A circular bioeconomy concept: Enhanced bioconversion of crude glycerol into 1,3-PDO production by immobilized Clostridium butyricum JKT 37

Aligning with Sustainable Development Goal 12, National Biomass Action Plan 2023–2030 and the transition of carbon-emission-intensive development to low-carbon solutions, this research proposes a circular bioeconomy concept that utilizes byproduct of the biodiesel industry to create high-value 1,3-propanediol (1,3-PDO). There are limited studies on the bioconversion of biodiesel-derived glycerol into 1,3-PDO via the immobilized cell biocatalysis route. In this study, the production of 1,3-PDO was enhanced by the wild-type Clostridium butyricum JKT 37 immobilized on the coconut shell activated carbon (CSAC) as supporting material using the acidic-pretreated glycerol as a carbon source. Among various mesh sizes of CSAC tested, 6–12 mesh immobilization material had enhanced cell density by about 94.43% compared to the suspended cell system. The immobilized cell fermentation using pretreated glycerol produced 8.04 ± 0.34 g/L 1,3-PDO with 0.62 ± 0.02 mol/mol of yield, 15.81% and 27.78% higher than the control, respectively. Five repeated batches of immobilized cell fermentation had resulted in the average 1,3-PDO titer, yield, and productivity of 16.40 ± 0.58 g/L, 0.60 ± 0.03 mol/mol, and 0.68 ± 0.02 g/L.h, respectively, with the biochemical equation of \({\text{C}}_{{3}} {\text{H}}_{{8}} {\text{O}}_{{2}} + \, 0.{\text{18NH}}_{{3}} \to 0.{6}0{\text{C}}_{{3}} {\text{H}}_{{8}} {\text{O}}_{{2}} + \, 0.0{\text{6C}}_{{4}} {\text{H}}_{{8}} {\text{O}}_{{2}} + \, 0.0{\text{4C}}_{{2}} {\text{H}}_{{4}} {\text{O}}_{{2}} + \, 0.{\text{18C}}_{{4}} {\text{H}}_{{7}} {\text{O}}_{{2}} {\text{N }} + \, 0.{\text{93H}}_{{2}} {\text{O }} + \, 0.{\text{16CO}}_{{2}}\) ${\text{C}}_3{\text{H}}_8{\text{O}}_2+0.{\text{18NH}}_3\to 0.60{\text{C}}_3{\text{H}}_8{\text{O}}_2+0.0{\text{6C}}_4{\text{H}}_8{\text{O}}_2+0.0{\text{4C}}_2{\text{H}}_4{\text{O}}_2+0.{\text{18C}}_4{\text{H}}_7{\text{O}}_2\text{N}+0.{\text{93H}}_2\text{O}+0.{\text{16CO}}_2$ . The metabolism pathway gradually shifted to a reductive branch when immobilized cells were reused in repeated batch fermentation, proven by the reduction in organic acid formation, increased ratio of 1,3-PDO-to-total organic acids, and experimental stoichiometry. An inclusive investigation on the variations of glycerol source and their impact on the carbonized immobilizer performance was conducted.