Production of optically pure L(+)-lactic acid from waste plywood chips using an isolated thermotolerant Enterococcus faecalis SI at a pilot scale.

Utilization of renewable and low-cost lignocellulosic wastes has received major focus in industrial lactic acid production. The use of high solid loadings in biomass pretreatment potentially offers advantages over low solid loadings including higher lactic acid concentration with decreased production and capital costs. In this study, an isolated Enterococcus faecalis SI with optimal temperature 42 °C was used to produce optically pure L-lactic acid (> 99%) from enzyme-saccharified hydrolysates of acid-impregnated steam explosion (AISE)-treated plywood chips. The L-lactic acid production increased by 10% at 5 L scale compared to the similar fermentation scheme reported by Wee et al. The fermentation with a high solid loading of 20% and 35% (w/v) AISE-pretreated plywood chips had been successfully scaled up to process development unit scale (100 L) and pilot scale (9 m3), respectively. This is the first report of pilot-scale lignocellulosic lactic acid fermentation by E. faecalis with high lactic acid titer (nearly 92 g L-1) and yield (0.97 kg kg-1). Therefore, large-scale L-lactic acid production by E. faecalis SI shows the potential application for industries.

Bioethanol production from recovered napier grass with heavy metals.

Using plants to absorb and accumulate heavy metals from polluted soil, followed by the recycling of explants containing heavy metals, can help achieve the goal of reverting contaminated soil to low heavy-metal content soil. However, the re-use of recovered explants can also be problematic. Meanwhile, bioethanol has become a popular energy source. In this study, napier grass was used for the remediation of soil contaminated with heavy metals (artificially contaminated soil). The influence of bioethanol production from napier grass after phytoremediation was also investigated. The concentration of Zn, Cd, and Cr in the contaminated soil was 1000, 100, and 250 mg/kg, respectively. After napier grass phytoremediation, the concentration (dry biomass) of Zn, Cd, and Cr in the explants was 2701.97 ± 173.49, 6.1 ± 2.3, and 74.24 ± 1.42 mg/kg, respectively. Biomass production in the unpolluted soil was 861.13 ± 4.23 g. The biomass production ratio in high Zn-polluted soil was only 3.89%, while it was 4.68% for Cd and 21.4% for Cr. The biomass obtained after napier grass phytoremediation was pretreated using the steam explosion conditions of 180 °C, for 10 min, with 1.5% H2SO2, followed by enzymatic hydrolysis. The efficiency of enzymatic hydrolysis for Zn-polluted biomass was 90% of the unpolluted biomass, while it was 77% for Cd, and approximately the same for Cr. The fermentation efficiency of the heavy-metal-containing biomass was higher than the control biomass. The fermentation ethanol concentration obtained was 8.69-12.68, 13.03-15.50, and 18.48-19.31 g/L in Zn, Cd, and Cr environments, respectively. Results show that the heavy metals had a positive effect on bacteria fermentation. However, the fermentation efficiency was lower for biomass with severe heavy metal pollution. Thus, the utilization of napier grass phytoremediation for bioethanol production has a positive effect on the sustainability of environmental resources.

Ethanol production from dilute-acid steam exploded lignocellulosic feedstocks using an isolated multistress-tolerant Pichia kudriavzevii strain.

Renewable and low-cost lignocellulosic wastes have attractive applications in bioethanol production. The yeast Saccharomyces cerevisiae is the most widely used ethanol-producing microbe; however, its fermentation temperature (30-35°C) is not optimum (40-50°C) for enzymatic hydrolysis in the simultaneous saccharification and fermentation (SSF) process. In this study, we successfully performed an SSF process at 42°C from a high solid loading of 20% (w/v) acid-impregnated steam explosion (AISE)-treated rice straw with low inhibitor concentrations (furfural 0.19 g l-1 and acetic acid 0.95 g l-1 ) using an isolate Pichia kudriavzevii SI, where the ethanol titre obtained (33.4 gp  l-1 ) was nearly 39% greater than that produced by conventional S. cerevisiae BCRC20270 at 30°C (24.1 gp  l-1 ). In addition, P. kudriavzevii SI exhibited a high conversion efficiency of > 91% from enzyme-saccharified hydrolysates of AISE-treated plywood chips and sugarcane bagasse, although high concentrations of furaldehydes, such as furfural 1.07-1.21 g l-1 , 5-hydroxymethyl furfural 0.20-0.72 g l-1 and acetic acid 4.80-7.65 g l-1 , were present. This is the first report of ethanol fermentation by P. kudriavzevii using various acid-treated lignocellulosic feedstocks without detoxification or added nutrients. The multistress-tolerant strain SI has greater potential than the conventional S. cerevisiae for use in the cellulosic ethanol industry.

Production of optically pure L-lactic acid from lignocellulosic hydrolysate by using a newly isolated and D-lactate dehydrogenase gene-deficient Lactobacillus paracasei strain.

The use of lignocellulosic feedstock for lactic acid production with a difficulty is that the release of inhibitory compounds during the pretreatment process which inhibit the growth of microorganism. Thus we report a novel lactic acid bacterium, Lactobacillus paracasei 7 BL, that has a high tolerance to inhibitors and produced optically pure l-lactic acid after the interruption of ldhD gene. The strain 7 BL fermented glucose efficiently and showed high titer of l-lactic acid (215 g/l) by fed-batch strategy. In addition, 99 g/l of l-lactic acid with high yield (0.96 g/g) and productivity (2.25-3.23 g/l/h) was obtained by using non-detoxified wood hydrolysate. Rice straw hydrolysate without detoxification was also tested and yielded a productivity rate as high as 5.27 g/l/h. Therefore, L. paracasei 7 BL represents a potential method of l-lactic acid production from lignocellulosic biomass and has attractive application for industries.

Method of 2,3-butanediol production from glycerol and acid-pretreated rice straw hydrolysate by newly isolated strains: pre-evaluation as an integrated biorefinery process.

The present study validated a bioconversion technology for the production of 2,3-butanediol (2,3-BD) using sugars, glycerol and lignocellulosic material by three newly isolated strains-two Klebsiella sp. and one Serratia sp. One Klebsiella sp. afforded a high diol production yield (0.45 g/g) using the less common sugar arabinose and Serratia sp. was used for the first time to convert glycerol to 2,3-BD and afforded a yield of 0.43 g/g. Furthermore, acid-pretreated rice straw hydrolysate was used to determine the feasibility of its conversion to 2,3-BD. Both cellulose and hemicellulose hydrolysate were successfully fermented to 2,3-BD and acetoin by the isolates with yields for the diol between 0.39 and 0.44 g/g (equivalent to 78-88% of the maximum yield). These results demonstrate that 2,3-butanediol can be considered as the main product or a value-added byproduct of biofuel production and then potentially improve the economy of lignocellulosic biorefinery.

Pilot-scale study on the acid-catalyzed steam explosion of rice straw using a continuous pretreatment system.

A continuous acid-catalyzed steam explosion pretreatment process and system to produce cellulosic ethanol was developed at the pilot-scale. The effects of the following parameters on the pretreatment efficiency of rice straw feedstocks were investigated: the acid concentration, the reaction temperature, the residence time, the feedstock size, the explosion pressure and the screw speed. The optimal presteaming horizontal reactor conditions for the pretreatment process are as follows: 1.7 rpm and 100-110 °C with an acid concentration of 1.3% (w/w). An acid-catalyzed steam explosion is then performed in the vertical reactor at 185 °C for 2 min. Approximately 73% of the total saccharification yield was obtained after the rice straw was pretreated under optimal conditions and subsequent enzymatic hydrolysis at a combined severity factor of 0.4-0.7. Moreover, good long-term stability and durability of the pretreatment system under continuous operation was observed.

An improved method of xylose utilization by recombinant Saccharomyces cerevisiae.

The aim of this study was to develop a method to optimize expression levels of xylose-metabolizing enzymes to improve xylose utilization capacity of Saccharomyces cerevisiae. A xylose-utilizing recombinant S. cerevisiae strain YY2KL, able to express nicotinamide adenine dinucleotide phosphate, reduced (NADPH)-dependent xylose reductase (XR), nicotinamide adenine dinucleotide (NAD(+))-dependent xylitol dehydrogenase (XDH), and xylulokinase (XK), showed a low ethanol yield and sugar consumption rate. To optimize xylose utilization by YY2KL, a recombinant expression plasmid containing the XR gene was transformed and integrated into the aur1 site of YY2KL. Two recombinant expression plasmids containing an nicotinamide adenine dinucleotide phosphate (NADP(+))-dependent XDH mutant and XK genes were dually transformed and integrated into the 5S ribosomal DNA (rDNA) sites of YY2KL. This procedure allowed systematic construction of an S. cerevisiae library with different ratios of genes for xylose-metabolizing enzymes, and well-grown colonies with different xylose fermentation capacities could be further selected in yeast protein extract (YPX) medium (1 % yeast extract, 2 % peptone, and 2 % xylose). We successfully isolated a recombinant strain with a superior xylose fermentation capacity and designated it as strain YY5A. The xylose consumption rate for strain YY5A was estimated to be 2.32 g/gDCW/h (g xylose/g dry cell weight/h), which was 2.34 times higher than that for the parent strain YY2KL (0.99 g/gDCW/h). The ethanol yield was also enhanced 1.83 times by this novel method. Optimal ratio and expression levels of xylose-metabolizing enzymes are important for efficient conversion of xylose to ethanol. This study provides a novel method that allows rapid and effective selection of ratio-optimized xylose-utilizing yeast strains. This method may be applicable to other multienzyme systems in yeast.

Pilot-scale ethanol production from rice straw hydrolysates using xylose-fermenting Pichia stipitis.

Ethanol was produced at pilot scale from rice straw hydrolysates using a Pichia stipitis strain previously adapted to NaOH-neutralized hydrolysates. The highest ethanol yield was 0.44 ± 0.02 g(p)/g(s) at an aeration rate of 0.05 vvm using overliming-detoxified hydrolysates. The yield with hydrolysates conditioned by ammonia and NaOH was 0.39 ± 0.01 and 0.34 ± 0.01 g(p)/g(s), respectively, were achieved at the same aeration rate. The actual ethanol yield from hydrolysate fermentation with ammonia neutralization was similar to that with overliming hydrolysate after taking into account the xylose loss resulting from these conditioning processes. Moreover, the ethanol yield from ammonia-neutralized hydrolysates could be further enhanced by increasing the initial cell density by two-fold or reducing the combined concentration of furfural and 5-hydroxymethyl furfural to 0.6g/L by reducing the severity of operational conditions in pretreatment. This study demonstrated the potential for commercial ethanol production from rice straw via xylose fermentation.

Pretreatment of rice straw using an extrusion/extraction process at bench-scale for producing cellulosic ethanol.

A combination of a twin-screw extrusion and an acid-catalyzed hot water extraction process performed at a bench-scale was used to prepare high monomeric xylose hydrolysate for cellulosic production. The influences of the screw speed (30-150 rpm), barrel temperature (80-160 °C) and corresponding specific mechanical energy of the extruder on the structural properties of the pretreated rice straw, sugar concentration and conversion were investigated. The optimal condition for the extrusion step was determined to be 40 rpm with 3% H2SO4 at 120 °C; the optimal condition for the extraction step was determined to be 130 °C for 20 min. After the pretreatment at the optimal condition, 83.7% of the xylan was converted to monomeric xylose, and the concentration reached levels of 53.7 g/L. Finally, after the subsequent enzymatic hydrolysis, an 80% yield of the total saccharification was obtained.

Ethanol production efficiency of an anaerobic hemicellulolytic thermophilic bacterium, strain NTOU1, isolated from a marine shallow hydrothermal vent in Taiwan.

A new extremely thermophilic, anaerobic, gram-negative bacterium, strain NTOU1, was enriched and isolated from acidic marine hydrothermal fluids off Gueishandao island in Taiwan with 0.5% starch and 0.5% maltose as carbon sources. This strain was capable of growth utilizing various sugars found in lignocellulosic biomass as well as xylan and cellulose, and produced ethanol, lactate, acetate, and CO(2) as fermentation products. The results of a 16S rRNA gene sequence analysis (1,520 bp) revealed NTOU1 to belong to the genus Thermoanaerobacterium. When tested for the ability to grow and produce ethanol from xylose or rice straw hemicellulosic hydrolysate at 70°C, the strain showed the highest levels of ethanol production (1.65 mol ethanol mol xylose(-1)) in a medium containing 0.5% xylose plus 0.5% yeast extract. Maximum ethanol production from the rice straw hemicellulose was 0.509 g g(-1), equivalent to 98.8% theoretical conversion efficiency. Low concentrations of inhibitors (derived from dilute acid hydrolysis) in the rice straw hemicellulose hydrolysate did not affect the ethanol yield. Thus, Thermoanaerobacterium strain NTOU1 has the potential to be used for ethanol production from hemicellulose.

Pretreatment efficiency and structural characterization of rice straw by an integrated process of dilute-acid and steam explosion for bioethanol production.

The combined pretreatment of rice straw using dilute-acid and steam explosion followed by enzymatic hydrolysis was investigated and compared with acid-catalyzed steam explosion pretreatment. In addition to measuring the chemical composition, including glucan, xylan and lignin content, changes in rice straw features after pretreatment were investigated in terms of the straw's physical properties. These properties included crystallinity, surface area, mean particle size and scanning electron microscopy imagery. The effect of acid concentration on the acid-catalyzed steam explosion was studied in a range between 1% and 15% acid at 180°C for 2 min. We also investigated the influence of the residence time of the steam explosion in the combined pretreatment and the optimum conditions for the dilute-acid hydrolysis step in order to develop an integrated process for the dilute-acid and steam explosion. The optimum operational conditions for the first dilute-acid hydrolysis step were determined to be 165°C for 2 min with 2% H(2)SO(4) and for the second steam explosion step was to be carried out at 180°C for 20 min; this gave the most favorable combination in terms of an integrated process. We found that rice straw pretreated by the dilute-acid/steam explosions had a higher xylose yield, a lower level of inhibitor in the hydrolysate and a greater degree of enzymatic hydrolysis; this resulted in a 1.5-fold increase in the overall sugar yield when compared to the acid-catalyzed steam explosion.

Development of a yeast strain for xylitol production without hydrolysate detoxification as part of the integration of co-product generation within the lignocellulosic ethanol process.

The present study verified an applicable technology of xylitol bioconversion as part of the integration of co-product generation within second-generation bioethanol processes. A newly isolated yeast strain, Candida tropicalis JH030, was shown to have a capacity for xylitol production from hemicellulosic hydrolysate without detoxification. The yeast gives a promising xylitol yield of 0.71 g(p) g(s)(-1) from non-detoxified rice straw hydrolysate that had been prepared by the dilute acid pretreatment under severe conditions. The yeast's capacity was also found to be practicable with various other raw materials, such as sugarcane bagasse, silvergrass, napiergrass and pineapple peel. The lack of a need to hydrolysate detoxification enhances the potential of this newly isolated yeast for xylitol production and this, in turn, has the capacity to improve economics of lignocellulosic ethanol production.

Effect of dilute acid pretreatment of rice straw on structural properties and enzymatic hydrolysis.

This study aim is to propose operational conditions for the dilute acid pretreatment of rice straw and to explore the effect of the structural properties of the solid residues on the enzymatic hydrolysis. A maximal sugar yield of 83% was achieved when the rice straw was pretreated with 1% (w/w) sulfuric acid with a reaction time of 1-5 min at 160 degrees C or 180 degrees C, followed by enzymatic hydrolysis. The completely release of sugar (xylose and glucose) increased the pore volume of the pretreated solid residues resulted in an efficiency of 70% for the enzymatic hydrolysis. The extra pore volume was generated by the release of acid-soluble lignin and this resulted in the enzymatic hydrolysis being enhanced by nearly 10%. The increase in the crystallinity index of the pretreated rice straw was limited. These results were consistent with those from the Fourier transformer infrared (FTIR) analysis.

Enhanced ethanol production by fermentation of rice straw hydrolysate without detoxification using a newly adapted strain of Pichia stipitis.

An enhanced inhibitor-tolerant strain of Pichia stipitis was successfully developed through adaptation to acid-treated rice straw hydrolysate. The ethanol production obtained by fermentation of NaOH-neutralized hydrolysate without detoxification using the adapted P. stipitis was comparable to fermentation of overliming-detoxified hydrolysate. The ethanol yield using the adapted P. stipitis with both types of hydrolysate at pH 5.0 achieved 0.45 g(p) g(s)(-1), which is equivalent to 87% of the maximum possible ethanol conversion. Furthermore, the newly adapted P. stipitis demonstrated significantly enhanced tolerance to sulfate and furfural despite the fact that both inhibitors had not been removed from the hydrolysate by NaOH neutralization. Finally, the ethanol conversion could be maintained at 60% and above when the neutralized hydrolysate contained 3.0% sulfate and 1.3gL(-1) furfural.

Characterization of dilute acid pretreatment of silvergrass for ethanol production.

Pretreatment with dilute sulfuric acid of silvergrass was compared with the pretreatment's effect on other commonly used lignocellulosic materials, namely rice straw and bagasse, in order to evaluate the potential of this feedstock for ethanol production. The highest yield of xylose from silvergrass was between 70% and 75%, which was similar to bagasse. However, silvergrass gave a higher level of fermentability than bagasse using the hydrolysate because less acetic acid was formed. The release of sugars resulted in an about 2.0-fold increase in specific surface area of the pretreated silvergrass. Increasing the specific surface area did not obviously enhance enzymatic digestibility. The hydrophilicity of the acid pretreated silvergrass was characterized using its Fourier transform infrared (FTIR) spectra. The increase in hydrophilicity may enhance enzymatic adsorption onto lignin and increase the accumulation of cellobiose for enzymatic hydrolysis as pretreatment severity increases.

Dose evaluation and measurement of the 188Re liquid-filled balloon in intravascular brachytherapy.

We compared the Monte Carlo evaluation and GafChromic MD-55 film experimental measurement of 188Re liquid-filled balloons in intravascular brachytherapy using two phantoms of 6 mm vascular diameter, a phantom of 4 mm vascular diameter and a phantom of 3 mm vascular diameter. A dose-evaluation interface program was developed and was shown to be capable of quickly providing information such as the necessary 188Re source irradiation time to deliver a prescribed dose.

The absolute counting of 166mHo, 58Co and 88Y.

In this study, absolute 4pi beta-gamma-coincidence counting was used to measure the mass activity of 166mHo, 58Co and 88Y. For 166mHo and 88Y, three gamma windows were set to study the systematic error caused by the different gamma window settings. To eliminate the effect arising from the large difference in counting efficiency of the 4pi beta counter between electron capture events and beta+ particles, the two-dimensional extrapolation method was used to measure 58Co. The measurement results for the three nuclides were linked with the BIPM SIR through two APMP regional comparisons, APMP.RI(II)-K2, Ho-166m and APMP.RI(II)K2.Co-58, Y-88. Results are presented.