UV-C Lights to Minimize Biofouling
By Christian Haag
Biofouling is a natural process marked by the accumulation of microorganisms, plants, and algae on artificial surfaces submerged or in contact with seawater or freshwater. This can affect a variety of structures, including ship hulls, water inlets, pipes and aquatic sensors. Such buildup not only compromises the integrity of these objects but also interferes with their intended functions.
To combat biofouling, several technologies have been developed, including paints, resins and chemical sprays that release biocidal substances to prevent microbial adhesion. While antifouling coatings can be effective, they often pose environmental risks due to their toxic components.
In contrast, a nontoxic and highly efficient alternative for biofouling control is the application of UV-C spectrum ultraviolet radiation. UV-C light damages the genetic material of microorganisms, inhibiting their reproduction and colonization.
Mariscope Meerestechnik has developed submersible lamps equipped with UV-C LEDs specifically designed to mitigate the adverse effects of biofouling on submerged surfaces. We tested two lamps with different light emission cycles underwater in Puerto Montt, Chile, from January to August 2024 to evaluate their efficiency and effectiveness in preventing biofouling growth over several months. Visual comparisons were made to discern variations across different light configurations.
Understanding Biofouling
The biofouling process commences when a substrate is immersed in an environment rich in living organisms that require stable surfaces to complete their reproductive cycles. Within hours of immersion, a submerged surface can develop initial bacterial colonization. These bacteria release substances that promote the adhesion of single-celled organisms and microscopic flora. This proliferation fosters an environment conducive to the attachment of larger species, including algae, sponges and various shellfish. Factors such as the hardness and chemical composition of the submerged material, temperature, and light conditions play critical roles in determining which species adhere.
Biofouling presents operational challenges, including excessive weight on floating objects, damage to vessel surfaces, and obstruction of measuring equipment and underwater sensors used in monitoring and research.
Antifouling Solutions
To address biofouling issues, various methodologies have been employed, primarily focusing on antifouling paints and ultraviolet light radiation. While antifouling coatings are effective, their use has raised regulatory concerns due to the harmful biocidal agents that leach into the water, endangering the marine environment.
In contrast, UV lights do not pose such environmental risks. They offer a targeted approach with low energy consumption, demonstrating exceptional efficacy in keeping illuminated surfaces free from biofilm.
The Science of UV-C Light
UV-C light operates at short wavelengths (240 to 280 nm) and is highly energetic, making it dangerous to human tissues yet nontoxic to the environment. Although UV-C light is naturally emitted by the sun, it is fully absorbed by the atmosphere. Organisms’ DNA and RNA absorb this short-wavelength energy, altering their genetic structure and rendering them unable to reproduce. Consequently, bacteria and other microorganisms are deactivated, leading to disinfection of the surface where UV-C light is concentrated.
The Mariscope UV-C LED Lamp
The concept and initial prototypes of this innovative antifouling UV light were developed by engineers at the Leibniz Institute for Baltic Sea Research Warnemünde, Germany (IOW). Successful tests were conducted on sensors operated by IOW in the Baltic Sea, providing continuous environmental monitoring. This antifouling system received production certification in 2021 and is now manufactured by Mariscope under IOW’s license.
Designed for user-friendly operation, the lamp employs a UV-C LED and features a robust pressure housing capable of withstanding up to 15 bar (equivalent to a water depth of 150 m). An acrylic glass cap protects against accidental exposure to UV-C light during handling and programming, which is removed during underwater use. The lamp measures 127 mm in length and 30 mm in diameter.
Fish Farm Experiment
Two Mariscope UV-C lamps were mounted on a stainless steel structure measuring 1 m², positioned 25 cm away from a fish net with a mesh size of 0.5 mm. The lamps were programmed to alternate between on and off cycles: lamp one was off for 1 sec., while lamp two was off for 4 sec., representing 25 percent of the maximum irradiating energy. Both lamps consumed 40 mW/s while operational.
The system was deployed on a pontoon near the shore of Puerto Montt in northern Chilean Patagonia. The region’s fjord waters are highly productive in spring and summer, with strong blooms of microalgae and bacteria that accelerate biofouling, posing significant challenges to aquaculture, a vital economic sector in the area.
To ensure stability, ropes were secured to the pontoon and weighted to maintain approximately 3 m of water over the structure, even at low tide. The system underwent visual inspections every two weeks over a 32-week period. At week seven, lamp two was adjusted to evaluate its effectiveness in addressing existing macrofouling on the mesh.
Results
After one week, the structure exhibited a thin layer of algae on the fish net, indicating rapid biofouling. By three weeks, distinct areas of the net illuminated by the lamps were evident, with significant algae growth on the unlit portions. Despite the short exposure time, both lamps effectively prevented biofouling.
After five weeks, the contrast was stark; only areas exposed to UV-C light remained free of fouling, while the rest of the structure, including the lamps themselves, was heavily covered in brown algae. Lamp one showed a larger disinfected area, suggesting greater effectiveness due to its shorter off-cycle. Lamp two, operating at 25 percent energy, also maintained fouling-free areas, albeit smaller ones. Observations revealed that small crustaceans were present only in unilluminated areas.
After seven weeks, no significant changes in efficiency were noted, and the disinfected areas remained clearly visible. Some unidentified microorganisms began to appear at the structure’s edges, indicating the initial stages of macrofouling. The angle of lamp two was modified to assess its ability to disinfect previously affected areas.
Lamp two was able to “burn” the fouled area and inhibit further growth of marine life. Lamp one kept the area it was illuminating free of fouling.
The experiment concluded after eight months of permanent installation.
Conclusion
The field experiment confirmed the high efficiency of Mariscope UV-C LED lamps in the highly productive waters of Patagonia, where strong algae blooms are prevalent. While the lamps’ effectiveness is influenced by radiation duration, they successfully maintained surfaces free of macrofouling, even when operating at just 25 percent of their maximum irradiating capacity. Increasing UV-C intensity or reducing the distance between the lamp and affected surfaces could further enhance biofouling control.