ORIGINAL PAPER A New Method for the Validation of Ultraviolet Reactors by Means of Photochromic Materials F. Solari 1 & G. Girolimetti 1 & R. Montanari 1 & G. Vignali 1 Received: 18 January 2015 /Accepted: 6 August 2015 /Published online: 23 August 2015 # Springer Science+Business Media New York 2015 Abstract 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, com- putational fluid dynamics (CFD) helps to predict the UV dose distribution, but it requires a validation; nowadays, such val- idation is possible only using the Lagrangian actinometry method. This promising technique, however, requires a com- plex 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 sustain- able procedure. To this aim, we used two photochromic ma- terials, 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. Keywords Photochromic materials . Ultraviolet . UV reactor . Validation . CFD . Water decontamination Introduction Ultraviolet (UV) ray technology is increasingly adopted in recent years in many water treatment applications, such as disinfection of drinking or recreational water and municipal wastewaters (Schalk et al. 2005; Hijnen et al. 2006). This is mainly due to the better control of the process, its cost-effec- tiveness, its potency over a wide range of microorganisms, and its ease of installation and use (Guerrero-Beltrán and Barbosa-Cánovas 2004; Bintsis et al. 2000). Moreover, con- trary to chlorine disinfection, during UV sterilization, no harmful by-products for human health are produced (e.g., trihalomethanes). However, unlike chemical disinfection systems, the pro- cess cannot be monitored by measuring the residual disinfec- tant concentration and the flow rate; for that reason, validation and certification of the UV system performance are often re- quired, in order to demonstrate the safe application of UV disinfection. Nowadays, reactor validation is achieved mainly through biodosimetry tests, based on standardized protocols (e.g., ÖNORM 2001; DVGW 2003; USEPA 2006). These proce- dures allow to determine the reduction equivalent dose (RED) of a UV reactor by measuring the inactivation of a target microorganism after its exposure to the UV light in a UV reactor and comparing the results with the known UV dose– response curve of the target microorganism (determined via bench-scale collimated beam testing). Such procedures have the advantage of allowing direct measurements on waterborne microorganism; however, the results cannot be used to predict the effect on microorganisms other than the target one, unless * G. Vignali giuseppe.vignali@unipr.it 1 Department of Industrial Engineering, University of Parma, Viale delle scienze 181/A, 43124 Parma PR, Italy Food Bioprocess Technol (2015) 8:2192–2211 DOI 10.1007/s11947-015-1581-1