| Anaerobic fermentation of biomass as a feedstock can be effective in achieving China’s "3060" dual carbon target.However,the degradation of lignocellulose in anaerobic fermentation from maize straw is a problem that limits the efficiency of methane production in anaerobic fermentation.An effective pre-treatment is needed to solve this problem.Therefore,the aim of this paper is to find an efficient and environmentally friendly pretreatment method for anaerobic fermentation of maize stover based on vacuum negative pressure-aerobic hydrolysis pretreatment experiments,to analyse the effects of the two pretreatment techniques separately on the physicochemical properties and anaerobic fermentation performance of maize stover,and subsequently to combine the two pretreatment techniques to explore the feasibility of combined pretreatment on the anaerobic fermentation performance of maize stover,so as to obtain the optimal The aim is to provide a theoretical reference for pretreatment technology in practical biogas projects.The main elements and conclusions of this study are as follows.(1)Pretreatment conditions with a vacuum range of 0.02-0.08 Mpa and a holding time of5-20 min were selected to investigate the changes in the volume weight,swelling and specific porosity of maize straw after pretreatment.Compared to the CK group,the bulk weight increased by 7.18%-28.72%,swelling increased by 3.18%-58.59% and specific porosity decreased by 9.34%-38.59%.Further regression analysis was carried out to establish the linear regression relationship with vacuum degree and holding time,which showed a significant negative correlation between vacuum degree and bulk capacity and swelling,and a significant positive correlation with specific porosity;time showed a positive correlation with bulk capacity and swelling,and a negative correlation with specific porosity.Analysis of variance(ANOVA)on vacuum degree and holding time revealed that vacuum degree could significantly affect the physical properties of maize straw.(2)CCD experiments were designed and conducted with a hydrolysis time of 16 h and a hydrolysis temperature of 35 °C as the central point.The changes in lignocellulose composition and microstructure of maize straw after aerobic hydrolysis were investigated.The results showed that the aerobic hydrolysis pretreatment resulted in different degrees of degradation of lignocellulose,which were cellulose(15.21%-25.12%),hemicellulose(10.52%-15.91%)and lignin(0.52%-2.13%).Scanning electron microscopy results showed that the microstructure of maize straw was disrupted,with the degree of disruption increasing with the intensity of aerobic hydrolysis.Compared to the CK group,the hydrolysed reducing sugar content was elevated by 26.56%-74.22% and volatile fatty acid content by 40.90%-86.82%.The optimal aerobic hydrolysis pretreatment conditions were obtained by RSM optimization in response to the volatile fatty acid content,and the hydrolysis temperature was39 ℃ and the hydrolysis time was 12.65 h.The effect of aerobic hydrolysis temperature on the volatile fatty acid content in the hydrolysis process was greater than that of aerobic hydrolysis time,as shown by ANOVA.(3)A combined pretreatment condition of 0.08 MPa vacuum,10 min holding time,12.65 h hydrolysis time and 39 ℃ hydrolysis temperature was selected to carry out anaerobic fermentation of maize straw to verify its effect on improving the methane production performance of anaerobic fermentation.The results showed that the cumulative methane production of the pretreated maize straw anaerobic fermentation was 260.44 m L/g VS,which was 22.71% higher than that of the CK group.Meanwhile,the combined pretreatment resulted in a 32.39% reduction in the delay period of anaerobic fermentation. |
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