Micro- and macroorganisms, the so-called biofouling, quickly settle on surfaces under water. Researchers from Kiel University are developing a protective coating without any environmentally harmful components to be used in aquaculture.
More and more freshwater and marine fish is bred in ponds, breeding tanks and net cages worldwide. Started as an alternative to overfishing the oceans, today every second fish for consumption comes from such aquacultures, according to the Food and Agriculture Organization (FAO) of the United Nations. The nets used in aquaculture are usually coated with copper-containing paints to prevent the heavy covering with algae, mussels or barnacles. However, these coatings release harmful substances into the water. To prevent this, scientists at Kiel University are developing an environmentally friendly net coating. Interim results from long-term tests in a local fish farm show that the project, funded by the German Federal Ministry of Economics and Energy (BMWi), could make a significant contribution to a more sustainable aquaculture. A patent application has already been submitted and the project is now to be expanded with further project partners.
Extensive cleaning was required so far
Marine organisms such as algae, mussels or barnacles quickly settle on nets used in fish farming. "The fouling can be really strong and hard to clean. The nets get heavier and could break, so we could lose our fish stock”, explains marine biologist Dr. Yvonne Rößner. After her PhD at Kiel University last year, she took over a local fish farm in the Kiel Fjord, together with Sophie Bodenstein. “In addition, the overgrown nets reduce the water exchange, which endangers the health of our salmon trout". To minimise these risks, they pull the nets out of the water every few days and let them dry by wind and sun. “This is time-consuming and exhausting manual work, but it means we can work without chemical treatment of the net”, says Rößner.
Marine biofouling also slows down ships and increases emission
Having a scientific background themselves the two biologists from the fish farm were especially happy to provide a part of their nets for the project on biofouling of the research group “Functional Nanomaterials” at Kiel University. For their aim of producing a protective coating for fish nets without any environmentally harmful components the material scientists can build upon experience in the development of environmentally friendly coating systems for ships. Since commercial and leisure ships around the world also have to deal with biofouling. The heavy fouling with micro- and macroorganisms reduces their speed and increases the fuel consumption, which leads to the emission of climate-damaging exhaust gases. Docking times and cleaning costs also increases. Previously, Kiel scientists developed a coating consisting of a polymer matrix and specially shaped ceramic particles. It provides an extremely smooth surface on which organisms can hardly adhere. A successful two-year practical test took the ship's paint from Kiel to the coast of Central Africa. "We were frequently asked whether our ship coating would also work on fishing nets," says technical biologist Dr. Martina Baum.
Cooperation project brings antifouling coating from laboratory to industry
Since then, the team from Kiel University has tried to modify their ship coating for fish nets. Together with the net manufacturer Walter Kremmin GmbH & Co. KG, they are examining different material variations for the applicability on commercially available nets. "Thanks to the cooperation with the local fish farm, we are now also able to test our coating under real conditions such as sun light, UV exposure and seawater flow," said Dr. Martina Baum. To conduct the long-term experiment, the research team coated two types of nets with different material components and placed them at different depths next to the net cages in the Kiel Fjord.
So far, more than 400 samples were tested, and the first long-term results after one-year immersion are now available. "Organisms on our coated test nets can be wiped off by hand very easily," explains Haoyi Qiu, project member and doctoral student at the Institute of Materials Science at Kiel University. "We observed that the easy-to-clean property also depends on the coating thickness. However, when a certain thickness is exceeded, the nets become too heavy and are more likely to fail," that is an interim conclusion of the materials scientist.
Further plans for applications worldwide
The ultimate goal is to introduce the coating to the worldwide market, and this coating should be equally effective against fouling in different water depths and ecosystems. In the ideal case, the biofouling is easily removed by the water current and the organisms are thus unable to permanently settle on the nets. "Together with industrial partners, we want to further develop our coating for various net types applied worldwide as well as for different water environments," says Dr. Martina Baum. In order to produce coatings on a larger scale for industrial application, the research team is cooperating with Phi-Stone AG, a spin-off company of Kiel University. The team has already applied for a patent of the coating.
The project "CleaNet - Fouling Release Coating for Aquaculture Networks" is funded by the Federal Ministry of Economics and Energy (BMWi) as part of the Central Innovation Programme for Small and medium-sized businesses (“Zentrales Innovationsprogramm Mittelstand ZiM”). The project is being managed by Kiel University. Another project partner is Mechanische Netzfabrik Walter Kremmin GmbH & Co. KG from Oldenburg.
In the nano-cosmos, different laws prevail than in the macroscopic world - those of quantum physics. Understanding structures and processes in these dimensions and implementing the findings in an application-oriented manner is the goal of the priority research area “Kiel Nano, Surface and Interface Science” (KiNSIS) at Kiel University. Intensive interdisciplinary cooperation between physics, chemistry, engineering and life sciences could lead to the development of novel sensors and materials, quantum computers, advanced medical therapies and much more. www.kinsis.uni-kiel.de/en