Effectiveness of a UV Treatment Using Light Emitting Diodes (LED) for the Inactivation of Phytoplanktonic Organisms Present in Two Reservoirs of Cádiz (Spain)

The irradiation with ultraviolet (UV) light is a treatment which is often used for the inactivation of waterborne organisms. UV-C radiation impacts directly on the organisms DNA, hindering their reproduction. The objective in this study is determining the efficacy of a UV treatment, using LEDs as a source of UV-C light, for the inactivation of phytoplanktonic organisms present in two reservoirs of the Province of Cadiz (Spain). Samples of surface water were subjected to UV irradiation using a collimated beam reactor equipped with UV-LED lamps. The treatment efficacy was determined, calculating the growth inhibition by means of monitoring the fluorescence throughout an incubation period and, additionally, quantifying the inactivation of viable organisms by means of the most probable number (MPN) method. The results regarding the growth inhibition showed, in general, significant but weak efficacy for the treatment of green algae, requiring UV doses between 109 and 712 mJ cm−2 for inhibiting their growth a 90%. In the case of cyanobacterial growth, there was not, in general, significant effect of the UV treatment. On the other hand, by means of the MPN method, levels of inactivation greater than 2 log-reductions were determined with UV doses of 25 mJ cm−2. The results obtained in this study indicate that the UV-LED treatment with high UV doses may be effective for the inactivation of green algae, but ineffective for the inactivation of cyanobacteria in the range of UV doses applied in this study.