Valorization of Activated Carbon as a Reusable Matrix for the Immobilization of Aspergillus oryzae Whole-Cells Expressing Fusarium heterosporum Lipase toward Biodiesel Synthesis

The biomass-derived source, low-cost and hydrophobicity/oleophilic advantages of activated carbon (AC) were explored for the immobilization of Aspergillus oryzae whole-cells expressing Fusarium heterosporum lipase. The adsorptive influence of AC favored growth of the cells into its porous interfaces with paralleled exterior dense film formation. Increasing AC weights hindered extracellular lipase activity. Cell aggregation of 0.34 ± 0.02 mg/BSP was found to be effective in catalyzing an industrially challenging feedstock (68.77% w/w free fatty acids, 20.48% w/w triglycerides) to 98% fatty acid methyl esters (FAME). In a comparative investigation with polyurethane as matrix, higher trans/esterification facilitation was observed with AC. Benefiting from the oleophilicity of AC; denaturation effect from methanol on the lipases was reduced. Surface characterization with FE-SEM, XPS and FT-IR evidenced effective cell-matrix adhesion and a retention of the AC's intrinsic properties. The advantageous tribology of AC ensured recyclability of the matrix for fresh cells immobilization. Comparable FAME (98.08% w/w) was achieved with the recycled matrix in successive batches. The spent-matrix valorization approach, thus, proposes sustainable biorefineries with immobilized lipase catalyzed biodiesel production.