Designing light-guiding carriers in microalgal-bacterial systems: From optimization to integration and development perspectives

The microalgal-bacterial biofilm (MABB) system integrates wastewater treatment with biomass resource generation and carbon sequestration. However, limited light distribution and scope remain a major bottleneck for its stable operation. Bio-carriers combining with light-guiding (LG) materials expand light distribution and scope inner biofilm by converting point or line light sources into uniform light. This review synthesizes current development situation of LG technology, including optimization of LG materials, shapes, and microscopic structure for better light energy guiding and transmit. Moreover, recent innovations of the development of LG carriers also focus on the surface modification and the improvement of its spatial configuration to increase the effective surface area for microalgae attachment and growth, and facilitate microalgae harvesting. Despite these technical advances, challenges of LG carriers remain in cost-efficient, large-scale application, particularly with capturing and utilizing sunlight. The combination of lenses, rotating devices, and optimized mixing systems within photobioreactors is proposed as a promising direction to enhance both capture and distribution of solar energy. This review has summarized the potential and limitations of LG materials on the application of MABB systems, and provide feasible solutions to improve its further development, offering a new approach for enhanced wastewater treatment, carbon fixation, and value-added biomass production.