Mitigating the negative impact of soluble and insoluble lignin in biorefineries

The presence of inhibitors is still an economic bottleneck that needs to be resolved in order to make the biorefineries feasible, requiring the development of technologies capable of improving their competitiveness in the biofuel marketplace. Soluble and insoluble lignin can impair the enzymatic hydrolysis process by inhibition, deactivation, and unproductive adsorption of enzymes. Washing the pretreated biomass or using lignin-blocking additives during saccharification could mitigate these negative effects in future biorefineries. Here, an investigation was performed of the combined mitigation processes, in terms of their technical and economic feasibility in an integrated first and second generation (1G2G) sugarcane biorefinery. Evaluation was made of the impacts of biomass washing and soybean protein addition, separately or in combination, on glucose yields for enzymatic hydrolysis in the presence of high (liquor) and low (buffer) concentrations of soluble inhibitors/deactivators. Combining washing and soybean protein addition provided the highest glucose yields, with an increase of up to 50%. The effect of the mitigation processes could be explained by a combination of catalytic mechanisms acting on both soluble and insoluble lignin. In an industrial context, biomass washing (90 °C, 15% (w/w) solids, 3 steps) followed by soybean protein addition (12% (w/v) solids) provided a cost-competitive methodology for bioethanol production, with an estimated net present value of US$ 9.16 × 107, optimizing hydrolysis process in the 1G2G sugarcane biorefinery.