Enzymatic pretreatment of algal biomass has different optimal conditions for biogas and bioethanol routes.

Enzymatic pretreatment is emerging as an efficient tool for the extraction of biofuel precursors from algal biomass. However, yardsticks for end-use directed selection of optimal pretreatment conditions are not yet identified. The present study, for the first time, reveals different optimal conditions for algal biomass solubilization and sugar release. Algal biomass pretreatment optimization was carried out using the Taguchi method. Crude enzyme from Aspergillus fischeri was found effective for pretreatment of Chlorella pyrenoidosa. Maximum sugar yield (190 mg g−1 biomass) from algal biomass was observed at a substrate concentration of 4 g L-1, with a 5% enzyme load at temperature 60°C, pH 5.5, and shaking speed of 80 rpm. In contrast, maximum sCOD (1350 mg g−1 biomass) was obtained at 2 g L−1 substrate concentration with enzyme load of 20% v/v, at 60°C, pH 4, and shaking speed of 100 rpm. Hence, the first set of conditions would be more beneficial for bioethanol production. Whereas another set of conditions would improve the biofuel production that requires maximum solubilization of algal biomass, such as fermentative methane production. Overall, the present observations established that process conditions required for enzymatic pretreatment of algal biomass should be selected according to the desired biofuel type. [Display omitted] • Rhizopus oryzae, Aspergillus sp. and Aspergillus fischeri were tested for enzymatic activity. • Maximum enzyme activity of 0.343 FPU ml−1 was seen in A. fischeri. • Key parameters for microalgae pretreatment were optimized using Taguchi Method. • Enzymatic pretreatment conditions are crucial to obtain desired biofuel type. • A mechanism for the recovery of optimal COD/sugar release was proposed. [ABSTRACT FROM AUTHOR]