Enhancing chlorella minutissima biofuel and bioproduct potential: chelated trace elements and sustainable metal recovery.

Abstract

High cultivation costs (~$0.30 L⁻¹) and inconsistent yields (1.5-2.5 g L⁻¹) limit microalgal biofuel scalability, necessitating optimized nutrient delivery and cost-effective resource recycling. This study evaluated iron, zinc, and manganese in chelated (Fe-EDTA, Zn-gluconate, Mn-citrate) versus inorganic (FeCl₃, ZnSO₄, MnCl₂) forms at 1.0 mg L⁻¹ to enhance Chlorella minutissima biomass and lipid productivity. Compared to the control (BG-11 without Fe, Zn, Mn; biomass content: 2.10 ± 0.03 g L⁻¹, Lipid content: 38.0 ± 1.2% w/w), Fe-EDTA increased biomass content by 50% (3.15 ± 0.05 g L⁻¹, p < 0.001) and Lipid content by 42% (54.0 ± 1.0% w/w, p < 0.001), achieving 121 ± 5 mg L⁻¹ day⁻¹ lipid productivity. Zn-gluconate and Mn-citrate yielded comparable gains (2.85-3.00 g L⁻¹, 48-50% w/w, p < 0.01). Elevated monounsaturated fatty acids (30.5% C18:1) improved biodiesel quality (cetane number ~ 58). This study's novel approach of using chelated trace elements and biochar-electrocoagulation recovered 85% Fe, 75% Zn, and 70% Mn, reducing costs by 35% ($0.05-$0.10 L⁻¹). This integrated approach-chelation for metabolic efficiency and recycling for sustainability-advances scalable biofuel production and supports bioproduct development (e.g., pigments). Pilot-scale trials are needed to validate cost savings and industrial applicability.