10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Development and Optimization of the Electrostatic Precipitator with Superhydrophobic Surface (EPSS) Mark III for Collection of Bioaerosols
TAEWON HAN, Nirmala Thomas, Gediminas Mainelis, Rutgers, The State University of New Jersey
Abstract Number: 540 Working Group: Bioaerosols
Abstract In our earlier research, we developed a liquid-based electrostatic precipitator with the superhydrophobic surface (EPSS Mark I and II) for bioaerosol sampling where airborne particles are deposited onto a narrow electrode (3.2 mm) covered by a superhydrophobic substance. The deposited particles are removed and collected by a rolling water droplet (a few tens of microliters) which results in high concentration rates. The Mark I featured a separate charger (commercially available ionizer) and collector, while the Mark II was a single-stage electrostatic precipitator (charger and collector placed in the same chamber). The Mark I and II versions showed high collection efficiency (~70%) for sampling airborne biological particles; however, a commercial ionizer used to charge incoming bioaerosols in Mark I resulted in particles losses as high as 50%, and the ionizer (for the Mark I) and the laboratory made ionizer (for the Mark II) produced high levels of ozone.
Thus, the latest version of EPSS (Mark III) has been entirely redesigned into a two-stage electrostatic sampler (separate charger and collector) for better control of charging process to prevent particle loss in the charger and to minimize damage to collected microorganism due to ozone production during ion generation. Mark III consists of a static air blender, a charger, a transition section, and a collector; it has a shape of a cylinder (1 inch in diameter and ~3 inches in length) and is made of a static dissipative material (Delrin). Also, our earlier developed and low-ozone-producing charger (wire-to-wire design) is integrated with a newly designed collector. This charger features a tungsten wire (0.003 inches in diameter and 1 inch in length) installed in the middle of the charging chamber and connected to high voltage. A ring of stainless steel (SS) wire 0.015 inches in diameter is installed on the inside of the charging chamber at the middle of the tungsten wire and grounded. The collector consists of a grounded SS cylinder (1 inch in diameter) inside the collection chamber and an SS collection rod (6/32 inches in diameter and 2.5 inches in length), which is positioned in the middle of the chamber and connected to a collection voltage. After completing the sampling, the collection rod is removed from the collector and transferred into a glass tube, and then the captured particles are easily extracted using a small volume of water (300-600 microliters) and by ultrasonic agitation for 30 min.
At this stage of development, the Mark III was tested at different collection voltages (-7 to -9 kV), while the charging voltage was fixed at +5.25 kV when challenged with 1 µm in diameter polystyrene (PSL) particles and at flow rates of 10 L/min. The sampler’s collection efficiency was determined by measuring the number of particles deposited on the collection rod and the reference filter using mass-balance analysis by a fluorometric method. The collection efficiency was about 55-70% at the flow rate of 10 L/min, and ozone production was below 10 ppb. Further, physical efficiencies were optimized as a function of the collection rod size at different PSL particle sizes (0.5, 1, and 3 μm) and flow rates (10 to 30 L/min). Viability and culturability of cells collected by Mark III were investigated by using ATP bioluminescence, a ratio of Live/Dead cells (flow cytometry), and Colony Forming Units, and compared against that of the reference filter when sampling for 10 min and 8 hours.