Acetone-butanol-ethanol fermentation in a continuous and closed-circulating fermentation system with PDMS membrane bioreactor

Separation of n-Butanol from Aqueous Solutions via Pervaporation Using PDMS/ZIF-8 Mixed-Matrix Membranes of Different Particle Sizes

The use of mixed matrix membranes (MMMs) to facilitate the production of biofuels has attracted significant research interest in the field of renewable energy. In this study, the pervaporation separation of butanol from aqueous solutions was studied using a series of MMMs, including zeolitic imidazolate frameworks (ZIF-8)-polydimethylsiloxane (PDMS) and zinc oxide-PDMS mixed matrix membranes. Although several studies have reported that mixed matrix membranes incorporating ZIF-8 nanoparticles showed improved pervaporation performances attributed to their intrinsic microporosity and high specific surface area, an in-depth study on the role of ZIF-8 nanoparticle size in MMMs has not yet been reported. In this study, different average sizes of ZIF-8 nanoparticles (30, 65, and 80 nm) were synthesized, and the effects of particle size and particle loading content on the performance of butanol separation using MMMs were investigated. Furthermore, zinc oxide nanoparticles, as non-porous fillers with the same metalcore as ZIF-8 but with a very different geometric shape, were used to illustrate the importance of the particle geometry on the membrane performance. Results showed that small-sized ZIF-8 nanoparticles have better permeability and selectivity than medium and large-size ZIF-8 MMMs. While the permeation flux increased continuously with an increase in the loading of nanoparticles, the selectivity reached a maximum for MMM with 8 wt% smaller-size ZIF-8 nanoparticle loading. The flux and butanol selectivity increased by 350% and 6%, respectively, in comparison to those of neat PDMS membranes prepared in this study.

Membrane applications in the food industry

Current trends in the food industry for the application of membrane techniques are presented. Industrial solutions as well as laboratory research, which can contribute to the improvement of membrane efficiency and performance in this field, are widely discussed. Special attention is given to the main food industries related to dairy, sugar and biotechnology. In addition, the potential of membrane techniques to assist in the treatment of waste sources arising from food production is highlighted.

Techno-Economic Analysis (TEA) of Different Pretreatment and Product Separation Technologies for Cellulosic Butanol Production from Oil Palm Frond

Among the driving factors for the high production cost of cellulosic butanol lies the pretreatment and product separation sections, which often demand high amounts of energy, chemicals, and water. In this study, techno-economic analysis of several pretreatments and product separation technologies were conducted and compared. Among the pretreatment technologies evaluated, low-moisture anhydrous ammonia (LMAA) pretreatment has shown notable potential with a pretreatment cost of $0.16/L butanol. Other pretreatment technologies evaluated were autohydrolysis, soaking in aqueous ammonia (SAA), and soaking in sodium hydroxide solution (NaOH) with pretreatment costs of $1.98/L, $3.77/L, and $0.61/L, respectively. Evaluation of different product separation technologies for acetone-butanol-ethanol (ABE) fermentation process have shown that in situ stripping has the lowest separation cost, which was $0.21/L. Other product separation technologies tested were dual extraction, adsorption, and membrane pervaporation, with the separation costs of $0.38/L, $2.25/L, and $0.45/L, respectively. The evaluations have shown that production of cellulosic butanol using combined LMAA pretreatment and in situ stripping or with dual extraction recorded among the lowest butanol production cost. However, dual extraction model has a total solvent productivity of approximately 6% higher than those of in situ stripping model.

Continuous Butanol Fermentation of Dilute Acid-Pretreated De-oiled Rice Bran by Clostridium acetobutylicum YM1

Continuous fermentation of dilute acid-pretreated de-oiled rice bran (DRB) to butanol by the Clostridium acetobutylicum YM1 strain was investigated. Pretreatment of DRB with dilute sulfuric acid (1%) resulted in the production of 42.12 g/L total sugars, including 25.57 g/L glucose, 15.1 g/L xylose and 1.46 g/L cellobiose. Pretreated-DRB (SADRB) was used as a fermentation medium at various dilution rates, and a dilution rate of 0.02 h^-1 was optimal for solvent production, in which 11.18 g/L of total solvent was produced (acetone 4.37 g/L, butanol 5.89 g/L and ethanol 0.92 g/L). Detoxification of SADRB with activated charcoal resulted in the high removal of fermentation inhibitory compounds. Fermentation of detoxified-SADRB in continuous fermentation with a dilution rate of 0.02 h^-1 achieved higher concentrations of solvent (12.42 g/L) and butanol (6.87 g/L), respectively, with a solvent productivity of 0.248 g/L.h. This study showed that the solvent concentration and productivity in continuous fermentation from SADRB was higher than that obtained from batch culture fermentation. This study also provides an economic assessment for butanol production in continuous fermentation process from DRB to validate the commercial viability of this process.

Two-stage pervaporation process for effective in situ removal acetone-butanol-ethanol from fermentation broth

Two-stage pervaporation for ABE recovery from fermentation broth was studied to reduce the energy cost. The permeate after the first stage in situ pervaporation system was further used as the feedstock in the second stage of pervaporation unit using the same PDMS/PVDF membrane. A total 782.5g/L of ABE (304.56g/L of acetone, 451.98g/L of butanol and 25.97g/L of ethanol) was achieved in the second stage permeate, while the overall acetone, butanol and ethanol separation factors were: 70.7-89.73, 70.48-84.74 and 9.05-13.58, respectively. Furthermore, the theoretical evaporation energy requirement for ABE separation in the consolidate fermentation, which containing two-stage pervaporation and the following distillation process, was estimated less than ∼13.2MJ/kg-butanol. The required evaporation energy was only 36.7% of the energy content of butanol. The novel two-stage pervaporation process was effective in increasing ABE production and reducing energy consumption of the solvents separation system.

Effect of chemical pretreatments on corn stalk bagasse as immobilizing carrier of Clostridium acetobutylicum in the performance of a fermentation-pervaporation coupled system

In this study, different pretreatment methods were evaluated for modified the corn stalk bagasse and further used the pretreated bagasse as immobilized carrier in acetone-butanol-ethanol fermentation process. Structural changes of the bagasses pretreated by different methods were analyzed by Fourier transform infrared, crystallinity index and scanning pictures by electron microscope. And the performances of batch fermentation using the corn stalk based carriers were evaluated. Results indicated that the highest ABE concentration of 23.86g/L was achieved using NaOH pretreated carrier in batch fermentation. Immobilized fermentation-pervaporation integration process was further carried out. The integration process showed long-term stability with 225-394g/L of ABE solvents on the permeate side of pervaporation membrane. This novel integration process was found to be an efficient method for biobutanol production.

Energy efficient of ethanol recovery in pervaporation membrane bioreactor with mechanical vapor compression eliminating the cold traps

An energy efficient pervaporation membrane bioreactor with mechanical vapor compression was developed for ethanol recovery during the process of fermentation coupled with pervaporation. Part of the permeate vapor at the membrane downstream under the vacuum condition was condensed by running water at the first condenser and the non-condensed vapor enriched with ethanol was compressed to the atmospheric pressure and pumped into the second condenser, where the vapor was easily condensed into a liquid by air. Three runs of fermentation-pervaporation experiment have been carried out lasting for 192h, 264h and 360h respectively. Complete vapor recovery validated the novel pervaporation membrane bioreactor. The total flux of the polydimethylsiloxane (PDMS) membrane was in the range of 350gm(-2)h(-1) and 600gm(-2)h(-1). Compared with the traditional cold traps condensation, mechanical vapor compression behaved a dominant energy saving feature.

Multiblock Copolymer Grafting for Butanol Biofuel Recovery by a Sustainable Membrane Process

Biobutanol is an attractive renewable biofuel mainly obtained by the acetone-butanol-ethanol (ABE) fermentation process. Nevertheless, the alcohol concentration has to be limited to a maximum of 2 wt % in ABE fermentation broths to avoid butanol toxicity to the microorganisms. The pervaporation (PV) membrane process is a key sustainable technology for butanol recovery in these challenging conditions. In this work, the grafting of azido-polydimethylsiloxane (PDMS-N3) onto a PDMS-based multiblock copolymer containing alkyne side groups led to a series of original membrane materials with increasing PDMS contents from 50 to 71 wt %. Their membrane properties were assessed for butanol recovery by pervaporation from a model aqueous solution containing 2 wt % of n-butanol at 50 °C. The membrane flux J50μm for a reference thickness of 50 μm strongly increased from 84 to 192 g/h m(2) with increasing PDMS content for free-standing dense membranes with thicknesses in the range of 38-95 μm. At the same time, the intrinsic butanol permeability increased from 1.47 to 4.68 kg μm/h m(2) kPa and the permeate butanol content was also strongly improved from 38 to 53 wt %, corresponding to high and very high membrane separation factors of 30 and 55, respectively. Therefore, the new grafted copolymer materials strongly overcame the common permeability/selectivity trade-off for butanol recovery by a sustainable membrane process.

Butanol production under microaerobic conditions with a symbiotic system of Clostridium acetobutylicum and Bacillus cereus

BACKGROUND

One major problem of ABE (acetone, butanol and ethanol) fermentation is high oxygen sensitivity of Clostridium acetobutylicum. Currently, no single strain has been isolated or genetically engineered to produce butanol effectively under aerobic conditions. In our previous work, a symbiotic system TSH06 has been developed successfully by our group, and two strains, C. acetobutylicum TSH1 and Bacillus cereus TSH2, were isolated from TSH06.

RESULTS

Compared with single culture, TSH06 showed promotion on cell growth and solvent accumulation under microaerobic conditions. To simulate TSH06, a new symbiotic system was successfully re-constructed by adding living cells of B. cereus TSH2 into C. acetobutylicum TSH1 cultures. During the fermentation process, the function of B. cereus TSH2 was found to deplete oxygen and provide anaerobic environment for C. acetobutylicum TSH1. Furthermore, inoculation ratio of C. acetobutylicum TSH1 and B. cereus TSH2 affected butanol production. In a batch fermentation with optimized inoculation ratio of 5 % C. acetobutylicum TSH1 and 0.5 % B. cereus TSH2, 11.0 g/L butanol and 18.1 g/L ABE were produced under microaerobic static condition. In contrast to the single culture of C. acetobutylicum TSH1, the symbiotic system became more aerotolerant and was able to produce 11.2 g/L butanol in a 5 L bioreactor even with continuous 0.15 L/min air sparging. In addition, qPCR assay demonstrated that the abundance of B. cereus TSH2 increased quickly at first and then decreased sharply to lower than 1 %, whereas C. acetobutylicum TSH1 accounted for more than 99 % of the whole population in solventogenic phase.

CONCLUSIONS

The characterization of a novel symbiotic system on butanol fermentation was studied. The new symbiotic system re-constructed by co-culture of C. acetobutylicum TSH1 and B. cereus TSH2 showed excellent performance on butanol production under microaerobic conditions. B. cereus TSH2 was a good partner for C. acetobutylicum TSH1 by providing an anaerobic environment. During fermentation process, the high ratio of Clostridium and low ratio of Bacillus composition indicated that this symbiotic system was an effective and easily controlled cultivation model for ABE fermentation under microaerobic conditions.

The vital role of citrate buffer in acetone-butanol-ethanol (ABE) fermentation using corn stover and high-efficient product recovery by vapor stripping-vapor permeation (VSVP) process

BACKGROUND

Butanol is not only an important solvent and chemical intermediate in food and pharmaceutical industries, but also considered as an advanced biofuel. Recently, there have been resurging interests in producing biobutanol especially using low-cost lignocellulosic biomass, but the process still suffers from low titer and productivity. The challenge for the bioconversion approach is to find an effective way of degrading materials into simple sugars that can then be converted into fuels by microorganisms. The pretreatment of lignocellulosic biomass is the great important process in influencing butanol production and recovery, finally determining its eco-feasibility in commercialization.

RESULTS

The effects of various strengths of citrate buffer on enzymatic hydrolysis and acetone-butanol-ethanol fermentation using corn stover or glucose as feedstock were investigated. The strengths of citrate buffer in the range of 20-100 mM had no effect on enzymatic hydrolysis, but greatly influenced the performance of ABE fermentation using corn stover hydrolysate. When 30 mM citrate buffer was used for enzymatic hydrolysis, the fermentation broth with the maximum butanol and ABE concentrations of 11.2 and 19.8 g/L were obtained from 30.9 g/L glucose and 9.7 g/L xylose, respectively, which was concentrated to 100.4 g/L butanol and 153.5 g/L ABE by vapor stripping-vapor permeation process. Furthermore, using glucose as sole carbon source, there were no cell growth and ABE production in the P2 medium with 80 or 100 mM citrate buffer, indicating that higher concentrations of citrate buffer had deleterious effect on cell growth and metabolism due to the variation of cells internal pH and cell membrane permeability. To mimic in situ product recovery for ABE fermentation, the VSVP process produced the condensate containing 212.0-232.0 g/L butanol (306.6-356.1 g/L ABE) from fermentation broth containing ~10 g/L butanol (~17 g/L ABE), the performance of which was more effective than pervaporation and gas stripping.

CONCLUSIONS

As it has significant impact on butanol fermentation, the strength of citrate buffer is of great importance in lignocellulosic butanol fermentation. Compared with pervaporation and gas stripping, the VSVP process has great potential for efficient butanol recovery in biobutanol production.

Evaluation of hydrophobic micro-zeolite-mixed matrix membrane and integrated with acetone-butanol-ethanol fermentation for enhanced butanol production

BACKGROUND

Butanol is regarded as an advanced biofuel that can be derived from renewable biomass. However, the main challenge for microbial butanol production is low butanol titer, yield and productivity, leading to intensive energy consumption in product recovery. Various alternative separation technologies such as extraction, adsorption and gas stripping, etc., could be integrated with acetone-butanol-ethanol (ABE) fermentation with improving butanol productivity, but their butanol selectivities are not satisfactory. The membrane-based pervaporation technology is recently attracting increasing attention since it has potentially desirable butanol selectivity.

RESULTS

The performance of the zeolite-mixed polydimethylsiloxane (PDMS) membranes were evaluated to recover butanol from butanol/water binary solution as well as fermentation broth in the integrated ABE fermentation system. The separation factor and butanol titer in permeate of the zeolite-mixed PDMS membrane were up to 33.0 and 334.6 g/L at 80°C, respectively, which increased with increasing zeolite loading weight in the membrane as well as feed temperature. The enhanced butanol separation factor was attributed to the hydrophobic zeolites with large pore size providing selective routes preferable for butanol permeation. In fed-batch fermentation incorporated with pervaporation, 54.9 g/L ABE (34.5 g/L butanol, 17.0 g/L acetone and 3.4 g/L ethanol) were produced from 172.3 g/L glucose. The overall butanol productivity and yield increased by 16.0 and 11.1%, respectively, which was attributed to the alleviated butanol inhibition by pervaporation and reassimilation of acids for ABE production. The zeolite-mixed membrane produced a highly concentrated condensate containing 169.6 g/L butanol or 253.3 g/L ABE, which after phase separation easily gave the final product containing >600 g/L butanol.

CONCLUSIONS

Zeolite loading in the PDMS matrix was attributed to improving the pervaporative performance of the membrane, showing great potential to recover butanol with high purity. Therefore, this zeolite-mixed PDMS membrane had the potential to improve biobutanol production when integrating with ABE fermentation.

Continuous acetone-butanol-ethanol (ABE) fermentation and gas production under slight pressure in a membrane bioreactor

Two rounds of acetone-butanol-ethanol (ABE) fermentation under slight pressure were carried out in the continuous and closed-circulating fermentation (CCCF) system. Spores of the clostridium were observed and counted, with the maximum number of 2.1 × 10(8) and 2.3 × 10(8)ml(-1) separately. The fermentation profiles were comparable with that at atmospheric pressure, showing an average butanol productivity of 0.14 and 0.13 g L(-1)h(-1). Moreover, the average gas productivities of 0.28 and 0.27 L L(-1)h(-1) were obtained in two rounds of CCCF, and the cumulative gas production of 52.64 and 25.92 L L(-1) were achieved, with the hydrogen volume fraction of 41.43% and 38.08% respectively. The results suggested that slight pressures have no obvious effect on fermentation performance, and also indicated the significance and feasibility of gas recovery in the continuous ABE fermentation process.

Inhibition effect of secondary metabolites accumulated in a pervaporation membrane bioreactor on ethanol fermentation of Saccharomyces cerevisiae

The secondary metabolites accumulated in a pervaporation membrane bioreactor during ethanol fermentation were mostly composed of acetic acid, lactic acid, propionic acid, citric acid, succinic acid and glycerol. The inhibition effect of these compounds at a broad concentration range was studied through ethanol fermentation by Saccharomyces cerevisiae. An increasing concentration of the secondary metabolites led to longer lag time and a reduction of cell growth. The specific cell growth rate, cell yield, ethanol productivity were only 0.061 h(-1), 0.024, 0.47 g L(-1) h(-1) respectively, when the medium contained 3.12 g of acetic acid, 10.23 g of lactic acid, 2.72 g of propionic acid, 1.35 g of citric acid, 2.26 g of succinic acid and 49.25 g of glycerol per liter (a concentration level in pervaporation membrane bioreactor at later fermentation period). By increasing pH of the medium to 6.0-8.0, the inhibition of these secondary metabolites could be greatly relieved.

Enhanced ethanol fermentation in a pervaporation membrane bioreactor with the convenient permeate vapor recovery

A continuous and closed-circulating fermentation (CCCF) system with a pervaporation membrane bioreactor was built for ethanol fermentation without a refrigeration unit to condense the permeate vapor. Two runs of experiment with a feature of complete and continuous coupling of fermentation and pervaporation were carried out, lasting for 192h and 264h, respectively. The experimental measurement indicated that the enhanced fermentation could be achieved with additional advantages of convenient permeate recovery and energy saving of the process. During the second experiment, the average cell concentration, glucose consumption rate, ethanol productivity, ethanol yield and total ethanol amount produced reached 19.8gL(-1), 6.06gL(-1)h(-1), 2.31gL(-1)h(-1), 0.38, and 609.8gL(-1), respectively. During the continuous fermentation process, ethanol removal in situ promoted the cell second growth obviously, but the accumulation of the secondary metabolites in the broth became the main inhibitor against the cell growth and fermentation.

"In situ" removal of isopropanol, butanol and ethanol from fermentation broth by gas stripping

In this study, the removal of IBE from aqueous solutions by gas stripping has been characterized. The effect of one or more components in the solution on the kinetics of the separation has been studied, both at 37°C and at 70°C. Gas stripping has been applied to batch, repeated batch and continuous cultures of Clostridium beijerinckii grown on a glucose/xylose mixed sugar substrate mimicking lignocellulosic hydrolysates, with the aim of finding optimal conditions for a stable IBE-producing culture with high productivity. An innovative repeated-batch process has been demonstrated in which the gas-stripping is performed at 70°C, resulting in a prolonged stable IBE culture.