Emission Characteristics Study Of Bioaerosol In Composting Plant

Organic solid waste composting plants are one of the important sources of bioaerosols.The relevant mechanical operations in the composting process such as transportation,breaking,turning,and screening will cause aerosolization of microorganisms in raw materials and finished fertilizers.Therefore,the air environment of composting plants contains a variety of bacteria,fungi and antibiotic-resistant bacteria,and the abundance and diversity of bacteria and fungi that escape from different working areas and different composting stages are significantly different.In view of the above problems,this study investigated the emission concentration characteristics,community structure,and regional and staged characteristics of potential pathogenic bacteria in bacterial aerosols,fungal aerosols,and antibiotic-resistant bacteria aerosols escaping from different areas in the composting plant.The influencing factors of bioaerosol emission,the level of microbial aerosolization,and the exposure risk of bioaerosols were systematically studied.In this study,two sludge composting plants and one animal manure composting plant were selected as the research objects,and the upwind direction,mixing area,heating area,high temperature area,decomposing area,screening area,finished product area and office area were selected as typical areas.The bioaerosols in each area were collected by the Anderson six-stage sampler and counted after culture.The bioaerosols were collected by medium flow atmospheric total suspended particulate matter cutter,and the community composition of bacteria and fungi were analyzed by high-throughput sequencing method.The results showed that the concentrations of bacterial and fungal aerosols escaped from sludge composting plants A、B and animal manure composting plants were 3993～25146 CFU/m³,3601～19806 CFU/m³,6511～21603 CFU/m³ and627～3171 CFU/m³,1564～13220 CFU/m³,327～1670 CFU/m³.Among them,the concentration of bacterial aerosols and antibiotic-resistant bacteria aerosols escaped from the mixing area,high temperature area and screening area was higher,and the concentration of fungal aerosols escaped from the mixing area and high temperature area was higher.And in the whole composting process,the emission concentrations of bacterial aerosol,fungal aerosol and antibiotic-resistant bacteria aerosol all increased first and then decreased.In addition,the bioaerosols escaped from the composting plant contain a certain amount of water-soluble inorganic ions,among which the cations are mainly Ca²⁺,Na⁺,K⁺,and the anions are mainly Cl^-and SO₄^2-.Comparative analysis of the microbial diversity and community structure of bacterial aerosols and fungal aerosols found that the dominant phyla of bacteria and fungi in the three composting plants were similar,and the first three dominant bacterial phyla were Firmicutes and Actinobacteria,Proteobacteria,the common dominant genera include Thermobifida.The first two dominant phyla of fungi are Ascomycota and Basidiomycota,and the common dominant genera include Cladosporium,Chaetomium,Thermomycetes and Aspergillus.Among the environmental factors,temperature,relative humidity,H₂S and VOC had a greater impact on bacterial and fungal community structure.Among the eight water-soluble inorganic ions,Ca²⁺and Mg²⁺were positively correlated with most genera of bacteria and fungi,while Cl^-and SO₄^2-were negatively correlated with most genera.Among the five heavy metals,Zn and Cu were significantly positively correlated with most genera of bacteria and fungi,while Pb was negatively correlated with most genera.Finally,the aerosolization level of microorganisms in the composting plant was explored.At the phylum level,Actinobacteriota,Deinococcota and Proteobacteria among bacteria preferentially aerosolize,and at the genus level,Thermobifida and Acinetobacter were preferentially aerosolized.At the phylum level,Basidiomycota among fungi was preferentially aerosolized,and at the genus level,Boeremia was preferentially aerosolized.Finally,sludge composting plant A was selected for exposure risk assessment.The results showed that when exposed to bioaerosols,adult males had higher exposure risks than adult females,and workers had higher exposure risks than nearby residents,and the disease burden decreased with increasing mask grades.