Characterization Of Efficient Biomass Enzymatic Hydrolysis Of Rice Straw For High Bioethanol Yield Coupled With Active Heavy Metal Biosorbent Production

Rice is a major food crop with huge lignocellulose-rich straw convertible for bioethanol and other bioproducts.Lignocellulose-based bioethanol production involves in three major steps:physical and chemical pretreatment,sequential enzymatic hydrolysis and final yeast fermentation.However,lignocellulose recalcitrance causes an unacceptable costly bioethanol production,and it may also release biomass residues and chemical wastes as the secondary pollution to the environment.Hence,this study attempted to find out the optimal physical and chemical pretreatments with rice?ZH11?straw for largely enhancing enzymatic saccharification and bioethanol production,and meanwhile to combine the liquors of the pretreatments and solid residues of yeast fermentation for generating active biosorbent for cadmium?II?adsorption.Here are major results described below:1. Four optimal physical and chemical pretreatments were established to enhance biomass enzymatic saccharification of rice straw including alkali pretreatments?1.5% NaOH,10%CaO?,acid?2%H₂SO₄?and liquid hot water?15 min 200?LHW?,leading to the hexoses yields?%cellulose?achieved from enzymatic hydrolysis as 98%,95%,86%and 92%,respectively.2. By performing yeast fermentation using all hexoses released from enzymatic hydrolysis,bioethanol yields?%dry matter?were obtained from the four optimal pretreatments?1.5%NaOH,10%CaO,2%H₂SO₄and 15 min 200?LHW?as 11.2%, 9.7%,9.3%and 8.9%,respectively.By comparison,the 1.5%NaOH pretreatment could lead to the highest yields of bioethanol among all four optimal pretreatments performed in this study,whereas the 200?LHW pretreatment caused the lowest ethanol yields and sugar-ethanol conversion rate.3. To test the four optimal pretreatments roles in lignocellulose modification of rice straw,two alkali pretreatments?1.5%NaOH,10%CaO?could mainly remove lignin to enlarge cellulose surface areas,whereas both acid and LHW pretreatments were able to extract partially hemicellulose,which reducing its arabinose substitution degree,and significantly reduced degree of polymerization?DP?of cellulose.4. Using H₂O₂chemical to link the liquor compounds of pretreatment and the solid residues of yeast fermentation,four biosorbents were generated from the four optimal pretreatments performed in this study,and their distinct Cd adsorption capacity was measured such as NaOH>CaO>H₂SO₄>LHW.By comparison,the optimal NaOH pretreatment led to the highest bioethanol yield?11.2%dry matter?and Cd adsorption rate?86.3%?among all optimal four pretreatments performed,while the optimal acid pretreatment was of the largest amounts of biosorbents.5. The Cd adsorption rates of four biosorbents were hardly affected by temperature condition during Cd adsorption process,but they were significant increased by raising pH values in the biosorbents generated from the optimal LHW and acid pretreatments.In addition,The Cd adsorption rates were unlikely affected by pH values in the biosorbents from two optimal alkali pretreatments.In conclusion,this study raised a hypothetic model highlighting the enhanced bioethanol and biosorbent production obtained from four optimal physical and chemical pretreatments with rice straw.Hence,this study has not only interpreted why high-yield bioethanol and high-active biosorbent could be achieved from the optimal biomass process technology,but it has also provided a cost-effective and green-like strategy for bioethanol production with value-added bioproducts using crop stalks.