Evaporation Mechanism Of Different Kinds Of Bacterial Droplets Deposited On The Interior Surface Of Buildings

In recent years,the proportion of deaths caused by respiratory diseases in cities has increased.Infectious diseases such as influenza and SARS not only threaten human health and life,but also cause certain social panic.Studies have shown that infectious diseases such as influenza and SARS can be transmitted through droplets of droplets exhaled by humans.Due to the difference in particle size,droplets of droplets exhaled by humans also have different transmission modes.The small particle size droplets will diffuse and evaporate in the air and eventually condense into nucleation.While the large particle size droplets will start to settle due to gravity and after the droplets settle to the solid surface,evaporation of the sessile droplets occurs,which in turn causes pollution to the indoor environment of the building.The evaporation of large particle size exhaled droplets after deposition is affected by its composition and environment.The temperature,pH and evaporation of droplets also affect the activity of carrying microorganisms.However,it is not clear whether the microorganisms carried in the droplets will affect their evaporation.Many studies have often simplified microbial droplets into pure water or salt solution droplets to reflect the effects of environmental humidity and chemical components such as hygroscopic salt ions on the evaporation rate.In this study,three kinds of bacteria of different genera(including Escherichia coli,Lactobacillus paracasei and Bacillus subtilis)and pathogenic bacteria such as Staphylococcus aureus were used to carry out a bacterial solution with a concentration of 107 CFU/ml.Changes in parameters when the droplets evaporate on a common surface in the room.The contact angle,droplet diameter and droplet height between the simulated droplet and the hydrophobic surface were measured by optical method,and the mass change of the droplet evaporation was measured with a high-precision analytical balance.Based on the existing relationship between contact angle and surface tension,the quantitative effects of bacterial species on droplet evaporation rate,contact angle,droplet diameter and height parameters were systematically analyzed.The evaporation of large particle size exhaled droplets after deposition is affected by its composition and environment.The temperature,pH and evaporation of droplets also affect the activity of carrying microorganisms.However,it is not clear whether the pathogens carried in the droplets will affect its evaporation.Therefore,this study used four species of bacteria of different genera(including Escherichia coli,Lactobacillus casei,Bacillus subtilis and Staphylococcus aureus)to replace the actual pathogenic bacteria.The contact angle,droplet diameter and droplet height between the simulated droplet and the hydrophobic surface were measured optically,and the mass change of the droplet evaporation was measured with a high-precision balance.The effects of bacterial species on the liquid surface tension and evaporation rate of droplets were studied.The experimental results show that under the same conditions,after adding bacteria of different genus(droplets of bacterial solution)to the droplets of 0.9%(w/v)sodium chloride solution,the bacterial droplets prolonged the evaporation time compared with the pure water droplets.Compared to 0.9%(w/v)sodium chloride solution,Bacillus subtilis accelerates evaporation rate by 0.9%;Staphylococcus aureus slows down evaporation rate by 51.8%;Escherichia coli slows evaporation The rate was 32.2%;Lactobacillus paracasei slowed the evaporation rate by 38.9%.Because the combined action of the components in the B.subtilis droplets reduces the chemical potential of water molecules escaping from the surface,resulting in faster evaporation rates than sodium chloride solutions;S.aureus droplets,Escherichia coli droplets.The combined action of various components in the Lactobacillus paracasei droplets increases the chemical potential of water molecules to escape from the surface,resulting in a slower droplet evaporation rate than the sodium chloride solution.This paper analyzed the effects of bacterial species on the evaporation of sediment droplets in bacteria in buildings.It provides a basis for pollution control and prevention of building indoor environment.