SUPERVISOR: Günter LANGERGRABER

PROJECT ASSIGNED TO: Shahd WEHBE

In hydropower plants, intake channels accelerate the water flow to drive the turbines and generate electricity. However, impaired hydrodynamic performance within these channels can disrupt the flow conditions and reduce energy production efficiency. One reason is biofilm accumulation. A biofilm is a self-produced matrix of extracellular DNA, proteins, and polysaccharides, which is formed by microbes when they attach to solid surfaces in aquatic environments. Conventional antifouling strategies often include the use of per- and polyfluoroalkyl substances (PFAS)-based coatings or biocidal chemicals. One alternative is the implementation of riblet microstructures, which are inspired by shark skin. Riblets are known for their antifouling properties and their ability to reduce hydrodynamic drag. Thus, their implementation in the hydropower plant intake channel is expected to increase the energy production efficiency by inhibiting biofilm formation and promoting a more laminar water flow profile. The GreenFlow consortium aims to develop a long-lasting riblet coating that is abrasion-resistant, eco-friendly, and inhibits biofilm formation. The ultimate goals are an 8-12% friction reduction, a 1,500-3,000 MWh/year energy gain for a 10 MW facility, and a 1,500 t/year CO2 reduction.

To achieve this, test films, made of a polyurethane-acrylate-based polymer, are manufactured with different riblet heights and alternative surface coatings to replace the PFAS-containing coatings conventionally used for such applications. Additionally, sol-gel coatings incorporating Zn particles and other antimicrobial materials are produced and tested.

A microbiological test workflow for static and dynamic tests is established to evaluate biofilm growth across different film surface properties. This standardized workflow includes static tests under controlled conditions in the laboratory, supporting scalability and reproducibility.

For static tests, test films are taped to the bottom of culture plates and incubated with three model microorganisms, Pseudomonas aeruginosa (bacterium), Candida albicans (yeast), and Chlamydomonas reinhardtii (green alga). Biofilm growth is assessed using flow cytometry, allowing the comparison of biofilm growth on different riblet heights.

A dynamic test setup is established with a similar workflow but the test films are instead incubated with water from the Danube Canal, acting as a proxy for water from the hydropower plant intake channel. Additionally, test films are subjected to a defined rotation speed of water circulation to simulate the realistic flow conditions of the intake channel.

Subsequently, to address the environmental compatibility of the riblet coating, antimicrobial tests are conducted, allowing the detection of any toxic effects of the coating on the aquatic environment. Leaching tests are performed to determine whether any toxic substances are released into the water, enabling the assessment of the environmental safety of the riblet coating.

In addition to laboratory-scale experiments, field tests are conducted in the intake channel of a hydropower plant in Carinthia. For this purpose, a pilot-scale test site is developed at the hydropower plant to enable long-term testing of the films under real operating conditions, allowing the evaluation of their durability, surface properties, and performance over time.

Finally, based on the results, taking environmental safety into account, the test film with the optimal riblet height and the coating shown to be eco-friendly will be installed in the
hydropower plant intake channel for varying exposure times to test the long-term stability of these coated riblets.