Development of a sustainable bioprocess for polyhydroxyalkanoate (PHA) production from biodiesel-derived crude...

Crude glycerol, a low-value byproduct of biodiesel production, contains impurities that pose disposal challenges. Hence, its valorization into value-added products like polyhydroxyalkanoates (PHAs) offers sustainable and cost-effective route for waste management. In this study, pure, purified (soap-free) and crude (soap-containing) glycerol were investigated as carbon substrates for PHA production using Cupriavidus necator NCIMB 11599. During shake flask experiments using 8 g carbon/L of medium, crude glycerol resulted in the highest biomass concentration (5.43 g/L) and PHA content (49.7% w/w) compared to pure (3.91 g/L; 41% w/w) and purified glycerol (4.03 g/L; 40% w/w). Increasing crude glycerol concentrations to 12-20 g/L led to growth inhibition and reduced PHA synthesis. Batch fermentation with optimized concentration of crude glycerol (8 g C/L) increased the biomass to 7.09 g/L and PHA content to 61.33% (w/w), yielding a PHA concentration of 4.35 g/L and a global yield of 0.43 g PHA/g carbon consumed. To further enhance the biomass and PHA concentration, fed-batch strategy was implemented with nutrient-rich feeding until 24 h followed by nutrient-limitation to promote PHA accumulation. This approach resulted in a biomass concentration of 25.55 g/L, PHA content of 80.18% (w/w) and PHA concentration of 20.49 g/L at 96 h. An improved PHA yield of 0.58 g of PHA/g of carbon consumed was obtained. Overall, the study demonstrates that soap-rich crude glycerol can serve as an efficient and cost-effective substrate for PHA production and establishes an optimized fed-batch strategy that significantly enhances the yields and productivity for biodiesel-waste valorization.