Efficacy of the UV-LED treatment to inactivate phytoplankton in port waters: viable organisms, re-growth, and changes in the phytoplankton community
The ultraviolet C (UVC) treatment is used commonly as a Ballast Water Treatment System as a way for the ships to comply with the Ballast Water Management Convention (BWMC) D-2 standards. Developments in the Light Emitting Diodes (LEDs) technology in the range UVC suggest they may become a more sustainable alternative to the conventional UVC sources based on mercury lamps. The objective of this study is to compare the inactivation efficacy of UV treatment using LEDs emitting at 265 and 275 nm with a conventional low-pressure mercury vapor lamp emitting at 254 nm, employing a natural phytoplankton assemblage from the Algeciras (Spain) port-water as the target. Most Probable Number (MPN) indicated a reduction from 490 cell mL-1 into values in compliance with the BWMC D-2 standards by applying UV doses as of 100 mJ cm-2. The growth inhibition was greater than the 90% between 5 and 8 days after the treatment with UV doses as of 100 mJ cm-2; however, greater UV doses resulted effective for limiting the subsequent phytoplankton regrowth. The application of 202.1 ± 25.7 mJ cm-2 caused the reduction of the photosynthetic yield into 0.25, used as a reference for a safe ballast water discharge in indicative analyses. The metabarcoding analysis reported a significant reduction of the phytoplankton taxa with a UV doses as of 200 mJ cm-2. The statistical analyses indicated absence of significant differences between the three wavelengths used in this study, indicating that the UV LEDs are as effective as conventional UVC lamp.