Testing the efficacy of UVC LEDs for biofouling control

Abstract

The use of ultraviolet-C (UVC) light as a biofouling preventative has been successfully demonstrated using mercury-based lamps. However, these lamps have several limitations (such as fragility and use of mercury), and the use of UVC LEDs (light-emitting diodes) has been suggested as an alternative. Several experiments were conducted to assess the efficacy of LED strips (29 W, 270 nm, emittance angle of 130º) for biofouling control, as well as to compare them to a classic lamp (25 W, 254 nm, emits UVC light at 360º). Experiment #1 assessed the biofouling abundance and community composition on test panels exposed to either UVC LEDs (270 nm) or a lamp (254 nm) at a field site in Port Canaveral, Florida. An intermittent dose (43.2 min/day) from the LEDs prevented a majority (>90%) of growth after 12 weeks. The lamp (10 min/day) outperformed the LEDs, but both sources prevented all macrofouling formation, with the LED allowing for a greater biofilm coverage. The different wavelengths (270 nm from LEDs vs. 254 nm from lamp) did not lead to a different fouling community composition. Experiment #2 determined the transmission of UVC in waters of varying turbidity (0 – 50 FNU) at set distances (every 2.54 cm for 63.5 cm) from a light source (LED strip vs. a 7 W lamp). The transmission for both the LED and lamp was greatly reduced with an increased in turbidity. The lower powered LEDs had a shorter maximum distance of transmission at all turbidities. For example, in a turbidity of 30 FNU, the LED was recorded at 17.78 cm as compared to the lamp which was still recorded at 21.17 cm. Lastly, Experiment #3 compared the LED and the 25 W lamp for impacts on three types of marine coatings (epoxy, fouling release, and antifouling coatings). The coatings were exposed to continuous or intermittent exposure (10 min/day lamp or 43.2 min/day LED) regimes for 2 weeks and assessed for changes in mechanical damage, specifically color changes, hardness, coating thickness, and, for the fouling release coating, adhesion strength. The continuous lamp treated fouling release coating slides exhibited some mechanical damage, with adhesion strength increasing from 0.114 MPa to 0.123 MPa and the coating became lighter in color. Continuous treatment for both light sources led to qualitative changes in the other tested coatings as well. The epoxy coating developed a darker and more yellow shade, and the antifouling coating grew darker. However, there was no measurable distinction with mechanical damage to either of the epoxy or antifouling coating. The results of this thesis show that LEDs can be a valuable alternative to mercury powered lamps for marine biofouling prevention. While they can prevent biofouling accumulation at a near equivalent rate as the lamps, there are still some limitations of these systems which should be addressed, such as excess heat generation and the smaller treatment area.