Effects of genetic modifications and fermentation conditions on 2,3-butanediol production by alkaliphilic Bacillus subtilis.

Two recombinants of alkaliphilic Bacillus subtilis LOCK 1086, constructed via different strategies such as cloning the gene encoding bacterial hemoglobin from Vitreoscilla stercoraria (vhb) and overexpression of the gene encoding acetoin reductase/2,3-butanediol dehydrogenase (bdhA) from B. subtilis LOCK 1086, did not produce more 2,3-butanediol (2,3-BD) than the parental strain. In batch fermentations, this strain synthesized 9.46 g/L in 24 h and 12.80 g/L 2,3-BD in 46 h from sugar beet molasses and an apple pomace hydrolysate, respectively. 2,3-BD production by B. subtilis LOCK 1086 was significantly enhanced in fed-batch fermentations. The highest 2,3-BD concentration (75.73 g/L in 114 h, productivity of 0.66 g/L × h) was obtained in the sugar beet molasses-based medium with four feedings with glucose. In a medium based on the apple pomace hydrolysate with three feedings with sucrose, B. subtilis LOCK 1086 produced up to 51.53 g/L 2,3-BD (in 120 h, productivity of 0.43 g/L × h).

Application of enzymatic apple pomace hydrolysate to production of 2,3-butanediol by alkaliphilic Bacillus licheniformis NCIMB 8059.

2,3-Butanediol (2,3-BD) synthesis by a nonpathogenic bacterium Bacillus licheniformis NCIMB 8059 from enzymatic hydrolysate of depectinized apple pomace and its blend with glucose was studied. In shake flasks, the maximum diol concentration in fed-batch fermentations was 113 g/L (in 163 h, from the hydrolysate, feedings with glucose) while in batch processes it was around 27 g/L (in 32 h, from the hydrolysate and glucose blend). Fed-batch fermentations in the 0.75 and 30 L fermenters yielded 87.71 g/L 2,3-BD in 160 h, and 72.39 g/L 2,3-BD in 94 h, respectively (from the hydrolysate and glucose blend, feedings with glucose). The hydrolysate of apple pomace, which was for the first time used for microbial 2,3-BD production is not only a source of sugars but also essential minerals.

Steam pretreatment of spruce forest residues: optimal conditions for biogas production and enzymatic hydrolysis.

Steam refining of non-debarked spruce forest residues was investigated as pretreatment for enzymatic hydrolysis as well as for biogas production. Pretreatment conditions were varied in the range of 190-220 °C, 5-10 min and 0-3.7% SO2 according to a statistical design. For both applications highest product yields were predicted at 220 °C and 2.4% SO2, whereas the reaction time had only a minor influence. The conformity of the model results allows the conclusion that enzymatic hydrolysis is a suitable test method to evaluate the degradability of lignocellulosic biomass in the biogas process. In control experiments under optimal conditions the results of the model were verified. The yield of total monomeric carbohydrates after enzymatic hydrolysis was equivalent to 55% of all theoretically available polysaccharides. The corresponding biogas yield from the pretreated wood amounted to 304 mL/gODM. Furthermore, furans produced under optimal process conditions showed no inhibitory effect on biogas production. It can be concluded that steam refining opens the structure of wood, thus improving the enzymatic hydrolysis of the polysaccharides to fermentable monomeric sugars and subsequently enabling a higher and faster production of biogas. Anaerobic fermentation of pretreated wood is a serious alternative to alcoholic fermentation especially when low quality wood grades and residues are used. Anaerobic digestion should be further investigated in order to diversify the biorefinery options for lignocellulosic materials.

Comparison of pretreatment methods for rye straw in the second generation biorefinery: effect on cellulose, hemicellulose and lignin recovery.

The increasing interest in lignocellulose-based biorefineries boosts the further development of the needed pretreatment methods for preprocessing biomass. There are a large number of different processes that are being investigated; however research is made mostly based on different types of biomass with the same pretreatment or several modifications of the same process for a given type of biomass. In this work a comparison of promising chemical pretreatments using the same biomass was performed. Organosolv (OS), Steam (SE) and Liquid-Hot-Water (LHW) processes were used for the pretreatment of rye straw and the treated solids further enzymatically hydrolyzed. Best results for carbohydrate and lignin yield were found for the OS pretreatment followed close by the LHW and SE with similar results. All of the processes showed satisfactory performance for the pretreatment of lignocellulosic biomass for application in the second generation biorefinery.

Steam refining as an alternative to steam explosion.

In steam pretreatment the defibration is usually achieved by an explosion at the end of the treatment, but can also be carried out in a subsequent refiner step. A steam explosion and a steam refining unit were compared by using the same raw material and pretreatment conditions, i.e. temperature and time. Smaller particle size was needed for the steam explosion unit to obtain homogenous slurries without considerable amounts of solid chips. A higher amount of volatiles could be condensed from the vapour phase after steam refining. The results from enzymatic hydrolysis showed no significant differences. It could be shown that, beside the chemical changes in the cell wall, the decrease of the particle size is the decisive factor to enhance the enzymatic accessibility while the explosion effect is not required.