Design On The Low Concentration Bioaerosol Concentrator And Its Verfication Of Capacity

Objectives:To design a virtual concentrator which can be joined to liquid impactor in order to sample low concentration bioaerosol; To evaluate the performance of virtual concentrator in laboratory and field.Methods:According to the design theory of the virtual concentrator, the Stk50 was identified based on the literature review,According to actual needs,the flow ratio and the sampling flow were fixed. And after considering the capture effect and facilitate the application, the orifice diameter and the number of nozzles were determined ultimately; To improve the collection effect, the study design the cut-off and flat nozzle type concentrators; 0.57,0.98,1.56,2.74,3.78,6.09 and 7.03μm monodisperse "NaCl-DEHS" liquid particles was generated by condensation monodisperse aerosol generator in the laboratory. The collection efficiency,internal loss and concentration factor of the two virtual concentrators (plat and cut-off nozzle) were evaluated; In biological exposure chamber, as a substitute for legionella bacteria, the Staphylococcus aerosol with certain concentration was generated, The "concentrator + Biosampler "joint sampling method and the "Biosampler" independent sampling method both collecting the same time. Using pour plate method to determine the concentration of Staphylococcus in collect liquid, Comparing the results to quantitative evaluation of the concentration effect of concentrator; Regulating the flow of concentrator, using the "U"-tube measure pressure drop; The two sampling methods were used to collect the same volume legionella aerosol and influenza virus aerosol in field, qualitative evaluate the concentration effect by nested PCR qualitatively detection. Results:(1) The concentrator flow rate was 120L/min,flow ratio was 10%,the number of nozzles was 24,cut size was 1.5μm, Reynolds number of this concentrator can meet the parameter conditions. The results showed that the collection effect of'cut-out" type concentrator is better than flat nozzle, the actually cut diameter is 2.16μm, collection efficiency greater than 90% for 3μm and bigger particles; (2)More Staphylococcus albus can be collected by Biosampler after using the concentrator, the ratio up to 3.7; (3) The pressure drop is 2000pa, be in low level in the designed flow rate; (4) On-site sampling for Legionella and influenza virus aerosol results indicated the positive rate between the two methods for legionella (P=0.453). influenza A virus (P=0.696) and influenza B viruses (P=1.000) were not statistically significant.Conclusions:(1) The virtual concentrator design method in this thesis is correct,virtual concentrator with cut-off nozzle structure have lower loss rate and higher collection efficiency; (2) laboratory studies show that the combination concentrator and the "Biosampler" increase the quantity of bacteria collected;(3)On-site sampling results indicated the use of concentrator can reduce the sampling time (1/9) in the premise of ensuring the collection efficiency, demonstrating the concentrator can be used in low concentration legionella aerosols sampling; The collection of influenza virus showed a similar result, indicating that the aerosol concentrator also has some applicability in the sampling of the virus.