Effects Of Biochar On Humification And Antibiotic Resistance Genes In Continuous High Temperature Composting Of Copper Rich Pig Manure

Aerobic composting is an important way to realize the harmless and resource utilization of pig manure.It is a biochemical process dominated by microorganisms that converts unstable organic matter into stable humus.However,since Cu compounds（Cu SO₄ and Cu Cl₂）are often widely used as feed additives in the pig industry,a large amount of Cu is enriched in pig manure,and its effective form will affect the activities of microorganisms involved in organic matter conversion in compost,increase the abundance of antibiotic resistance genes（ARGs）,resulting in a decline in the quality of compost products.To solve the above problems,this study adopted a continuous high temperature aerobic composting method,on the basis of which biochar was added to achieve the passivation effect of enhanced composting on the effective form of Cu.Based on this,this study took Cu-rich pig manure as the research object,focused on the effects of biochar on the main physical and chemical indexes,humification process,microbial community diversity and ARGs in the continuous high-temperature composting process of Cu-rich pig manure,and clarified the mechanism of microbial community on humus generation under the action of biochar.To investigate the mechanism of biochar’s passivation of Cu in continuous high temperature compost and its reduction of ARGs.The main conclusions of this paper are as follows:（1）The addition of biochar can reduce the p H and EC values of the pile,make the EC value of the final compost product less than 4 m S/cm,and also reduce the NH₄⁺-N content by 27.1%,increase the NO₃^--N content by 134.7%,and increase the total nitrogen（TN）content by 20.1%.The total organic carbon（TOC）level in biochar treatment can be increased by 6.2～11.5%,but the addition of biochar can cause the decrease of water-soluble organic carbon（DOC）,and the DOC content is reduced by 19.2%at the end of composting（2）Biochar treatment reduces the content of fulvic acid in the reactor,makes its HA/FA ratio（humic acid/fulvic acid）higher than other treatments,and improves the humification process.The results of bacterial community and correlation analysis showed that biochar treatment increased the abundance of bacteria genera that can degrade cellulose and lignin（e.g.,Bacillus,Sinibacillus,Ammoniibacillus and Thermobacillus）.The main bacterial genera related to the changes of humic acid and fulvic acid in compost were changed.（3）The addition of biochar can promote the conversion of bioavailable Cu components to residual state,promote the mineralization of organophosphorus,and increase the proportion of available phosphorus（H₂O-P and Na HCO₃-P）in total phosphorus.The correlation analysis between the morphology of Cu and humus and phosphorus components showed that H₂O-P was positively correlated with EXCH-Cu and Redu-Cu,and Na HCO₃-P was positively correlated with Oxid-Cu.The composition of humic acid in humus was positively correlated with Oxid-Cu.（4）Aerobic composting reduced the relative abundance of macrolide ARGs（erm A and erm B）,sulfonamides ARGs（sul1 and sul2）,copper resistant genes（pco A）and mobile genetic elements（TN916,int I1 and int I2）in composting.The addition of biochar increased the reduction of cop A,erm A,int I1 and sulfonamides ARGs in Cu-rich pig manure composting.Redundancy analysis showed that Oxid-Cu was the main cause of cop A gene increase,and EXCH-Cu mainly affected the distribution of erm A,erm B and TN916 in composting.Network analysis showed that bacterial community was the dominant factor affecting the change of resistance genes in composting.Adding biochar could reduce the abundance of potential host bacteria of resistance genes in Cu-rich pig manure composting,and weaken the association between mobile genetic elements and resistance genes in bacterial community.