Effect of UV-LED fluence rate and reflection on inactivation of microorganisms

Ultraviolet light emitting diodes (UV-LEDs) are emerging as viable alternative to traditional UV lamps for water disinfection. UV-LEDs possess many advantages, some of which include robust configuration, long lifetime, and small size. With UV-LED being an incipient technology, there are also a number of knowledge gaps and challenges towards their widespread applications to water disinfection. The research presented here focuses on addressing two such knowledge gaps; first, the impact of reflection from the reactor wall on the fluence rate distribution inside a UV-LED reactor, and second, the effect of UV fluence rate on the inactivation of microorganisms. Three UV-LEDs: 265nm, 275nm, and 285nm were utilized as the UV sources. The test microorganisms were E.coli ATCC 11229 and Fecal Coliform. Teflon (OD98), stainless steel and aluminum petri dishes were built and used as reflective materials. A new experimental method for evaluating the absorbed energy by a water sample during the UV-LED’s irradiation was proposed. This method was used to derive the E.coli kinetic models at wavelengths of interest. These kinetic models were useful for calculating the inactivation improvement due to reflection inside different reactors. At the same experimental condition, the E.coli log inactivation inside different reactors (reflective and non-reflective as control) was calculated and the kinetic models were utilized to back calculate the correspondent value for the UV fluence in the system. The ratio of the absorbed energy by the solution in a reflective material over that of the control experiment was reported as the improvement arising from reflection within the reactor. The maximum improvement in inactivation of E.coli was around 100% obtained in a reactor made of Teflon followed by nearly 60% and 30% increase in aluminum and stainless steel, respectively. The results also showed that the E.coli inactivation kinetics followed the time-dose reciprocity rule meaning that the same level of inactivation was observed for both high and low fluence rates; whereas the low fluence rate resulted in more Fecal Coliform inactivation than the high fluence rate at the same UV fluence. These observations were consistent for all three LEDs.Applied Science, Faculty ofChemical and Biological Engineering, Department ofGraduat