Integrated kinetic modeling of batch and fed-batch high-solids simultaneous saccharification and fermentation for ethanol production from pretreated oil palm trunk under different feeding strategies.

High-solids lignocellulosic ethanol production can increase ethanol concentration, but is often limited by poor mass transfer, reduced enzyme accessibility, and ethanol inhibition. This study evaluated batch and fed-batch simultaneous saccharification and fermentation (SSF) for ethanol production from pretreated oil palm trunk (OPT) and developed an integrated kinetic model. Batch SSF at 5% (w/v) solids established reference kinetics and verified model structure. Four fed-batch strategies were tested at 23% (w/v) final solids by varying initial feeding time and feeding interval. The model described glucose, ethanol, and biomass dynamics by integrating microbial growth, ethanol formation, and two-phase hydrolysis kinetics, with a feeding input term in the substrate balance. Time-course glucose, ethanol, and biomass data were used for fitting and validation. The fed-batch model reproduced experimental profiles across all cases, with R2 > 0.97. Feeding interval significantly affected ethanol concentration and residual glucose (p < 0.05), whereas initial feeding time was not significant. An 8 h feeding interval with the first 3% (w/v) substrate addition at 6 h (Case II) gave the highest ethanol concentration (58.60 ± 1.54 g/L) and productivity (0.70 ± 0.02 g/L/h). In contrast, a 6 h feeding interval with the first 3% (w/v) substrate addition delayed to 12 h (Case III) gave the lowest productivity (0.58 ± 0.01 g/L/h). Elasticity analysis indicated that ethanol inhibition, maximum specific growth rate, and slow hydrolysis controlled ethanol formation at high solids. These results identify feeding interval as a critical operational variable and support an integrated mechanistic framework for fed-batch SSF design.