Modeling a UVGI Reactor for airborne microorganisms inactivation

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

Jacksonville, Florida

Congreso; AOTs-18: Advanced Oxidation Technologies for Treatment of Water, Air and Soil; 2012

Airborne transmission of respiratory infections is recognized as a public health problem which could involve some pathogenic human microorganism. These microorganisms could travel long distances suspended on small droplet nuclei and remain in environments along enough time to promote an infectious incident. 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 pathogenic microorganisms, this work has as objective modeling a UV photoreactor for airborne microorganism inactivation. In order to obtain experimental data on airborne microorganisms UV inactivation, an experimental device was designed and constructed. The reactor was of annular shape, with a total volume of 0.67 liters, at whose centerline an ultraviolet germicidal lamp (15 watt, 253.7 nm) was placed. Through the annular space, an Escherichia coli airstream was flowed. A nebulizer was designed and built to generate the desired bioaerosol concentration. 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 h at 37°C for subsequent counting. 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. Experimental runs were performed at the same residential time (0.02 min), with a relative humidity and temperature between 40% a 75% and 19ºC a 27ºC, respectively. Different concentrations of E. coli inlet were used, ranging from 1x105 to 1x109 UFC/m3, and two different levels of UV irradiation. All experiments were conducted inside a biological safety cabinet. From these experimental data, it was possible to determine the percentage of bacterial inactivation between input and output of the reactor, for different operating conditions. Values showed a 98.9% inactivation of E. coli during 1.198 seconds residential time. Besides, collected data were used to get the intrinsic kinetic parameters of the process under study using a simple mathematical expression. This study provides the basis for modeling a bigger photoreactor which have greater disinfection efficiency. Experimental data from this device with a bigger volume of 2.56 liters were obtained to develop experimental verification. Results obtained will 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.