"UV Radiation: an Alternative Disinfectant of Waters"

MARISOL LABAS; CARLOS A. MARTIN; ALBERTO E. CASSANO

Rio de Janeiro (Brasil)

Congreso; 2º Congreso de Ingeniería del Mercosur y 4º Congreso del Mercosur de Ingeniería de Sistemas y Procesos, ENPROMER.; 2005

Microbiological contamination of water has always been a problem of general concern. Among the proposed ways to deal with this type of pollution without difficulties associated with the use of chlorine, UV radiation is an established technology. This work presents a detailed kinetic study of the rate of removal of a model bacteria (Escherichia coli) employing UV radiation (253.7 nm) in a laboratory reactor where all the significant operating variables were carefully measured and controlled. A modification of the Series-Event Model was used to interpret the experimental data which were collected employing four different levels of the incident radiation fed to the reactor. The developed model is based on a rather complex dependence with respect to the Escherichia coli concentration and to the radiation that is effectively absorbed by the bacteria which was precisely quantified. The study was carried out in a well-stirred reactor of cylindrical shape irradiated from both flat sides with two tubular lamps placed in the axial position of two parabolic reflectors. The reactor was operated in a recycle. The concentration evolution was analyzed employing the plate count method with Petrifilm (TM) specific plates. The Incident Radiation at the reactor windows was measured with ferrioxalate actinometry. The kinetic constants of the model were obtained using a multiparameter optimization program. They are: n = 2 (damage threshold); k=1.3142 x 102 s-1 (cm3 s/ Einstein)m (inactivation constant), m = 0.205 (the reaction order with respect to the absorbed radiation by the bacteria). One of the most important conclusions of this work is the observed reaction order with respect to the volumetric rate of radiation absorption by the bacteria. This result may have very important economical consequences.