Nutrient removal, biomass accumulation, lipid production, and biostimulant activity of floating photosynthetic biofilm in synthetic wastewater

This study applied an easily harvestable floating photosynthetic biofilm (FPB) for nutrient removal from synthetic wastewater (SW) supplied with organic carbon (SWO), inorganic carbon (SWI), and atmospheric carbon dioxide (SWC). The FPB dry biomass concentration was measured on day 22 and the highest biomass concentration was obtained as 0.97 g L^-1 in SWI, followed by 0.43 g L^-1 in SWO, and the lowest as 0.33 g L^-1 in SWC (day 22). The FPB exhibited maximum NH₃-N, NO₃^--N, and PO₄^3--P removal of ca. 100% (day 22), 76% (day 14), and 73% (day 22) in SWI, SWO, and SWI, respectively. The lipid percentages of FPB biomass harvested from SWI, SWO, and SWC were 2.50%, 5.87%, and 5.00%, respectively. Furthermore, the cellular extract of defatted biomass from SWI and SWC improved the germination percentage of tomato seeds by 13% compared to the control (water). The highest germination improvement index (GII) and biomass improvement index (BII) values were obtained for defatted biomass from SWI. The GII and BII values for SWI were 1.32-fold on day 4 and 1.27-fold on day 8, compared to the control (water). The results indicated that FPB is effective for nutrient removal, facilitates biomass harvesting, and serves as a valuable feedstock for biomass biorefinery.