported previously for vacuum fermentations with yeasts. The productivity of 85 g/1/h found in the continuous cell recycle experiments was similar to that reported previously for a strain of S.cerevisiae.     

亚硫酸盐甘蔗渣浆酶解液发酵制备乙醇

以亚硫酸盐甘蔗渣浆酶解液作为原料,利用C. shehatae发酵制取燃料乙醇。结果表明：还原糖最适初始质量浓度为葡萄糖140 g/L、木糖60 g/L、酶解液总糖80 g/L。利用初始葡萄糖55.06 g/L、木糖11.18 g/L、纤维二糖4.51 g/L的亚硫酸盐甘蔗渣浆酶解液发酵,经18 h获得乙醇22.98 g/L。乙醇得率为67.23%,葡萄糖利用率为99.27%,木糖利用率为32.96%,C. shehatae适合作为蔗渣为原料的乙醇发酵菌株。     

Pilot-scale multi-stage multi-feeding continuous ethanol fermentation using non-sterile cane molasses

Summary Non-aseptic fermentation of a 28 brix cane molasses solution was successfully carried out in a pilot-scale 5-stage multi-feeding continuous system for 30 days. The effluent ethanol concentration, overall volumetric productivity and sugar conversion yield averaged 8.54 % (v/v), 5.35 g/L-hr and 92.4 % of theoretical, respectively.     

酿酒酵母 L-阿拉伯糖转化乙醇代谢工程的研究进展简

L-阿拉伯糖是木质纤维素原料中一种重要的五碳糖组分,但传统的乙醇生产菌株酿酒酵母（ Saccharomyces cerevisiae）不能利用L 阿拉伯糖。通过代谢途径工程手段,在酿酒酵母中引入L 阿拉伯糖初始代谢途径可以获得能利用L 阿拉伯糖乙醇发酵的重组菌株。并且,通过代谢途径的疏通以及吸收系统的优化可以强化重组菌株代谢L 阿拉伯糖的能力。笔者从以上角度综述了近年来酿酒酵母转化L 阿拉伯糖生产乙醇的研究进展。     

An on-line approach to monitor ethanol fermentation using FTIR spectroscopy

Fermentation process control is currently limited by its inability to measure parameters such as substrate, product, and biomass concentrations rapidly for consistent on-line feedback. Physical and chemical parameters, such as temperature and pH, currently can be obtained on-line using appropriate sensors. However, to obtain information on the concentration of the substrate, product, and biomass, samples must be taken off-line for measurement. With the use of spectroscopic techniques, real-time monitoring of process constituents such as product and substrate is possible. Spectroscopic techniques are rapid and nondestructive, require minimal or no sample preparation, and can be used to simultaneously assess several constituents in complex matrices. The production of ethanol is the largest fermentation process in terms of production volume and economic value as a result of its prominence in the food, agricultural, and fuel industries. This study attempts to develop an on-line ethanol fermentation monitoring technique using Fourier transform infrared (FTIR) spectroscopy with a flow-through ATR capability. Models developed using multivariate statistics, employed to obtain on-line FTIR measurements, were successfully validated by off-line HPLC analysis and spectrophotometry data. Standard errors of prediction (SEP) values of 0.985 g/L (R2 = 0.996), 1.386 g/L (R2 = 0.998), and 0.546 (R2 = 0.972) were obtained for ethanol, glucose, and OD, respectively. This work demonstrates that FTIR spectroscopy could be used for rapid on-line monitoring of fermentation.