Sustainable Integrated Algal Biomass Biorefinery: Synergistic Macronutrient Optimization and Electro-Flocculation Coagulation Harvesting

Algal biorefineries constitute an emerging platform for the sustainable production of renewable bioproducts; however, their economic viability remains constrained by the high costs associated with microalgal cultivation and biomass harvesting. This study investigated an integrated strategy combining macronutrient optimization with electrocoagulation–flocculation (ECF) harvesting for Chlorella vulgaris. A Central Composite Design (CCD) was employed to optimize concentrations of NaNO3, KH2PO4, and MgSO4 with the dual objective of maximizing biomass yield and enhancing biocompound content. Subsequently, the ECF process parameters—current density, electrolysis duration, pH, and electrolyte concentration—were optimized to improve harvesting efficiency. Under the optimal macronutrient conditions (NaNO3: 100.00 mg/L; KH2PO4: 222.12 mg/L; MgSO4: 100.84 mg/L), the model predicted a maximum biomass concentration of 0.475 g/L, along with 32.79% w/w carbohydrates and 6.79 mg/L chlorophyll-a. Optimal ECF harvesting conditions (current: 0.57 A; pH: 4.00; electrolysis time: 12.70 min; electrolyte: 1.74 g/L) achieved a biomass recovery efficiency of 89.51% w/v. These results demonstrate that coupling nutrient optimization with ECF-based harvesting offers a synergistic, scalable, and cost-effective pathway to improve the sustainability of algal biorefineries.