Use of discards of bovine bone, yeast and carrots for producing second generation bio-ethanol

Abstract

Abstract The reutilization of agroindustrial wastes for the production of new products is an attractive option for reducing environmental pollution, generating value-added products and decreasing costs. Slaughterhouse discard bovine bone, brewery discard yeast and carrot discards from the Santa Fe province (Argentina) were used for producing ethanol. Bovine bone and yeast provided the support and active phase for fermentation biocatalysts while carrot discards were a sugar source. Discard bovine bone was collected directly from a slaughterhouse and then subjected to extraction with acetone for removing lipids and blood traces. Both uncalcined and heat-treated bovine bone (calcined for 2 h at 400, 600 and 800 °C) were studied. Uncalcined bovine bone had a suitable pore structure for yeast immobilization and a suitable mechanical resistance for being used in stirred tanks. Two different strains of Saccharomyces cerevisiae were immobilized and tested. One was a brewery yeast discarded from a local beer brewery and the other one a commercial yeast. The biocatalysts thus obtained were subjected to a thermal treatment at 35 °C for 72 h in order to dehydrate cells and form adhesins. The activity of the biocatalysts was tested in the fermentation of carrot discards. The maximum concentration of the obtained ethanol was 11.98 g L−1. It was possible to reuse the biocatalysts for 11 reaction cycles. The possibility of regenerating the biocatalyst bone support by ultrasound is an advantage of this kind of material in comparison to common gel supports.