Preparation Of Fe/Mg Modified Biochar And Its Intensification On The Anaerobic Digestion Of Lignocellulosic Biomass

China is a large agricultural country in the world and has abundant straw biomass resources,but due to the single utilization method and low processing efficiency,a large amount of straw resources have been wasted and caused some environmental pressure.The use of high-temperature thermal cracking of straw biomass to prepare biochar for microbial anaerobic fermentation has been proven to be beneficial,but little research has been done to add trace elements necessary for microbial growth to biochar to prepare modified biochar for anaerobic fermentation.Ruminal microorganisms have received wide attention as natural and efficient anaerobic fermentation reactors that can effectively ferment lignocellulose.In this paper,based on the principle of efficient and sufficient resource utilization of straw agricultural waste and the concept of green environment protection,we investigate the preparation of modified biochar and the selection of anaerobic fermentation substrate from two aspects: on the one hand,straw is transformed into a booster with good adsorption properties and rich in nutrients,and on the other hand,straw is pretreated as fermentation substrate and rumen flora is used as inoculum to improve its hydrolysis efficiency.The optimal conditions for the preparation of modified biochar and its coupling with rumen microorganisms in the anaerobic fermentation process were investigated to analyze the reaction mechanism.In this study,the optimal preparation conditions of modified biochar were investigated by controlling four single-factor conditions of temperature gradient,maintenance time,urea concentration,and iron-magnesium ratio during the preparation process;the modified biochar produced under the optimal conditions was applied to the anaerobic fermentation process,and the effects of different modified biochar types,addition amounts,and solid concentrations on the hydrolysis process of lignocellulose were investigated to analyze the coupling between modified biochar and rumen microorganisms.By further analyzing the structure of the bacterial flora at the end of the reaction,Illumina Miseq sequencing technology was used to analyze the changes in the structure of the bacterial flora after the completion of the fermentation,to further investigate the mechanism of the efficiency of the anaerobic fermentation of rumen microorganisms from the perspective of changes in the structure of the microbial flora and to predict the functional structure of the flora.The main conclusions were obtained as follows:(1)The optimal temperature conditions for the preparation of Fe-Mg modified biochar was 400°C,the maintenance time was 30 min,the urea addition ratio was 0.75mol/L,and the Fe-Mg ratio was 0.5M:0.5M.Prepared under optimal conditions reached92.82% for the acidic reagent rhodamine B solution,and the adsorption of alkaline adsorbent reagent methyl orange solution reached up to 100.00%.The adsorption efficiency is high,and the dynamic equilibrium of adsorption is reached within 120 min.The analysis of characterization parameters such as BET and SEM reveals that the surface area of biochar modified by doped metal Fe-Mg increases more than 20 times compared to the control group,and the porosity increases and the structure is loosened,which provides more adsorption sites.FTIR and XRD analysis revealed the detection of Fe-Mg-related peaks in the produced modified biochar,indicating that Fe-Mg elements were successfully loaded.The intraparticle diffusion model indicates that the rate of the adsorption process of modified biochar is controlled by both membrane diffusion and intraparticle diffusion.(2)At a substrate concentration of 4% and an added Mg@BC content of 12 g/L,the reducing sugar content of the fermentation process increased by 77.78% compared to the control group.Fe@BC was the most effective in the fermentation process of hydrogen production.Different substrate concentrations also had important effects on reducing sugar concentration,SCOD,and VFAs content during fermentation.(3)Sequencing analysis of microorganisms at the end of modified biochar domestication revealed significant changes in microbial flora structure.Microbial diversity decreased significantly after the addition of Mg@BC,but the abundance of norank＿f＿Tannerellaceae(25.59%),Bacteroides(17.97%),and Globicatella(6.15%)increased,and Fe@BC was beneficial for the growth enrichment of most microorganisms,mainly hydrogen-producing bacteria enrichment.Fe-magnesium modified biochar was screened for dominant bacterial groups during anaerobic fermentation.Bacreroidote,Spirochaetota and Proteobacteria were the key strains for the fermentation process.These studies will help the application of modified biochar in the direction of anaerobic fermentation to achieve better digestion.