Microbial Aerosol Characteristics And Health Risk Analysis During Reclaimed Water Utilization

The reclaimed water treatment system,the reclaimed water transmission and distribution system and the reclaimed water utilization system constitute the reclaimed water system.One of the sources of reclaimed water is sewage,in which there are many kinds and high content of pathogenic microorganism.The malfunction of any process of the reclaimed water system may lead microorganisms into the sector of using.The disturbance of each device in the sector of using will bring microorganisms into the air in the form of aerosol,It is therefore necessary to study the health risks associated with this.Based on the experimental results of Escherichia coli content of 10~7 CFU/L and 0CFU/L in the reclaimed water of a wastewater treatment plant before and after disinfection,the experiment of using reclaimed water for flushing,green field spraying and car washing was carried out by replacing Escherichia coli with 2μm monodisperse fluorescent particles.Meanwhile,aerosol particles generated from these process were sampled using the air sampling pump and analyzed using laser confocal microscope.No particulate aerosols were produced in the recycled water after disinfection,while particulate aerosols were produced in the recycled water before disinfection.,and the content of particulate aerosols produced by different recycling ways was different:the maximum aerosol concentration of recycled water for flushing was 200 droplets/m~3,and the maximum aerosol concentration of recycled water for greenfield spraying and car washing was 167 droplets/m~3and 437 droplets/m~3.Therefore,the disinfection process of reclaimed water should be strictly controlled before reuse.In addition,through literature investigation,it was found that the concentration of aerosol particles in the toilet flushing experiment based on the bacterial content in human excreta and vomit ranged from 10 to 10~3 CFU/m~3.Then,taking reclaimed water for gravity toilet as an example,the variation law of air flow caused by flushing process was simulated by Fluent.The simulation results show that the process of toilet flushing does cause the change of air flow field over the toilet,and the range of air change can reach the average breathing height of adults.In addition,the velocity in the plane of adults’average breathing height increased first and then decreased,with a fluctuation range of 0～0.09 m/s.Finally,based on the particulate aerosol content distribution of reclaimed water in the process of reuse obtained by experimental test and the microbial aerosol content of air generated in the process of flushing excreta obtained by literature survey,the health risk assessment model was combined with the Crystal ball software to conduct the health risk analysis.The results showed that the microbial aerosols produced in the process of reclaimed water reuse had no or negligible risks to the environment or human body.Microbial aerosols generated when tap water is used to flush human excreta in toilets pose no or negligible risks to the environment and human body.The health risks are small in both scenarios,and the risks are considered safe and manageable when the recycled water is used to flush the excrement in the toilet.