Bioreceptive Building Facades: Codesigning with Nature

Abstract

Although interactions between microorganisms and building materials have long been studied in the context of biodeterioration, actively enhancing the bioreceptivity of materials for microbially greened facades is a relatively new field. In our research we explore how concrete cladding used on building facades can be engineered to support the natural development of photosynthetic biofilms. Various factors related to concrete composition and surface texture were evaluated through a multi-phase testing process. A model dual-species biofilm composed of an alga and a microcolonial fungus was developed and successfully integrated into the experimental setup. The algal's growth and vitality were assessed using Pulse-Amplitude Modulation (PAM) fluorometry. Findings underscore the importance of surface near pH value in supporting both the growth and health of the algal component, with artificial concrete carbonation playing a key role in lowering the materials pH value and enhancing bioreceptivity. In a static, axenic laboratory growth experiment, the addition of nutrients onto the materials surface had a minor impact on bioreceptivity. Subsequent adhesion tests also revealed that a certain level of stress might enhance the biofilm's resilience to environmental pressures, such as water flow. Dynamic laboratory simulations with artificial rain showed that surface texture significantly influences biofilm adhesion, with near-surface porosity aiding in the retention of water and microorganisms and thereby promoting growth. Achieving an effective and lasting algal biofilm-based green facade system requires a careful balance between concrete surface pH value, material porosity and water retention.