Egg shell powder: an inexpensive material for detoxification of sugarcane bagasse acid hydrolysate, cells immobilization agent and nutritional supplement for ethanol and xylitol production.

Abstract

Enhancing the sustainability of fermentation processes increasingly involves the reuse of bio-residues to replace synthetic reagents and reduce environmental impact, as well as the increase process yield and optimization reducing cost of process. This study investigates the integration of eggshell as a low-cost, renewable alternative in the production of second-generation (2G) ethanol and xylitol from sugarcane bagasse hydrolysates. Eggshell naturally comprises of about 97% calcium carbonate in its composition, besides being readily available due to the extensive consumption of eggs in various sectors. Applications of eggshell were evaluated across multiple process stages, including pretreatment, detoxification, cell immobilization, and nutritional supplementation. Eggshell proved effective in supporting fermentation, particularly due to its high calcium carbonate content and natural alkalinity, which contribute to pH regulation and nutrient supply. Using immobilized cells in flask-scale fermentations, ethanol and xylitol production yields (Y_P/S) of 0.21 and 0.20 g/g, and productivities (Q_P) of 0.09 and 0.31 g/L·h, respectively were achieved. Furthermore, eggshell proved to be successful to decrease concentrations of inhibitors molecules present in hemicellulosic hydrolysate derived from sugarcane bagasse in more than 90% of 5-HMF and furfural, besides of partial removal of other compounds such as syringaldehyde and ferulic acid. These results demonstrate the feasibility of using eggshell powder as a multifunctional additive, offering an environmentally friendly and cost-effective approach to improve the overall performance of 2 G ethanol and xylitol bioproduction.