Mathematical Modeling of UV Disinfection

Mathematical modeling of the UV disinfection process provides a basis for sizing ultraviolet disinfection equipment and for interpreting test results. It also allows for adaptation of UV systems to specific disinfection processes and for the disinfection of specific microorganisms. Disinfection is generally modeled in terms of the survival, or its converse the inactivation rate, and may be rendered as a fraction or a percentage. Disinfection is invariably a logarithmic process, as is microbial growth. The disinfection rate of the microorganisms varies widely and is subject to many complexities, including shoulder effects, second stage decay, relative humidity effects, and photoreactivation. Not all these processes need be considered for every design application, but a familiarity with these effects is essential for understanding UV disinfection. Furthermore, not all of these processes can be completely and accurately modeled at present, but enough is known to adequately design reliable UV disinfection systems. All of these processes can be modeled with basic exponential equations and by using computational methods if necessary. For more detailed background information on theoretical decay models for general disinfection purposes see Kowalski (2006), Chick et al. (1963), or Hiatt (1964).