Inactivation kinetics in a flow-through UV reactor

The disinfection of treated water and wastewater effluents by ultraviolet light (UV) is a viable alternative to chlorination. One interesting aspect of UV inactivation is the relation of rapid kinetics to the effects of various mixing regimes within nonuniform light intensity fields. Most available literature has been confined to the description of results obtained from UV reactors of proprietory design with little effort to describe disinfection results in continuous-flow reactor systems with known mixing character. Cortelyou et al. reported an increase in disinfection efficiency by increasing turbulence in a single-lamp, continuous-flow reactor. The character of the flow regime in the reactor, however was not established. In batch and plug-flow reactors, the mathematics simulating the inactivation of Escherichia coli were described as a first order rate with respect to the surviving fraction of organisms. Oliver and Cosgrove showed that the rate of inactivation of coliform organisms is first order with respect to UV intensity. Haas and Sakellaropoulos used the assumptions of mixed second-order kinetics with respect to both organism density and UV light intensity and presented mathematical solutions describing the efficiency of single lamp reactors subjected to various flow regimes. In addition, there is still an accepted notion that inactivation data can be treated using simple mixed second-order kinetics by ignoring initial resistance in batch data and extracting a kinetic constant from the linear portion of the inactivation curve. This study examines the inactivation of Escherichia coli, bacterial virus f2, and Candida parapsilosis in a batch UV reactor and in a completely mixed flow-through reactor. Results indicate that mixed second-order kinetics are not generally applicable as a means of scaling between reactor systems with different mixing regimes.