| The airborne microbiological components usually have aerodynamic diameters of 0.3-100μm. Exposure to those pathogenic ones could cause many adverse health effects. Accordingly, improving sampling and detection methods becomes an important topic in the field. The purpose of bioaerosol sampling is to quantify the presence of bioaerosols to identity the sources for control.Electrostatic precipitator is more effective in collection of fine particles than that in the common sampling technologies, e.g. bioaerosol impactors and impingers. Also, it is less harmful to microorganisms. The major study of this thesis is the theory of the aerosols collection and the factors affecting the electrostatic precipitation efficiency. The bio-aerosol size distribution was monitored by Electrical Low Pressure Impactor (ELPI).This thesis investigates physical and biological efficiencies of a portable homemade electrostatic sampler considering some factors. The results showed that the E.coli aerosols were in the range of 0.028-4.01 μm in aerodynamic diameter with positive electric charges, and half of culturable E.coli were in the range of 0.95-1.61 μm; C.albicans aerosols were in the range of 0.028-9.96μm with negative electric charges, and a majority of culturable C.albicans were around 2.40-4.01μm.The self-designed electrostatic sampler without charging region utilizes the natural electrical charges on airborne microorganisms for their collection.The collecting efficiency was increased by increasing the collection length and the applied voltage. When the length of collection plate is 10 cm and the applied voltage is 10 kV, the physical collecting efficiency of E.coli aerosols and C.albicans aerosols were 60% and 75%, respectively.The biological collecting efficiency of electrostatic sampler was compared with traditional microbial impactor AGI-30 and filter sampler. The biological collecting efficiency was increased with increasing the collection length, while decreased with increasing the flow rate. The opitimal voltage was 10 kV, because the higher applied voltage may cause gas discharge in the system and inactivate microorganisms. When the length of collection plate is 10 cm with a flow rate of 10 L/min, the electrostatic sampler collects more culturable bioaerosols than the AGI-30 as larger as 1.27 times and 4.0 times of E.coli and C.albicans aerosols; than filter sampler as larger as 1.4 times and 2.8 times of E.coli and C.albicans aerosols, respectively. At the same time, the study found that the sampling time, microbial aerosol concentration, air humidity has little effect on collecting efficiency. Hence, the electrostatic sampler is suitable for long time and low concentration of microbial sampling.Positive corona discharge is more suitable for bioaerosols precharging than the negative corona discharge. When the charging voltage is+5 kV, electrostatic sampler collects the maxium concentration of culturable bioaerosols. The concentration of culturable bioaerosols is collected as 10 times and 7.7 times higher than AGI-30 sampled for E.coli and C.albicans aerosols, as 11 times and 5.2 times higher than filter sampler sampled for E.coli and C.albicans aerosols, respectively. At the same time, the bioaerosols pre-charging could make bioaerosols mainly collected in a plate, which could simplify the sampling work.According to the data of school stationing experimental sampling, electrostatic sampler is also suitable for sampling microbial aerosols of the environment. And electrostatic sampler is better than the AGI-30 sampler. There is a high level of microbial content in the hospital, cafeteria and toilet. But in toilet, fungal concentrations are the highest. |
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