UV Disinfection sensitivity index of spores or protozoa: A model to predict the required fluence of spores or protozoa

During UV disinfection, the required UV dose in terms of fluence depends upon the species of bacteria spore and protozoa. To rank their UV disinfection sensitivity, spore sensitivity index (SPSI) and protozoan sensitivity index (PSI) are defined. For spores, shoulder effect exists, therefore, SPSI is defined as the ratio between the k_i of any spores for the linear portion of the dose response curve to the k_ir of Bacillus subtilis as the reference spore. After statistical analysis, the fluence of any spore can be predicted by SPSI through equation, H ¼ (0.8358 + 0.126)*LogI*SPSI þ H₀. PSI is defined as the ratio between the inactivation rate constants of a protozoa in reference to that of Cryptosporidium parvum. The equation predicting the fluence of any protozoa in reference to Cryptosporidium parvum is: H ¼ 107.45*(3.86 + 2.68)*LogI/PSI. Two regression equations suggest that protozoa require significantly higher UV dose than bacteria spores.