Optimal K₃PO₄ Pretreatment For Enhanced Enzymatic Saccharification Of Sugarcane Bagasse And Bioethanol Production Along With Liquid Fertilizer Application

Sugarcane is an important industry crop for sugar production and also provides large amounts of bagasse residues as lignocellulose-rich biomass resource.Although various biomass pretreatment technologies have been attempted for sugarcane bagasse process,lignocellulose recalcitrance decides a costly biomass enzymatic saccharification unacceptable for large-scale biofuel production.Hence,it becomes essential to explore the optimal biomass pretreatment for efficient enzymatic saccharification of sugarcane bagasse.In this study,therefore,we collected total nine sugarcane cultivars and determined their cell wall compositions and biomass enzymatic saccharification.By using two representative bagasse samples,this study performed optimal K₃PO₄pretreatments to achieve high yields of hexoses and bioethanol,and further sorted out how K₃PO₄pretreatment could significantly reduce lignocellulose recalcitrance for much enhanced biomass enzymatic saccharification.In addition,this study explored to use the liquid waste remained from ethanol fermentation as fertilizer for enhancing plant growth and biomass yield.The main results are described below:1.By collecting total nine sugarcane bagasse samples,this study determined similar cellulose and hemicellulose levels,but their lignin contents were largely varied.By performing direct enzymatic hydrolyses with all bagasse residues,this study sorted out that the F134 and ROC22 samples were of the highest and lowest hexoses yields,respectively,which should be mainly due to much lower lignin level in the F134 relative to the ROC22.By using F134 and ROC22 as two representative samples,this study initially conducted single-factor experiments for K₃PO₄pretreatments and classic response surface methodology were further applied to establish the optimal K₃PO₄pretreatments for F134（6.4%K₃PO₄at 144℃）and ROC22（6.8%K₃PO₄at 167℃）samples.2.Under optimal K₃PO₄pretreatment,the F134 and ROC22 samples respectively showed the hexoses yields of 98.98%and 95.21%released from enzymatic hydrolyses of pretreated bagasse residues,which were higher than those of their controls（without pretreatments）by 1.7 and 3.7 folds.Accordingly,two bagasse samples showed total sugar yields（hexoses and pentoses）at 76.15%and 71.31%（%dry matter）,being higher than those of the controls by 2.4 and 4.3 folds.By performing yeast fermentation with all hexoses released,the F134 and ROC22 samples achieved the bioethanol yields at 15.41%and 14.90%（%dry matter）,which were higher than those of the controls by 1.5 and 3.1folds.3.After the optimal K₃PO₄pretreatment（6.4%K₃PO₄,144℃）,the F134 and ROC22samples showed their lignin levels reduced by 58%and 63%,leading to relatively raised cellulose contents by 33%and 30%.Meanwhile,two pretreated bagasse residues were of significantly reduced cellulose DP（degree of polymerization）values for cellulose accessibility raised by 1.5 and 3.5 folds,which should be accounting for remarkably enhanced biomass enzymatic saccharification examined above.Based on Fourier Transform Infrared Spectrometer and X-ray Photoelectron Spectroscopy analyses,this study raised a hypothetic model about effective wall polymers extractions from the K₃PO₄pretreatment to reduce lignocellulose recalcitrance,which should be distinct from classic acid,alkali and liquid hot water pretreatments preformed previously.4.By supplying the K₃PO₄liquid remained from ethanol fermentation into rice water culture at low concentration,this study found significantly enhanced rice growth with higher biomass yield compared to the control（without K₃PO₄supply）.In conclusion,this study has demonstrated that the optimal K₃PO₄pretreatments could lead to near-complete biomass enzymatic saccharification of sugarcane bagasse.Therefore,this work has not only explored how the optimal K₃PO₄pretreatment could largely enhance biomass enzymatic saccharification,but it has also found out an approach to recycle K₃PO₄as an effective fertilizer for enhanced plant growth and biomass production,providing a powerful strategy for efficient biomass process under a green-like manner.