| During the transportation of the sewage pipe network,the sewage is affected by hydraulic fluctuations to generate a large amount of aerosols,and the pathogenic microorganisms carried by it will spread to the external environment through the inspection well,which has a potential risk of exposure to the contact population.In order to assess the risk of exposure of viral aerosols in the manhole catchment area,this study used a combination of numerical simulation and experimental analysis to explore the hydrodynamic law of the sewage manhole bus area and the mechanism of aerosol generation and diffusion propagation.Based on this,the infection probability of typical viral aerosols was analyzed by means of quantitative microbial risk assessment methods,combined with the detection results of virus population and content in actual sewage.The research results provide scientific basis and theoretical support for the risk study and source control of virus transmission in the process of sewage transportation,and the specific results were as follows:(1)Through the establishment of a set of sewage pipeline pilot experimental system,the characteristics of microbial aerosol generation and diffusion propagation of sewage pipelines are studied and analyzed under different speed conditions.The results show that under low flow rate(0.6-0.8m/s),the average aerosol concentration detected on the surface of sewage is 205 CFU/m~3;At medium flow rates(1.0-1.5 m/s),the average aerosol concentration was 245 CFU/m~3,an increase of 16.1%compared to low flow rates.At high flow rates(2.0-5.0 m/s),the average aerosol concentration was 961 CFU/m~3,an increase of 78.6%.In addition,the concentration of aerosol production is also significantly positively correlated with the COD content in the sewage and the temperature of the sewage.It can be seen that the inlet water flow rate,sewage temperature and COD content are important influencing factors for aerosol generation and diffusion propagation.(2)Through the three-dimensional numerical simulation of CFD and the combination of VOF and DPM model,a model of viral aerosol generation and diffusion in sewage inspection wells was constructed.The simulation results are reliably analyzed with the help of experimental measurement data.The verification results show that the model can well simulate the generation and diffusion distribution of aerosols in sewage inspection wells.Using the established physical geometric model,the hydraulic characteristics of the manhole convergence area and the distribution of aerosol generation were simulated.The results show that with the increase of the inlet water flow rate,the pressure in the pipeline increases,the turbulence effect increases,and the probability of the virus-carrying aerosol spreading from the inspection well into the atmosphere increases accordingly.It shows that there is a significant risk of viral aerosol infection when the flow rate in the catchment area of the sewage inspection well is turbulent.(3)By detecting typical viruses that can easily cause human health diseases in actual municipal sewage,the content of adenovirus,rotavirus,enterovirus and norovirus in sewage ranges from 10~3-10~6 copies/L.Based on the above four virus concentrations measured experimentally,the risk of microbial aerosol exposure in the sewage network was assessed by means of quantitative microbial risk assessment methods.In the case of rapid flow rate in manholes,the probability of infection of adenovirus and rotavirus is greater than 0.8,and the probability of infection of enterovirus and norovirus is less than0.6.It can be seen,for urban sewer network systems,the risk of virus-carrying aerosol-borne viruses in the manhole convergence area needs to be paid attention to,especially adenovirus and rotavirus with a strong risk of infection.This study can provide a theoretical basis for the monitoring of aerosols of the virus in urban sewage pipelines and the early warning of infection risk. |
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