Effects Of Biochar And Zeolite On Antibiotic Resistance Genes And Pathogens During Sludge Composing

Municipal sewage sludgeis an important repository of antibiotic resistance genes(ARGs)and pathogens.Its land use may lead to the proliferation of ARGs and pathogens in soil and endanger human health through the food chain.In view of the possible transmission risk of ARGs and pathogens,it is of great significance to comprehensively investigate the safety and performance of sludge and protect human health by investigating the pathogens and the occurrence characteristics and risks of ARGs before the utilization of sludge.At present,due to different geographical conditions of sewage treatment plant and sewage sludge treatment plant,it was not found that the final biological composition of ARGs is different from that of sewage sludge treatment plant.In addition,composting is usually one of the pretreatment methods for sludge treatment and resource utilization,while natural zeolite and biochar are often used as nitrogen preservation and heavy metal fixative in the process of sludge composting,so as to improve the quality of sludge composting and land use safety,but their impact on ARGs and pathogenic bacteria control is not clear.Firstly,the occurrence characteristics of ARGs,pathogenic bacteria and virulence factors(VFs)in municipal sludge of 11 sewage treatment plants in Guangzhou,Guangdong Province were investigated.On this basis,taking the sludge of a sewage treatment plant in Jiangmen City,Guangdong Province as composting material,the changes of ARGs,pathogenic bacteria and virulence factors with the addition of biochar,zeolite and their mixtures were studied by macrogenome sequencing.The main results are as follows:(1)The dominant species of sludge samples from 11 sewage treatment plants in Guangzhou are proteus.Among these bacteria,201 kinds of pathogenic bacteria were detected,of which 189 kinds are common,and the dominant species is salmonella?enterica.According to drug resistance,13 types of antibiotic resistance genes were detected in 11 sludge water treatment plants.The most species were aminoglycoside resistance genes.A total of 57 ARGs subtypes were counted.A maximum of 54 ARGs could be detected in the same sample.ade F and sul1 were the most abundant ARGs subtypes.The main resistance mechanism of all ARGs was efflux.(2)Among the sludge samples from 11 sewage treatment plants in Guangzhou,aggressive virulence factors were dominant in all sludge samples,and the risk of pathogenic bacteria was high.The main virulence factors include adhesion,secretory system and anti phagocytosis.Xanthomonas campestris,Legionella pneumophila and Pseudomonas aeruginosa are important potential hosts of ARGs.Overall,municipal sludge is an important ARGs and VFs reservoir.(3)Biochar and zeolite can reduce the abundance of sludge composting product Actinomadura in varying degrees.The relative abundance of actinomycetes decreased significantly in the later stage of composting.At the species level,composting can effectively remove some pathogenic bacteria.The addition of biochar and zeolite reduced the abundance of most pathogenic bacteria,and a few pathogenic bacteria were almost completely eliminated,including most pathogenic bacteria closely related to ARGs.(4)The addition of biochar reduced the relative abundance of VFs related to adhesion and positional variation after composting,while zeolite reduced the abundance of virulence genes related to toxins.Nevertheless,the types of virulence factors of all compost products have not changed significantly,and the aggressive virulence factors are still dominant in all sludge samples.(5)The ARGs subtypes with the most obvious diversity changes in the whole composting process are aminocoumarin resistance gene and multidrug resistance gene.Biochar can increase the diversity of ARGs subtypes in the composting process,while zeolite leads to the decline of ARGs diversity.The abundance of multidrug resistance genes accounts for the highest proportion of all ARGs.The addition of biochar and zeolite can effectively reduce their abundance after sludge composting.Composting can effectively remove some specific ARGs(such as iri resistance gene)from sludge.The addition of biochar significantly reduced the relative abundance of sulfonamide resistance genes sul4,macrolide resistance genes bac A,mac B,lmr D and tetracycline resistance genes tet A(46),tet B(60),tet T,tet A(60),but there were still a small number of ARGs whose abundance was higher than that of the control at the end of composting,such as pat B,cpx A,car A and other genes.The effect of composting time on the relative abundance of some ARGs seems to be more significant than different treatment methods.Efflux mediated antibiotic resistance is widespread and dominant in all samples.The changes of antagonistic mechanism before and after composting and the addition of biochar and zeolite additives have no significant effect.In conclusion,municipal sewage sludge is one of the main recipients of ARGs and pathogenic bacteria in urban environment.Although human and animal derived bacteria are removed during the treatment process,some bacteria can survive and persist in the final sewage.The presence of these bacteria,especially those containing ARGs,may have a direct impact on the quality of treated wastewater returned to the environment.Composting can reduce the relative abundance of some pathogenic bacteria and some kinds of ARGs to a certain extent,and change the community structure of bacteria at the same time.