Performance comparison of ethanol and butanol production in a continuous and closed-circulating fermentation system with membrane bioreactor

Since both ethanol and butanol fermentations are urgently developed processes with the biofuel-demand increasing, performance comparison of aerobic ethanol fermentation and anerobic butanol fermentation in a continuous and closed-circulating fermentation (CCCF) system was necessary to achieve their fermentation characteristics and further optimize the fermentation process. Fermentation and pervaporation parameters including the average cell concentration, glucose consumption rate, cumulated production concentration, product flux, and separation factor of ethanol fermentation were 11.45?g/L, 3.70?g/L/h, 655.83?g/L, 378.5?g/m²/h, and 4.83, respectively, the corresponding parameters of butanol fermentation were 2.19?g/L, 0.61?g/L/h, 28.03?g/L, 58.56?g/m²/h, and 10.62, respectively. Profiles of fermentation and pervaporation parameters indicated that the intensity and efficiency of ethanol fermentation was higher than butanol fermentation, but the stability of butanol fermentation was superior to ethanol fermentation. Although the two fermentation processes had different features, the performance indicated the application prospect of both ethanol and butanol production by the CCCF system.     

Ethanol production in a continuous fermentation/membrane pervaporation system

The productivity of ethanol fermentation processes, predominantly based on batch operation in the U.S. fuel ethanol industry, could be improved by adoption of continuous processing technology. In this study, a conventional yeast fermentation was coupled to a flat-plate membrane pervaporation unit to recover continuously an enriched ethanol stream from the fermentation broth. The process employed a concentrated dextrose feed stream controlled by the flow rate of permeate from the pervaporation unit via liquid-level control in the fermentor. The pervaporation module contained 0.1 m² commercially available polydimethylsiloxane membrane and consistently produced a permeate of 20%–23% (w/w) ethanol while maintaining a level of 4%–6% ethanol in a stirred-tank fermentor. The system exhibited excellent operational stability. During continuous operation with cell densities of 15–23 g/l, ethanol productivities of 4.9–7.8 gl^–1 h^–1 were achieved utilizing feed streams of 269–619 g/l glucose. Pervaporation flux and ethanol selectivities were 0.31–0.79 lm^–2 h^–1 and 1.8–6.5 respectively.     

Effective ethanol production by reutilizing waste distillage anaerobic digestion effluent in an integrated fermentation process coupled with both ethanol and methane fermentations

An integrated ethanol–methane fermentation coupled system characterized with full wastewater reutilization was proposed. The waste distillage originated from ethanol distillation was treated with anaerobic digestion and then recycled for medium preparation in the next ethanol fermentation run. This process could enhance wastewater reutilization, save fresh water and reduce energy consumption in the cassava-based ethanol production. The results indicated that, when using anaerobic effluents from the digestion process with only one tank, an ethanol concentration of 10.5% (v/v) compatible with that of conventional one could be achieved, but ethanol fermentation was partially inhibited and operation time gradually prolonged from 48 to 105 h. Using anaerobic effluents from the digestion process with two subsequently connected tanks, ethanol fermentation performance could be largely improved, and the fermentation lag could be completely eliminated. The performance enhancement was due to the concentrations reduction in organic acids, such as acetic and propionic acids in the digestion effluents using two digestion tanks in-series.     

Ethanol fermentation in an immobilized cell reactor using Saccharomyces cerevisiae

Fermentation of sugar by Saccharomyces cerevisiae, for production of ethanol in an immobilized cell reactor (ICR) was successfully carried out to improve the performance of the fermentation process. The fermentation set-up was comprised of a column packed with beads of immobilized cells. The immobilization of S. cerevisiae was simply performed by the enriched cells cultured media harvested at exponential growth phase. The fixed cell loaded ICR was carried out at initial stage of operation and the cell was entrapped by calcium alginate. The production of ethanol was steady after 24 h of operation. The concentration of ethanol was affected by the media flow rates and residence time distribution from 2 to 7 h. In addition, batch fermentation was carried out with 50 g/l glucose concentration. Subsequently, the ethanol productions and the reactor productivities of batch fermentation and immobilized cells were compared. In batch fermentation, sugar consumption and ethanol production obtained were 99.6% and 12.5% v/v after 27 h while in the ICR, 88.2% and 16.7% v/v were obtained with 6 h retention time. Nearly 5% ethanol production was achieved with high glucose concentration (150 g/l) at 6 h retention time. A yield of 38% was obtained with 150 g/l glucose. The yield was improved approximately 27% on ICR and a 24 h fermentation time was reduced to 7 h. The cell growth rate was based on the Monod rate equation. The kinetic constants (K(s) and mu(m)) of batch fermentation were 2.3 g/l and 0.35 g/lh, respectively. The maximum yield of biomass on substrate (Y(X-S)) and the maximum yield of product on substrate (Y(P-S)) in batch fermentations were 50.8% and 31.2% respectively. Productivity of the ICR were 1.3, 2.3, and 2.8 g/lh for 25, 35, 50 g/l of glucose concentration, respectively. The productivity of ethanol in batch fermentation with 50 g/l glucose was calculated as 0.29 g/lh. Maximum production of ethanol in ICR when compared to batch reactor has shown to increase approximately 10-fold. The performance of the two reactors was compared and a respective rate model was proposed. The present research has shown that high sugar concentration (150 g/l) in the ICR column was successfully converted to ethanol. The achieved results in ICR with high substrate concentration are promising for scale up operation. The proposed model can be used to design a lager scale ICR column for production of high ethanol concentration.     

Ethanol recovery from corn fiber hydrolysate fermentations by pervaporation

Corn fiber, a byproduct of corn wet milling, is an attractive feedstock for biomass ethanol production. Corn fiber was hydrolyzed by dilute sulfuric acid and neutralized by one of two methods: conventional lime treatment or neutralization by strongly basic anion exchange. The anion exchange neutralized (AEN) hydrolysate contained substantially lower levels of the inhibiting compounds furfural, 5-hydroxymethylfurfural, and acetic acid compared to the lime neutralized hydrolysate. In batch fermentations the ethanol yields and final ethanol concentration of the two hydrolysates were similar at 0.32-0.43 g/g and 29-44 g/l, respectively. Sugar consumption in the AEN fermentations was superior. Coupling of a membrane pervaporation unit to a fed-batch fermentation of AEN hydrolysate maintained the ethanol concentration below 25 g/l with complete sugar utilization for approximately 5 days. A concentrated ethanol stream of 17 wt.% ethanol was produced by the pervaporation unit.     

Continuous ethanol production by immobilized yeast reactor coupled with membrane pervaporation unit

A system comprised of an immobilized yeast reactor producing ethanol, with a membrane pervaporation module for continuously removing and concentrating the produced ethanol, was developed. The combined system consisted of two integrated circulation loops: In one the sugar-containing medium is circulated through the membrane pervaporation module. The two loops were interconnected in a way allowing for separate parameter optimization (e.g., flow rate, temperature, pH) for each loop.The fermentation unit was 2.0 L bioreactor with five equal segments, packed with 5-mm beads of immobilized yeasts. The bead matrix was a crosslinked polyacrylamide hydrazide gel coated with calcium alginate. The fast circulation loop of the bioreactor allowed for efficient liberation of CO(2) at the top of the immobilized yeast reactor. Continuous operation of the uncoupled reactor for over 50 days with inflowing defined medium or dilute molasses at a residence time of 1.25 h yielded ethanol at a rate of about 10 g/L h.The pervaporation unit was constructed from four 60-cm-long tubular membranes of silicone composite on a polysulfone support. The output from the fermentor was circulated through the inside of the tubes of a unit with a total surface area of 800 cm(2), having an average flux of 150 mL/h, and selectivities to ethanol vs. water up to 7. A vacuum of 30 mb was applied to the outside of the tubes, removing 20-30 g of ethanol per hour, which was collected in condensors. The continuous removal of ethanol, avoiding inhibition of the fermentation process, resulted in an improved productivity and allowed the use of high sugar concentrations (40% wt/vol) offering the potential of a compact system with reduced stillage.The combined system of ethanol production and removal enabled an operative steady state at which the liquid volume of the system, and the concentrations of ethanol within the reactor ( 4% wt/vol), as well as within the flux crossing the pervaporation membrane (17%-20% wt/vol) were kept constant. At the steady state, a 40% wt/vol sugar solution could be continuously added to the fermentor when 12%-20% wt/vol clear ethanol solution was continuously removed by the pervaporation unit. Membrane fouling was reversed by short washing steps, and continuous step operation was maintained by working with two different modules that were interchanged. In this manner, long term continuous operation (over 40 days) was achieved with a productivity of 20-30 g/L h, representing over a twofold increase relative to the continuously operated reactor uncoupled from the membrane and a fivefold increase in comparison with the value obtained fro a corresponding batch fermentation.     

Repeated use of yeast biomass in ethanol fermentation of juniper berry sugars

Summary The object of this study was to establish the possibility of using the yeast biomass separated from the fermentation broth at the end of ethanol fermentation of juniper berry sugars as an inoculum in successive batch fermentation processes. A part of the fermentation broth (10% v/v) and a suspension of yeast biomass (separated from the same broth) into the water extract of juniper berries (2 g of wet yeast biomass per liter of water extract) were used as inocula. It was shown that the suspension of yeast biomass could be used as inoculum in successive batch processes without negative effects on the kinetics and ethanol yield, but with positive effects on the capacity and economy of the bioprocess. The addition of ammonium salts at optimum levels did not affect the final ethanol concentrations (4.3–4.4% v/v), but enhanced the specific rate of ethanol production, thus reducing the process duration by about five times.     

Ethanol extraction by supported liquid membrane during fermentation

A supported liquid membrane system was developed for the extraction of ethanol during semicontinuous fermentation of Saccharomyces bayanus. it consisted of a porous Teflon sheet as support, soaked with isotridecanol. This assembly permitted combining biocompatibility, permeation efficiency, and stability. The removal of ethanol from the cultures led to decreased inhibition and, thus, to a gain in conversion of 452 g/L glucose versus 293 g/L glucose without extraction. At the same time, the ethanol volumetric productivity was enhanced 2.5 times, due to an improvement of yeast viability, while the substrate conversion yield was maintained above 95% of its theoretical value. Besides these improvements in fermentation performances, the process resulted in ethanol purification, since the separation was selective towards microbial cells and carbon substrate, and likely selective to mineral ions present in the fermentation broth. For pervaporation, a concentration of ethanol four times greater was obtained in the collected permeate.     

A continuous, farm-scale, solid-phase fermentation process for fuel ethanol and protein feed production from fodder beets

Fuel ethanol (95%) was produced from fodder beets in two farm-scale processes. In the first process, involving conventional submerged fermentation of the fodder beets in a mash, ethanol and a feed (PF) rich in protein, fat, and fiber were produced. Ethanol yields of 70 L/metric ton (7 gal/ton) were obtained; however, resulting beers had low ethanol concentrations [3-5% (v/v)]. The high viscosity of medium and low sugar, beet mashes caused mixing problems which prevented any further increase of beet sugar in the mash. The severely limited the maximum attainable ethanol concentration during fermentation, thereby making the beer costly to distill into fuel ethanol and the process energy inefficient. In order to achieve distillably worthwhile ethanol concentrations of 8-10% (v/v), we developed and tested a solid-phase fermentation process (continuous). In preliminary trials, this system produced fermented pulp with over 8% (v/v) ethanol corresponding to an ethanol yield of 87 L/metric ton (21 gal/ton). Production costs with this novel process are $0.47/L ($1.77/gal) and the energy balance is 2.11. These preliminary cost estimates indicate that fodder beets are potentially competitive with corn as an ethanol feedstock. Additional research, however, is warranted to more precisely refine individual costs, energy balances and the actual value of the PF.     

Rapid ethanol fermentation of cellulose hydrolysate. I. Batch versus continuous systems

Rapid fermentation of bagasse hydrolysate to ethanol under anaerobic conditions by a strain of Saccharomyces cerevisiae has been studied in batch and continuous cultures at pH 4.0 and 30°C temperature with cell recycle. By using a 23.6 g/liter cell concentration, a concentation of 9.7% (w/v)ethanol was developed in a period of 6 hr. The rate of fermentation was found to increase with supplementation of yeast vitamins in the hydrolysate. In continuous culture employing cell recycle and a 0.127 v/v/m air flow rate, a cell mass concentration of 48.5 g/liter has been achieved. The maximum fermentor productivity of ethanol obtained under these conditions was 32.0 g/liter/hr, which is nearly 7.5 times higher than the normal continuous process without cell recycle and air sparging. The ethanol productivity was found to decrease linearly with ethanol concentration. Conversion of glucose in the hydrolysate to ethanol was achieved with a yield of 95 to 97% of theoretical.     

Improvements in ethanol tolerance of Kluyveromyces fragilis in jerusalem artichoke juice

Alcoholic fermentation of Jerusalem artichoke juice, a natural complex medium, allowed the production of 13% (v/v) ethanol utilizing an inulin-fermenting strain of Kluyveromyces fragilis, strongly sensitive to ethanol. However, the fermentation of a simple medium with a similar concentration of fermentable sugars (235 g/L) as saccharose stopped prematurely when only 7% (v/v) ethanol had been produced. Differences in the two fermentation profiles were attributed to the significantly lower ethanol tolerance of K. fragilis IGC 2671 in the simple medium with 2% saccharose as compared with diluted J.a. juice with a similar sugar concentration, in fact, (1) in diluted J. a. juice, growth was possible up to 8% (v/v) added ethanol compared with 6% (v/v) in simple medium and (2) ethanol-induced inhibition of the specific growth and fermentation rate as well as ethanol-induced stimulation of the specific death rate were much more drastic in simple medium. Present results show that (1) the complex composition of the medium used for alcoholic fermentation plays a marked role in the ability of the yeast to tolerate and produce ethanol; (2) J. a. juice proved a very appropriate medium for a productive alcoholic fermentation, namely, in processes based on strains with a low ethanol resistance; and (3) to characterize and compare the ethanol tolerance of fermenting yeasts, the standardization of the medium composition must be taken in consideration.     

Ethanol production from concentrated whey permeate using a fed-batch culture ofKluyveromyces fragilis

Summary Fed-batch fermentation of non-supplemented concentrated whey permeate resulted in high ethanol productivity for feeds of lactose for which batch fermentation had a poor performance. At an initial lactose concentration of 100 g/L and a constant lactose feeding rate of 18 g/h we have obtained: ethanol concentration 64 g/L, ethanol productivity 3.3 g/Lh, lactose consumption 100%, ethanol yield 0.47 g/g, and biomass yield 0.058 g/g.Nomenclature St total lactose fed per medium volume in the bioreactor, g/L - Si initial lactose concentration, g/L - F lactpse feeding rate, g/h - P final ethanol concentration, g/L - Y_p/s ethanol yield, g ethanol/g lactose - Y_x/s biomass yield, g biomass/g lactose - X_S lactose consumption, % - Qp overall ethanol volumetric productivity, g/Lh - m maximum specific growth rate, h - qsm maximum specific lactose consumption rate, g/gh - qpm maximum specific ethanol production rate, g/gh     

Study of in situ 1-butanol pervaporation from A-B-E fermentation using a PDMS composite membrane: validity of solution-diffusion model for pervaporative A-B-E fermentation

In this study, the application of a new polydimethylsiloxane (PDMS)/dual support composite membrane was investigated by incorporating the pervaporation process into the A-B-E (acetone-butanol-ethanol) fermentation. The performance of the A-B-E fermentation using the integrated pervaporation/fermentation process showed higher biomass concentrations and higher glucose consumption rates than those of the A-B-E fermentation without pervaporation. The performance of the membrane separation was studied during the separation of 1-butanol from three different 1-butanol solutions: binary, model, and fermentation culture solutions. The solution-diffusion model, specifically the mass transfer equation based on Fick's First Law, was shown to be applicable to the undefined A-B-E fermentation culture solutions. A quantitative comparison of 1-butanol separation from the three different solutions was made by calculating overall mass transfer coefficients of 1-butanol. It was found that the overall mass transfer coefficients during the separation of binary, model, and fermentation culture solutions were 1.50, 1.26, and 1.08 mm/h, respectively.     

Ethanol production in an integrated process of fermentation and ethanol recovery by pervaporation

In ethanol fermentations inhibition of the microorganism by ethanol limits the amount of substrate in the feed that can be converted. In a process high feed concentrations are desirable to minimize the flows. Such high feed concentrations can be realized in integrated processes in which ethanol is recovered from the fermentation broth as it is formed. In this study ethanol recovery by pervaporation was coupled to glucose fermentations by baker's yeast. Pervaporation was carried out with commercial silicone based hollow-fibre membrane modules with relatively high fluxes. Three different types of process configurations with pervaporation were investigated. Two of these configurations also included cell retention by microfiltration, in order to optimize the productivity. In the systems with pervaporation a feed containing 360 kg/m³ glucose could be converted almost completely. This feed concentration is a factor three higher than in a process without ethanol recovery. The productivity was 14 kg/m³ h in a system with pervaporation only, and could be increased to 43 kg/m³ h in the system with all recycle by microfiltration. The kinetic data suggest that accumulation of inhibitory compounds occurs in the integrated system. The integrated process was relatively easy in operation.     

Comparison of SHF and SSF processes from steam-exploded wheat straw for ethanol production by xylose-fermenting and robust glucose-fermenting Saccharomyces cerevisiae strains

In this study, bioethanol production from steam-exploded wheat straw using different process configurations was evaluated using two Saccharomyces cerevisiae strains, F12 and Red Star. The strain F12 has been engineerically modified to allow xylose consumption as cereal straw contain considerable amounts of pentoses. Red Star is a robust hexose-fermenting strain used for industrial fuel ethanol fermentations and it was used for comparative purposes. The highest ethanol concentration, 23.7 g/L, was reached using the whole slurry (10%, w/v) and the recombinant strain (F12) in an SSF process, it showed an ethanol yield on consumed sugars of 0.43 g/g and a volumetric ethanol productivity of 0.7 g/L h for the first 3 h. Ethanol concentrations obtained in SSF processes were in all cases higher than those from SHF at the same conditions. Furthermore, using the whole slurry, final ethanol concentration was improved in all tests due to the increase of potential fermentable sugars in the fermentation broth. Inhibitory compounds present in the pretreated wheat straw caused a significantly negative effect on the fermentation rate. However, it was found that the inhibitors furfural and HMF were completely metabolized by the yeast during SSF by metabolic redox reactions. An often encountered problem during xylose fermentation is considerable xylitol production that occurs due to metabolic redox imbalance. However, in our work this redox imbalance was counteracted by the detoxification reactions and no xylitol was produced.     

Production of ethanol from cassava whey

Investigations were conducted into the potential use of enzyme hydrolysed cassava whey for ethanol production by Saccharomyces cerevisiae Aspergillus niger grown on whct bran was used as crude enzyme source to saccharify the whey starch. The whey with an initial HCN concentration of 54.0μg/ml was fermented at pH 4.5 and 30°C in a one-step process to produce ethanol. A maximum ethanol concentration of 4.5% (v/v) was obtained in 120 h with a decrease in HCN level to 4.0 μg/ml. In a two-stage fermentation, in which the raw whey was pre-hydrolysed and under the same fermentation conditions, the unsterilized hydrolysate yielded alcohol content of 5.5% (v/v), while the sterilized hydrolysate gave higher alcohol yield, 7.5% (v/v), in 48 h. No HCN was detected in the fermented liquour at the end of the two-stage process.     

Improvement in fermentation characteristics of degermed ground corn by lipid supplementation

With rapid growth of fuel ethanol industry, and concomitant increase in distillers dried grains with solubles (DDGS), new corn fractionation technologies that reduce DDGS volume and produce higher value coproducts in dry grind ethanol process have been developed. One of the technologies, a dry degerm, defiber (3D) process (similar to conventional corn dry milling) was used to separate germ and pericarp fiber prior to the endosperm fraction fermentation. Recovery of germ and pericarp fiber in the 3D process results in removal of lipids from the fermentation medium. Biosynthesis of lipids, which is important for cell growth and viability, cannot proceed in strictly anaerobic fermentations. The effects of ten different lipid supplements on improving fermentation rates and ethanol yields were studied and compared to the conventional dry grind process. Endosperm fraction (from the 3D process) was mixed with water and liquefied by enzymatic hydrolysis and was fermented using simultaneous saccharification and fermentation. The highest ethanol concentration (13.7% v/v) was achieved with conventional dry grind process. Control treatment (endosperm fraction from 3D process without lipid supplementation) produced the lowest ethanol concentration (11.2% v/v). Three lipid treatments (fatty acid ester, alkylphenol, and ethoxylated sorbitan ester 1836) were most effective in improving final ethanol concentrations. Fatty acid ester treatment produced the highest final ethanol concentration (12.3% v/v) among all lipid supplementation treatments. Mean final ethanol concentrations of alkylphenol and ethoxylated sorbitan ester 1836 supplemented samples were 12.3 and 12.0% v/v, respectively.Mention of brand or firm names does not constitute an endorsement by University of Illinois or USDA above others of similar nature not mentioned     

Application of multistage continuous fermentation for production of fuel alcohol by very-high-gravity fermentation technology

A fermentation system to test the merging of very-high-gravity (VHG) and multistage continuous culture fermentation (MCCF) technologies was constructed and evaluated for fuel ethanol production. Simulated mashes ranging from 15% to 32% w/v glucose were fermented by Saccharomyces cerevisiae and the dilution rates were adjusted for each glucose concentration to provide an effluent containing less than 0.3% w/v glucose (greater than 99% consumption of glucose). The MCCF can be operated with glucose concentrations up to 32% w/v, which indicates that the system can successfully operate under VHG conditions. With 32% w/v glucose in the medium reservoir, a maximum of 16.73% v/v ethanol was produced in the MCCF. The introduction of VHG fermentation into continuous culture technology allows an improvement in ethanol productivity while producing ethanol continuously. In comparing the viability of yeast by methylene blue and plate count procedures, the results in this work indicate that the methylene blue procedure may overestimate the proportion of dead cells in the population. Ethanol productivity (Yps) increased from the first to the last fermentor in the sequence at all glucose concentrations used. This indicated that ethanol is more effectively produced in later fermentors in the MCCF, and that the notion of a constant Yps is not a valid assumption for use in mathematical modeling of MCCFs. Journal of Industrial Microbiology & Biotechnology (2001) 27, 87–93. Received 20 January 2001/ Accepted in revised form 28 April 2001     

Pervaporation behavior and integrated process for concentrating lignocellulosic ethanol through polydimethylsiloxane (PDMS) membrane

The effects of by-products from ethanol fermentation and hydrolysates of lignocelluloses on ethanol diffusion through polydimethylsiloxane (PDMS) membranes with/without silicalite-1 were investigated. A pervaporation process was integrated with lignocellulosic fermentation to concentrate bioethanol using bare PDMS membranes. Results showed that yeasts, solid particles, and salts increased ethanol flux and selectivity through the membranes (PDMS with/without silicalite-1), whereas glucose exerted negative effects on the performance. On bare PDMS membrane, the performance was not obviously affected by the existence of aliphatic acids. However, on PDMS-silicalite-1 membrane, a remarkable decrease in ethanol selectivity and a rapid growth of total flux in the presence of aliphatic acids were observed. These phenomena were due to the interaction of acids with silanol (Si–OH) groups to break the dense membrane surface. On the PDMS membranes with/without silicalite-1, degradation products of lignocellulosic hydrolysates such as furfural and hydroxyacetone slightly influenced separation performance. These results revealed that an integrated process can effectively eliminate product inhibition, improve ethanol productivity, and enhance the glucose conversion rate.     

Improving ethanol production and viability of Saccharomyces cerevisiae by a vitamin feeding strategy during fed-batch process

Several bottlenecks in the alcoholic fermentation process must be overcome to reach a very high and competitive performance of bioethanol production by the yeast Saccharomyces cerevisiae. In this paper, a nutritional strategy is described that allowed S. cerevisiae to produce a final ethanol titre of 19% (v/v) ethanol in 45 h in a fed-batch culture at 30 degrees C. This performance was achieved by implementing exponential feeding of vitamins throughout the fermentation process. In comparison to an initial addition of a vitamin cocktail, an increase in the amount of vitamins and an exponential vitamin feeding strategy improved the final ethanol titre from 126 g l(-1) to 135 g l(-1) and 147 g l(-1), respectively. A maximum instantaneous productivity of 9.5 g l(-1) h(-1) was reached in the best fermentation. These performances resulted from improvements in growth, the specific ethanol production rate, and the concentration of viable cells in response to the nutritional strategy.