Kinetics of bacteria (Escherichia coli) disinfection employing Hydrogen Peroxide

MARISOL D. LABAS; CRISTINA S. ZALAZAR; RODOLFO J. BRANDI; ALBERTO E. CASSANO

Campinas, Brasil

Congreso; III EPOA Encontro Sobre Aplicações Ambientais de Processos Oxidativos Avançados; 2005

The antimicrobial and /or antiseptic properties of hydrogen peroxide have been known for many years now because of its efficacy, versatility and reasonable manipulation safety. The bactericidal effect of hydrogen peroxide on biological systems has been reported, showing growth inhibition and/or inactivation of pathological microorganisms with remarkable effectiveness in vegetative bacteria, fungi, viruses, mycobacteria and bacterial spores when using the appropriate disinfectant concentration and operating conditions. Hydrogen peroxide is an excellent source of hydroxyl radicals OH that are highly reactive and very toxic for biomolecules. Although the exact mechanism by which H2O2 produces lethal consequences for many microorganisms has not been clearly elucidated, it is well known that due to its strong oxidative properties it can produce damage to nucleic acids, proteins and cellular lipids. There are several ways that hydrogen peroxide can bring forth hydroxyl radicals; among them it can be mentioned: (1) interaction with transition metal ions existing in the medium (e.g., copper, iron, etc.), (2) the existence of intra or extra cellular Fe2+ to produce a Fenton reaction, (3) UV irradiation and (4) oxidative stress resulting from the cell own respiration. The lethal damage can be produced by the hydrogen peroxide existing in the medium (exogenous effect) or the one produced by the cell (endogenous effect). However, bacteria have their own enzymatic mechanisms or catalases that, within limits, exert a self protecting action. In this work we have studied the kinetics of Escherichia coli disinfection in water environments employing hydrogen peroxide alone. Experiments were performed in a specially designed, well mixed batch reactor that is part of a recycling system. Initial bacteria concentrations were always in the order of 105 CFU/cm3 and H2O2 concentrations were varied between 25 and 300 ppm. It was observed that the inactivation rate presents a direct dependence on the H2O2 concentration and, an additional effect, producing a significant reduction in the usually observed lag time at the beginning of the process. The inactivation rate was modeled and the corresponding model parameters were calculated. These results are useful for scaling-up purposes because the obtained parameters are independent of the reactor geometry, size and operation.