The current work is concerned with the development of a kinetic model for UV disinfection process at 254 nm. The micro-organism was Escherichia coli (E. coli). The inactivation of E. coli active cells, suspended in sterile double-distilled water, free-of solids, nutrient and any trace of broth, was carried out in a bench-scale annular photoreactor, designed specifically for developing kinetic studies. The UV-C light source used was a tubular low pressure Philips lamp, model TUV-36W. The reactor model was based on the conservation principles. The radiation field was modelled according to the radial incidence model. The incident radiation energy at the photoreactor optical entrance was measured by homogeneous potassium ferrioxalte actinometry (1.4 x 10(-9) Einstein cm(-2) s(-1)). The Naperian absorption coefficient of the E. coli active cells was obtained (1.05 x 10(-8) cm(2) MPN-1). The kinetic model proposed was a simple phenomenological equation relating the reaction rate to both the concentration of microbial active cells and the radiation energy absorbed by these cells. A term related to the rate of growth of microbial cells was added to the kinetic model. The experimental runs were carried out for conditions where the initial concentration of E. coli active cells varied from 2.0 x 10(4) MPN cm(-3) to 2.0 x 10(6) MPN cm(-3), pH7 and temperature 25 degrees C. Disinfection efficacies of 4.3-Log and 6.3-Log were achieved for both conditions and the respective required UV doses were 23.4 mW cm(-2) and 31.2 mW s cm(-2). The kinetic model fitted the data well (to 95%). The kinetic parameters, n and K, were estimated in 0.5 and 2.9 x 10(-2) s(-1)(cm(3) Einstein(-1))(0.5), respectively. (C) 2012 Elsevier Ltd. All rights reserved.