Aerosols and Electrical Discharge: 1. Examination of Potential Climate Impact of Mercury Control in Electrostatic Precipitators (ESPs); 2. Instantaneous Bioaerosol Inactivation by Non-Thermal Plasma

Abstract

One common technology for airstream aerosol (or particulate matter) control is through electrical discharge. Electrical discharge within a neutral gas under atmospheric conditions has two major essential applications related to either its physical or chemical properties. Devices such as electrostatic precipitators (ESPs) are widely applied to reduce stationary PM emission utilizing physical properties of electrical discharge. Separately, the chemical properties of the high voltage discharge can be utilized in several chemical processes, including bioaerosol disinfection. This dissertation had two research focuses related to either the physical or chemical properties of electrical discharge on aerosol control.

The first study focus is on potential impact of mercury emission control by powdered activated carbon (PAC) injection to climate change due to low removal efficiency of PAC in ESPs. The injection into the flue gas of PAC is the most mature technology for controlling mercury emissions from coal combustion. However, carbonaceous particles are known to have poor capture in ESPs. Thus, the advent of mercury emissions standards for power plants has the potential for increased emissions of PAC, whose climate change impact is unclear. The study conducted the first comparative measurements of optical scattering and absorption of aerosols comprised of varying mixtures of coal combustion fly ash and PAC. A partially fluidized bed (FB) containing fly ash-PAC admixtures with varying PAC concentrations elutriates aerosol agglomerates. A photo-acoustic extinctiometer (PAX) extractively samples from the FB flow, providing measurements of optical absorption and scattering coefficients of fly ash (FA) alone and FA-PAC admixtures. The results indicate that the increase of carbonaceous particles in the FB emissions can cause a significant linear increase of their mass absorption cross sections. Thus, widespread adoption of activated carbon injection in conjunction with ESPs has the potential to constitute a new source of light absorbing (and climate warming) particle emissions.

The second research focus is on packed-bed non-thermal plasma (NTP) discharges and its in-flight inactivation of bacteriophage MS2 and Porcine Reproductive and Respiratory Syndrome virus (PRRSv). To reduce threats of airborne infectious disease outbreaks, there exists a need for control measures that provide effective protection while imposing minimal pressure differential, where NTP can be a solution. In the first part of this study, a low-cost consumer-grade ultrasonic humidifier is proved to consistently suspend dry MS2 aerosols into a constant air flow, and the ultrasonic atomization rate can be monitored in real-time by laser-photodiode light attenuation measurements. In the second part, suspended viral aerosols in a controlled airstream were subjected to NTP exposure within a packed-bed dielectric barrier discharge reactor. Results of plaque assays for MS2 and TCID50 (50% Tissue culture infective dose) for PRRSv showed increasing inactivation of aerosolized viruses (42% to >99%) with increasing applied voltage. No evidence showed that the lipid layer of enveloped PRRSv offered any protection against inactivation, and the virus were inactivated comparably to MS2 by the reactor. Increasing the air flow rate did not significantly impact virus inactivation effectiveness. Activated carbon based ozone filters greatly reduced residual ozone, in some cases down to background levels, while adding less than 20 Pa pressure differential to the 45 Pa differential pressure across the packed bed. The study shows promising results that the prototype packed bed NTP reactor has the potential to reduce airborne infectious disease transmission into indoor environment without significant ozone emission and pressure drop.