Actinometers are physical or chemical systems that can be employed to determine photon fluxes. Chemical actinometers are photochemical systems with known quantum yields that can be employed to determine accurate photon fluxes for specific photochemical reactions. This review explores in detail several practical chemical actinometers (ferrioxalate, iodide–iodate, uranyl oxalate, nitrate, uridine, hydrogen peroxide and several actinometers for the vacuum ultraviolet). Each actinometer is described with recommended conditions for its use.

A ring-shaped disinfection apparatus has been developed containing twenty ultraviolet-light-emitting diodes (UV-LEDs) with emission at 285 nm. The apparatus was applied to Escherichia coli, Qβ, MS2, and adenovirus in water. The reduction-equivalent fluence in the apparatus was determined, based on a modification of the protocol for the bench-scale challenge test by low-pressure (LP) UV lamp systems (LPUV). All species demonstrated log-linear inactivation profiles versus the fluence, and the inactivation rate constants for E. coli, Qβ, MS2, and adenovirus were 0.157, 0.037, 0.029, and 0.023 cm2/mJ, respectively. The inactivation rate constant for adenovirus under the UV-LED exposure (kUV-LED′) was higher than that under a LPUV lamp (kLPUV′), and the ratio of kUV-LED′ to kLPUV′, which is approximated as a germicidal factor at 285 nm, was 1.15 for adenovirus. To conclude, this study demonstrated a high potential of the 285 nm UV-LEDs to inactivate microorganisms in water. The germicidal factor found...