Single-Factor Screening and Response Surface Optimization of Co-Culture Simultaneous Saccharification and Fermentation of Rice Husk (Oryza sativa cv. Ciherang) for Bioethanol Production

Rice husk is an abundant agricultural residue in Indonesia and represents a promising non-food lignocellulosic feedstock for second-generation bioethanol.This study investigated the production of bioethanol from rice husk (Oryza sativa cv.Ciherang) through simultaneous saccharification and fermentation (SSF) using Aspergillus niger and Saccharomyces cerevisiae.Rice husk was pretreated with 2 M NaOH at ambient temperature to disrupt the lignocellulosic matrix and improve substrate accessibility prior to simultaneous saccharification and fermentation.Singlefactor experiments were first conducted to evaluate the effects of fermentation time, pH, temperature, and starter concentration on ethanol yield.Response Surface Methodology (RSM) employing a Central Composite Design (CCD) with 31 experimental runs was subsequently used to optimize the SSF process.The quadratic model produced a high coefficient of determination (R² = 0.9575) and a non-significant lack-of-fit, indicating excellent model adequacy.Temperature and fermentation time were identified as the most influential factors, while quadratic effects were significant for all variables, confirming the nonlinear behavior of the system.The stationary point of the response surface was located at 98.80 h, pH 5.18, 42.38 °C and 2.07 mL of each starter, at which the ethanol concentration reached 9.08 ± 0.63% (v/v).This study demonstrates the potential of rice husk valorization through SSF and highlights the effectiveness of RSM for optimizing multivariable bioethanol processes.