Study of inactivation of airborne microorganisms in a photoreactor UV

M. EUGENIA MARTINEZ RETAMAR; CASSANO, A. E.; BRANDI, R. J.; LABAS, M. D.

San Diego, California

Congreso; 17th International Conference on Advanced Oxidation Technologies for Treatment of Water, Air and Soil (AOTs-17); 2011

Indoor air pollution by microbial contaminants is receiving increasing attention as a public health problem. The reason is that the majority of people, at least in developed societies, spend over 90% of their time in confined environments, either at home or at work, which facilitate to a greater extend their susceptibility to different pathogens. Therefore, there is great interest in the engineering of air pollution control to reduce indoor infectious diseases caused by airborne pathogens. Germicidal UV systems are one of the most promising technologies to inactivate these pathogenic microorganisms. Thus, the goal of present work is to study the inactivation of airborne microorganisms, using an UVC photoreactor. With this purpose, an experimental device was designed and constructed in order to obtain experimental data of UV inactivation airborne microorganisms. The experimental device consists of three main parts: a generation system for feeding the stream of air, a photoreactor, and a bioaerosol capture system. The reactor is of annular shape with a total volume of 2.8 liters. A nebulizer was designed and built to generate the desired bioaerosol concentration. A strain of E. coli was selected as test organism. The bioaerosol generated pass through the reactor, and it was irradiated by an UV lamp emitting at 253.7 nm wavelength, which is placed at the centerline of the annular space of the photoreactor. 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. Flow rates of the described streams were measured using variable area rotameters. Measuring points were at the input of nebulizer, in the air stream without microorganisms, and at output of the impinger. All experiments were conducted inside a biological safety cabinet. 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 h at 37°C for subsequent counting. From the obtained data in preliminary experimental runs it was possible to determine the level of reduction in bacteria concentration between input and output of the reactor, for different operating conditions. Values showed a 99.9% inactivation of E. coli during rather short irradiation time. This indicates that, under the studied experimental conditions, the viability of E. coli was affected by the 253.7 nm wavelength UV irradiation. Collected data are used to develop the intrinsic kinetic parameters of the process under study and the subsequent modeling of a reactor with a different and more complex configuration having greater disinfection efficiency. These studies provide the basis for designing of new device for controlling microbiological pollution in indoor environments that can be very easily attached to existing ventilation systems.