Ultraviolet light is absorbed by the proteins RNA and DNA in micro-organisms. Absorption of high doses of UV by proteins in cell membranes ultimately leads to the death of the cell. However, at much lower doses of UV, absorption by DNA merely disrupts the ability of the micro-organism to reproduce. A cell that cannot reproduce cannot infect other cells. UV reactors are designed to deliver a dose of UV radiation to micro-organisms in the water as it flows around a lamp. The disinfection efficiency of these reactors depends on the lamp power and residence time of the water around the lamp. Simulations of UV reactors are targeted toward resolving the hydrodynamics of the reactor while including the radiation field. The radiation models provided by FLUENT can be used for this purpose. Many particles (representing micro-organisms) are introduced to the flow field, and the received UV dose is determined for each one. Engineers can then ascertain the percentage of micro-organisms that receives a sufficient dose to be inactivated and the percentage that receives too high a dose.

Particle tracks colored by incident radiation represent trajectories of microorganisms in a UV reactor
Courtesy of Veolia Environnement