A New Method for the Validation of Ultraviolet Reactors by Means of Photochromic Materials

The interest in ultraviolet (UV) water sterilization has grown significantly in recent years. The main difficulty in designing a UV reactor is to assess the UV dose delivered. In fact, that dose depends on both the UV radiation field and the flow distribution within the reactor. At the design phase, computational fluid dynamics (CFD) helps to predict the UV dose distribution, but it requires a validation; nowadays, such validation is possible only using the Lagrangian actinometry method. This promising technique, however, requires a complex and expensive equipment, which makes it difficult to apply in most of the real contexts. The purpose of this work is to develop a new method to make the validation of the UV reactor performance a faster, less expensive, and more sustainable procedure. To this aim, we used two photochromic materials, sensitive to the UV-C radiation. Each material has been characterized by relating its color variation with the absorbed UV dose. Samples of such materials, in some cases stuck on supports characterized by different densities, were then inserted within a pilot UV reactor under three different flow rates, to measure the dose distributions. These latter were then compared with the results obtained by the CFD simulations performed on the same reactor geometry, and by biodosimetry analyses. The best results, both in terms of average value and distributions of the UV dose, were obtained from the photochromic amorphous polypropylene samples, having a density similar to that of water. This method emerges then as a promising validation technique, able also to assess the dose distribution of a UV reactor.