Experimental Assessment of Photon Fluence Rate Distributions in a Medium-Pressure UV Photoreactor.

The performance of a medium-pressure (MP) mercury lamp photoreactor is strongly influenced by the spatial photon fluence rate (PFR) distributions which are wavelength-dependent. To address this issue, PFR distributions in an MP lamp photoreactor were measured using a 360-degree response microfluorescent silica detector (MFSD). To accurately express the optical behavior in an MP photoreactor, PFR, MFSD response PFR (PFRMFSD), and effective germicidal PFR (PFRGER) were defined and compared. The measured axial and radial PFRMFSD values agreed well with the corresponding results from a simulation model (UVCalc). The PFR and PFRGER were obtained from the measured PFRMFSD by using correction factors calculated by the UVCalc. Under identical UV transmittance (254 nm) conditions (75% and 85%), the weighted average PFRGER values were 13.3-18.7% lower than the corresponding PFR values, indicating that PFRGER, rather than PFR should be used in MP photoreactor design to meet disinfection standards. Based on measured lamp output, medium absorption spectrum, MFSD response, and microbial DNA response spectrum, the detailed relationships between the PFR, PFRMFSD, and PFRGER were elucidated. This work proposes a new method for the accurate description of wavelength-dependent PFR distributions in MP photoreactors, thus providing an important tool for the optimal design of these systems.