A New Method For The Validation Of UV Reactors Through The Use Of Photochromic Materials

The interest in UV sterilization has grown significantly in recent years, due, in particular, to the low investment it requires, its limited operating costs and its effectiveness over a broad range of microorganisms. The main difficulty in designing a UV reactor is to understand what is the actual UV dose delivered. In fact, that dose depends upon both the UV radiation field and the flow distribution within the reactor. These two factors contribute to define the paths of the microorganisms and their residence times, on one hand, and the light intensity they are subject to along their trajectory, on the other one. At the design phase, computational fluid dynamics (CFD) allows to predict the performance of a plant with good approximation; hence, it can help to optimize the design of a UV reactor. Then, once the reactor has been built, a validation of its performance has to be carried out. Nowadays, the validation is typically based on microbiological testing (bioassay). This latter verifies, through appropriate procedures, the minimum dosage provided by a plant. However, it is a delicate and expensive procedure. The purpose of this work is to develop a new method that makes the validation of a reactor’s performance a faster, less expensive and more sustainable procedure. To this aim, we used materials sensitive to UVC radiation. Those materials change their colors while passing through the reactor, and their chromatic change is proportional to the dose absorbed. To identify the most appropriate material, a pilot plant has been built and several photo-sensitive materials have been tested. For each material, through an image analysis tool, we measured the color variation and correlated it to the absorbed UV dose. Future researches will be oriented in testing the materials under real operating conditions: some samples of appropriate shape and density will be made and dispersed within a water stream and pumped through the reactor. Comparing the color of the samples before their entry into the reactor with their color at the outlet, we will measure the dose distribution delivered by the reactor. This method will be then used to test a reactor under specific operating conditions, but also as a validation test for the numerical simulations.