Development of cell recycle technology incorporating nutrient supplementation for lignocellulosic ethanol fermentation using industrial yeast Saccharomyces cerevisiae

Abstract

For the efficient production of lignocellulosic ethanol, a technology of recycling yeast cells at a high-solid load was developed. The yeast Saccharomyces cerevisiae TJ14 grew up to 5.0 × 107 cells/mL at 39 °C during the simultaneous saccharification and fermentation of hydrothermally pretreated rice straw. By exploiting the viability of the cells, a portion of the fermentation residue was recycled, yielding 52.3 g/L ethanol (90.3% yield) at 1.12 g/(L·h) in six batches. This result is attributable to the maintenance of a viable cell count (cells/mL) on the order of 107. In accordance with this principle, the effects of low-cost nutrients on yeast recycling were elucidated, where 0.125% corn steep liquor was deemed sufficient for fermenting rice straw and empty fruit bunch hydrolysates. The supplementation of sugarcane molasses into bagasse was found to be a practical approach, resulting in 63.5–67.7 g/L ethanol and 5.3 × 106–4.4 × 107 cells/mL in six batches. Here, we describe that the high cell-growth potential in industrially relevant media minimizes the retention of lignocellulosic residues in subsequent batches, thus eliminating the problematic operations in yeast recycling.