Tubular photobioreactors outperform conventional photobioreactor designs in solar-driven wastewater treatment and resource recovery: pilot-scale study

Photosynthetic bacteria (PSB) present a sustainable approach for wastewater treatment by converting organic pollutants into valuable biomass using solar energy. However, conventional photobioreactor (PBR) fail to optimize PSB's photoheterotrophic metabolism under natural illumination. This study bridges critical gaps by systematically evaluating four pilot-scale PBRs (raceway pond, cylindrical, flat-panel, tubular) for PSB-driven sugar wastewater treatment to optimize reactor geometry, light provision, and resource recovery. Results showed that tubular PBRs performed best in biomass yield and daily productivity at batch mode. In outdoor pilot semi-batch operation, the tubular PBR group showed the highest biomass production (3488.4 mg/L) and COD removal (99.0%). The highest carbon recovery ratio (31.5-51.2%) was also obtained in the tubular PBR group, surpassing flat-panel and cylindrical designs by 12.6-118.6%. These findings highlight the potential of tubular PBRs for scalable, light-driven wastewater treatment and establish design principles to balance organic load, light penetration, and metabolic efficiency under natural conditions. This study lays the foundation for the application of photosynthetic bacteria in industrial-scale wastewater resource recovery and holds great significance for advancing sustainable biotechnology.