Statistical optimization and kinetic study of biofuel production from wastes fruits by saccharification and fermentation

This study is to evaluate Washington fruits for the production of ethanol. Using design of experiments (DOE) under full factorial design (2n), a simultaneous fermentation and saccharification process has been modeled and optimized. Furthermore, Logistic and modified Gompertz models were utilized to test the kinetic study under optimal conditions. Batch studies were performed to investigate the impact of operational parameters: temperature (30–40 °C), pH (3–4), and substrate concentration (100–300 g/L) in order to maximize the production of bioethanol by using full factorial design (2n). A maximum bioethanol degree was obtained under the optimum process circumstances of 40 °C (temperature), 4 (pH) and 300 g/L (substrate concentration) where the model prediction is in good agreement with experimental result (R2 = 0.9999, Adj-R2 = 0.9997 and Pred-R2 = 0.9978). ANOVA results indicated that the process was extensively affected by pH and substrate concentration, while the temperature depicted a negative effect. The investigation of cell growth kinetics revealed that the maximal cell biomass concentration (Xmax) was 6.84 g/L, and the maximum specific growth rate (μmax) was 0.17 h−1. Using the modified Gompertz model, the maximum bioethanol concentration (Pm) and maximum bioethanol production rate (rp,m) of 47.01 g/L and 0.9 g/L/h, sequentially, were obtained. Under optimal conditions, the best bioethanol degree (>99°), refractive index (1.3615), density (0.7988), were obtained. The analysis by Fourier transform infrared spectroscopy (FTIR) and gas chromatography (GC) have confirmed the good quality of the produced bioethanol, and this latter has a lower heating value (LHV) of 25.5 MJ/kg and an energy yield of 20.37 MJ/L. These results provide valuable insights into process design for large-scale operations and showed the potential of washingtonia fruits valorization for bioethanol production showcasing their advantageous use as biofuel.