New kinetic model for predicting the photoreactivation of bacteria with sunlight

Exposure to ultraviolet radiation is a disinfection process that is used worldwide for the treatment of wastewater in order to minimize microbial contamination caused by wastewater discharge to natural waters. Once organisms have been exposed to ultraviolet radiation, they are able to repair the damage through two processes - dark repair and photoreactivation. In the work described here, the photoreactivation process after ultraviolet disinfection has been studied in pure culture of Escherichia coli ATCC 11229, ATCC 15597 and in real wastewater, using both a laboratory plant and a pilot plant. A new kinetic model is proposed that is a modification of the model proposed by Kashimada et al. [15] including a first order decay phase. This model was applied to the photoreactivation process with sunlight. The new model incorporates a decay rate constant (M(s)) for solar reactivation in order to explain correctly the decay phase detected in the experimental data for photoreactivation with sunlight. The new model fits the data obtained in reactivation experiments, thus allowing the interpretation of the kinetic parameters S(m), S(m)-S(o), k(s), and M(s) and their relationship with UV dose.