Mixed glycerol and orange peel-based substrate for fed-batch microbial biodiesel production
Eleonora Carota, Maurizio Petruccioli, AlessandroD'Annibale, Silvia Crognale
Department for Innovation in Biological, Agro-food and Forest Systems (DIBAF), University of Tuscia, Via S. Camillo De Lellis snc, 01100, Viterbo, Italy.
The aqueous extraction of orange peel waste (OPW), the byproduct of the juice extraction process generated annually in massive amounts (21 Mton), yields a carbohydrate-rich liquid fraction, termed orange peel extract (OPE). Several studies highlight that the combination of glycerol, a biodiesel byproduct, with carbohydrate mixtures might boost microbial lipid production. This study performed first a shaken flask screening of 15 oleaginous yeast strains based on their growth and lipid-producing abilities on OPE- and glycerol-based media. This screening enabled the selection of R. toruloides NRRL 1091 for the assessment of the process transfer in a stirred tank reactor (STR). This assessment relied, in particular, on either single- and double-stage feeding fed-batch (SSF-FB and DSF-FB, respectively) processes where OPE served as the primary medium and nitrogen-containing glycerol-OPE mixtures as the feeding one. The continuous supply mode at low dilution rates (0.02 and 0.01 h-1 for SSF-FB and DSF-FB, respectively) starting from the end of the exponential growth of the initial batch phase enabled the temporal extension of biomass and lipid production. The SSF-FB and DSF-FB processes attained high biomass and lipid volumetric productions (LVP) and ensured significant lipid accumulation on a dry cell basis (YL/X). The SSF-FB process led to LVP of 20.6 g L-1 after 104 h with volumetric productivity (rL) of 0.20 g L-1 h-1 and YL/X of 0.80; the DSF-FB process yielded LVP, rL and YL/X values equal to 15.92 g L-1, 0.11 g L-1 h-1 and 0.65, respectively. The fatty acid profiles of lipids from both fed-batch processes were not significantly different and resembled that of Jatropha oil, a vastly used feedstock for biodiesel production. These results suggest that OPE constitutes an excellent basis for the fed-batch production of R. toruloides lipids, and this process might afford a further option in OPW-based biorefinery.
Keywords: Biotechnology, Microbiology, Waste treatment, Green engineering, Sustainable development, Microbial biotechnology, Biofuel, Orange peel waste, Biodiesel, Fed-batch process, Rhodosporidium toruloides, Oleaginous yeasts, Circular economy.