| Reclaimed water is an important water source for landscape recreation and urban municipal,and its reuse safety has attracted people’s attention.Various reuse methods such as fountains,landscape waterfalls,green space sprinkling irrigation and sprinklers spraying roads can form tiny droplets in the air which are difficult to settle by atomization spraying.Bacteria in the water can attach to the droplets and spread widely in the form of aerosols,which enter the body through mouth and inhalation,causing infection.However,the current research on bacterial aerosols related risks is still insufficient.In this study,the spatial distribution of bacterial aerosols in the spraying environment and the characteristics of the population’s exposure parameters are thoroughly studied by means of simulated spraying experiment and population survey.On this basis,the inhalation risks of bacterial aerosols was quantitatively assessed in order to provide scientific basis for safe reuse of reclaimed water.This research mainly using Escherichia coli NK5449 as test strain,the Bio Sampler（SKC,Inc.）and the 6-stage Andersen impactor were used to collect the bacterial aerosols around the spraying device through simulated spray experiments to study saturation time,concentration and particle size distribution characteristics,activity characteristics and residence time of bacterial aerosols.The annual exposure frequency and duration of watching fountains,interactive fountains,green space sprinkling irrigation and sprinklers spraying roads were obtained through questionnaire survey and scene observation shooting.The single health risks and annual health risks of bacterial aerosols through inhalation were calculated based on the microbial quantitative risk assessment model.The results showed that the concentration of bacterial aerosols around the spraying device reaches saturation after 8 min of spraying.The concentration of bacterial aerosols is related to spatial location and bacterial concentration in water source.Within 1～4 m from the spraying device,when the bacterial concentration in the spraying water is 5×102CFU/m L,2×103CFU/m L,5×104CFU/m L and 5×105CFU/m L,The total concentration of bacterial aerosolsis0～（1.1×104±708）CFU/m3,0～（8.6×104±1.1×104）CFU/m3,（28±6）～（1.3×106±2.3×104）CFU/m3and（56±13）～（1.5×107±1.7×105）CFU/m3.And it gradually decreases with the increase of the horizontal distance from the nozzle at a distance of 0 m to 4m.Among the bacterial aerosols formed by atomization spray,there are a large number of live but non-cultivable bacteria.and the concentration of bacterial aerosols measured by flow cytometry is about 3 orders of magnitude higher than the result of plate count.The atomization factor gradually decreases with the increase of the horizontal distance from the nozzle.The atomization factor(m Lwater/m3air)at a height of 1.5m and a distance of 1 m,2 m,3m and 4 m is:30.25,8.52,0.81 and 1.33×10-3.The particle size distribution of bacterial aerosols is independent of the concentration of bacteria in the water source,and the peak particle size all appears between 2.1～4.7μm,and the concentration proportion is more than50%.The retention time of bacterial aerosols at different locations is related to the bacterial concentration of the spraying water source.When the bacterial concentration of the spraying water source is 102CFU/m L,103CFU/m L,104CFU/m L and 105CFU/m L,The retention time of the bacterial aerosols around the sprinkler head is 15,20,25 and 30 min,respectively after turning off the spraying device.The exposure parameters are different in north and south regions,different genders and different age groups.The exposure frequency and duration of Chinese adults participating in watching fountains,interactive fountains,green space sprinkling irrigation and sprinkler spraying roads are 11.3 visits/yr,23.4 min/visit;6.9 visits/yr,26.1 min/visit;18.5 visits/yr,2.21 s/visit;35.5 visits/yr,2.15 s/visit.The exposure frequency and duration of children in the four scenarios are 11.4 visits/yr,18.3 min/visit;8.5 visits/yr,26.1min/visit;9.8 visits/yr,2.21s/visit;21.2 visits/yr,2.15 s/visit.Exposure parameters of populations of different genders and regions obey log-normal distribution.Taking Escherichia coli as a typical pathogenic microorganism,the concentration is the concentration limit（126/100m L）specified in Recreational Water Quality Criteria（U.S.EPA）.The average single health risk of people participating in watching fountains,interactive fountains,green space sprinkling irrigation and sprinkler spraying roads is:4.1×10-9～1.5×10-8,6.8×10-9～1.4×10-8,8.5×10-10～2.1×10-9and 1.2×10-9～2.9×10-9,respectively.The average annual health risk of exposure is:3.5×10-8～1.5×10-7,3.7×10-8～1.1×10-7,4.4×10-9～2.8×10-8and 1.3×10-9～8.2×10-8,respectively.Calculated based on the concentration of live bacteria aerosol cells detected by flow cytometry,the risks of people exposed to the four scenarios is correspondingly increased by about 3 orders of magnitude.The inhalation health risk of people participating in watching fountains and interactive fountains is higher,but none of them exceeded the acceptable annual risk level of 10-4. |
PDF Full Text Request