Comparing the Effectiveness of UV-C on Dynamically Formed Field Biofilms

The application of ultraviolet-C irradiation (UV-C) irradiances is being explored to control marine biofilms due to their abundance, influence on macrofouling settlement, and ability to be cultivated in a laboratory setting. Most field and laboratory studies focus on understanding the efficacy of UV-C on biofilms that are formed under static conditions; however, studying biofilm growth in situ under dynamic or flowing conditions can be challenging. This study aims to understand how UV-C influences biofilms grown in the field under different water flow and shear stresses. Natural biofilms were grown on microscope slides positioned within a flow channel, allowing growth without macrofouling. The channel was divided into three sections for testing: high shear (front), medium shear (middle), and low shear (back). The low shear produced thicker and denser biofilms. Biofilms were subjected to pulsing exposures of 30 (5.58 J/cm²), 60 (11.16 J/cm²), and 90 (16.74 J/cm²) minutes, three times a day. Chlorophyll <i>a</i>, a metric used to determine the effectiveness of UV-C, was reduced under all shear stresses and UV-C trials. Community analysis found groupings of specific bacterial species with diatoms, potentially creating a more robust community structure. Findings indicated that UV-C can control biofilm densities even under continuous flow; however, higher doses appear to be optimal for biofilm reduction.