Sustainable valorization of food waste for microalgal production of value-added compounds, bio-oil, and biochar

Abstract

The environmental burden of food waste (FW), a major source of greenhouse gases, necessitates advanced upcycling strategies. This study presents an integrated biorefinery to sustainably valorize FW into a suite of valuable products. Physically pretreated FW was utilized as an alternative culture medium at varying concentrations (10–50%) for microalgae cultivation. This approach successfully recycled waste nutrients and significantly enhanced the microalgae's bioproduct profile. Among saturated fatty acids (SFAs), palmitic acid (C16:0) was the dominant component in both groups and increased significantly from 42.60 ± 0.40% in the control to 47.40 ± 0.52% in FWCM. Similarly, arachidic acid (C20:0) increased from 1.67 ± 0.49% to 3.03 ± 0.15% following food waste culture medium (FWCM). The antioxidant capacity was also modulated, as evidenced by changes in DPPH scavenging activity, total phenolic (TPC) and flavonoid (TFC) content, and reactive oxygen species (ROS) levels. Food waste solid residues were subsequently processed via hydrothermal liquefaction (HTL) at 250 °C and 350 °C to produce bio-oil and hydrochar, while the hydrochar was further pyrolyzed at 550, 650, and 750 °C to produce biochar. The biochar was thoroughly characterized using FTIR, SEM, and XRD. This work demonstrates a circular economy model that mitigates FW by generating a nutrient-rich growth medium and sequentially converting the biomass into energy (bio-oil) and biochar.