UV-C inactivation of microorganisms in a highly opaque model fluid using a pilot scale ultra-thin film annular reactor: Validation of delivered dose

The efficacy of UV-C light for inactivating bacteria and endospores in an opaque fluid (diluted humic acid at pH 7.2, absorbance = 13.1/cm) using an annular pilot ultra-thin film (1 mm thickness) UV system was investigated in this study. The effect of fluid flow conditions on UV dose distribution was also assessed. UV dose delivery under experimental conditions was verified and validated by a bio-dosimetry method. The results revealed that efficient UV dose distribution was achieved at turbulent flow (Re > 3960) with superior (>2.6 times) microbial inactivation efficiency compared to laminar flow (Re = 1980). Verified reduction equivalent fluence correlated well with calculated UV dose. Microbial inactivation studies at commercial relevant flow-rates (159 gal/h) showed > 5 log reduction of vegetative bacteria (E. coli ATCC 25922, S. Typhimurium ATCC 13311, L. monocytogenes ATCC 19115) and >4 log reduction of endospores (B. cereus ATCC 14579) at UV-C reduction equivalent fluence (REF) of 26 and 34 mJ/cm2, respectively. Comparative operational cost analysis indicated that UV-C pasteurization was 1.3 and 14 times less costly than reported heat and HPP pasteurization, respectively. •Validated a ultra-thin film UV system to disinfect opaque fluids.•Efficient dose distribution and microbial inactivation rates were observed.•Delivered dose was verified by biodosimetry method.•5 log reduction of vegetative bacteria and ~3 log reduction of endospores was achieved.•Lower operation costs as compared to heat and HPP pasteurization.