The Characteristics And Sources Of Airb Orne Bacteria And Human Pathogenic Bacteria In Composting Plant

The escaping air of animal manure composting plant is rich in many kinds of bacteria and even human pathogenic bacteria.There are certain differences in the species and abundance of the escaping microorganisms in different working areas.The particle size of bacterial aerosol affects its transmission behavior and the degree of harm to human health.In the process of composting,bacteria escape is affected by many environmental factors.To solve above problems,this study was conducted to study the regional differences in the community structure of bacteria and pathogenic bacteria aerosols in different areas of animal manure composting plant,in-depth analysis of particle size distribution characteristics and dynamics of particle size,and systematically studied the variation of bacterial aerosol and its influencing factors during composting.In this study,air samples were collected from the composting area,packaging area and office area of the animal manure composting plant.The bacterial biodiversity and community structure in the air in the above three areas were compared and analyzed,and the differences in relative abundance of pathogenic bacteria under human conditions in different areas were analyzed.The results showed that the distribution of dominant bacteria phyla in the composting area,packaging area and office area was similar overall,but the relative abundance of specific dominant bacteria phyla was different in regions.The first three dominant phyla are Firmicutes,Proteobacteria and Actinobacteria,and the common dominant bacterial genus are Acinetobacter and Corynebacterium.The abundance and diversity of bacteria in the air in the office area is the highest.There are significant differences in the bacterial communities in the air in the three areas,and the bacterial phyla community structure in the composting area and the packaging area is more similar.The proportion of endemic bacteria genus and phylum in the air in office areas is the highest.The results of the analysis of common microorganisms in the three districts showed that the proportions of common bacteria genus and phylum in the composting area were both the highest,which were 85.19%and 85.14%,respectively.There was no significant difference in the community structure of human pathogenic bacteria in different regions,and the relative abundance of Acinetobacter is the highest.In the air of compost area and packaging area,the relative abundance of two kinds of human pathogenic bacteria was positively correlated with the office area,while there was no significant correlation between the relative abundance of human pathogenic bacteria was detected in the air of composting area and packaging area.Exploring the particle size distribution of airborne bacteria is essential to fully understand their transmission behavior and the risk to human health.In this study,an eight-stage impactor bioaerosol sampler was used to collect bioaerosols with different particle size ranges in different areas of the composting plant.Using 16S rRNA gene sequencing combined with droplet digital PCR technology,we investigated the abundance,diversity and community structure of airborne bacteria and human pathogenic bacteria under different particle sizes.The results show that the concentration of 8 grades of bacteria is between 104～105 copies/m3.Although no statistical correlation between particle size and Shannon index was detected,the effect of particle size on bacterial lineage was observed in both the composting area and the packaging area.The dominant bacteria phyla for airborne transmission under different particle sizes are Firmicutes,Proteobacteria and Actinobacteria,and the dominant genus is Bacillus.Among them,human pathogenic bacteria with a smaller aerodynamic geometric mean diameter have a higher concentration in the composting area.Through calculations,it is found that the aerodynamic geometric mean diameter of human pathogenic bacteria conditions in the composting area is between 2.42 and 5.09 microns,and it is expected that most of them will be deposited on the bronchi and secondary bronchi.In the packaging area,human pathogenic bacteria(3.70～8.96 microns in diameter)are expected to be deposited on the upper respiratory tract of the human body.It is of great significance to study the influence of composting process on airborne bacteria and human pathogenic bacteria for controlling the pollution caused by composting process.In this study,the pile,the finished fertilizer,and the air samples of the near and far piles were collected for 12 consecutive days.To explore the effect of composting process on bacteria and human pathogenic bacteria in the air.The results of the study showed that with the increase of composting time,the concentration of bacteria in the pile and the air decreased.The concentration of bacteria in the pile is between(1.28×109～2.14×1010)copies/g,and the human conditional pathogens are between(3.58×108～8.68×109)copies/g.The concentration of bacteria in the air of the composting plant is between(8.94×103～1.25×106)copies/m3,and the pathogenic bacteria of human conditions are between(1.16×102～3.04×105)copies/m3.The bacterial diversity in the air(Shannon index 7.55～9.10)of the composting plant was significantly higher than in the pile(Shannon index 6.63～8.03)and finished fertilizer(Shannon index 4.04～8.02)(ANOVA,P<0.05).The dominant bacteria genera in the top 3 relative abundances in the heap,the finished fertilizer or the air of the composting plant all contain 2～3 human pathogenic bacteria.When investigating the source of human pathogenic bacteria in the air,it was found that there are no unique human pathogenic bacteria in composting plant air.The types of human pathogenic bacteria in the air of near/distant piles all come from the escape of piles and finished fertilizers.This study comprehensively analyzed the abundance,diversity and distribution characteristics of bacteria and human pathogenic bacteria under the different particle sizes.The results of this study provide important information for the systematic evaluation of the pathogenicity of bacteria and their potential health effects on the composting factory worker and the surrounding residents.