UVGI inactivation kinetics of airborne microorganisms

MARTINEZ RETAMAR, M. E; CASSANO, ALBERTO E.; BRANDI, RODOLFO J.; LABAS, MARISOL D.

Cartagena, Colombia

Conferencia; First Latin American Conference on Semiconductor Photocatalysis, Solar Energy Conversion and Advanced Oxidation Technologies; 2013

Several events of indoor pollution, at least in developed cities, have involved some pathogenic human microorganisms. In recently years, these airborne microorganisms, called bioaerosols, have been responsible for a great number of infectious outbreak. Therefore, there is great interest in the engineering of air pollution control to reduce indoor infectious diseases caused by airborne pathogens. Because employing UV germicidal irradiation (UVGI) is one of the technologies to inactivate these bioaerosols, this work has the objective of determining the UVGI inactivation kinetics for microorganism employing a photoreactor.   In order to obtain experimental data, an annular photoreactor, with a total volume of 0.67 liters, was employing. The UVGI source was an ultraviolet germicidal lamp (15 watts, 253.7 nm) that was placed at the centerline of photoreactor. Through the annular space, an airstream with Escherichia coli was flowed. The desired bioaerosol concentration was generated with a nebulizer. An additional clean airstream was coupled to obtain about 33 L/min at the inlet of the reactor. At the exit of the reactor, the sampling system composed of an all glass impinger was placed. The impinger collects bioaerosols in a capture liquid which can then be plated out for microbial counts. The sampling was performed before, during and after the irradiation period, at fixed time intervals. After this time, the capture liquid was collected in another recipient, and the impinger was filled with new fresh capture liquid. The capture liquid was plated on EMB and incubated for 24 hours at 37°C for subsequent counting. Experimental runs were performed at the same residence time (0.02 min). Relative humidity and temperature were reported. Different E. coli concentrations at the inlet of the photoreactor were used, ranging from 1x105 to 1x109 UFC/m30; and four different levels of UV irradiation were experienced.   From these experimental data,  it was possible determinating the overall reaction rate. These results showed a first order inactivation rate respect to E. coli concentration and incident radiation. In consequence, a simple mathematical expression was used to get the intrinsic kinetic constant of the process under study. This parameter was obtained resolving the mass and the photons balance inside the photoreactor, and using a computational routine that minimize the mean squared differences between the observed data and the predictions of the model. It was possible proved that model data adjusted with experimental data. The results were used to calculated the dose required to inactivate E. coli aerosolized employing a UV photoreactor. This kinetic constant determinated is independent of the system and it could be applied for simulation and optimization processes, as well as change of scale.   This study provide significant information for designing a new device for controlling microbiological pollution in indoor environments that can be very easily attached to existing ventilation systems.