Biofilm prevention on optics by chlorine compound generation on tin oxide coating

Biofilm reduction is still a major problem for underwater instrumentation and more specifically in the case of optical measurements or viewing. The aim of the present work which is supported by the EC-MAST III programme BROS, is to assess the effectiveness of a window protection technique against biofilm growth. This technique is based on the generation of hypochlorous acid and hypochlorite ions by sea water electrolysis on a transparent conductive tin oxide coating. The work has been first focused on tin oxide corrosion resistance. Then, in house and in situ experiments have been carried out to assess the efficiency against natural biofilm. The original optical set-up, allowing the authors to check continuously the evolution the protected and unprotected optical path on different glass samples described elsewhere has been used. In house and in situ experiments have been performed. In situ experiments have been performed with two underwater video cameras. A tin oxide coated window has been set up on first one, an unprotected reference window was set up on the second. Cameras have been deployed on sea floor at Ifremer marine test station (Brest Bay) for four months. The different results presented allow the authors to conclude that generation of chlorine biocide compounds by sea water electrolysis on a transparent conductive tin oxide coating is a good strategy to prevent biofilm growth on optical surfaces. The surface treatment is efficient after a long time in use, the window optical characteristics were not strongly affected and the overall energy demand is low enough to enable application of this technique to a large range of equipment.