A novel dual-collimation batch reactor for determination of ultraviolet inactivation rate constants for microorganisms in aqueous suspensions

We developed, characterized, and tested a new dual-collimation aqueous UV reactor to improve the accuracy and consistency of aqueous k-value determinations. This new system is unique because it collimates UV energy from a single lamp in two opposite directions. The design provides two distinct advantages over traditional single-collimation systems: 1) realtime UV dose (fluence) determination; and 2) simple actinometric determination of the Reactor Factor (RF = 1.06) that relates measured irradiance levels to actual irradiance levels experienced by the microbial suspension. This RF replaces three of the four typical correction factors required for single-collimation reactors. Using this dual-collimation reactor, Bacillus subtilis spores demonstrated inactivation following the classic multi-hit model with k=0.1395 cm ²/mJ. Aspergillus niger spores exhibited two-stage decay with a shoulder, with the resistant fraction of the population (f) of 0.251, k ₁=0.1968 cm²/mJ, k₂=0.0426 cm²/mJ.