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...
