Sustainable Removal of Green Growth on Surfaces: Efficacy of Non-Chemical Alternatives to Algaecides

Chemical green growth removers designed to control algae, which are classified as biocidal products, are used in open-air environments and, in some cases, over large areas such as roofs, façades, fences, or pavements, and can have adverse environmental effects. To minimise the use of green growth removers, users must have access to information on appropriate non-chemical alternatives against the target organisms. In this study, the authors developed an efficacy test for non-chemical green growth removal methods using a high-pressure cleaner with cold and hot water. After determining a dose-response curve concerning the efficacy of high water temperature on green growth control, naturally infested surfaces of a wooden fence and sandstone were treated with different water pressures and temperatures: 15 and 70 °C for both surfaces, 60, 70, 90, and 100 bar for the wooden fence, and 120 and 170 bar for sandstone. The results after six months showed that all treatments on the wooden fence remained highly effective (>96%). The efficacy of the treatments on the sandstone was lower, with the highest efficacy of 90% achieved with cold (15 °C) water and a water pressure of 170 bar. In summary, the methods used demonstrated high efficacy, constituting a sustainable alternative for algaecides. The regreening after six months remained low if thorough removal of the green growth was ensured.