Integrated Bioethanol Production and Energy Recovery from Sugarcane Waste: Predictive Modeling Under Constraints on the National Sugar Supply

Decarbonizing transport in agro-exporting economies requires tools that couple biofuel production with by-product valorization without displacing food. This study extends a low-data predictive model of sugarcane by-product bioenergy with three ethanol pathways—direct juice fermentation (1G-A), flexible sugar–ethanol production (1G-B) and simultaneous saccharification and fermentation of bagasse (2G)—coupled to anaerobic digestion, and applies it to Peru, a structurally net sugar-importing sector. The research question is how much fuel ethanol such a sector can supply without reducing its commercial sugar output, and which route carries that supply with the least sensitivity to the sugar balance. The sugar-preserving allocation coefficient fjuicemax,SP is derived in closed form and shown to depend on the industrial configuration mix only through the aggregate sucrose diverted. The sugar reference is the 2011–2018 mean of the official series, the same window as the cane baseline, and the recovery chain is calibrated on that pair (λ∗=0.9604). The 1G-A cascade reproduces the nominal capacity ratio of the only Peruvian juice-to-ethanol plant within 1.24%, a design-level benchmark rather than an industrial validation; the 2G coefficient (254.9 L t−1 dry bagasse) agrees within 10% with an independent process simulation but remains unvalidated for Peruvian bagasse. Without productive growth the constraint is exactly binding: no juice can be diverted and the 2030 potential is 297 ML yr−1 from residual molasses and bagasse, rising to 498 and 731 ML yr−1 under 2.5% and 5% annual cane growth, with 790–1231 GWh yr−1 of cogenerated electricity as a gross upper bound. Single-year sugar references move the no-growth margin between 0 and 0.067; the 0.104 of an earlier formulation is an artefact of pairing an uncalibrated recovery chain with the lowest year of the series. Analytically, the constrained yield is a hinge function of cane sucrose content with an 8.3-fold slope change where domestic sugar demand is met, and the elasticity of the diversion margin to every multiplicative input of the sugar balance equals (1−f)/f. This structure explains why sucrose content governs 85–90% of the flexible-pathway variance, why the null-margin probability is 52% at the binding point, and why, within the model, the lignocellulosic route is least exposed to the sugar balance, its absolute level remaining conditional on the transferability of the 2G coefficient.