Enhancing nutrient removal efficiency and biomass yield in Oedogonium: controlling nitrogen and phosphorus...

Reclaimed water with elevated nitrogen (N), phosphorus (P), and organics triggers eutrophication in replenished landscape waters. Conventional remediation methods face challenges of complexity and high costs. Filamentous algae ponds (FAPs) efficiently absorb N and P and produce harvestable biomass. Oedogonium is particularly adept at converting nutrients in reclaimed water into algal biomass. The effects of these cultivation conditions on Oedogonium sp. nutrient assimilation, photosynthetic parameters, and biomass recovery were evaluated with batch experiments using varying light-dark ratios (L: D ratios), nitrogen-phosphorus concentrations and their ratios (N/P mass ratios of 7, 14, 21, 28, and 35), and initial biomass loading. Specifically, Oedogonium sp. exhibits an optimal N/P mass ratio of 14. At a P concentration of 1 mg-P L^- 1, N removal efficiency reaches 0.56 mg-N L^- 1 d^- 1, with protein yield at 4.17 mg L^- 1 d^- 1 and polysaccharide yield at 11.21 mg L^- 1 d^- 1. However, when P concentration increases to 1.5 mg-P L^- 1, N removal efficiency decreases to 0.50 mg-N L^- 1 d^- 1. Correlation analysis indicates that N and P removal efficiency peaks when Oedogonium sp. is harvested on day 12. Furthermore, increasing the initial biomass loading does not yield better results. When the biomass is 1.5 g L^- 1 and the L: D ratio is 16:8, higher nutrient removal efficiency and biomass yields can be achieved. This study refined the theoretical framework governing the regulation of Oedogonium sp. growth by nutrients, light-dark ratios, and initial biomass, providing fundamental principles and regulatory thresholds for achieving efficient nutrient removal and biomass production in FAPs.