Our Research Multifunctional light-diffusing fibers for simultaneous light management and fluid transport in microalgae bioreactors

Sustainable energy generation, food security, water management, and climate change are among the most critical global challenges of the 21st century. The generation of microalgae biomass is expected to become a key component in a viable portfolio of strategies aimed at securing fuel, food, and water for a world population that is expected to exceed nine billion people by 2050. Microalgae have several advantages over terrestrial crops. Cultivated on non-arable land they are orders of magnitude more efficient in the generation of biomass for biofuel, food, and feed than higher crops and simultaneously can also contribute to waste water treatment and carbon fixation. However, current algae farming approaches are not economically viable. A significant cost is attributed to the energy used for algae culture mixing, which ensures that all the microorganisms are exposed uniformly to sunlight and adequate carbon dioxide levels. In standard algae systems, the mixing energy ranges from 20% - 80% of the total energy demand in biomass generation, and still neither uniform sunlight exposure nor adequate CO₂ level, which are both needed for maximum generation of photo-autotrophic biomass, are sufficiently well achieved. Many systems rely on additional CO₂ sparging, an approach that wastes 50% or more of the concentrated gas, which is economically and ecologically highly unfavorable. In addition, mixing-induced variations in light exposure lower the phototropic algae’s productivity due to photoinhibition.

Recent research into the generation of food, feedstock, and biofuel using microalgae suggests that algae are orders of magnitude more efficient in the generation of usable biomass than higher crops. Systematic culturing of microalgae will therefore be one important component in a portfolio of strategies needed to ensure food and fuel security for a rapidly increasing world population. However, current efforts in culturing algae on an industrial scale are not yet economically viable. Major costs are associated with the energy needed for the actuation of large water masses in the culture volume to ensure adequate supply of light and carbon dioxide to the entire culture.

We aim to increase the productivity of industrial algae cultures by several orders of magnitude using multifunctional polymeric fibers that enable light level homogenization and adequate CO₂ delivery throughout the entire algae culture via 100% efficient membrane transfer. Our approach will allow us to increase algae productivity in deeper culture volumes and simultaneously dramatically reduce the need for energy-intensive mixing. This goal can only be attained through fundamental research that centers on identifying promising light and CO₂ supply strategies for industrial-scale algae cultivation (1), developing suitable material constituents and scalable, cost-efficient fiber fabrication strategies (2), and systematically assessing the impacts of the new CO₂- and light-delivery methods on the physiology, ecology, and productivity of microalgal cultures (3).

This simple, energy-efficient means of ensuring homogeneous light distribution together with simultaneous delivery of carbon dioxide in dense, highly absorbing microalgae will help to achieve the full economic and social potential of algae cultures for food, feedstock, and biofuel generation. The fiber technology will form a platform for bioreactor and open pond designs that allow for significantly more efficient management of light and nutrient supply in microalgae cultures without the need of energy-intensive culture actuation.