Fossil fuels are still major energy sources, but the search for renewable energy sources has been encouraged. Bioethanol has been recognized as an alternative to fossil fuels and nowadays it represents more than 90% of the global biofuel production. Bioethanol production from raw sugar beet cossettes as a semi-solid substrate was studied. The study was carried out in the horizontal rotating tubular bioreactor (HRTB) with Saccharomyces cerevisiae as a microbial production strain. The impact of different combinations of HRTB operational parameters such as, rotation speed (5-15 min), rotation type [constant or interval (3-15 min h)] and working volume (ratio V /V = 0.2-0.7) on the bioethanol production was examined. In this study, the highest bioprocess efficiency parameters ([Formula: see text] = 0.47 g g, E = 87.36% and Pr = 0.618 g L h) were observed at 0.20 V /V, interval rotation of 12 min h and rotation speed of 15 min. It has to be pointed out that bioethanol production efficiency in the HRTB was on the similar level as observed by bioethanol production from the raw sugar beet juice. Naturally present microorganisms of sugar beet could have a significant impact on bioethanol production. Higher yeast inoculation rate could reduce contaminant activities and, consequently, the bioethanol production efficiency would be improved.

Alternative to the use of fossil fuels are biofuels (e.g., bioethanol, biodiesel and biogas), which are more environmentally friendly and which can be produced from different renewable resources. In this investigation, bioethanol production from raw sugar beet cossettes (semi-solid substrate) by yeast Saccharomyces cerevisiae in a horizontal rotating tubular bioreactor (HRTB) was studied. Obtained results show that HRTB rotation mode (constant or interval) and rotation speed have considerable impact on the efficiency of bioethanol production in the HRTB. The main goal of this research was to develop a non-structural mathematical model of bioethanol production from raw sugar beet cossettes in the HRTB. The established mathematical model of bioethanol production in the HRTB describes substrate utilization and product formation (glycerol, ethanol and acetate) and presumes negative impact of high substrate concentration on the working microorganism (substrate inhibition) by using Andrews inhibition kinetics. All simulations of bioethanol production in the HRTB were performed by using Berkeley Madonna software, version 8.3.14 (Berkeley Madonna, Berkeley, CA, USA). The established non-structural bioprocess model describes relatively well the bioethanol production from raw sugar beet cossettes in the HRTB.

Various fungal species can degrade lignocellulolytic materials with their enzyme cocktails composed of cellulolytic and lignolytic enzymes. In this work, seven fungal species (Mucor indicus DSM 2185, Paecilomyces variotii CBS 372.70, Myceliophthora thermophila CBS 663.74, Thielavia terrestris CBS 456.75, Botryosphaeria dothidea JCM 2738, Fusarium oxysporum f.sp. langenariae JCM 9293, and Fusarium verticillioides JCM 23107) and four nutrient media were used in the screening for effective lignocellulose degrading enzymes. From the seven tested fungi, F. oxysporum and F. verticilliodes, along with nutrient medium 4, were selected as the best medium and producers of lignocellulolytic enzymes based on the determined xylanase (>4 U mg−1) and glucanase activity (≈2 U mg−1). Nutrient medium 4 supplemented with pretreated corn cobs was used in the production of lignocellulolytic enzymes by sequential solid-state and submerged cultivation of F. oxysporum, F. verticilliodes, and a mixed culture of both strains. F. oxysporum showed 6 times higher exoglucanase activity (3.33 U mg−1) after 5 days of cultivation in comparison with F. verticillioides (0.55 U mg−1). F. oxysporum also showed 2 times more endoglucanase activity (0.33 U mg−1). The mixed culture cultivation showed similar endo- and exoglucanase activities compared to F. oxysporum (0.35 U mg−1; 7.84 U mg−1). Maximum xylanase activity was achieved after 7 days of cultivation of F. verticilliodes (≈16 U mg−1), while F. oxysporum showed maximum activity after 9 days that was around 2 times lower compared to that of F. verticilliodes. The mixed culture achieved maximum xylanase activity after only 4 days, but the specific activity was similar to activities observed for F. oxysporum. It can be concluded that both fungal strains can be used as producers of enzyme cocktails for the degradation of lignocellulose containing raw materials, and that corn cobs can be used as an inducer for enzyme production.

The biomass of the bacterium Azotobacter chroococcum can be used as a biofertilizer due to its ability to fix nitrogen from the atmosphere. In order to optimize the production of bacterial biomass for this purpose, a cultivation of A. chroococcum was done by using different media and cultivation techniques (batch, fed batch and repeated batch). Chemically defined and complex media with 20 g/l of sugar were selected as the most appropriate media for batch cultivation in stirred tank bioreactor. In order to obtain higher fed batch and repeated batch techniques were examined. During these cultivations, increase of bioprocess efficiency parameters (yield coefficient and productivity) were observed compared with the batch cultivation. On the basis of the obtained results, repeated batch technique appeared to be the most suitable for the bacterial biomass production at industrial scale.

Brewers’ spent grains (BSG) are a by-product of the brewing industry that is mainly used as feedstock; otherwise, it has to be disposed according to regulations. Due to the high content of glucose and xylose, after pretreatment and hydrolysis, it can be used as a main carbohydrate source for cultivation of microorganisms for production of biofuels or biochemicals like 2,3-butanediol or lactate. 2,3-Butanediol has applications in the pharmaceutical or chemical industry as a precursor for varnishes and paints or in the food industry as an aroma compound. So far, Klebsiella pneumoniae, Serratia marcescens, Clostridium sp., and Enterobacter aerogenes are being used and investigated in different bioprocesses aimed at the production of 2,3-butanediol. The main drawback is bacterial pathogenicity which complicates all production steps in laboratory, pilot, and industrial scales. In our study, a gram-positive GRAS bacterium Paenibacillus polymyxa DSM 742 was used for the production of 2,3-butanediol. Since this strain is very poorly described in literature, bacterium cultivation was performed in media with different glucose and/or xylose concentration ranges. The highest 2,3-butanediol concentration of 18.61 g l–1 was achieved in medium with 70 g l–1 of glucose during 40 h of fermentation. In contrast, during bacterium cultivation in xylose containing medium there was no significant 2,3-butanediol production. In the next stage, BSG hydrolysates were used for bacterial cultivation. P. polymyxa DSM 742 cultivated in the liquid phase of pretreated BSG produced very low 2,3-butanediol and ethanol concentrations. Therefore, this BSG hydrolysate has to be detoxified in order to remove bacterial growth inhibitors. After detoxification, bacterium cultivation resulted in 30 g l–1 of lactate, while production of 2,3-butanediol was negligible. The solid phase of pretreated BSG was also used for bacterium cultivation after its hydrolysis by commercial enzymes. In these cultivations, P. polymyxa DSM 742 produced 9.8 g l–1 of 2,3-butanediol and 3.93 g l–1 of ethanol. On the basis of the obtained results, it can be concluded that different experimental setups give the possibility of directing the metabolism of P. polymyxa DSM 742 toward the production of either 2,3-butanediol and ethanol or lactate.