Techno-economic feasibility of P(3-hydroxybutyrate) bioprocess with concentrated sugarcane vinasse as carbon and minerals source: an experimental and in silico approach

The Brazilian ethanol industry is very relevant in the global market; however, vinasse is generated in significant amounts and its management has become costly for distilleries. In this study, the aim was to evaluate vinasse as basal culture medium for P(3-hydroxybutyrate) (PHB) biosynthesis. Two bacterial strains were evaluated, a sucrose-consuming halophilic strain, Halomonas sp. HG03; and Ralstonia eutropha L359PCJ, which used glycerol from vinasse as carbon source. Firstly, shake flask bioprocesses analyzed cellular growth and PHB biosynthesis in vinasse-based media: in natura and concentrated vinasses were both evaluated in volumetric dilutions of 50% and 75% in mineral medium. Increasing vinasse concentration improved cellular growth rather than PHB accumulation for both bacteria. In vinasse-based treatments, Halomonas sp. HG03 had PHB content between 19.6 and 75.2% and R. eutropha L359PCJ, 48.4–68.5%. Further experiments in CSTR bioreactors used concentrated vinasse-based medium and R. eutropha L359PCJ had PHB content of 66.3%, concentration of residual cell dry weight (rCDW) = 9.4 g L⁻¹, PHB = 18.6 g L⁻¹, Y_X/S = 0.16 g_rCDW g_GLYCEROL⁻¹, Y_P/S = 0.32 g_PHB g_GLYCEROL⁻¹, and 0.25 g_PHB Lh⁻¹. Halomonas sp. HG03 had PHB content of 42.2%, rCDW = 10.2 g L⁻¹, PHB = 7.4 g L⁻¹ and Y_X/S = 0.22 g_rCDW g_SUCROSE⁻¹, Y_P/S = 0.16 g_PHB g_SUCROSE⁻¹ and 0.14 g_PHB Lh⁻¹. Finally, cost reductions by concentrated vinasse-based medium were evaluated. As glycerol source for PHB production by R. eutropha L359PCJ, vinasse reduced overall production costs by 22.2%. Unit production costs between US$ 2.8 and 5.4 kg_PHB⁻¹ were determined for scenarios that combined vinasse-based medium with high cell density culture and improvements of productivity. The investment payback times ranged from 1.6 to 4.5 years.