Exploring the effect of glycerol and low-cost agricultural fertilizer for enhanced microalgae biomass production and wastewater treatment

Abstract

Microalgae may prove to be a dependable feedstock to produce value-added bioproducts if their production can be made economically viable and environmentally sustainable. This study evaluated the performance of a locally isolated microalga, Chlorella sp. BRE4 for biomass growth and nutrient removal efficiency in wastewater supplemented with NPK fertilizers and an organic carbon source. The maximum biomass yield was 2.91 g L⁻¹ with urea (0.75 g L⁻¹), 2.95 g L⁻¹ with single super phosphate (SSP) (0.75 g L⁻¹), and 2.83 g L⁻¹ with muriate of potash (MoP) (0.1 g L⁻¹) when each was added separately to the wastewater. In the photobioreactor (PBR), the developed wastewater-based medium was supplemented with glycerol and grown under different trophic modes. The microalga showed a maximum biomass yield of 3.16 g L⁻¹ under mixotrophy with CO₂ sparging (PBR4-MC), which was 4.93, 2.53, and 1.03 times higher than heterotrophy with simple air sparging (PBR1-HA), heterotrophy with CO₂ sparging (PBR2-HC), and mixotrophy with simple air sparging (PBR3-MA), respectively. Biochemical analysis shows that maximum lipid (106.5 mg L⁻¹ d⁻¹) and carbohydrate (94.8 mg L⁻¹ d⁻¹) productivities were achieved in PBR4-MC, being 2.8 and 7.8 times higher than under heterotrophic conditions. Moreover, the cultivation of Chlorella sp. in glycerol-supplemented low-cost medium (LCM) removed 92.9 % total nitrogen and 94.1 % total phosphate during the microalgal growth period of 10 days. These findings demonstrate the feasibility of integrating low-cost agricultural fertilizer and industrial by-products like glycerol in wastewater to enhance microalgal biomass and lipid production, enabling waste valorization and supporting circular bioeconomy strategies.