Response surface optimization of ammonium sulfite pretreatment for fermentable sugar production from wheat straw

Abstract

The development of a clean and sustainable pretreatment is of great importance for the production of fermentable sugars. In this study, an ammonium sulfite (AS) pretreatment of wheat straw was optimized based on response surface methodology with a three-level, three-factor Box-Behnken design. The investigated factors were AS dosage, pretreatment time, and pretreatment temperature. The effectiveness of the AS pretreatment was evaluated using the standard enzymatic hydrolysis procedure. A second-order polynomial fit was performed to fit the experimental data, and the model analysis showed that the effect of the AS dosage on the final total sugar yields was much more significant than that of the other two factors. Under the optimum pretreatment conditions (27% of the AS dosage (based on the dry wheat straw) at 160 ºC for 63 min), the final total sugar yield achieved was 74.4% after saccharification, which was in agreement with the predicted value (76.5%). Furthermore, it was found that pre-impregnation with acetic acid before AS pretreatment or the post-mechanical refining after AS pretreatment could further increase the fermentable sugar yields to approximately 77%. In addition, the spent liquor containing nitrogen could be used for the production of lignin-based fertilizer, thus making the whole process clean and sustainable.

Delignification of Wheat Straw Using DES-like Mixtures

“…The stretching of the aromatic core in lignin is observed at peaks with the value 1595 and 1510 cm −1 . These signals describe the aromatic vibrations characteristic of lignin syringyl and guaiacyl type [18,19]. Subsequently, to further confirm our hypothesis, we left the dioxane solution with dissolved brown fragments to dry in the oven.…”

“…Subsequently, we compared the isolated lignin from the leachate with the lignin obtained from the fibers (Figure 6). Observing the absorbance at a wavenumber of 897 cm −1 and 1055 cm −1 characteristic for cellulose, we see smaller values compared to the original biomass [19]. We observe the same at a wavelength of 1247 cm −1 .…”

“…We chose samples 2, 4, 10 and 14 for comparison. The amount of C=C bonds belonging to lignin at a wavenumber of 1380 cm −1 in sample 10 differs rapidly compared to the other three samples [18,19]. This smaller amount of lignin isolated from the leachate could be explained by the adsorption of lignin on the fibers during delignification, thus suggesting a lower lignin content in the leachate.…”

“…The area between 3100 and 3500 cm −1 is due to the stretching of hydroxyl groups in holocellulose and lignin. Value 897 cm −1 corresponds to β-glycosidic bonds in cellulose, which can be proven presence of increased cellulose content in samples after delignification [15][16][17][18][19]. As it increases absorbance value at a wavelength of 897 cm −1 , thereby increasing the cellulose content in the sample.…”

Synergistic Effect of Ultrasonic and Fungal Pretreatment on Enzymatic Saccharification of Switchgrass

“…Pretreatment is crucial in cellulosic ethanol production, and the selection of an ideal pretreatment strategy is based on economic feasibility, environmentally benign, its ability to improve enzymatic hydrolysis efficiency, avoid degradation of carbohydrates, and prevent the release of compounds that inhibit subsequent saccharification and fermentation [5]. Several laboratory and pilot-scale investigations have reported that chemical and some thermal pretreatment methods led to high enzymatic hydrolysis efficiency [6][7][8][9]. However, these methods are limited by high energy input and the use or release of harmful substances associated with the process.…”