Development of an Integrated Bioprocess System for Bioethanol and Arabitol Production from Sugar Beet Cossettes

Abstract

Research background: An innovative integrated bioprocess system for bioethanol production from raw sugar beet cossettes (SBC) and arabitol from remaining exhausted sugar beet cossettes (ESBC) was studied. This integrated three-stage bioprocess system is an example of the biorefinery concept to maximise the use of raw SBC for the production of high value-added products such as sugar alcohols and bioethanol.

Experimental approach: The first stage of the integrated bioprocess system was simultaneous sugar extraction from SBC and its alcoholic fermentation to produce bioethanol in an integrated bioreactor system (vertical column bioreactor and stirred tank bioreactor) containing a high-density suspension of yeast Saccharomyces cerevisiae (30 g/L). The second stage was the pretreatment of ESBC with dilute sulfuric acid to release fermentable sugars. The resulting liquid hydrolysate of ESBC was used in the third stage as a nutrient medium for arabitol production by non-Saccharomyces yeasts (Spathaspora passalidarum CBS 10155 and Spathaspora arborariae CBS 11463).

Results and conclusions: The obtained results show that the efficiency of bioethanol production increased with increasing temperature and prolonged residence time in the integrated bioreactor system. The maximum bioethanol production efficiency (87.22 %) was observed at a time of 60 min and a temperature of 36 °C. Further increase in residence time (above 60 min) did not result in the significant increase of bioethanol production efficiency. Weak acid hydrolysis was used for ESBC pretreatment and the highest sugar yield was reached at 200 °C and residence time of 1 min. The inhibitors of the weak acid pretreatment were produced below bioprocess inhibition threshold. The use of the obtained liqiud phase of ESBC hydrolysate for the production of arabitol in the stirred tank bioreactor under constant aeration clearly showed that S. passalidarum CBS 10155 with 8.48 g/L of arabitol (Y_P/S=0.603 g/g and bioprocess productivity of 0.176 g/(L^.h)) is a better arabitol producer than Spathaspora arborariae CBS 10155.

Novelty and scientific contribution: An innovative integrated bioprocess system for the production of bioethanol and arabitol was developed based on the biorefinery concept. This three-stage bioprocess system shows great potential for maximum use of SBC as a feedstock for bioethanol and arabitol production and it could be an example of a sustainable 'zero waste' production system.

Keywords: acid pretreatment; arabitol; bioethanol; biorefinery concept; integrated bioprocess system; sugar beet cossettes.

Fig. 1

Concentrations of: a) glucose and b) fructose during simultaneous extraction and fermentation of raw sugar beet cossettes (SBC). Bioprocess was performed by continuous extraction of SBC using yeast suspension (x=30 g/L) at three different temperatures and four different medium residence times in the integrated bioreactor system

Fig. 2

Concentrations of: a) ethanol, b) glycerol and c) acetate during simultaneous extraction and fermentation of raw sugar beet cossettes (SBC). Bioprocess was performed by continuous extraction of SBC using yeast suspension (x=30 g/L) at three different temperatures and four different medium residence times in the integrated bioreactor system

Fig. 3

Concentration profiles during cultivation of Spathaspora passalidarum CBS 10155 in the stirred tank bioreactor (STR) on the weak acid exhausted sugar beet cossette (ESBC) hydrolysate

Fig. 4

Concentration profiles during cultivation of yeast Spathaspora arborarie CBS 11463 in the stirred tank bioreactor (STR) on the weak acid exhausted sugar beet cossette (ESBC) hydrolysate

Fig. S1

Scheme of an integrated bioprocess system for bioethanol and arabitol production from sugar beet cossettes. ESBC=exhausted sugar beet cossettes