Sugar beet pulp as support for Saccharomyces cerivisiae immobilization in bioethanol production

Abstract

The potential of sugar beet pulp (SBP) and dried sugar beet pulp (DSBP) as economically cheap and renewable supports for immobilization of Saccharomyces cerevisiae cells was investigated. The hydrated supports showed similar cells retention capacities of 0.178±0.038g/g and 0.182±0.041g/g for SBP and DSBP, respectively. The DSBP-immobilized biocatalyst was used for repeated ethanol fermentation, because DSBP is more stable material. Yeast cells immobilization was confirmed by the scanning electron microscopy (SEM). Repeated batch ethanol fermentation of thick juice by yeast immobilized on hydrated DSBP was successfully carried out for at least seven successive cycles without any significant decrease in ethanol production, while in the case of molasses, after the third batch, significant decrease was observed. A maximum ethanol concentration of 52.26±2.0g/l and ethanol yield of 0.446±0.017g/g was achieved in the seventh fermentation batch of thick juice (initial sugar of 120g/l) with almost complete utilization of sugar (97.52±0.15%). The sugar beet thick juice was found to be more convenient industrial substrate for repeated batch ethanol fermentation than molasses and can be used without any nutrient supplementation. The production of bioethanol from sugar beet thick juice and molasses using DSBP-immobilized cell system enables one more opportunity for achieving the zero-waste goal, through a rational use of intermediate and by-products of sugar beet processing.