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.
Preliminary research on supercritical ammonia pulping of bamboo was completed using a differential thermal analyzer, scanning electron microscope, X-ray diffractometer, and an energy spectrometer. The results showed that ammonia can be recovered from bamboo raw materials under the supercritical condition of 185 to 190 °C. Compared with conventional kraft bamboo pulp, the separated bamboo pulp met the pulp quality requirements of industrial paper, achieving high efficiency and a multi-level utilization of biomass resources. Ammonia in the system can be recycled.
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