Statistical optimization of pretreatment of orange processing waste using response surface methodology for bioethanol production

This study aims to maximize total sugar yield of two varieties of sweet orange processing waste OPW: Valencia Late and Double fine. They were collected from two different Algerian juice factories. The initial total sugar yield of both varieties was 49.33 +/- 0.78% and 44.04 +/- 1.32%, respectively. Therefore, statistical optimization of the pretreatment of orange processing waste powder OPWP was established using sulfuric acid and steam explosion to achieve a high-level rate of total sugar from OPWP. The acid hydrolysis steam explosion used in this study due of its efficiency and simplicity. The hydrolysis factors, such as acid (0.25%, 0.50% and 0.75%), solid loading (2%, 6% and 10%) and time (10 min, 20 min and 30 min), were further optimized using response surface methodology. Results revealed that the yield of total sugar was 74.57% and 70.70% dry weight for Valencia Late and Double fine respectively. The optimized conditions were obtained by 0.5% v/v acid, 2% w/v OPWP and 20 min residence time. The derived regression model shows a strong positive relationship between the obtained yield and the variables with a coefficient of determination (R-2) values of 0.9219 and 0.9367 for Valencia Late and Double fine, respectively. Furthermore, scanning electron microscopy, Fourier transform infrared, X-ray diffraction and thermogravimetric analysis for comparison of untreated and pretreated material confirms that the pretreatment is a crucial step to enhance the total sugar yield, solubilize hemicellulose and remove lignin. These results appear to be a promising source of carbohydrates for producing bioethanol.