Lignocellulosic bioethanol production from grasses pre-treated with acid mine drainage: Modeling and comparison of SHF and SSF

Acid mine drainage (AMD) was used for the pre-treatment of indigenous South African grass (Eragrostis curvula), and compared to H2SO4 (1 wt%) pre-treatment. The optimal pre-treatment duration were investigated and found to be 1 day for H2SO4 and 3 days for AMD pre-treatment. The optimal biomass solid loadings were found to be 20 wt% for both pre-treatment methods. Additionally, enzymatic hydrolysis and fermentation to produce ethanol were investigated for both separate hydrolysis and fermentation (SHF) and simultaneous saccharification and fermentation (SSF). In both SHF and SSF, the H2SO4 pre-treatment obtained higher concentrations of glucose/ethanol compared to AMD pre-treatment. The concentration of glucose/ethanol obtained using AMD pre-treatment was 70–80% of that achieved using H2SO4 pre-treatment. Empirical equations modeling the glucose/ethanol concentration in all processes were determined using a least squares method. Concentrations predicted by the models were found to have a high correlation (r2 = 0.87–0.99) to concentrations determined experimentally. © 2019 Elsevier Ltd