Harnessing waste glycerol to mitigate salinity constraints in freshwater microalgae cultivation for enhanced biodiesel recovery

Abstract

The current study investigated the synergistic effect of waste glycerol and salinity on Scenedesmus obliquus cultivation for enhanced biomass and biodiesel production. Optimal glycerol concentration was identified at 0.08 M supplementation, resulting in 23.1 % significant increase in biomass productivity. However, higher glycerol concentrations resulted in growth retardation. Salinity of +200 % NaCl showed positive impact on the growth, with the highest recorded dry weight of 1.76 g/L and biomass productivity of 0.206 g/L.day. However, further increases in salinity resulted in 53.4 % reduction in biomass yield at +800 % NaCl compared to +200 % NaCl. The combined treatment of the optimum glycerol concentration at different salinities (Glyc + Salin) showed superior growth performance up to +600 % NaCl, which confirmed mitigation of salinity inhibitory effects. Glyc + Salin exhibited the highest recorded nitrogen and phosphorus removal efficiencies (98.1 % and 96.6 %, respectively at day 8), dry weight (2.02 g/L), and biomass productivity (0.231 g/L.day). Notably, lipid content increased to 240.4 mg/g dw, and lipid productivity reached 56.0 mg/L.day, representing 76.1 % improvement over the control. Biodiesel characteristics, including cetane numbers and iodine values, showed also improvement, confirming the potential of Glyc + Salin for sustainable microalgal cultivation and biodiesel production.

Keywords

• Green energy
• Desalination
• Waste recycling
• Circular economy
• Sustainability