Estimating Solar and Nonsolar Inactivation Rates of Airborne Bacteria

Abstract

Land application of biosolids is a wide spread practice in the United States, Canada, and Western Europe. Given the potential for biosolid aerosolization during land application, both solar and nonsolar induced inactivation rate information is needed to more accurately predict the fate of bacteria in air. Pilot-scale bioaerosol reactor experiments that independently measure the solar and nonsolar (absence of solar radiation) inactivation rates of airborne Mycobacterium parafortuitum and Escherichia coli were performed. Direct fluorescent microscopy measurements for total airborne bacteria and culture-based assays were used to measure concentrations in a 1m3 aerosol reactor that was transparent to UV-A and UV-B wavelengths, and to produce decay curves of airborne bacteria under moderate (50–60%) and high (85–95%) levels of relative humidity (RH). E. coli was more susceptible to airborne decay than M. parafortuitum at all RH levels tested. RH strongly influenced solar and nonsolar airborne inactivation rates in both bacteria. These inactivation rates for both bacteria were greatest at moderate RH levels.