Impact Of Pore Structure Of Biochar On Methane Emissions During Municipal Sludge Aerobic Fermentation

Biochar has attracted extensive attention in improving fermentation efficiency and controlling the emissions of methane（CH₄）from aerobic fermentation of municipal sludge due to its advantages of porosity,stability and environmental friendliness.At present,most studies on biochar and CH₄emissions focus on macroscopical levels such as biochar addition amount,preparation materials and particle size,and there is a lack of in-depth studies on the effect of porous properties of biochar on CH₄emissions during aerobic fermentation of municipal sludge.Therefore,from the perspective of pore structure（microporous and macroporous structure）of biochar,this study explored its impact on CH₄release during aerobic fermentation of municipal sludge.The specific surface area test（BET）was used to analyze the pore structure of biochar,and the influence of the pore structure of biochar on the aerobic fermentation efficiency was explored by measuring the physical and chemical indexes of the reactor.At the same time,the CH₄emissions during the aerobic fermentation process was studied by gas chromatography（GC）,and the influence of the pore structure of biochar on the microbial diversity and community succession in the reactor was analyzed by 16S r RNA high-throughput sequencing technology,Finally,combined with correlation analysis（Spearman correlation analysis,redundancy analysis）,the relationship between the pore structure of biochar and CH₄emissions was discussed in depth.The main conclusions of this study are as follows:（1）Three kinds of biochar with different pore structures were used as the regulator of aerobic fermentation of municipal sludge,namely beech wood biochar（WBC）,rice husk biochar（RBC）and corncob biochar（CBC）.BET result showed that WBC and RBC were dominated by microporous structure（87.84%and 73.72%,respectively）,while CBC was dominated by macroporous structure（89.94%）.SEM showed that,in general,the micro morphology of the three biochar is characterized by uniform pore distribution and honeycomb shape.Among them,WBC has dense pores,RBC has thin pore wall,and CBC has the largest pore diameter and small holes on the pore wall（2）GC result showed that compared with the control group without biochar（CK）,the emissions of CH₄in aerobic fermentation group with WBC,RBC and CBC decreased by 41.83%,33.59%and 8.20%,respectively.In this study,the external experimental results of HS-GC further revealed that the pore structure of biochar reduced CH₄release mainly by improving the pile environment.（3）From the physical and chemical indexes of the reactor,the maximum temperature of CK,WBC,RBC and CBC groups was 68.53℃,72.60℃,70.96℃,and 67.11℃,respectively,and the high temperature period was 4 d,8 d,8 d and 7 d,respectively.The WBC group and RBC group had a better degree of harmless fermentation and higher fermentation efficiency.At the end of fermentation,the free air space of CK,CBC,RBC and WBC groups increased by 1.74%,7.93%,10.03%and 16.48%,respectively.WBC was more conducive to improving the bulk volume and promoting oxygen circulation in the bulk.（4）The results of high-throughput sequencing showed that the Shannon index of CK,WBC,RBC and CBC groups were 2.04,1.94,1.93 and 2.15respectively,indicating that WBC and RBC inhibited the activity of microorganisms by increasing the fermentation temperature,thereby inhibiting CH₄production by methanogens.Adding CBC could increase the microbial diversity of the reactor.（5）Spearman correlation analysis showed that Methanosata and norank＿f＿＿Methylococcaceae contributes most to CH₄production and oxidation,respectively.Redundancy analysis revealed that the pore size of biochar was positively correlated with the release rate of CH₄.Temperature and ammonium nitrogen were the environmental factors that had the greatest impact on methane release and microbial community succession during aerobic fermentation of municipal sludge,and the result showed that WBC and RBC with microporous structure were more conducive to reduce methane release.