Potencial uses of Ultraviolet Radiation: The Impact of Bacterial Reactivation on Disinfection Applications.

MARTÍN, C.A.; TROMBERT, A.R.; ZALAZAR, F.; MARTÍN, C.A.

Bilbao, Vizcaya, Spain

Congreso; Chemical Reaction Engineering XI: Green Chemical Reactor Engineering.; 2007

Engineering Conferences International

The access to safe water is one of the Global Environmental Issues for the 21st century. The combination of the increase in water demand and the pollution of superficial and groundwater sources determines a critical situation for the future. Water used for consumption must be provided in both adequate quantity as well as quality to minimize impacts on human health such those producing water-borne diseases. The use of chlorine as disinfectant was introduced in the 19th century. It is very effective, easily applied, and it is fairly persistent and relatively cheap. However, its use is now in discussion since the detection of some disinfection by-products (DBPs) as the trihalomethanes (THMs) generated by the interaction of chlorine with natural organic matter (NOM). This situation requires efforts to develop alternative disinfection processes, such as those based on the germicidal effects of UV radiation. The main advantage of these Advanced Oxidation Processes is the absence of generation of DBPs and then, it is considered an environment friendly process. The effect of the germicidal UV light (253.7 nm) is primarily due to the absorption of photons by thymine bases in DNA and the consequent formation of products that inhibit bacterial replication and produce loss of viability. In this complex mechanism underlies the limitations in the application of UV: the absence of disinfectant residual capacity and the potential bacterial reactivation. From the standpoint of the Chemical Engineering (i.e., from the reactor design) these effects have to be considered in detail, not only for the application to water disinfection but also in the UV use in the food industry. This paper proposes, and experimentally verifies a kinetic scheme for the complete sequence of UV inactivation, and dark repair or photoreactivation for a typical microbiological contaminant (Escherichia coli). The kinetic scheme, based in the formation of pyrimidine dimers, was tested in a lab scale photoreactor, provided with a 15 W lamp (253.7 nm). Besides the standard measurements (bacteria plate count, medium optical characterization, radiation field modeling), molecular biology techniques were applied to improve the quality of the interpretation of experimental data.