Photoreactivation and Dark Repair in UV-Treated Microorganisms: Effect of Temperature

Abstract

Because of the lack of readily available information about the influence of temperature on microorganism reactivation processes subsequent to inactivation with UV radiation, a series of batch reactivation studies were performed at 5, 10, 15, 20, 25, and 30°C. A special effort was made to model the reactivation process to enable the effect of the temperature variable to be quantified. Because an earlier-proposed kinetic model (K. Kashi UV light is one of the most practical methods used for disinfection in wastewater treatment systems because it can inactivate bacteria, viruses, bacterial spores, and oocysts of protozoa (6, 9). Unlike those for other technologies, such as chlorination and ozonation, one of the technological advantages often put forward for UV disinfection is its lack of sensitivity to temperature variations. This independence from temperature would be expected if UV were a simple photochemical reaction (11). Severin et al. (12) performed a series of batch inactivation studies with bacteria, yeast, and viruses and demonstrated that the effect of temperature on UV inactivation was very small. Abu-ghararah (1) found that the effect of water temperature on the kinetics of the UV disinfection process in the normal operating range of most treatment plants (20 to 40°C) is not statistically significant.However, the physiological effect of inactivation is not well understood and is complicated by the ability of many organisms to repair UV damage inflicted to their nucleic acids. While the infliction of damage is a purely photochemical reaction that occurs in the few seconds while water is exposed to UV radiation in the disinfection channels, the interplay of reactions which eventually lead to inactivation includes some biochemical reactions which can be affected by temperature. The latter phenomena can take place during the irradiation period, but it is mostly during the postirradiation time that reactivation processes occur if adequate conditions exist.The principal inactivating effect of UV irradiation is the formation of photoproducts in DNA. Of these photoproducts, the most important is the pyrimidine dimer formed between adjacent pyrimidine molecules on the same strand of DNA, which can interrupt both the transcription and the replication of the DNA. The formation of a dimer can be reversed by two repair mechanisms: photoreactivation and dark repair. Systematic quantitative study of photoreactivation, the more important of the two mechanisms, has suggested a two-step reaction scheme (4).Step 1 is the formation of a complex between a photoreactivation enzyme (PRE) and the dimer to be repaired. This step does not require light, but it is dependent on temperature, pH, and ionic strength (8).Step 2 is the release of PRE and repaired DNA. The restoration of the dimer to its original monomerized form is absolutely dependent upon light energy intensity. The reaction occurs in less than a millisecond; consequently, the limiting step of the whole reactivation process is the formation of the PREdimer complex. A...

Modeling of ultraviolet (UV) radiation under a large pilot-scale designed for wastewater disinfection and inactivation of selected bacteria of Pseudomonas aeruginosa in a laboratory UV device

“…Contrary to the hypothesis advanced by Salcedo et al (2007), that chemical and biochemical rates are supposed to increase by increasing temperature, according to the Arrhenius relationship; however, in the studied case the opposite was observed (Table 3). In fact, k 2 is not a pure reaction rate constant, but rather is a model parameter that is adjusted to predict the experimental data.…”

“…A typical inactivation-reactivation curve as a function of time is shown by Salcedo et al (2007). In the figure, it is possible to separate the various phases of (the process: exponential UV inactivation and the reactivation process, which includes an induction period, the growth phase, the stabilization phase and the decay period.…”

Comparative effect of simulated solar light, UV, UV/H2O2 and photo-Fenton treatment (UV–Vis/H2O2/Fe2+,3+) in the Escherichia coli inactivation in artificial seawater

“…The bacteria that have received sub-lethal damage are able to utilize repair processes. These may occur with light through enzymes like photolyase (Hallmich and Gehr, 2010), but this is possible also in the dark (Rincon and Pulgarin, 2007;Salcedo et al, 2007). In addition, the nutritional sources for bacteria growth as the NOM present in seawater and the organic material from dead bacteria, favor the growth processes.…”

Tecnologia De Ultravioleta Para Preservação De Alimentos

“…A radiação ultravioleta, um dos métodos mais práticos para descontaminação usados no tratamento de água residual, pode inativar bactérias, vírus, esporos de bactérias e oocistos de protozoários (SALCEDO et al, 2007). Como vantagem apresenta baixa sensibilidade à temperatura em relação à cloração e à ozonação nas faixas de operação (20-40ºC).…”