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By-products from hydrothermal pretreatment of lignocellulosic biomass inhibit enzymatic saccharification and microbial fermentation. Three long-chain organic extractants (Alamine 336, Aliquat 336 and Cyanex 921) were compared to two conventional organic solvents (ethyl acetate and xylene) with regard to conditioning of birch wood pretreatment liquid (BWPL) for improved fermentation and saccharification. In the fermentation experiments, extraction with Cyanex 921 resulted in the best ethanol yield, 0.34 ± 0.02 g g⁻¹ on initial fermentable sugars. Extraction with xylene also resulted in a relatively high yield, 0.29 ± 0.02 g g⁻¹, while cultures consisting of untreated BWPL and BWPL treated with the other extractants exhibited no ethanol formation. Aliquat 336 was most efficient with regard to removing by-products, but the residual Aliquat after the extraction was toxic to yeast cells. Enzymatic digestibility increased by 19-33% after extraction with the long-chain organic extractants. The investigation demonstrates that conditioning with long-chain organic extractants has the potential to relieve inhibition of both enzymes and microbes.

The effects of the redox environment on acidic hydrothermal pretreatment were investigated in experiments with sugarcane bagasse (190 degrees C, 14 min) and Norway spruce (205 degrees C, 5 min). To modulate the redox environment, pretreatment was performed without gas addition, with N-2 , or with O-2. Analyses covered pretreated solids, pretreatment liquids, condensates, enzymatic digestibility, and inhibitory effects of pretreatment liquids on yeast. Addition of gas, especially O-2 , resulted in increased severity, as reflected by up to 18 percent units lower recoveries of pretreated solids, up to 31 percent units lower glucan recoveries, improved hemicellulose removal, formation of pseudo-lignin, improved overall glucan conversion, and increased concentrations of several microbial inhibitors. Some inhibitors, such as formaldehyde and coniferyl aldehyde, did not, however, follow that pattern. TAC (Total Aromatic Content) values reflected inhibitory effects of pretreatment liquids. This study demonstrates how gas addition can be used to modulate the severity of acidic hydrothermal pretreatment.

The impact of strain selection and culture conditions on bacterial nanocellulose (BNC) productivity and quality was investigated by using four strains, static and agitated cultures, and an initial pH in the range 4-6. With agitation, strain DHU-ATCC-1 displayed highest productivity [1.14 g/(L x d)]. In static cultures, DHU-ZGD-1186 exhibited superior BNC yield on consumed glucose (0.79 g/g), and lowest by-product formation with respect to gluconic acids [<= 0.07 g/(L x d)]. By-product formation typically decreased in the order gluconic acid > 2-keto-gluconic acid > 5-keto-gluconic acid, and was lowest in cultures with high initial pH. The BNC from DHU-ZGD-1186 exhibited higher average viscometric degree of polymerization (DPv), higher crystallinity index, and higher tear index. In conclusion, both strain selection and cultivation conditions had an impact on BNC productivity and properties. Productivity, DPv, crystallinity, and mechanical strength of BNC from agitated cultures could be similar to or even higher than the corresponding values for static cultures.

Hydrothermal pretreatment improves bioconversion of lignocellulose, but the effects of different acid catalysts are poorly understood. The effects of sulfuric acid (SA) and sulfur dioxide (SD) in continuous steam pretreatment of wood of Norway spruce were compared in the temperature range 195 degrees C-215 degrees C. The inhibitory effects of the pretreatment liquid on cellulolytic enzymes and Saccharomyces cerevisiae yeast were higher for SD-than for SApretreated material, and the inhibitory effects increased with increasing pretreatment temperature. However, the susceptibility to cellulolytic enzymes of wood pretreated with SD was 2.0-2.9 times higher than that of wood pretreated with SA at the same temperature. Data conclusively show that the superior convertibility of SDpretreated material was not due to inhibition phenomena but rather to the greater capability of the SD pretreatment to reduce the particle size through partial delignification and cellulose degradation. Particle size was shown to be correlated with enzymatic digestibility (R-2 0.97-0.98).

Wood chips of Norway spruce were pretreated by steam explosion at 195–215 °C after impregnation with either sulfuric acid (SA) or sulfur dioxide (SD). The effects of different pretreatment conditions on formation of microbial inhibitors were investigated, and the inhibitory effects on yeast of pretreatment liquids and of specific inhibitors that were found in the pretreatment liquids were elucidated. Whereas the concentrations of most inhibitors increased with increasing pretreatment temperatures, there were exceptions, such as formaldehyde and p-hydroxybenzaldehyde. The highest concentration of each inhibitor was typically found in SD-pretreated material, but formic acid was an exception. The toxic effects on yeast were studied using concentrations corresponding to loadings of 12 and 20% total solids (TS). Among individual inhibitors that were quantitated in pretreatment liquids, the concentrations of formaldehyde were by far most toxic. There was no or minimal yeast growth in the formaldehyde concentration range (5.8–7.7 mM) corresponding to 12% TS.

BACKGROUND More extensive utilization of bacterial nanocellulose (BNC) is severely restricted by the low efficiency and small scale of the traditional static cultivation. Submerged fermentation in stirred-tank reactors (STRs) is potentially favourable for large-scale production of BNC, but scale-up of cultivation remains challenging. Even though the STR is most commonly used for submerged cultivation in the fermentation industry, there are few previous attempts to scale-up production of BNC to pilot scale using an STR. Furthermore, the question of how scale-up of submerged cultivation affects the properties of the BNC has received very little attention.

RESULTS Four strains were compared in 250-mL shake flasks. Strain DHU-ATCC-1 displayed the highest volumetric productivity, 0.56 g L-1 d(-1), and was then cultivated in a 400-mL STR, showing a similar productivity of 0.55 g L-1 d(-1). Scale-up using a 75-L STR pilot bioreactor resulted in enhancement of the BNC production rate from 0.056 g d(-1) in the shake flasks to 17.3 g d(-1) in the 75-L STR, although the productivity decreased to 0.43 g L-1 d(-1). During scale-up from shake flasks to 400-mL STR and further on to 75-L STR, the BNC fibers formed more bundles, whereas the fiber diameter decreased from 25.6 to 21.7 nm. The BNC from the 75-L STR exhibited a higher degree of polymerization, specifically 3230, higher degree of crystallinity, specifically 83%, larger crystallites, and improved strength including higher tensile energy absorption index and superior stretch at break.

CONCLUSION It is possible to enhance BNC production, and maintain or improve its properties when scaling up submerged cultivation in STRs.

Utilization of bacterial nanocellulose (BNC) for large-scale applications is restricted by low productivity in static cultures and by the high cost of the medium. Fiber sludge, a waste stream from pulp and paper mills, was enzymatically hydrolyzed to sugar, which was used for the production of BNC by the submerged cultivation of Komagataeibacter xylinus. Compared with a synthetic glucose-based medium, the productivity of purified BNC from the fiber sludge hydrolysate using shake-flasks was enhanced from 0.11 to 0.17 g/(L x d), although the average viscometric degree of polymerization (DPv) decreased from 6760 to 6050. The cultivation conditions used in stirred-tank reactors (STRs), including the stirring speed, the airflow, and the pH, were also investigated. Using STRs, the BNC productivity in fiber-sludge medium was increased to 0.32 g/(L x d) and the DPv was increased to 6650. BNC produced from the fiber sludge hydrolysate was used as an additive in papermaking based on the chemithermomechanical pulp (CTMP) of birch. The introduction of BNC resulted in a significant enhancement of the mechanical strength of the paper sheets. With 10% (w/w) BNC in the CTMP/BNC mixture, the tear resistance was enhanced by 140%. SEM images showed that the BNC cross-linked and covered the surface of the CTMP fibers, resulting in enhanced mechanical strength.

Background: Through pretreatment and enzymatic saccharification lignocellulosic biomass has great potential as a low-cost feedstock for production of bacterial nanocellulose (BNC), a high value-added microbial product, but inhibitors formed during pretreatment remain challenging. In this study, the tolerance to lignocellulose-derived inhibitors of three new BNC-producing strains were compared to that of Komagataeibacter xylinus ATCC 23770. Inhibitors studied included furan aldehydes (furfural and 5-hydroxymethylfurfural) and phenolic compounds (coniferyl aldehyde and vanillin). The performance of the four strains in the presence and absence of the inhibitors was assessed using static cultures, and their capability to convert inhibitors by oxidation and reduction was analyzed.

Results: Although two of the new strains were more sensitive than ATCC 23770 to furan aldehydes, one of the new strains showed superior resistance to both furan aldehydes and phenols, and also displayed high volumetric BNC yield (up to 14.78 ± 0.43 g/L) and high BNC yield on consumed sugar (0.59 ± 0.02 g/g). The inhibitors were oxidized and/or reduced by the strains to be less toxic. The four strains exhibited strong similarities with regard to predominant bioconversion products from the inhibitors, but displayed different capacity to convert the inhibitors, which may be related to the differences in inhibitor tolerance.

Conclusions: This investigation provides information on different performance of four BNC-producing strains in the presence of lignocellulose-derived inhibitors. The results will be of benefit to the selection of more suitable strains for utilization of lignocellulosics in the process of BNC-production.