Utilization of Seawater for the Biorefinery of Lignocellulosic Biomass: Ionic Liquid Pretreatment, Enzymatic Hydrolysis, and Microbial Lipid Production

The biorefineries of lignocellulosic biomass have attracted increasing interest recently. However, large water consumption in the large-scale biorefineries remains a major problem. In this work, utilization of abundant seawater as an alternative to freshwater for ionic liquid (IL) pretreatment of lignocellulosic biomass was reported for the first time. In addition, enzymatic hydrolysis of IL-pretreated biomass and microbial lipid production from wheat straw hydrolysate were conducted in seawater. It was found that seawater had no significantly negative effect on enzymatic hydrolysis as well as IL pretreatment. After grass lignocelluloses were pretreated by 50% cholinium IL–seawater mixtures at 90 °C for 6 h and washed by seawater, the residues became highly susceptible to enzymatic hydrolysis; the reducing sugar yields of 54–72% were obtained in pH 4.8 seawater in the subsequent enzymatic hydrolysis of the residues. The lipid yield of 4.5 g/L and lipid coefficient of 0.21 g/g of sugar were achieved after cultivation of Trichosporon fermentans on wheat straw hydrolysate with the sugar concentration of approximately 30 g/L for 3 days.